Biomedical subjects

M Khodas

Publications and source records attributed to M Khodas.

5 recordsLinked to original sources

PubMed2006

Dynamic response of one-dimensional interacting fermions.

We evaluate the dynamic structure factor S(q, omega) of interacting one-dimensional spinless fermions with a nonlinear dispersion relation. The combined effect of the nonlinear dispersion and of the interactions leads to new universal features of S(q, omega). The sharp peak S(q, omega) approximately q(delta(omega -uq), characteristic for the Tomonaga-Luttinger model, broadens up; for a fixed becomes finite at arbitrarily large . The main spectral weight, however, is confined to a narrow frequency interval of the width deltaomega approximately q(2)/m. At the boundaries of this interval the structure factor exhibits power-law singularities with exponents depending on the interaction strength and on the wave number q.

Journal Article↗

PubMed2004

Spin polarization of electrons by nonmagnetic heterostructures: the basics of spin optics.

We propose to use the lateral interface between two regions with different strengths of the spin-orbit interaction(s) to spin polarize the electrons in gated two-dimensional semiconductor heterostructures. For a beam with a nonzero angle of incidence, the transmitted electrons will split into two spin polarization components propagating at different angles. We analyze the refraction at such an interface and outline the basic schemes for filtration and control of the electron spin.

Journal Article↗

PubMed2000

Relaxation and diffusion for the kicked rotor

The dynamics of the kicked rotor, which is a paradigm for a mixed system, where the motion in some parts of phase space is chaotic and in other parts is regular, is studied statistically. The evolution operator of phase space densities in the chaotic component is calculated in the presence of noise, and the limit of vanishing noise is taken in the end. The relaxation rates to the equilibrium density are calculated analytically within an approximation that improves with increasing stochasticity. The results are tested numerically. A global picture is presented of relaxation to the equilibrium density in the chaotic component when the system is bounded and to diffusive behavior when it is unbounded.

Journal Article↗

PubMed2000

Relaxation to the invariant density for the kicked rotor

The relaxation rates to the invariant density in the chaotic phase space component of the kicked rotor (standard map) are calculated analytically for a large stochasticity parameter K. These rates are the logarithms of the poles of the matrix elements of the resolvent, Rinsertion mark(z)=(z-Uinsertion mark)(-1), of the classical evolution operator Uinsertion mark. The resolvent poles are located inside the unit circle. For hyperbolic systems this is a rigorous result, but little is known about mixed systems such as the kicked rotor. In this work, the leading relaxation rates of the kicked rotor are calculated in the presence of noise, to the leading order in 1/sqrt[K]. Then the limit of vanishing noise is taken and the relaxation rates are found to be finite, corresponding to poles lying inside the unit circle. It is found that the slow relaxation rates, in essence, correspond to diffusion modes in the momentum direction. Faster relaxation modes intermix the motion in the momentum and the angle space. The slowest relaxation rate of distributions in the angle space is calculated analytically by studying the dynamics of inhomogeneities projected down to this space. The analytical results are verified by numerical simulations.

Journal Article↗

PubMed1987

Clinical experience with bypass of the left ventricle using a roller pump.

Left ventricular bypass (LVB) using a roller pump was performed in 39 patients in the immediate postoperative period. In one group, LVB was performed as a last measure to restore cardiac function. The LVB was temporarily effective in this group, but independent circulation was restored in only 2 of 15 patients. Results were considered unsatisfactory. In a second group, LVB was used immediately when acute left ventricular insufficiency refractory to drug treatment developed. In this group, independent circulation was restored in 17 of 18 patients, demonstrating a therapeutic effect. Overall, cardiac activity was restored in 25 patients; 15 patients recovered and were released. Conditions for the recovery of patients are noted.

Adolescent↗