Hole spin coherence in a Ge/Si heterostructure nanowire.

Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2* 0.18 µs exceeds corresponding measurements in III­V semiconductors by more than an order of magnitude, as expected for predominately nuclear-spin-free materials. Dephasing is observed to be exponential in time, indicating the presence of a broadband noise source, rather than Gaussian, previously seen in systems with nuclear-spin-dominated dephasing.

Machining oxide thin films with an atomic force microscope: pattern and object formation on the nanometer scale.

An atomic force microscope (AFM) has been used to machine complex patterns and to form free structural objects in thin layers of MoO(3) grown on the surface of MoS(2). The AFM tip can pattern lines with

Functional nanoscale electronic devices assembled using silicon nanowire building blocks.

Because semiconductor nanowires can transport electrons and holes, they could function as building blocks for nanoscale electronics assembled without the need for complex and costly fabrication facilities. Boron- and phosphorous-doped silicon nanowires were used as building blocks to assemble three types of semiconductor nanodevices. Passive diode structures consisting of crossed p- and n-type nanowires exhibit rectifying transport similar to planar p-n junctions. Active bipolar transistors, consisting of heavily and lightly n-doped nanowires crossing a common p-type wire base, exhibit common base and emitter current gains as large as 0.94 and 16, respectively. In addition, p- and n-type nanowires have been used to assemble complementary inverter-like structures. The facile assembly of key electronic device elements from well-defined nanoscale building blocks may represent a step toward a "bottom-up" paradigm for electronics manufacturing.

Hepatic collagen metabolism: effect of alcohol consumption in rats and baboons.

Long-term ethanol feeding causes collagen accumulation in livers of rats and baboons. Activity of collagen proline hydroxylase in the liver is also stimulated, and incorporation of proline into collagen hydroxyproline in rat liver slices is significantly enhanced, a result indicating that increased synthesis is responsible, in part, for the collagen accumulation.

Experimental alcoholic hepatitis: a new primate model.

Research into the pathogenesis of alcoholic cirrhosis has suffered from the lack of an animal model of alcoholic hepatitis, considered by many to be the link between alcoholic fatty liver and cirrhosis. The entire constellation of histologic features characteristic of alcoholic hepatitis has been produced for the first time in baboons by administration of ethanol with a nutritionally adequate diet. This includes fat, necrosis. inflammation, alcoholic hyaline, fibrosis, and central hyaline sclerosis.

Hepatic microsomal enzymes in man and rat: induction and inhibition by ethanol.

The feeding of ethanol increased significantly the activities of hepatic pentobarbital and benzpyrene hydroxylases in rats, and, in human volunteers, doubled pentobarbital hydroxylase activity. In vitro ethanol inhibited aniline, pentobarbital, and benzpyrene hydroxylases. These data may explain, at least in part, the increased tolerance of alcoholics to sedatives when sober, and the enhanced sensitivity to sedatives when inebriated.

Tunneling Spectroscopy of M3C60 Superconductors: The Energy Gap, Strong Coupling, and Superconductivity.

Tunneling spectroscopy has been used to characterize the magnitude and temperature dependence of the superconducting energy gap (triangle up) for K(3)C(60) and Rb(3)C(60). At low temperature the reduced energy gap, 2triangle upkappaT(c) (where T(c) is the transition temperature) has a value of 5.3 +/- 0.2 and 5.2 +/- 0.3 for K(3)C(60) and Rb(3)C(60), respectively. The magnitude of the reduced gap for these materials is significantly larger than the value of 3.53 predicted by Bardeen-Cooper-Schrieffer theory. Hence, these results show that the pair-coupling interaction is strong in the M(3)C(60) superconductors. In addition, measurements of triangle up(T) for both K(3)C(60) and Rb(3)C(60) exhibit a similar mean-field temperature dependence. The characterization of triangle up and triangle up(T) for K(3)C(60) and Rb(3)C(60) provides essential constraints for theories evolving to describe superconductivity in the M(3)C(60) materials.

