What is Derivation: Definition and 1000 Discussions

In cryptography, a key derivation function (KDF) is a cryptographic hash function that derives one or more secret keys from a secret value such as a main key, a password, or a passphrase using a pseudorandom function. KDFs can be used to stretch keys into longer keys or to obtain keys of a required format, such as converting a group element that is the result of a Diffie–Hellman key exchange into a symmetric key for use with AES. Keyed cryptographic hash functions are popular examples of pseudorandom functions used for key derivation.

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  1. Hardik Batra

    Discover the Derivation of Solid Angle: Short and Simple Method

    I want to know the derivation of solid angle. I have found on net. But the derivation is to long, is there any short method?
  2. ChrisVer

    Problem with derivation of phase for 1-fermion state

    Take a look at the attachment, my question is obvious from the colored points. The attachment is from: "state-of-the-art formulas for helicity amplitude calculation and all that (version 2.4) PART Ia. Spherical-Vector Method for Helicity Amplitudes (FORMALISM) Ken-ichi Hikasa" I think...
  3. F

    Power Law Derivation for dynamic systems

    Just a quick question. Let A and B be two points. Electrical work is defined as the amount of energy it takes to move an amount of charge Q through a potential difference VB-VA (for our purposes here, we will assume that the voltage values are measured with respect to an Earth ground) and is...
  4. E

    Derivation of Velocity from Acceleration in Special Relativity

    I got stuck in deriving the velocity of the particle from the acceleration equation. Here are the details of the problem. The acceleration of a particle with a relativistic momentum is \vec{a} = \frac{\vec{F}}{\gamma m} - \frac{\vec{v}}{\gamma m c^2}\left(\vec{F} \cdot \vec{v}\right)...
  5. C

    Derivation eqn motion particle rotating frame

    Homework Statement So this isn't a homework problem but I don't know where else I am supposed to post for general help. I am basically trying to understand the derivation for the equation of motion of a particle in a rotating frame. See attachment for derivation and which steps I am stuck on...
  6. MathematicalPhysicist

    Derivation in Srednicki's which got me puzzled.

    Hi. on page 95 , I am not sure how did he derive the second term on the RHS of equation (13.16). http://books.google.co.il/books?id=5OepxIG42B4C&printsec=frontcover&dq=srednicki+page+95&hl=en&sa=X&ei=XDLFU8bCIobV4QSnhYFA&ved=0CBsQ6AEwAA#v=onepage&q&f=false I mean if I plug back I should get...
  7. I

    Derivation of Faraday's Law of Induction?

    I was wondering if someone could show me the derivation of Faraday's Law of induction from the more fundamental Lorentz Force.
  8. S

    RC time Circuit; charge of capacitor as a function of time derivation

    Hey guys! New to physicsforums. I wanted to ask a more conceptual question regarding RC time Circuits. I spent some time trying to derive the equations, and I feel like I'm not setting up the problem correctly. Here's my attempt: Solutions according to profecssor: 1)...
  9. L

    Josephson junction. Derivation.

    Homework Statement ## \alpha \frac{d^2\theta}{dt^2}+\beta\frac{d\theta}{dt}+V'(\theta)=V(t) ## Inertial effects are negligible at frequencies of up to several hundred megahertz, so the first therm can be neglected. I'm not sure if that means that ## \beta\frac{d\theta}{dt}+V'(\theta)=V(t) ##...
  10. hideelo

    Problem understanding the derivation of the Boltzman distribution

    I am currently reading "Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles" by Robert Eisberg and Robert Resnick (2nd edition). In Appendix C they derive the boltzman distribution and they seem to be saying something that seems to me to be patently false. If you have the book...
  11. A

    Derivation of relativistic momentum

    Hi all, Is it possible to derive the equation p = ymv, and hence based on this, kinetic energy formula, without referring to 4-vectors or 2-dimensional collisions, that is derive it in one dimension? I tried this website/pdf but the mathematics is beyond my understanding. So could some one...
  12. C

