992 research outputs found
Analytical description of spin-Rabi oscillation controlled electronic transitions rates between weakly coupled pairs of paramagnetic states with S=1/2
We report on an analytical description of spin-dependent electronic
transition rates which are controlled by a radiation induced spin-Rabi
oscillation of weakly spin-exchange and spin-dipolar coupled paramagnetic
states (S=1/2). The oscillation components (the Fourier content) of the net
transition rates within spin-pair ensembles are derived for randomly
distributed spin resonances with account of a possible correlation between the
two distributions that correspond to the two individual pair partners. The
results presented here show that when electrically or optically detected Rabi
spectroscopy is conducted under an increasing driving field B_ 1, the Rabi
spectrum evolves from a single resonance peak at s=\Omega_R, where
\Omega_R=\gamma B_1 is the Rabi frequency (\gamma is the gyromagnetic ratio),
to three peaks at s= \Omega_R, s=2\Omega_R, and at low s<< \Omega_R. The
crossover between the two regimes takes place when \Omega_R exceeds the
expectation value \delta_0 of the difference of the Zeeman energies within the
pairs, which corresponds to the broadening of the magnetic resonance lines in
the presence of disorder caused by hyperfine field or distributions of Lande
g-factors. We capture this crossover by analytically calculating the shapes of
all three peaks at arbitrary relation between \Omega_R and \delta_0. When the
peaks are well-developed their widths are \Delta s ~ \delta_0^2/\Omega_R.Comment: 10 page, 5 figure
Transport and recombination through weakly coupled localized spin pairs in semiconductors during coherent spin excitation
Semi-analytical predictions for the transients of spin-dependent transport
and recombination rates through localized states in semiconductors during
coherent electron spin excitation are made for the case of weakly spin-coupled
charge carrier ensembles. The results show that the on-resonant Rabi frequency
of electrically or optically detected spin-oscillation doubles abruptly as the
strength of the resonant microwave field gamma B_1 exceeds the Larmor frequency
separation within the pair of charge carrier states between which the transport
or recombination transition takes place. For the case of a Larmor frequency
separation of the order of gamma B_1 and arbitrary excitation frequencies, the
charge carrier pairs exhibit four different nutation frequencies. From the
calculations, a simple set of equations for the prediction of these frequencies
is derived
Graph Contrastive Learning for Materials
Recent work has shown the potential of graph neural networks to efficiently
predict material properties, enabling high-throughput screening of materials.
Training these models, however, often requires large quantities of labelled
data, obtained via costly methods such as ab initio calculations or
experimental evaluation. By leveraging a series of material-specific
transformations, we introduce CrystalCLR, a framework for constrastive learning
of representations with crystal graph neural networks. With the addition of a
novel loss function, our framework is able to learn representations competitive
with engineered fingerprinting methods. We also demonstrate that via model
finetuning, contrastive pretraining can improve the performance of graph neural
networks for prediction of material properties and significantly outperform
traditional ML models that use engineered fingerprints. Lastly, we observe that
CrystalCLR produces material representations that form clusters by compound
class.Comment: 7 pages, 3 figures, NeurIPS 2022 AI for Accelerated Materials Design
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Pigment Dispersing Factors and Their Cognate Receptors in a Crustacean Model, With New Insights Into Distinct Neurons and Their Functions
Pigment dispersing factors (PDFs, or PDHs in crustaceans) form a structurally related group of neuropeptides found throughout the Ecdysozoa and were first discovered as pigmentary effector hormones in crustaceans. In insects PDFs fulfill crucial neuromodulatory roles, most notably as output regulators of the circadian system, underscoring their central position in physiological and behavioral organization of arthropods. Intriguingly, decapod crustaceans express multiple isoforms of PDH originating from separate genes, yet their differential functions are still to be determined. Here, we functionally define two PDH receptors in the crab Carcinus maenas and show them to be selectively activated by four PDH isoforms: PDHR 43673 was activated by PDH-1 and PDH-2 at low nanomolar doses whilst PDHR 41189 was activated by PDH-3 and an extended 20 residue e-PDH. Detailed examination of the anatomical distribution of all four peptides and their cognate receptors indicate that they likely perform different functions as secreted hormones and/or neuromodulators, with PDH-1 and its receptor 43,673 implicated in an authentic hormonal axis. PDH-2, PDH-3, and e-PDH were limited to non-neurohemal interneuronal sites in the CNS; PDHR 41189 was largely restricted to the nervous system suggesting a neuromodulatory function. Notably PDH-3 and e-PDH were without chromatophore dispersing activity. This is the first report which functionally defines a PDHR in an endocrine system in a crustacean and to indicate this and other putative roles of this physiologically pivotal peptide group in these organisms. Thus, our findings present opportunities to further examine the endocrine and circadian machinery in this important arthropod phylum
