34,322 reputation
347117
bio website inspirehep.net/…
location Duchy of Grand Fenwick
age 43
visits member for 3 years, 10 months
seen 12 mins 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.


7m
comment Special relativity and missing factors of $c$
Kyle has covered what is happening here just fine, but let me note that learning how to put the c's back in is a useful skill, and it works by paying careful attention to the dimensionality of each quantity. Masses get two c's and momenta and times get 1 if you want to leave energy and distances without them.
14h
comment Leakage of X-ray radiation
As usual the chapter of the The Review of Particle Physics on "Passage of Particles Through Matter" is very good on the fundamentals but requires a certain amount of experience to translate into good shielding practice.
14h
comment Leakage of X-ray radiation
"he value of $\mu/\rho$ is about $0.5 \,\mathrm{cm^2/g}$ [...]" They use goofy units at NIST. Or is this common in shielding applications outside of the experimental world? Most particle experimenters think in terms of the energy loss which is roughly $2 \,\mathrm{MeV/(g\,cm^2)}$ at minimum inonization or the radiation length. I had to read that a couple of times to parse it correctly I agree that worrying about showering is always the main issue with photons.
17h
comment What would happen if an accelerated particle collided with a person?
Related: physics.stackexchange.com/questions/6435/cosmic-ray-hazards physics.stackexchange.com/questions/31752/… physics.stackexchange.com/questions/92209/…
2d
comment Can beamer presentation can be used at APS meetings?
I've been in rooms where PowerPoint presentations have met with quiet and half-joking boos. Not at an open meeting like APS, but in working groups where it is considered reasonable to grouse about colleagues making everyone's life harder. PDFs work properly on almost everyone's machine, FSM bedamned slideware formats that f#*(&@#ing change every few year work correctly on only a few peoples machines. Do the right thing.
Sep
27
comment The earth is spinning, so why don't we jump and land on a different location?
"The big idea of Newton was it to understand" Galileo had it first. Newton worked out a proper mathematical formulation for dynamics, but relativity and inertia were both already known.
Sep
27
comment Voltage drop due to a resistor
@David Electric field and potential are related by the line integral $\Delta V = \int_s \, \vec{E}\cdot \mathrm{d}\vec{s}$ (or $\Delta V = E \Delta s \cos\theta$ for my algebra/trig students). The potential across the resistor follow from the battery and the properties of conduction charge on conductors, so the field will find the right configuration.
Sep
27
comment Voltage drop due to a resistor
Perhaps you are simply using it as a shorthand but asking how things "know" almost always clouds the issue and keeps you from seeing how it happens. Instead ask what regulates the process.
Sep
27
comment Why is equivalent resistance in parallel circuit always less than each individual resistor?
With experience, you will find this fact obvious, and it is worth taking the time to ponder it until it becomes so.
Sep
27
comment Why is equivalent resistance in parallel circuit always less than each individual resistor?
I have to confess that when I saw that you had exhibited the harmonic sum form ($1/R_e = 1/R_1 + 1/R_2 + \dots$), I found the question confusing because I didn't understand what you didn't get. It's worth your time to think about this until it becomes obvious, not because this problem is so important but because it will start teaching you the habit of learning things from the functional form of the relationships that appear in your studies.
Sep
27
comment Planet order in solar system
Note the Uranus is lighter than Neptune. There is no neat and satisfying pattern and no particular reason to expect one.
Sep
27
comment Why should I believe that “elementary” particles are indeed elementary?
Because it is really awkward to call them "elementary-as-far-as-we-know-and-we've-looked-really-hard particles" which is what the word actually means when used by physicists.
Sep
26
comment How far ahead can we predict solar and lunar eclipses?
"That's on Wikipedia! It's safe to say that if wikipedia knows something, the experts know quite a bit more." Well ... mostly. But I suspect that this is true in this case because it is an uncontroversial and rather geeky topic and that's what Wikipedia does best.
Sep
26
comment Neutrinos at Super-Kamiokande
No, the received flavor distribution depends on the distance traveled and that is expressed as a difference between the upward and downward traveling rates.
Sep
25
comment Neutrinos at Super-Kamiokande
This may be a confusion about some basic facts about the super-k measurement. There is a factor of 2,nut between muon and electron flavors in the starting distributions, and the is an up/down difference that depends on the distance traveled.
Sep
25
comment Black Holes can't exist?
In all seriousness papers on arXiv that attract any attention (as this one has done) are reviewed by the author's peers. There is not the formal step in a which an editor then gives it a up/down check, but this will receive plenty of attention sussing out any errors that might exist.
Sep
24
comment Handedness of Reference Frames?
Er ... you're right about that. Don't know where that came from. In any case, the notion that there are "proper rotation" and "improper rotations" (which are a proper rotation plus a reflection) is not mine. You find it in various texts on group theory.
Sep
24
comment Handedness of Reference Frames?
It's not really me, it's mathematicians. The transformations that include reflections have all the same properties as the pure (proper) rotations, and in 2D there is no distinction at all.
Sep
24
comment How come neutrons in a nucleus don't decay?
"but 1H2 is unstable (but has a longer life than n)" If you mean the deuteron, then no it isn't.
Sep
24
comment HW Question: Force of a Car on a Truck
The 4500 N is presumably a horizontal force, not a vertical one: it's the force which will cause the vehicles to move.