2,287 research outputs found
Transmission line for S-band masers
Transmission-line is coaxial. Its outer conductor is made of thin-wall stainless-steel tube; inside is plated with 0.0025 mm copper and 0.0003 mm gold. This combination gives little microwave loss and adequate thermal isolation
CB17: Inferring the dynamical history of a prestellar core with chemo-dynamical models
We present a detailed theoretical study of the isolated Bok globule CB17
(L1389) based on spectral maps of CS, HCO, CO, CS, and
HCO lines. A phenomenological model of prestellar core evolution, a
time-dependent chemical model, and a radiative transfer simulation for
molecular lines are combined to reconstruct the chemical and kinematical
structure of this core. We developed a general criterion that allows to
quantify the difference between observed and simulated spectral maps. By
minimizing this difference, we find that very high and very low values of the
effective sticking probability are not appropriate for the studied
prestellar core. The most probable value for CB17 is 0.3--0.5. The spatial
distribution of the intensities and self-absorption features of optically thick
lines is indicative of UV irradiation of the core. By fitting simultaneously
optically thin and optically thick transitions, we isolate the model that
reproduces all the available spectral maps to a reasonable accuracy. The line
asymmetry pattern in CB17 is reproduced by a combination of infall, rotation,
and turbulent motions with velocities km s, km
s, and km s, respectively. These parameters corresponds
to energy ratios , , and (the rotation
parameters are determined for ). The chemical age of the core is
about 2 Myrs. In particular, this is indicated by the central depletion of CO,
CS, and HCO. Based on the angular momentum value, we argue that the core is
going to fragment, i.e., to form a binary (multiple) star. (abridged)Comment: ApJ, in pres
Higher Order Decompositions of Ordered Operator Exponentials
We present a decomposition scheme based on Lie-Trotter-Suzuki product
formulae to represent an ordered operator exponential as a product of ordinary
operator exponentials. We provide a rigorous proof that does not use a
time-displacement superoperator, and can be applied to non-analytic functions.
Our proof provides explicit bounds on the error and includes cases where the
functions are not infinitely differentiable. We show that Lie-Trotter-Suzuki
product formulae can still be used for functions that are not infinitely
differentiable, but that arbitrary order scaling may not be achieved.Comment: 16 pages, 1 figur
Magnetic Ordering in the Spin-Ice Candidate HoRuO
Neutron scattering measurements on the spin-ice candidate material
HoRuO have revealed two magnetic transitions at T 95 K and T
1.4 K to long-range ordered states involving the Ru and Ho sublattices,
respectively. Between these transitions, the Ho moments form
short-ranged ordered spin clusters. The internal field provided by the ordered
S=1 Ru moments disrupts the fragile spin-ice state and drives the
Ho moments to order. We have directly measured a slight shift in the
Ho crystal field levels at 95 K from the Ru ordering.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Letter
Two inequivalent sublattices and orbital ordering in MnV2O4 studied by 51V NMR
We report detailed 51V NMR spectra in a single crystal of MnV2O4. The
vanadium spectrum reveals two peaks in the orbitally ordered state, which arise
from different internal hyperfine fields at two different V sublattices. These
internal fields evolve smoothly with externally applied field, and show no
change in structure that would suggest a change of the orbital ordering. The
result is consistent with the orbital ordering model recently proposed by
Sarkar et al. [Phys. Rev. Lett. 102, 216405 (2009)] in which the same orbital
that is a mixture of t_2g orbitals rotates by about 45 alternately
within and between orbital chains in the I4_1/a tetragonal space group.Comment: 4 pages, 4 figures, title changed, published in PRB as a rapid com
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