32,801 research outputs found
Exchange interaction and correlations radically change behaviour of a quantum particle in a classically forbidden region
Exchange interaction strongly influences the long-range behaviour of
localised electron orbitals and quantum tunneling amplitudes. It violates the
oscillation theorem (creates extra nodes) and produces a power-law decay
instead of the usual exponential decrease at large distances. For inner
orbitals inside molecules decay is , for macroscopic systems , where is the Fermi momentum and for 1D, 3.5
for 2D and 4 for 3D crystal. Correlation corrections do not change these
conclusions. Slow decay increases the exchange interaction between localized
spins and the under-barrier tunneling amplitude. The under-barrier transmission
coefficients in solids (e.g. for point contacts) become temperature-dependent
Cheban loops
Left Cheban loops are loops that satisfy the identity x(xy.z) = yx.xz. Right
Cheban loops satisfy the mirror identity {(z.yx)x = zx.xy}. Loops that are both
left and right Cheban are called Cheban loops. Cheban loops can also be
characterized as those loops that satisfy the identity x(xy.z) = (y.zx)x. These
loops were introduced in Cheban, A. M. Loops with identities of length four and
of rank three. II. (Russian) General algebra and discrete geometry, pp.
117-120, 164, "Shtiintsa", Kishinev, 1980. Here we initiate a study of their
structural properties. Left Cheban loops are left conjugacy closed. Cheban
loops are weak inverse property, power associative, conjugacy closed loops;
they are centrally nilpotent of class at most two.Comment: 6 page
Search for Physics Beyond the Standard Model
We survey some recent ideas and progress in looking for particle physics
beyond the Standard Model, connected by the theme of Supersymmetry (SUSY). We
review the success of SUSY-GUT models, the expected experimental signatures and
present limits on SUSY partner particles, and Higgs phenomenology in the
minimal SUSY model.Comment: Standard Latex file. 18 pages without figures. (Calls to postscript
figure files blocked out. Full 32 page version with 37 in-text figures
available via regular mail.) MAD/PH/75
The atomistic structure and energy of nascent dislocation loops
An harmonic lattice theory is used, in conjunction with Mura's theory of eigendistorsions, to study the structure and energetics of nascent dislocation loops in face-centred-cubic (FCC) crystals. An analytical expression for the activation energies of such loops is derived. The results obtained herein indicate that thermal activation of small dislocation loops is possible at high stress levels such as those found in the vicinity of a crack tip. The implications of these results in understanding phenomena such as the brittle-ductile transition are discussed
Light storage in an optically thick atomic ensemble under conditions of electromagnetically induced transparency and four-wave mixing
We study the modification of a traditional electromagnetically induced
transparency (EIT) stored light technique that includes both EIT and four-wave
mixing (FWM) in an ensemble of hot Rb atoms. The standard treatment of light
storage involves the coherent and reversible mapping of one photonic mode onto
a collective spin coherence. It has been shown that unwanted, competing
processes such as four-wave mixing are enhanced by EIT and can significantly
modify the signal optical pulse propagation. We present theoretical and
experimental evidence to indicate that while a Stokes field is indeed detected
upon retrieval of the signal field, any information originally encoded in a
seeded Stokes field is not independently preserved during the storage process.
We present a simple model that describes the propagation dynamics of the fields
and the impact of FWM on the spin wave.Comment: 13 pages, 10 figure
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