5,552 research outputs found
Point-contact tunneling involving low-dimensional spin-triplet superconductors
We modify and extend previous microscopic calculations of tunneling in
superconducting junctions based on a non-equilibrium Green function formalism
to include the case of spin-triplet pairing. We show that distinctive features
are present in the I-V characteristics of different kinds of junctions, in
particular when the effects of magnetic fields are taken into account, that
permit to identify the type of pairing. We discuss the relevance of these
results in the context of quasi one-dimensional organic superconductors like
(TMTSF)_2(PF_6) and layered compounds like Sr_2RuO_4.Comment: 4 pages, 1 figur
Scaling study of Si/SiGe MODFETs for RF applications
Based on the successful calibration on a 0.25 /spl mu/m strained Si/SiGe n-type MODFET, this paper presents a gate length scaling study of double-side doped Si/SiGe MODFETs. Our simulations show that gate length scaling improves device RF performance. However, the short channel effects (SCE) along with the parasitic delays limit the device performance improvements. We find that it is necessary to consider scaling (dimensions and doping) of both the lateral and vertical architecture in order to optimize the device design
Inductive algebras and homogeneous shifts
Inductive algebras for the irreducible unitary representations of the
universal cover of the group of unimodular two by two matrices are classified.
The classification of homogeneous shift operators is obtained as a direct
consequence. This gives a new approach to the results of Bagchi and Misra
Keldysh study of point-contact tunneling between superconductors
We revisit the problem of point-contact tunnel junctions involving
one-dimensional superconductors and present a simple scheme for computing the
full current-voltage characteristics within the framework of the
non-equilibrium Keldysh Green function formalism. We address the effects of
different pairing symmetries combined with magnetic fields and finite
temperatures at arbitrary bias voltages. We discuss extensively the importance
of these results for present-day experiments. In particular, we propose ways of
measuring the effects found when the two sides of the junction have dissimilar
superconducting gaps and when the symmetry of the superconducting states is not
the one of spin-singlet pairing. This last point is of relevance for the study
of the superconducting state of certain organic materials like the Bechgaard
salts and, to some extent, for ruthenium compounds.Comment: 10 pages, 4 figure
Platinum(II) phosphonate complexes derived from endo-8-camphanylphosphonic acid
The reactions of cis-[PtCl₂L₂] [L = PPh₃, PMe₂Ph or L₂ = Ph₂P(CH₂)₂PPh₂ (dppe)] with endo-8-camphanylphosphonic acid (CamPO₃H₂) and Ag₂O in refluxing dichloromethane gave platinum(II) phosphonate complexes [Pt(O₃PCam)L₂]. The X-ray crystal structure of [Pt(O₃PCam)(PPh₃)₂]•₂CHCl₃ shows that the bulky camphanyl group, rather than being directed away from the platinum, is instead directed into a pocket formed by the Pt and the two PPh₃ ligands. This allows the O₃P–CH₂ group to have a preferred staggered conformation. The complexes were studied in detail by NMR spectroscopy, which demonstrates non-fluxional behaviour for the sterically bulky PPh₃ and dppe derivatives, which contain inequivalent phosphine ligands in their ³¹P NMR spectra. These findings are backed up by theoretical calculations on the PPh₃ and PPhMe₂ derivatives, which show, respectively, high and low energy barriers to rotation of the camphanyl group in the PPh₃ and PPhMe₂ complexes. The X-ray crystal structure of CamPO₃H₂ is also reported, and consists of hydrogen-bonded hexameric aggregates, which assemble to form a columnar structure containing hydrophilic phosphonic acid channels surrounded by a sheath of bulky, hydrophobic camphanyl groups
Thermal regimes in the detachment fault environment as deduced from fluid inclusions
Extensional tectonism, which dominates middle- and late-Tertiary geology in western Arizona, southeastern California, and southern Nevada, is characterized by normal regionally extensive, low-angle detachment faults. The decollement movement of Fupper plate rocks relative to lower plate assemblages created extensive zones of dilatency, including synthetic and antithetic listric normal faults, tear faults, tectonic crush breccias, shatter breccias, and gash veins in lithologic units above and below the detachment. The tectonically enhanced permeability above and below the detachment fault permitted mass migration of large volumes of hydrothermal solutions along the fault zone during and following upper plate movement. Major quantities of MgO, CaO, K2O, FeO/Fe2O3, SiO2 and CO2 were added to rocks in and near the detachment and related structures. Also introduced were varying amounts of trace elements including Mn, Cu, S, Mo, Ba, Au, Pb, Zn, U and/or Ag. Minerals containing fluid incusions were collected from all of these loci at locations in detachment faulted terranes in western Arizona and southeastern California
Evolution and Expression of MYB Genes in Diploid and Polyploid Cotton
R2R3-MYB transcription factors have been implicated in a diversity of plant-specific processes. Among the functions attributed to myb factors is the determination of cell shape, including regulation of trichome length and density. Because myb transcription factors are likely to play a role in cotton fiber development, the molecular evolutionary properties of six MYB genes previously shown to be expressed in cotton fiber initiation were examined. In accordance with their presumed central role, each of the genes display conservative substitution patterns and limited sequence divergence in diploid members of the genus Gossypium, and this pattern is conserved in allotetraploid cottons. In contrast to highly reiterated rDNA repeats, GhMYB homologues (duplicated gene pairs) exhibit no evidence of concerted evolution, but instead appear to evolve independently in the allopolyploid nucleus. Expression patterns for the MYB genes were examined in several organs to determine if there have been changes in expression patterns between the diploids (G. raimondii and G. arboreum) and the tetraploid (G. hirsutum) or between the duplicated copies in the tetraploid. Spatial and temporal expression patterns appear to have been evolutionarily conserved, both during divergence of the diploid parents of allopolyploid cotton and following polyploid formation. However, the duplicated copies of MYB1 in the tetraploid are not expressed at equal levels or equivalently in all organs, suggesting possible functional differentiation
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
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