Strongly Metallic Electron and Hole 2D Transport in an Ambipolar Si-Vacuum Field Effect Transistor.

We report experiment and theory on an ambipolar gate-controlled Si(111)-vacuum field effect transistor where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility (∼18 m2/V s) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using random phase approximation screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.

Hormonal control of sexual morphogenesis in achlya: dependence on protein and ribonucleic Acid syntheses.

The induction of the male sexual organ primordia (antheridial hyphae) by the steroid hormone antheridiol in the water mold Achlya ambisexualis requires both transcription and translation. Inhibition of either of these processes eliminates the expected increase in the production and release of the enzyme cellulase, which accompanies the formation of the antheridial hyphae.

Depression in HIV-infected patients: allopathic, complementary, and alternative treatments.

OBJECTIVES: The purpose of this review article is to synthesize the current knowledge related to depression and HIV disease. METHODS: The research literature was critically evaluated for several selected therapies that are prescribed for HIV-infected persons to treat depression. These therapies included pharmacotherapy, psychotherapy, alternative, and complementary therapies. RESULTS: Several therapies are currently available for the treatment of depression in HIV disease. When prescribing treatments, clinicians should be aware of problems associated with diagnoses, drug-drug interactions, and the benefits of some of the new therapies that are now available. Treatment regimes should be carefully designed to meet the individual needs of the patient and will optimally include a combination of approaches including psychotherapy, pharmacotherapy, education, and/or complementary therapies. CONCLUSIONS: Although HIV is now a treatable disease, the prevalence of depression in the HIV population remains high and should be continually addressed.

Integer quantum Hall effect on a six-valley hydrogen-passivated silicon (111) surface.

We report magnetotransport studies of a two-dimensional electron system formed in an inversion layer at the interface between a hydrogen-passivated Si(111) surface and vacuum. Measurements in the integer quantum Hall regime demonstrate that the expected sixfold valley degeneracy for these surfaces is broken, resulting in an unequal occupation of the six valleys and anisotropy in the resistance. We hypothesize the misorientation of Si surface breaks the valley states into three unequally spaced pairs, but the observation of odd filling factors is difficult to reconcile with noninteracting electron theory.

Hydrogenic spin quantum computing in silicon: a digital approach.

We suggest an architecture for quantum computing with spin-pair encoded qubits in silicon. Electron-nuclear spin-pairs are controlled by a dc magnetic field and electrode-switched on and off hyperfine interaction. This digital processing is insensitive to tuning errors and easy to model. Electron shuttling between donors enables multiqubit logic. These hydrogenic spin qubits are transferable to nuclear spin-pairs, which have long coherence times, and electron spin-pairs, which are ideally suited for measurement and initialization. The architecture is scalable to a highly parallel operation.

Multiplexed fluorescent bead-based immunoassays for quantitation of human cytokines in serum and culture supernatants.

BACKGROUND: An increasing volume of data suggests a relationship between cytokine levels in human body fluids and disease pathogenesis. Traditionally, many individual assays would be performed to measure the large number of known cytokines and determine their associations with disease. A new technique for the simultaneous measurement of multiple cytokines in cell culture supernatants by fluorescent microsphere-based flow cytometry was adapted to human sera. METHODS: Multiplexed sandwich immunoassays for eight cytokines were developed by coupling cytokine-specific capture antibodies to beads with different emission spectra. The binding of biotinylated detection antibodies bound with a streptavidin-conjugated fluorochrome was analyzed. Recovery of "spiked" cytokines, sensitivity, and variability of the assays were evaluated. In addition, the results of the bead assays were compared with the results of commercial enzyme-linked immunosorbent assays (ELISAs) that used the same antibody pairs. RESULTS: Correlations of the bead assays and the ELISAs were 0.974 (n = 18) for supernatant samples and 0.859 (n = 28) for serum samples. High, false-positive values observed with some sera, assumed to be produced by heterophilic antibodies, were reduced by preincubation with a cocktail of animal sera. CONCLUSIONS: Fluorescent bead-based immunoassays can be used to quantitate multiple cytokines in human sera and contribute to an understanding of the role of cytokines in disease processes. This methodology is applicable to many combinations of purified analytes and high-affinity antibodies. Published 2001 Wiley-Liss, Inc.

Density-dependent spin polarization in ultra-low-disorder quantum wires.

There is controversy as to whether a one-dimensional (1D) electron gas can spin polarize in the absence of a magnetic field. Together with a simple model, we present conductance measurements on ultra-low-disorder quantum wires supportive of a spin polarization at B=0. A spin energy gap is indicated by the presence of a feature in the range (0.5-0.7)x2e(2)/h in conductance data. Importantly, it appears that the spin gap is not constant but a function of the electron density. Data obtained using a bias spectroscopy technique are consistent with the spin gap widening further as the Fermi level is increased.