Influence of carrier-carrier and carrier-phonon correlations on optical absorption and gain in quantum-dot systems

A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line-shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes. We investigate the density dependence of both mechanisms and clarify the importance of various dephasing channels involving the localized and delocalized states of the system.Comment: 12 pages, 10 figure

Mechanism, dynamics, and biological existence of multistability in a large class of bursting neurons

Multistability, the coexistence of multiple attractors in a dynamical system, is explored in bursting nerve cells. A modeling study is performed to show that a large class of bursting systems, as defined by a shared topology when represented as dynamical systems, is inherently suited to support multistability. We derive the bifurcation structure and parametric trends leading to multistability in these systems. Evidence for the existence of multirhythmic behavior in neurons of the aquatic mollusc Aplysia californica that is consistent with our proposed mechanism is presented. Although these experimental results are preliminary, they indicate that single neurons may be capable of dynamically storing information for longer time scales than typically attributed to nonsynaptic mechanisms.Comment: 24 pages, 8 figure

Saturation Magnetostriction and Volume Magnetostriction of Amorphous Ribbons Based on Fe-Ni and Fe-Co

The saturation magnetostriction and the forced volume magnetostriction of Fe-Ni and Fe-Co amorphous ribbons were measured from 77°K to room temperature by a three terminal capacitance method. It was found that the magnetostriction was nearly isotropic. In Fe-Ni amorphous system, the saturation λ_s and the volume magnetostriction constants δω/δH decreased monotonously with the increase of Ni concentration from 31×10^ and 21×10^/Oe respectively for Fe_P_C_ to 15×10^ and 7×10^/Oe respectively for Fe_Ni_P_C_. The temperature dependence of the saturation magnetostriction was not simple decreasing function of the temperature. In Fe-Co system, there was a remarkable change of the sign of the magnetostriction nearly equal to Fe_Co_Si_B_

Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures, with climatic impacts on the surrounding continents. The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Nino/Southern Oscillation (ENSO) in the equatorial Pacific, where air-sea coupling leads to a positive feedback between surface winds in the western basin, sea surface temperature in the eastern basin, and equatorial oceanic heat content. Here we use a suite of observational data, climate reanalysis products, and general circulation model simulations to reassess the factors driving the interannual variability. We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics. Instead, these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator. We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability

Rapid generation of long synthetic tandem repeats and its application for analysis in human artificial chromosome formation

Human artificial chromosomes (HACs) provide a unique opportunity to study kinetochore formation and to develop a new generation of vectors with potential in gene therapy. An investigation into the structural and the functional relationship in centromeric tandem repeats in HACs requires the ability to manipulate repeat substructure efficiently. We describe here a new method to rapidly amplify human alphoid tandem repeats of a few hundred base pairs into long DNA arrays up to 120 kb. The method includes rolling-circle amplification (RCA) of repeats in vitro and assembly of the RCA products by in vivo recombination in yeast. The synthetic arrays are competent in HAC formation when transformed into human cells. As short multimers can be easily modified before amplification, this new technique can identify repeat monomer regions critical for kinetochore seeding. The method may have more general application in elucidating the role of other tandem repeats in chromosome organization and dynamics

Se-Atom Incorporation in Fullerene and the MD Simulation(II. Radiochemistry)

The formation of Se atom-incorporated fullerenes has been investigated by using radionuclides produced by nuclear reactions. From the trace of radioactivities of ^Se after High Performance Liquid Chromatography (HPLC), it was found that the formation of endohedral fullerenes or heterofullerenes is possible by a recoil process following the nuclear reactions. To confirm the produced materials, ab initio molecular-dynamics simulations based on an all-electron mixed-basis approach were carried out. We found that the insertion of Se atom into C_ cage is much easier than that of As and Ge atoms

Soft Ferromagnetic Properties of Some Amorphous Alloys

In rapidly quenched amorphous alloys of (Fe_Co_x)_P_C_7 and (Fe_Co_x)_Si_B_, it was found that the zero magnetostrictive alloys are remarkably soft magnetic materials, while the magnetostrictive alloys have rather large coercive force. To investigate the effect of magnetostriction on the properties of the B-H loop, some fundamental magnetic properties in these alloys were studied. The magnetic domain pattern observed by Bitter\u27s method shows a periodic domain structure consisting of 180° and maze domain walls (the periodicity can be seen along the specimen long axis) in all the magnetostrictive alloys, suggesting the existence of magnetic anisotropy whose easy axis varies locally. The estimated value of the anisotropy energy varies with x similar to the composition dependence of magnetostriction. Torque measurements support the above estimation. The coercive force also varies with x and is nearly proportional to the magnetostriction to magnetization ratio. It is, therefore, considered that the anisotropy is caused by the anisotropic internal stress field, and that the stress fluctuation which inevitably exists is responsible for the large coercive force