Experimental realization of the covalent solid carbon nitride.

Pulsed laser ablation of graphite targets combined with an intense, atomic nitrogen source has been used to prepare C-N thin film materials. The average nitrogen content in the films was systematically varied by controlling atomic nitrogen flux. Rutherford backscattering measurements show that up to 40 percent nitrogen can be incorporated on average into these solids under the present reaction conditions. Photoelectron spectroscopy further indicates that carbon and nitrogen form an unpolarized covalent bond in these C-N materials. Qualitative tests indicate that the C-N solids are thermally robust and hard. In addition, strong electron diffraction is observed from crystallites within the films. Notably, analysis of these diffraction data show that the only viable structure for the C-N crystallites is that of beta-C(3)N(4), a material predicted theoretically to exhibit superhardness. The experimental synthesis of this new C-N material offers exciting prospects for both basic research and engineering applications.

Hexagonal Domain-Like Charge Density Wave Phase of TaS2 Determined by Scanning Tunneling Microscopy.

The structure of the room-temperature charge density wave (CDW) phase in octahedrally coordinated tantalum disulfide, 1T-TaS2, has been a controversial issue for over 15 years. Large-scale scanning tunneling microscope images of the intralayer structure of this phase exhibit a domain-like pattern defined by a variation in the maximum CDW amplitude. The circular domains, consisting of high-amplitude CDWs, are arranged in a regular hexagonal lattice (period 73+/-3 angstroms) that is rotated relative to the CDWs. In addition, from the analysis of atomic resolution images it was determined that there is a well-defined phase shift between the CDWs in adjacent domains, and that within a domain the CDW superlattice is commensurate with the atomic lattice. These results provide evidence for the hexagonal discommensurate CDW phase in 1T-TaS2 and also suggest an explanation for the long-standing controversy concerning the structure of this phase.

Reduced nicotinamide-adenine dinucleotide phosphate oxidase: activity enhanced by ethanol consumption.

Prolonged consumption of ethanol enhances the activities of the hepatic microsomal ethanol oxidizing system and of reduced nicotinamide-adenine dinucleotide phosphate oxidase, but not of catalase. The oxidase-catalase system is not part of the microsomal ethanol oxidizing system since catalase inhibitors dissociate ethanol oxidation by the two pathways. Enhanced reduced nicotinamide-adenine dinucleotide phosphate oxidase activity may contribute to liver injury, possibly by favoring lipoperoxidation.

Plasma alpha amino-n-butyric acid to leucine ratio: an empirical biochemical marker of alcoholism.

The plasma ratio of alpha-amino-n-butyric acid to leucine was elevated in ambulatory and hospitalized alcoholics as well as in baboons fed alcohol along with an adequate diet. There was a statistically significant positive correlation between this ratio and the degree of alcoholism assessed by three separate medical and psychological criteria in patients maintained on methadone.

Acetaldehyde oxidation by hepatic mitochondria: decrease after chronic ethanol consumption.

Prolonged consumption of ethanol significantly reduces the capacity of rat liver mitochondria to oxidize acetaldehyde. This is associated with decreased mitochondrial respiration with acetaldehyde as substrate. The reduced ability of mitochondria to metabolize acetaldehyde may explain the high levels of acetaldehyde in the blood of alcoholics, which in turn could promote the perpetuation of liver injury.

Ethanol increases hepatic smooth endoplasmic reticulum and drug-metabolizing enzymes.

Rats were fed ethanol for 2 weeks along with diets either adequate or deficient in protein and choline, the latter intake being similar to that of many alcoholics. Hepatic lipids, smooth endoplasmic reticulum, and the activities of drug-metabolizing enzymes (aniline hydroxylase and nitroreductase) were increased with the adequate diet but more so with the deficient one. These results may explain the increased tolerance by alcoholics of drugs such as sedatives.

Ethanol oxidation by hepatic microsomes: adaptive increase after ethanol feeding.

