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Search Results: 1 - 10 of 150667 matches for " H. Zimmermann "
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High-End Silicon PDICs
H. Zimmermann
Advances in Radio Science : Kleinheubacher Berichte , 2008,
Abstract: An overview on integrated silicon photodiodes and photodiode integrated circuits (PDICs) or optoelectronic integrated circuits (OEICs) for optical storage systems (OSS) and fiber receivers is given. It is demonstrated, that by using low-cost silicon technologies high-performance OEICs being true competitors for some III/V-semiconductor OEICs can be realized. OSS-OEICs with bandwidths of up to 380 MHz and fiber receivers with maximum data rates of up to 11 Gbps are described. Low-cost data comm receivers for plastic optical fibers (POF) as well as new circuit concepts for OEICs and highly parallel optical receivers are described also in the following.
Funneling with the Two-Beam RFQ
H. Zimmermann
Physics , 2000,
Abstract: New high current accelerator facilities like proposed for HIDIF or ESS require a beam with a high brilliance. These beams can not be produced by a single pass rf-linac. The increase in brightness in such a driver linac is done by several funneling stages at low energies, in which two identically bunched ion beams are combined into a single beam with twice the frequency current and brightness. Our Two-Beam-RFQ funneling experiment is a setup of two ion sources, a two beam RFQ, a funnel deflector and beam diagnostic equipment to demonstrate funneling of ion beams as a model for the first funneling stage of a HIIF driver. The progress of the funneling experiment and results of simulations will be presented.
A 3rd-order current-mode filter in 0.12 μm CMOS
R. Kolm,H. Zimmermann
Advances in Radio Science : Kleinheubacher Berichte , 2008,
Abstract: For software radio applications in system-on-chips, a 3rd-order current-mode Butterworth filter in 120 nm CMOS is realized. This filter is used for reconstruction purposes between a current-steering DAC and a current-mode mixer. Power can be reduced by using a current-mode architecture. The cut-off frequency of this filter is switchable between 1 MHz and 4 MHz, the current consumption is 4.5 mA at VDD=1.5 V, the inband noise density is 100 pA/√Hz and it has a dynamic range up to 65 dB.
Coherent Control for a Two-level System Coupled to Phonons
H. Castella,R. Zimmermann
Physics , 1998, DOI: 10.1103/PhysRevB.59.R7801
Abstract: The interband polarizations induced by two phase-locked pulses in a semiconductor show strong interference effects depending on the time tau_1 separating the pulses. The four-wave mixing signal diffracted from a third pulse delayed by tau is coherently controlled by tuning tau_1. The four-wave mixing response is evaluated exactly for a two-level system coupled to a single LO phonon. In the weak coupling regime it shows oscillations with the phonon frequency which turn into sharp peaks at multiples of the phonon period for a larger coupling strength. Destructive interferences between the two phase-locked pulses produce a splitting of the phonon peaks into a doublet. For fixed tau but varying tau_1 the signal shows rapid oscillations at the interband-transition frequency, whose amplitude exhibits bursts at multiples of the phonon period.
XMM-Newton observation of SN1993J in M81
H. -U. Zimmermann,B. Aschenbach
Physics , 2003, DOI: 10.1051/0004-6361:20030687
Abstract: In April 2001 SN1993J was observed with both the PN and MOS cameras of the XMM-Newton observatory, resulting in about 7. x 10^4 s of acceptable observation time. Fit results with both the PN and MOS2 camera spectra studying different spectral models are presented. The spectra are best fitted in the energy range between 0.3 and 11 keV by a 2-component thermal model with temperatures of kT_1 = 0.34+-0.04 keV and kT_2 = 6.54+-4 keV, adopting ionization equilibrium. A fit with a shock model also provides acceptable results. Combining the XMM-Newton data with former X-ray observations of the supernova, we discuss the general trend of L_x propto t^{-0.30} and the bump of the X-ray light curve as well as former and recent spectral results in the light of the standard SN model as first proposed by Chevalier in 1982.
