2,205 research outputs found
LiV2O4: evidence for two-stage screening
LiV2O4, a frustrated mixed valent metal (d^1 d^2), is argued to undergo
two spin-screening processes. The first quenches the effective spin to produce
the spin 1/2 behavior seen below room temperature[1], while the second produces
the heavy fermi liquid character seen at low temperatures[2]. We present here a
preliminary discussion of a t-J model with strong Hund's coupling of the
strongly correlated d-electrons. Valence fluctuations of the Hubbard operators
(S = {1/2} 1) combined with the frustration of the underlying corner-shared
tetrahedral vanadium lattice are the essential components of our model.Comment: 5 pages, 1 figure, accepted for proceedings of SCES'2001 Physica B,
minor change
Diagnostic Test and Therapy for Manganese Superoxide Dismutate (MSOD) Associated Diseases
The present invention provides a diagnostic method and a kit for detection of mutations localized within the 5′ promoter region of the MnSOD gene. Such mutations are associated with diseases characterized by decreased MnSOD activity such as certain formes of cancer, and ALS. Accordingly, the diagnostic method this invention provides, comprising RFLP, direct sequencing, or PCR analysis of the region within 3 kb, the transcription initiation site will detect these disorders. This invention also provides a therapeutic method for such disorders comprising transfection of affected cells or tissues with high activity, MnSOD expression vectors, or the administration of exogenous MnSOD enzyme
Identification of an HIV-1 mutation in spacer peptide 1 that stabilizes the immature CA-SP1 lattice
Upon release of HIV-1 particles from the infected cell, the viral protease cleaves the Gag polyprotein at specific sites, triggering maturation. During this process, which is essential for infectivity, the capsid protein (CA) reassembles into a conical core. Maturation inhibitors (MIs) block HIV-1 maturation by interfering with protease-mediated CA-spacer peptide 1 (CA-SP1) processing, concomitantly stabilizing the immature CA-SP1 lattice; virions from MI-treated cells retain an immature-like CA-SP1 lattice, whereas mutational abolition of cleavage at the CA-SP1 site results in virions in which the CA-SP1 lattice converts to a mature-like form. We previously reported that propagation of HIV-1 in the presence of MI PF-46396 selected for assembly-defective, compound-dependent mutants with amino acid substitutions in the major homology region (MHR) of CA. Propagation of these mutants in the absence of PF-46396 resulted in the acquisition of second-site compensatory mutations. These included a Thr-to-Ile substitution at SP1 residue 8 (T8I), which results in impaired CA-SP1 processing. Thus, the T8I mutation phenocopies PF-46396 treatment in terms of its ability to rescue the replication defect imposed by the MHR mutations and to impede CASP1 processing. Here, we use cryo-electron tomography to show that, like MIs, the T8I mutation stabilizes the immature-like CA-SP1 lattice. These results have important implications for the mechanism of action of HIV-1 MIs; they also suggest that T8I may provide a valuable tool for structural definition of the CA-SP1 boundary region, which has thus far been refractory to highresolution analysis, apparently because of conformational flexibility in this region of Gag. IMPORTANCE HIV-1 maturation involves dissection of the Gag polyprotein by the viral protease and assembly of a conical capsid enclosing the viral ribonucleoprotein. Maturation inhibitors (MIs) prevent the final cleavage step at the site between the capsid protein (CA) and spacer peptide 1 (SP1), apparently by binding at this site and denying the protease access. Additionally, MIs stabilize the immature-like CA-SP1 lattice, preventing release of CA into the soluble pool. We previously found that T8I, a mutation in SP1, rescues a PF-46396-dependent CA mutant and blocks CA-SP1 cleavage. In this study, we imaged T8I virions by cryo-electron tomography and showed that T8I mutants, like MI-treated virions, contain an immature CA-SP1 lattice. These results lay the groundwork needed to understand the structure of the CA-SP1 interface region and further illuminate the mechanism of action of MIs
Gravitational GUT Breaking and the GUT-Planck Hierarchy
It is shown that non-renormalizable gravitational interactions in the Higgs
sector of supersymmetric grand unified theories (GUT's) can produce the
breaking of the unifying gauge group at the GUT scale ~GeV. Such a breaking offers an attractive alternative to the