    Derivation of the Noether current

    (The problem I have is really at the end, however, I have provided my whole argument in detail for clarity and completeness at the cost of perhaps making the thread very unappealing to read) Homework Statement (c.f Di Francesco's book, P.41) We are given that the transformed action under an...
  13. D

    Cannot make sense of a derivation step involving dirac delta

    I am self studying the 17th Chapter of "Mathematical Methods for Physics and Engineering", Riley, Hobson, Bence, 3rd Edition. It is about eigenfunction methods for the solution of linear ODEs. Homework Statement On page 563, it states: "As noted earlier, the eigenfunctions of a...
  14. B

    Derivation of Noether currents under Lorentz Transformation

    Is there anywhere I can see the explicit derivation for a massless real scalar and for the EM field? thank you.
  15. D

    Why Does Planck's Law Assume Oscillator Energy Applies to Electromagnetic Modes?

    The derivation of Planck's law in my textbook begins with the assumption that the energy of an oscillator with frequency ##\nu## is quantised in units of ##h\nu##. It follows that the average energy of such an oscillator (in equilibrium with a reservoir at temperature ##T##) will be...
  16. J

    Derivation in classical mechanics

    I'm studying classical mechanics and I'm stumbling in the quantity of differential identities. Being S the action, H the hamiltonian, L the lagrangian, T the kinetic energy and V the potential energy, following the relationships: But, the big question is: that's all? Or has exist more...
  17. Runei

    Integrating a differential (Problem in thermodynamic derivation)

    Hi, I'm looking at a derivation of the thermodynamics of black-body radiation. My question is in regards to the math of the derivation. Using the first law of thermodynamics and considering an adiabatic expansion of the cavity, it can be stated that dU = -\frac{u}{3}dV Here small u...
  18. A

    Derivation of Kinetic energy formula and energy principle

    Hi all, Here is the derivation of kinetic energy from Work: W = ∫Fds From the second law of motion F = dp/dt, which is equal to mdv/dt, so: W = m∫dvdx/dt which = m∫dv x v because dx/dt = v Therefore W = 1/2mv2, when integrated. However from simple algebra derivation, W = Δ1/2mv2...
  19. E

    Longitudinal strain rate derivation

    Hi, The attachment below is about strain rate in fluids*. It shows how the strain rate d\phi/dt is related to the velocity field derivative du/dx when you stretch the element in x (i.e. longitudinal strain). It has no intermediate steps, and I can't see how the angle has been related to...
  20. D

    Derivation of Rayleigh-Jeans law

    All the derivations of the Rayleigh-Jeans 'Law' I've seen assume that the electromagnetic radiation is enclosed in a cube. I'm trying to derive the law using less arbitrary circumstances. That is, by starting with the equation U=\int \left[ \frac{\epsilon_0}{2}E^2 + \frac{1}{2\mu_0}B^2...
  21. K

    Derive PV=nRT: Exploring the Ideal Gas Equation

    http://quantumfreak.com/derivation-of-pvnrt-the-equation-of-ideal-gas/ here is the link. so we assume the particle hits two surfaces of the cube, thus pressure is 1/3. combine the equation #11 and #12 we solve kinetic energy equation #12 for mv2. 13...
  22. ABunyip

    Time Slowing Rate & Gravity: A Derivation

    I want to consider the rate at which time slows as gravity increases near a massive object such as a sun or even a black hole. Obviously there is a distance component here but I am after a generalisation that simply shows the relationship between time and gravity (ought to be possible)...
  23. F

    Correlation function poles in Peskin's derivation of LSZ formula

    Hi folks, Been trying to fill some of the more formal gaps in my knowledge by tackling the more technical stuff in P&S Chapter 7. Their derivation of the LSZ formula is quite different to those of books like, say, Srednicki, as they basically Fourier transform the whole argument as I...
  24. davidbenari

    Derivation of Bernoulli's Equation via conservation of E

    So I'm not OK with how some people derive this equation. These people consider a pipe whose endings have cross-sectional areas and heights which are different. They then use the conservation of energy principle by saying dW = dK + dU (Where W is work, K is kinetic energy, and U is potential...
  25. R

    Derivation of damped frequency

    Hiya can anyone show how to derive the euqation of damped frequency for a spring ωd = ωnsqrt(1-ζ2)
  26. S

    Derivation of an integral identity from the kdv equation.

