What is Domain: Definition and 741 Discussions

A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet. Domain names are used in various networking contexts and for application-specific naming and addressing purposes. In general, a domain name identifies a network domain, or it represents an Internet Protocol (IP) resource, such as a personal computer used to access the Internet, a server computer hosting a website, or the web site itself or any other service communicated via the Internet. In 2017, 330.6 million domain names had been registered.Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name. Domain names are organized in subordinate levels (subdomains) of the DNS root domain, which is nameless. The first-level set of domain names are the top-level domains (TLDs), including the generic top-level domains (gTLDs), such as the prominent domains com, info, net, edu, and org, and the country code top-level domains (ccTLDs). Below these top-level domains in the DNS hierarchy are the second-level and third-level domain names that are typically open for reservation by end-users who wish to connect local area networks to the Internet, create other publicly accessible Internet resources or run web sites.
The registration of these domain names is usually administered by domain name registrars who sell their services to the public.
A fully qualified domain name (FQDN) is a domain name that is completely specified with all labels in the hierarchy of the DNS, having no parts omitted. Traditionally a FQDN ends in a dot (.) to denote the top of the DNS tree. Labels in the Domain Name System are case-insensitive, and may therefore be written in any desired capitalization method, but most commonly domain names are written in lowercase in technical contexts.

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  1. B

    MHB Noise signal in freq domain

    Hi Folks, I have an article which explains the modulation of 2 signals given by X_1(f) e^{-j 2 \pi f t_i} and X_2(f) e^{-j 2 \pi f t_i} The only difference between the 2 signals is a time delay, however i don't see a phase difference in either expression It states the convolution of these...
  2. Maged Saeed

    MHB Finding Domain & Range of $$y=\sqrt{x^2+y^2}$$

    I was thinking about a function whose domain and range are absolutely one point , then I'm stuck in finding the domain and range of the following function .. could anyone help $$y=\sqrt{x^2+y^2}$$
  3. evinda

    MHB Is $C[x,y,z]/<y-x^2,z-x^3>$ an Integral Domain?

    Hi! (Smile) Can I justify like that, that $C[x,y,z]/<y-x^2,z-x^3>$ is an integral domain? We show that $ker(\phi)=<y-x^2,z-x^3>$. From the theorem of isomorphism, we have that $C[x,y,z]/<y-x^2,z-x^3> \cong im(\phi)$ $im(\phi)$ is a subring of $\mathbb{C}[x]$ $\mathbb{C}[x]$ is an...
  4. A

    Prime Ideal & Noetherian Integral Domain

    I am reading a graduate-level Abstract Algebra lemma on noetherian integral domain, I am bring it up here hoping for pointers. The original passage is in one big-fat paragraph but I broke it down here for your easy reading. Let me know if I forget to include any underlying lemmas, thank you for...
  5. A

    Prime Ideal & Noetherian Integral Domain

    I am reading a graduate-level Abstract Algebra lemma on noetherian integral domain, I am bring it up here hoping for help. The original passage is in one big-fat paragraph but I broke it down here for your easy reading. Let me know if I forget to include any underlying lemmas, and especially...
  6. PhysicsKid0123

    Surface integrals/Surface areas of arbitrary domain regions

    I'm having trouble evaluating this surface integral. This would be very simple to solve if the parameter domain of the variables u and u was a square region. However, that isn't the case here. I've tried using a change of variables and saying that u = r cos x, and v = r sin x. Where 0 < x < 2pi...
  7. B

    Is the given set path connected? A Domain?

    Hello everyone, Here is the definition of path connected and domain my textbook provides: Definition 171. An open set S is path connected if each pair of points in S can be connected by a polygonal line (e.g. a finite number of line segments connected end to end). A domain is an open set that...
  8. T

    MHB Finding domain of a trigonometric function

    I need to find the domain of this function: $$f(x) = \frac{1+x}{ e^{cos(x)}}$$ I set $${ e^{cos(x)}}> 0$$ But I'm not sure what to do after this.
  9. Math Amateur

    MHB Elements of the form a/b in an integral domain - simple question

    In Alaca and Williams' (A&W) book: Introductory Algebraic Number Theory , Theorem 1.2.1 reads as follows:Without any earlier definition or clarification, A&W refer to a/p and b/p (see text above) ... BUT ... how should we regard such elements? What exactly do they mean and how do we know they...
  10. I

    Domain of a composite function

    Homework Statement Given the Functions f(x)=4x-1 g(x)=3-2x^2 h(x)= sqrt (x+5) What is the domain of h(g(x))? Homework Equations the subject is finding the domain of a composite function The Attempt at a Solution I don't understand what I have to 'bring over' from g(x). I think x cannot equal...
  11. T