traditional method where the superheavy GUT scale mass parameters are added ad
hoc into the theory. The mechanism also offers a natural explanation for the
closeness of the GUT breaking scale to the Planck scale. A study of the minimal
SU(5) model endowed with this mechanism is presented and shown to be
phenomenologically viable. A second model is examined where the Higgs doublets
are kept naturally light as Goldstone modes. This latter model also achieves
breaking of at but cannot easily satisfy the current
experimental proton decay bound.Comment: 11 pages, REVTeX, 1 figure included as an uuencoded Z-compressed
PostScript file. Our Web page at
http://physics.tamu.edu/~urano/research/gutplanck.html contains ready to
print PostScript version (with figures) as well as color version of plot
The role of ECL2 in CGRP receptor activation: a combined modelling and experimental approach
The calcitonin gene-related peptide (CGRP) receptor is a complex of a calcitonin receptor-like receptor (CLR), which is a family B G-protein-coupled receptor (GPCR) and receptor activity modifying protein 1. The role of the second extracellular loop (ECL2) of CLR in binding CGRP and coupling to Gs was investigated using a combination of mutagenesis and modelling. An alanine scan of residues 271–294 of CLR showed that the ability of CGRP to produce cAMP was impaired by point mutations at 13 residues; most of these also impaired the response to adrenomedullin (AM). These data were used to select probable ECL2-modelled conformations that are involved in agonist binding, allowing the identification of the likely contacts between the peptide and receptor. The implications of the most likely structures for receptor activation are discussed.</jats:p
Unification Picture in Minimal Supersymmetric SU(5) Model with String Remnants
The significant heavy threshold effect is found in the supersymmetric SU(5)
model with two adjoint scalars, one of which is interpreted as a massive string
mode decoupled from the lower-energy particle spectra. This threshold related
with the generic mass splitting of the basic adjoint moduli is shown to alter
properly the running of gauge couplings, thus giving a natural solution to the
string-scale grand unification as prescribed at low energies by LEP precision
measurements and minimal particle content. The further symmetry condition of
the (top-bottom) Yukawa and gauge coupling superunification at a string scale
results in the perfectly working predictions for the top and bottom quark
masses in the absence of any large supersymmetric threshold corrections.Comment: published versio
The infinite-range quantum random Heisenberg magnet
We study with exact diagonalization techniques the Heisenberg model for a
system of SU(2) spins with S=1/2 and random infinite-range exchange
interactions. We calculate the critical temperature T_g for the spin-glass to
paramagnetic transition. We obtain T_g ~ 0.13, in good agreement with previous
quantum Monte Carlo and analytical estimates. We provide a detailed picture for
the different kind of excitations which intervene in the dynamical response
chi''(w,T) at T=0 and analyze their evolution as T increases. We also calculate
the specific heat Cv(T). We find that it displays a smooth maximum at TM ~
0.25, in good qualitative agreement with experiments. We argue that the fact
that TM>Tg is due to a quantum disorder effect.Comment: 17 pages, 14 figure
Thermal and Electrical Properties of gamma-NaxCoO2 (0.70 < x < 0.78)
We have performed specific heat and electric resistivity measurements of
NaCoO (-0.78). Two anomalies have been observed in the
specific heat data for , corresponding to magnetic transitions at
K and K reported previously. In the electrical
resistivity, a steep decrease at and a bending-like variation at
(=120K for ) have been observed. Moreover, we have investigated
the -dependence of these parameters in detail. The physical properties of
this system are very sensitive to , and the inconsistent results of previous
reports can be explained by a small difference in . Furthermore, for a
higher value, a phase separation into Na-rich and Na-poor domains occurs as
we previously proposed, while for a lower value, from characteristic
behaviors of the specific heat and the electrical resistivity at the
low-temperature region, the system is expected to be in the vicinity of the
magnetic instability which virtually exists below .Comment: 4 pages (3 figures included) and an extra figure (gif), to be
published in J. Phys. Soc. Jpn. 73 (9) with possible minor revision
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