Electrically driven magnetization of diluted magnetic semiconductors actuated by the Overhauser effect.

It is well known that the Curie temperature, and hence the magnetization, in diluted magnetic semiconductors (DMS) like Ga(1-x)Mn(x)As can be controlled by changing the equilibrium density of holes in the material. Here, we propose that even with a constant hole density, large changes in the magnetization can be obtained with a relatively small imbalance in the quasi-Fermi levels for up-spin and down-spin electrons. We show, by coupling the mean field theory of diluted magnetic semiconductor ferromagnetism with master equations governing the Mn spin-dynamics, that a mere splitting of the up-spin and down-spin quasi-Fermi levels by 0.1 meV will produce the effect of an external magnetic field as large as 1 T as long as the alternative relaxation paths for Mn spins (i.e. spin-lattice relaxation) can be neglected. The physics is similar to the classic Overhauser effect, also called the dynamic nuclear polarization, with the Mn impurities playing the role of the nucleus. We propose that a lateral spin-valve structure in an anti-parallel configuration with a DMS as the channel can be used to demonstrate this effect, as quasi-Fermi level splitting of such magnitude, inside the channel of similar systems, has already been experimentally demonstrated to produce polarization of paramagnetic impurity spins.

Electrically driven spin dynamics of paramagnetic impurities.

The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.

The role of many-particle excitations in Coulomb blockaded transport.

We discuss the role of electron-electron and electron-phonon correlations in current flow in the Coulomb blockade regime, focusing specifically on non-trivial signatures arising from the breakdown of mean-field theory. By solving transport equations directly in Fock space, we show that electron-electron interactions manifest as gateable excitations experimentally observed in the current-voltage characteristic. While these excitations might merge into an incoherent sum that allows occasional simplifications, a clear separation of excitations into slow 'traps' and fast 'channels' can lead to further novelties such as negative differential resistance, hysteresis and random telegraph signals. Analogous novelties for electron-phonon correlation include the breakdown of commonly anticipated Stokes-anti-Stokes intensities, and an anomalous decrease in phonon population upon heating due to reabsorption of emitted phonons.

A self-consistent transport model for molecular conduction based on extended Hückel theory with full three-dimensional electrostatics.

We present a transport model for molecular conduction involving an extended Hückel theoretical treatment of the molecular chemistry combined with a nonequilibrium Green's function treatment of quantum transport. The self-consistent potential is approximated by CNDO (complete neglect of differential overlap) method and the electrostatic effects of metallic leads (bias and image charges) are included through a three-dimensional finite element method. This allows us to capture spatial details of the electrostatic potential profile, including effects of charging, screening, and complicated electrode configurations employing only a single adjustable parameter to locate the Fermi energy. As this model is based on semiempirical methods it is computationally inexpensive and flexible compared to ab initio models, yet at the same time it is able to capture salient qualitative features as well as several relevant quantitative details of transport. We apply our model to investigate recent experimental data on alkane dithiol molecules obtained in a nanopore setup. We also present a comparison study of single molecule transistors and identify electronic properties that control their performance.

Chlamydia trachomatis.

The frequency of positive serological tests for Chlamydia trachomatis, the most common sexually transmitted pathogen in the United States, was assessed in 18,622 specimens derived from New Jersey clinics. From the results, 13 percent female patients and 17 percent male patients were reactive for chlamydial antigen.

Rise in plasma trimethyllysine levels in humans after oral lysine load.

Oral administration of 5 g of lysine to healthy male volunteers produced a marked and progressive rise in plasma trimethyllysine (TML) from 3 to 24 h after the lysine load. Urinary TML did not register a similar rise. Plasma and urinary carnitine also increased after the lysine load. A similar rise in TML or carnitine was not seen after a 5 g tryptophan load. This suggests that the effect is specific for lysine and is not a nonspecific consequence of amino acid load.

Lysine-carnitine conversion in normal and undernourished adult men-suggestion of a nonpeptidyl pathway.

Administration of 5 g L-lysine orally to normal adults produced a significant increase in plasma carnitine levels within 6 h followed by a further rise by 48 h. Levels remained high up to 72 h. Similar changes in plasma carnitine were not observed if blood was sampled without lysine load or after administering a load of other amino acids such as tryptophan or threonine. Maximum excretion of carnitine per g creatinine was observed in 24 to 48 h collection after lysine load. Two subjects showed an early peak in 3-h and 6-h collections, respectively. Undernourished subjects failed to demonstrate similar change. After rehabilitation the undernourished subjects behaved as did the well-nourished subjects. These observations suggest that there may be a rapid in vivo conversion of orally administered lysine to carnitine in humans. Conversion of lysine to carnitine may be impaired in malnutrition.

Plasma carnitine levels in adult males in India: effects of high cereal, low fat diet, fat supplementation, and nutrition status.

Effects of diet and nutrition status on plasma carnitine levels was examined in adult Indian men. Apparently healthy subjects from middle and low income groups, consuming predominantly cereal-based diets had normal levels of plasma carnitine and albumin. Subjects with clear-cut evidence of malnutrition as judged by anthropometry, who, however, had normal plasma albumin, tended to have higher concentrations of plasma carnitine. Conversely, subjects with nutritional edema had markedly reduced plasma carnitine which improved with treatment. Among subjects with plasma albumin above 3.0 g/dl, plasma carnitine showed a weak but significant inverse correlation with anthropometric index (weight/height2 X 100). Increased intake of dietary fat reduced plasma free carnitine markedly and total carnitine marginally, but raised acyl carnitine. The results suggest that plasma carnitine levels in adults may be regulated by a balance between factors influencing its availability through the diet or its synthesis (availability of precursor amino acids, activity of synthetic enzymes), and utilization (body weight, quality and quantity of fat).