2,469 research outputs found
Transition times in the Landau-Zener model
This paper presents analytic formulas for various transition times in the
Landau-Zener model. Considerable differences are found between the transition
times in the diabatic and adiabatic bases, and between the jump time (the time
for which the transition probability rises to the region of its asymptotic
value) and the relaxation time (the characteristic damping time of the
oscillations which appear in the transition probability after the crossing).
These transition times have been calculated by using the exact values of the
transition probabilities and their derivatives at the crossing point and
approximations to the time evolutions of the transition probabilities in the
diabatic basis, derived earlier \protect{[}N. V. Vitanov and B. M. Garraway,
Phys. Rev. A {\bf 53}, 4288 (1996)\protect{]}, and similar results in the
adiabatic basis, derived in the present paper.Comment: 7 pages, two-column revtex style, 5 figures, to appear in Phys. Rev.
A (Feb 1999
On sets of irreducible polynomials closed by composition
Let be a set of monic degree polynomials over a finite field
and let be the compositional semigroup generated by . In this
paper we establish a necessary and sufficient condition for to be
consisting entirely of irreducible polynomials. The condition we deduce depends
on the finite data encoded in a certain graph uniquely determined by the
generating set . Using this machinery we are able both to show
examples of semigroups of irreducible polynomials generated by two degree
polynomials and to give some non-existence results for some of these sets in
infinitely many prime fields satisfying certain arithmetic conditions
Geometrical Defects in Josephson Junction Arrays
Dislocations and disclinations in a lattice of Josephson junctions will
affect the dynamics of vortex excitations within the array. These defects
effectively distort the space in which the excitations move and interact. The
interaction energy between such defects and excitations are determined and
vortex trajectories in twisted lattices are calculated. Finally, possible
experiments observing these effects are presented.Comment: 26 pages including 5 figure
Risk Factors for Severe Violence in Intimate Partner Stalking Situations: An Analysis of Police Records
Stalkers can be violent, and empirical studies have sought to identify factors associated with violence perpetrated by the stalker. Most of these works view physical violence as a homogeneous construct and do not differentiate between moderate and severe violence. The present study aims to identify correlates of nonviolent, moderate, and severe physical violence within an archival sample of 369 domestically violent police incident reports, where stalking behavior was indicated. The incident reports utilized in this study occurred between 2013 and 2017, among intimate or ex-intimate partners. The present study explored 12 independent variables that have yielded mixed findings in previous stalking violence literature, as well as two previously untested factors of nonfatal strangulation and child contact. The police records were coded for severity of physical violence using the Revised Conflict Tactics Scale and analyzed using a logistic regression. The regression analysis revealed significant independent associations between the outcome variable of severe physical violence and child contact, history of domestic violence, separation, nonfatal strangulation, jealousy, previous injury, and victim belief of potential harm. These results may help produce pragmatic recommendations for law enforcement agencies and other relevant bodies who seek to identify victims at risk of severe violence, increasing the potential for early intervention and prevention of physical harm. The awareness of factors that are shown to be related to serious physical violence may assist first responders in recognizing which victims may be at risk of serious harm, as well as effectively allocating any appropriate resources to reduce and prevent harm
Zero--Bias Anomaly in Finite Size Systems
The small energy anomaly in the single particle density of states of
disordered interacting systems is studied for the zero dimensional case. This
anomaly interpolates between the non--perturbative Coulomb blockade and the
perturbative limit, the latter being an extension of the Altshuler--Aronov zero
bias anomaly at d=0. Coupling of the zero dimensional system to a dissipative
environment leads to an effective screening of the interaction and a
modification of the density of states.Comment: 25 pages and 6 figure
Nonlinear level crossing models
We examine the effect of nonlinearity at a level crossing on the probability
for nonadiabatic transitions . By using the Dykhne-Davis-Pechukas formula,
we derive simple analytic estimates for for two types of nonlinear
crossings. In the first type, the nonlinearity in the detuning appears as a
{\it perturbative} correction to the dominant linear time dependence. Then
appreciable deviations from the Landau-Zener probability are found to
appear for large couplings only, when is very small; this explains why the
Landau-Zener model is often seen to provide more accurate results than
expected. In the second type of nonlinearity, called {\it essential}
nonlinearity, the detuning is proportional to an odd power of time. Then the
nonadiabatic probability is qualitatively and quantitatively different from
because on the one hand, it vanishes in an oscillatory manner as the
coupling increases, and on the other, it is much larger than . We
suggest an experimental situation when this deviation can be observed.Comment: 9 pages final postscript file, two-column revtex style, 5 figure
Zero Frequency Current Noise for the Double Tunnel Junction Coulomb Blockade
We compute the zero frequency current noise numerically and in several limits
analytically for the coulomb blockade problem consisting of two tunnel
junctions connected in series. At low temperatures over a wide range of
voltages, capacitances, and resistances it is shown that the noise measures the
variance in the number of electrons in the region between the two tunnel
junctions. The average current, on the other hand, only measures the mean
number of electrons. Thus, the noise provides additional information about
transport in these devices which is not available from measuring the current
alone.Comment: 33 pages, 10 figure
An accurate effective action for `baby' to `adult' skyrmions
Starting with a Chern-Simons theory, we derive an effective action for
interacting quantum Hall skyrmions that takes into account both large-distance
physics and short-distance details as well. We numerically calculate the
classical static skyrmion profile from this action and find excellent agreement
with other, microscopic calculations over a wide range of skyrmion sizes
including the experimentally relevant one. This implies that the essential
physics of this regime might be captured by a continuum classical model rather
than resorting to more microscopic approaches. We also show that the skyrmion
energy closely follows the formula suggested earlier by Sondhi et al. for a
broad parameter range of interest as well.Comment: 13 pages (Revtex) + 3 ps-figure
Theory of Coherent Time-dependent Transport in One-dimensional Multiband Semiconductor Superlattices
We present an analytical study of one-dimensional semiconductor superlattices
in external electric fields, which may be time-dependent. A number of general
results for the (quasi)energies and eigenstates are derived. An equation of
motion for the density matrix is obtained for a two-band model, and the
properties of the solutions are analyzed. An expression for the current is
obtained. Finally, Zener-tunneling in a two-band tight-binding model is
considered. The present work gives the background and an extension of the
theoretical framework underlying our recent Letter [J. Rotvig {\it et al.},
Phys. Rev. Lett. {\bf 74}, 1831 (1995)], where a set of numerical simulations
were presented.Comment: 15 pages, Revtex 3.0, uses epsf, 2 ps figures attache
Zinc(II) coordination polymers with pseudopeptidic ligands
Two new phenyl-bridged pseudopeptidic ligands have been prepared and structurally characterised. The nature of the ligands’ substituents play an important role in the nature of the solid state structure yielding either hydrogen bonded linked sheets of molecules or infinite hydrogen bonded networks. Both these ligands were reacted with a range of zinc(II) salts with the aim of synthesising coordination polymers and networks and exploring the role that anions could play in determining the final structure. The crystal structures of four of these systems (with ZnSO4 and ZnBr2) were determined; in one case, a 3D coordination network was obtained where zinc–ligand coordination bonds generated the 3D arrangements. Three other 3D networks were obtained by anion-mediated hydrogen bonding of coordination 1D chains or 2D sheets. These four very different structures highlight the important role played by the ligands’ substituents and the counteranions present in the system
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