Mean Definition and 1000 Threads

  1. ChrisVer

    A Mean volume of sphere (normal distributed radius)

    I read in http://www-library.desy.de/preparch/books/vstatmp_engl.pdf page 29 (43 for pdf) that the mean volume is: <V> = \int_{-\infty}^\infty dr V(r) N(r| r_0,s) I have two questions. Q1: why do they take the radius to be from -infinity to +infinity and not from 0 to infinity? Q2: is there an...
  2. M

    I What does "expansion of the universe" mean?

    [Moderator's note: thread spun off from post in a different thread quoted below.] That seems to me a rather extraordinary claim. Could you demonstrate how for instance cosmological redshift can be explained in a coordinate independent fashion?
  3. Xico Sim

    I Relative Mean lifetime of decays

    Hi there. I want to compare the mean lifetimes of two particles which decay in a way given by two known reaction formulas, such as ##\rho^0 \rightarrow \pi^+ + \pi^-## and ##\Xi^- \rightarrow \Lambda^0 + \pi^-## In this case it's easy: since the first one corresponds to a first interaction...
  4. S

    MHB What Are Singly and Doubly Indexed Functions in Philosophy?

    Hi guys. New here. I'm reading philosophy, and this philosopher uses some mathematics which I am having trouble understanding. I am interested in both an understanding of what the signs mean (in themselves and in this context, please), and why someone regularly chooses to use these functions...
  5. Mariam Abalo-Toga

    What does Astrophysics/Astronomy mean to you?

    What made you interested in astrophysics/astronomy? Why is it beautiful? Why is it important?
  6. Raul Trejo

    Fractioned electrons, what do they mean?

    Homework Statement Excess electrons are placed on a small lead sphere with mass 8.00g so that it's net charge is -3.20x10^-9C (a) Find the number of excess electrons on the sphere. (b) how many excess electrons are there per lead atom? The atomic number of lead is 82, and its atomic mass is...
  7. L

    MATLAB How can I use MATLAB to take the derivative of an experimental plot?

    In MATLAB, what does ./ mean? Also, I would like to take the derivative of an experimental plot. How do I do so?
  8. tasos

    Pion's mean free path in a lake. exercIse question

    Homework Statement Charged pion with average life time $$\tau=10^{-8} sec$$, and mean free path in the water$$\ell=100m$$ falls prependicular to a lake (depth of lake is at $$\ell_0 =30m$$ with velocity $$V=0.9999c$$ What of the next is correct? 1). The particle isn't gona touch the bottom of...
  9. avito009

    B Does more angular monentum mean faster spin?

    If a top has angular momentum of 12 units and the Earth has angular momentum of 100. Does this mean that Earth is spinning faster than the top since it has more angular momentum? The answer is there at the back of my head but can't articulate it.
  10. Gonzalo Chumillas

    B What Does it Mean When a Black Hole is Spinning?

    The angular momentum is related to the rotation. And when a black hole has angular momentum, it is said that it is a "rotating black hole". But what does it mean? A black hole does not have a conventional surface, like a basketball. How should we interpret that angular momentum? I asked this...
  11. H

    Mean value of energy <E> for a QM state?

    Homework Statement If the system is in a state |ψ> = 1/sqrt(6) |v1> + 1/sqrt(3) |v2> - i/sqrt(2) |v3> with Hamiltonian satisfying H|vj> = (2-j)a|vj> Find the mean value of energy <E> and the root mean square deviation √(<E2> - <E>2 ) that would result from making a number of measurements of...
  12. Andy24

    Model Rocket- What does the 'v' in drag=kv^2 really mean?

    Hello! I am predicting the peak altitude of a model rocket based on some ground tests. I know that Total Force on the rocket=Thrust-mg-kv^2 but am stuck as to which value for 'v' to use? Is it the velocity of the rocket with the effects of gravity and air resistance taken into account or the...
  13. P

    MHB Eccentric anomaly as function of the eccentric and the mean anomaly

    I'm reading, or more like deciphering a book about rocket science (Rocket propulsion and spaceflight dynamics from Cornelisse, Schoyer and Wakker). Most of my math skills are self taught from books and I usually figure things out but this one keeps haunting me. It's some kind of series...
  14. amrmohammed

    Logarithmic mean temperature difference for heat transfer

    Homework Statement [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts)...
  15. Dusty912

    What does it mean for a linear approximation to be reliable?

    Homework Statement In regards to linearization of a nonlinear system in differential equations. What does it mean for a linear approximation to be reliable to describe the long term behavior of the non-linear system around the equilibrium point? Homework Equations jacobian matrix The Attempt...
  16. S

    B Calculating Uncertainty of Mean Values for Enthalpy Change Measurements

    I am trying to find the uncertainty of the mean of 3 values. These values were calculated from experiments to calculate the enthalpy change of various alcohols. These values are independent values. −283 ± 11, −175 ± 9, −282 ± 11 How would I calculate the uncertainty of these values? Thank you.
  17. E

    MHB What Do Q1 and Q3 Represent in a Data Set?

    what would Q1 and Q3 mean? I can't answer these questions until I know what these columns represent. Is Q1 the lowest grade given and Q3 the highest?
  18. Jilang

    I What does simplicial mean in the context of QM?

