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What does 'to the right' mean, regarding the >> operator in PostGIS?

What does 'to the right' mean, regarding the >> operator in PostGIS?


I am reading the documentation on the>>operator in PostGIS, and I cannot understand the meaning ofstrictly to the rightbecause on the plane, right or left depends on the direction at which one is looking.

Reference: https://postgis.net/docs/ST_Geometry_Right.html

What would be that direction?


The language of left, right, above and below used for the bounding box operators refer to relative directions on a Cartesian grid. So "right" is a relatively positive direction along the x-axis, which is usually "to the east of" or "eastwards" for most projection systems (and ignoring that the world is round, where one could argue that everything is east of anything else).

So, in SQL-speak: Question: "is some geometry (A) to the right of another (B)"…

SELECT A << B as A_leftof_B, A >> B AS A_rigthtof_B FROM ( SELECT 'POINT (-40 30)'::geometry AS A, 'POINT (90 10)'::geometry AS B ) AS d; a_leftof_b | a_rigthtof_b ------------+-------------- t | f (1 row)

Answer: A is not right of B (but it is left of B).

As for the use of strictly, it depends if there is any overlap of the two bounding boxes along that dimension (the x-dimension for the case of left and right). For example, Italy is strictly east of Spain (since they don't even overlap east-west), but Spain is not strictly east of Portugal, since they overlap east to west. However, Spain is over to the east of Portugal, as demonstrated using the &>operator, since the bounding box for Spain is further to the east than Portugal's.


Addendum

The<<or>>(or many other bounding box operators) do not consider the sequence of coordinates.

To determine what is left or right of the trajectory of a linestring you will need a custom-built function. One such promising function is from Andreas Neumann, calledleft_of_test.


I must rescind this statement in favor of the answer by Mike T

The correct answer is greater X as stated by Mike T; after much digging around the function is renamed several times and is in reality:

static bool box2df_right(const BOX2DF *a, const BOX2DF *b) { if ( ! a || ! b ) return FALSE; /* TODO: might be smarter for EMPTY */ /* a.xmin > b.xmax */ return a->xmin > b->xmax; }

The function I was thinking of was not this one, and may well have been a function in another API. I must sincerely apologize for my mistake. For those that don't speak "C" it is saying if the minimum X of the first is greater than the maximum X of the second then it's to the right.

I have left this as it was written just in case someone else becomes confused on the same point.

Left side and right side are considered by the order of the vertices; imagine yourself standing on the first vertex looking at the second, then walk to the second and look at the third and so on until you get to the end of the line. As you are standing on a vertex facing the next in sequence there is a definite left and right side regardless of which direction the segment is traversing in.

Sidedness is determined in a manner similar to the cross product of two vectors which has the mathematical properties of being negative if the point falls on the right of the line and positive if the point falls on the left of the line, for a programmatic explanation see here, which is repeated for each vertex in turn.

In order to give any real usefulness to this operator on polygons you should be using ST_ForceRHR to ensure that polygons are oriented in a clockwise order for the first exterior ring. Then in this case on-the-right would mean inside. PostGIS does not enforce any particular ring orientation but instead the first ring is the exterior and then interior rings follow.


Eigenvalues of an operator correspond to energy states in quantum mechanics, why?

When finding the discrete energy states of a operator I have been taught to use the time-independent Schrodinger equation which restates the definition of eigenvalues and eigenvectors. What I don’t understand is why the eigenvalues are the energy states, is there firstly a mathematical reason and secondly a physical reason?

Does this arise from Hamiltonian or Lagrangian mechanics which I am not familiar with?


B. Redirection Operators

In the shell command language, a token that performs a redirection function. It is one of the following symbols:

These allow you to control the input and output of your commands. They can appear anywhere within a simple command or may follow a command. Redirections are processed in the order they appear, from left to right.

The above will execute command on the contents of file.txt .

<> : same as above, but the file is open in read+write mode instead of read-only:

If the file doesn't exist, it will be created.

That operator is rarely used because commands generally only read from their stdin, though it can come handy in a number of specific situations.

> : Directs the output of a command into a file.

The above will save the output of command as out.txt . If the file exists, its contents will be overwritten and if it does not exist it will be created.

This operator is also often used to choose whether something should be printed to standard error or standard output:

In the example above, > will redirect standard output and 2> redirects standard error. Output can also be redirected using 1> but, since this is the default, the 1 is usually omitted and it's written simply as > .

So, to run command on file.txt and save its output in out.txt and any error messages in error.txt you would run:

>| : Does the same as > , but will overwrite the target, even if the shell has been configured to refuse overwriting (with set -C or set -o noclobber ).

If out.txt exists, the output of command will replace its content. If it does not exist it will be created.

>> : Does the same as > , except that if the target file exists, the new data are appended.

If out.txt exists, the output of command will be appended to it, after whatever is already in it. If it does not exist it will be created.

>& : (per POSIX spec) when surrounded by digits ( 1>&2 ) or - on the right side ( 1>&- ) either redirects only one file descriptor or closes it ( >&- ).

A >& followed by a file descriptor number is a portable way to redirect a file descriptor, and >&- is a portable way to close a file descriptor.

If the right side of this redirection is a file please read the next entry.

>& , &> , >>& and &>> : (read above also) Redirect both standard error and standard output, replacing or appending, respectively.

Both standard error and standard output of command will be saved in out.txt , overwriting its contents or creating it if it doesn't exist.

As above, except that if out.txt exists, the output and error of command will be appended to it.

The &> variant originates in bash , while the >& variant comes from csh (decades earlier). They both conflict with other POSIX shell operators and should not be used in portable sh scripts.

<< : A here document. It is often used to print multi-line strings.

Here, command will take everything until it finds the next occurrence of WORD , Text in the example above, as input . While WORD is often EoF or variations thereof, it can be any alphanumeric (and not only) string you like. When WORD is quoted, the text in the here document is treated literally and no expansions are performed (on variables for example). If it is unquoted, variables will be expanded. For more details, see the bash manual.

If you want to pipe the output of command << WORD . WORD directly into another command or commands, you have to put the pipe on the same line as << WORD , you can't put it after the terminating WORD or on the line following. For example:

<<< : Here strings, similar to here documents, but intended for a single line. These exist only in the Unix port or rc (where it originated), zsh, some implementations of ksh, yash and bash.

Whatever is given as WORD is expanded and its value is passed as input to command . This is often used to pass the content of variables as input to a command. For example:

A few other operators ( >&- , x>&y x<&y ) can be used to close or duplicate file descriptors. For details on them, please see the relevant section of your shell's manual (here for instance for bash).

That only covers the most common operators of Bourne-like shells. Some shells have a few additional redirection operators of their own.

Ksh, bash and zsh also have constructs <(…) , >(…) and =(…) (that latter one in zsh only). These are not redirections, but process substitution.


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Last Updated: December 31, 2019
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  1. Introduction
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The Digital Services may contain links to websites, mobile apps or other services operated by companies not affiliated with Hearst. In addition, the Digital Services may be made available to you through third-party platforms (such as app stores or Social Media Platforms) or other channels. We are not responsible for the privacy practices of any non-Hearst operated websites, mobile apps or other services and channels, and we encourage you to review the privacy policies or notices published by relevant third parties.

J. CAREERS/JOB OPPORTUNITIES

This Privacy Notice does not apply to web pages hosting our careers or job opportunities. Any information obtained through such pages is governed by the privacy notice published thereon.

K. DISPUTE RESOLUTION/TERMS OF USE

Any dispute concerning the Digital Services (including our use of your personal information) will be resolved per the dispute resolution provision in the Terms of Use, which govern your use of the Digital Services. Please take a few minutes to read the Terms of Use before using the Digital Services.

L. CHANGES TO THIS PRIVACY NOTICE

We may update this Privacy Notice from time to time to reflect changes in our privacy practices or applicable laws. In accordance with applicable law, we may make such changes without prior notice. We will publish the updated version on the relevant Digital Services and indicate at the top of the Privacy Notice when it was most recently updated. Your use of the Digital Services will be governed by the then-current version of the Privacy Notice.

M. CONTACT US

If you have any questions about this Privacy Notice, please contact us by email at [email protected] For questions related to your California Consumer Privacy Act of 2018 (“CCPA”) rights, please contact us by email at [email protected] Please note that we do not accept CCPA rights requests through that mailbox and we ask you to submit your CCPA rights requests using the form(s) linked in the “Your California Consumer Privacy Act of 2018 (CCPA) Rights” section further down below.

N. ADDITIONAL INFORMATION FOR CALIFORNIA RESIDENTS

Under California law, specific disclosures are required and California residents have additional rights regarding their personal information. Please review this section to learn more.

Your California Consumer Privacy Act of 2018 (CCPA) Rights

Categories of Personal Information We Collect

The California Consumer Privacy Act of 2018, as amended from time to time (“CCPA”) requires specific disclosures for each category of personal information that we collect. The table below summarizes our general data handling practices which are more fully described in Sections B, C and D of this Privacy Notice.

