174 research outputs found
Simple Model For Asymptotic Level Clusters In Sf6 Rotational Spectra
We construct a simple model to explain the qualitative features of level clusters in the asymptotic regions or limbs of centrifugally split J levels in SF6, as observed in diode spectroscopy and computer experiments. Parametric formulas for cluster splittings are derived by use of methods which may be useful for analysis of other molecular and solid-state resonance effects. © 1977 The American Physical Society.38522422
Canonical Symmetrization For The Unitary Bases. Ii. Boson And Fermion Bases
The canonical Weyl basis described in Paper I is generalized to give a boson and fermion calculus which generates the symmetric and antisymmetric bases of U(nm) respectively contained in the irreducible bases of U(n)XU(m). The boson calculus may be used to find the multiplicity free Clebsch-Gordan coefficients of U(n). Copyright © 1976 American Institute of Physics.1771137114
Alternative Basis For The Theory Of Complex Spectra. Ii
The atomic angular-factor calculation methods given in a previous work are simplified and extended to include a treatment of spin-orbit operators and multiple shell configuration (ll′<̄)n. A tableau formula is given for the matrix between Slater states and states of definite total spin. © 1976 The American Physical Society.1331067108
An integrated approach to modelling the fluid-structure interaction of a collapsible tube
The well known collapsible tube experiment was conducted to obtain flow, pressure and materials property data for steady state conditions. These were then used as the boundary conditions for a fully coupled fluid-structure interaction (FSI) model using a propriety computer code, LS-DYNA. The shape profiles for the tube were also recorded. In order to obtain similar collapse modes to the experiment, it was necessary to model the tube flat, and then inflate it into a circular profile, leaving residual stresses in the walls. The profile shape then agreed well with the experimental ones. Two departures from the physical properties were required to reduce computer time to an acceptable level. One of these was the lowering of the speed of sound by two orders of magnitude which, due to the low velocities involved, still left the mach number below 0.2. The other was to increase the thickness of the tube to prevent the numerical collapse of elements. A compensation for this was made by lowering the Young's modulus for the tube material. Overall the results are qualitatively good. They give an indication of the power of the current FSI algorithms and the need to combine experiment and computer models in order to maximise the information that can be extracted both in terms of quantity and quality
Accretion among preplanetary bodies: the many faces of runaway growth
(abridged) When preplanetary bodies reach proportions of ~1 km or larger in
size, their accretion rate is enhanced due to gravitational focusing (GF). We
have developed a new numerical model to calculate the collisional evolution of
the gravitationally-enhanced growth stage. We validate our approach against
existing N-body and statistical codes. Using the numerical model, we explore
the characteristics of the runaway growth and the oligarchic growth accretion
phases starting from an initial population of single planetesimal radius R_0.
In models where the initial random velocity dispersion (as derived from their
eccentricity) starts out below the escape speed of the planetesimal bodies, the
system experiences runaway growth. We find that during the runaway growth phase
the size distribution remains continuous but evolves into a power-law at the
high mass end, consistent with previous studies. Furthermore, we find that the
largest body accretes from all mass bins; a simple two component approximation
is inapplicable during this stage. However, with growth the runaway body stirs
up the random motions of the planetesimal population from which it is
accreting. Ultimately, this feedback stops the fast growth and the system
passes into oligarchy, where competitor bodies from neighboring zones catch up
in terms of mass. Compared to previous estimates, we find that the system
leaves the runaway growth phase at a somewhat larger radius. Furthermore, we
assess the relevance of small, single-size fragments on the growth process. In
classical models, where the initial velocity dispersion of bodies is small,
these do not play a critical role during the runaway growth; however, in models
that are characterized by large initial relative velocities due to external
stirring of their random motions, a situation can emerge where fragments
dominate the accretion.Comment: Accepted for publication in Icaru
On the Change of the Inner Boundary of an Optically Thick Accretion Disk around White Dwarfs Using the Dwarf Nova SS Cyg as an Example
We present the results of our studies of the aperiodic optical flux
variability for SS Cyg, an accreting binary systemwith a white dwarf. The main
set of observational data presented here was obtained with the ANDOR/iXon
DU-888 photometer mounted on the RTT-150 telescope, which allowed a record(for
CCD photometers) time resolution up to 8 ms to be achieved. The power spectra
of the source's flux variability have revealed that the aperiodic variability
contains information about the inner boundary of the optically thick flow in
the binary system. We show that the inner boundary of the optically thick
accretion disk comes close to the white dwarf surface at the maximum of the
source's bolometric light curve, i.e., at the peak of the instantaneous
accretion rate onto the white dwarf, while the optically thick accretion disk
is truncated at distances 8.5e9 cm ~10 R_{WD} in the low state. We suggest that
the location of the inner boundary of the accretion disk in the binary can be
traced by studying the parameters of the power spectra for accreting white
dwarfs. In particular, this allows the mass of the accreting object to be
estimated.Comment: 9 pages, 7 figures, Published in Astronomy Letter
Measurement of the B-Meson Inclusive Semileptonic Branching Fraction and Electron-Energy Moments
We report a new measurement of the B-meson semileptonic decay momentum
spectrum that has been made with a sample of 9.4/fb of electron-positron
annihilation data collected with the CLEO II detector at the Y(4S) resonance.
