10,896 research outputs found
Signaling from blood vessels to CNS axons through nitric oxide
Brain function is usually perceived as being performed by neurons with the support of glial cells, the network of blood vessels situated nearby serving simply to provide nutrient and to dispose of metabolic waste. Revising this view, we find from experiments on a rodent central white matter tract (the optic nerve) in vitro that microvascular endothelial cells signal persistently to axons using nitric oxide (NO) derived from the endothelial NO synthase (eNOS). The endogenous NO acts to stimulate guanylyl cyclase-coupled NO receptors in the axons, leading to a raised cGMP level which then causes membrane depolarization, apparently by directly engaging hyperpolarization-activated cyclic nucleotide-gated ion channels. The tonic depolarization and associated endogenous NO-dependent cGMP generation was absent in optic nerves from mice lacking eNOS, although such nerves responded to exogenous NO, with raised cGMP generation in the axons and associated depolarization. In addition to the tonic activity, exposure of optic nerves to bradykinin, a classical stimulator of eNOS in endothelial cells, elicited reversible NO- and cGMP-dependent depolarization through activation of bradykinin B-2 receptors, to which eNOS is physically complexed. No contribution of other NO synthase isoforms to either the action of bradykinin or the continuous ambient NO level could be detected. The results suggest that microvascular endothelial cells participate in signal processing in the brain and can do so by generating both tonic and phasic NO signals
Globalising assessment: an ethnography of literacy assessment, camels and fast food in the Mongolian Gobi
What happens when standardised literacy assessments travel globally? The paper presents an ethnographic account of adult literacy assessment events in rural Mongolia. It examines the dynamics of literacy assessment in terms of the movement and re-contextualisation of test items as they travel globally and are received locally by Mongolian respondents. The analysis of literacy assessment events is informed by Goodwin’s ‘participation framework’ on language as embodied and situated interactive phenomena and by Actor Network Theory. Actor Network Theory (ANT) is applied to examine literacy assessment events as processes of translation shaped by an ‘assemblage’ of human and non-human actors (including the assessment texts)
Emergence of long-range order in BaTiO3 from local symmetry-breaking distortions
By using a symmetry motivated basis to evaluate local distortions against
pair distribution function data (PDF), we show without prior bias, that the
off-centre Ti displacements in the archetypal ferroelectric BaTiO3 are zone
centred and rhombohedral-like in nature across its known ferroelectric and
paraelectric phases. With our newly-gained insight we construct a simple Monte
Carlo (MC) model which captures our main experimental findings and demonstrate
how the rich crystallographic phase diagram of BaTiO3 emerges from correlations
of local symmetry-breaking distortions alone. Our results strongly support the
order-disorder picture for these phase transitions, but can also be reconciled
with the soft-mode theory of BaTiO3 that is supported by some spectroscopic
techniques.Comment: 5 pages, 3 figure
High-rate, high-fidelity entanglement of qubits across an elementary quantum network
We demonstrate remote entanglement of trapped-ion qubits via a
quantum-optical fiber link with fidelity and rate approaching those of local
operations. Two Sr qubits are entangled via the polarization
degree of freedom of two photons which are coupled by high-numerical-aperture
lenses into single-mode optical fibers and interfere on a beamsplitter. A novel
geometry allows high-efficiency photon collection while maintaining unit
fidelity for ion-photon entanglement. We generate remote Bell pairs with
fidelity at an average rate (success
probability ).Comment: v2 updated to include responses to reviewers, as published in PR
Why do starless cores appear more flattened than protostellar cores?
We evaluate the intrinsic three dimensional shapes of molecular cores, by
analysing their projected shapes. We use the recent catalogue of molecular line
observations of Jijina et al. and model the data by the method originally
devised for elliptical galaxies. Our analysis broadly supports the conclusion
of Jones et al. that molecular cores are better represented by triaxial
intrinsic shapes (ellipsoids) than biaxial intrinsic shapes (spheroids).
However, we find that the best fit to all of the data is obtained with more
extreme axial ratios () than those derived by Jones et al.
