9,744 research outputs found
Optimization of the extraordinary magnetoresistance in semiconductor-metal hybrid structures for magnetic-field sensor applications
Semiconductor-metal hybrid structures can exhibit a very large geometrical
magnetoresistance effect, the so-called extraordinary magnetoresistance (EMR)
effect. In this paper, we analyze this effect by means of a model based on the
finite element method and compare our results with experimental data. In
particular, we investigate the important effect of the contact resistance
between the semiconductor and the metal on the EMR effect. Introducing
a realistic in our model we find
that at room temperature this reduces the EMR by 30% if compared to an analysis
where is not considered.Comment: 4 pages; manuscript for MSS11 conference 2003, Nara, Japa
Quasimodularity and large genus limits of Siegel-Veech constants
Quasimodular forms were first studied in the context of counting torus
coverings. Here we show that a weighted version of these coverings with
Siegel-Veech weights also provides quasimodular forms. We apply this to prove
conjectures of Eskin and Zorich on the large genus limits of Masur-Veech
volumes and of Siegel-Veech constants.
In Part I we connect the geometric definition of Siegel-Veech constants both
with a combinatorial counting problem and with intersection numbers on Hurwitz
spaces. We introduce modified Siegel-Veech weights whose generating functions
will later be shown to be quasimodular.
Parts II and III are devoted to the study of the quasimodularity of the
generating functions arising from weighted counting of torus coverings. The
starting point is the theorem of Bloch and Okounkov saying that q-brackets of
shifted symmetric functions are quasimodular forms. In Part II we give an
expression for their growth polynomials in terms of Gaussian integrals and use
this to obtain a closed formula for the generating series of cumulants that is
the basis for studying large genus asymptotics. In Part III we show that the
even hook-length moments of partitions are shifted symmetric polynomials and
prove a formula for the q-bracket of the product of such a hook-length moment
with an arbitrary shifted symmetric polynomial. This formula proves
quasimodularity also for the (-2)-nd hook-length moments by extrapolation, and
implies the quasimodularity of the Siegel-Veech weighted counting functions.
Finally, in Part IV these results are used to give explicit generating
functions for the volumes and Siegel-Veech constants in the case of the
principal stratum of abelian differentials. To apply these exact formulas to
the Eskin-Zorich conjectures we provide a general framework for computing the
asymptotics of rapidly divergent power series.Comment: 107 pages, final version, to appear in J. of the AM
Detection of nanoparticles by means of reflection electron energy loss spectroscopy depth profiling
The various studies of nanoparticles are of great importance because of the wide application of nanotechnology. The shape and structure of the nanoparticles can be determined by transmission electron microscopy (TEM) and their chemistry by electron energy loss spectroscopy. TEM sample preparation is an expensive and difficult procedure, however. Surface sensitive, analytical techniques, such as Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are well applicable to detect the atoms that make up the nanoparticles, but cannot determine whether particle formation occurred. On the other hand, reflection electron energy loss spectroscopy (REELS) probes the electronic structures of atoms, which are strongly different for the atoms being in solution or in precipitated form. If the particle size is in the nm range, plasmon resonance can be excited in it, which appears as a loss feature in REELS spectrum. Thus, by measuring AES (XPS) spectra parallel with those of REELS, besides the atomic concentrations the presence of the nanoparticles can also be identified. As an example, the appearance of nanoparticles during ion beam induced mixing of C/Si layer will be shown
Stabilization of colloidal palladium particles by a block copolymer of polystyrene and a block containing amide sidegroups
A block copolymer of polystyrene and poly(tert-butylmethacrylate) was prepared by anionic polymerization. The ester groups of the poly(tert-butylmethacrylate) were hydrolyzed, after wich the remaining carboxyl groups were reacted with pyrrolidine. The resulting block copolymer with amide sidegroups was used for stabilization of a palladium colloid in toluene
Evaluation of the probing profile of scanning force microscopy tips
It is demonstrated that a high-temperature-treated (305) surface of a SrTiO3 crystal can be used to evaluate the probing profile of AFM tips routinely, to provide a means of selecting perfect tips and to evaluate possible image distortions. This is important in order to recognize typical AFM artifacts which are caused by tips with truncated or twinned peaks which occur rather often in the case of microfabricated AFM needles. By means of selected needles, it is shown that also defective tips can give apparently rather perfect atomic resolution from flat crystal surfaces. Scope and limitations of the resolution of structural defects are discussed as the criterion for real atomic resolution
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