Electrons from primary semileptonic decays and secondary charm decays were
separated by using charge and angular correlations in Y(4S) events with a
high-momentum lepton and an additional electron. We determined the semileptonic
branching fraction to be (10.91 +- 0.09 +- 0.24)% from the normalization of the
electron-energy spectrum. We also measured the moments of the electron energy
spectrum with minimum energies from 0.6 GeV to 1.5 GeV.Comment: 36 pages postscript, als available through
http://w4.lns.cornell.edu/public/CLNS/, Submitted to PRD (back-to-back with
preceding preprint hep-ex/0403052
Angular momentum exchange during secular migration of two-planet systems
We investigate the secular dynamics of two-planet coplanar systems evolving
under mutual gravitational interactions and dissipative forces. We consider two
mechanisms responsible for the planetary migration: star-planet (or
planet-satellite) tidal interactions and interactions of a planet with a
gaseous disc. We show that each migration mechanism is characterized by a
specific law of orbital angular momentum exchange. Calculating stationary
solutions of the conservative secular problem and taking into account the
orbital angular momentum leakage, we trace the evolutionary routes followed by
the planet pairs during the migration process. This procedure allows us to
recover the dynamical history of two-planet systems and constrain parameters of
the involved physical processes.Comment: 20 pages, 9 figures, accepted for publication in Celestial Mechanics
and Dynamical Astronomy (special issue on Exoplanets
Applicability of precision medicine approaches to managing hypertension in rural populations
As part of the Heart Healthy Lenoir Project, we developed a practice level intervention to improve blood pressure control. The goal of this study was: (i) to determine if single nucleotide polymorphisms (SNPs) that associate with blood pressure variation, identified in large studies, are applicable to blood pressure control in subjects from a rural population; (ii) to measure the association of these SNPs with subjects’ responsiveness to the hypertension intervention; and (iii) to identify other SNPs that may help understand patient-specific responses to an intervention. We used a combination of candidate SNPs and genome-wide analyses to test associations with either baseline systolic blood pressure (SBP) or change in systolic blood pressure one year after the intervention in two genetically defined ancestral groups: African Americans (AA) and Caucasian Americans (CAU). Of the 48 candidate SNPs, 13 SNPs associated with baseline SBP in our study; however, one candidate SNP, rs592582, also associated with a change in SBP after one year. Using our study data, we identified 4 and 15 additional loci that associated with a change in SBP in the AA and CAU groups, respectively. Our analysis of gene-age interactions identified genotypes associated with SBP improvement within different age groups of our populations. Moreover, our integrative analysis identified AQP4-AS1 and PADI2 as genes whose expression levels may contribute to the pleiotropy of complex traits involved in cardiovascular health and blood pressure regulation in response to an intervention targeting hypertension. In conclusion, the identification of SNPs associated with the success of a hypertension treatment intervention suggests that genetic factors in combination with age may contribute to an individual’s success in lowering SBP. If these findings prove to be applicable to other populations, the use of this genetic variation in making patient-specific interventions may help providers with making decisions to improve patient outcomes. Further investigation is required to determine the role of this genetic variance with respect to the management of hypertension such that more precise treatment recommendations may be made in the future as part of personalized medicine
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