495 research outputs found

    Temperature Dependence of the Cyclotron Mass in n-Type CdS

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    Recent cyclotron resonance experiments in n-type CdS at ultra-high magnetic fields have revealed a pronounced maximum of the electron cyclotron mass as a function of temperature. In order to interpret these data, we calculate the magneto-absorption spectra of polarons in n-CdS using the arbitrary-coupling approach. We show that in high magnetic fields the polaron effects beyond the weak-coupling approximation clearly reveal themselves in the magneto-optical absorption even at relatively small values of the Froehlich coupling constant. In particular, those effects result in a non-monotonous behaviour of the cyclotron mass as a function of temperature. We extend the theory to take into account a combined effect of several scattering mechanisms on the magneto-absorption spectra. The extended theory allows us to interpret quantitatively the experimentally observed behaviour of the cyclotron mass in CdS.Comment: 4 pages, 3 figures, E-mail addresses: [email protected], [email protected]

    A catalytic combustion-type CO gas sensor incorporating aluminum nitride as an intermediate heat transfer layer for accelerated response time

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    A catalytic combustion-type carbon monoxide gas sensor exhibiting good sensing performance even at moderate temperatures was previously developed by employing a Pt loaded CeO2–ZrO2–SnO2 solid solution as the CO oxidizing catalyst. The addition of aluminum nitride as an intermediate heat transfer layer between the Pt coil and the CO oxidizing catalyst drastically accelerated the response of this device to CO at temperatures as low as 70 °C

    DNA Nucleobase Synthesis at Titan Atmosphere Analog by Soft X-rays

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    Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of N2 and CH4 and includes traces of many simple organic compounds. This atmosphere also partly consists of haze and aerosol particles which during the last 4.5 gigayears have been processed by electric discharges, ions, and ionizing photons, being slowly deposited over the Titan surface. In this work, we investigate the possible effects produced by soft X-rays (and secondary electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic photochemistry. The experiments have been performed inside a high vacuum chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian Synchrotron Light Source, Campinas, Brazil. In-situ sample analyses were performed by a Fourier transform infrared spectrometer. The infrared spectra have presented several organic molecules, including nitriles and aromatic CN compounds. After the irradiation, the brownish-orange organic residue (tholin) was analyzed ex-situ by gas chromatographic (GC/MS) and nuclear magnetic resonance (1H NMR) techniques, revealing the presence of adenine (C5H5N5), one of the constituents of the DNA molecule. This confirms previous results which showed that the organic chemistry on the Titan surface can be very complex and extremely rich in prebiotic compounds. Molecules like these on the early Earth have found a place to allow life (as we know) to flourish.Comment: To appear in Journal of Physical Chemistry A.; Number of pages: 6; Number of Figures: 5; Number of Tables: 1; Number of references:49; Full paper at http://pubs.acs.org/doi/abs/10.1021/jp902824

    Thermal stability of amorphous sugar matrix, dried from methanol, as an amorphous solid dispersion carrier

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    [EN] Developing a technique to disperse hydrophobic ingredients homogeneously in a water-soluble solid matrix (solid dispersion) is one of the topics that have been extensively investigated in the pharmaceutical and food industries. Recently, we have devised a novel solid dispersion technique (surfactant-free solid dispersion), in which a preliminarily amorphized sugar was dissolved in an organic media containing hydrophobic component, without using any surface active substances, and then vacuum dried into the amorphous solid mixture [Food Chem., 197 (2016) 1136; Mol. Pharm., 14 (2017) 791]. In this study, the physicochemical properties, especially thermal stability of the surfactant-free amorphous solid dispersion, were investigated.Imamura, K.; Takeda, K.; Yamamoto, K.; Imanaka, H.; Ishida, N. (2018). Thermal stability of amorphous sugar matrix, dried from methanol, as an amorphous solid dispersion carrier. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 997-1004. https://doi.org/10.4995/IDS2018.2018.7716OCS997100