    MHB Working on evaluating an 'e' equation to find the domain of an equation

    Find the domain of the equation $$1 \ne e^{1-x^2}$$ Is there a way to evaluate this function?
  12. T

    MHB Finding domain of a function with square root in bottom of fraction\infty

    I need to find the domain of this function.$$h(x) = 1 / \sqrt[4]{x^2 - 5x}$$ So, I understand that I need to set $$x^2 -5x > 0$$ from that I get $$ x(x-5) > 0$$ and $$ x > 5$$ However, the answer in the textbook is given: $$ ( \infty, 0) \cup (5, \infty)$$ Which mean that the graph has a...
  13. Dethrone

    MHB Domain and range of inverse functions (circular and hyperbolic)

    I've always been having trouble with the domain and range of inverse trigonometric functions. For example, let's start with an easy one: $\sin^{-1}\left({x}\right)$ Process: First, I draw out the function of $\sin\left({x}\right)$. Then I look at its range and attempt to restrict it so that it...
  14. L

    MHB Exploring the Domain and Asymptotes of x^2y+xy^2=2

    ¿domain and asinptotestotes of x^2y+xy^2 = 2? Answer (inf -2]U(0, inf +) asinptotes AV x = 0 AH y = 0 Oblique x-y = 0 I can isolate y or i mean solving for y
  15. D

    Identifying Domain and Range of Ovals with Given Points

    Homework Statement There are two vertical ovals, one containing the x-coordinate values and one containing the y-coordinate values. The x-axis values: -1, 8, 0 and the y-axis values: -4, 0, -1 (-1,-4) (8,0) and (0,-1) are the three points. Homework Equations I'm not sure this is an equation...
  16. T

    Domain of validity of an integral

    Homework Statement This integral is actually part of a question I had on an exam about analytic continuation. The integral is \int_0^1 dx \frac{x^n}{\sqrt{x^3+5}} . The first part of the question is "what is its domain of validity for absolute convergence of the integral?" It then goes...
  17. chisigma

    MHB Behavior of the logarithm function in the complex domain ....

    In...... it has beenshown in an elementary way that is ... $\displaystyle\int_{0}^{\infty}\frac{\ln x}{x^{2}+a^{2}}\ dx = \frac{\pi\ \ln a}{2\ a}\ (1)$The integral (1) isvery useful to shed light on the behavior of the logarithm functionin the complex field. Let's suppose we want to solve the...
  18. Y

    MHB Finding Domain of $\sqrt{sin(\sqrt{x})}$

    Hello all, First, congratulations on the quick LATEX bar on the side, will try it now the first time. I am looking for the domain of \sqrt{sin(\sqrt{x})} I need that the expression under the square root will be non-negative. The expression involves sin. The sin function is non-negative at...
  19. Math Amateur

    MHB If R is a domain , then units in R[x] are non-zero constants

    I am reading Joseph Rotman's book Advanced Modern Algebra. I need help with Problem 2.21 Part (i) on page 94. Problem 2.21 Part (i) reads as follows: -------------------------------------------------------------------- Let R be a domain. Prove that if a polynomial in R[x] is a unit, then it...
  20. E

    Circle in the Complex Domain where Mean is not the Centre

    Hello people of Physics Forums, In my research into transmission lines, I have come across the following function: x = ( a - i * b * tan(t) ) / ( c - i * d * tan(t) ) In the above equation x, a, b, c and d are complex and t is real. If my analysis is correct, varying t from -pi/2 to...
  21. C

    Finding the domain for a rational function.

    Hi I have the function I have worked out the domain as not equal to 1 using the fact the denominator can't equal 0. Now I am stuck finding the range. How would I find it without graphing. The answer is y<0 , y=>3.
  22. J

    Time Domain (Oscilloscope) View of a Photon or Light Wave

    We can view the amplitude vs time variation of an EM wave using an oscilloscope with the needed bandwidth. Such a view shows us the shape of the wave (sinusoid or other), the number of cycles contained in a given burst, any modulating signal etc. Though it wouldn't be measured with an...
  23. K

    Show F is Injective & Cardinality of Domain

    Homework Statement Let ## S = \{ (m,n) : m,n \in \mathbb{N} \} \\ ## a.) Show function ## f: S -> \mathbb{N} ## defined by ## f(m,n) = 2^m 3^n ## is injective b.) Use part a.) to show cardinality of S. The Attempt at a Solution a.) ## f(a,b) = f(c, d ) ; a,b,c,d \in \mathbb{N} \\\\ 2^a...
  24. S

    Exploring the 'Quantum Domain': A Look at a Higher Level of Existence

    What is 'Quantum Domain'? I read something about it being a level of existence... If it is a level of existence, what sort of classification of existence are we talking about?
  25. Y

    MHB Domain of f(x,y): Open or Closed?

