12,704 research outputs found
A Twisting Electrovac Solution of Type II with the Cosmological Constant
An exact solution of the current-free Einstein-Maxwell equations with the
cosmological constant is presented. It is of Petrov type II, and its double
principal null vector is geodesic, shear-free, expanding, and twisting. The
solution contains five constants. Its electromagnetic field is non-null and
aligned. The solution admits only one Killing vector and includes, as special
cases, several known solutions.Comment: 4 pages, LaTeX 2e, no figures. The present (second) version,
identical to that published in General Relativity and Gravitation, is derived
from the first version by presenting the admitted Killing vector, and by
adding the last paragraph, two footnotes (here Footnotes 1 and 3), and two
references (here Refs. [3,4]
Spacecraft attitude control for a solar electric geosynchronous transfer mission
A study of the Attitude Control System (ACS) is made for a solar electric propulsion geosynchronous transfer mission. The basic mission considered is spacecraft injection into a low altitude, inclined orbit followed by low thrust orbit changing to achieve geosynchronous orbit. Because of the extended thrusting time, the mission performance is a strong function of the attitude control system. Two attitude control system design options for an example mission evolve from consideration of the spacecraft configuration, the environmental disturbances, and the probable ACS modes of operation. The impact of these design options on other spacecraft subsystems is discussed. The factors which must be considered in determining the ACS actuation and sensing subsystems are discussed. The effects of the actuation and sensing subsystems on the mission performance are also considered
Combining 3D printing and liquid handling to produce user-friendly reactionware for chemical synthesis and purification
We use two 3D-printing platforms as solid- and liquid-handling fabricators, producing sealed reactionware for chemical synthesis with the reagents, catalysts and purification apparatus integrated into monolithic devices. Using this reactionware, a multi-step reaction sequence was performed by simply rotating the device so that the reaction mixture flowed through successive environments under gravity, without the need for any pumps or liquid-handling prior to product retrieval from the reactionware in a pure form
Airborne observed solar elevation and row direction effects on the near-IR/red ratio of cotton
An airborne multispectral scanner was used to obtain data over two adjacent cotton fields having rows perpendicular to one another, at three times of day (different solar elevations), and on two dates (different plant size). The near IR/red ratios were displayed in image form, so that within-field variations and differences between fields could be easily assessed. The ratio varied with changing Sun elevation for north-south oriented rows, but no variation was detected for east-west oriented rows
B_s-\bar{B_s} mixing with a chiral light quark action
We study the mixing amplitude in Standard Model by
computing the relevant hadronic matrix element in the static limit of lattice
HQET with the Neuberger light quark action. In the quenched approximation, and
after matching to the scheme in QCD, we obtain .Comment: 6 pages, 3 figures, talk presented at Lattice 2005 (Heavy quark
physics
Photoassociation of a cold atom-molecule pair: long-range quadrupole-quadrupole interactions
The general formalism of the multipolar expansion of electrostatic
interactions is applied to the calculation the potential energy between an
excited atom (without fine structure) and a ground state diatomic molecule at
large separations. Both partners exhibit a permanent quadrupole moment, so that
their mutual quadrupole-quadrupole long-range interaction is attractive enough
to bind trimers. Numerical results are given for an excited Cs(6P) atom and a
ground state Cs2 molecule. The prospects for achieving photoassociation of a
cold atom/dimer pair is thus discussed and found promising. The formalism can
be easily generalized to the long-range interaction between molecules to
investigate the formation of cold tetramers.Comment: 5 figure
Gluon propagator, triple gluon vertex and the QCD coupling constant
We study the UV-scaling of the flavorless gluon propagator in the Landau
gauge in an energy window up to 9 GeV. Dominant hypercubic lattice artifacts
are eliminated. A large set of renormalization schemes is used to test
asymptotic scaling. We compare with our results obtained directly from the
triple gluon vertex. We end-up with \Lambda_{\bar{\rm{MS}}} = 318(12)(5) MeV
and 292(5)(15) MeV respectively for these two methods, compatible which each
other but significantly above the Schrodinger method estimate.Comment: 3 pages, LaTeX with two figures; presented at LATTICE9
Phonon runaway in nanotube quantum dots
We explore electronic transport in a nanotube quantum dot strongly coupled
with vibrations and weakly with leads and the thermal environment. We show that
the recent observation of anomalous conductance signatures in single-walled
carbon nanotube (SWCNT) quantum dots can be understood quantitatively in terms
of current driven `hot phonons' that are strongly correlated with electrons.
Using rate equations in the many-body configuration space for the joint
electron-phonon distribution, we argue that the variations are indicative of
strong electron-phonon coupling requiring an analysis beyond the traditional
uncorrelated phonon-assisted transport (Tien-Gordon) approach.Comment: 8 pages, 6 figure
Strand Coating for the Superconducting Cables of the LHC Main Magnets
The electrical resistance of contacts between strands in the Rutherford type superconducting cables has a major effect on the eddy current loss in cables, and on the dynamic magnetic field error in the LHC main magnets. In order to guarantee the value and constancy of the contact resistance, various metallic coatings were studied from the electrical and mechanical points of view in the past. We report on the molten bath Sn95wt.Ag5wt. coating, oxidized thermally in air after the cabling is completed, that we adopted for the cables of the LHC main magnets. The value of the con-tact resistance is determined by the strand coating and cabling procedures, oxidation heat treatment, and the magnet coil cu-ring and handling. Chemical analysis helps to understand the evolution of the contacts. We also mention results on two electrolytic coatings resulting in higher contact resistance
Light hadron spectroscopy on the lattice with the non-perturbatively improved Wilson action
We present results for the light meson masses and decay constants as obtained
from calculations with the non-perturbatively improved (`Alpha') action and
operators on a 24^3 \times 64 lattice at beta = 6.2, in the quenched
approximation. The analysis was performed in a way consistent with O(a)
improvement. We obtained: reasonable agreement with experiment for the
hyperfine splitting; f_K=156(17) MeV, f_pi =139(22) MeV, f_K/f_pi = 1.13(4) ;
f_{K*}=219(7) MeV, f_rho =199(15) MeV, f_phi =235(4) MeV; f_{K*}^{T}(2 GeV) =
178(10) MeV, f_rho^{T}(2 GeV) =165(11) MeV, where f_V^{T} is the coupling of
the tensor current to the vector mesons; the chiral condensate
^\bar{MS} (2 GeV)= - (253 +/- 25 MeV)^3. Our results are compared to
those obtained with the unimproved Wilson action. We also verified that the
free-boson lattice dispersion relation describes our results very accurately
for a large range of momenta.Comment: 29 pages (LaTeX), 14 Postscript figure
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