1,766 research outputs found
Computational study of structural and elastic properties of random AlGaInN alloys
In this work we present a detailed computational study of structural and
elastic properties of cubic AlGaInN alloys in the framework of Keating valence
force field model, for which we perform accurate parametrization based on state
of the art DFT calculations. When analyzing structural properties, we focus on
concentration dependence of lattice constant, as well as on the distribution of
the nearest and the next nearest neighbour distances. Where possible, we
compare our results with experiment and calculations performed within other
computational schemes. We also present a detailed study of elastic constants
for AlGaInN alloy over the whole concentration range. Moreover, we include
there accurate quadratic parametrization for the dependence of the alloy
elastic constants on the composition. Finally, we examine the sensitivity of
obtained results to computational procedures commonly employed in the Keating
model for studies of alloys
Mapping two neurosteroid-modulatory sites in the prototypic pentameric ligand-gated ion channel GLIC
Superconducting properties of nanocrystalline MgB thin films made by an in situ annealing process
We have studied the structural and superconducting properties of MgB thin
films made by pulsed laser deposition followed by in situ annealing. The
cross-sectional transmission electron microscopy reveals a nanocrystalline
mixture of textured MgO and MgB with very small grain sizes. A
zero-resistance transition temperature () of 34 K and a zero-field
critical current density () of A/cm were obtained.
The irreversibility field was 8 T at low temperatures, although severe
pinning instability was observed. These bulk-like superconducting properties
show that the in situ deposition process can be a viable candidate for MgB
Josephson junction technologies
Effect of atomic transfer on the decay of a Bose-Einstein condensate
We present a model describing the decay of a Bose-Einstein condensate, which
assumes the system to remain in thermal equilibrium during the decay. We show
that under this assumption transfer of atoms occurs from the condensate to the
thermal cloud enhancing the condensate decay rate
Multiple functional neurosteroid binding sites on GABAA receptors
Neurosteroids are endogenous modulators of neuronal excitability and nervous system development and are being developed as anesthetic agents and treatments for psychiatric diseases. While gamma amino-butyric acid Type A (GABAA) receptors are the primary molecular targets of neurosteroid action, the structural details of neurosteroid binding to these proteins remain ill defined. We synthesized neurosteroid analogue photolabeling reagents in which the photolabeling groups were placed at three positions around the neurosteroid ring structure, enabling identification of binding sites and mapping of neurosteroid orientation within these sites. Using middle-down mass spectrometry (MS), we identified three clusters of photolabeled residues representing three distinct neurosteroid binding sites in the human α1β3 GABAA receptor. Novel intrasubunit binding sites were identified within the transmembrane helical bundles of both the α1 (labeled residues α1-N408, Y415) and β3 (labeled residue β3-Y442) subunits, adjacent to the extracellular domains (ECDs). An intersubunit site (labeled residues β3-L294 and G308) in the interface between the β3(+) and α1(-) subunits of the GABAA receptor pentamer was also identified. Computational docking studies of neurosteroid to the three sites predicted critical residues contributing to neurosteroid interaction with the GABAA receptors. Electrophysiological studies of receptors with mutations based on these predictions (α1-V227W, N408A/Y411F, and Q242L) indicate that both the α1 intrasubunit and β3-α1 intersubunit sites are critical for neurosteroid action
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Hyperpolarized 13C-pyruvate MRI detects real-time metabolic flux in prostate cancer metastases to bone and liver: a clinical feasibility study.
BackgroundHyperpolarized (HP) 13C-pyruvate MRI is a stable-isotope molecular imaging modality that provides real-time assessment of the rate of metabolism through glycolytic pathways in human prostate cancer. Heretofore this imaging modality has been successfully utilized in prostate cancer only in localized disease. This pilot clinical study investigated the feasibility and imaging performance of HP 13C-pyruvate MR metabolic imaging in prostate cancer patients with metastases to the bone and/or viscera.MethodsSix patients who had metastatic castration-resistant prostate cancer were recruited. Carbon-13 MR examination were conducted on a clinical 3T MRI following injection of 250 mM hyperpolarized 13C-pyruvate, where pyruvate-to-lactate conversion rate (kPL) was calculated. Paired metastatic tumor biopsy was performed with histopathological and RNA-seq analyses.ResultsWe observed a high rate of glycolytic metabolism in prostate cancer metastases, with a mean kPL value of 0.020 ± 0.006 (s-1) and 0.026 ± 0.000 (s-1) in bone (N = 4) and liver (N = 2) metastases, respectively. Overall, high kPL showed concordance with biopsy-confirmed high-grade prostate cancer including neuroendocrine differentiation in one case. Interval decrease of kPL from 0.026 at baseline to 0.015 (s-1) was observed in a liver metastasis 2 months after the initiation of taxane plus platinum chemotherapy. RNA-seq found higher levels of the lactate dehydrogenase isoform A (Ldha,15.7 ± 0.7) expression relative to the dominant isoform of pyruvate dehydrogenase (Pdha1, 12.8 ± 0.9).ConclusionsHP 13C-pyruvate MRI can detect real-time glycolytic metabolism within prostate cancer metastases, and can measure changes in quantitative kPL values following treatment response at early time points. This first feasibility study supports future clinical studies of HP 13C-pyruvate MRI in the setting of advanced prostate cancer
Study on Evolvement Complexity in an Artificial Stock Market
An artificial stock market is established based on multi-agent . Each agent
has a limit memory of the history of stock price, and will choose an action
according to his memory and trading strategy. The trading strategy of each
agent evolves ceaselessly as a result of self-teaching mechanism. Simulation
results exhibit that large events are frequent in the fluctuation of the stock
price generated by the present model when compared with a normal process, and
the price returns distribution is L\'{e}vy distribution in the central part
followed by an approximately exponential truncation. In addition, by defining a
variable to gauge the "evolvement complexity" of this system, we have found a
phase cross-over from simple-phase to complex-phase along with the increase of
the number of individuals, which may be a ubiquitous phenomenon in multifarious
real-life systems.Comment: 4 pages and 4 figure
Bridgeness: A Local Index on Edge Significance in Maintaining Global Connectivity
Edges in a network can be divided into two kinds according to their different
roles: some enhance the locality like the ones inside a cluster while others
contribute to the global connectivity like the ones connecting two clusters. A
recent study by Onnela et al uncovered the weak ties effects in mobile
communication. In this article, we provide complementary results on document
networks, that is, the edges connecting less similar nodes in content are more
significant in maintaining the global connectivity. We propose an index named
bridgeness to quantify the edge significance in maintaining connectivity, which
only depends on local information of network topology. We compare the
bridgeness with content similarity and some other structural indices according
to an edge percolation process. Experimental results on document networks show
that the bridgeness outperforms content similarity in characterizing the edge
significance. Furthermore, extensive numerical results on disparate networks
indicate that the bridgeness is also better than some well-known indices on
edge significance, including the Jaccard coefficient, degree product and
betweenness centrality.Comment: 10 pages, 4 figures, 1 tabl
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