1,211 research outputs found
Spectral modeling of type II supernovae. I. Dilution factors
We present substantial extensions to the Monte Carlo radiative transfer code
TARDIS to perform spectral synthesis for type II supernovae. By incorporating a
non-LTE ionization and excitation treatment for hydrogen, a full account of
free-free and bound-free processes, a self-consistent determination of the
thermal state and by improving the handling of relativistic effects, the
improved code version includes the necessary physics to perform spectral
synthesis for type II supernovae to high precision as required for the reliable
inference of supernova properties. We demonstrate the capabilities of the
extended version of TARDIS by calculating synthetic spectra for the
prototypical type II supernova SN1999em and by deriving a new and independent
set of dilution factors for the expanding photosphere method. We have
investigated in detail the dependence of the dilution factors on photospheric
properties and, for the first time, on changes in metallicity. We also compare
our results with two previously published sets of dilution factors by Eastman
et al. (1996) and by Dessart & Hillier (2005), and discuss the potential
sources of the discrepancies between studies.Comment: 16 pages, 12 figures, 2 tables, accepted for publication in A&
Spectroscopy of atomic rubidium at 500 bar buffer gas pressure: approaching the thermal equilibrium of dressed atom-light states
We have recorded fluorescence spectra of the atomic rubidium D-lines in the
presence of several hundreds of bars buffer gas pressure. With additional
saturation broadening a spectral linewidth comparable to the thermal energy of
the atoms in the heated gas cell is achieved. An intensity-dependent blue
asymmetry of the spectra is observed, which becomes increasingly pronounced
when extrapolating to infinitely high light intensity. We interpret our results
as evidence for the dressed (coupled atom-light) states to approach thermal
equilibrium.Comment: 4 page
Mars orbiter conceptual systems design study
Spacecraft system and subsystem designs at the conceptual level to perform either of two Mars Orbiter missions, a Climatology Mission and an Aeronomy Mission were developed. The objectives of these missions are to obtain and return data
Grafting of 2 (2-hydroxy-5-vinylphenyl) 2H-benzotriazole onto polymers with aliphatic groups. Synthesis and polymerization of 2 (2-hydroxy-5-isopropenylphenyl) 2H-benzotriazole and a new synthesis of 2 (2-hydroxy-5-vinylphenyl) 2H-benzotriazole
Successful grafting of 2(2-hydroxy-5-vinylphenyl)2H-benzotriazole onto saturated aliphatic C-H groups of polymers has been accomplished. When the grafting reaction was carried out in chlorobenzene at 150 C = 160 C with di-tertiarybutylperoxide as the grafting initiator, grafts as high as 20 percent - 30 percent at a grafting efficiency of 50 percent and 80 percent have readily been obtained. The grafting reaction was carried out in tubes sealed under high vacuum since trace amounts of oxygen cause complete inhibition of the grafting reaction by the phenolic monomer. On a variety of different polymers including atactic polypropylene, ethylene/vinyl acetate copolymer, poly(methyl methacrylate), poly(butyl acrylate), and polycarbonate were used
Copula-based assimilation of radar and gauge information to derive bias corrected precipitation fields
This study addresses the problem of combining radar information and gauge measurements. Gauge measurements are the best available source of absolute rainfall intensity albeit their spatial availability is limited. Precipitation information obtained by radar mimics well the spatial patterns but is biased for their absolute values. <br><br> In this study copula models are used to describe the dependence structure between gauge observations and rainfall derived from radar reflectivity at the corresponding grid cells. After appropriate time series transformation to generate "iid" variates, only the positive pairs (radar >0, gauge >0) of the residuals are considered. As not each grid cell can be assigned to one gauge, the integration of point information, i.e. gauge rainfall intensities, is achieved by considering the structure and the strength of dependence between the radar pixels and all the gauges within the radar image. Two different approaches, namely <i>Maximum Theta</i> and <i>Multiple Theta</i>, are presented. They finally allow for generating precipitation fields that mimic the spatial patterns of the radar fields and correct them for biases in their absolute rainfall intensities. The performance of the approach, which can be seen as a bias-correction for radar fields, is demonstrated for the Bavarian Alps. The bias-corrected rainfall fields are compared to a field of interpolated gauge values (ordinary kriging) and are validated with available gauge measurements. The simulated precipitation fields are compared to an operationally corrected radar precipitation field (RADOLAN). The copula-based approach performs similarly well as indicated by different validation measures and successfully corrects for errors in the radar precipitation
Theory of semiconductor quantum-wire based single- and two-qubit gates
A GaAs/AlGaAs based two-qubit quantum device that allows the controlled
generation and straightforward detection of entanglement by measuring a
stationary current-voltage characteristic is proposed. We have developed a
two-particle Green's function method of open systems and calculate the
properties of three-dimensional interacting entangled systems
non-perturbatively. We present concrete device designs and detailed, charge
self-consistent predictions. One of the qubits is an all-electric Mach-Zehnder
interferometer that consists of two electrostatically defined quantum wires
with coupling windows, whereas the second qubit is an electrostatically defined
double quantum dot located in a second two-dimensional electron gas beneath the
quantum wires. We find that the entanglement of the device can be controlled
externally by tuning the tunneling coupling between the two quantum dots.Comment: 16 pages, 13 figures, RevTex4 two-column format, to appear in Phys.
Rev.
Triplet-singlet relaxation in semiconductor single and double quantum dots
We study the triplet-singlet relaxation in two-electron semiconductor quantum
dots. Both single dots and vertically coupled double dots are discussed. In our
work, the electron-electron Coulomb interaction, which plays an important role
in the electronic structure, is included. The spin mixing is caused by
spin-orbit coupling which is the key to the triplet-singlet relaxation. We show
that the selection rule widely used in the literature is incorrect unless near
the crossing/anticrossing point in single quantum dots. The triplet/singlet
relaxation in double quantum dots can be markedly changed by varying barrier
height, inter-dot distance, external magnetic field and dot size.Comment: 7 pages, 4 figures, PRB in pres
Nucleon Structure Functions from Relativistic Constituent Quarks
We investigate deep inelastic lepton scattering from the nucleon within a
constituent quark picture, in which the internal structure of constituent
quarks is modeled by meson and diquark dressing. In a covariant framework this
structure leads to a breakdown of the factorization necessary for a convolution
formulation. We perform our analysis in time-ordered perturbation theory in the
infinite momentum frame where factorization of subprocesses is automatic.
Numerical results are compared with recent data on valence quark distributions
in the proton.Comment: 10 pages LaTeX, 3 figures available upon request, TPR-94-7, to appear
in Physics Letters
Versuche zur Synthese des Cytisins. Dehydrierung von Tetrahydro-cytisin zu Cytisin
Die Dehydrierung von Tetrahydro-cytisin zu Cytisin mit Palladium verläuft glatt, wenn man die Iminogruppe durch Acetylierung schützt. Durch Erhitzen des N-Acetyl-tetrahydrocytisins mit Pd-Mohr bei 280° erhält man so in guter Ausbeute N-Acetyl-cytisin und daraus durch Abspaltung der Acetyl-gruppe mit Salzsäure das Cytisin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41696/1/706_2004_Article_BF00899864.pd
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