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72.
Room‐temperature terahertz emission from ZnSe‐based quantum cascade structures: A simulation study 下载免费PDF全文
We identified conditions for room‐temperature operation of terahertz quantum cascade lasers (THz QCLs) where variable barrier heights are used on ZnSe/Zn1–xMgx Se material systems. The THz QCL devices are based on three‐level two‐well design schemes. The THz QCL lasers with alternating quantum barriers with different heights were compared with THz QCL laser structures with fixed quantum barrier heights. It is found that the THz QCL device with novel design employing variable barrier heights achieved the terahertz emission of about 1.45 THz at room‐temperature (300 K), and has improved laser performance due to the suppression of thermally activated carrier leakage via higher‐energy parasitic levels. Thus, THz QCL devices employing the design with variable barrier heights may lead to future improvements of the operating temperature and performance of THz QCL lasers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
73.
An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows. 相似文献
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Nataliya F. Lazareva Tamara I. Vakul'skaya Alexander I. Albanov Vadim A. Pestunovich 《应用有机金属化学》2006,20(10):696-705
The introduction of the organosilicon substituent into the α‐position of an amino group results in cardinal change of the amine reactivity irrespective of the coordination state of silicon. Amines R2NCH2SiX3 [R = Me, Et, PhCH2, CH2SiX3; SiX3 = SiMe3, Si(OEt)3, Si(OCH2CH2)3N] easily react with AgNO3, to give the corresponding ammonium salts (R2NH+ CH2SiX3)·NO3?. At the same time, Ag(I) is reduced to Ag(0). The interaction of N‐methyl‐N,N‐bis(silatranylmethyl)amine with AgNO3 has been investigated by EPR spectroscopy. It was proven that the reaction involved a single electron transfer stage with the formation of cation radical of this amine. A mechanism of the reaction is proposed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
76.
Quantum Bayesian computation is an emerging field that levers the computational gains available from quantum computers. They promise to provide an exponential speed-up in Bayesian computation. Our article adds to the literature in three ways. First, we describe how quantum von Neumann measurement provides quantum versions of popular machine learning algorithms such as Markov chain Monte Carlo and deep learning that are fundamental to Bayesian learning. Second, we describe quantum data encoding methods needed to implement quantum machine learning including the counterparts to traditional feature extraction and kernel embeddings methods. Third, we show how quantum algorithms naturally calculate Bayesian quantities of interest such as posterior distributions and marginal likelihoods. Our goal then is to show how quantum algorithms solve statistical machine learning problems. On the theoretical side, we provide quantum versions of high dimensional regression, Gaussian processes and stochastic gradient descent. On the empirical side, we apply a quantum FFT algorithm to Chicago house price data. Finally, we conclude with directions for future research. 相似文献
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Vadim Mogilevskii 《Journal of Functional Analysis》2011,261(7):1955-1968
Let H be a Hilbert space and let A be a simple symmetric operator in H with equal deficiency indices d:=n±(A)<∞. We show that if, for all λ in an open interval I⊂R, the dimension of defect subspaces Nλ(A) (=Ker(A?−λ)) coincides with d, then every self-adjoint extension has no continuous spectrum in I and the point spectrum of is nowhere dense in I. Application of this statement to differential operators makes it possible to generalize the known results by Weidmann to the case of an ordinary differential expression with both singular endpoints and arbitrary equal deficiency indices of the minimal operator. 相似文献
80.
In this paper, we present new upper bounds for the global domination and Roman domination numbers and also prove that these
results are asymptotically best possible. Moreover, we give upper bounds for the restrained domination and total restrained
domination numbers for large classes of graphs, and show that, for almost all graphs, the restrained domination number is
equal to the domination number, and the total restrained domination number is equal to the total domination number. A number
of open problems are posed. 相似文献