A low-noise current preamplifier in 120 nm CMOS technology
H. Uhrmann,W. Gaberl,H. Zimmermann
Advances in Radio Science : Kleinheubacher Berichte , 2008,
Abstract: In this paper we examine the impact of deep sub-micron CMOS technology on analog circuit design with a special focus on the noise performance and the ability to design low-noise preamplifiers. To point out, why CMOS technology can grow to a key technology in low-noise and high-speed applications, various amplifier stages, applied in literature, are compared. One, that fits as a current preamplifier for low-noise applications, is the current mirror. Starting from the basic current mirror, an enhanced current preamplifier is developed, that offers low-noise and high-speed operation. The suggested chip is realized in 0.12 μm CMOS technology and needs a chip area of 100 μm×280 μm. It consumes about 15 mW at a supply voltage of 1.5 V. The presented current preamplifier has a bandwidth of 750 MHz and a gain of 36 dB. The fields of application for current preamplifiers are, for instance, charge amplifiers, amplifiers for low-voltage differential signaling (LVDS) based point-to-point data links or preamplifiers for photodetectors.
Dynamics of a Bose-Einstein Condensate in an Anharmonic Trap
H. Ott,J. Fortagh,C. Zimmermann
Physics , 2002, DOI: 10.1088/0953-4075/36/13/311
Abstract: We present a theoretical model to describe the dynamics of Bose-Einstein condensates in anharmonic trapping potentials. To first approximation the center-of-mass motion is separated from the internal condensate dynamics and the problem is reduced to the well known scaling solutions for the Thomas-Fermi radii. We discuss the validity of this approach and analyze the model for an anharmonic waveguide geometry which was recently realized in an experiment \cite{Ott2002c}.
Electron-Phonon Interacation in Quantum Dots: A Solvable Model
T. Stauber,R. Zimmermann,H. Castella
Physics , 2005, DOI: 10.1103/PhysRevB.62.7336
Abstract: The relaxation of electrons in quantum dots via phonon emission is hindered by the discrete nature of the dot levels (phonon bottleneck). In order to clarify the issue theoretically we consider a system of $N$ discrete fermionic states (dot levels) coupled to an unlimited number of bosonic modes with the same energy (dispersionless phonons). In analogy to the Gram-Schmidt orthogonalization procedure, we perform a unitary transformation into new bosonic modes. Since only $N(N+1)/2$ of them couple to the fermions, a numerically exact treatment is possible. The formalism is applied to a GaAs quantum dot with only two electronic levels. If close to resonance with the phonon energy, the electronic transition shows a splitting due to quantum mechanical level repulsion. This is driven mainly by one bosonic mode, whereas the other two provide further polaronic renormalizations. The numerically exact results for the electron spectral function compare favourably with an analytic solution based on degenerate perturbation theory in the basis of shifted oscillator states. In contrast, the widely used selfconsistent first-order Born approximation proves insufficient in describing the rich spectral features.
Statistical model of the powder flow regulation by nanomaterials
D. Kurfess,H. Hinrichsen,I. Zimmermann
Physics , 2005, DOI: 10.1016/j.powtec.2005.06.004
Abstract: Fine powders often tend to agglomerate due to van der Waals forces between the particles. These forces can be reduced significantly by covering the particles with nanoscaled adsorbates, as shown by recent experiments. In the present work a quantitative statistical analysis of the effect of powder flow regulating nanomaterials on the adhesive forces in powders is given. Covering two spherical powder particles randomly with nanoadsorbates we compute the decrease of the mutual van der Waals force. The dependence of the force on the relative surface coverage obeys a scaling form which is independent of the used materials. The predictions by our simulations are compared to the experimental results.
On Binomial Ideals associated to Linear Codes
N. Dück,K. -H. Zimmermann
Mathematics , 2014,
Abstract: Recently, it was shown that a binary linear code can be associated to a binomial ideal given as the sum of a toric ideal and a non-prime ideal. Since then two different generalizations have been provided which coincide for the binary case. In this paper, we establish some connections between the two approaches. In particular, we show that the corresponding code ideals are related by elimination. Finally, a new heuristic decoding method for linear codes over prime fields is discussed using Gr\"obner bases.
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