Recent content by paultsui

Hey guys, A simplified diagram for the energy levels involved in Nd:YAG laser can be found here: http://upload.wikimedia.org/wikipedia/commons/6/69/YAG2.svg Two (short) questions: 1. Selection Rules The lasing transition happens between ^{4}F_{3/2} and ^{4}I_{11/2}. In the process J (of the...

Thank you for your reply mfb! And then can we use the Breit Wigner Formula to understand the non-zero energy resonances in http://pdg.lbl.gov/2011/hadronic-xse...crpp_page6.pdf?

Thank you for your replies guys! Bill_K and mfb: I agree with you guys that this formula should apply. However, if E_{0} = 0, this would suggests that the resonance would happen when E_{CM} = 0 for all positron electron annihilation reactions. In particular, if you like at...

Hey guys! Breit Wigner Formula describes the cross section for interactions that proceed dominantly via a intermediate particle (O*) A+B → O* → C + D: σ = \frac{2\Pi}{k^{2}}\frac{Γ_{i}Γ_{f}}{(E-E_{o})^{2} + (Γ/2)^{2}} A short question: Does the formula apply to situations when the...

As far as I am aware, Pauli Paramagnetism applies to electrons in bands while Curie Paramagnetism applies to localised electrons. Pauli Paramagnetism is usually much weaker because only the electrons near the Fermi Surface can change its spin to align with the magnetic field. On the other hand...

What do you mean by including a cosmological constant? This equation can be obtained by eliminating the cosmological constant from the other two Friedman Equations. So I guess cosmological constant is irrelavant here. I think this is a local energy conservation problem - we are considering a...

The first law of thermodynamics states that dU = -PdV + dQ We can apply this to the expansion of the universe by assuming the expansion of space is a adiabatic process, i.e. dQ = 0. Together with the FW metric, we end up with one of the Friedman Equations: \dot{\rho} = -\frac{3\dot{a}}{a}(p +...

Thank you for your replies. But I am still not entirely understand the concept. So when we write down the line element (or a metric), we assumed a coordinate system. Do you guys mean the coordinate system is not related to a physical reference frame directly (i.e. no physical reference frame...

Hi there, I am confused about the relationship between coordinate systems and reference frame in GR. I understand the coordinate systems can be used to describe reference frames, for example, Local inertial frames in GR can be defined by Riemann Normal Coordinates. However, take the...

Thank you for replying! It is true that we can always choose a coordinates system such that g_{00} to be 1 at the point of interest, but why do we have to pick g_{00} = 1 instead of ,say, g_{00} = 2? Consider the following: Imagine person A is at infinity while person B is at a point...

In relativity, proper time along a world-line is be defined by d\tau^{2} = ds^{2} / c^{2} However, proper time can also be understood as the time lapsed by an observer who carries a clock along the world-line. In special relativity, this can easily be proven: The line element in special...

Is there any parameter that represents the chaotic-ness of a system? For example, can we show that a 4-body system is in general more chaotic than a 3-body problem? Thank you : )