Derivation Definition and 1000 Threads

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. K

    Experimental Derivation of the Drag Force

    I am trying to experimentally derive the drag equation. I have dropped coffee filters with varying masses and determined their resulting terminal velocity. I plotted the data and found that the mass of the coffee filter is proportional to the terminal velocity squared. I was now wondering how I...
  2. A

    Under-damped simple harmonic motion solution derivation

    I have learned in 1st year that the under-damped simple harmonic motion can be described by the differential equation m \frac {d^2 x} {dt^2} + b \frac {dx} {dt} + kx = 0 where m is the mass, b is the constant of linear drag and k is the spring constant But the derivation is skipped...
  3. A

    Derivation of LLG equation in polar coordinates

    The torque contribution due to the uniaxial anisotropy is given by the equation below \frac{\Gamma}{l_m K} = (2 \sin\theta \cos\theta)[\sin\phi e_x - \cos\phi e_y] (3) This contribution can be taken in the LLG equation to derive the LLG equation in polar coordinates \frac{\partial...
  4. R

    Derivation of the Lagrangian for Rotating Polar Coordinates

    I'm reading Leonard Susskind's The Theoretical Minimum Vol. 1. 1. The problem: I'm on the section in which he asks the readers to derive the Lagrangian for a particle on a rotating carousel in polar coordinates. 2. Relevant ideas: The same Lagrangian in Cartesian coordinates is given as...
  5. R

    Derivation of Lorentz transformation (time)

    Hi all, I'm trying to derive that t=δ(t'+vx'/c^2) Using x'=δ(x-vt) then substituting for x=δ(x'+vt') I should be able to isolate t and solve the problem but I am getting to the following point after simplification and can't figure out where to go next...? x'= δ[δ(x'+vt')-vt] (isolate...
  6. WannabeNewton

    Original derivation of Papapetrou equations

    Hi all. As you may be aware, there are a handful of modern derivations of the Papapetrou equations i.e. the equations of motion for a pole-dipole particle in curved space-times. These are usually along the lines of a Hamiltonian or Lagrangian derivation (c.f. Racine et al 2009 and Anandan et al...
  7. S

    Geomertical optics- derivation of graph of (u+v) against u

    Homework Statement may i know how to derive the the sha[pe of graph and get the point of min (2f , 4f) ? i really have no idea how to get the shape of the graph and the min point. The book give it without any explanation. Homework Equations The Attempt at a Solution
  8. D

    Derivation of graph of v against u

    Homework Statement This is the graph of v against u . i am having problem of getting the shape of graph and getting the point (2f, 2f) . can anyone teach me how to derive it? Homework Equations The Attempt at a Solution sorry. i don't know how to use LATEX. it may be quite...
  9. J

    MHB Derivation Application in Differential Calculus, verification question problem.

    Greetings everyone in MHB. :) Well I've just created a thread to just verify if my answer is correct. On a simple problem that using implicit differentiation. A cylindrical tank of radius 10 ft is having drained with water at the rate of 200 f^3/ min. How fast is the height of water changed...
  10. B

    Moment of Inertia of Hollow Cylinder Derivation

    For a uniform, hollow cylinder, why is this derivation wrong? M = mass of whole solid cylinder m = mass of missing cylindrical piece R = radius of whole cylinder r = radius of missing cylindrical piece moment of inertia = moment of inertia of whole cylinder - moment of inertia of...
  11. I

    Derivation of Faraday's Law from Lorentz's

    $$\vec{F}=q\vec{v}\times\vec{B}$$ $$\frac{d\vec{F}}{dq}=\vec{v}\times\vec{B}$$ $$\int\frac{d\vec{F}}{dq} \cdot ds=\int(\frac{d\vec{s}}{dt}\times\vec{B}) \cdot ds$$ from here, I went about it two different ways: 1.) Here I assumed everything was at right angles and got rid of all the vectors...
  12. schrodingerscat11

    Derivation of completeness relation from Jackson's Classical Electrody

    Homework Statement Greetings! I am reading section 2.8 of Jackson and trying to understand how completeness relation was derived. It starts with the orthonormality condition: ∫U_N ^*(ε) U(ε) dε =δ_{nm} We can represent a function as a sum of orthonormal functions if N is finite...
  13. 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?
  14. 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...
  15. 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...
  16. 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)...
  17. 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...
  18. 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...
  19. 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.
  20. 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)...
  21. L

    Is ## \frac{V_T}{\beta} ## the Crossover Frequency in Josephson Junctions?

    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) ##...
  22. 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...
  23. 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...
  24. C

    Noether Current Derivation Issue: Why Don't the Last Two Terms Vanish?

    (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...
  25. 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...
  26. 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.
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. 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...
  32. 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...
  33. 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...
  34. 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)...
  35. 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...
  36. 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...
  37. R

    How Do You Derive the Equation for Damped Frequency in a Spring System?

    Hiya can anyone show how to derive the euqation of damped frequency for a spring ωd = ωnsqrt(1-ζ2)
  38. 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) -...
  39. 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...
  40. 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...
  41. 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.
  42. 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...
  43. 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...
  44. 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.
  45. 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.
  46. 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...
  47. 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
  48. 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!
  49. 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...
  50. 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...
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