X-ray diffraction studies of the effects of N incorporation in amorphous CNx, materials
The effects of nitrogen incorporation on the atomic-scale structure of amorphous CNx samples have been studied for 0, 5, 20, and 30 at. % N concentration, by x-ray diffraction. Significant differences in the structure are observed on the incorporation of only 5 at. % N, and the changes in structure continue as further N is added. From the experimental data, we are able to obtain directly the average bond distances and then calculate the average bond angles for each of the samples. The average first neighbor distance shows a gradual decrease from 1.55 Angstrom for 0 at. % N, to 1.44 Angstrom for 30 at. % N, and a similar trend is observed in the position of the second neighbor peak. This gives a corresponding increase in the average bond angle from 108 degrees to 114 degrees. The results show an increase in the fraction of sp(2) bonded carbon atoms with increasing N concentration, and there is evidence for the presence of significant numbers of C=N and C=N bonds. These results are also consistent with stress, hardness, and optical gap measurements for these samples. (C) 1998 American Institute of Physics. [S0021-8979(98)03907-3]
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The effect of temporal pulse shape on optical damage
The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. We present here data from a simple single-parameter model and a supporting experiment which predicts that a Flat-In-Time-pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same FWHM duration
Assessment of the Nova StatSensor whole blood point-of-care creatinine analyser for the measurement of kidney function in screening for chronic kidney disease
Point-of-care testing for creatinine using a fingerprick sample and resultant estimated glomerular filtration rate has potential for screening for chronic kidney disease in
community settings. This study assessed the applicability of the Nova StatSensor creatinine analyzer for this purpose. Fingerprick samples from 100 patients (63 renal,
37 healthy volunteers; range 46–962 mmol/L) were assayed
using two StatSensor analyzers. Lithium heparin venous
plasma samples collected simultaneously were assayed in
duplicate using the isotope dilution mass spectrometryaligned
Roche Creatinine Plus enzymatic assay on a Hitachi
Modular P unit. Method comparison statistics and the ability
of the StatSensor to correctly categorise estimated glomerular
filtration rate above or below 60 mL/min were calculated
pre- and post-alignment with the laboratory method.
Isotope dilution mass spectrometry alignment
of the StatSensor will identify most patients with estimated glomerular filtration rate -60 mL/min, but there will be
many falsely low estimated glomerular filtration rate results
that require laboratory validation. Creatinine results need
improvement
Microstructure of Nunas: Andean Popping Beans (Phaseolus Vulgaris L.)
Nunas, popping beans (Phaseous vulgaris L.), burst and expand when heated rapidly. Differences in seed microstructure between popping and conventional (non-popping) bean genotypes conceivably contribute to popping in nunas However, the microstructural characteristics which contribute to the popping attribute and sites of expansion have not been identified. Seeds and excised cotyledons of unpopped and popped nunas were examined using scanning electron microscopy (SEM). Protoplasts of unpopped nunas were similar to protoplasts of conventional beans. Intercellular spaces of unpopped nunas were occluded by schizogenous cell walls. The occluded form of intercellular spaces differed distinctively from the open form in popped nunas and untreated conventional beans. The expansion of cotyledon mesophyll in popped nunas came primarily from expansion of cell walls and secondarily by expansion of the intercellular spaces. Cell wall thickness and dimensions of protoplasts were not changed during popping. Expansion of cell walls away from protoplasts created intracellular voids. SEM images indicated that starch granules (grains) in popped nunas were generally not altered by popping. Starch granules did not gelatinize or melt during popping as indicated by retention of birefringence. In contrast to popcorn (Zea mays L.), starch granules did not contribute to expansion of popped nuna cotyledons
The Role of the Mucus Barrier in Digestion
Mucus forms a protective layer across a variety of epithelial surfaces. In the gastrointestinal (GI) tract, the barrier has to permit the uptake of nutrients, while excluding potential hazards, such as pathogenic bacteria. In this short review article, we look at recent literature on the structure, location, and properties of the mammalian intestinal secreted mucins and the mucus layer they form over a wide range of length scales. In particular, we look at the structure of the gel-forming glycoprotein MUC2, the primary intestinal secreted mucin, and the influence this has on the properties of the mucus layer. We show that, even at the level of the protein backbone, MUC2 is highly heterogeneous and that this is reflected in the networks it forms. It is evident that a combination of charge and pore size determines what can diffuse through the layer to the underlying gut epithelium. This information is important for the targeted delivery of bioactive molecules, including nutrients and pharmaceuticals, and for understanding how GI health is maintained
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