1,978 research outputs found
Dissipative quantum disordered models
This article reviews recent studies of mean-field and one dimensional quantum
disordered spin systems coupled to different types of dissipative environments.
The main issues discussed are: (i) The real-time dynamics in the glassy phase
and how they compare to the behaviour of the same models in their classical
limit. (ii) The phase transition separating the ordered -- glassy -- phase from
the disordered phase that, for some long-range interactions, is of second order
at high temperatures and of first order close to the quantum critical point
(similarly to what has been observed in random dipolar magnets). (iii) The
static properties of the Griffiths phase in random Ising chains. (iv) The
dependence of all these properties on the environment. The analytic and numeric
techniques used to derive these results are briefly mentioned.Comment: Contribution to the 12th International Conference on Recent Progress
in Many-Body Theories, Santa Fe, New Mexico, USA, August 2004; 10 pages no
fig
Alzheimer\u27s Disease: Cholesterol, Membrane Rafts, Isoprenoids and Statins
Alzheimer\u27s disease (AD) is a heterogeneous neurodegenerative disorder and the most prevalent form of dementia worldwide. AD is characterized pathologically by amyloid-? plaques, neurofibrillary tangles and neuronal loss, and clinically by a progressive loss of cognitive abilities. At present, the fundamental molecular mechanisms underlying the disease are unclear and no treatment for AD is known. Epidemiological evidence continues to mount linking vascular diseases, such as hypertension and diabetes, and hypercholesterolaemia with an increased risk for developing AD. A growing amount of evidence suggests a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques in AD development. Cholesterol and statins clearly modulate ?-amyloid precursor protein (?APP) processing in cell culture and animal models. Statins not only reduce endogenous cholesterol synthesis but also exert other various pleiotrophic effects, such as the reduction in protein isoprenylation. Through these effects statins modulate a variety of cellular functions involving both cholesterol (and membrane rafts) and isoprenylation. Although clearly other factors, such as vascular inflammation, oxidative stress and genetic factors, are intimately linked with the progression of AD, this review focuses on the present research findings describing the effect of cholesterol, membrane rafts and isoprenylation in regulating ?APP processing and in particular ?-secretase complex assembly and function and AD progression, along with consideration for the potential role statins may play in modulating these events
Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7
We report the X-ray study for the pyrochlore oxide Cd2Re2O7. Two
symmetry-lowering structural transitions were observed at Ts1=200K and
Ts2=120K. The former is of the second order from the ideal cubic pyrochlore
structure with space group Fd-3m to a tetragonally distorted structure with
I-4m2, while the latter is of the first order likely to another tetragonal
space group I4122. We discuss the feature of the lattice deformation.Comment: 4 pages, 4 figure
Mammalian ECD protein is a novel negative regulator of the PERK arm of the unfolded protein response
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
Effect of toroidal field ripple on plasma rotation in JET
Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect
Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas
The stability with respect to a peeling–ballooning mode (PBM) was investigated numerically with
extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI
code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift
( *w i), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear
dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively
that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into
account both the rotation and *w i effects in the numerical analysis. When deuterium poloidal rotation
is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes
the PBM because of an acceleration of rotation and a decrease in *w i. The difference in the amount of
ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with
JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the
difference in the linear stability property, due not to the rotation direction but to the plasma density
profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A
predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and *w i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.JSPS KAKENHI 15K06656EURATOM 63305
Estrogens promote misfolded proinsulin degradation to protect insulin production and delay diabetes
Summary: Conjugated estrogens (CE) delay the onset of type 2 diabetes (T2D) in postmenopausal women, but the mechanism is unclear. In T2D, the endoplasmic reticulum (ER) fails to promote proinsulin folding and, in failing to do so, promotes ER stress and β cell dysfunction. We show that CE prevent insulin-deficient diabetes in male and in female Akita mice using a model of misfolded proinsulin. CE stabilize the ER-associated protein degradation (ERAD) system and promote misfolded proinsulin proteasomal degradation. This involves activation of nuclear and membrane estrogen receptor-α (ERα), promoting transcriptional repression and proteasomal degradation of the ubiquitin-conjugating enzyme and ERAD degrader, UBC6e. The selective ERα modulator bazedoxifene mimics CE protection of β cells in females but not in males. : Estrogens prevent diabetes in women, but the mechanism is poorly understood. Xu et al. report that estrogens activate the endoplasmic-reticulum-associated protein degradation pathway, which promotes misfolded proinsulin degradation, suppresses endoplasmic reticulum stress, and protects insulin secretion in mice and in human pancreatic β cells. Keywords: estrogens, beta cell, islet, endoplasmic reticulum stress, proinsulin misfolding, diabetes, bazedoxifene, sex dimorphism, ERAD, SER
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
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
- …