Category of Personal Information

Categories of Sources From Which Personal Information Was Collected

(See Section B of this Privacy Notice for additional information)

Business or Commercial Purpose for Collecting and Sharing the Category of Personal Information

(See Sections C and D of this Privacy Notice for additional information)

Categories of Third Parties and Other Entities We Share Personal Information With

(See Section D of this Privacy Notice for additional information)

Identifiers (§1798.140 (o)(1)(A) and (B)) which include elements such as: (i) contact information (e.g., name, mailing address, email address, phone number) and (ii) online identifiers (e.g., Internet protocol (IP) address, account numbers, device identifiers such as mobile advertising IDs)

From your friends or contacts (for example, if they forward you one of our articles)

From cookies and similar technologies

From third-party sites or apps, content distribution channels and platforms

From third-party data suppliers and business partners

From social media platforms and similar services

To provide you with and to improve the Digital Services

For advertising and marketing purposes for us or third-parties, including interest-based advertising

To protect our or others’ rights

With affiliates and subsidiaries

With advertising and marketing service providers and partners

With content measurement companies

With social media platforms

With government authorities as required by law or as necessary to protect our rights

Demographics (§1798.140 (o)(1)(C)) which include elements such as age and gender

From cookies and similar technologies

From third-party sites or apps, content distribution channels and platforms

From third-party data suppliers and business partners

From social media platforms and similar services

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· With affiliates and subsidiaries

· With advertising and marketing service providers and partners

· With content measurement companies

· With social media platforms

· With government authorities as required by law or as necessary to protect our rights

Personal Information under subdivision (e) of Section 1798.80 of the California Civil Code (§1798.140 (o)(1)(B)) which includes payment information

(e.g., payment card number, expiration date and billing information)

· To provide you with and to improve the Digital Services

· To protect our or others’ rights

· With affiliates and subsidiaries

· With government authorities as required by law or as necessary to protect our rights

Commercial Information (§1798.140 (o)(1)(D)) which includes elements such as transactional information

(e.g., activity, subscriptions, requests, purchases, items in your cart but not completed purchases)

· From cookies and similar technologies

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· To protect our or others’ rights

With affiliates and subsidiaries

With advertising and marketing service providers and partners

With social media platforms

With government authorities as required by law or as necessary to protect our rights

Internet or other electronic network activity (§1798.140 (o)(1)(F)) which includes elements such as information about how you use, access, or interact with the Digital Services such as comments, photos, videos and other content you choose to publish on the Digital Services, information about your device, browser or operating system

· From cookies and similar technologies

· From third-party sites and apps, content distribution channels and platforms

· From third-party data suppliers and business partners

· From social media platforms and similar services

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· To protect our or others’ rights

· With affiliates and subsidiaries

· With advertising and marketing service providers and partners

· With content measurement companies

· With social media platforms

· With government authorities as required by law or as necessary to protect our rights

Geolocation Data (§1798.140 (o)(1)(G)) which includes elements such as location information

(e.g., city and state, or precise location information if location services are active on your device)

· From cookies and similar technologies

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· To protect our or others’ rights

· With affiliates and subsidiaries

· With advertising and marketing service providers and partners

· With content measurement companies

· With social media platforms

· With government authorities as required by law or as necessary to protect our rights

Audio, Electronic, Visual, Thermal, Olfactory or Similar Information (§1798.140 (o)(1)(H)) which includes elements such as recordings of your calls with our call center

· To provide you with and to improve the Digital Services

· To protect our or others’ rights

· With affiliates and subsidiaries

Professional or Employment-Related Information (§1798.140 (o)(1)(I)) which includes elements such as your professional email address, phone number or other contact information if you have used such professional or employment related personal information to order a subscription, register for an account or to receive communications

· From third-party data suppliers and business partners

· From social media platforms and similar services

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· To protect our or others’ rights

· With affiliates and subsidiaries

· With advertising and marketing service providers and partners

· With content measurement companies

· With social media platforms

· With government authorities as required by law or as necessary to protect our rights

Inferences (§1798.140 (o)(1)(K)) which include elements such as inferences regarding your preferences or other characteristics (e.g., cooking enthusiast, travel, food and dining)

· From cookies and similar technologies

· From third-party sites and apps, content distribution channels and platforms

· From third-party data suppliers and business partners

· From social media platforms and similar services

· To provide you with and to improve the Digital Services

· For advertising and marketing purposes for us or third-parties, including interest-based advertising

· To protect our or others’ rights

· With affiliates and subsidiaries

· With advertising and marketing service providers and partners

· With content measurement companies

· With social media platforms

· With government authorities as required by law or as necessary to protect our rights

Residents of California may have the following rights:

1. Right to know and access your personal information. Under CCPA, you have the right to:

Know the categories of personal information we collect and the categories of sources from which we got the information

Know the business or commercial purposes for which we collect and share personal information

Know the categories of third parties and other entities with whom we share personal information and

Access the specific pieces of personal information we have collected about you.

To do so, please complete the form available here and include your name, email address, California postal address as well as your subscription, if you have an active subscription. You may also exercise your right by calling 1-800-310-2455.

2. Right to deletion. In some circumstances, you may ask us to delete your personal information. To do so, please complete the form available here and include your name, email address, California postal address as well as your subscription account number, if you have an active subscription. You may also exercise your right by calling 1-800-310-2455.

3. Right to opt out of sales. We may share your personal information with third parties in ways that may constitute a “sale” under CCPA. You may request that we not “sell” your personal information on a going forward basis. To do so, please complete the form available here and include your name, email address, California postal address as well as your subscription account number, if you have an active subscription. You may also exercise your right by calling 1-800-310-2455. If you reengage with us after opting out of the “sale” of your personal information, such as by ordering a new subscription, buying a product, signing up for a newsletter and/or entering a sweepstakes or contest your personal information will be collected and used in accordance with this Privacy Notice.

For some of our Digital Services, we may participate in the IAB CCPA Compliance Framework for Publishers & Technology Companies (“IAB Framework”). This means that where you exercise your right to opt out of the sale your personal information through the Do Not Sell My Info link we make available on the participating Digital Services, to the extent we sell your personal information in order to deliver ads tailored to your interests based on your activities across third-party sites, we will notify downstream participants of the IAB Framework that receive personal information about you to only use your personal information for those specific and limited purposes that are permitted under the IAB Framework.

Please note that the scope of the IAB Framework opt-out may only apply to personal information from the specific browser or device from which you opt out. In addition, exercising your right to opt out of the sale of your personal information does not mean that you will stop seeing ads or that you will stop seeing interest-based ads. To learn more about interest-based advertising across sites and additional opt-out choices, you should visit one or more of the following industry opt-out links: http://optout.aboutads.info, http://optout.networkadvertising.org and http://www.aboutads.info/appchoices. Where you opt out of the sale for purposes of CCPA, but do not opt out of interest-based advertising more generally, you may continue to receive ads tailored to your interests based upon personal information not sold by us, sold to other IAB participants at least 90 days before you opted out, or sold by other sources from which you have not opted out. We are not responsible for any downstream participants’ compliance with the IAB Framework or the accuracy of their privacy policies or statements regarding their opt-out options or programs.

4. Right to be free from discrimination. You may exercise any of the above rights without fear of being discriminated against. We are permitted to provide a different price or rate to you if the difference is directly related to the value provided to you by your data.

For any of the above mentioned rights, you may designate an authorized agent to make a request on your behalf. In the request, you or your authorized agent must provide including information sufficient for us to confirm the identity of an authorized agent. We are required to verify that your agent has been properly authorized to request information on your behalf and this may take additional time to fulfill your request.

We will use the information you provide to make your CCPA rights requests to verify your identity, identify the personal information we may hold about you and act upon your request. We strongly recommend that you submit the email and postal address that you used when you created accounts, ordered subscriptions or signed up for a newsletter. After you submit a CCPA rights requests using one of our forms, you will be required to verify access to the email address you submitted. You will receive an email with a follow-up link to complete your email verification process. You are required to verify your email in order for us to proceed with your CCPA rights requests. Please check your spam or junk folder in case you can't see the verification email in your inbox. If you are a California resident and have any questions regarding your CCPA rights under this Privacy Notice, please contact us at [email protected]

Minors

We do not knowingly collect or disclose personal information of minors under the age of 16, without affirmative authorization.

Your Shine the Light California Rights (CA Civil Code § 1798.83)

You may also have the right to request a list of third parties to which certain personal information (as defined by California Civil Code § 1798.83) obtained through a Digital Service was disclosed by Hearst during the preceding year for those third parties’ direct marketing purposes. If you are a California resident and want such a list, please contact us at Office of General Counsel, Attn: Privacy, 300 West 57th Street, New York, NY 10019. For such request, you must put the statement “Your California Privacy Rights” in the body of your request, as well as your name, street address, city, state, and zip code. In your request, you need to attest to the fact that you are a California resident and provide a current California address for our response. Please also indicate in your request the name of the Digital Service to which your request applies. Please note that we will not accept requests via the telephone, email, or by facsimile.

