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31.
M. Geller C. Kapteyn E. Stock L. Müller-Kirsch R. Heitz D. Bimberg 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):474
The hole confinement in type-II self-organized GaSb/GaAs quantum dots (QDs) was investigated by combining optical excitation and time-resolved capacitance spectroscopy. The experimental results indicate energy-selective charging even for type-II QDs. With increasing excitation energy the apparent hole activation energy decreases, which is attributed to light absorption in sub-ensembles of QDs with decreasing hole localization. The large localization energy of about 450 meV and the possibility of optical-multiplexing makes type-II GaSb/GaAs QDs a potential material system for QD memory concepts. 相似文献
32.
Accurate measurement of sputtered depth for ion sputtering rates and yields: the mesh replica method
For the accurate measurements of crater depths, ion sputtering rates and ion sputtering yields in studies of sputter‐depth profiling using Auger electron spectroscopy (AES) or X‐ray photoelectron spectroscopy (XPS), a proposed mesh replica method has been evaluated. In this method, during ion sputtering, grids of between 50 and 400 mesh (per inch) are placed on the sample to retain unsputtered regions of the original surface to be used as reference. This enables a more accurate measurement of the depth to be made using a stylus profilometer close to the analytical region. The closer‐pitch meshes were thought to offer the prospect of measurements of higher accuracy. Calculations show that sputter deposits from the mesh sides may limit the mesh numbers used to 100 or those of a wider pitch for both stationary and rotated samples. A correlation with published data for stationary samples and new data for rotated samples confirms the calculations. In practice, it is difficult, without a special holder, to have intimate contact between the grid and sample. Such a holder is described. Further calculations concerning the shadowed profiles at the grid bar regions show that the grids may lift off the sample surface by 4–16 µm. This leads to non‐vertical crater walls in each mesh aperture. This effect, however, does not change the above conclusion on the mesh sizes to be used. In this range, the spurious appearance of Auger electrons emitted from the grid material is calculated to be less than 1%. This conclusion applies to the meshes evaluated here, which range in thickness from 13 to 29 µm. Thinner meshes may lead to the applicability of proportionately closer meshed grids in sputter‐profiling applications. Copyright © 2006 John Wiley & Sons, Ltd. The contribution of Martin P. Seah of the National Physical Laboratory is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland. 相似文献
33.
First- and second-order perturbation theory in a polarization approximation was employed to calculate interaction energies of planar xanthine–xanthine pairs in stable configurations. Electrostatic energy was obtained in the atomic-dipole approximation. The results provided a basis for formulation of a four-stranded model of poly(xanthylic acid) that allows two hydrogen bonds per base. The model accounts satisfactorily for the unusual thermal stability and the observed pH transition of the polymer. The latter is due to the gradual dissociation of the N3 protons accompanying by disrupture of the weak N3? H ··· O6 hydrogen bonds. However, the structure is only moderately weakened since the configuration of the coplanar bases remains stabilized by four N1? H ··· O2 hydrogen bonds. 相似文献
34.
35.
Bay S. Herzet C. Brossier J.-M. Barbot J.-P. Geller B. 《Signal Processing, IEEE Transactions on》2008,56(1):61-70
In this paper, we present a closed-form expression of a Bayesian Cramer-Rao lower bound for the estimation of a dynamical phase offset in a non-data-aided BPSK transmitting context. This kind of bound is derived considering two different scenarios: a first expression is obtained in an offline context, and then a second expression in an online context logically follows. The SNR-asymptotic expressions of this bound drive us to introduce a new asymptotic bound, namely the asymptotic Bayesian Cramer-Rao Bound. This bound is close to the classical Bayesian bound but is easier to evaluate. 相似文献
36.
Let G be a stratified Lie group and L be the sub-Laplacian on G. Let
We show that Lf(L)δ, the distribution kernel of the operator Lf(L), is an admissible function on G. It is always in the Schwartz
space; one can choose f so that it has all moments vanishing, or has compact support with arbitrarily many moments vanishing.