    What does simplicial and non simplicial mean in the context of quantum mechanics?
  19. DevonZA

    Mean temperature of winding when current falls

    Homework Statement Homework Equations R2=R1(1+alpha(t2-t1)) The Attempt at a Solution R1=250/5=50ohms R2=250/3.91=63.94ohms R2=R1(1+alpha15degrees(t2-t1)) 63.94=50(1+1/254.5(t2-15)) t2= Now I found this online but the answers provided still don't match, 84.25 being the closest. When...
  20. E

    I Calculation of mean energy value of photons in recombination

    I am interested in the calculation of the mean energy value of CMB (Cosmic Microwave Background) photons from which the recombination is performed. The subject on French Wikipedia says : "Intuitively, one might say that recombination occurs when energy average of photons is of the order of the...
  21. F

    I What does "completeness" mean in completeness relations

    From my humble (physicist) mathematics training, I have a vague notion of what a Hilbert space actually is mathematically, i.e. an inner product space that is complete, with completeness in this sense heuristically meaning that all possible sequences of elements within this space have a...
  22. reddvoid

    I Most effective of 1000 groups given mean median mode and N

    Hi, For a SoC project I am working on I need to select one cell which is most critical. example, If a bus is going through 1000 stops 1000 times I have mean median mode of delay contribution of that stop compared to the total delay to reach from start to stop point and N (number of times bus...
  23. Q

    Expectation Value- Mean Time to Failure

    Homework Statement (a) Suppose we flip a fair coin until two Tails in a row come up. What is the expected number, NTT, of flips we perform? Hint: Let D be the tree diagram for this process. Explain why D = H · D + T · (H · D + T). Use the Law of Total Expectation (b) Suppose we flip a fair...
  24. S

    Finding pressure, mean speed and mean free path

    Homework Statement A right circular cylinder of ##4## cm (inner) radius and ##19.9## cm (inner) length contains ##4 \times 10^{14}## Argon atoms (atomic number ##18##). The cylinder is maintained at room temperature, nominally ##300## K. (a) Estimate the momentum transfer per square meter per...
  25. C

    Mean field approximation and entropy

    Homework Statement Consider a D dimensional Ising model with N sites, defined by the Hamiltonian $$\mathcal H = -J \sum_{\langle i j \rangle} \sigma_i \sigma_j - h \sum_i \sigma_i$$ where the sum extends over nearest neighbours and each spin variable ##\sigma_i = \pm 1##. For a given spin...
  26. Villa

    In fluid mechanics what does pressure energy mean?

    In Bernoulli equation we use pressure energy... Pressure* volume gives the unit of energy... But what does this mean... If someone says it is potential energy per unit volume, then what does datum head refers to?... Please help... Can't go ahead without having thorough knowledge about this..
  27. A

    What does current density mean?

    Homework Statement Current density is the amount of current per cross sectional of flow. I'm having trouble wrapping my head around this definition. Surface charge or volume charge I understand better since they are almost analogous to the density we all understand (amount of matter/charge...
  28. E

    B What does this Change in Representing a Function mean?

    I have encountered this form of a function: ##f \left(x, y\right)##. Later throughout the discussion, the function was represented as ##f \left(y \right)##. Does this change in representation imply anything? I have been looking through the discussion if ##x## was considered constant, but it...
  29. 1

    What does divergence of electric field = 0 mean?

    Homework Statement I just want to focus on the divergence outside the cylinder (r >R) Homework Equations The Attempt at a Solution For r > R, I said ∇ * E = p/ε But that's wrong. The answer is ∇ * E = 0 I'm confused because there is definitely an electric field outside the cylinder (r...
  30. thebosonbreaker

    What does this symbol mean in a chemical equation?

    I recently stumbled across a chemical equation, which had a symbol I have never seen before. If anyone can tell me what this symbol means, I would be very grateful. Here's the equation: Ca(OH)2(aq) + Na2CO3(s) → CaCO3 ↓ + 2 NaOH(aq) ...and I'd like to know what the "↓" symbol means. Many...
  31. P

    I What does total number of atomic sites mean ?

    i know this might seem as a very simple question , but i am confused : in order to calculate the total number of vacancies we need the total number of atomic sites N , and since N depends on the density of the material , then N refers to the number of atoms , right ? what confuses me is the word...
  32. CynicusRex

    What is the Quotient Rule for Calculating Derivatives?

    Homework Statement Homework Equations The Quotient rule for calculating the derivative. The Attempt at a Solution The derivative f'(x) = (x+5)-(x+3) / (x+5)^2 I tried a previous similar problem but failed as I didn't and still don't know what '' means.
  33. P

    Root Mean Square: What It Is & Why It Matters in Electrical Engineering

    What is the root mean squad (RMS) of a signal (or wave) and why is it important for electrical engineering? How do you Find it? What is it used for? Thank You All
  34. T

    A What do people mean by "dynamical phase transition"?

