2,790 research outputs found
Observation of the Kohn anomaly near the K point of bilayer graphene
The dispersion of electrons and phonons near the K point of bilayer graphene
was investigated in a resonant Raman study using different laser excitation
energies in the near infrared and visible range. The electronic structure was
analyzed within the tight-binding approximation, and the
Slonczewski-Weiss-McClure (SWM) parameters were obtained from the analysis of
the dispersive behavior of the Raman features. A softening of the phonon
branches was observed near the K point, and results evidence the Kohn anomaly
and the importance of considering electron-phonon and electron-electron
interactions to correctly describe the phonon dispersion in graphene systems.Comment: 4 pages, 4 figure
On the speed of convergence to stationarity of the Erlang loss system
We consider the Erlang loss system, characterized by servers, Poisson arrivals and exponential service times, and allow the arrival rate to be a function of We discuss representations and bounds for the rate of convergence to stationarity of the number of customers in the system, and display some bounds for the total variation distance between the time-dependent and stationary distributions. We also pay attention to time-dependent rates
Helicobacter Genotyping and Detection in Peroperative Lavage Fluid in Patients with Perforated Peptic Ulcer
Introduction and Objectives Certain Helicobacter pylori genotypes are associated with peptic ulcer disease; however, little is known about associations between the H. pylori genotype and perforated peptic ulcer (PPU). The primary aim of this study was to evaluate which genotypes are present in patients with PPU and which genotype is dominant in this population. The secondary aim was to study the possibility of determining the H. pylori status in a way other than by biopsy.
Materials and Methods Serum samples, gastric tissue biopsies, lavage fluid, and fluid from the nasogastric tube were collec
Design and characterization of dielectric filled TM microwave cavities for ultrafast electron microscopy
Microwave cavities oscillating in the TM mode can be used as dynamic
electron-optical elements inside an electron microscope. By filling the cavity
with a dielectric material it becomes more compact and power efficient,
facilitating the implementation in an electron microscope. However, the
incorporation of the dielectric material makes the manufacturing process more
difficult. Presented here are the steps taken to characterize the dielectric
material, and to reproducibly fabricate dielectric filled cavities. Also
presented are two versions with improved capabilities. The first, called a
dual-mode cavity, is designed to support two modes simultaneously. The second
has been optimized for low power consumption. With this optimized cavity a
magnetic field strength of 2.84 0.07 mT was generated at an input power
of 14.2 0.2 W. Due to the low input powers and small dimensions, these
dielectric cavities are ideal as electron-optical elements for electron
microscopy setups
Technological and Disruptive Innovations in a Nation\u27s Industrialization and Leadership Development
The turn of this new century has been witnessing the effort of various leading developed and developing countries in their attempt to materialize next round of industrialization by emphasizing on innovations. To potentially provide guidance to such national efforts, this paper explores the relationship between technological innovation and industrialization and the importance of disruptive innovation in the development of a nation\u27s international leadership. By employing the rigor of game theory, this work first looks at key conditions under which an established market invites competition and innovation. On top of such generally true results, it is consequently shown that technological innovation is a driving force behind industrialization and that disruptive innovation can assist a nation to become an international leader. Other than providing policy recommendations, this paper concludes with open problems for future research
About the computation of the signature of surface singularities z^N+g(x,y)=0
In this article we describe our experiences with a parallel
SINGULAR-implementation of the signature of a surface singularity defined by
z^N+g(x,y)=0.Comment: 6 page
Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers
We investigate the polarization fluctuations caused by quantum noise in
quantum well vertical cavity surface emitting lasers (VCSELs). Langevin
equations are derived on the basis of a generalized rate equation model in
which the influence of competing gain-loss and frequency anisotropies is
included. This reveals how the anisotropies and the quantum well confinement
effects shape the correlations and the magnitude of fluctuations in ellipticity
and in polarization direction. According to our results all parameters used in
the rate equations may be obtained experimentally from precise time resolved
measurements of the intensity and polarization fluctuations in the emitted
laser light. To clarify the effects of anisotropies and of quantum well
confinement on the laser process in VCSELs we therefore propose time resolved
measurements of the polarization fluctuations in the laser light. In
particular, such measurements allow to distinguish the effects of frequency
anisotropy and of gain-loss anisotropy and would provide data on the spin
relaxation rate in the quantum well structure during cw operation as well as
representing a new way of experimentally determinig the linewidth enhancement
factor alpha.Comment: 16 pages and 3 Figures, RevTex, to be published in Phys. Rev.
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