We also show that, if ξ f(ξ) satisfies Daubechies' criterion, then L f(L)δ generates a frame for any sufficiently fine latticesubgroup
of G. Moreover, we show that the ratio of the frame bounds approaches 1 nearly quadratically as the dilation parameter approaches
1, so that the frame quickly becomes nearly tight (again assuming that the lattice subgroup is sufficiently fine). In particular,
if the dilation parameter is 21/3, and the lattice subgroup is sufficiently fine, then the "Mexican hat" wavelet, Le-L/2δ, generates a wavelet frame, for which the ratio of the optimal frame bounds is 1.0000 to four significant digits. 相似文献
37.
In recent years, a rapidly growing literature has focussed on the construction of wavelet systems to analyze functions defined
on the sphere. Our purpose in this paper is to generalize these constructions to situations where sections of line bundles,
rather than ordinary scalar-valued functions, are considered. In particular, we propose needlet-type spin wavelets as an extension of the needlet approach recently introduced by Narcowich et al. in SIAM J. Math. Anal. 38, 574–594 (2006) and J. Funct. Anal. 238, 530–564 (2006) and then considered for more general manifolds by Geller and Mayeli in Math. Z. 262, 895–927 (2009), Math. Z. 263, 235–264 (2009), and Indiana Univ. Math. J. (2009). We discuss localization properties in the real and harmonic domains, and investigate stochastic properties for the analysis
of spin random fields. Our results are strongly motivated by cosmological applications, in particular in connection to the
analysis of Cosmic Microwave Background polarization data. 相似文献
38.
Jordan Geller Ivor Wharf Francine Blanger‐Garipy Anne‐Marie Lebuis Ian S. Butler Denis F. R. Gilson 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):m466-m468
Chlorotris(2,4,6‐trimethylphenyl)tin(IV), crystallizes from ethanol as solvent‐free needles, [Sn(C9H11)3Cl], (I), and as the hemisolvate, [Sn(C9H11)3Cl]·0.5C2H6O, (II). The asymmetric unit in (I) has three independent molecules, whereas in (II), there are two [Sn(C9H11)3Cl] molecules together with one ethanol molecule. In the unit cell of (II), the ethanol molecules lie in channels between stacks of (Mes)3SnCl molecules (Mes is 2,4,6‐trimethylphenyl) and each ethanol molecule is disordered (0.50:0.50) over two positions. A comparison of the structures of the title compounds and other (Mes)3SnX (X = F, Br or I) systems with those of the triphenyltin analogues shows that the steric requirements of the o‐CH3 groups are met by a flattening of the SnC3 skeleton and increases in the average Sn—X and Sn—C values. Comparing Sn—X data for (Mes)3SnX (X = F, Cl, Br or I) systems with values for the tris(o‐methoxyphenyl)tin analogues suggests that the Sn—F distance of 1.961 Å in (Mes)3SnF may well be characteristic of sterically unhindered four‐coordinate Ar3SnF systems. 相似文献
39.
40.
Yu. I. Geller D. E. Sovkov A. T. Hakim’yanov A. V. Sharypov 《Russian Physics Journal》2007,50(3):259-266
The influence of heat motion of atoms in gaseous media on the features of manifestation of electromagnetically induced transparency
is investigated. Taking into account elastic and inelastic collisions, fairly general and compact analytical relations are
derived for the absorption and refraction coefficients of the probe wave in the presence of high-power inducing radiation,
resonant to the adjacent atomic transition. It is shown, that occurrence of narrow resonance structures in the Doppler absorption
and refraction profile is due to “overlap” of effective resonance velocities of atoms. The atomic level splitting in the strong
wave field is uniformly analyzed in the entire intensity range. Interference transparency in a particular region of the Doppler
profile is found to be accompanied by high resonance dispersion of the refraction coefficient, which is important for generating
slow radiation and controlling its parameters.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 56–62, March, 2007. 相似文献