2,375 research outputs found
Cotunneling-mediated transport through excited states in the Coulomb blockade regime
We present finite bias transport measurements on a few-electron quantum dot.
In the Coulomb blockade regime, strong signatures of inelastic cotunneling
occur which can directly be assigned to excited states observed in the
non-blockaded regime. In addition, we observe structures related to sequential
tunneling through the dot, occuring after it has been excited by an inelastic
cotunneling process. We explain our findings using transport calculations
within the real-time Green's function approach, including diagrams up to fourth
order in the tunneling matrix elements.Comment: 4 pages, 3 figure
Auxiliary field diffusion Monte Carlo calculations of magnetic moments of light nuclei with chiral EFT interactions
We calculate the magnetic moments of light nuclei () using the
auxiliary field diffusion Monte Carlo method and local two- and three-nucleon
forces with electromagnetic currents from chiral effective field theory. For
all nuclei under consideration, we also calculate the ground-state energies and
charge radii. We generally find a good agreement with experimental values for
all of these observables. For the electromagnetic currents, we explore the
impact of employing two different power countings, and study theoretical
uncertainties stemming from the truncation of the chiral expansion
order-by-order for select nuclei within these two approaches. We find that it
is crucial to employ consistent power countings for interactions and currents
to achieve a systematic order-by-order convergence.Comment: 7 pages, 4 figures, supplemental materia
Lipodystrophy as a late effect after stem cell transplantation
Survivors of childhood cancer are at high risk of developing metabolic diseases in adulthood. Recently, several patients developing partial lipodystrophy following hematopoietic stem cell transplantation (HSCT) have been described. In this review, we summarize the cases described so far and discuss potential underlying mechanisms of the disease. The findings suggest that HSCT-associated lipodystrophies may be seen as a novel form of acquired lipodystrophy
Diagnostic Potential of the NMDA Receptor Peptide Assay for Acute Ischemic Stroke
Background
The acute assessment of patients with suspected ischemic stroke remains challenging. The use of brain biomarker assays may improve the early diagnosis of ischemic stroke. The main goal of the study was to evaluate whether the NR2 peptide, a product of the proteolytic degradation of N-methyl-D-aspartate (NMDA) receptors, can differentiate acute ischemic stroke (IS) from stroke mimics and persons with vascular risk factors/healthy controls. A possible correlation between biomarker values and lesion sizes was investigated as the secondary objective.
Methods and Findings
A total of 192 patients with suspected stroke who presented within 72 h of symptom onset were prospectively enrolled. The final diagnosis was determined based on clinical observations and radiological findings. Additionally gender- and age-matched healthy controls (n = 52) and persons with controlled vascular risk factors (n = 48) were recruited to compare NR2 peptide levels. Blinded plasma was assayed by rapid magnetic particles (MP) ELISA for NR2 peptide within 30 min and results for different groups compared using univariate and multivariate statistical analyses. There was a clinical diagnosis of IS in 101 of 192 (53%) and non-stroke in 91 (47%) subjects. The non-stroke group included presented with acute stroke symptoms who had no stroke (n = 71) and stroke mimics (n = 20). The highest NR2 peptide elevations where found in patients with IS that peaked at 12 h following symptom onset. When the biomarker cut off was set at 1.0 ug/L, this resulted in a sensitivity of 92% and a specificity of 96% to detect IS. A moderate correlation (rs = 0.73) between NR2 peptide values and acute ischemic cortical lesions (\u3c200 \u3emL) was found.
Conclusions
This study suggests that the NR2 peptide may be a brain specific biomarker to diagnose acute IS and may allow the differentiation of IS from stroke mimics and controls. Additional larger scale clinical validation studies are required
Stringent constraints on neutron-star radii from multimessenger observations and nuclear theory
The properties of neutron stars are determined by the nature of the matter
that they contain. These properties can be constrained by measurements of the
star's size. We obtain stringent constraints on neutron-star radii by combining
multimessenger observations of the binary neutron-star merger GW170817 with
nuclear theory that best accounts for density-dependent uncertainties in the
equation of state. We construct equations of state constrained by chiral
effective field theory and marginalize over these using the gravitational-wave
observations. Combining this with the electromagnetic observations of the
merger remnant that imply the presence of a short-lived hyper-massive neutron
star, we find that the radius of a neutron star is
(90% credible
interval). Using this constraint, we show that neutron stars are unlikely to be
disrupted in neutron-star black-hole mergers; subsequently, such events will
not produce observable electromagnetic emission.Comment: 39 pages, 4 figure
Reproducing the results for NICER observation of PSR J0030+0451
NASA's Neutron Star Interior Composition Explorer (NICER) observed X-ray
emission from the pulsar PSR J0030+0451 in 2018. Riley et al. reported Bayesian
parameter measurements of the mass and the star's radius using pulse-profile
modeling of the X-ray data. This paper reproduces their result using the
open-source software X-PSI and publicly available data within expected
statistical errors. We note the challenges we faced in reproducing the results
and demonstrate that the analysis can be reproduced and reused in future works
by changing the prior distribution for the radius and the sampler
configuration. We find no significant change in the measurement of the mass and
radius, demonstrating that the original result is robust to these changes.
Finally, we provide a containerized working environment that facilitates
third-party reproduction of the measurements of mass and radius of PSR
J0030+0451 using the NICER observations.Comment: 13 pages, 4 figures, 2 tables. Final version accepted for publication
in Computing in Science & Engineerin
Substrate-Assisted Catalysis Unifies Two Families of Chitinolytic Enzymes
Hen egg-white lysozyme has long been the paradigm for enzymatic glycosyl hydrolysis with retention of configuration, with a protonated carboxylic acid and a deprotonated carboxylate participating in general acid-base catalysis. In marked contrast, the retaining chitin degrading enzymes from glycosyl hydrolase families 18 and 20 all have a single glutamic acid as the catalytic acid but lack a nucleophile on the enzyme. Both families have a catalytic (βα)8-barrel domain in common. X-ray structures of three different chitinolytic enzymes complexed with substrates or inhibitors identify a retaining mechanism involving a protein acid and the carbonyl oxygen atom of the substrate’s C2 N-acetyl group as the nucleophile. These studies unambiguously demonstrate the distortion of the sugar ring toward a sofa conformation, long postulated as being close to that of the transition state in glycosyl hydrolysis.
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