16,608 research outputs found
Quantum Calculation of Inelastic CO Collisions with H. II. Pure Rotational Quenching of High Rotational Levels
Carbon monoxide is a simple molecule present in many astrophysical
environments, and collisional excitation rate coefficients due to the dominant
collision partners are necessary to accurately predict spectral line
intensities and extract astrophysical parameters. We report new quantum
scattering calculations for rotational deexcitation transitions of CO induced
by H using the three-dimensional potential energy surface~(PES) of Song et al.
(2015). State-to-state cross sections for collision energies from 10 to
15,000~cm and rate coefficients for temperatures ranging from 1 to
3000~K are obtained for CO(, ) deexcitation from to all lower
levels, where is the rotational quantum number. Close-coupling and
coupled-states calculations were performed in full-dimension for =1-5, 10,
15, 20, 25, 30, 35, 40, and 45 while scaling approaches were used to estimate
rate coefficients for all other intermediate rotational states. The current
rate coefficients are compared with previous scattering results using earlier
PESs. Astrophysical applications of the current results are briefly discussed.Comment: 8 figures, 1 tabl
Masses for the Local Group and the Milky Way
We use the very large Millennium Simulation of the concordance CDM
cosmogony to calibrate the bias and error distribution of Timing Argument
estimators of the masses of the Local Group and of the Milky Way. From a large
number of isolated spiral-spiral pairs similar to the Milky Way/Andromeda
system, we find the interquartile range of the ratio of timing mass to true
mass to be a factor of 1.8, while the 5% and 95% points of the distribution of
this ratio are separated by a factor of 5.7. Here we define true mass as the
sum of the ``virial'' masses of the two dominant galaxies. For
current best values of the distance and approach velocity of Andromeda this
leads to a median likelihood estimate of the true mass of the Local Group of
5.27\times 10^{12}\msun, or , with an
interquartile range of and a 5% to 95% range of . Thus a 95% lower confidence limit on the true mass of the Local Group
is 1.81\times 10^{12}\msun. A timing estimate of the Milky Way's mass based
on the large recession velocity observed for the distant satellite Leo I works
equally well, although with larger systematic uncertainties. It gives an
estimated virial mass for the Milky Way of 2.43 \times 10^{12}\msun with a
95% lower confidence limit of 0.80 \times 10^{12}\msun.Comment: 11 pages, 6 figures, MNRAS accepted. Added a new discussion paragraph
and a new figure regarding the relative transverse velocity but conclusions
unchange
A simplified procedure for the purification of the protein phosphatase modulator (inhibitor-2) from rabbit skeletal muscle
On the mechanism of activation of rabbit skeletal muscle ATP-Mg-dependent protein phosphatase
Gravitational anomaly and fundamental forces
I present an argument, based on the topology of the universe, why there are
three generations of fermions. The argument implies a preferred gauge group of
SU(5), but with SO(10) representations of the fermions. The breaking pattern
SU(5) to SU(3)xSU(2)xU(1) is preferred over the pattern SU(5) to SU(4)xU(1). On
the basis of the argument one expects an asymmetry in the early universe
microwave data, which might have been detected already.Comment: Contribution to the 2nd School and Workshop on Quantum Gravity and
Quantum Geometry. Corfu, september 13-20 2009. 10 page
Complete Solving for Explicit Evaluation of Gauss Sums in the Index 2 Case
Let be a prime number, for some positive integer , be a
positive integer such that , and let \k be a primitive
multiplicative character of order over finite field \fq. This paper
studies the problem of explicit evaluation of Gauss sums in "\textsl{index 2
case}" (i.e. f=\f{\p(N)}{2}=[\zn:\pp], where \p(\cd) is Euler function).
Firstly, the classification of the Gauss sums in index 2 case is presented.
Then, the explicit evaluation of Gauss sums G(\k^\la) (1\laN-1) in index 2
case with order being general even integer (i.e. N=2^{r}\cd N_0 where
are positive integers and is odd.) is obtained. Thus, the
problem of explicit evaluation of Gauss sums in index 2 case is completely
solved
Raman Spectroscopy Study of alpha-, beta-, gamma-NaxCoO2 and gamma-(Ca,Sr)xCoO2
Raman spectroscopy measurements have been performed on alpha-, beta-,
gamma-NaxCoO2 phases differing in their stacking of CoO6 octahedra along the
c-axis direction. The results demonstrate that, in general, there are five
active phonons for gamma-Na0.75CoO2, two Raman active phonons for alpha-NaCoO2,
and four Raman active phonons for beta-NaCoO2. We have also performed Raman
scattering measurements on several gamma-(Ca,Sr)xCoO2 (0.15 <= x <= 0.35)
samples which show well-defined intercalated Ca/Sr-ordering. The experimental
data show that the intercalated cation ordering could result in visible
alterations on Raman spectral structures. The observations of the spectral
changes along with the variation of the CoO6 stacking, as well as the
intercalated Sr/Ca ordering suggest that the interlayer interaction plays an
important role for understanding the lattice dynamics in this layered system.Comment: 23 pages, 5 figures, Physical Review B, in pres
Model selection in High-Dimensions: A Quadratic-risk based approach
In this article we propose a general class of risk measures which can be used
for data based evaluation of parametric models. The loss function is defined as
generalized quadratic distance between the true density and the proposed model.
These distances are characterized by a simple quadratic form structure that is
adaptable through the choice of a nonnegative definite kernel and a bandwidth
parameter. Using asymptotic results for the quadratic distances we build a
quick-to-compute approximation for the risk function. Its derivation is
analogous to the Akaike Information Criterion (AIC), but unlike AIC, the
quadratic risk is a global comparison tool. The method does not require
resampling, a great advantage when point estimators are expensive to compute.
The method is illustrated using the problem of selecting the number of
components in a mixture model, where it is shown that, by using an appropriate
kernel, the method is computationally straightforward in arbitrarily high data
dimensions. In this same context it is shown that the method has some clear
advantages over AIC and BIC.Comment: Updated with reviewer suggestion
An Electronic Mach-Zehnder Interferometer
Double-slit electron interferometers, fabricated in high mobility
two-dimensional electron gas (2DEG), proved to be very powerful tools in
studying coherent wave-like phenomena in mesoscopic systems. However, they
suffer from small fringe visibility due to the many channels in each slit and
poor sensitivity to small currents due to their open geometry. Moreover, the
interferometers do not function in a high magnetic field, namely, in the
quantum Hall effect (QHE) regime, since it destroys the symmetry between left
and right slits. Here, we report on the fabrication and operation of a novel,
single channel, two-path electron interferometer that functions in a high
magnetic field. It is the first electronic analog of the well-known optical
Mach-Zehnder (MZ) interferometer. Based on single edge state and closed
geometry transport in the QHE regime the interferometer is highly sensitive and
exhibits very high visibility (62%). However, the interference pattern decays
precipitously with increasing electron temperature or energy. While we do not
understand the reason for the dephasing we show, via shot noise measurement,
that it is not a decoherence process that results from inelastic scattering
events.Comment: to appear in Natur
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