    Organic chemistry of NH<sub>3</sub> and HCN induced by an atmospheric abnormal glow discharge in N<sub>2</sub>-CH<sub>4</sub> mixtures

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    The formation of the chemical products produced in an atmospheric glow discharge fed by a N2-CH4 gas mixture has been studied using Fourier Transform InfraRed (FTIR) and Optical Emission Spectrometry (OES). The measurements were carried out in a flowing regime at ambient temperature and pressure with CH4 concentrations ranging from 0.5% to 2%. In the recorded emission spectra the lines of the second positive system CN system and the first negative system of N2 were found to be the most intensive but atomic Hα, Hβ, and C (247 nm) lines were also observed. FTIR-measurements revealed HCN and NH3 to be the major products of the plasma with traces of C2H2. These same molecules have been detected in Titan's atmosphere and the present experiments may provide some novel insights into the chemical and physical mechanisms prevalent in Titan's atmosphere with these smaller species believed to be the precursors of heavier organic species in Titan's atmosphere and on its surface

    Pathological Investigation of Congenital Bicuspid Aortic Valve Stenosis, Compared with Atherosclerotic Tricuspid Aortic Valve Stenosis and Congenital Bicuspid Aortic Valve Regurgitation

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    Congenital bicuspid aortic valve (CBAV) is the main cause of aortic stenosis (AS) in young adults. However, the histopathological features of AS in patients with CBAV have not been fully investigated.We examined specimens of aortic valve leaflets obtained from patients who had undergone aortic valve re/placement at our institution for severe AS with CBAV (n = 24, CBAV-AS group), severe AS with tricuspid aortic valve (n = 24, TAV-AS group), and severe aortic regurgitation (AR) with CBAV (n = 24, CBAV-AR group). We compared the histopathological features among the three groups. Pathological features were classified using semi-quantitative methods (graded on a scale 0 to 3) by experienced pathologists without knowledge of the patients' backgrounds. The severity of inflammation, neovascularization, and calcium and cholesterol deposition did not differ between the CBAV-AS and TAV-AS groups, and these four parameters were less marked in the CBAV-AR group than in the CBAV-AS (all p<0.01). Meanwhile, the grade of valvular fibrosis was greater in the CBAV-AS group, compared with the TAV-AS and CBAV-AR groups (both p<0.01). In AS patients, thickness of fibrotic lesions was greater on the aortic side than on the ventricular side (both p<0.01). Meanwhile, thickness of fibrotic lesions was comparable between the aortic and ventricular sides in CBAV-AR patients (p = 0.35).Valvular fibrosis, especially on the aortic side, was greater in patients with CBAV-AS than in those without, suggesting a difference in the pathogenesis of AS between CBAV and TAV

    Effective weakly supervised semantic frame induction using expression sharing in hierarchical hidden Markov models

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    We present a framework for the induction of semantic frames from utterances in the context of an adaptive command-and-control interface. The system is trained on an individual user's utterances and the corresponding semantic frames representing controls. During training, no prior information on the alignment between utterance segments and frame slots and values is available. In addition, semantic frames in the training data can contain information that is not expressed in the utterances. To tackle this weakly supervised classification task, we propose a framework based on Hidden Markov Models (HMMs). Structural modifications, resulting in a hierarchical HMM, and an extension called expression sharing are introduced to minimize the amount of training time and effort required for the user. The dataset used for the present study is PATCOR, which contains commands uttered in the context of a vocally guided card game, Patience. Experiments were carried out on orthographic and phonetic transcriptions of commands, segmented on different levels of n-gram granularity. The experimental results show positive effects of all the studied system extensions, with some effect differences between the different input representations. Moreover, evaluation experiments on held-out data with the optimal system configuration show that the extended system is able to achieve high accuracies with relatively small amounts of training data

    Biogenesis of mitochondrial porin

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    We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavble lsquosignalrsquo sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein wich is characterized by its extreme protease resistance
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