601 research outputs found
Suppressed spin dephasing for 2D and bulk electrons in GaAs wires due to engineered cancellation of spin-orbit interaction terms
We report a study of suppressed spin dephasing for quasi-one-dimensional
electron ensembles in wires etched into a GaAs/AlGaAs heterojunction system.
Time-resolved Kerr-rotation measurements show a suppression that is most
pronounced for wires along the [110] crystal direction. This is the fingerprint
of a suppression that is enhanced due to a strong anisotropy in spin-orbit
fields that can occur when the Rashba and Dresselhaus contributions are
engineered to cancel each other. A surprising observation is that this
mechanisms for suppressing spin dephasing is not only effective for electrons
in the heterojunction quantum well, but also for electrons in a deeper bulk
layer.Comment: 5 pages, 3 figure
A distance for partially labeled trees
In a number of practical situations, data have structure and the relations among its component parts need to be coded with suitable data models. Trees are usually utilized for representing data for which hierarchical relations can be defined. This is the case in a number of fields like image analysis, natural language processing, protein structure, or music retrieval, to name a few. In those cases, procedures for comparing trees are very relevant. An approximate tree edit distance algorithm has been introduced for working with trees labeled only at the leaves. In this paper, it has been applied to handwritten character recognition, providing accuracies comparable to those by the most comprehensive search method, being as efficient as the fastest.This work is supported by the Spanish Ministry projects DRIMS (TIN2009-14247-C02), and Consolider Ingenio 2010 (MIPRCV, CSD2007-00018), partially supported by EU ERDF and the Pascal Network of Excellence
Black hole mass and spin measurements through the Relativistic Precession Model: XTE J1859+226
The X-ray light curves of accreting black holes and neutron stars in binary
systems show various types of quasi-periodic oscillations (QPOs), the origin of
which is still debated. The Relativistic Precession Model identifies the QPO
frequencies with fundamental time scales from General Relativity, and has been
proposed as a possible explanation of certain types of such oscillations. Under
specific conditions (i.e., the detection of a particular QPOs triplet) such a
model can be used to obtain self-consistent measurements of the mass and spin
of the compact object. So far this has been possible only in the black hole
binary GRO J1655-40. In the RXTE/PCA data from the 1999-2000 outburst of the
black hole transient XTE J1859+226 we found a QPO triplet, and used the the
Relativistic Precession Model to obtain high-precision measurements of the
black hole mass and spin - M = (7.85+/-0.46) Msun, a* = 0.149+/-0.005 - the
former being consistent with the most recent dynamical mass determination from
optical measurements. Similarly to what has been already observed in other
black hole systems, the frequencies of the QPOs and broad-band noise components
match the general relativistic frequencies of particle motion close to the
compact object predicted by the model. Our findings confirm previous results
and further support the validity of the Relativistic Precession Model, which is
the only electromagnetic-measurement-based method that so far has consistently
yielded spins close to those from the gravitational waves produced by merging
binary black holes.Comment: 8 pages, 5 figures, accepted for publication in MNRA
Evidence for a black hole in the historical X-ray transient A 1524-61 (=KY TrA)
We present VLT spectroscopy, high-resolution imaging and time-resolved
photometry of KY TrA, the optical counterpart to the X-ray binary A 1524-61. We
perform a refined astrometry of the field, yielding improved coordinates for KY
TrA and the field star interloper of similar optical brightness that we locate
arcsec SE. From the spectroscopy, we refine the radial velocity
semi-amplitude of the donor star to km s by employing
the correlation between this parameter and the full-width at half-maximum of
the H emission line. The -band light curve shows an ellipsoidal-like
modulation with a likely orbital period of d (
h). These numbers imply a mass function M. The
KY TrA de-reddened quiescent colour is consistent
with a donor star of spectral type K2 or later, in case of significant
accretion disc light contribution to the optical continuum. The colour allows
us to place a very conservative upper limit on the companion star mass, M, and, in turn, on the binary mass ratio, . By exploiting the correlation between the binary inclination and the
