5,584 research outputs found
Abrupt Onset of Second Energy Gap at Superconducting Transition of Underdoped Bi2212
The superconducting gap - an energy scale tied to the superconducting
phenomena-opens on the Fermi surface at the superconducting transition
temperature (TC) in conventional BCS superconductors. Quite differently, in
underdoped high-TC superconducting cuprates, a pseudogap, whose relation to the
superconducting gap remains a mystery, develops well above TC. Whether the
pseudogap is a distinct phenomenon or the incoherent continuation of the
superconducting gap above TC is one of the central questions in high-TC
research. While some experimental evidence suggests they are distinct, this
issue is still under intense debate. A crucial piece of evidence to firmly
establish this two-gap picture is still missing: a direct and unambiguous
observation of a single-particle gap tied to the superconducting transition as
function of temperature. Here we report the discovery of such an energy gap in
underdoped Bi2212 in the momentum space region overlooked in previous
measurements. Near the diagonal of Cu-O bond direction (nodal direction), we
found a gap which opens at TC and exhibits a canonical (BCS-like) temperature
dependence accompanied by the appearance of the so-called Bogoliubov
quasiparticles, a classical signature of superconductivity. This is in sharp
contrast to the pseudogap near the Cu-O bond direction (antinodal region)
measured in earlier experiments. The emerging two-gap phenomenon points to a
picture of richer quantum configurations in high temperature superconductors.Comment: 16 pages, 4 figures, authors' version Corrected typos in the abstrac
Towards Subject and Diagnostic Identifiability in the Alzheimer’s Disease Spectrum Based on Functional Connectomes
Alzheimer’s disease (AD) is the only major cause of mortality in the world without an effective disease modifying treatment. Evidence supporting the so called “disconnection hypothesis” suggests that functional connectivity biomarkers may have clinical potential for early detection of AD. However, known issues with low test-retest reliability and signal to noise in functional connectivity may prevent accuracy and subsequent predictive capacity. We validate the utility of a novel principal component based diagnostic identifiability framework to increase separation in functional connectivity across the Alzheimer’s spectrum by identifying and reconstructing FC using only AD sensitive components or connectivity modes. We show that this framework (1) increases test-retest correspondence and (2) allows for better separation, in functional connectivity, of diagnostic groups both at the whole brain and individual resting state network level. Finally, we evaluate a posteriori the association between connectivity mode weights with longitudinal neurocognitive outcomes
Identification of ER-000444793, a Cyclophilin D-independent inhibitor of mitochondrial permeability transition, using a high-throughput screen in cryopreserved mitochondria
Growing evidence suggests persistent mitochondrial permeability transition pore (mPTP) opening is a key pathophysiological event in cell death underlying a variety of diseases. While it has long been clear the mPTP is a druggable target, current agents are limited by off-target effects and low therapeutic efficacy. Therefore identification and development of novel inhibitors is necessary. To rapidly screen large compound libraries for novel mPTP modulators, a method was exploited to cryopreserve large batches of functionally active mitochondria from cells and tissues. The cryopreserved mitochondria maintained respiratory coupling and ATP synthesis, Ca(2+) uptake and transmembrane potential. A high-throughput screen (HTS), using an assay of Ca(2+)-induced mitochondrial swelling in the cryopreserved mitochondria identified ER-000444793, a potent inhibitor of mPTP opening. Further evaluation using assays of Ca(2+)-induced membrane depolarisation and Ca(2+) retention capacity also indicated that ER-000444793 acted as an inhibitor of the mPTP. ER-000444793 neither affected cyclophilin D (CypD) enzymatic activity, nor displaced of CsA from CypD protein, suggesting a mechanism independent of CypD inhibition. Here we identified a novel, CypD-independent inhibitor of the mPTP. The screening approach and compound described provides a workflow and additional tool to aid the search for novel mPTP modulators and to help understand its molecular nature
Two Energy Scales and two Quasiparticle Dynamics in the Superconducting State of Underdoped Cuprates
The superconducting state of underdoped cuprates is often described in terms
of a single energy-scale, associated with the maximum of the (d-wave) gap.
