227 research outputs found

    Accurate first principles detailed balance determination of Auger recombination and impact ionization rates in semiconductors

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    The technologically important problem of predicting Auger recombination lifetimes in semiconductors is addressed by means of a fully first--principles formalism. The calculations employ highly precise energy bands and wave functions provided by the full--potential linearized augmented plane wave (FLAPW) code based on the screened exchange local density approximation. The minority carrier Auger lifetime is determined by two closely related approaches: \emph{i}) a direct evaluation of the Auger rates within Fermi's Golden Rule, and \emph{ii}) an indirect evaluation, based on a detailed balance formulation combining Auger recombination and its inverse process, impact ionization, in a unified framework. Calculated carrier lifetimes determined with the direct and indirect methods show excellent consistency \emph{i}) between them for nn-doped GaAs and \emph{ii}%) with measured values for GaAs and InGaAs. This demonstrates the validity and accuracy of the computational formalism for the Auger lifetime and indicates a new sensitive tool for possible use in materials performance optimization.Comment: Phys. Rev. Lett. accepte

    Impact Ionization in ZnS

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    The impact ionization rate and its orientation dependence in k space is calculated for ZnS. The numerical results indicate a strong correlation to the band structure. The use of a q-dependent screening function for the Coulomb interaction between conduction and valence electrons is found to be essential. A simple fit formula is presented for easy calculation of the energy dependent transition rate.Comment: 9 pages LaTeX file, 3 EPS-figures (use psfig.sty), accepted for publication in PRB as brief Report (LaTeX source replaces raw-postscript file

    A novel, aerosol-nanocrystal floating-gate device for non-volatile memory applications

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    This paper describes the fabrication, and structural and electrical characterization of a new, aerosol-nanocrystal floating-gate FET, aimed at non-volatile memory (NVM) applications. This aerosol-nanocrystal NVM device features program/erase characteristics comparable to conventional stacked gate NVM devices, excellent endurance (>l0^5 P/E cycles), and long-term non-volatility in spite of a thin bottom oxide (55-60Å). In addition, a very simple fabrication process makes this aerosol-nanocrystal NVM device a potential candidate for low cost NVM applications

    Sugar metabolism in expanding husk leaves of flint corn (Zea mays L.) genotypes differing in husk leaf size

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    Relationships between leaf expansion and MeOH-soluble (cytosol) and cell-wall fractions, and their sugar composition prior to silking in flint corn lines were studied. A greater husk leaf area of one genotype, X-15 is mainly due to prolonged and higher rate of expansion. Prior to rapid expansion of husk leaf area, neutral sugars in the cytosol fraction accounted for most of the non-starch carbohydrates (56-62%), while hemicellulose and cellulose fractions accounted for less than 20%.0 In mature leaf parts, however, sugars in the cytosol fraction decreased but those in hemicellulose and cellulose fractions increased by 30 0x1.e499cp-891nd 42%, respectively. The predominant sugar in the cytosol fraction was glucose (Glc), while in the hemicellulose fraction xylose (Xyl) and arabinose (Ara) dominated. During rapid expansion of husk leaves, 13C was incorporated at a higher rate into hemicellulose than cellulose, and this process was more active in X-15 than in other genotypes. During an identical period, 13C atom 0.000000e+00xcess in Xyl increased markedly in the hemicellulose fraction, however it remained low in the cytosol one. The current results suggest that synthesis of Xyl and xylan plays an important role in renewal of hemicellulose, which may be required for expansion

    Der diskrete Charme der Bourgeoisie - Ein Beitrag zur Soziologie des modernen WirtschaftsbĂŒrgertums

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    Entgegen der These der Auflösungserscheinungen des BĂŒrgertums stellt der Autor die Annahme auf den PrĂŒfstand, dass wir es nach wie vor mit gesellschaftlichen Fraktionierungen bĂŒrgerlicher Lebensweisen zu tun haben. Am Beispiel autobiographischer Schriften von deutschen Topmanagern stellt der Text ein modernes VerstĂ€ndnis des WirtschaftsbĂŒrgertums vor, das organisational (durch die Karrieremechanismen der Organisation) und institutionell (im Feld der Wirtschaft) verankert ist. Die moderne Sozialformation des WirtschaftsbĂŒrgertums ist nur noch auf der Grundlage von Organisationen denkbar. Sie lĂ€sst sich, jenseits von Klasse und Stand, als Positionselite beschreiben. Anhand der Autobiographien lĂ€sst sich die Reproduktion dieser Elite auf Basis einer engen VerknĂŒpfung zwischen familialer Herkunft, an organisationale Karrieren gebundene Leistungsbereitschaft und hoher formaler Bildung nachzeichnen. Die Abgrenzung in der Statusreproduktion zwischen Bildungs- und WirtschaftsbĂŒrgertum weist der Autor am jeweiligen VerhĂ€ltnis zur Bildung nach; zwar können beide einen hohen Bildungsgrad in Form von Bildungspatenten nachweisen, doch im Falle des WirtschaftsbĂŒrgertums herrscht ein instrumentelles VerhĂ€ltnis zur Bildung vor. Der hohe Bildungsgrad folgt hier dem BedĂŒrfnis, den Status mittels formaler Bildung abzusichern und damit die Gefahr der eigenen Austauschbarkeit - als Personal der Organisation - zu kompensieren. Der Text macht außerdem generationale Effekte sichtbar; insbesondere indem er darlegt, inwieweit der "moderne Manager" einerseits in der Betonung seines Status seinen VorgĂ€ngern gleicht und sich doch gleichzeitig in der Art der UnternehmensfĂŒhrung abgrenzt - indem er bspw. die Managementkonzepte seiner Zeit aufgreift

