187 research outputs found
New Electronic Phase Transitions in \alpha-(BEDT-TTF)2KHg(SCN)4
\alpha-(BEDT-TTF)2KHg(SCN)4 is considered to be in the charge-density-wave
(CDW) state below 8 K. We present new magnetoresistance data suggesting that
the material undergoes a series of field-induced CDW (FICDW) transitions at
pressures slightly exceeding the critical pressure Pc at which the zero-field
CDW state is destroyed. Further, we argue that a novel kind of FICDW
transitions, entirely determined by a superposition of the strong Pauli and
quantizing orbital effects of magnetic field on the CDW wavevector, arises when
the field is strongly tilted towards the conducting layers. These new
transitions can take place even in the case of a relatively well nested Fermi
surface. Finally we report on the superconducting (SC) state and its
coexistence with the CDW in the title compound under quasi-hydrostatic
pressure. Below Pc the material is most likely a heterogeneous SC/CDW mixture,
with the SC phase persisting down to ambient pressure. The SC onset temperature
appears to drastically increase upon entering the SC/CDW coexistence region.Comment: 7 pages, 6 figures; invited talk at ISCOM'2003, 21-26.09.2003, Port
Bourgenay, France to be published in J. Phys. IV Franc
Modeling and MEG evidence of early consonance processing in auditory cortex
Pitch is a fundamental attribute of auditory perception. The interaction of concurrentpitches gives rise to a sensation that can be characterized by its degree of consonance ordissonance. In this work, we propose that human auditory cortex (AC) processes pitchand consonance through a common neural network mechanism operating at earlycortical levels. First, we developed a new model of neural ensembles incorporatingrealistic neuronal and synaptic parameters to assess pitch processing mechanisms atearly stages of AC. Next, we designed a magnetoencephalography (MEG) experiment tomeasure the neuromagnetic activity evoked by dyads with varying degrees ofconsonance or dissonance. MEG results show that dissonant dyads evoke a pitch onsetFebruary 15, 20191/44
response (POR) with a latency up to 36 ms longer than consonant dyads. Additionally,we used the model to predict the processing time of concurrent pitches; here, consonantpitch combinations were decoded faster than dissonant combinations, in line with theexperimental observations. Specifically, we found a striking match between thepredicted and the observed latency of the POR as elicited by the dyads. These novelresults suggest that consonance processing starts early in human auditory cortex andmay share the network mechanisms that are responsible for (single) pitch processing
Superconductivity in the charge-density-wave state of the organic metal \alpha-(BEDT-TTF)2KHg(SCN)4
The superconducting transition in the layered organic compound
\alpha-(BEDT-TTF)_2KHg(SCN)_4 has been studied in the two hydrostatic pressure
regimes where a charge-density wave is either present or completely suppressed.
Within the charge-density-wave state the experimental results reveal a network
of weakly coupled superconducting regions. This is especially seen in a strong
enhancement of the measured critical field and the corresponding positive
curvature of its temperature dependence. Further, it is shown that on lowering
the pressure into the density-wave state traces of a superconducting phase
already start to appear at a much higher temperature.Comment: 8 pages, 9 figures, Phys. Rev. B, in pres
Dynamical versus Stellar Masses of Ultracompact Dwarf Galaxies in the Fornax Cluster
The origin of ultracompact dwarf (UCD) galaxies, compact extragalactic
stellar systems, is still a puzzle for present galaxy formation models. We
present the comprehensive analysis of high resolution multi-object
spectroscopic data for a sample of 24 Fornax cluster UCDs obtained with VLT
FLAMES. It comprises previously published data for 19 objects (Mieske et al.
2008) which we re-analysed, including 13 with available HST photometric data.