More surprisingly, we find that starless cores have more extreme axial ratios
than protostellar cores -- starless cores appear more `flattened'. This is the
opposite of what would be expected from modeling the freefall collapse of
triaxial ellipsoids. The collapse of starless cores would be expected to
proceed most swiftly along the shortest axis - as has been predicted by every
modeller since Zel'dovich - which should produce more flattened cores around
protostars, the opposite of what is seen.Comment: 7 pages, 3 figure
A host–guest approach for determining drug–DNA interactions: an example using netropsin
Netropsin is a well-characterized DNA minor groove binding compound that serves as a model for the study of drug–DNA interactions. Our laboratory has developed a novel host–guest approach to study drug–DNA interactions in which the host, the N-terminal fragment of Moloney murine leukemia virus reverse transcriptase (MMLV RT) is co-crystallized with a DNA oligonucleotide guest in the presence and absence of drug. We have co-crystallized netropsin with the RT fragment bound to the symmetric 16mer d(CTTAATTCGAATTAAG)(2) and determined the structure of the complex at 1.85 Å. In contrast to previously reported netropsin–DNA structures, our oligonucleotide contains two AATT sites that bind netropsin with flanking 5′ and 3′ sequences that are not symmetric. The asymmetric unit of the RT fragment–DNA–netropsin crystals contains one protein molecule and one-half of the 16mer with one netropsin molecule bound. The guanidinium moiety of netropsin binds in a narrow part of the minor groove, while the amidinium is bound in the widest region within the site. We compare this structure to other Class I netropsin–DNA structures and find that the asymmetry of minor groove widths in the AATT site contributes to the orientation of netropsin within the groove while hydrogen bonding patterns vary in the different structures
Robust inference of neutron-star parameters from thermonuclear burst observations
Thermonuclear (type-I) bursts arise from unstable ignition of accumulated
fuel on the surface of neutron stars in low-mass X-ray binaries. Measurements
of burst properties in principle enable observers to infer the properties of
the host neutron star and mass donors, but a number of confounding
astrophysical effects contribute to systematic uncertainties. Here we describe
some commonly-used approaches for determining system parameters, including
composition of the burst fuel, and introduce a new suite of software tools,
concord, intended to fully account for astrophysical uncertainties. Comparison
of observed burst properties with the predictions of numerical models is a
complementary method of constraining host properties, and the tools presented
here are intended to make comprehensive model-observation comparisons
straightforward. When combined with the extensive samples of burst observations
accumulated by X-ray observatories, these software tools will provide a
step-change in the amount of information that can be inferred about typical
burst sources.Comment: 22 pages, 11 figures, 1 table & 1 machine-readable table as
supplementary data; submitted to ApJS. Accompanying software package
available at https://github.com/outs1der/concor
The normalization of sibling violence: Does gender and personal experience of violence influence perceptions of physical assault against siblings?
Despite its pervasive and detrimental nature, sibling violence (SV) remains marginalized as a harmless and inconsequential form of familial aggression. The present study investigates the extent to which perceptions of SV differ from those of other types of interpersonal violence. A total of 605 respondents (197 males, 408 females) read one of four hypothetical physical assault scenarios that varied according to perpetrator–victim relationship type (i.e., sibling vs. dating partner vs. peer vs. stranger) before completing a series of 24 attribution items. Respondents also reported on their own experiences of interpersonal violence during childhood. Exploratory factor analysis reduced 23 attribution items to three internally reliable factors reflecting perceived assault severity, victim culpability, and victim resistance ratings. A 4 × 2 MANCOVA—controlling for respondent age—revealed several significant effects. Overall, males deemed the assault less severe and the victim more culpable than did females. In addition, the sibling assault was deemed less severe compared to assault on either a dating partner or a stranger, with the victim of SV rated just as culpable as the victim of dating, peer, or stranger-perpetrated violence. Finally, respondents with more (frequent) experiences of childhood SV victimization perceived the hypothetical SV assault as being less severe, and victim more culpable, than respondents with no SV victimization. Results are discussed in the context of SV normalization. Methodological limitations and applications for current findings are also outlined
Probing Qubit Memory Errors at the Part-per-Million Level
Robust qubit memory is essential for quantum computing, both for near-term
devices operating without error correction, and for the long-term goal of a
fault-tolerant processor. We directly measure the memory error for
a Ca trapped-ion qubit in the small-error regime and find
for storage times t\lesssim50\,\mbox{ms}. This exceeds
gate or measurement times by three orders of magnitude. Using randomized
benchmarking, at t=1\,\mbox{ms} we measure ,
around ten times smaller than that extrapolated from the time,
and limited by instability of the atomic clock reference used to benchmark the
qubit.Comment: 8 pages, 5 figure
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