In-Plane Magnetolumnescence of Modulation-Doped GaAs/AlGaAs Coupled Double Quantum Wells

In-plane magnetic field photoluminescence spectra from a series of GaAs/AlGaAs coupled double quantum wells show distinctive doublet structures related to the symmetric and antisymmetric states. The magnetic field behavior of the upper transition from the antisymmetric state strongly depends on sample mobility. In lower mobility samples, the transition energy shows an $\cal N$-type kink with fields (namely a maximum followed by a minimum), whereas higher mobility samples have a linear dependence. The former is due to a homogeneous broadening of electron and hole states and the results are in good agreement with theoretical calculations.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let

A possible explanation for the inconsistency between the Giotto grain mass distribution and ground-based observations

Giotto measured the in situ Halley dust grain mass distribution with 2 instruments, Particle Impact Analyzer and Dust Impact Detection System (DIDSY), as well as the total intercepted mass from the deceleration of the spacecraft (Giotto Radio-Science Experiment, GRE). Ground based observations made shortly before encounter have fluxes much higher than would be predicted from Giotto data. It is concluded that Giotto DIDSY and GRE data represent observations of dust originating from a narrow track along the nucleus. They are consistent with ground based data, if assumptions are made about the level of activity along this track. The actual size distribution that should be used for modeling of the whole coma should not include the large mass excess actually observed by Giotto. Extrapolation of the small grain data should be used, since for these grains the velocity dispersion is low and temporal changes at the nucleus would not affect the shape of the mass distribution

Photoluminescence Detected Doublet Structure in the Integer and Fractional Quantum Hall Regime

We present here the results of polarized magneto-photoluminescence measurements on a high mobility single-heterojunction. The presence of a doublet structure over a large magnetic field range (2>nu>1/6) is interpreted as possible evidence for the existence of a magneto-roton minima of the charged density waves. This is understood as an indication of strong electronic correlation even in the case of the IQHE limit.Comment: submitted to Solid State Communication

The Chemokine CCL2 Mediates the Seizure-enhancing Effects of Systemic Inflammation

Epilepsy is a chronic disorder characterized by spontaneous recurrent seizures. Brain inflammation is increasingly recognized as a critical factor for seizure precipitation, but the molecular mediators of such proconvulsant effects are only partly understood. The chemokine CCL2 is one of the most elevated inflammatory mediators in patients with pharmacoresistent epilepsy, but its contribution to seizure generation remains unexplored. Here, we show, for the first time, a crucial role for CCL2 and its receptor CCR2 in seizure control. We imposed a systemic inflammatory challenge via lipopolysaccharide (LPS) administration in mice with mesial temporal lobe epilepsy. We found that LPS dramatically increased seizure frequency and upregulated the expression of many inflammatory proteins, including CCL2. To test the proconvulsant role of CCL2, we administered systemically either a CCL2 transcription inhibitor (bindarit) or a selective antagonist of the CCR2 receptor (RS102895). We found that interference with CCL2 signaling potently suppressed LPS-induced seizures. Intracerebral administration of anti-CCL2 antibodies also abrogated LPS-mediated seizure enhancement in chronically epileptic animals. Our results reveal that CCL2 is a key mediator in the molecular pathways that link peripheral inflammation with neuronal hyperexcitability

Coulomb Driven New Bound States at the Integer Quantum Hall States in GaAs/Al(0.3)Ga(0.7)As Single Heterojunctions

Coulomb driven, magneto-optically induced electron and hole bound states from a series of heavily doped GaAs/Al(0.3)Ga(0.7)As single heterojunctions (SHJ) are revealed in high magnetic fields. At low magnetic fields (nu > 2), the photoluminescence spectra display Shubnikov de-Haas type oscillations associated with the empty second subband transition. In the regime of the Landau filling factor nu < 1 and 1 < nu <2, we found strong bound states due to Mott type localizations. Since a SHJ has an open valence band structure, these bound states are a unique property of the dynamic movement of the valence holes in strong magnetic fields

The Importance of Static Correlation in the Band Structure of High Temperature Superconductors

Recently we presented a new band structure for La(2-x)Sr(x)CuO(4) and other high temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work we present details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates. In particular, we use a number of chemical analogues to describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing.Comment: The Journal of Physical Chemistry, in press. References and figures updated. See www.firstprinciples.com for more information related to this wor

The effects of an active-assisted stretching program on functional performance in elderly persons: A pilot study

This study examined the impact of an eight-week active-assisted (AA) stretching program on functionality, mobility, power, and range of motion (ROM) in elderly residents of a residential retirement community. Seventeen volunteers (4 male, 13 female; 88.8 ± 5.36 years) were randomly assigned to an AA or control group. The AA group performed 10 different AA stretches targeting the major joints of the body twice weekly for eight weeks. Controls attended classes requiring limited physical activity. All participants were assessed using four flexibility and six functional tests, one week before and after the eight-week training period. A fully randomized repeated-measures ANCOVA with pretest scores as a covariate was used to detect differences between groups across time. The AA group demonstrated significant increases in ROM for most of the joints evaluated (p < 0.05) and significant increases in all performance measures (p < 0.05). Controls showed no improvements in functional or ROM measures (α = 0.05). Additionally, the AA group showed significantly better performance outcomes across the training period than controls. We conclude that our eight-week flexibility program effectively reduces age-related losses in ROM and improves functional performance in elderly persons with insufficient physical reserves to perform higher-intensity exercises

Variation with mass of \boldmath{B(E3; 0_1^+ \to 3_1^-)} transition rates in A=124−134A=124-134 even-mass xenon nuclei

$B(E3; 0_1^+ \to 3_1^-)$ transition matrix elements have been measured for even-mass $^{124-134}$Xe nuclei using sub-barrier Coulomb excitation in inverse kinematics. The trends in energy $E(3^-)$ and $B(E3; 0_1^+ \to 3_1^-)$ excitation strengths are well reproduced using phenomenological models based on a strong coupling picture with a soft quadrupole mode and an increasing occupation of the intruder $h_{11/2}$ orbital.Comment: 5 pages, 4 figures, PRC in pres