depth of the H line trough, we establish deg. All these
values lead to a compact object and donor mass of
M and M, respectively, thus confirming the
black hole nature of the accreting object. In addition, we estimate a distance
toward the system of kpc.Comment: 7 pages, 5 figure
The orbital period, black hole mass and distance to the X-ray transient GRS 1716-249 (=N Oph 93)
We present evidence for a 0.278(8) d (=6.7 h) orbital period in the X-ray
transient GRS 1716-249 (=N Oph 93), based on a superhump modulation detected
during the 1995 mini-outburst plus ellipsoidal variability in quiescence. With
a quiescent magnitude of r=23.19+-0.15 N Oph 93 is too faint to warrant a full
dynamical study through dedicated time-resolved spectroscopy. Instead, we apply
the FWHM-K2 correlation to the disc Halpha emission line detected in Gran
Telescopio Canarias spectra and obtain K2=521+-52 km/s. This leads to a mass
function f(M)=4.1+-1.2 Msun, thus indicating the presence of a black hole in
this historic X-ray transient. Furthermore, from the depth of the Halpha trough
and the quiescent light curve we constrain the binary inclination to i=61+-15
deg, while the detection of superhumps sets an upper limit to the donor to
compact star mass ratio q=M2/M1<=0.25. Our de-reddened (r-i) colour is
consistent with a ~K6 main sequence star that fills its Roche lobe in a 0.278 d
orbit. Using all this information we derive a compact object mass
M1=6.4+3.2-2.0 Msun at 68 per cent confidence. We also constrain the distance
to GRS 1716-249 to 6.9+-1.1 kpc, placing the binary ~0.8 kpc above the Galactic
Plane, in support of a large natal kick.Comment: Accepted for publication in MNRAS, 12 pages, 9 figures, 2 Table
Phosphorylation of Syntaxin‐1a by casein kinase 2α (CK2α) regulates presynaptic vesicle exocytosis from the reserve pool
The t-soluble NSF-attachment protein receptor protein Syntaxin-1a (Stx-1a) is abundantly expressed at pre-synaptic terminals where it plays a critical role in the exocytosis of neurotransmitter-containing synaptic vesicles. Stx-1a is phosphorylated by Casein kinase 2α (CK2α) at Ser14, which has been proposed to regulate the interaction of Stx-1a and Munc-18 to control of synaptic vesicle priming. However, the role of CK2α in synaptic vesicle dynamics remains unclear. Here, we show that CK2α over-expression reduces evoked synaptic vesicle release. Furthermore, shRNA-mediated knockdown of CK2α in primary hippocampal neurons strongly enhanced vesicle exocytosis from the reserve pool, with no effect on the readily releasable pool of primed vesicles. In neurons in which endogenous Stx-1a was knocked down and replaced with a CK2α phosphorylation-deficient mutant, Stx-1a(D17A), vesicle exocytosis was also increased. These results reveal a previously unsuspected role of CK2α phosphorylation in specifically regulating the reserve synaptic vesicle pool, without changing the kinetics of release from the readily releasable pool
An Integrated Conceptual Model to Understand Suicidality among Queer Youth to Inform Suicide Prevention
In this article, we apply and combine elements from four theoretical frameworks (i.e., Minority Stress Theory, Person-in-Environment and Risk and Resilience Framework, Interpersonal-Psychological Theory of Suicide, and Intersectionality) to explain the problem of queer youth suicide through our integrated conceptual model, Queer Prevention of Youth Suicidality Model (Queer-PRYSM). The need for this conceptual model is based on the current state of the literature, including mixed empirical findings on factors related to queer youth suicidality, no scholarly consensus on specific contributing factors regarding high rates of suicidality among queer youth (including queer youth subgroups), and the absence of a unifying theory to explain the queer youth suicide risk. To address these limitations in theory, evidence, and scholarship explaining suicidality among queer youth we present our integrated model with growing, current, relevant research with queer youth. Queer-PRYSM includes minority stressors specific to queer youth, mental health problems, interpersonal-psychological factors, socioecological factors (i.e., family, school, peers, and community), and intersectionality concepts. Queer-PRYSM is essential to understanding the relationship of distal and proximal risk and protective factors in queer youth suicide and developing evidence-informed suicide preventive interventions that can be incorporated into practice, policy, and system structures
Recommended from our members
Mechanistic basis of an epistatic interaction reducing age at onset in hereditary spastic paraplegia
