6,930 research outputs found
Parametric correlations versus fidelity decay: the symmetry breaking case
We derive fidelity decay and parametric energy correlations for random matrix
ensembles where time--reversal invariance of the original Hamiltonian is broken
by the perturbation. Like in the case of a symmetry conserving perturbation a
simple relation between both quantities can be established.Comment: 8 pages, 8 figure
Star formation environments and the distribution of binary separations
We have carried out K-band speckle observations of a sample of 114 X-ray
selected weak-line T Tauri stars in the nearby Scorpius-Centaurus OB
association. We find that for binary T Tauri stars closely associated to the
early type stars in Upper Scorpius, the youngest subgroup of the OB
association, the peak in the distribution of binary separations is at 90 A.U.
For binary T Tauri stars located in the direction of an older subgroup, but not
closely associated to early type stars, the peak in the distribution is at 215
A.U. A Kolmogorov-Smirnov test indicates that the two binary populations do not
result from the same distibution at a significance level of 98%. Apparently,
the same physical conditions which facilitate the formation of massive stars
also facilitate the formation of closer binaries among low-mass stars, whereas
physical conditions unfavorable for the formation of massive stars lead to the
formation of wider binaries among low-mass stars. The outcome of the binary
formation process might be related to the internal turbulence and the angular
momentum of molecular cloud cores, magnetic field, the initial temperature
within a cloud, or - most likely - a combination of all of these. We conclude
that the distribution of binary separations is not a universal quantity, and
that the broad distribution of binary separations observed among main-sequence
stars can be explained by a superposition of more peaked binary distributions
resulting from various star forming environments. The overall binary frequency
among pre-main-sequence stars in individual star forming regions is not
necessarily higher than among main-sequence stars.Comment: 7 pages, Latex, 4 Postscript figures; also available at
http://spider.ipac.caltech.edu/staff/brandner/pubs/pubs.html ; accepted for
publication in ApJ Letter
Formation Scenario for Wide and Close Binary Systems
Fragmentation and binary formation processes are studied using
three-dimensional resistive MHD nested grid simulations. Starting with a
Bonnor-Ebert isothermal cloud rotating in a uniform magnetic field, we
calculate the cloud evolution from the molecular cloud core (n=10^4 cm^-3) to
the stellar core (n \simeq 10^22 cm^-3). We calculated 147 models with
different initial magnetic, rotational, and thermal energies, and the
amplitudes of the non-axisymmetric perturbation. In a collapsing cloud,
fragmentation is mainly controlled by the initial ratio of the rotational to
the magnetic energy, regardless of the initial thermal energy and amplitude of
the non-axisymmetric perturbation. When the clouds have large rotational
energies in relation to magnetic energies, fragmentation occurs in the
low-density evolution phase (10^12 cm^-3 < n < 10^15 cm^-3) with separations of
3-300 AU. Fragments that appeared in this phase are expected to evolve into
wide binary systems. On the other hand, fragmentation does not occur in the
low-density evolution phase, when initial clouds have large magnetic energies
in relation to the rotational energies. In these clouds, fragmentation only
occurs in the high-density evolution phase (n > 10^17 cm^-3) after the clouds
experience significant reduction of the magnetic field owing to Ohmic
dissipation in the period of 10^12 cm^-3 < n < 10^15 cm^-3. Fragments appearing
in this phase have separations of < 0.3 AU, and are expected to evolve into
close binary systems. As a result, we found two typical fragmentation epochs,
which cause different stellar separations. Although these typical separations
are disturbed in the subsequent gas accretion phase, we might be able to
observe two peaks of binary separations in extremely young stellar groups.Comment: 45 pages,12 figures, Submitted to ApJ, For high resolution figures
see
http://www2.scphys.kyoto-u.ac.jp/~machidam/protostar/proto/main-astroph.pd
Torsion Degrees of Freedom in the Regge Calculus as Dislocations on the Simplicial Lattice
Using the notion of a general conical defect, the Regge Calculus is
generalized by allowing for dislocations on the simplicial lattice in addition
to the usual disclinations. Since disclinations and dislocations correspond to
curvature and torsion singularities, respectively, the method we propose
provides a natural way of discretizing gravitational theories with torsion
degrees of freedom like the Einstein-Cartan theory. A discrete version of the
Einstein-Cartan action is given and field equations are derived, demanding
stationarity of the action with respect to the discrete variables of the
theory
The efficacy of halofantrine in the treatment of acute malaria in nonimmune travelers