    Hi everybody! First post!(atleast in years and years). The stationary KdV equation given by $$ 6u(x)u_{x} - u_{xxx} = 0 $$. It has a solution given by $$ \bar{u}(x)=-2\sech^{2}(x) + \frac{2}{3} $$ This solution obeys the indentity $$ \int_{0}^{z}\left(\bar{u}(y) -...
  27. N

    Osmotic pressure, question on derivation (TD)

    I'm currently reading about thermodynamics and osmosis and I happened to stumble across this paper. There is one thing I don't really understand, though.. In chapter 8 the author wishes to give a thermodynamic explanation of the osmotic pressure so I've been reading through the derivation. When...
  28. C

    Semi-Classical/Classical derivation of ideal gas partition function

    In the semi-classical treatment of the ideal gas, we write the partition function for the system as $$Z = \frac{Z(1)^N}{N!}$$ where ##Z(1)## is the single particle partition function and ##N## is the number of particles. It is semi-classical in the sense that we consider the...
  29. C

    Relativistic Energy Derivation

    Whilst reading following a derivation of the Relativistic Energy equation I came across the following: d/dt[mu/(1-u2/c2)1/2] = [m/(1-u2/c2)3/2] du/dt. I was wondering how that step was done.
  30. maverick280857

    Derivation of the Tolman-Oppenheimer-Volkoff equation

    Hi, I am working through Section 5.8 of Sean Carroll's book on GR. Does someone know where I can find the bridging steps that take me from \nabla_\mu T^{\mu\nu} = 0 to (\rho + p)\frac{d\alpha}{dr} = -\frac{dp}{dr} This is equation 5.153, and when I try to derive it through the...
  31. S

    Understanding derivation of scattering from Maxwells eqns

    I am trying to follow a Maxwell's equations derivation for light scattering but don't understand 'why' the authors do the steps they do at this start bit. Help would be greatly appreciated... It starts with the incident electric field equation. \textbf{E}_{0}(\textbf{r},t) = \textbf{E}_0...
  32. D

    Derivation of Marcus Electron Transfer Theory

    Dear , Can someone please tell me what material I can refer to for the derivation of Marcus Electron Transfer Theory.
  33. D

    Derivation of Marcus Electron Transfer Theory

    Dear , Can someone please tell me what material I can refer to for the derivation of Marcus Electron Transfer Theory.
  34. O

    Deriving E=mc^2: Special Relativity Explained

    Reading into some special relativity, I have seen E=mc^2 proposed from the assumption of four momentum conservation and the fact that the 'mass' component varies with velocity with the gamma factor, like a kinetic energy. This seems a bit of a leap of faith to me so I was wondering if there...
  35. Soumalya

    Derivation of ideal gas equation

    Is the following approach used for the derivation of the ideal gas equation correct? Here's the link: http://www.mikeblaber.org/oldwine/chm1045/notes/Gases/IdealGas/Gases04.htm
  36. paulmdrdo

    PIV (diode peak inverse voltage) derivation formula

    can you check if my solution here is correct. If not can you tell me how to do it properly. thanks!
  37. I

    Derivation of 1st london equation.

    This is my first time posting here, I apologize if this is the wrong place to ask such a question. In my book I have the following London equation written (1st) for a superconductor: E=μ0λ2L∂J/∂t where: λ2L is the london penetration depth. My understanding is that it can be derived...
  38. B

    Derivation of r (radius) in terms of f (frequency)? Help please.

