207 reputation
215
bio website math.stackexchange.com/users/…
location Champaign, IL
age 35
visits member for 3 years, 5 months
seen 2 days ago

Amateur mathematician, professional software engineer. Interested in all kinds of math, becoming a better mathematician, and helping others do the same.

email: jdb1729 (at) gmail.com

let's be friends: http://facebook.com/jdb1729


Mar
20
comment Can a car get better mileage driving over hills?
Do the uphill and downhill parts of the road have the same slope, or equivalently (because of the same-elevation constraint), do they have the same length? If not, what determines the ratio? Also, are you saying that the most efficient mileage on the flat road is obtained by driving at the slowest possible speed? (I see that this minimizes air resistance but I just want to confirm). Favorite answer so far but having some trouble working out a specific example.
Mar
19
accepted How much energy can be extracted from hydrogen?
Mar
19
accepted What is the effect of temperature on electrostatic-gravitational balance?
Mar
18
comment Double-slit experiment with alternating on-off switch
Roy and Peter, I am not assuming the switching happens instantaneously, only that it happens in a time somewhat shorter than the difference in arrival time. This seems practical to me because we can use sufficiently low-frequency EMR (with a correspondingly larger distance between the slits), or sufficiently slow electrons (maintaining the slit distance on the order of an X-ray). Luboš's answer is in agreement with my idea but I do not feel that he has explained it in any depth. I am not really asking for an analysis of my own reasoning so I did not include it in the question.
Mar
17
comment Can a car get better mileage driving over hills?
In my previous comment I was supposing that the uphill and downhill parts of the hilly road are of the same length (each part half the length of the flat road): "/\". This is not necessarily the case but I wonder if such a road could satisfy the question positively for some real car?
Mar
17
comment Double-slit experiment with alternating on-off switch
If we detect a photon immediately after the light is turned off, then it probably came from the more distant slit. If we detect it immediately after the light is turned on, then it probably came from the nearer slit. If the light has been on for some time (and will be on for some time) we have no such information and the probabilities are equal and we see maximum destructive interference.
Mar
17
comment Can a car get better mileage driving over hills?
It is both, and I agree with all of your assertions. Suppose it is possible to coast downhill at a 10% grade without using any fuel. Does it require twice as much fuel to climb uphill at the same grade as it takes to drive flat for the same distance?
Mar
17
comment Double-slit experiment with alternating on-off switch
My understanding is that the source can be anything: a hot cathode, an LED, or a even a low-frequency AC. Its energy can be constrained by some means and then focused to a plane-wave by an intermediate single-slit. I don't know very much about lasers. I think the peaks should exist because if a photon/electron is detected near the switching time, then we have information about which slit it passed through, therefore there is less interference than in the case when that information is absent. I am seeking a qualitative explanation, assuming the switching frequency is small.
Mar
17
asked Double-slit experiment with alternating on-off switch
Mar
16
comment Will a machine or a technique ever be possible that allows artificial gravity in interplanetary space?
Still probably a good idea to bolt down the furniture.
Mar
16
comment Will a machine or a technique ever be possible that allows artificial gravity in interplanetary space?
Two gotchas: in the former case you eventually have to start decelerating again (off, turn around, and back on again?), and in the latter case you have a Coriolis force which may be somewhat uncomfortable. en.wikipedia.org/wiki/For_the_Birds_(short_story%29
Mar
16
accepted Paradoxical interaction between a massive charged sphere and a point charge
Mar
14
awarded  Critic
Mar
13
comment Readings of the detectors at Japan and Izu-Bonin-Mariana Trenches
ndbc.noaa.gov/maps/Northwestern_Pacific.shtml
Mar
13
comment How good is current tsunami prediction?
The buoy data is available to the public in real-time. ndbc.noaa.gov/dart.shtml
Mar
13
comment How good is current tsunami prediction?
Georg, I think Graviton is asking how accurately can the tsunami height be predicted at a particular location after the epicenter and magnitude of the earthquake are known. I guess it depends not only on the distance but also on the shape of the coastline.
Mar
13
revised What is the effect of temperature on electrostatic-gravitational balance?
include radiation pressure in initial conditions
Mar
13
comment What is the effect of temperature on electrostatic-gravitational balance?
en.wikipedia.org/wiki/Capacitor#Capacitance_instability says that capacitance depends on temperature. Wouldn't a change in capacitance cause a re-arrangement of the charges? Would that change the net Coulomb force?
Mar
13
awarded  Scholar
Mar
13
accepted Knotted token-ring network