Cross Definition and 1000 Threads

A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally.
A cross of oblique lines, in the shape of the Latin letter X, is also termed a saltire in heraldic terminology.
Throughout centuries the cross in its various shapes and forms was a symbol of various beliefs. In pre-Christian times it was a pagan religious symbol throughout Europe and western Asia. In ancient times, the effigy of a man hanging on a cross was set up in the fields to protect the crops. The cross was even considered a male symbol of the phallic Tree of Life; thus it often appeared in conjunction with the female-genital circle or oval, to signify the sacred marriage, as in Egyptian amulet Nefer with male cross and female orb, considered as an amulet of blessedness, a charm of sexual harmony.

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  1. G

    Electron impact ionization cross section

    Homework Statement I want to find the ionization cross section in a mass spectrometer for the gas Argon. The value obtained should be in the 2x10-16 cm2 range. Homework Equations Q = ionization cross section I = K(V,B)xNxQxdxIe Where I = (0.17 x 10-11, K(V,B) =1, d = 0.1 cm, and Ie = 5 x...
  2. W

    Suzuki Cross-Coupling work-up question

    Hi, in class I'm doing a Suzuki Cross Coupling reaction based on "Nickel-Catalyzed SuzukiMiyaura Couplings in Green Solvents" by Stephen D. Ramgren, Liana Hie, Yuxuan Ye, and Neil K. Garg. The reaction involved the bromo-aryl reacting with the boronic acid in heated t-amyl alcohol in the...
  3. J

    Why Is the Cross Section for e- + e+ -> γ Zero?

    Homework Statement I am making an old exam of a particle physics course, and i know how to calculate the cross section for example for bhabha or moller scattering. now one of the questions on the old exam is: Explain why e-+ e+ -> γ is zero, but i am not sure why this is, can someone explain...
  4. Matt atkinson

    Calc Nuclear Cross Section for Alpha Particles Reacting with 48-Ca

    1) Alpha particles can react with 48-Ca to produce protons. Consider a beam of alpha particles of current 20nA fired at a think target of Ca of thickness $$1mg/cm^2$$. A detector subtending a solid angle of 4*10^-3 steradians, records 20 protons per second. Determine the total cross section (in...
  5. M

    Magnetic Interaction: parallel rods, cross bar free to slide

    Homework Statement Two horizontal parallel conducting rods are connected such that a conducting crossbar free to slide along them has a constant current I running through it (Figure 1) . The rods are separated by a distance ℓ and are in an external uniform magnetic field of magnitude B directed...
  6. 10Exahertz

    Relationship of curl and cross product.

    Hi all, I am very confused on how to define the vector product or cross product in a physical sense. I know the vector product is a psuedovector, and that it is the area of a parallelogram geometrically. However, I know it used used to describe rotation in physics. As with torque, magnetism and...
  7. L

    Minimum Speed for Motorcyclist to Successfully Cross a Ravine

    Homework Statement A motorcyclist must cross a ravine. The far side of the ravine is 2.0 meters higher than the launch point, a ramp that makes an angle of 40◦ with the horizontal. If the ravine is 10.0 meters wide, what minimum speed v must the biker have when leaving the ramp to successfully...
  8. J

    Discover Solutions for Vectors Cross Product Homework | AM x BC = AM x AC

    Homework Statement Find the set of points of M such that: AM x BC=AM x AC (Vectors) The Attempt at a Solution [/b] AM x (BM+MC) =AMx(AM+MC) AMxBM+AMxMC=AMxAM +AM x MC Then AMxBM=0 MA X MB=0 I am new to this lesson and this is my first time i solve such a question and i had no idea...
  9. A

    Does scalar multiplication affect the cross product of vectors?

