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321.
Given a potentially bounded signed measure on a Brelot space (X,) with Green function G, it is well known that -harmonic functions (i.e., in the classical case, finely continuous versions of solutions to uu=0) may be very discontinuous. In this paper it is shown that under very general assumptions on G (satisfied for large classes of elliptic second-order linear differential operators) normalized perturbation, however, leads to a Brelot space (X, ) admitting a Green function T (G) which is locally (or even globally) comparable with G and has all properties required of G before. In particular, iterated perturbation is possible. Moreover, intrinsic Hölder continuity of quotients of harmonic functions with respect to the local quasimetric :=(G –1+* G –1)/2 yields -Hölder continuity for quotients of -harmonic functions as well.  相似文献   
322.
An electron-phonon cavity consisting of a quantum dot embedded in a freestanding GaAs/AlGaAs membrane is characterized using Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at discrete magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.  相似文献   
323.
The Kondo effect is investigated in a many-electron quantum ring as a function of the magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground-state spin of the ring. The observed splitting of the Kondo-related zero-bias anomaly in this configuration is tuned with an in-plane magnetic field.  相似文献   
324.
The Aharonov-Bohm effect is measured in a four-terminal open ring geometry. Two quantum dots are embedded in the structure, one in each of the two interfering paths. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots. Although the measured phase shifts are in qualitative agreement with theoretical predictions, the phase evolution exhibits unexpected dependence on the magnetic field. Phase lapses are found only in certain ranges of the magnetic field.  相似文献   
325.
Momentum-resolved magnetotunneling spectroscopy is performed at a single sharp quantum Hall (QH) edge to probe the structure of integer QH edge modes. An epitaxially overgrown cleaved edge is shown to realize the sharp-edge limit with interchannel distances smaller than both the magnetic length and the Bohr radius where the Chklovskii soft-edge picture is no longer valid. The line shape of principal conductance peaks is explained, and an edge filling factor is determined from the peak position. A step in the dispersion is attributed to fluctuations in the QH ground energy.  相似文献   
326.
We report on the dramatic evolution of the quantum Hall ferromagnet in the fractional quantum Hall regime at nu=2/5 filling. A large enhancement in the characteristic time scale gives rise to a dynamical transition into a novel quantized Hall state. The observed Hall state is determined to be a zero-temperature phase distinct from the spin-polarized and spin-unpolarized nu=2/5 fractional quantum Hall states. It is characterized by a strong temperature dependence and puzzling correlation between temperature and time.  相似文献   
327.
Composition of bauxite samples was determined by ICP-AES. Twelve trace and two matrix elements are investigated: Ba, Cr, Cu, La, Mn, Mg, Sr, Ti, V, W, Y, and Zn and Al and Fe, respectively. Three types of evaluation methods are employed and the results compared to each other as well as to the certificates of standard bauxite samples. Of these three methods one is a single-element evaluation, the second is the Kaiman filter technique, and the third is a multivariate calibration method. In terms of a general assessment of the Kaiman filter, it can be observed that in the example given this method is not much better than the single-element method. The Káimán filter accomodates all the points in a spectrum including those with high error. In trace element analysis, however, the Káimán filter performs better and gives more reliable results.  相似文献   
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