102 research outputs found
Hysteretic characteristics of a double stripline in the critical state
Analytical investigations of the critical state are carried out for a
superconducting stripline consisting of two individual coplanar strips with an
arbitrary distance between them. Two different cases are considered: a
stripline with transport current and strips exposed to a perpendicular magnetic
field. In the second case, the obtained solutions correspond to "fieldlike"
(for unclosed strips) and "currentlike" (for a long rectangular superconducting
loop) states in an isolated strip to which both a transport current and a
magnetic field are applied with constant ratio.Comment: 8 pages, 6 figures. accepted by SS
The Flux-Line Lattice in Superconductors
Magnetic flux can penetrate a type-II superconductor in form of Abrikosov
vortices. These tend to arrange in a triangular flux-line lattice (FLL) which
is more or less perturbed by material inhomogeneities that pin the flux lines,
and in high- supercon- ductors (HTSC's) also by thermal fluctuations. Many
properties of the FLL are well described by the phenomenological
Ginzburg-Landau theory or by the electromagnetic London theory, which treats
the vortex core as a singularity. In Nb alloys and HTSC's the FLL is very soft
mainly because of the large magnetic penetration depth: The shear modulus of
the FLL is thus small and the tilt modulus is dispersive and becomes very small
for short distortion wavelength. This softness of the FLL is enhanced further
by the pronounced anisotropy and layered structure of HTSC's, which strongly
increases the penetration depth for currents along the c-axis of these uniaxial
crystals and may even cause a decoupling of two-dimensional vortex lattices in
the Cu-O layers. Thermal fluctuations and softening may melt the FLL and cause
thermally activated depinning of the flux lines or of the 2D pancake vortices
in the layers. Various phase transitions are predicted for the FLL in layered
HTSC's. The linear and nonlinear magnetic response of HTSC's gives rise to
interesting effects which strongly depend on the geometry of the experiment.Comment: Review paper for Rep.Prog.Phys., 124 narrow pages. The 30 figures do
not exist as postscript file
The spin label amino acid TOAC and its uses in studies of peptides: chemical, physicochemical, spectroscopic, and conformational aspects
We review work on the paramagnetic amino acid 2,2,6,6-tetramethyl-N-oxyl-4-amino-4-carboxylic acid, TOAC, and its applications in studies of peptides and peptide synthesis. TOAC was the first spin label probe incorporated in peptides by means of a peptide bond. In view of the rigid character of this cyclic molecule and its attachment to the peptide backbone via a peptide bond, TOAC incorporation has been very useful to analyze backbone dynamics and peptide secondary structure. Many of these studies were performed making use of EPR spectroscopy, but other physical techniques, such as X-ray crystallography, CD, fluorescence, NMR, and FT-IR, have been employed. The use of double-labeled synthetic peptides has allowed the investigation of their secondary structure. A large number of studies have focused on the interaction of peptides, both synthetic and biologically active, with membranes. In the latter case, work has been reported on ligands and fragments of GPCR, host defense peptides, phospholamban, and β-amyloid. EPR studies of macroscopically aligned samples have provided information on the orientation of peptides in membranes. More recent studies have focused on peptide–protein and peptide–nucleic acid interactions. Moreover, TOAC has been shown to be a valuable probe for paramagnetic relaxation enhancement NMR studies of the interaction of labeled peptides with proteins. The growth of the number of TOAC-related publications suggests that this unnatural amino acid will find increasing applications in the future
The Structural Biology Knowledgebase: a portal to protein structures, sequences, functions, and methods
The Protein Structure Initiative’s Structural Biology Knowledgebase (SBKB, URL: http://sbkb.org) is an open web resource designed to turn the products of the structural genomics and structural biology efforts into knowledge that can be used by the biological community to understand living systems and disease. Here we will present examples on how to use the SBKB to enable biological research. For example, a protein sequence or Protein Data Bank (PDB) structure ID search will provide a list of related protein structures in the PDB, associated biological descriptions (annotations), homology models, structural genomics protein target status, experimental protocols, and the ability to order available DNA clones from the PSI:Biology-Materials Repository. A text search will find publication and technology reports resulting from the PSI’s high-throughput research efforts. Web tools that aid in research, including a system that accepts protein structure requests from the community, will also be described. Created in collaboration with the Nature Publishing Group, the Structural Biology Knowledgebase monthly update also provides a research library, editorials about new research advances, news, and an events calendar to present a broader view of structural genomics and structural biology
Preparation and Properties of Bismuth Ruthenate Thin Film Electrodes for Chlorine Evolution
Sol-Gel Synthesis of High Surface Area Aluminum Phosphate: A Thermally Reversible Sol-Gel System
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