83 research outputs found

    Band Edge Localization Beyond Regular Floquet Eigenvalues

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    We prove that localization near band edges of multi-dimensional ergodic random Schr\"odinger operators with periodic background potential in L2(Rd)L^2(\mathbb{R}^d) is universal. By this we mean that localization in its strongest dynamical form holds without extra assumptions on the random variables and independently of regularity or degeneracy of the Floquet eigenvalues of the background operator. The main novelty is an initial scale estimate the proof of which avoids Floquet theory altogether and uses instead an interplay between quantitative unique continuation and large deviation estimates. Furthermore, our reasoning is sufficiently flexible to prove this initial scale estimate in a non-ergodic setting, which promises to be an ingredient for understanding band edge localization also in these situations.Comment: 13 pages; now the stronger dynamical localization in the short range case is formulated, a few references have beed added, minor editorial change

    A 3D radiative transfer framework: VII. Arbitrary velocity fields in the Eulerian frame

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    A solution of the radiative-transfer problem in 3D with arbitrary velocity fields in the Eulerian frame is presented. The method is implemented in our 3D radiative transfer framework and used in the PHOENIX/3D code. It is tested by comparison to our well- tested 1D co-moving frame radiative transfer code, where the treatment of a monotonic velocity field is implemented in the Lagrangian frame. The Eulerian formulation does not need much additional memory and is useable on state-of-the-art computers, even large-scale applications with 1000's of wavelength points are feasible

    Protecting points from operator pencils

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    We classify all sets of the form ⋃t∈Rspec(A+tB)\bigcup_{t\in\mathbb{R}}\mathrm{spec}(A+tB) where AA and BB are self-adjoint operators and BB is bounded, non-negative, and non-zero. We show that these sets are exactly the complements of discrete subsets of R\mathbb{R}, that is, of at most countable subsets of R\mathbb{R} that contain none of their accumulation points.Comment: 6 pages; a counterexample for sign-indefinite perturbations and some references have been added, some editorial change

    Polarity in GaN and ZnO: Theory, measurement, growth, and devices

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    This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade

    Discovery of Yttrium, Zirconium, Niobium, Technetium, and Ruthenium Isotopes

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    Currently, thirty-four yttrium, thirty-five zirconium, thirty-four niobium, thirty-five technetium, and thirty-eight ruthenium isotopes have been observed and the discovery of these isotopes is discussed here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented.Comment: To be published in Atomic Data and Nuclear Data Table

    Role of supplemental foods and habitat structural complexity in persistence and coexistence of generalist predatory mites

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    Variation in the strength of intraguild predation (IGP) may be related to habitat structural complexity and to additional resources outside the narrow predator-prey relationship. We studied the food web interactions on grape, which involves two generalist predatory mites. We evaluated the effects of grape powdery mildew (GPM) as supplemental food, and habitat structural complexity provided by domatia. Our findings suggest that structural and nutritional diversity/complexity promote predatory mite abundance and can help to maintain the beneficial mites - plants association. The effect of these factors on coexistence between predators is influenced by the supplemental food quality and relative differences in body size of interacting species

    A versatile and cryogenic mHEMT-model including noise

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    A versatile scalable small signal model for high electron mobility transistors (HEMTs) of gate length 50 nm and 100 nm has been developed. The model covers a large bias range and includes the temperature dependence from 300 K to 15 K. Especially, it is capable to predict the noise behaviour of the transistor in dependence of ambient temperature and frequency

    A PLL-stabilized W-band MHEMT push-push VCO with integrated frequency divider circuit

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    In this paper, a PLL-based stabilization technique for monolithic integrated W-band voltage controlled oscillators (VCOs) is presented. A 92 GHz push-push oscillator in coplanar waveguide technology and a frequency divider by eight were developed and integrated on a single MMIC using our established 100 nm metamorphic HEMT technology. The oscillator achieves a tuning range of 3.4 GHz around the center frequency of 92 GHz and an output power of more than 5.5 dBm. By applying this concept, the VCO was synchronized to a low frequency reference signal at 180 MHz using a commercially available PLL circuit. Compared to the free running oscillator, the phase-noise was improved by 24 dB to 77 dBc/Hz at 100 kHz offset from the carrier

    20 nm metamorphic HEMT technology for terahertz monolithic integrated circuits

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    A metamorphic high electron mobility transistor (mHEMT) technology with 20 nm gate length for manufacturing of terahertz monolithic integrated circuits (TMICs) is presented. The passive elements include up to four interconnection metallization layers separated by low-k dielectrics (BCB), SiN and air which can be used to realize front side signal lines. Shielding the substrate from the electromagnetic field on the wafer front side eliminates the need of a costly back side process including wafer thinning, through substrate via etching and back side metallization. The semiconductor heterostructure of the mHEMT comprises a strained pure InAs channel with high electron mobility and high electron density for proper device scaling. The realized mHEMTs achieve a source resistance r(s) of 0.12 (omega)mm which is required to minimize resistive losses in combination with an extrinsic maximum transconductance g(m max) of 2850 mS/mm. Elaborated on wafer calibration procedures and optimized test transistor layouts were used to improve the precision of the S-parameter measurements up to a frequency of 450 GHz which than could be used for model extraction. The presented 20 nm mHEMT technology was employed for the design of a compact eight stage low-noise amplifier (LNA) using miniaturized microstrip lines on BCB. The measured small signal gain of the LNA exceeds 15 dB from 500 - 635 GHz
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