O. ADDITIONAL INFORMATION FOR EUROPEAN VISITORS

In order to address our legal obligations in Europe (including the UK), Hearst provides the following additional information for Europe-based visitors to Hearst's U.S. Digital Services.

Who is Responsible for Your Information?

If you use or interact with a Hearst U.S. Digital Service then the data controller will be the entity listed at the top of this Privacy Notice. The contact details for this entity are provided in the “Contact Us” section above.

Legal Bases for Using Your Information

We process personal information for different purposes (as described in the “How We Use Information We Obtain” section, above) on the following legal bases:

To perform our contractual obligations to you. We and our service providers process your information to perform our contractual obligations to you when we use your information to provide you with the Digital Services and related content, products or services and to communicate with you. For example, when you purchase a subscription from us, we process your payment and contact information as necessary to confirm the subscription and we process your contact information and other details to provide you with support services you request. We also send you informational communications on this basis, including to confirm a subscription or to notify you of a change to a Digital Service. Failure to provide requested information could prevent or delay the fulfilment of our contractual obligations.

To pursue our legitimate interests. We process your information to meet our legitimate interests when we use your information to provide you with the Digital Services and related content, products or services, to communicate with you and for our advertising and marketing purposes. For example, our legitimate interests include making improvements to, customizing and understanding how you interact with the Digital Services and related content, products or services, and sending you communications about products and services we think may be of interest to you. To accomplish our legitimate interests, we may share your information with our affiliates and subsidiaries, service providers and business partners (including for our advertising and marketing purposes) and in the context of a corporate transaction. We maintain safeguards to protect the information we process to pursue our legitimate interests.

To comply with our legal obligations. We process and share your information as necessary to comply with our legal obligations when we use your information to protect our rights or the rights of others and when we share your information with other parties where required by law or as necessary to protect our rights. For example, we are required to collect certain information from you when processing your subscription payment for tax or financial reporting reasons.

With your consent. We obtain your consent to process your information when we are required to do so by law. If consent is the legal basis on which we process your personal information, you can withdraw your consent at any time by contacting us using the information provided in the “Contact Us” section above.

Your Rights Over Your Information

In certain circumstances, you have a right to access or object to the use of personal information held about you (including in relation to direct marketing). You can also ask us to rectify, update, erase, restrict or to share your information in a usable format with another company. Such requests are subject to applicable law. We encourage you to contact us to update or correct your information if it changes or if the personal information we hold about you is inaccurate.

If you would like to discuss or exercise such rights, please contact us at [email protected] We will contact you if we need additional information from you in order to honor your requests.

Storing Your Information

We will keep your personal information for as long as we have a relationship with you. Once our relationship with you has come to an end, we will retain your personal information for a period of time that enables us to:

Maintain business records for analysis, understanding market trends and/or audit purposes and to improve the Digital Services.

Comply with record retention requirements under applicable laws or other relevant legal or regulatory requirements.

Defend, establish, exercise or bring any existing or potential legal claims.

Carry out fraud detection and prevention.

Deal with any complaints regarding the Digital Services, our products and services.

We will delete your personal information when it is no longer required for these purposes. If there is any information that we are unable, for technical reasons, to delete from our systems, we will put in place appropriate measures to prevent any further processing or use of the data.

International Data Transfers

Information collected through the Digital Services will be processed in and subject to the laws of the United States, which may not provide the same level of protection for your personal information as your home country. If we transfer personal data from the European Economic Area and Switzerland we put in place safeguards. In particular, such safeguards include European Commission-approved standard contractual clauses. For more information on these safeguards, please contact us at the details provided in the “Contact Us” section above.

Changes to the Privacy Notice

Where changes to this Privacy Notice have a fundamental impact on the nature of the processing or otherwise have a substantial impact on you, we will give you advanced notice so that you have the opportunity to exercise your rights (e.g. to object to the processing).

Privacy Officer and Complaints

Our Privacy Officer can be contacted at [email protected]

We are committed to working with you to obtain a fair resolution in the event you have a complaint or concern about privacy. If, however, you believe that we have not been able to assist with your complaint or concern, you have the right to make a complaint to a data protection authority.


1 Answer 1

The fact that two (or more) hermitian operators do not commute does not mean they are not observables. For instance, $x$ and $p$ do not commute but are surely observables. Likewise, the kinetic energy $p^2/2m$ and the potential energy $V(x)$ usually do not commute, but they are observables and finding eigenvectors for their sum $p^2/2m+V(x)=H$ amounts to solving the time-independent Schrodinger equation.

It's not a problem to diagonalize your Eq.(1) either: simply write each operator in matrix form, sum the matrices (the result is still a hermitian matrix) and find the eigenvectors of this hermitian matrix. You will then get eigenvectors that represents states with definite projection in the $vec i+vec j+vec k$ direction. Again, the fact that the various projections do not pairwise commute does not mean that the sum is not an observable. For example, the Pauli matrices $sigma_x$ and $sigma_y$ do not commute, but their sum $ sigma_x+sigma_y=left( egin 0 & 1-i 1+i & 0 end ight) $ has eigenvectors $ left(egin-frac<1><2>+frac <2> frac<1>>end ight)qquad left(eginfrac<1><2>-frac <2> frac<1>>end ight) $

When the Hilbert space is finite dimensional, every hermitian operator corresponds in theory to an observable, although it might be difficult in practice to design a physical experiment that will measure this observable, and it may be difficult to write something like a classical version of the operator you start with.

When the Hilbert space is infinite dimensional, there are additional subtle points and there are operators which are hermitian (or more properly not self-adjoint) but do not correspond to observables.


6 Answers 6

This generally seems to be done as a 'value added service' in the Andriod SIM Toolkit, as per this question here.

However, in this case it may be a Cell Broadcast.

Cell Broadcast is designed for simultaneous delivery to multiple users in a specified area. Whereas the Short Message Service-Point to Point (SMS-PP) is a one-to-one and one-to-a-few service (requires multiple SMS messages, as each message can only carry one phone number), Cell Broadcast is a one-to-many geographically focused messaging service. Cell Broadcast messaging is also supported by UMTS.

If you go to your SMS app and go SMS > Settings > Cell Broadcast and disable it, this should stop this popup.


3 Answers 3

These are not the usual definitions as I know them.$ ewcommand[2]$

First, I am only familiar with the situation that $H$ is a Hilbert space and $D(T)$ is dense in $H$ (which entails no loss of generality, as we can replace $H$ with the completion of $D(T)$.)

$T$ is symmetric if $inner = inner$ for all $x,y in D(T)$. (Note your definition doesn't make sense, because you are applying $T$ to vectors that may not be in $D(T)$.)

$T$ is Hermitian if it is symmetric and bounded. (If $T$ is bounded then it has a unique bounded extension to all of $H$, so we may as well assume $D(T) = H$ in this case.) Since a symmetric operator is always closable, the closed graph theorem implies that a symmetric operator with $D(T) = H$ is automatically bounded.

$T$ is self-adjoint if the following, more complicated condition holds. Let $D(T^*)$ be the set of all $y in H$ such that $|inner| le C_y ||x||$ for all $x in D(T)$, where $C_y$ is some constant depending on $y$. If $T$ is symmetric, one can show that $D(T) subset D(T^*)$ $T$ is said to be self-adjoint if it is symmetric and $D(T) = D(T^*)$.

With these definitions, we have Hermitian implies self-adjoint implies symmetric, but all converse implications are false.

The definition of self-adjoint is rather subtle and this may not be the place for an extended discussion. However, I'd recommend a textbook such as Reed and Simon Vol. I. Perhaps I'll just say that symmetric operators, although the definition is simple, turn out not to be good for much, per se. One needs at least self-adjointness to prove useful theorems.

The definition is quite simple when you realize it. But it takes some time to realize the difference. There are some contradictions with Nate answer, but this just a matter of terminology.

  • $mathrm T$ is Hermitian if $forall x,y in D(mathrm T) (mathrm Tx,y) = (x,mathrm T y)$
  • $mathrm T$ is symmetric if $mathrm T$ is Hermitian and densely defined. As far as i understand the only advantage of symmetric op over Hermitian is guaranted exitance of $mathrm T

    Contents

    When telephone numbers were first used they were very short, from one to three digits, and were communicated orally to a switchboard operator when initiating a call. As telephone systems have grown and interconnected to encompass worldwide communication, telephone numbers have become longer. In addition to telephones, they have been used to access other devices, such as computer modems, pagers, and fax machines. With landlines, modems and pagers falling out of use in favor of all-digital always-connected broadband Internet and mobile phones, telephone numbers are now often used by data-only cellular devices, such as some tablet computers, digital televisions, video game controllers, and mobile hotspots, on which it is not even possible to make or accept a call.

