17 research outputs found
Anomalous behaviour of the in-plane electrical conductivity of the layered superconductor -(BEDT-TTF)Cu(NCS)
The quasiparticle scattering rates in high-quality crystals of the
quasi-two-dimensional superconductor -(BEDT-TTF)Cu(NCS) ~are
studied using the Shubnikov-de Haas effect and MHz penetration-depth
experiments. There is strong evidence that the broadening of the Landau-levels
is primarily caused by spatial inhomogeneities, indicating a quasiparticle
lifetime for the Landau states ps. In contrast to the predictions of
Fermi-liquid theory, the scattering time derived from the intralayer
conductivity is found to be much shorter ( ps)
How close can one approach the Dirac point in graphene experimentally?
The above question is frequently asked by theorists who are interested in
graphene as a model system, especially in context of relativistic quantum
physics. We offer an experimental answer by describing electron transport in
suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with
the onset of Landau quantization occurring in fields below 5 mT. The observed
charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state
with a few charge carriers per entire micron-scale device. Above liquid helium
temperatures, the electronic properties of such devices are intrinsic, being
governed by thermal excitations only. This yields that the Dirac point can be
approached within 1 meV, a limit currently set by the remaining charge
inhomogeneity. No sign of an insulating state is observed down to 1 K, which
establishes the upper limit on a possible bandgap
Magnetotransport in a pseudomorphic GaAs/GaInAs/GaAlAs heterostructure with a Si delta-doping layer
Magnetotransport properties of a pseudomorphic
GaAs/Ga0.8In0.2As/Ga0.75Al0.25As heterostructure are investigated in pulsed
magnetic fields up to 50 T and at temperatures of T=1.4 K and 4.2 K. The
structure studied consists of a Si delta-layer parallel to a Ga0.8In0.2As
quantum well (QW). The dark electron density of the structure is n_e=1.67x
10^16 m^-2. By illumination the density can be increased up to a factor of 4;
this way the second subband in the Ga0.8In0.2As QW can become populated as well
as the Si delta-layer. The presence of electrons in the delta-layer results in
drastic changes in the transport data, especially at magnetic fields beyond 30
T. The phenomena observed are interpreted as: 1) magnetic freeze-out of
carriers in the delta-layer when a low density of electrons is present in the
delta-layer, and 2) quantization of the electron motion in the two dimensional
electron gases in both the Ga0.8In0.2As QW and the Si delta-layer in the case
of high densities. These conclusions are corroborated by the numerical results
of our theoretical model. We obtain a satisfactory agreement between model and
experiment.Comment: 23 pages, RevTex, 11 Postscript figures (accepted for Phys. Rev. B
Development of SNP genotyping arrays in two shellfish species
Use of SNPs has been favored due to their abundance in plant and animal genomes, accompanied by the falling cost and rising throughput capacity for detection and genotyping. Here, we present in vitro (obtained from targeted sequencing) and in silico discovery of SNPs, and the design of medium-throughput genotyping arrays for two oyster species, the Pacific oyster, Crassostrea gigas, and European flat oyster, Ostrea edulis. Two sets of 384 SNP markers were designed for two Illumina GoldenGate arrays and genotyped on more than 1000 samples for each species. In each case, oyster samples were obtained from wild and selected populations and from three-generation families segregating for traits of interest in aquaculture. The rate of successfully genotyped polymorphic SNPs was about 60% for each species. Effects of SNP origin and quality on genotyping success (Illumina functionality score) were analyzed and compared with other model and non-model species. Furthermore, a simulation was made based on a subset of the C. gigas SNP array with a minor allele frequency of 0.3 and typical crosses used in shellfish hatcheries. This simulation indicated that at least 150 markers were needed to perform an accurate parental assignment. Such panels might provide valuable tools to improve our understanding of the connectivity between wild (and selected) populations and could contribute to future selective breeding programs
Ultrasound-mediated gene delivery of factor VIII plasmids for hemophilia A gene therapy in mice
Gene therapy offers great promises for a cure of hemophilia A resulting from factor VIII (FVIII) gene deficiency. We have developed and optimized a non-viral ultrasound-mediated gene delivery (UMGD) strategy. UMGD of reporter plasmids targeting mice livers achieved high levels of transgene expression predominantly in hepatocytes. Following UMGD of a plasmid encoding human FVIII driven by a hepatocyte-specific promoter/enhancer (pHP-hF8/N6) into the livers of hemophilia A mice, a partial phenotypic correction was achieved in treated mice. In order to achieve persistent and therapeutic FVIII gene expression, we adopted a plasmid (pHP-hF8-X10) encoding an FVIII variant with significantly increased FVIII secretion. By employing an optimized pulse-train ultrasound condition and immunomodulation, the treated hemophilia A mice achieved 25%–150% of FVIII gene expression on days 1–7 with very mild transient liver damage, as indicated by a small increase of transaminase levels that returned to normal within 3 days. Therapeutic levels of FVIII can be maintained persistently without the generation of inhibitors in mice. These results indicate that UMGD can significantly enhance the efficiency of plasmid DNA transfer into the liver. They also demonstrate the potential of this novel technology to safely and effectively treat hemophilia A
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Argonne program to assess superconducting stability
To assess superconductor stability, a complete program is developed to obtain basic information on the effects of local mechanical perturbations on the cryostatic stability. An analytical model for computing the transient recovery following the mechanical perturbation is developed. A test program is undertaken to develop data needed to verify the conclusions reached through the analytical studies
Exchange enhancement of the Landau-level separation for two-dimensional electrons in GaAs/Ga1-xAlxAs heterojunctions
Exchange enhancement of the Landau-level separation of up to 30% has been observed in three high mobility GaAs/Ga1-xAlxAs single heterojunctions. Analysis of the amplitude of Shubnikov-de Haas oscillations as a function of temperature and magnetic field has allowed measurement of this enhancement at filling factors as high as nu = 100