    Mod note: Member warned about posting with no effort. 1. Homework Statement Expand to the general case to explore how the cross product behaves under scalar multiplication k (a x b) = (ka) x b = a x (kb). The Attempt at a Solution would this be the right general case to portray the situation?
  10. Manta173

    Small scale application of structural cross sections

    I am working on fixing a heavy walnut cedar chest lid that has bowed convexly from the chest. It is about 1/4" high in the center of a 24" deep lid. The lid is ~2' x 5'. It is made from 3/4" walnut with 3/4" x 3" ribbing on the top. I thought that adding in some C-channel or square tubing would...
  11. U

    Scattering Cross Section - At high energies

    Homework Statement Why does ## \frac{ e^+ + e^- \rightarrow \mu^+ + \mu^- }{e^+ + e^- \rightarrow \tau^+ + \tau^- } \rightarrow 1## at high energies? Would it be the same if it was ## \frac{ e^+ + e^- \rightarrow \mu^+ + \mu^- }{e^+ + e^- \rightarrow e^+ + e^- }##? Homework EquationsThe...
  12. binbagsss

    Deep Inelastic Scattering, peak of cross section, width?

    I'm looking at deep inelastic scattering of a low-energy inelastic electron scattering from a stationary proton target. I am given ##E## and ## \theta ## where ##\theta ## is the scaterring angle. ##E=4.879 GeV , \theta=10^{0} ## I am given a figure of cross section...
  13. P

    How to calculate yields from the cross section?

    I have a result for the differential cross section d\sigma/d\eta dP_T^2, but I want to obtain the corresponding differential yields dN/d\eta dP_T^2. How to relate yields to cross section?
  14. E

    Cross Section for Asteroid Impact

    Homework Statement In this problem, you will estimate the cross section for an earth-asteroid collision. In all that follows, assume that the Earth is fixed in space and that the radius of the asteroid is much less than the radius R of the earth. The mass of the Earth is M_e, and the mass of...
  15. W

    What is the magnitude of the cross product y cross x?

    If I choose the positive y direction to be vertically downwards, and the positive x direction to be to the right, and take the cross product y cross x, then the direction of the resultant is out of the page (if I draw x and y as lines on paper). The magnitude is yx sin(φ), where φ is the angle...
  16. RJLiberator

    Simple Cross Product Equation Question

    Homework Statement This is a general question about the equation. So, I know that the cross product requires a vector in at least 3 dimensions crossed with another. Here is the formula that I am using: uxv = My problem is the negative/positive sign orientation in front of the y element and z...
  17. Y

    Dependence of resistance on cross section area

    The electrons flow on the outer surface of the resistor, why then does the resistance of a resistor depend on it's cross sectional area and not on it's perimeter?
  18. Prof. 27

    Current through Point or Cross Sectional Area

    Homework Statement I'm finding conflicting statements. One says that current is measured as the amount of charge per time that enters through a cross sectional area. Another says that current is measured as the amount of charge per time that passed through a point. Could someone clarify this...
  19. ognik

    Vector multiply that is NOT dot or cross?

    Hi - just working through my text (studying by correspondence) on Del operator - so Curl, div etc. Came across some identities parts of which which have me confused. what does it mean when a vector is shown as multiplying something - but without dot or cross? For example F(∇.G) or ∇(F.G) or...
  20. J

    Compton scattering differential cross section

    1. The problem statement, all variables and given/known I have to prove an equation for the differential cross section of compton scattering of an electron and a photon (electron (P) + photon(K) ⇒ electron(P') + photon (K') ) where P and so on are the inital and final four momenta. Given is...
  21. Coffee_

    The use of cross section in a particle collision exercise.

    1. Situation: I have no specific exercise in mind but just the general form. ''A beam of protons is colliding with a plate of a given particle density ##\rho## and thickness ##l##. The cross section is ##\sigma##. What should the thickness of the plate be such that the intensity of the outgoing...
  22. hideelo

    Is Wedge Product the Same as Cross Product?

    I guess the title really says it all. I'm reading "space-time algebra" by David Hestenes, and he explains the properties of the wedge product (area of parallelogram, antisymmetric, etc.) and it sounds just like the cross product to me. He then says clearly however that this is not to be...
  23. P

    Cross Product Angle: 0 to π or ACW from a to b?

