8,795 research outputs found
Local moment, itinerancy and deviation from Fermi liquid behavior in NaCoO for
Here we report the observation of Fermi surface (FS) pockets via the
Shubnikov de Haas effect in NaCoO for and 0.84,
respectively. Our observations indicate that the FS expected for each compound
intersects their corresponding Brillouin zones, as defined by the previously
reported superlattice structures, leading to small reconstructed FS pockets,
but only if a precise number of holes per unit cell is \emph{localized}. For
the coexistence of itinerant carriers and localized spins on a paramagnetic triangular superlattice leads at low temperatures
to the observation of a deviation from standard Fermi-liquid behavior in the
electrical transport and heat capacity properties, suggesting the formation of
some kind of quantum spin-liquid ground state.Comment: 4 pages, 4 figure
Coded Modulation for Satellite Broadcasting
In this paper, three-level block coded 8-PSK modulations, suitable for satellite broadcasting of digital TV signals, are presented. A design principle to achieve unequal error protection is introduced. The coding scheme is designed in such a way that the information bits carrying the basic definition TV signal have a lower error rate than the high definition information bits. The large error coefficients, formally associated with standard mapping by set partitioning, are reduced by considering a nonstandard partition of an 8-PSK signal set. The bits-to-signal mapping induced by this partition allows the use of suboptimal low-complexity soft-decision decoding of binary block codes. Parallel operation of the first and second stage decoders is possible, for high data rate transmission. Furthermore, there is no error propagation from the first-stage decoder to the second-stage decoder
SUMO Modification Stabilizes Enterovirus 71 Polymerase 3D To Facilitate Viral Replication.
Accumulating evidence suggests that viruses hijack cellular proteins to circumvent the host immune system. Ubiquitination and SUMOylation are extensively studied posttranslational modifications (PTMs) that play critical roles in diverse biological processes. Cross talk between ubiquitination and SUMOylation of both host and viral proteins has been reported to result in distinct functional consequences. Enterovirus 71 (EV71), an RNA virus belonging to the family Picornaviridae, is a common cause of hand, foot, and mouth disease. Little is known concerning how host PTM systems interact with enteroviruses. Here, we demonstrate that the 3D protein, an RNA-dependent RNA polymerase (RdRp) of EV71, is modified by small ubiquitin-like modifier 1 (SUMO-1) both during infection and in vitro Residues K159 and L150/D151/L152 were responsible for 3D SUMOylation as determined by bioinformatics prediction combined with site-directed mutagenesis. Also, primer-dependent polymerase assays indicated that mutation of SUMOylation sites impaired 3D polymerase activity and virus replication. Moreover, 3D is ubiquitinated in a SUMO-dependent manner, and SUMOylation is crucial for 3D stability, which may be due to the interplay between the two PTMs. Importantly, increasing the level of SUMO-1 in EV71-infected cells augmented the SUMOylation and ubiquitination levels of 3D, leading to enhanced replication of EV71. These results together suggested that SUMO and ubiquitin cooperatively regulated EV71 infection, either by SUMO-ubiquitin hybrid chains or by ubiquitin conjugating to the exposed lysine residue through SUMOylation. Our study provides new insight into how a virus utilizes cellular pathways to facilitate its replication. IMPORTANCE: Infection with enterovirus 71 (EV71) often causes neurological diseases in children, and EV71 is responsible for the majority of fatalities. Based on a better understanding of interplay between virus and host cell, antiviral drugs against enteroviruses may be developed. As a dynamic cellular process of posttranslational modification, SUMOylation regulates global cellular protein localization, interaction, stability, and enzymatic activity. However, little is known concerning how SUMOylation directly influences virus replication by targeting viral polymerase. Here, we found that EV71 polymerase 3D was SUMOylated during EV71 infection and in vitro Moreover, the SUMOylation sites were determined, and in vitro polymerase assays indicated that mutations at SUMOylation sites could impair polymerase synthesis. Importantly, 3D is ubiquitinated in a SUMOylation-dependent manner that enhances the stability of the viral polymerase. Our findings indicate that the two modifications likely cooperatively enhance virus replication. Our study may offer a new therapeutic strategy against virus replication
Non-Fermi liquid behavior with and without quantum criticality in Ce(1-x)Yb(x)CoIn(5)
One of the greatest challenges to Landau's Fermi liquid theory - the standard
theory of metals - is presented by complex materials with strong electronic
correlations. In these materials, non-Fermi liquid transport and thermodynamic
properties are often explained by the presence of a continuous quantum phase
transition which happens at a quantum critical point (QCP). A QCP can be
revealed by applying pressure, magnetic field, or changing the chemical
composition. In the heavy-fermion compound CeCoIn, the QCP is assumed to
play a decisive role in defining the microscopic structure of both normal and
superconducting states. However, the question of whether QCP must be present in
the material's phase diagram to induce non-Fermi liquid behavior and trigger
superconductivity remains open. Here we show that the full suppression of the
field-induced QCP in CeCoIn by doping with Yb has surprisingly little
impact on both unconventional superconductivity and non-Fermi liquid behavior.
This implies that the non-Fermi liquid metallic behavior could be a new state
of matter in its own right rather then a consequence of the underlying quantum
phase transition.Comment: 7 pages, 5 figure
Distribution of Spectral Lags in Gamma Ray Bursts
Using the data acquired in the Time To Spill (TTS) mode for long gamma-ray
bursts (GRBs) collected by the Burst and Transient Source Experiment on board
the Compton Gamma Ray Observatory (BATSE/CGRO), we have carefully measured
spectral lags in time between the low (25-55 keV) and high (110-320 keV) energy
bands of individual pulses contained in 64 multi-peak GRBs. We find that the
temporal lead by higher-energy gamma-ray photons (i.e., positive lags) is the
norm in this selected sample set of long GRBs. While relatively few in number,
some pulses of several long GRBs do show negative lags. This distribution of
spectral lags in long GRBs is in contrast to that in short GRBs. This apparent
difference poses challenges and constraints on the physical mechanism(s) of
producing long and short GRBs. The relation between the pulse peak count rates
and the spectral lags is also examined. Observationally, there seems to be no
clear evidence for systematic spectral lag-luminosity connection for pulses
within a given long GRB.Comment: 20 pages, 4 figure
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