    The number contains the information necessary to identify uniquely the intended endpoint for the telephone call. Each such endpoint must have a unique number within the public switched telephone network. [ dubious – discuss ] Most countries use fixed-length numbers (for normal lines at least) and therefore the number of endpoints determines the necessary length of the telephone number. It is also possible for each subscriber to have a set of shorter numbers for the endpoints most often used. These "shorthand" or "speed calling" numbers are automatically translated to unique telephone numbers before the call can be connected. Some special services have their own short numbers (e.g., 1-1-9, 9-1-1,1-0-0, 1-0-1, 1-0-2, 0-0-0, 9-9-9, 1-1-1, and 1-1-2 being the Emergency Services numbers for China, Japan, India, South Korea, Taiwan and Sri Lanka Canada and the United States Israel (Police) Israel (Paramedic) Israel (Fire) Australia the United Kingdom, Ireland, South Africa, Poland, Saudi Arabia, the United Arab Emirates, Morocco, Macao, Bahrain, Qatar, Bangladesh, Botswana, Ghana, Kenya, Hong Kong, Malaysia, Mauritius, Singapore, Zimbabwe, Trinidad, Tobago, New Zealand, Kuwait, the European Union and the Philippines respectively.)

    The dialing plan in some areas permits dialing numbers in the local calling area without using area code or city code prefixes. For example, a telephone number in North America consists of a three-digit area code, a three-digit central office code, and four digits for the line number. If the area has no area code overlays or if the provider allows it, seven-digit dialing may be permissible for calls within the area, but some areas have implemented mandatory ten-digit dialing.

    Other special phone numbers are used for high-capacity numbers with several telephone circuits, typically a request line to a radio station where dozens or even hundreds of callers may be trying to call in at once, such as for a contest. For each large metro area, all of these lines will share the same prefix (such as 404-741-xxxx in Atlanta and 305-550-xxxx in Miami), the last digits typically corresponding to the station's frequency, callsign, or moniker.

    In the international telephone network, the format of telephone numbers is standardized by ITU-T recommendation E.164. This code specifies that the entire number should be 15 digits or shorter, and begin with a country prefix. For most countries, this is followed by an area code or city code and the subscriber number, which might consist of the code for a particular telephone exchange. ITU-T recommendation E.123 describes how to represent an international telephone number in writing or print, starting with a plus sign ("+") and the country code. When calling an international number from a landline phone, the + must be replaced with the international call prefix chosen by the country the call is being made from. Many mobile phones allow the + to be entered directly, by pressing and holding the "0" for GSM phones, or sometimes "*" for CDMA phones.

    The 3GPP standards for mobile networks provide a BCD-encoded field of ten bytes for the phone number ("Dialling Number/SCC String"). The international call prefix or "+" is not counted as it encodes a value in a separate byte (TON/NPI - type of number / numbering plan identification). If the MSISDN is longer than 20 digits then additional digits are encoded into extension blocks (EFEXT1) each having a BCD-encoded field of 11 bytes. [5] This scheme allows to extend the subscriber number with a maximum of 20 digits by additional function values to control network services. In the context of ISDN the function values were transparently transported in a BCD-encoded field with a maximum of 20 Bytes named "ISDN Subaddress". [6]

    The format and allocation of local phone numbers are controlled by each nation's respective government, either directly or by sponsored organizations (such as NANPA in the US or CNAC in Canada). In the United States, each state's public service commission regulates, as does the Federal Communications Commission. In Canada, which shares the same country code with the U.S. (due to Bell Canada's previous ownership by the U.S.-based Bell System), regulation is mainly through the Canadian Radio-television and Telecommunications Commission.

    Local number portability (LNP) allows a subscriber to request moving an existing telephone number to another telephone service provider. Number portability usually has geographic limitations, such as an existing local phone company only being able to port to a competitor within the same rate centre. Mobile carriers may have much larger market areas, and can assign or accept numbers from any area within the region. In many telephone administrations, cell phone telephone numbers are in organized in prefix ranges distinct from land line service, which simplifies mobile number portability, even between carriers.

    Within most North American rate centres, local wireline calls are free, while calls to all but a few nearby rate centres are considered long distance and incur toll fees. In a few large US cities, as well as many points outside North America, local calls are not flat-rated or "free" by default.


    Contents

    Installation of receivers and transmitters at the same fixed location allowed exchange of messages wirelessly. As early as 1907, two-way telegraphy traffic across the Atlantic Ocean was commercially available. By 1912, commercial and military ships carried both transmitters and receivers, allowing two-way communication in close to real-time with a ship that was out of sight of land.

    The first truly mobile two-way radio was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police. The Victoria Police were the first in the world to use wireless communication in cars, putting an end to the inefficient status reports via public telephone boxes which had been used until that time. The first sets took up the entire back seat of the Lancia patrol cars. [2]

    As radio equipment became more powerful, compact, and easier to use, smaller vehicles had two-way radio communication equipment installed. Installation of radio equipment in aircraft allowed scouts to report back observations in real-time, not requiring the pilot to drop messages to troops on the ground below or to land and make a personal report.

    In 1933, the Bayonne, New Jersey police department successfully operated a two-way system between a central fixed station and radio transceivers installed in police cars this allowed rapidly directing police response in emergencies. [3] During World War II walkie-talkie hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Axis.

    Early two-way schemes allowed only one station to transmit at a time while others listened since all signals were on the same radio frequency – this was called "simplex" mode. Code and voice operations required a simple communication protocol to allow all stations to cooperate in using the single radio channel so that one station's transmissions were not obscured by another's. By using receivers and transmitters tuned to different frequencies and solving the problems introduced by operation of a receiver immediately next to a transmitter, simultaneous transmission and reception was possible at each end of a radio link, in so-called "full duplex" mode.

    The first radio systems could not transmit voice. This required training of operators in use of Morse code. On a ship, the radio operating officers (sometimes shortened to "radio officers") typically had no other duties than handling radio messages. When voice transmission became possible, dedicated operators were no longer required and two-way radio use became more common. Today's two-way mobile radio equipment is nearly as simple to use as a household telephone, from the point of view of operating personnel, thereby making two-way communications a useful tool in a wide range of personal, commercial and military roles.

    Two-way radio systems can be classified in several ways depending on their attributes.

    Conventional versus trunked Edit

    Conventional Edit

    Conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time. The proper channel is selected by a user. The user operates a channel selector (dial or buttons) on the radio control panel to pick the appropriate channel.

    In multi-channel systems, channels are used for separate purposes. [4] A channel may be reserved for a specific function or for a geographic area. In a functional channel system, one channel may allow City of Springfield road repair crews to talk to the City of Springfield's road maintenance office. A second channel may allow road repair crews to communicate with state highway department crews.

    In a wide-area or geographic system, a taxi company may use one channel to communicate in the Boston, Massachusetts area and a second channel when taxis are in Providence, Rhode Island. This is referred to as Multisite operation. In this case, the driver or the radio must switch channels to maintain coverage when transitioning between each area. Most modern conventional digital radios and systems (i.e., NXDN and DMR) are capable of automatic "roaming" where the radio automatically switches channels on a dynamic basis. The radio accomplishes this based on the received signal strength of the radio repeater's recurring "beacon" signal and a "site" or "roam" list that identifies available geographic channels. Some analog conventional systems can be equipped with a feature called "vote-scan" that provides more limited roaming (rarely used in practice). Radio "simulcast" technology can also be used in adjacent areas, where each site is equipped with the same channel. Here, the transmitters must be closely synchronized, and a centralized voter or receiver comparator device is required to select the best quality signal from the mobile radio. This is often used in public safety and utility radio systems.

    In marine radio operations, one channel is used as an emergency and calling channel, so that stations may make contact before moving to a separate working channel for continued communication.

    Motorola uses the term mode to refer to channels on some conventional two-way radio models. In this use, a mode consists of a radio frequency channel and all channel-dependent options such as selective calling, channel scanning, power level, and more.

    Scanning in conventional radios Edit

    Some conventional radios scan more than one channel. That is, the receiver searches more than one channel for a valid transmission. A valid transmission may be a radio channel with any signal or a combination of a radio channel with a specific Continuous Tone-Coded Squelch System (CTCSS) (or selective calling) code.

    There are a wide variety of scan configurations that vary from one system to another. Some radios have scan features that receive the primary selected channel at full volume and other channels in a scan list at reduced volume. This helps the user distinguish between the primary channel and others without looking at the radio control panel. An overview:

    • A scanning feature can be defined and preset: when in scanning mode, a predetermined set of channels is scanned. Channels are not changeable by the radio user.
    • Some radios allow an option for user-selected scan: this allows either lockout of pre-selected channels or adding channels to a scan list by the operator. The radio may revert to a default scan list each time it is powered off or may permanently store the most recent changes. In professional radios, scan features are programmable and have many options. Scan features can affect system latency. If the radio has a twenty-channel scan list and some channels have CTCSS, it can take several seconds to search the entire list. The radio must stop on each channel with a signal and check for a valid CTCSS before resuming scanning. This can cause missed messages.

    For this reason, scan features are either not used or scan lists are intentionally kept short in emergency applications. Part of APCO Project 16 set standards for channel access times and delays caused by system overhead. Scan features can further increase these delays. One study said delays of longer than 0.4 seconds (400 milliseconds) in emergency services are not recommended. [5] No delay from user push-to-talk until the user's voice is heard in the radio's speaker is an unattainable ideal.