    When we talk about the angle between two vectors while computing the cross product, which angle are we referring to exactly? According to most sources, the angle should be between 0 and π; yet according to my math book, "the angle is measured in an anticlockwise sense from a to b, if the vector...
  24. A

    Curl of a function and vector field

    Hello, I'm having some difficulty with a conceptual question on a practice test I was using to study. I have the answer but not the solution unfortunately. 1. Homework Statement "For every differentiable function f = f(x,y,z) and differentiable 3-dimensional vector field F=F(x,y,z), the...
  25. R

    Hydrogen - Halpha cross section

    Greetings, i need the absorption cross section for the absorption of an H-alpha photon by a hydrogen atom, in the correct state of course, which I'm pretty sure is neutral hydrogen, n=2. I am needing this for a project, so i also need a reliable source where this comes from. Thanks beforehand...
  26. M

    Proof of a property of the cross product

    Homework Statement I could prove a, trying b now. Homework Equations The definition of the cross prod.? The Attempt at a Solution https://www.dropbox.com/s/0sauaexkl4j2yko/proof_cross_prod.pdf?dl=0 I did not manage to get a scalar times v and a scalar times w. (No need to point this...
  27. teroenza

    Is the Commutator of a Cross Product a Vector Operator?

    Homework Statement Given that \vec{V} and \vec{W} are vector operators, show that \vec{V}\times \vec{W} is also a vector operator. 2. The attempt at a solution The only way I know how to do this is by showing that the commutator with the angular momentum vector operator ( \vec{J}) is zero...
  28. jk22

    Variation on Quantum cross covariance and CHSH

    I tried another approach to the problem of covariance like in Bell's theorem :from the definition ##Cov(A,B)=\langle\Psi|A\otimes B|\Psi\rangle-\langle\Psi|A\otimes 1|\Psi\rangle\langle\Psi|1\otimes B|\Psi\rangle## (##A=diag(1,-1)=B##) we can see that this 'average' is in fact a quadratic form...
  29. KleZMeR

    What is the vector cross product in an oblique coordinate system?

    Homework Statement Find vector product of C = A \times B of two vectors in oblique coord. system. Give explicit expressions of components of C in covariant and contravariant components (constructing reciprocal basis from direct basis will be useful). Homework Equations I am basically just...
  30. K

    Difference between: Absorbance and Absorption Cross section

    Hello, hello, I ask you to tell me the difference between the "absorbance" calculated from the dielectric function, and the "absorption cross section" calculated from Real-time TDDFT. is that they can give the same appearance spectrum? Thank you very much
  31. tom.stoer

    Time dependent scattering theory - cross section

    I am looking for a realistic explanation of the double-slit experiment in terms of wave packets (instead of stationary waves). First of all this results in using the scattering cross section, i.e. the probability current (not the density). Then, I guess, there is a kind of time average. So one...
  32. thankz

    Semiconductor cross referance book

    I'm looking to buy a semiconductor cross reference book, for part numbers and diode and transistor parameters, including new smt parts. I had an old sgs Thomson book but it got lost in a move, if anyone could recommend me one that would be great. I don't want a link to a website cross...
  33. L

    Cross Section: Quark-Gluon vs. Quark-Photon

    This isn't a homework problem. I am preparing for a particle physics exam and although I understand the theoretical side of field theory, I have little idea how to approach practical scattering questions like these. THE PROBLEM: Dark matter might be observed at the LHC with monojet and...
  34. M

    Cube Projectile Motion: Air Resistance & Cross Sectional Area

    We have a solid cube with some mass that we fire as a projectile at some angle. The cube is launched in such a way that two of the faces are perpendicular to the initial velocity vector. Assuming there is air resistance, would the cube change its orientation while it flies, even if the mass is...
  35. D

    How to find cross sectional dimension of beam

    Homework Statement If the electric motor of problem 3.66 is to be mounted at the free end of a steel cantilever beam of length ##5## m and the amplitude of vibration is to be limited to ##0.5## cm, find the necessary cross-sectional dimension of the beam. Include the weight of the beam in the...
  36. F

    Using v= omega cross r to find instantaneous velocity

    Homework Statement An object is rotating at 4 rad/s about an axis in direction of (2 \hat{i} - 4 \hat{j} + 3\hat{k} ) which then passes through a point (1,2,0)m . Calculate the instantaneous velocity at the point (2,0,3)m (Hint: use \vec{v} = \vec{\omega} \times \vec{r} )Homework Equations...
  37. bohm2

    Pilot wave models and "no cross" rule

    From my understanding, average trajectories based on weak "measurements", obey the 'no-crossing rule'. These average trajectories strongly resemble the single-photon trajectories predicted by Bohmian mechanics: For instance compare these average trajectories...
  38. C