    Hello all, I am trying to determine if the domain of the function: \[f(x,y)=\frac{\sqrt{ln(x^{2}+y^{2}+1)}}{\left | x \right |+\left | y \right |+\sqrt[4]{xy-1}}\] Is an open set or closed set and if it's bounded. The domain is in the attached graph. The book say it is closed and...
  26. A

    How to get transfer function (freq. domain) from Newton's 2nd Law Eqn

    Homework Statement I am given the following dynamic system. I want to find the transfer function, θ1(s)/T(s). The main body of the satellite, J1, acts like a large mass flying through space; space is essentially without friction and therefore no damping is imparted on the main body...
  27. gfd43tg

    AC Op-Amp output voltage expression in time domain

    Homework Statement For vi(t) =V0 cosωt, obtain an expression for vout(t) in the circuit below and then evaluate it for V0 = 4 V, ω = 400 rad/s, R = 5 kΩ, and C = 2.5 μF. Homework Equations The Attempt at a Solution For this problem, I am having difficulty taking that second term...
  28. M

    Why not Rectangular Mesh for Arbitrary Shape Domain?

    Hi all, It is well know that, rectangular or quadrilateral element gives better result over triangular meshes in finite element method. I know, Rectangular meshes has more discretization error, but my question is that, if i refine mesh up to 4 to 6 pixel width of screen, where i am wrong?
  29. L

    MHB Drawing Arrow Diagrams & Explaining Domain, Codomain & Range

    Hi Folks, Have a task , but no idea how to resolve. Will appreciate any help. Consider the function f: {5,6,7} →{A,B,C} given by f(5)=A, f(6)=C, and f(7)=B Draw its arrow diagram and state its domain, codomain and range. Is it (i) onto and (ii) one-to-one ? Explain. Does it have...
  30. D

    MHB Understanding the First Order Prototype Solution in Time Domain

    Consider the first order prototype, \[ \frac{dy(t)}{dt} + \frac{1}{\tau}y(t) = f(t),\] driven by a step function, \[ f(t) =...
  31. B

    What is the domain of a function?

    Homework Statement Homework Equations How do you find the domain? The Attempt at a Solution I figure (1,10) makes sense because it can't be 0 because its needs a quantity to exist. Right? I see they came up wit 5, but how did they get 5 exactly? They say its just because its...
  32. S

    Engineering Solve Series-Parallel Circuit in Phasor Domain

    Homework Statement Where Vs = 120 ∠0° V Homework Equations All values are represented in ohms, so they are treated as resistors. The Attempt at a Solution Series inductor + resistor 30+j10 ohms = 31.62∠18.435° Parallel resistor and inductor+resistor (1/50)= 0.02∠0°...
  33. M

    Finite Difference Solution to Poisson's Equation on Irregular Domain

    Hi, Are there any open source C or Fortran libraries for solving 3D Poisson'sequation on an irrefular domain? I'm having difficulty finding them. If not, is there any papers or recipes that would be useful so I could write my own? Speed is not a priority, I just need anything that works...
  34. B

    Fourier transform and the frequency domain

    I understand that the Fourier transform maps one function onto another. So it is a mapping from one function space onto another. My question is, why is it often referred to as a mapping from time domain to the frequency domain? I don't understand why the image of the Fourier transform...
  35. P

    MHB Question about domain under a curve with derivative?

    So I have this question: After screen-shotting it I realized I added instead of subtracting, so my answer to the first part is about 4.7...is that right? The second part I'm not sure at all how to find the equation for the derivative of the curve.. when I don't have the equations for h(x)...
  36. C

    Smooth maps between manifolds domain restriction

    Let ##M## and ##N## be smooth manifolds and let ##F:M \to N## be a smooth map. Iff ##(U,\phi)## is a chart on ##M## and ##(V,\psi)## is a chart on ##N## then the coordinate representation of ##F## is given by ##\psi \circ F \circ \phi^{-1}: \phi(U \cap F^{-1}(V)) \to \psi(V)##. My question is...
  37. G

