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961.
C. Janke R. Jones S. Öberg P. R. Briddon 《Journal of Materials Science: Materials in Electronics》2007,18(7):775-780
Boron is observed to diffuse very slowly in germanium, as opposed to its behaviour in silicon where it exhibits Transient
Enhanced Diffusion effects in implanted samples. As a result of this slow diffusion, boron is a very stable dopant, allowing
devices to be created with very well-defined doping regions. To understand this superior performance, calculations were performed
on a variety of boron diffusion paths, within vacancy and interstitial mediated methods. It was found that the vacancy mediated
diffusion which is associated with the fast diffusion of many other species in germanium exhibits a total barrier of 5.8 eV.
Interstitial-mediated diffusion had a total barrier for migration of 3.4 eV in the neutral and singly negative charge states,
3.2 eV for the positive charge state, but a formation barrier of 4.1 eV. Thus the barrier for interstitial-mediated diffusion
is dominated by the formation energy of the self-interstitial. 相似文献
962.
Trust on a Nationwide Scale 总被引:1,自引:0,他引:1
Singapore is a small island nation with roughly 4.5 million inhabitants, but it has a highly developed international economy based on trade, services, and knowledge management. Singapore launched its lofty goals by defining the nationpsilas e-security. Current research in the Singaporean telecommunications and IT security community attempts to model such peer-to-peer ad hoc transactions and leverage the existing standard infrastructure described in this article. 相似文献
963.
Discussed in this paper is the Cartesian stiffness matrix, which recently has received special attention within the robotics
research community. Stiffness is a fundamental concept in mechanics; its representation in mechanical systems whose potential
energy is describable by a finite set of generalized coordinates takes the form of a square matrix that is known to be, moreover,
symmetric and positive-definite or, at least, semi-definite. We attempt to elucidate in this paper the notion of “asymmetric
stiffness matrices”. In doing so, we show that to qualify for a stiffness matrix, the matrix should be symmetric and either
positive semi-definite or positive-definite. We derive the conditions under which a matrix mapping small-amplitude displacement
screws into elastic wrenches fails to be symmetric. From the discussion, it should be apparent that the asymmetric matrix
thus derived cannot be, properly speaking, a stiffness matrix. The concept is illustrated with an example. 相似文献
964.
Modeling mechatronic multibody systems requires the same type of methodology as for designing and prototyping mechatronic
devices: a unified and integrated engineering approach. Various formulations are currently proposed to deal with multiphysics
modeling, e.g., graph theories, equational approaches, co-simulation techniques. Recent works have pointed out their relative
advantages and drawbacks, depending on the application to deal with: model size, model complexity, degree of coupling, frequency
range, etc. This paper is the result of a close collaboration between three laboratories, and aims at showing that for “non-academic”
mechatronic applications (i.e., issuing from real industrial issues), multibody dynamics formulations can be generalized to
mechatronic systems, for the model generation as well as for the numerical analysis phases. Model portability being also an
important aspect of the work, they must be easily interfaced with control design and optimization programs. A global “demonstrator”,
based on an industrial case, is discussed: multiphysics modeling and mathematical optimization are carried out to illustrate
the consistency and the efficiency of the proposed approaches. 相似文献
965.
In this report, we describe the nature of intermediate order in silicon as determined by recent measurements on thin films using transmission electron microscopy (TEM) and Raman scattering. The TEM images show in addition to the expected continuous random network (CRN), the presence of highly ordered quasi-one-dimensional “chain-like objects” (CLO's) that are 1–2 nm wide and tens of nm long that meander and show some evidence of cross-linking with each other. The presence of these objects correlate to a Raman feature centered at 490 cm−1 whose width is 35–40 cm−1, and is used to quantify the heterogeneity in terms of the CLO and CRN (=475 cm−1 scattering) concentrations. The 490 and 35 cm−1 values are consistent with bond angle deviations approaching 0°, and thus reinforces an association with the CLOs. We find that in reference quality a-Si:H (made using pure SiH4), the CLO concentration is about 5 vol%, while in state-of-the-art material using high H2 levels of dilution during processing, it increases to about 15%. Increased stability of such material to light-soaking is thus not mediated by a direct volumetric replacement of poor with high-quality components. Rather, an important characteristic of intermediate order in silicon is the low-dimensional aspect of its order, which allows it to influence more total volume than which it is itself composed. Consistent with these and other recent findings, we propose a tensegrity model of amorphous silicon. 相似文献
966.
E. M. Gavrishchuk E. Yu. Vilkova O. V. Timofeev U. P. Borovskikh E. L. Tikhonova 《Inorganic Materials》2007,43(6):579-583
Chemical interaction between polished surfaces of polycrystalline zinc selenide and inorganic acid solutions of various concentrations has been studied. 相似文献
967.
V. V. Ustinov A. B. Rinkevich L. N. Romashev E. A. Kuznetsov 《Technical Physics Letters》2007,33(9):771-774
The reflection of electromagnetic waves in the millimeter wave band from Fe/Cr nanostructures has been studied. It is established that the giant magnetoresistance (GMR) in the nanostructure leads to an increase in the reflection and a decrease in the transmission of microwaves, while the magnetic resonance leads to a decrease in both the reflection and transmission coefficients. 相似文献
968.
I. V. Oryshich N. E. Poryadchenko N. P. Brodnikovskii 《Powder Metallurgy and Metal Ceramics》2004,43(9-10):497-503
We have studied the oxidation resistance of chromium intermetallics: TiCr2, HfCr2, and ZrCr2, in the temperature interval 873–1473 K with isothermal holding of the specimens for up to 20 h. We have shown that the intermetallics TiCr2 and HfCr2 are oxidized 2–3 times more slowly than pure titanium and hafnium, but more than 1–2 orders of magnitude faster than chromium at T≤1273 K and 4–6 times faster at 1473 K. In this temperature interval, the intermetallic ZrCr2 is rapidly oxidized at an increasing rate as the heating temperature rises. The scaling resistance of intermetallics of Group IV d metals with chromium is determined by formation of scales in which the major role is played by the oxides TiO2, HfO2, and ZrO2, with weak protective properties. 相似文献
969.
V. P. Efimov 《Journal of Mining Science》2003,39(4):384-386
The procedure is proposed for estimating the crack resistance and tensile strength of rocks by the results of experiments on disk samples with holes. The gradient approach to the strength problem is employed in processing the experimental data. 相似文献
970.
The results of a comparative numerical investigation of three types of resonator systems of a cyclotron for acceleration of negative hydrogen and deuterium ions up to maximum energy 30 and 15 MeV, respectively, are presented. It is shown that a vertical system with two half-wave resonators excited in-phase has the smallest active losses and the smallest differential of the amplitude of the accelerating voltage along the edge of the dees and is effective for accelerating particles at dual working frequencies. 相似文献