    Okay, so the job I need to do is derive an equation for the radius of an object in terms of its frequency. These are the equations that we are allowed to use: v(Linear velocity) = rω v=2πr/T ω (angular velocity)=2πf f (frequency)= 1/T (time period) T= 2πr/v a (centripetal...
  39. P

    Derivation of Noether's theorem in Lagrangian dynamics

    I'm going to run through a derivation I've seen and ask a few questions about some parts that I'm unsure about. Firstly the theorem: For every symmetry of the Lagrangian there is a conserved quantity. Assume we have a Lagrangian L invariant under the coordinate transformation qi→qi+εKi(q)...
  40. BiGyElLoWhAt

    Exploring LaGrangian Derivation: Why is It T-V?

    Last semester I had intermediate mechanics, and we spent a good amount of the class studying the LaGrangian. One thing that I never got an explanation for was why ##L = T-V##, as opposed to ##T+V##. The only reason I can think of is the "give and take" relationship that Kinetic and Potential...
  41. B

    Geometric Derivation of the Complex D-Bar Operator

    This picture from https://www.amazon.com/dp/0198534469/?tag=pfamazon01-20 is all you need to derive the Cauchy-Riemann equations, i.e. from the picture we see i \frac{\partial f}{\partial x} = \frac{\partial f}{\partial y} should hold so we have i \frac{\partial f}{\partial x} = i...
  42. D

    Lorentz Transformations: Deriving from Einstein's Postulates

    I'm currently going through my courses notes for relativity. We looked at Einsteins two postulates and then said that time must therefore dilate due to constant speed of light. That I understand, however I'm still confused about the Lorentz's transformations. My notes start with a basic form of...
  43. B

    Derivation of Breit-Wigner formula

    Homework Statement The start of the derivation is shown in the attached image. I don't follow the argument that takes us from (91) to (92). The Attempt at a Solution I accept that the wavefunction of (91) is not an eigenstate of the Hamiltonian. I'm not clear where equation (92) came...
  44. M

    Navier-stokes derivation question

    hey pf! so i have a small question when deriving the navier-stokes equations from Newton's 2nd law. specifically, Newton states that $$\Sigma \vec{F} = m \vec{a} = m \frac{d \vec{v}}{dt}$$ when setting a control volume of fluid and dealing with the time rate-of-change of momentum we write...
  45. P

    Derivation of telegrapher's equations

    When deriving telegrapher's equations using Kirchhoff current/voltage laws (this equivalent circuit), are the shunt capacitance and shunt conductance in parallel? I assume not, and if not, are they in parallel with the voltages at each corresponding end? I am confused by this; in Pozar's...
  46. B

    Engineering Derivation of Source-Free RC circuit

    Homework Statement Hi, If there is a series combination of a resistor and an initially charged capacitor, I know that the decay of the voltage is given by the equation v(t) = Ae^(-t/RC) where V(0) = A = V0. But i am unsure of how to get to this equations. Homework Equations If I assume...
  47. A

    Understanding the Boltzmann Equation Derivation in Electric and Magnetic Fields

    Below is part of derivation of the Boltzmann equation in an electric and magnetic field. I don't understand how to arrive at the bottom equation though. It is known that the dependence of the original distribution function is the given. My idea is to use chain rule but I don't see how to get a...
  48. nomadreid

    A step in derivation of E-t uncertainty not clear

    I am not sure if I should be posting this under QM or under Linear Algebra, since it appears to be an algebraic step that I do not see, and am asking the wonderful people on this forum to spell it out for me. In John Baez's derivation of the Energy-time Uncertainty relation...
  49. S

    Derivation of gravitational redshift: Mass of a photon?

    This is not exactly a homework question. In a physics textbook, they derive an expression for gravitational redshift of a photon emitted by a star at a large distance from the source by taking photon as a mass traveling up, against a gravitational potential and hence expending its...
  50. H

    Christofell Symbols: Derivation in Schutz & Wald

    In Schutz, the christofell symbols are dervied from applying the product rule to a vector in a curvillinear basis. In Wald, the christofell symbols are dervied by making an ansatz of the form a covariant derivative must take and then imposing conditions on it like the metric covariant...
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