    Talk-back on scan Edit

    Some conventional radios use, or have an option for, a talk-back-on-scan function. If the user transmits when the radio is in a scan mode, it may transmit on the last channel received instead of the selected channel. This may allow users of multi-channel radios to reply to the last message without looking at the radio to see which channel it was on. Without this feature, the user would have to use the channel selector to switch to the channel where the last message occurred. (This option can cause confusion and users must be trained to understand this feature.)

    This is an incomplete list of some conventional radio types:

    Trunked Edit

    In a trunked radio system, the system logic automatically picks the physical radio frequency channel. There is a protocol that defines a relationship between the radios and the radio backbone which supports them. The protocol allows channel assignments to happen automatically.

    Digital trunked systems may carry simultaneous conversations on one physical channel. In the case of a digital trunked radio system, the system also manages time slots on a single physical channel. The function of carrying simultaneous conversations over a single channel is called multiplexing.

    Instead of channels, radios are related by groups which may be called, groups, talk groups, or divided into a hierarchy such as fleet and subfleet, or agency-fleet-subfleet. These can be thought of as virtual channels which appear and disappear as conversations occur.

    As with wide-area geographic conventional systems, geographic trunked radio systems require the user to switch channels as they travel unless the radio is equipped with automatic roaming. As of 2018, most all modern trunked radio systems were capable of automatic roaming.

    Systems make arrangements for handshaking and connections between radios by one of these two methods:

    • A computer assigns channels over a dedicated control channel. The control channel sends a continual data stream. All radios in the system monitor the data stream until commanded by the computer to join a conversation on an assigned channel.
    • Electronics embedded in each radio communicate using a protocol of tones or data in order to establish a conversation, (scan-based).

    If all physical channels are busy, some systems include a protocol to queue or stack pending requests until a channel becomes available.

    Some trunked radios scan more than one talk group or agency-fleet-subfleet.

    Visual clues a radio may be trunked include the 1) lack of a squelch knob or adjustment, 2) no monitor button or switch, and 3) a chirp (made famous by Nextel) showing the channel is available and ready at the moment the push-to-talk is pressed.

    This is an incomplete list of some trunked technologies and manufacturer marketing names:

      Phase I (trunking models) Phase II Tier III (abbreviated LTR)
  • Motorola SmartZone and SmartNet
  • Ericsson/Harris EDACS
  • Icom IDAS Digital Advanced System
  • PositionPTT - Push to Talk Two-Way Mobile Radio communication Network
  • Simplex versus duplex channels Edit

    Simplex Edit

    Simplex channel systems use a single channel for transmit and receive. This is typical of aircraft VHF AM, citizen's band and marine radios. Simplex systems are often legacy systems that have existed since the 1930s. The architecture allows old radios to work with new ones in a single network. In the case of all ships worldwide or all aircraft worldwide, the large number of radios installed, (the installed base,) can take decades to upgrade. Simplex systems often use open architectures that allow any radio meeting basic standards to be compatible with the entire system.

    • Advantage: as the simplest system configuration, there is reliability since only two radios are needed to establish communication between them, without any other infrastructure.
    • Disadvantages: The simplex configuration offers communication over the shortest range or distance because mobile units must be in effective range of each other. The available channel bandwidth limits the number of simultaneous conversations, since "dead" air time cannot be easily used for additional communication.

    Duplex Edit

    Duplex channel systems transmit and receive on different discrete channels. This defines systems where equipment cannot communicate without some infrastructure such as a repeater, base station or Talk-Through Base. Most common in the US is a repeater configuration where a base station is configured to simultaneously re-transmit the audio received from mobile units. This makes the mobiles, or hand-helds, able to communicate amongst one another anywhere within reception range of the base station or repeater. Typically the base or repeater station has a high antenna and high power, which allows much greater range, compared with a ground vehicle or hand-held transceiver.

    Duplex systems can be divided into two types. The term half-duplex refers to systems where use of a push-to-talk switch is required to communicate. Full duplex refers to systems like mobile telephones with a capability to simultaneously receive and transmit. Repeaters are by nature full duplex, most mobiles and almost all handhelds are half duplex.

    • Advantage: duplex channels usually allow repeater operation which extends range (in most cases due to increased transmit power and improved aerial location / height) – especially where hand-held radios are in use.
    • Disadvantage: If a radio cannot reach the repeater, it cannot communicate.

    Hybrid simplex/duplex Edit

    Some systems use a mix of the two where radios use duplex as a default but can communicate simplex on the base station channel if out-of-range. [6] In the US, the capability to talk simplex on a duplex channel with a repeater is sometimes called talk-around, direct, or car-to-car.

    Push-to-talk (PTT) Edit

    In two-way radios with headsets, a push-to-talk button may be included on a cord or wireless electronics box clipped to the user's clothing. In fire trucks or an ambulance a button may be present where the corded headset plugs into the radio wiring. Aircraft typically have corded headsets and a separate push-to-talk button on the control yoke or control stick. Dispatch consoles often have a hand-operated push-to-talk buttons along with a foot switch or pedal. If the dispatcher's hands are on a computer keyboard, the user can step on the foot pedal to transmit. Some systems have muting so the dispatcher can be on a telephone call and the caller cannot hear what is said over the radio. Their headset microphone will mute if they transmit. This relieves the dispatcher of explaining every radio message to a caller.

    In some circumstances, voice-operated transmit (VOX) is used in place of a push-to-talk button. Possible uses are handicapped users who cannot push a button, amateur radio operators, firefighters, crane operators, or others performing critical tasks where hands must be free but communication is still necessary.

    Analog versus digital Edit

    One example of analog radios are AM aircraft radios used to communicate with control towers and air traffic controllers. Another is a Family Radio Service walkie talkie. Analog equipment is less complex than the simplest digital.

    • Advantage: In high-quality equipment, better ability to communicate in cases where a received signal is weak or noisy.
    • Disadvantage: Only one conversation at a time can occur on each channel.

    Examples of digital communication technologies are all modern cellphones plus TETRA considered to be the best standard in digital radio and being the baseline infrastructure for whole of country networks, including manufacturers such as DAMM, Rohill, Cassidian, Sepura and others, APCO Project 25, a standard for digital public safety radios, and finally other systems such as Motorola's MotoTRBO, HQT's DMR, Nextel's iDEN, Hytera's DMR, EMC's DMR, and NXDN implemented by Icom as IDAS and by Kenwood as NEXEDGE. Only NXDN and Mototrbo are proprietary. DMR is an ETSI open standard.

    • Advantage: More simultaneous talking paths are possible and information such as unit ID, status buttons, or text messages can be embedded into a single digital radio channel. The interoperability standard of TETRA means that any brand TETRA radio can work with any Brand TETRA infrastructure, not locking the user into expensive and proprietary systems.
    • Disadvantage: Radios must be designed to the same, compatible standard, radios can become obsolete quickly (although this is mitigated by properly implemented interoperability standards such as those set down by ETSI for TETRA), cost more to purchase, and are more complicated.

    Data over two-way radio Edit

    In some cases, two-way radio is used to communicate analog or digital data. Systems can be simplex or duplex and may employ selective calling features such as CTCSS. In full-duplex systems, data can be sent real-time between two points. In simplex or half-duplex, data can be sent with a time lag between many points.

    Some two-way digital systems carry both audio and data over a single data stream. Systems of this type include NXDN and APCO Project 25. Other more advanced systems under the TETRA standard are capable of joining time slots together to improve data bandwidth, allowing advanced data polling and telemetry applications over radio. The method of encoding and decoding the audio stream is called a codec, such as the AMBE or the ACELP family of codecs.

    After market GPS tracking and mobile messaging devices can be interfaced with popular two-way radio models providing a range of features.

    Analog Edit

    Analog systems may communicate a single condition, such as water level in a livestock tank. A transmitter at the tank site continually sends a signal with a constant audio tone. The tone would change in pitch to indicate the tank's water level. A meter at the remote end would vary, corresponding to the tone pitch, to indicate the amount of water present in the livestock tank. Similar methods can be used to telemeter any analog condition. This type of radio system serves a purpose equivalent to a four-to-twenty milliampere loop. [7] In the US, mid-band 72–76 MHz or UHF 450–470 MHz interstitial channels are often used for these systems. Some systems multiplex telemetry of several analog conditions by limiting each to a separate range of tone pitches, for example. [8]

    Digital Edit

    Digital systems may communicate text messages from computer-aided dispatch (CAD). For example, a display in a tow truck may give a textual location for a call and any related details. The tow truck driver may press an acknowledge button, sending data in the opposite direction and flagging the call as received by the driver. They can be used for analog telemetry systems, such as the livestock tank levels, as described above. Another possibility is the lubricating oil pressure in a transit bus engine, or the current speed of the bus. Analog conditions are translated into data words. Some systems send radio paging messages which can either 1) beep a paging receiver, 2) send a numeric message, or 3) send a text message. [9]

    Digital systems typically use data rates in the 1,200–19,200 kilobit-per-second rates and may employ modulation schemes such as frequency shift keying, audio frequency shift keying, or quadrature phase shift keying to encode characters. Modern equipment have the same capabilities to carry data as are found in Internet Protocol. Working within the system's protocol constraints, virtually anything can be sent or received.

