Resonant Transport in Nb/GaAs/AlGaAs/GaAs Microstructures

Resonant transport in a hybrid semiconductor-superconductor microstructure grown by MBE on GaAs is presented. This structure experimentally realizes the prototype system originally proposed by de Gennes and Saint-James in 1963 in \emph{all}-metal structures. A low temperature single peak superimposed to the characteristic Andreev-dominated subgap conductance represents the mark of such resonant behavior. Random matrix theory of quantum transport was employed in order to analyze the observed magnetotransport properties and ballistic effects were included by directly solving the Bogoliubov-de Gennes equations.Comment: 7 pages REVTeX, 4 figures, to be published by World Scientific in Proceedings of International Symposium on Mesoscopic Superconductivity and Spintronics (NTT R&D Center Atsugi, Japan, March 2002

Andreev reflection in Si-engineered Al/InGaAs hybrid junctions

Andreev-reflection dominated transport is demonstrated in Al/n-In0.38Ga0.62As superconductor-semiconductor junctions grown by molecular beam epitaxy on GaAs(001). High junction transparency was achieved in low-doped devices by exploiting Si interface bilayers to suppress the native Schottky barrier. It is argued that this technique is ideally suited for the fabrication of ballistic transport hybrid microstructures.Comment: 9 REVTEX pages + 3 postscript figures, to be published in APL 73, (28dec98

Reflectionless tunneling in planar Nb/GaAs hybrid junctions

Reflectionless-tunneling was observed in Nb/GaAs superconductor/semiconductor junctions fabricated through a two-step procedure. First, periodic $\delta$-doped layers were grown by molecular beam epitaxy near the GaAs surface, followed by an As cap layer to protect the surface during {\it ex-situ} transfer. Second, Nb was deposited by dc-magnetron sputtering onto the GaAs(001) 2 $\times$ 4 surface {\it in-situ} after thermal desorption of the cap layer. The magnetotransport behavior of the resulting hybrid junctions was successfully analyzed within the random matrix theory of phase-coherent Andreev transport. The impact of junction morphology on reflectionless tunneling and the applicability of the fabrication technique to the realization of complex superconductor/semiconductor mesoscopic systems are discussed.Comment: 10 pages, 3 figures, to be published in Appl. Phys. Let

Changing the approach to sustainable constructions: An adaptive mix-design calibration process for earth composite materials

One major drawback of excavation earth-based composite construction materials is the variability in excavation earth characteristics from site to site. This variability can affect certain physical properties, and, in turn, the design models used to create a structure. To solve this problem, a methodology has been developed to predict the physical properties of earth-based composites for any mix-design variation, which enables a robust structural design process. This new methodology has been tested for Shot-earth, a new class of earth-based composite material made using high rates of excavation earth, aggregates, and a low rate of stabilization if needed. Shot-earth is placed using a high-speed dry-mix process. The methodology was tested by preparing small, inexpensive specimens through a process that simulates the dry-process used to fabricate Shot-earth in the field. An adaptive technique, used in conjunction with the experimental methodology, allows for the identification of the variant of possible Shot-earth mix-designs that provides optimal physical properties for a specific project. This technique is potentially applicable to any type of earth-based composite. The proposed methodology’s reliability enables a fast and cost-effective detailing of Shot-earth constructions

Thermoreflectance investigation of the antiferromagnetic and paramagnetic phases of Cr

Thermoreflectance measurements have been performed on Cr single crystals at several temperatures above and below the Néel temperature. We observe dramatic changes induced by the magnetic phase transition. In contrast, static optical data fail to show appreciable differences in the (0.5-5.0)-eV photon-energy range. Magnetic ordering gives rise to the disappearance of transitions involving specific regions of the Fermi surface. New critical-point absorptions appear at the boundaries of the new Brillouin zone in antiferromagnetic Cr. Most of the observed experimental features have been identified by comparison with recent band-structure calculations

Vitamin E as Adjuvant in Emulsified Vaccine for Chicks

Abstract Mineral oil was partially replaced with D, L-α-tocopheryl acetate (vitamin E) in bacterial and viral inactivated emulsified vaccines. Vitamin E increased the immune response to the viral antigen (Newcastle disease virus) used but not to the bacterial antigen (Escherichia coli) when its presence in the oil phase did not exceed 30%. Inoculated vitamin E may have enhanced the immune response by interacting with the immune-competent cells involved in the inflammatory reaction that followed inoculation of emulsified vaccines

A study of the endogenous opioid system in the sudden infant death syndrome

To investigate the possible role of the endogenous opioid system in the pathogenesis of the sudden infant death syndrome (SIDS), we measured met-enkephalin immunoreactivity by radioimmunoassay in brain, lung, and adrenal glands of SIDS victims and of infants (controls) dying of nonneurologic causes. Met-enkephalin was stable in brain tissue up to 24 hours after death. On inspection, met-enkephalin levels in the cerebral cortex of SIDS victims were similar to those in controls. Levels in the caudate nucleus were lower in infants than in adults. In the medulla, the levels in SIDS cases and controls were not found to differ significantly. The linear relationship between the levels in the medulla and age was not detectably different in SIDS and controls. However, as a subset, levels in the control group significantly decreased with increasing age ( = 0.005), whereas levels in the SIDS group showed no correlation with age ( = 0.33). Levels of met-enkephalin in the adrenal gland of SIDS victims were similar to those in controls and were considerably lower than adult values. Lung tissue was assayed for beta-endorphin immunoreactivity and met-enkephalin: for both peptides the values in SIDS cases were low (femtomolar range) and similar to those in controls. These data suggest that met-enkephalin is not markedly overproduced in brains of SIDS victims. Future postmortem studies should focus on more subtle evidence of endogenous opioid overactivity such as differences in age related changes, receptor number, and levels of other endogenous opioid peptides.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25258/1/0000701.pd