    I heard of it several times in colloquiums. But I still cannot grasp the meaning. What is the control parameter in this phase transition?
  35. darida

    Derivative of Mean Curvature and Scalar field

    Homework Statement Page 16 (attached file) \frac{dH}{dt}|_{t=0} = Δ_{Σ}φ + Ric (ν,ν)φ+|A|^{2}φ \frac{d}{dt}(dσ_{t})|_{t=0} = - φHdσ H = mean curvature of surface Σ A = the second fundamental of Σ ν = the unit normal vector field along Σ φ = the scalar field on three manifold M φ∈C^{∞}(Σ)...
  36. J

    Mean Radius of Annulus with Bolt Hole Pattern

    Hello all, I am trying to remember (I did it in Uni) how to calculate the effective mean radius of an annulus that contains a pattern of holes on a PCD. Consider the following image (pinched from: https://www.solenoid-valves.com/ ): If one was to vary the value of PCD, then the effective...
  37. vktsn0303

    What does this mean? (equation for viscous flows)

    While reading a textbook on viscous flows, I came across the following interpretation of an equation: where, v is the vertical component of the free stream velocity and y is the vertical distance from the surface of a solid and Re is the reynolds number. Can someone please help me understand...
  38. pellman

    B What does this set notation mean?

    $$ A \oplus B $$ where A and B are sets
  39. Kevin McHugh

    I Solve Ra[bcd]=0: What Permutations Work?

    Given: Ra[bcd] = 0 What permutations of bcd make this expression 0? TIA for your response.
  40. B

    Does Faster Mean More Energy: Comparing 0-60 in 3 & 8 secs

    Homework Statement What takes more energy a car going 0 to 60 in 3 seconds or a car going 0 to 60 in 8 seconds. Homework Equations 1/2 k v ^2 The Attempt at a Solution I know the answer is they are the same but the power is different. But doesn't the car that goes faster lose more gas. And...
  41. R

    I Bubble cavitation - what does a dash mean?

    For a bubble in water in equilibrium the supporting forces due to pressure of the gas Pg and vapour Pv in the bubble must equal the crushing forces i.e. the hydrostatic forces Ph and those due to surface tension 2sigma/R0. So we have ##P_{v}+P_{g}=P_{h}+ \frac{2\sigma }{R_{0}}## Now we apply...
  42. ff4ever

    What does it mean? (Graph theory)

    Hi, In the paper "A triangle-free circle graph with chromatic number 5" from A.A. Ageev, I don't understand what the author mean with the following definition: Somebody can explain it to me? (I'm not mathematician). Thanks ! Link to the whole paper...
  43. ShayanJ

    Do we really mean Hermitian conjugate here?

    When people want to find a conserved current which is constructed from a Dirac spinor, they consider the Dirac equation and its "Hermitian conjugate". But the equations they consider are ## (i\gamma^\mu \partial_\mu -m)\psi=0 ## and ##\bar{\psi}(i\gamma^\mu \overleftarrow{\partial_\mu}+m)=0 ##...
  44. J

    Mean free path and speed as a function of pressure and temp

    Homework Statement I know that at 18,000 ft. above mean sea level, the atm. pressure ~half of what it is at seal level (760 Torr). The temperature also decreases by 70C. a. How would this change the speed distribution of the air molecules quanitatively? b.How would it change the mean free...
  45. naima

    How Does Trace Relations in Fock Space Reflect on Quantum Expectations?

    Consider the state ##\rho_n## obtained by applying n times the same creation operator on the vacuum and an observable A. How is ##Tr(\rho_n A)## related to ##Tr(\rho_1 A)## ? And if ##\rho## is a coherent state?
  46. Sophia

    What does Double slit experiment actually mean

    I'd like to ask what exactly do the results of double slit experiment mean? I must confess that I've read about this mainly in New Age literature where it was used as a "proof" that our consciousness changes reality. I know that Physicists probably don't like such explanations :eek: So I'd like...
  47. RJLiberator

    Mean Input Power & Q value , Damped Harmonic Motion

    Homework Statement Homework EquationsThe Attempt at a Solution I'm working on part a. The numerical value of Q. I have an equation stating that Q = ω_0/ϒ. I don't really know what ϒ is, in other places (http://farside.ph.utexas.edu/teaching/315/Waves/node13.html) it seems like the...
  48. Sam19KY

    What does this thing on batteries mean?

    Say that 6V battery is connected to a lamp that takes 3V from each coulomb. Does that mean that the battery can supply 6V or dependent upon the need of components in the circuit ?
  49. C

    How Are Mean Orbital Elements Calculated?

    Good morning, I was making some investigation regarding the calculation of mean orbital elements - not osculating. Is this done simply by fitting (with the best equation) several osculating elements across time, or is there a mathematical approach already settled? Cheers,
  50. CivilSigma

    What does it mean to find the centroid of a shape?

    Hello, I am currently studying how to find the centroid of shapes. And I understand that to find the location of the centroid, we must analyze the distribution of the mass over the x and y-axis (i.e calculating Qx and Qy). However what baffles me is that, given an L shaped beam, the centroid...
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