Hepatic microsomes contain an ethanol-oxidizing system distinct from alcohol dehydrogenase. In vitro, it has characteristics comparable to those of microsomal drug-detoxifying enzymes and, in vivo, it is capable of adaptation to the administration of ethanol. The existence of this microsomal ethanol-oxidizing system may explain ultrastructural, pharmacological, and biochemical effects of ethanol.

(RbxK1-x)3C60 Superconductors: Formation of a Continuous Series of Solid Solutions.

By means of an approach that employs alkali-metal alloys, bulk single-phase (RbxK1-x)(3)C(6O) superconductors have been prepared for all x between 0 and 1. For x = 1 it is shown that the maximum superconducting fraction, which approaches 100% in sintered pellets, occurs at a Rb to C(60) ratio of 3:1. More importantly, single-phase superconductors are formed at all intermediate values of x, and it is shown that the transition temperature (T(c)) increases linearly with x in this series of materials. The formation of a continuous range of solid solutions demonstrates that the rubidium- and potassium-doped C(60) superconducting phases must be isostructural, and furthermore, suggests that the linear increase in T(c) with x results from a chemical pressure effect.

Surface pinning as a determinant of the bulk flux-line lattice structure in copper oxide superconductors.

Direct knowledge of crystal defects and their perturbation of magnetic flux lines is essential to understanding pinning and to devising approaches that enhance critical currents in superconductors with high critical temperatures (T(c)). Atomic force microscopy was used to simultaneously characterize crystal defects and the magnetic flux-line lattice in single crystals of Bi(2)Sr(2)CaCu(2)O(8). Images show that surface defects, which are present on all real samples, pin the flux-line lattice. Above a critical height, the pinning interaction is sufficiently strong to form grain boundaries in the bulk flux-line lattice. These results elucidate the structure of the defects that pin flux lines and demonstrate that surface pinning, through the formation of grain boundaries, can determine the bulk flux-line lattice structure in high-T(c) materials. The implications of these results to the bulk flux-line lattice structure observed in previous experiments and to enhancing critical currents are discussed.

Directed assembly of one-dimensional nanostructures into functional networks.

One-dimensional nanostructures, such as nanowires and nanotubes, represent the smallest dimension for efficient transport of electrons and excitons and thus are ideal building blocks for hierarchical assembly of functional nanoscale electronic and photonic structures. We report an approach for the hierarchical assembly of one-dimensional nanostructures into well-defined functional networks. We show that nanowires can be assembled into parallel arrays with control of the average separation and, by combining fluidic alignment with surface-patterning techniques, that it is also possible to control periodicity. In addition, complex crossed nanowire arrays can be prepared with layer-by-layer assembly with different flow directions for sequential steps. Transport studies show that the crossed nanowire arrays form electrically conducting networks, with individually addressable device function at each cross point.

Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species.

Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible binding of the metabolic indicator Ca2+ was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.

Lack of correlation between hepatic mitochondrial membrane structure and functions in ethanol-fed rats.

A current hypothesis suggests that alterations in the chemical composition and the subsequent changes in the structure of the membrane could account for the functional derangements observed in the hepatic mitochondria of animals fed ethanol for extended periods. An examination of this hypothesis reveals that the liver mitochondria of ethanol-fed rats show a dissociation between the respiratory functions and the lipid composition and microviscosity of the membranes.

Prolonged ethanol consumption increases testosterone metabolism in the liver.

Male alcoholics often suffer from features of hypogonadism related to abnormal metabolism of sex steroids. Since the activity of testosterone reductases is rate limiting for testosterone metabolism in the liver, the effect of prolonged ethanol consumption by rats and human volunteers on the activities of these microsomal and cytosolic enzymes was studied. In rats, long-term ethanol ingestion doubled microsomal 5alpha-testosterone reductase activity, a major pathway for testosterone metabolism, while in human volunteers the activity was increased two- to fivefold. These changes may play a role in the altered androgenic activity of the chronic alcoholic.