A multicenter prospective trial was performed to investigate the efficacy and the tolerability of halofantrine in nonimmune patients with malaria imported from areas with drug-resistant falciparum parasites (mainly Africa). Forty-five of the 74 subjects were treated with a one-day regimen (3 x 500 mg) of halofantrine, and the other 29 received the same regimen with an additional treatment on day 7. In the second group, a 100% efficacy rate was demonstrated, but in the group receiving the one-day regimen, four recrudescences were observed in patients with falciparum malaria. Only five mild adverse reactions were seen, which disappeared spontaneously after the end of the treatment. We conclude that halofantrine is highly effective in curing malaria in nonimmune subjects. The treatment scheme for such persons should include an additional treatment on day 7 for nonimmune individuals. This drug was well tolerated in our patients, indicating that halofantrine will be useful in the treatment of multidrug-resistant malaria in nonimmune persons
Injectable Famphur for Control of Grubs in Cattle
Grubs are a major pest of cattle and cause considerable economic loss to the cattle industry. Running of cattle and standing in available water sources during heel fly strikes no doubt are reflected in lighter weaning weights of claves because of reduced grazing time and cows becoming separated from their calves. Other losses to producers and feeders include possible reduced feedlot performance by grub infested animals, weight loss and down grading of carcasses that are trimmed to remove areas damaged by grubs and a lower value for hides due to grub holes. Several effective products and methods of treatment are available for control of grubs. Timely administration of a proper dosage to all animals from problem areas is necessary for effective control
CONTROL OF END-TIDAL HALOTHANE CONCENTRATION: Part A: Anaesthesia Breathing System and Feedback Control of Gas Delivery
Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient a circulating pump and feedback controllers for system volume and anaesthetic concentration. Feedback control was implemented to adjust and control automatically the end-tidal anaesthetic concentration and the volume of the system with oxygen supplied through a mass flow controller and with halothane supplied by a titrating syringe. Controller gains, as a function of body weight, were found using a nine-compartment tissue uptake model. Stability was maintained with ±50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal Concentration and system volume to provide a rapid and optimized induction of anaesthesi
Force calculation and atomic-structure optimization for the full-potential linearized augmented plane-wave code WIEN
Following the approach of Yu, Singh, and Krakauer [Phys. Rev. B 43 (1991)
6411] we extended the linearized augmented plane wave code WIEN of Blaha,
Schwarz, and coworkers by the evaluation of forces. In this paper we describe
the approach, demonstrate the high accuracy of the force calculation, and use
them for an efficient geometry optimization of poly-atomic systems.Comment: submitted to Comp. Phys. Commun., 27 pages, 3 figure
VLTI/MIDI 10 micron interferometry of the forming massive star W33A
We report on resolved interferometric observations with VLTI/MIDI of the
massive young stellar object (MYSO) W33A. The MIDI observations deliver
spectrally dispersed visibilities with values between 0.03 and 0.06, for a
baseline of 45m over the wavelength range 8-13 micron. The visibilities
indicate that W33A has a FWHM size of approximately 120AU (0.030'') at 8 micron
which increases to 240AU at 13 micron, scales previously unexplored among
MYSOs. This observed trend is consistent with the temperature falling off with
distance. 1D dust radiative transfer models are simultaneously fit to the
visibility spectrum, the strong silicate feature and the shape of the mid
infrared spectral energy distribution (SED). For any powerlaw density
distribution, we find that the sizes (as implied by the visibilities) and the
stellar luminosity are incompatible. A reduction to a third of W33A's
previously adopted luminosity is required to match the visibilities; such a
reduction is consistent with new high resolution 70 micron data from Spitzer's
MIPSGAL survey. We obtain best fits for models with shallow dust density
distributions of r^(-0.5) and r^(-1.0) and for increased optical depth in the
silicate feature produced by decreasing the ISM ratio of graphite to silicates
and using optical grain properties by Ossenkopf et al. (1992).Comment: 4 pages, 4 figures. Accepted for ApJ letter
A Multiplicity Census of Young Stars in Chamaeleon I
We present the results of a multiplicity survey of 126 stars spanning ~0.1-3
solar masses in the ~2-Myr-old Chamaeleon I star-forming region, based on
adaptive optics imaging with the ESO Very Large Telescope. Our observations
have revealed 30 binaries and 6 triples, of which 19 and 4, respectively, are
new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is
similar to those reported for other dispersed young associations, but
significantly higher than seen in denser clusters and the field, for comparable
samples. Both the frequency and the maximum separation of Cha I binaries
decline with decreasing mass, while the mass ratios approach unity; conversely,
tighter pairs are more likely to be equal mass. We confirm that brown dwarf
companions to stars are rare, even at young ages at wide separations. Based on
follow-up spectroscopy of two low-mass substellar companion candidates, we
conclude that both are likely background stars. The overall multiplicity
fraction in Cha I is in rough agreement with numerical simulations of cloud
collapse and fragmentation, but its observed mass dependence is less steep than
predicted. The paucity of higher-order multiples, in particular, provides a
stringent constraint on the simulations, and seems to indicate a low level of
turbulence in the prestellar cores in Cha I.Comment: Accepted for publication in Ap
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