34,505 reputation
347118
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 3 years, 11 months
seen 36 secs ago

Experimental nuclear and particle physicist. These days I'm teaching, but I've spent a lot of time on nucleon structure in fixed target electron scattering and neutrino oscillations using reactors and beam sources.


4h
comment Underdetermined forces in a statics problem
@BenCrowell He's right for static friction with a non-deformation assumption (i.e. the sort we teach in PHYS 101). In that case it is always "just enough to prevent relative motion" up to the point where it fails and motion begins. The difficulty here is that examined at high resolution there can be deformation both normal to and across the surface so both the normal force on one side and the static friction on the other can be supporting the cylinder against motion along one direction (i.e. both can have non-zero values in a quiescent state), and ambiguity arises. Time to break out the FEA.
5h
comment How can we tell if a molecule is in thermodynamic equilibrium from scattering data?
I've a (roughly third-hand) story about people assuming equilibrium and later finding it wasn't so. Their system exhibited an anisotropic Doppler broading, which is one way to rule out equilibrium.
9h
comment Theory on what would happen if a proton touches anouther
This happens all the time. In every nucleus that is not hydrogen protons are "in contact".
10h
comment Electric Field due to volume charge
You integrate the expression for field (i.e. Coulomb's Law divided by the test charge) over the source volume, hopefully applying lots of mathematical trickery as you go. This problem is given to everyone at some point and working through it is good for you even if it is not much fun.
11h
comment Would using Cherenkov radiation for lighting be feasible?
@SteveJessop Those were the days when (in the words of a nuclear physics professor I had) "Men were men and radiation didn't hurt you." It was also the time when you could ship a 2 Curie AmBe source in a cardboard box by US post.
11h
comment What is the Weak force?
"they said that it's the interaction between Protons and Electrons(Electronegativity)" This is wrong. While there is a weak interaction between protons and neutrons it is swamped by the plain electromagnetic interaction and it has nothing to do with chemistry. "Electronegativity" is a chemistry idea and applies at much longer length scales and much lower energy scales than any manifestation of the weak force.
1d
comment Underdetermined forces in a statics problem
@BenCrowell Dude, making me think when I'm trying to prepare lecture slides... but I think you're right.
1d
comment A new interpretation of QM
Here's the rub: Physics SE is not a discussion site. We deal in questions that have correct and well understood answers (or at most a few good bets). Open ended discussion is strongly discouraged. I think @HDE226868 is too strong in invoking "non-mainstream"-ness, but there is no way to ask "Hey guys whats your opinion of my new theory?" even if you got it published in Nature.
1d
comment Would using Cherenkov radiation for lighting be feasible?
@CuriousOne That depends. For instance the Cerenkov glow from a water-moderated, fission reactor is not a sign of danger because by design the moderator absorbs essentially all the dose. And it's pretty.
1d
comment Underdetermined forces in a statics problem
I do think that you would have to be very careful in setting up an actual experiment to get the assumption of symmetry to hold. Even a small deviation will break the symmetry and make the system determined again.
1d
comment Underdetermined forces in a statics problem
For a different class of underdetermined problems (a object supported at four points in a rectangular grid) you can convince yourself that when you stop neglecting elastic deformation you can "fix" the system (at the cost of making it a larger system). It's not obvious to me if that is the case here.
1d
comment Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
@garyp I suppose that's a matter of interpretation. As far as I'm concern you can't add a torque to an energy so they are not the same no matter that you write the units as mass*distance^2/time^2 in each case. In other words, I'm including the identification of the mathematical class in the units because both are about identifying what sort of critter you're talking about.
1d
comment Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
In that case you want the answer to 37881 that talks about $dW = \tau \cdot d\theta$ implying that torque is in Joules per radian.
1d
comment Reconciling Units in Classical System Analogies: Why Does Torque Have Units of Energy?
physics.stackexchange.com/q/37881 Short-short version the cross-product develops a different kind of entity than the dot-product so they are not the same units at all.
1d
comment Magnetic field of magnetic screwdriver?
It is actually surprisingly difficult to generate reliable and consistent strength in permanent magnets, so for most purposes people don't try. They just set some minimum operation test (...picks up a 1 gram test object from 5 mm distance...) to use for quality control and leave it at that. They may very well not know the field strength, and that doesn't bother them. If you care get (or build, they're pretty simple) a Hall probe and measure it as best you can.
2d
comment Can a box on a frictionless rotating table rotate?
Who told you it was started by the motion of the table? I could have walked by and given it a thwack with a mallet while you were out of the notional room? It is a homework exercise that takes place in the Physics 101 frictionless vacuum full of massless, rigid objects: it's doesn't have to make all possible kinds of sense.
2d
comment Scintillator Length Calculations
"so is my reasoning correct when I assume that I'm supposed to get my $constants * int(ta∗e−bt)=0.98$ ?" That's right. But there is no loop in the answer Wolfram gives and more than an integral that gives you $\sin (3x + 2)$ has gotten you into a "trig-loop". You just need the inverse function. Or numerical solutions are fine for this job. I'm afraid that as you move your colleagues will simply assume that you can find a solution to things like this without aid. That's why the sources don't mention it.
2d
comment Scintillator Length Calculations
Wolfram alpha gives answers mostly in Gamma-function forms. But in all seriousness there is no reason you need an exact solution. Use a numeric integration.
2d
comment Gamma Spectrum: What is causing this behavior?
In any case, that may just be the detection tail of the peak. I'm not sure why it would be so much more prominent on that line, though.
2d
comment Gamma Spectrum: What is causing this behavior?
Uhg. And you're using Ortec's software, too, aren't you? While there is nothing actually wrong with the data recording Ortec's display software does a rotten job of dealing with calibration drift and issues that these detectors are subject to.