    Laplace Transform Within a Domain

    Homework Statement Find the Laplace transform of f(t) = t \forall 0≤t≤T, 0 otherwise Homework Equations The Attempt at a Solution I write the function as tu(t)-t*u(t-T) That is turn on the function t at t=0 and turn the function t off at t=T. It seems to be right to me...
  38. C

    Determine domain for a trig ratio and the general solution of angle me

    Problem statement Given sin theta (sqrt 3)/2 Determine the domain for the following solution https://www.physicsforums.com/attachments/655052) determine each general solution using the angle measure specified. Revelant equations Attempt at solution1What is the reasoning behind that? For...
  39. C

    Domain of composite function

    Let's say f(x) = sqrt(x-1) And g(x) =x^2 What is the domain of f(g(x)) Well the domain of g(x) is all real numbers and the equation for the new function is sqrt(x^2-1) Am I right to say that the domain for f(g(x)) is x greater than or equal to 1 and less than and equal to -1??
  40. NATURE.M

    Prove Domain of Identity: (-1, 1], C is Any Real Number

    Homework Statement Prove that there is a constant C such that arctan\sqrt{\frac{1-x}{1+x}} = C - \frac{1}{2}arcsinx for all x in a certain domain. What is the largest domain on which this identity is true? What is the value of the constant C? The Attempt at a Solution Now I know how...
  41. Y

    MHB Domain of a function with 2 variables

    Hello all, I am trying to find and draw the domain of this function: \[f(x,y)=\sqrt{ln(\frac{9}{x^{2}+y^{2}})}\] Somehow I find some technical difficulty with it. I have found 3 conditions: \[\ln \left ( \frac{9}{x^{2}-y^{2}} \right )\geq 0\] and \[\frac{9}{x^2-y^2}>0\] and \[x^2\neq...
  42. Lebombo

    Change in domain as variable changes in Parametric Equations.

    This question is from the parametric equations chapter of my calc book. I am given x =\frac{1}{\sqrt{t+1}} and y = \frac{t}{t+1}, for (x> -1) Solving the x(t) for t, we get \frac{1- x^{2}}{x^{2}} Eliminating the parameters by substitution, we get y = 1 - x^{2} for (x > 0) My question is...
  43. S

    How Can I Analyze the Frequency Response of an Electric Current Shell in Comsol?

    Hello people, i need help with frequency domain study in electric current shell modul. I have one IDC and i have electrodes from gold, and i don't know what should i do to see my frequency response on diagramm? Does anyone has any idea?
  44. C

    Finding domain and ranges for composition function

    Homework Statement Find the domain and range of (f+g)(x) Given that F(x)= 1/(x-1) and g(x) = sqrt(x) Homework Equations The Attempt at a Solution I added the two functions to get 1/(x-1) + sqrt(x) To get domain, i look at the restrictive x values for both to get x greater than 0 and not...
  45. C

    Domain and ranges of composition function

    My teacher discussed an in and out method that could be used however I don't understand how that works. Can someone explain it to me? The teacher said this method would allow us to determine the domain and range without knowing what the graph looked like. How I have been doing it is looking at...
  46. S

    MHB  Domain of y = x\sqrt{1-x^2}: -1 ≤ x ≤ 1

    state the domain y = x\sqrt{1 - x^2} so 1 - x^2 >= 0 -x^2 >= -1 x^2 <= 1 d = {x <= (+)(-) 1} or should I say d = {-1, 1} which one is correct?
  47. C

    DSP, going from freq domain to time domain

    Homework Statement X(w) = 3cos(2w) + 2 sin(3w) calculate x(n) Homework Equations x(n) = (1/2pi) ∫ X(w) e^(jwn)dw The Attempt at a Solution When integrating over 0 to 2 pi, my answer is 0. Which would not be the case.
  48. L

    Solving Multivariable Domain: x^2+y^2<=|z^2|

    Homework Statement I'm having a problem with solving the domain of |x^2+y^2|<=|z^2|. Homework Equations The Attempt at a Solution From what I got this should be separated into two expressions: x^2+y^2<=z^2, and x^2+y^2>=-z^2. The later doesn't have a real solution because of the...
  49. N

    How do you find the zero-input response in the frequency domain?

    I'm working on a problem and one part of it is finding the zero-input response of a system in the frequency (or "s") domain. The zero-state response can be easily found in the frequency domain, it's just: Y_{zs} = X(S)H(S) But I can't for the life of me find the equation for calculating...
  50. K

    Natural frequency from time domain and frequency domain plot

    Anyone have an idea to find a first and second natural frequency from time domain and frequency domain plot resulting from an accelerometer measuring the vibration in cantilever beam ? Thanks very much :)
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