Here, we report on electronic Raman scattering results, which show that the gap
function in the underdoped regime is characterized by two energy scales,
depending on doping in opposite manners. Their ratios to the maximum critical
temperature are found to be universal in cuprates. Our experimental results
also reveal two different quasiparticle dynamics in the underdoped
superconducting state, associated with two regions of momentum space: nodal
regions near the zeros of the superconducting gap and antinodal regions. While
antinodal quasiparticles quickly loose coherence as doping is reduced, coherent
nodal quasiparticles persist down to low doping levels. A theoretical analysis
using a new sum-rule allows us to relate the low-frequency-dependence of the
Raman response to the temperature-dependence of the superfluid density, both
controlled by nodal excitations.Comment: 16 pages, 5 figure
Polymorphisms in Nucleotide Excision Repair Genes, Arsenic Exposure, and Non-Melanoma Skin Cancer in New Hampshire
Background: Arsenic exposure may alter the efficiency of DNA repair. UV damage is specifically repaired by nucleotide excision repair (NER), and common genetic variants in NER may increase risk for non-melanoma skin cancer (NMSC). Objective: We tested whether polymorphisms in the NER genes XPA (A23G) and XPD (Asp312Asn and Lys751Gln) modify the association between arsenic and NMSC. Methods: Incident cases of basal and squamous cell carcinoma (BCC and SCC, respectively) were identified through a network of dermatologists and pathology laboratories across New Hampshire. Population-based controls were frequency matched to cases on age and sex. Arsenic exposure was assessed in toenail clippings. The analysis included 880 cases of BCC, 666 cases of SCC, and 780 controls. Results: There was an increased BCC risk associated with high arsenic exposure among those homozygous variant for XPA [odds ratio (OR) = 1.8; 95% confidence interval (CI), 0.9–3.7]. For XPD, having variation at both loci (312Asn and 751Gln) occurred less frequently among BCC and SCC cases compared with controls (OR = 0.8; 95% CI, 0.6–1.0) for both case groups. In the stratum of subjects who have variant for both XPD polymorphisms, there was a 2-fold increased risk of SCC associated with elevated arsenic (OR = 2.2; 95% CI, 1.0–5.0). The test for interaction between XPD and arsenic in SCC was of borderline significance (p < 0.07, 3 degrees of freedom). Conclusions: Our findings indicate a reduced NMSC risk in relation to XPD Asp312Asn and Lys751Gln variants. Further, these data support the hypothesis that NER polymorphisms may modify the association between NMSC and arsenic
Nodal quasiparticle meltdown in ultra-high resolution pump-probe angle-resolved photoemission
High- cuprate superconductors are characterized by a strong
momentum-dependent anisotropy between the low energy excitations along the
Brillouin zone diagonal (nodal direction) and those along the Brillouin zone
face (antinodal direction). Most obvious is the d-wave superconducting gap,
with the largest magnitude found in the antinodal direction and no gap in the
nodal direction. Additionally, while antinodal quasiparticle excitations appear
only below , superconductivity is thought to be indifferent to nodal
excitations as they are regarded robust and insensitive to . Here we
reveal an unexpected tie between nodal quasiparticles and superconductivity
using high resolution time- and angle-resolved photoemission on optimally doped
BiSrCaCuO. We observe a suppression of the nodal
quasiparticle spectral weight following pump laser excitation and measure its
recovery dynamics. This suppression is dramatically enhanced in the
superconducting state. These results reduce the nodal-antinodal dichotomy and
challenge the conventional view of nodal excitation neutrality in
superconductivity.Comment: 7 pages, 3 figure. To be published in Nature Physic
A model for transition of 5 '-nuclease domain of DNA polymerase I from inert to active modes
Bacteria contain DNA polymerase I (PolI), a single polypeptide chain consisting of similar to 930 residues, possessing DNA-dependent DNA polymerase, 3'-5' proofreading and 5'-3' exonuclease (also known as flap endonuclease) activities. PolI is particularly important in the processing of Okazaki fragments generated during lagging strand replication and must ultimately produce a double-stranded substrate with a nick suitable for DNA ligase to seal. PolI's activities must be highly coordinated both temporally and spatially otherwise uncontrolled 5'-nuclease activity could attack a nick and produce extended gaps leading to potentially lethal double-strand breaks. To investigate the mechanism of how PolI efficiently produces these nicks, we present theoretical studies on the dynamics of two possible scenarios or models. In one the flap DNA substrate can transit from the polymerase active site to the 5'-nuclease active site, with the relative position of the two active sites being kept fixed; while the other is that the 5'-nuclease domain can transit from the inactive mode, with the 5'-nuclease active site distant from the cleavage site on the DNA substrate, to the active mode, where the active site and substrate cleavage site are juxtaposed. The theoretical results based on the former scenario are inconsistent with the available experimental data that indicated that the majority of 5'-nucleolytic processing events are carried out by the same PolI molecule that has just extended the upstream primer terminus. By contrast, the theoretical results on the latter model, which is constructed based on available structural studies, are consistent with the experimental data. We thus conclude that the latter model rather than the former one is reasonable to describe the cooperation of the PolI's polymerase and 5'-3' exonuclease activities. Moreover, predicted results for the latter model are presented
Quasi-particle interference and superconducting gap in a high-temperature superconductor Ca2-xNaxCuO2Cl2
High-transition-temperature (high-Tc) superconductivity is ubiquitous in the
cuprates containing CuO2 planes but each cuprate has its own character. The
study of the material dependence of the d-wave superconducting gap (SG) should
provide important insights into the mechanism of high-Tc. However, because of
the 'pseudogap' phenomenon, it is often unclear whether the energy gaps
observed by spectroscopic techniques really represent the SG. Here, we report
spectroscopic imaging scanning tunneling microscopy (SI-STM) studies of
nearly-optimally-doped Ca2-xNaxCuO2Cl2 (Na-CCOC) with Tc = 25 ~ 28 K. They
enable us to observe the quasi-particle interference (QPI) effect in this
material, through which unambiguous new information on the SG is obtained. The
analysis of QPI in Na-CCOC reveals that the SG dispersion near the gap node is
almost identical to that of Bi2Sr2CaCu2Oy (Bi2212) at the same doping level,
while Tc of Bi2212 is 3 times higher than that of Na-CCOC. We also find that SG
in Na-CCOC is confined in narrower energy and momentum ranges than Bi2212. This
explains at least in part the remarkable material dependence of TcComment: 13pages, 4fig
Implicit Temporal Expectation Attenuates Auditory Attentional Blink
Attentional blink (AB) describes a phenomenon whereby correct identification of a first target impairs the processing of a second target (i.e., probe) nearby in time. Evidence suggests that explicit attention orienting in the time domain can attenuate the AB. Here, we used scalp-recorded, event-related potentials to examine whether auditory AB is also sensitive to implicit temporal attention orienting. Expectations were set up implicitly by varying the probability (i.e., 80% or 20%) that the probe would occur at the +2 or +8 position following target presentation. Participants showed a significant AB, which was reduced with the increased probe probability at the +2 position. The probe probability effect was paralleled by an increase in P3b amplitude elicited by the probe. The results suggest that implicit temporal attention orienting can facilitate short-term consolidation of the probe and attenuate auditory AB
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