    Engineered versus not engineered Edit

    Engineered systems are designed to perform close to a specification or standard. They are designed as systems with all equipment matched to perform together. For example, a modern, local government two-way radio system in the US may be designed to provide 95% area coverage in an urban area. System designers use radio frequency models, terrain models, and signal propagation modeling software in an attempt to accurately estimate where radios will work within a defined geographic area. The models help designers choose equipment, equipment locations, antennas, and estimate how well signals will penetrate buildings. These models will be backed-up by drive testing and actual field signal level measurements. Designers adjust antenna patterns, add or move equipment sites, and design antenna networks in a way that will accomplish the intended level of performance. [10]

    Some systems are not engineered. Legacy systems are existing systems which were never designed to meet a system performance objective. They may have started with a base station and a group of mobile radios. Over a period of years, they have equipment added on in a building block style. Legacy systems may perform adequately even though they were not professionally designed as a coherent system. A user may purchase and locate a base station with an expectation that similar systems used in the past worked acceptably. A City Road Department may have a system that works acceptably, so the Parks Department may build a new similar system and find it equally usable. General Mobile Radio Service systems are not usually engineered.

    Options, duty cycle, and configuration Edit

    1940s tube-type land mobile two-way radios often had one channel and were carrier squelch. Because radios were costly and there were fewer radio users, it might be the case that no one else nearby used the same channel. A transmit and receive crystal had to be ordered for the desired channel frequency, then the radio had to be tuned or aligned to work on the channel. 12-volt mobile, tube-type radios drew several amperes on standby and tens-of-amperes on transmit. Equipment worked ideally when new. The performance of vacuum tubes gradually degraded over time. U.S. regulations required an indicator lamp showing the transmitter had power applied and was ready to transmit and a second indicator, (usually red,) that showed the transmitter was on. In radios with options, wire jumpers and discrete components were used to select options. To change a setting, the technician soldered an option jumper wire then made any corresponding adjustments.

    Many mobile and handhelds have a limited duty cycle. Duty Cycle is the ratio of listening time to transmit time and is generally dependent on how well the transmitter can shed the heat from the heat sink on the rear of the radio. A 10% duty cycle (common on handhelds) translates to 10 seconds of transmit time to 90 seconds of receive time. Some mobile and base equipment is specified at different power levels – for example 100% duty cycle at 25 watts and 15% at 40 watts. [11]

    The trend is toward increasing complexity. Modern handheld and mobile radios can have capacities as high as 255 channels. Most are synthesized: the internal electronics in modern radios operate over a range of frequencies with no tuning adjustments. High-end models may have several hundred optional settings and require a computer and software to configure. Sometimes, controls on the radio are referred to as programmable. By changing configuration settings, a system designer could choose to set up a button on the radio's control panel to function as:

    • turn scan on or off,
    • alert another mobile radio, (selective calling),
    • turn on an outside speaker, or
    • select repeater locations.

    In most modern radios these settings are done with specialized software (provided by the manufacturer) and a connection to a laptop computer.

    Microprocessor-based radios can draw less than 0.2 amperes on standby and up to tens-of-amperes on high-powered, 100 watt transmitters.

    Base stations, repeaters, and high-quality mobile radios often have specifications that include a duty cycle. A repeater should always be continuous duty. This means the radio is designed to transmit in a continuous broadcast without transmitter overheating and resulting failure. Handhelds are intermittent duty, mobile radios and base station radios are available in normal or continuous duty configurations. Continuous duty is preferred in mobile emergency equipment because any one of an entire fleet of ambulances, for example, could be pressed into service as command post at a major incident. Unfortunately budgets frequently get in the way and intermittent duty radios are purchased.

    Time delay is always associated with radio systems, but it is apparent in spacecraft communications. NASA regularly communicates with exploratory spacecraft where a round-trip message time is measured in hours (like out past Jupiter). For the Apollo program and the Space Shuttle, Quindar tones were used for transmit PTT control.

    Life of equipment Edit

    Though the general life term for the two-way radio is 5 to 7 years and 1 to 2 years for its accessories but still the usage, atmosphere and environment plays a major role to decide its life term (radios are often deployed in harsh environments where more fragile communication equipment such as phones and tablets may fail). There are so many speculations on the life term of two-way radios and their accessories i.e. batteries, chargers, headset etc.

    In government systems, equipment may be replaced based on budgeting rather than any plan or expected service life. Funding in government agencies may be cyclical or sporadic. Managers may replace computing systems, vehicles, or budget computer and vehicle support costs while ignoring two-way radio equipment. Equipment may remain in use even though maintenance costs are unreasonable when viewed from an efficiency standpoint. [12]

    Different system elements will have differing service lifetimes. These may be affected by who uses the equipment. An individual contacted at one county government agency claimed equipment used by 24-hour services wears out much faster than equipment used by those who work in positions staffed eight hours a day.

    One document says "seven years" is beyond the expected lifetime of walkie-talkies in police service. Batteries are cited as needing replacement more often. Twelve-year-old dispatch consoles mentioned in the same document were identified as usable. These were compared to problematic 21-year-old consoles used elsewhere in the same system. [13]

    Another source says system backbone equipment like consoles and base stations are expected to have a fifteen-year life. Mobile radios are expected to last ten years. Walkie talkies typically last eight. [14] In a State of California document, the Department of General Services reports expected service life for a communications console used in the Department of Forestry and Fire Protection is 10 years. [15]

    Two-way radio rental is an option for firms that need use of radios for only a limited time.

    Two-way radios can operate on many different frequencies, and these frequencies are assigned differently in different countries. Typically channelized operations are used, so that operators need not tune equipment to a particular frequency but instead can use one or more pre-selected frequencies, easily chosen by a dial, a pushbutton or other means. For example, in the United States, there is a block of 5 channels (pre-selected radio frequencies) are allocated to the Multiple Use Radio System. A different block of 22 channels are assigned, collectively, to the General Mobile Radio Service and Family Radio Service. The citizen's band radio service (""CB"") has 40 channels.

    In an analog, conventional system, (the simplest type of system) a frequency or channel serves as a physical medium or link carrying communicated information. The performance of a radio system is partly dependent on the characteristics of frequency band used. The selection of a frequency for a two-way radio system is affected, in part, by: [16]

    • government licensing and regulations.
    • local congestion or availability of frequencies.
    • terrain, since radio signals travel differently in forests and urban viewsheds.
    • the presence of noise, interference, or intermodulation.
    • sky wave interference below 50–60 MHz and tropospheric bending at VHF.
    • in the US, some frequencies require approval of a frequency coordination committee.

    A channel number is just a shorthand notation for a frequency. It is, for instance, easier to remember "Channel 1" than to remember "26.965 MHz" (US CB Channel 1) or "462.5625 MHz" (FRS/GMRS channel 1), or "156.05 MHz" (Marine channel 1). It is necessary to identify which radio service is under discussion when specifying a frequency by its channel number. Organizations such as electric power utilities or police departments may have several assigned frequencies in use with arbitrarily assigned channel numbers. For example, one police department's "Channel 1" might be known to another department as "Channel 3" or may not even be available. Public service agencies have an interest in maintaining some common frequencies for inter-area or inter-service coordination in emergencies (modern term: interoperability).

    Each country allocates radio frequencies to different two-way services, in accordance with international agreements. In the United States, some examples of two-way services are: citizen's band radio, Digital Electronic Message Service (DEMS), Family Radio Service (FRS), General Mobile Radio Service (GMRS), Multi-Use Radio Service (MURS), Business Radio Service (BRS), and PMR446.

    Amateur radio operators nearly always use frequencies rather than channel numbers, since there is no regulatory or operating requirement for fixed channels in this context. Even amateur radio equipment will have "memory" features to allow rapidly setting the transmitter and receiver to favorite frequencies.

    The most common two-way radio systems operate in the VHF and UHF parts of the radio spectrum. Because this part of the spectrum is heavily used for broadcasting and multiple competing uses, spectrum management has become an important activity of governments to regulate radio users in the interests of both efficient and non-interfering use of radio. Both bands are widely applied for different users.

    UHF has a shorter wavelength which makes it easier for the signal to find its way through smaller wall openings to the inside of a building. The longer wavelength of VHF means it can transmit further under normal conditions. For most applications, lower radio frequencies are better for longer range and through vegetation. A broadcasting TV station illustrates this. A typical VHF TV station operates at about 100,000 watts and has a coverage radius range of about 60 miles. A UHF TV station with a 60-mile coverage radius requires transmitting at 3,000,000 watts. Another factor with higher frequencies (UHF) is that smaller sized objects will absorb or reflect the energy more which causes range loss and/or multipath reflections which can weaken a signal by causing an "Out of Time/Out of Phase" signal to reach the antenna of the receiver (this is what caused the "Ghost" image on old over the air television).