Using Virtual Observatory technologies we found archival HST images for two
more UCDs and then determined their structural properties. For all objects we
derived internal velocity dispersions, stellar population parameters, and
stellar mass-to-light ratios (M/L)* by fitting individual simple stellar
population (SSP) synthetic spectra convolved with a Gaussian against the
observed spectra using the NBursts full spectral fitting technique. For 14
objects we estimated dynamical masses suggesting no dark matter (DM) in 12 of
them and no more than 40 per cent DM mass fraction in the remaining two, in
contrast to findings for several UCDs in the Virgo cluster. Some Fornax UCDs
even have too high values of (M/L)* estimated using the Kroupa stellar initial
mass function (IMF) resulting in negative formally computed DM mass fractions.
The objects with too high (M/L)* ratios compared to the dynamical ones have
relatively short dynamical relaxation timescales, close to the Hubble time or
below. We therefore suggest that their lower dynamical ratios (M/L)dyn are
caused by low-mass star depletion due to dynamical evolution. Overall, the
observed UCD characteristics suggest at least two formation channels: tidal
threshing of nucleated dwarf galaxies for massive UCDs (~10^8 M_sun), and a
classical scenario of red globular cluster formation for lower-mass UCDs (<
10^7 M_sun).Comment: Accepted for publication in MNRAS; 13 pages, 9 figures, 2 table
Fundamental parameter-free solutions in Modified Gravity
Modified Gravity (MOG) has been used successfully to explain the rotation
curves of galaxies, the motion of galaxy clusters, the Bullet Cluster, and
cosmological observations without the use of dark matter or Einstein's
cosmological constant. We now have the ability to demonstrate how these
solutions can be obtained directly from the action principle, without resorting
to the use of fitted parameters or empirical formulae. We obtain numerical
solutions to the theory's field equations that are exact in the sense that no
terms are omitted, in two important cases: the spherically symmetric, static
vacuum solution and the cosmological case of an homogeneous, isotropic
universe. We compare these results to selected astrophysical and cosmological
observations.Comment: 11 pages, 8 figures; accepted for publication in CQ
Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2
We have performed elastic neutron-scattering experiments on the
heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found
that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly
enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at
1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m
increases slightly at a rate ~ 1 K/GPa, roughly following the transition
temperature T_o determined from macroscopic anomalies. We have also observed a
sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of
antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced
lattice constant.Comment: RevTeX, 4 pages, 4 eps figures, accepted for publication in Phys.
Rev. Let
CAR-T cell. the long and winding road to solid tumors
Adoptive cell therapy of solid tumors with reprogrammed T cells can be considered the "next generation" of cancer hallmarks. CAR-T cells fail to be as effective as in liquid tumors for the inability to reach and survive in the microenvironment surrounding the neoplastic foci. The intricate net of cross-interactions occurring between tumor components, stromal and immune cells leads to an ineffective anergic status favoring the evasion from the host's defenses. Our goal is hereby to trace the road imposed by solid tumors to CAR-T cells, highlighting pitfalls and strategies to be developed and refined to possibly overcome these hurdles
The Tissue-Specific Rep8/UBXD6 Tethers p97 to the Endoplasmic Reticulum Membrane for Degradation of Misfolded Proteins
The protein known as p97 or VCP in mammals and Cdc48 in yeast is a versatile ATPase complex involved in several biological functions including membrane fusion, protein folding, and activation of membrane-bound transcription factors. In addition, p97 plays a central role in degradation of misfolded secretory proteins via the ER-associated degradation pathway. This functional diversity of p97 depends on its association with various cofactors, and to further our understanding of p97 function it is important that these cofactors are identified and analyzed. Here, we isolate and characterize the human protein named Rep8 or Ubxd6 as a new cofactor of p97. Mouse Rep8 is highly tissue-specific and abundant in gonads. In testes, Rep8 is expressed in post-meiotic round spermatids, whereas in ovaries Rep8 is expressed in granulosa cells. Rep8 associates directly with p97 via its UBX domain. We show that Rep8 is a transmembrane protein that localizes to the ER membrane with its UBX domain facing the cytoplasm. Knock-down of Rep8 expression in human cells leads to a decreased association of p97 with the ER membrane and concomitantly a retarded degradation of misfolded ER-derived proteasome substrates. Thus, Rep8 tethers p97 to the ER membrane for efficient ER-associated degradation
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