Many genetic neurological disorders exhibit variable expression within affected families, often exemplified by variations in disease age at onset. Epistatic effects (i.e. effects of modifier genes on the disease gene) may underlie this variation, but the mechanistic basis for such epistatic interactions is rarely understood. Here we report a novel epistatic interaction between SPAST and the contiguous gene DPY30, which modifies age at onset in hereditary spastic paraplegia, a genetic axonopathy. We found that patients with hereditary spastic paraplegia caused by genomic deletions of SPAST that extended into DPY30 had a significantly younger age at onset. We show that, like spastin, the protein encoded by SPAST, the DPY30 protein controls endosomal tubule fission, traffic of mannose 6-phosphate receptors from endosomes to the Golgi, and lysosomal ultrastructural morphology. We propose that additive effects on this pathway explain the reduced age at onset of hereditary spastic paraplegia in patients who are haploinsufficient for both genes.This work was supported by grants to E.R.; Project Grant from United States Spastic Paraplegia Foundation, UK Medical Research Council Project Grant [MR/M00046X/1], Project grant from NIHR Biomedical Research Centre at Addenbrooke’s Hospital, Wellcome Trust Senior Research Fellowship in Clinical Science [082381], Project Grant from Tom Wahlig Stiftung (project 33). J.E. and P.M. are supported by a Wellcome Trust Principal Research Fellowship Grant to Margaret S. Robinson [086598]. T.M.N. was supported by an MRC PhD studentship [G0800117]. B.W. is supported by the Tom Wahlig Advanced Fellowship, the German Federal Ministry of Education and Research (BMBF, 01GQ113), the Bavarian Ministry of Education and Culture, Sciences and Arts in the framework of the Bavarian Molecular Biosystems Research Network and ForIPS, and the Interdisciplinary Centre for Clinical Research (IZKF, University Hospital of Erlangen, N3 and F3). T.R. was supported by research grant DFG GRK2162/1 of the Deutsche Forschungsgemeinschaft. The study was also supported by the European Union within the 7th European Community Framework Program for Research and Technological Development through funding for the NEUROMICS network (F5-2012-305121 to L.S. and A.D.), the E-Rare Network NEUROLIPID (01GM1408B to R.S. and ANR-13-RARE-0003-02 to G.S.), and a Marie Curie International Outgoing Fellowship (grant PIOF-GA-2012-326681 to R.S. and L.S.). This work was further supported by the US National Institutes of Health (NIH) (grant 5R01NS072248 to R.S.), the German HSP-Selbsthilfegruppe e.V. (grant to R.S. and L.S.), and grants to C.B.: Project Grant from Tom Wahlig Stiftung (project 20), grant from the Stiftung für Pathobiochemie und Molekulare Diagnostik. CIMR is supported by a Wellcome Trust Strategic Award [100140] and Equipment Grant [093026]
Membrane Bridging and Hemifusion by Denaturated Munc18
Neuronal Munc18-1 and members of the Sec1/Munc18 (SM) protein family play a critical function(s) in intracellular membrane fusion together with SNARE proteins, but the mechanism of action of SM proteins remains highly enigmatic. During experiments designed to address this question employing a 7-nitrobenz-2-oxa-1,3-diazole (NBD) fluorescence de-quenching assay that is widely used to study lipid mixing between reconstituted proteoliposomes, we observed that Munc18-1 from squid (sMunc18-1) was able to increase the apparent NBD fluorescence emission intensity even in the absence of SNARE proteins. Fluorescence emission scans and dynamic light scattering experiments show that this phenomenon arises at least in part from increased light scattering due to sMunc18-1-induced liposome clustering. Nuclear magnetic resonance and circular dichroism data suggest that, although native sMunc18-1 does not bind significantly to lipids, sMunc18-1 denaturation at 37°C leads to insertion into membranes. The liposome clustering activity of sMunc18-1 can thus be attributed to its ability to bridge two membranes upon (perhaps partial) denaturation; correspondingly, this activity is hindered by addition of glycerol. Cryo-electron microscopy shows that liposome clusters induced by sMunc18-1 include extended interfaces where the bilayers of two liposomes come into very close proximity, and clear hemifusion diaphragms. Although the physiological relevance of our results is uncertain, they emphasize the necessity of complementing fluorescence de-quenching assays with alternative experiments in studies of membrane fusion, as well as the importance of considering the potential effects of protein denaturation. In addition, our data suggest a novel mechanism of membrane hemifusion induced by amphipathic macromolecules that does not involve formation of a stalk intermediate
- …