    If an application requires working mostly outdoors, a VHF radio is probably the best choice, especially if a base station radio indoors is used and an external antenna is added. The higher the antenna is placed, the further the radio can transmit and receive.

    If the radios are used mainly inside buildings, then UHF is likely the best solution since its shorter wavelength travels through small openings in the building better. There are also repeaters that can be installed that can relay any frequencies signal (VHF or UHF) to increase the communication distance.

    There are more available channels with UHF. Since the range of UHF is also not as far as VHF under most conditions, there is less chance of distant radios interfering with the signal. UHF is less affected than VHF by manmade electrical noise.

    The useful direct range of a two-way radio system depends on radio propagation conditions, which are a function of frequency, [17] antenna height and characteristics, atmospheric noise, reflection and refraction within the atmosphere, transmitter power and receiver sensitivity, and required signal-to-noise ratio for the chosen modulation method. An engineered two-way radio system will calculate the coverage of any given base station with an estimate of the reliability of the communication at that range. Two-way systems operating in the VHF and UHF bands, where many land mobile systems operate, rely on line-of-sight propagation for the reliable coverage area. The "shadowing" effect of tall buildings may block reception in areas within the line-of-sight range which can be achieved in open countryside free of obstructions. The approximate line-of-sight distance to the radio horizon can be estimated from: horizon in kilometers = 3.569 times the square root of the antenna height in meters.

    There are other factors that affect the range of a two-way radio such as weather, exact frequency used, and obstructions. [17] [18]

    Not all two-way radios are hand-held devices. The same technology that is used in two-way radios can be placed in other radio forms. An example of this is a wireless callbox. A wireless callbox is a device that can be used for voice communication at security gates and doors. Not only can they be used to talk to people at these entry points, personnel can remotely unlock the door so the visitor can enter. There are also customer service callboxes that can be placed around a business that a customer can use to summon help from a two-way radio equipped store employee.

    Another use of two-way radio technology is for a wireless PA system. A wireless PA is essentially a one-way two-way radio that enables broadcasting messages from handheld two-way radios or base station intercoms.


    Contents

    The concept of a human "right to privacy" begins when the Latin word "ius" expanded from meaning "what is fair" to include "a right - an entitlement a person possesses to control or claim something," by the Decretum Gratiani in Bologna, Italy in the 12th Century. [6]

    In the United States, an article in the December 15, 1890 issue of the Harvard Law Review, written by attorney Samuel D. Warren and future U.S. Supreme Court Justice, Louis Brandeis, entitled "The Right to Privacy", is often cited as the first explicit finding of a U.S. right to privacy. Warren and Brandeis wrote that privacy is the "right to be let alone", and focused on protecting individuals. This approach was a response to recent technological developments of the time, such as photography and sensationalist journalism, also known as "yellow journalism". [7]

    Privacy rights are inherently intertwined with information technology. In his widely cited dissenting opinion in Olmstead v. United States (1928), Brandeis relied on thoughts he developed in his 1890 article The Right to Privacy. [7] In that dissent, he urged that personal privacy matters were more relevant to constitutional law, going so far as to say that "the government was identified as a potential privacy invader." He writes, "Discovery and invention have made it possible for the Government, by means far more effective than stretching upon the rack, to obtain disclosure in court of what is whispered in the closet." At that time, telephones were often community assets, with shared party lines and potentially eavesdropping switchboard operators. By the time of Katz, in 1967, telephones had become personal devices with lines not shared across homes and switching was electro-mechanical. In the 1970s, new computing and recording technologies raised more concerns about privacy, resulting in the Fair Information Practice Principles.

    In recent years there have been few attempts to clearly and precisely define the "right to privacy". [8]

    An individual right Edit

    Alan Westin believes that new technologies alter the balance between privacy and disclosure and that privacy rights may limit government surveillance to protect democratic processes. Westin defines privacy as "the claim of individuals, groups, or institutions to determine for themselves when, how, and to what extent information about them is communicated to others". Westin describes four states of privacy: solitude, intimacy, anonymity, reserve. These states must balance participation against norms:

    Each individual is continually engaged in a personal adjustment process in which he balances the desire for privacy with the desire for disclosure and communication of himself to others, in light of the environmental conditions and social norms set by the society in which he lives.

    — Alan Westin, Privacy and Freedom, 1968 [9]

    Under liberal democratic systems, privacy creates a space separate from political life, and allows personal autonomy, while ensuring democratic freedoms of association and expression. Privacy to individuals is the ability to behave, think, speak, and express ideas without the monitoring or surveillance of someone else. Individuals exercise their freedom of expression through attending political rallies and choosing to hide their identities online by using pseudo names.

    David Flaherty believes networked computer databases pose threats to privacy. He develops 'data protection' as an aspect of privacy, which involves "the collection, use, and dissemination of personal information". This concept forms the foundation for fair information practices used by governments globally. Flaherty forwards an idea of privacy as information control, "individuals want to be left alone and to exercise some control over how information about them is used". [10]

    Marc Rotenberg has described the modern right to privacy as Fair Information Practices: "the rights and responsibilities associated with the collection and use of personal information." Rotenberg emphasizes that the allocation of rights are to the data subject and the responsibilities are assigned to the data collectors because of the transfer of the data and the asymmetry of information concerning data practices. [11]

    Richard Posner and Lawrence Lessig focus on the economic aspects of personal information control. Posner criticizes privacy for concealing information, which reduces market efficiency. For Posner, employment is selling oneself in the labor market, which he believes is like selling a product. Any 'defect' in the 'product' that is not reported is fraud. [12] For Lessig, privacy breaches online can be regulated through code and law. Lessig claims "the protection of privacy would be stronger if people conceived of the right as a property right", and that "individuals should be able to control information about themselves". [13] Economic approaches to privacy make communal conceptions of privacy difficult to maintain.

    A collective value and a human right Edit

    There have been attempts to reframe privacy as a fundamental human right, whose social value is an essential component in the functioning of democratic societies. [14] Amitai Etzioni suggests a communitarian approach to privacy. This requires a shared moral culture for establishing social order. [15] Etzioni believes that "[p]rivacy is merely one good among many others", [16] and that technological effects depend on community accountability and oversight. He claims that privacy laws only increase government surveillance. [17]

    Priscilla Regan believes that individual concepts of privacy have failed philosophically and in policy. She supports a social value of privacy with three dimensions: shared perceptions, public values, and collective components. Shared ideas about privacy allow freedom of conscience and diversity in thought. Public values guarantee democratic participation, including freedoms of speech and association, and limits government power. Collective elements describe privacy as a collective good that cannot be divided. Regan's goal is to strengthen privacy claims in policy making: "if we did recognize the collective or public-good value of privacy, as well as the common and public value of privacy, those advocating privacy protections would have a stronger basis upon which to argue for its protection". [18]

    Leslie Regan Shade argues that the human right to privacy is necessary for meaningful democratic participation, and ensures human dignity and autonomy. Privacy depends on norms for how information is distributed, and if this is appropriate. Violations of privacy depend on context. The human right to privacy has precedent in the United Nations Declaration of Human Rights. Shade believes that privacy must be approached from a people-centered perspective, and not through the marketplace. [19]

    Privacy laws can apply to both government and private sector actors.

    United States Edit

    The Constitution and United States Bill of Rights do not explicitly include a right to privacy. [20]

    The Supreme Court in Griswold v. Connecticut, 381 U.S. 479 (1965) found in that the Constitution guarantees a right to privacy against governmental intrusion via penumbras located in the founding text. [21]

    The 1890 Warren and Brandeis Harvard Law Review article "The Right To Privacy" is often cited as the first implicit finding of a U.S. right to privacy. [7]

    This right to privacy has been the justification for decisions involving a wide range of civil liberties cases, including Pierce v. Society of Sisters, which invalidated a successful 1922 Oregon initiative requiring compulsory public education, Roe v. Wade, which struck down a Texas abortion law and thus restricted state powers to enforce laws against abortion, and Lawrence v. Texas, which struck down a Texas sodomy law and thus eliminated state powers to enforce laws against sodomy.

    Most states of the United States [ who? ] also grant a right to privacy and recognize four torts based on that right:

    1. Intrusion upon seclusion or solitude, or into private affairs
    2. Public disclosure of embarrassing private facts which places a person in a false light in the public eye and of name or likeness.

    The four privacy torts above were introduced by William Prosser in his California Law Review article titled "Privacy" in 1960. [22] Some argue that these torts, along with the "Right to Privacy" article by Samuel Warren and Louis Brandeis form the basis for modern U.S. privacy legislation. [23]

    European Union Edit

    Compared to the United States, the European Union (EU) has more extensive data protection laws. [24]

    The Council of Europe gathered to discuss the protection of individuals, during the Convention Treaty No.108 was created and opened for signature by members States and for accession by non-member States. [25]

    The Convention closed and the was renamed Convention 108: Convention for the Protection of Individuals with regard to Automatic Processing of Personal Data.

