Biomedical subjects
Publications and source records attributed to Doron Cohen.
We propose a random matrix modeling for the parametric evolution of eigenstates. The model is inspired by a large class of quantized chaotic systems. Its unique feature is having parametric invariance while still possessing the nonperturbative breakdown that had been discussed by Wigner 50 years ago. Of particular interest is the emergence of an additional crossover to multifractality.
Recent evidence reported on increased pain sensitivity in animals following parenteral opioid administration and in humans subsequent to intravenously of short-acting opioids and possibly in drug addicts. The aims of the present study were to explore the possibilities that (1) pain perception is altered in chronic opioid addicts (OAs); (2) if indeed so, the cessation of opioid consumption resets their altered pain perception. Sixty heroin or methadone OAs who attended a 4-week inpatient detoxification program were exposed to the cold pressor test (CPT) upon entrance to the program, at 7 and 28 days subsequent to the cessation of opioid consumption (verified by repeated urine toxicology tests). Latency of pain onset (s), pain intensity (0-100 VAS), and tolerance (time for hand withdrawal) in response to the CPT were measured. In comparison with 70 healthy controls, the OAs demonstrated prolonged latency (6.6+/-3.5s versus 10.9+/-7.7s; p < 0.0001); decreased VAS (74+/-16 versus 55+/-20; p < 0.0001); shorter tolerance (56.4+/-51.3s versus 31.7+/-40.7s; p = 0.001). No differences between the three time points in any of the three measures were detected in the OAs. The results provide further evidence of opioid-induced hyperalgesia in the OA population, as manifested by their quicker hand withdrawal. In addition, it appears that detoxification from opioids does not reset pain perception for at least 1 month.
Considering a quantized chaotic system, we analyze the evolution of its eigenstates as a result of varying a control parameter. As the induced perturbation becomes larger, there is a crossover from a perturbative to a non-perturbative regime, which is reflected in the structural changes of the local density of states. The full scenario is explored for a physical system: an Aharonov-Bohm cylindrical billiard. As we vary the magnetic flux, we discover an intermediate twilight regime where perturbative and semiclassical features coexist. This is in contrast with the simple crossover from a Lorentzian to a semicircle line shape which is found in random-matrix models.
The amount of charge that is pushed by a moving scatterer is dQ= -GdX , where dX is the displacement of the scatterer. The question is: what is G ?. Does it depend on the transmission g(0) of the scatterer? Does the answer depend on whether the system is open (with leads attached to reservoirs) or closed? In the latter case what are the implications of having "quantum chaos" and/or coupling to the environment? The answers to these questions illuminate some fundamental aspects of the theory of quantum pumping. For the analysis we take a network (graph) as a model system, and use the Kubo formula approach.
We discuss the possibility of having "quantum dissipation" due to the interaction with chaotic degrees of freedom. We define the conditions that should be satisfied in order to have a dissipative effect similar to the one due to an interaction with a (many body) bath. We also compare with the case where the environment is modeled by a random matrix model. In the case of interaction with "chaos" we observe a regime where the relaxation process is nonuniversal and reflects the underlaying semiclassical dynamics. As an example we consider a two level system (spin) that interacts with a two-dimensional anharmonic oscillator.
We study the possibility to undo the quantum mechanical evolution in a time reversal experiment. The naive expectation, as reflected in the common terminology ("Loschmidt echo"), is that maximum compensation results if the reversed dynamics extends to the same time as the forward evolution. We challenge this belief and demonstrate that the time t(r) for maximum return probability is in general shorter. We find that t(r) depends on lambda=epsilon(evol)/epsilon(prep), being the ratio of the error in setting the parameters (fields) for the time-reversed evolution to the perturbation which is involved in the preparation process. Our results should be observable in spin-echo experiments where the dynamical irreversibility of quantum phases is measured.
We study the evolution of the energy distribution for a stadium with moving walls. We consider a one period driving cycle, which is characterized by an amplitude A and a wall velocity V. This evolving energy distribution has both "parametric" and "stochastic" components. The latter are important for the theory of quantum irreversibility and dissipation in driven mesoscopic devices. For an extremely slow wall velocity V, the spreading mechanism is dominated by transitions between neighboring levels, while for larger (nonadiabatic) velocities, the spreading mechanism has both perturbative and nonperturbative features. We present a numerical study which is aimed at identifying the latter features. A procedure is developed for the determination of the various V regimes. The possible implications of linear response theory are discussed.
We present an optical "enantio-selective switch" that, in two steps, turns a ("racemic") mixture of left-handed and right-handed chiral molecules into the enantiomerically pure state of interest. The optical switch is composed of an "enantio-discriminator" and an "enantio-converter" acting in tandem. The method is robust, insensitive to decay processes, and does not require molecular preorientation. We demonstrate the method on the purification of a racemate of (transiently chiral) D2S2 molecules, performed on the nanosecond time scale.
The idea of perturbation independent decay (PID) has appeared in the context of survival-probability studies, and lately has emerged in the context of quantum irreversibility studies. In both cases the PID reflects the Lyapunov instability of the underlying semiclassical dynamics, and it can be distinguished from the Wigner-type decay that holds in the perturbative regime. The theory of the survival probability is manifestly related to the parametric theory of the local density of states (LDOS). In contrast to that the physics of quantum irreversibility requires subtle cross correlations, which are not captured by the LDOS alone, to be taken into account.
We consider the motion of a particle, taking into account its interaction with environmental degrees of freedom. The dephasing time is determined by the nature of the environment and depends on the particle velocity. Our interest is in the case where the environment consists of few chaotic degrees of freedom. We obtain results for the dephasing time and compare them with those of the effective-bath approach. The latter approach is based on the conjecture that the environment can be modeled as a collection of infinitely many harmonic oscillators. The work is related to studies of driven systems, quantum irreversibility, and fidelity. The specific model that we consider requires the solution of the problem of a particle in a box with a moving wall, whose one-dimensional version is related to the Fermi acceleration problem.