19,460 research outputs found
Principles of equilibrium statistical mechanics revisited: The idea of vortex energy
We show that the law of energy conservation with the fact of matter stability
imply the existence of energy complementary to that given by the function of
states of interacting systems and treated, with the environment, the function
of states of interacting extended systems. The complementary energy, we called
it vortex, is integral, not quantized, and causes trends contrary to that
prescribed by equilibrium statistical mechanics. We formulate its principles
and theorems, and question traditional insights in thermodynamics, entropy law,
phase transitions, persistent currents, Brownian motion.Comment: 8 pages. Refined the title and wording, corrected typos, added the
acknowledgement. arXiv admin note: substantial text overlap with
arXiv:1109.2605; refined the title, clarified some phrases, refined
concluding remarks, results unchange
On two conjectures concerning convex curves
We recall two basic conjectures on the developables of convex projective
curves, prove one of them and disprove the other in the firdt nontrivial case
of curves in RP^3. Namely, we show that i) the tangent developable surface of
any convex curve in RP^3 has 'degree' 4 and ii) construct an example of 4
tangent lines to a convex curve in RP^3 such that no real line intersects all
four of them.Comment: AMSTEX, 15 pages, 3 eps pictures. to appear in Int. J. Mat
On moments of a polytope
We show that the multivariate generating function of appropriately normalized
moments of a measure with homogeneous polynomial density supported on a compact
polytope P in R^d is a rational function. Its denominator is the product of
linear forms dual to the vertices of P raised to the power equal to the degree
of the density function. Using this, we solve the inverse moment problem for
the set of, not necessarily convex, polytopes having a given set S of vertices.
Under a weak non-degeneracy assumption we also show that the uniform measure
supported on any such polytope is a linear combination of uniform measures
supported on simplices with vertices in S.Comment: 28 pages, 3 figure
Photoassociation adiabatic passage of ultracold Rb atoms to form ultracold Rb_2 molecules
We theoretically explore photoassociation by Adiabatic Passage of two
colliding cold ^{85}Rb atoms in an atomic trap to form an ultracold Rb_2
molecule. We consider the incoherent thermal nature of the scattering process
in a trap and show that coherent manipulations of the atomic ensemble, such as
adiabatic passage, are feasible if performed within the coherence time window
dictated by the temperature, which is relatively long for cold atoms. We show
that a sequence of ~2*10^7 pulses of moderate intensities, each lasting ~750
ns, can photoassociate a large fraction of the atomic ensemble at temperature
of 100 microkelvin and density of 10^{11} atoms/cm^3. Use of multiple pulse
sequences makes it possible to populate the ground vibrational state. Employing
spontaneous decay from a selected excited state, one can accumulate the
molecules in a narrow distribution of vibrational states in the ground
electronic potential. Alternatively, by removing the created molecules from the
beam path between pulse sets, one can create a low-density ensemble of
molecules in their ground ro-vibrational state.Comment: RevTex, 23 pages, 9 figure
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