    Calculating Magnetic Force on a Moving Charge

    Homework Statement Considera 1.0 C charge moving with a velocity of v = -2.0i + 2.0j - 1.0k in a magnetic field of B = -4.0i + 1.0j – 3.0k. What force is this charge experiencing? What is the angle between the velocity and magnetic field vectors? Homework Equations F = q(E + v x B)...
  39. M

    Conduction Heat Transfer Cross Check

    Hi, I was provided a http://eng-tips.com/viewthread.cfm?qid=372664# that I'm lost on. I was given an equation that we solved for earlier in the semester using the finite difference (dx method). (first image below). The http://eng-tips.com/viewthread.cfm?qid=372664# wasn't clear when...
  40. N

    Levi Civita symbol on Curl of Vector cross product

    Homework Statement Use the LC symbol to calculate the following: $$\nabla \times \frac{\vec{m} \times \hat{r}}{r^2}$$ Where ##\vec{m}## is just a vector, and ##\hat{r}## is the unit radial vector and ##r## is the length of the radial vector. Homework Equations On the Levi Civita symbol...
  41. K

    Is there a connection between cross product and determinant?

    Is this just a coincidence that cross product can be found from determinant of 3*3 matrix? what is the differences between wedge product and cross product?Thanks.
  42. S

    MHB What is the role of $$\hat{\jmath} \times r$$ in computing vorticity?

    A fluid motion has velocity $$\underline{u}=\sin{(at)}\hat{\imath}+\hat{\jmath} \times r +\cos{(at)}\hat{k}$$ I need to know what is $$\hat{\jmath} \times r$$ to find Vorticity and other things.
  43. A

    Cross Products in Spherical Coordinates: Is A x B True?

    Is A x B = | i j k | also true for Spherical Coordinates? | r1 theta1 phi1 | | r2 theta2 phi2 | Or I have to convert them to Cartesian Coordinates and do the cross product and then...
  44. M

    No Cross Product in higher dimensions?

    Is there an intuitive reason or proof demonstrating that in general dimensions, there is no direct analogue of the binary cross product that yields specifically a vector? I came across Wedge Product as the only alternative, but am just learning linear algebra and don't quite comprehend yet...
  45. I

    MHB Reviewing Cross Product: Simplest Method Possible

    HEY GUYS! (Wave) ok so i have this question i did. and now I am reviewing for the test and i looked at how i did it and i did in the most complicated way ever. i don't FULLY understand chegg's method. so i hope someone can provide me with the SIMPLEST method possible. thank u! (Blush) (p.s...
  46. deedsy

    Deriving sin(a-b) trig identity using Cross Product of Unit Vectors

    Homework Statement A and B are two unit vectors in the x-y plane. A = <cos(a), sin(a)> B = <cos(b), sin(b)> I need to derive the trig identity: sin(a-b) = sin(a) cos(b) - sin(b) cos (a) I'm told to do it using the properties of the cross product A x B Homework Equations A x B =...
  47. G

    Question for the total collisional cross section for the neutrals

    Hello. I'm trying to calculate the total collisional cross section of the hydrogen atom impacted with the proton. (ion of the hydrogen plasma) I've found many good papers but they're showing specific cross section, for example, total cross section when n = 1 state is direct-excited to n =...
  48. F

    Finding the Angle Between Vectors A and B in the Cross Product

    Homework Statement Vectors A & B lie in an xy plane. A has a magnitude 7.4 and an angle 142(deg) with respect to the +x direction. B has components (-6.84i, -7.37j) B) What is the angle between the -y axis and the direction of the Cross product between A and B? Homework Equations Cross...
  49. N

    Levi-Civita symbol for cross products?

    Hi. Is using the Levi-Civita symbol to calculate cross-product combos like A x (B x C) allot faster than just using the good old determinant method? I ask because my lecturer in electrodynamics 2 told us it is better, but it seems to me that it's going to cost me time to learn to use this...
  50. P

    Why Are Absorption Cross Sections Larger for Atoms Than for Molecules?

    Why are absorption cross sections for atoms so much larger than that of molecules. For example, the absorption cross section for the D2 line in Rubidium is ~1E-9 cm^2. Specifically, the cross section is basically σ~λ^2 The absorption cross sections for say, I2, is 9 orders of magnitude...
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