    Digitalisierte Beratung zur effizienteren Selbstoptimierung: Kritische Anmerkungen zu digitalen Formaten arbeitsbezogener Beratung aus einer GouvernementalitÀtsperspektive

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    "Digital(isiert)e" Beratung verspricht neben Innovation auch FlexibilitĂ€t, UbiquitĂ€t, GlobalitĂ€t, Geschwindigkeit und LegitimitĂ€t durch evidenzbasierte Wirksamkeit. FĂŒr eine sozialwissenschaftlich fundierte arbeitsweltliche Beratung wie Coaching und Supervision ist danach zu fragen, welches Menschen- und Weltbild sich hinter der Digitalisierung verbirgt und welche Anliegen sie transportiert. Dazu wird mit den Theorien Michel Foucaults der gegenwĂ€rtige Diskurs auf Steuerungslogiken und MachtverhĂ€ltnisse hin kritisch analysiert. Dabei zeigt sich, dass die Digitalisierung das "Zeitalter der GouvernementalitĂ€t" (Foucault) festigt: Humanistisch geprĂ€gte Werte und Ziele wie Reflexion, Anerkennung und Selbsterkenntnis treten in den Hintergrund, wĂ€hrend die Nutzbarmachung und Optimierung des Selbst sowie des Beratungsprozesses wichtiger werden: Beratung will und muss effizienzgetrieben ihre Wirksamkeit evidenzbasiert legitimieren, und Digitalisierung erleichtert dies

    Increased ion temperature and neutron yield observed in magnetized indirectly driven D_{2}-filled capsule implosions on the national ignition facility

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    The application of an external 26 Tesla axial magnetic field to a D_{2} gas-filled capsule indirectly driven on the National Ignition Facility is observed to increase the ion temperature by 40% and the neutron yield by a factor of 3.2 in a hot spot with areal density and temperature approaching what is required for fusion ignition [1]. The improvements are determined from energy spectral measurements of the 2.45 MeV neutrons from the D(d,n)^{3}He reaction, and the compressed central core B field is estimated to be ∌4.9  kT using the 14.1 MeV secondary neutrons from the D(T,n)^{4}He reactions. The experiments use a 30 kV pulsed-power system to deliver a ∌3  Όs current pulse to a solenoidal coil wrapped around a novel high-electrical-resistivity AuTa_{4} hohlraum. Radiation magnetohydrodynamic simulations are consistent with the experiment

    2022 Review of Data-Driven Plasma Science

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    Data-driven science and technology offer transformative tools and methods to science. This review article highlights the latest development and progress in the interdisciplinary field of data-driven plasma science (DDPS), i.e., plasma science whose progress is driven strongly by data and data analyses. Plasma is considered to be the most ubiquitous form of observable matter in the universe. Data associated with plasmas can, therefore, cover extremely large spatial and temporal scales, and often provide essential information for other scientific disciplines. Thanks to the latest technological developments, plasma experiments, observations, and computation now produce a large amount of data that can no longer be analyzed or interpreted manually. This trend now necessitates a highly sophisticated use of high-performance computers for data analyses, making artificial intelligence and machine learning vital components of DDPS. This article contains seven primary sections, in addition to the introduction and summary. Following an overview of fundamental data-driven science, five other sections cover widely studied topics of plasma science and technologies, i.e., basic plasma physics and laboratory experiments, magnetic confinement fusion, inertial confinement fusion and high-energy-density physics, space and astronomical plasmas, and plasma technologies for industrial and other applications. The final section before the summary discusses plasma-related databases that could significantly contribute to DDPS. Each primary section starts with a brief introduction to the topic, discusses the state-of-the-art developments in the use of data and/or data-scientific approaches, and presents the summary and outlook. Despite the recent impressive signs of progress, the DDPS is still in its infancy. This article attempts to offer a broad perspective on the development of this field and identify where further innovations are required
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