    Convention 108 has undergone 5 ratifications with the last ratification 10 January 1985 officially changing the name to Convention 108+ and providing the summary stating the intent of the treaty as:

    The first binding international instrument which protects the individual against abuses which may accompany the collection and processing of personal data, and which seeks to regulate at the same time the transfrontier flow of personal data. [26]

    Increase use of the Internet and technological advancement in products lead to the Council of Europe to look at Convention 108+ and the relevance of the Treaty in the wake of the changes.

    In 2011 the modernization of Convention 108+ started and completed in 2012 amending the treaty with Protocol CETS No223. [27]

    This modernization of Convention 108+ was in progress while the EU data protection rules were developed, the EU data protection rules would be adapted to become the General Data Protection Regulation (GDPR).

    Under GDPR, data about citizens may only be gathered or processed under specific cases, and with certain conditions. Requirements of data controller parties under the GDPR include keeping records of their processing activities, adopting data protection policies, transparency with data subjects, appointing a Data Protection Officer, and implementing technical safeguards to mitigate security risks.[1]

    China Edit

    Privacy rights have been applied to China. [28] However, in many cases these rights have been overlooked. China regularly spies on its citizens, largely through mass surveillance and CCTV. China has also been known to censor historical events that put the government of China in a bad light.

    Israel Edit

    In 2005, students of the Haifa Center for Law & Technology asserted that the right to privacy "should not be defined as a separate legal right" at all. By their reasoning, existing laws relating to privacy, in general, should be sufficient. [29] Other experts, such as William Prosser, have attempted but failed, to find a "common ground" between the leading kinds of privacy cases in the court system, at least to formulate a definition. [29] One law school treatise from Israel, however, on the subject of "privacy in the digital environment," suggests that the "right to privacy should be seen as an independent right that deserves legal protection in itself." It has therefore proposed a working definition for a "right to privacy":

    The right to privacy is our right to keep a domain around us, which includes all those things that are part of us, such as our body, home, property, thoughts, feelings, secrets, and identity. The right to privacy gives us the ability to choose which parts in this domain can be accessed by others and to control the extent, manner, and timing of the use of those parts we choose to disclose. [29]

    Russia Edit

    The Russian Federal Law of Personal Data was implemented on July 27, 2006. Its main target is to protect individuals' personal data. On March 1, 2021, the new amendment came into effect. Consent from the data subject is required if the data operator wants to use the data publicly. [30]

    India Edit

    A nine-judge bench of the Supreme Court headed by Chief Justice JS Khehar, ruled on August 24, 2017, that the Right to Privacy is a fundamental right for Indian citizens under the Constitution of India (mostly under Article 21 and additionally under Part III rights). Thus no legislation passed by the government can unduly violate it. Specifically, the court adopted the three-pronged test required for the encroachment of any Article 21 right – legality-i.e. through an existing law necessity, in terms of a legitimate state objective and proportionality, that ensures a rational nexus between the object of the invasion and the means adopted to achieve that object. This clarification was crucial to prevent the dilution of the right in the future on the whims and fancies of the government in power. [31] The Court adopted a liberal interpretation of the fundamental rights in order to meet the challenges posed an increasing digital age. It held that individual liberty must extend to digital spaces and individual autonomy and privacy must be protected. [32]

    This ruling by the Supreme Court paved the way for decriminalization of homosexuality in India on 6 September 2018, thus legalizing same-sex sexual intercourse between two consenting adults in private. [33] India is the world's biggest democracy and with this ruling, it has joined United States, Canada, South Africa, the European Union, and the UK in recognizing this fundamental right. [34]

    The new data sharing policy of Whatsapp with Facebook after Facebook acquired Whatsapp in 2014 has been challenged in the Supreme Court. The Supreme Court must decide if the right to privacy can be enforced against private entities. [35]

    Australia Edit

    In Australia, it is a chargeable offense to look at private or classified material.

    Governmental organizations such as the National Security Agency (NSA), CIA, and GCHQ amongst others are authorized to conduct mass surveillance throughout other nations in the world. Programs such as PRISM, MYSTIC, and other operations conducted by NATO-member states are capable of collecting a vast quantity of metadata, internet history, and even actual recordings of phone calls from various countries.

    Domestic law enforcement at the federal level is conducted by the Federal Bureau of Investigation, so these agencies have never been authorized to collect US data. [36]

    After the September 11 attacks, the NSA turned its surveillance apparatus on the US and its citizens. [37]

    In March 2013, James Clapper, the Director of National Intelligence at the time, testified under oath that the NSA does not "wittingly" collect data on Americans. Clapper later retracted this statement. [38]

    The Government's own Privacy and Civil Liberties Oversight Board (PCLOB) reviewed the confidential security documents, and found in 2014 that the program did have "a single instance involving a threat to the United States in which the program made a concrete difference" in counterterrorism or the disruption of a terrorist attack. [39]

    It is often claimed, particularly by those in the eye of the media, that their right to privacy is violated when information about their private lives is reported in the press. The point of view of the press, however, is that the general public has a right to know personal information about those with status as a public figure. This distinction is encoded in most legal traditions as an element of freedom of speech.

    Publication of private facts Edit

    Publication of private facts speaks of the newsworthiness of private facts according to the law and the protections that private facts have. [40] If a fact has significant newsworthiness to the public, it is protected by law under the freedom of the press. However, even if the fact is true, if it is not newsworthy, it is not necessarily protected. Digital Media Law Project uses examples such as sexual orientation, HIV status, and financial status to show that these can be publicly detrimental to the figure being posted about. [40] The problem arises from the definition of newsworthiness.

    Newsworthiness Edit

    According to Digital Media Law Project, the courts will usually side with the press in the publication of private facts. [40] This helps to uphold the freedom of the press in the US Constitution. “there is a legitimate public interest in nearly all recent events, as well as in the private lives of prominent figures such as movie stars, politicians, and professional athletes.” [40] Digital Media Law Project supports these statements with citations to specific cases. While most recent events and prominent figures are considered newsworthy, it cannot go too far and too deep with a morbid curiosity. [40] The media gain a lot of leverage once a person becomes a prominent figure and many things about their lives become newsworthy. Multiple cases such as Strutner v. Dispatch Printing Co., 442 N.E.2d 129 (Ohio Ct. App. 1982) [41] show that the publication of a person's home address and full name who is being questioned by the police is valid and “a newsworthy item of legitimate public concern.” The last part to consider is whether this could be considered a form of doxxing. With the court upholding the newspaper's right to publish, this is much harder to change in the future. Newsworthiness has much around it that is held up by court rulings and case law. This is not in legislation but is created through the courts, as many other laws and practices are. These are still judged on a case-by-case basis as they are often settled through a lawsuit of some form. [40] While there is a fair amount of case law supporting newsworthiness of subjects, it is hardly comprehensive and, news publications can publish things not covered and defend themselves in court for their right to publish these facts.

    Private sector actors can also threaten the right to privacy—particularly technology companies, such as Amazon, Apple, Facebook, Google, and Yahoo that use and collect personal data.

    In some American jurisdictions, the use of a person's name as a keyword under Google's AdWords for advertising or trade purposes without the person's consent [42] has raised certain personal privacy concerns. [43]

    The right to privacy and social media content laws have been considered and enacted in several states, such as California's “online erasure” law protecting minors from leaving a digital trail. However, the United States is still far behind that of European Union countries in protecting privacy online. For example, the “right to be forgotten” ruling by the EU Court of Justice protects both adults and minors. [44]

    United Kingdom Edit

    Laws and courts in the UK hold up the protection of minors in the journalistic space. The Independent Press Standards Organisation (IPSO) in the UK have shown that the usage of footage of a 12-year-old girl being bullied in 2017 can be retroactively taken down due to fears of cyber-bullying and potential harm done to the child in the future. [45] This was after the Mail Online published the video without any attempt to hide the identity of the child. Following the newsworthiness point, it is possible that content like this would be allowed in the United States due to the recentness of the event. [40] Protection of minors is a different matter in the United States with new stories about minors doing certain things and their faces are shown in a news publication. The Detroit Free Press, as an example, chose to do a hard-hitting story about prostitution and drugs from a teenager but never named her or showed her face, only referring to her and the “16-year-old from Taylor”. [46] In the UK, During the case of Campbell v MGN, Lord Hope stated that the protection of minors will be handled on a case-by-case basis and affected by the child's awareness of the photo and their expectation of privacy. [45] Many factors will be considered such as the age of the children, activity, usage of real names, etc. [45]

    United States Edit

    The protection of minors and children in the United States often falls on the shoulders of The Children's Online Privacy Protection Act (COPPA). [47] This protects any children under the age of 13 from the collection of their data without the parent's or guardian's permission. This law is the reason why many sites will ask if you are under 13 or require you to be 13 to sign up. While this law is good for protecting children's information, it fails to protect the information of anyone older than 13. It also begins to overlap with other privacy protection laws such as the Health Insurance Portability and Accountability Act (HIPPA)