143 research outputs found
Forced vibration analysis of rotating cyclic structures in NASTRAN
A new capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axis of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical, user's, programmer's and demonstration manuals for this new capability are presented
Bladed-shrouded-disc aeroelastic analyses: Computer program updates in NASTRAN level 17.7
In October 1979, a computer program based on the state-of-the-art compressor and structural technologies applied to bladed-shrouded-disc was developed. The program was more operational in NASTRAN Level 16. The bladed disc computer program was updated for operation in NASTRAN Level 17.7. The supersonic cascade unsteady aerodynamics routine UCAS, delivered as part of the NASTRAN Level 16 program was recorded to improve its execution time. These improvements are presented
Comparison of Statistical Population Reconstruction Using Full and Pooled Adult Age-Class Data
BACKGROUND: Age-at-harvest data are among the most commonly collected, yet neglected, demographic data gathered by wildlife agencies. Statistical population construction techniques can use this information to estimate the abundance of wild populations over wide geographic areas and concurrently estimate recruitment, harvest, and natural survival rates. Although current reconstruction techniques use full age-class data (0.5, 1.5, 2.5, 3.5, … years), it is not always possible to determine an animal's age due to inaccuracy of the methods, expense, and logistics of sample collection. The ability to inventory wild populations would be greatly expanded if pooled adult age-class data (e.g., 0.5, 1.5, 2.5+ years) could be successfully used in statistical population reconstruction. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the performance of statistical population reconstruction models developed to analyze full age-class and pooled adult age-class data. We performed Monte Carlo simulations using a stochastic version of a Leslie matrix model, which generated data over a wide range of abundance levels, harvest rates, and natural survival probabilities, representing medium-to-big game species. Results of full age-class and pooled adult age-class population reconstructions were compared for accuracy and precision. No discernible difference in accuracy was detected, but precision was slightly reduced when using the pooled adult age-class reconstruction. On average, the coefficient of variation (i.e., SE(θ)/θ) increased by 0.059 when the adult age-class data were pooled prior to analyses. The analyses and maximum likelihood model for pooled adult age-class reconstruction are illustrated for a black-tailed deer (Odocoileus hemionus) population in Washington State. CONCLUSIONS/SIGNIFICANCE: Inventorying wild populations is one of the greatest challenges of wildlife agencies. These new statistical population reconstruction models should expand the demographic capabilities of wildlife agencies that have already collected pooled adult age-class data or are seeking a cost-effective method for monitoring the status and trends of our wild resources
Superfluid density and penetration depth in Fe-pnictides
We consider the superfluid density in a two-band superconductor
with extended s-wave symmetry () in the presence of non-magnetic
impurities and apply the results to Fe-pnictides. We show that the behavior of
the superfluid density is essentially the same as in an ordinary s-wave
superconductor with magnetic impurities. We show that, for moderate to strong
inter-band impurity scattering, behaves as a power-law with
over a wide range of . We argue that the power-law
behavior is consistent with recent experiments on the penetration depth
in BaFeAs, but disagree quantitatively with the data on
LaFePO.Comment: 4 pages, 2 figures; replaced with updated versio
Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters
A single impurity problem is investigated for multiband s-wave
superconductors with different sign order parameters (+-s-wave superconductors)
suggested in Fe-pnictide superconductors. Not only intraband but also interband
scattering is considered at the impurity. The latter gives rise to
impurity-induced local boundstates close to the impurity. We present an exact
form of the energy of the local boundstates as a function of strength of the
two types of impurity scattering. The essential role of the impurity is
unchanged in finite number of impurities. The main conclusions for a single
impurity problem help us understand effects of dense impurities in the +-s-wave
superconductors. Local density of states around the single impurity is also
investigated. We suggest impurity site nuclear magnetic resonance as a suitable
experiment to probe the local boundstates that is peculiar to the +-s-wave
state. We find that the +-s-wave model is mapped to a chiral dx2-y2+-idxy-wave,
reflecting the unconventional nature of the sign reversing order parameter. For
a quantum magnetic impurity, interband scattering destabilizes the Kondo
singlet.Comment: 23 pages, 7 figures, to be published in J. Phys. Soc. Jpn. (2009) No.
Evidence of Electromagnetic Absorption by Collective Modes in the Heavy Fermion Superconductor UBe13
We present results of a microwave surface impedance study of the heavy
fermion superconductor UBe13. We clearly observe an absorption peak whose
frequency- and temperature-dependence scales with the BCS gap function.
Resonant absorption into a collective mode, with energy approximately
proportional to the superconducting gap, is proposed as a possible
explantation
Impurity scattering in unconventional density waves
We have investigated the effect of nonmagnetic impurities on the
quasi-one-dimensional unconventional density wave (UDW) ground state. The
thermodynamics were found to be close to those of a d-wave superconductor in
the Born limit. Four different optical conductivity curves were found depending
on the direction of the applied electric field and on the wavevector dependence
of the gap.Comment: 14 pages, 9 figure
Magnetic pair-breaking in superconducting (Ba,K)BiO_3 investigated by magnetotunneling
The de Gennes and Maki theory of gapless superconductivity for dirty
superconductors is used to interpret the tunneling measurements on the strongly
type-II high-Tc oxide-superconductor Ba1-xKxBiO3 in high magnetic fields up to
30 Tesla. We show that this theory is applicable at all temperatures and in a
wide range of magnetic fields starting from 50 percent of the upper critical
field Bc2. In this magnetic field range the measured superconducting density of
states (DOS) has the simple energy dependence as predicted by de Gennes from
which the temperature dependence of the pair-breaking parameter alpha(T), or
Bc2(T), has been obtained. The deduced temperature dependence of Bc2(T) follows
the Werthamer-Helfand-Hohenberg prediction for classical type-II
superconductors in agreement with our previous direct determination. The
amplitudes of the deviations in the DOS depend on the magnetic field via the
spatially averaged superconducting order parameter which has a square-root
dependence on the magnetic field. Finally, the second Ginzburg-Landau parameter
kappa2(T) has been determined from the experimental data.Comment: 11 pages, 5 figure
Isotope Effect for the Penetration Depth in Superconductors
We show that various factors can lead to an isotopic dependence of the
penetration depth . Non-adiabaticity (Jahn-Teller crossing) leads to
the isotope effect of the charge carrier concentration and, consequently,
of in doped superconductors such as the cuprates. A general equation
relating the isotope coefficients of and of is presented for
London superconductors. We further show that the presence of magnetic
impurities or a proximity contact also lead to an isotopic dependence of
; the isotope coefficient turns out to be temperature dependent,
, in these cases. The existence of the isotope effect for the
penetration depth is predicted for conventional as well as for high-temperature
superconductors. Various experiments are proposed and/or discussed.Comment: 11 pages, 8 figures, accepted for publication in Phys. Rev.
Shape Coexistence and the Effective Nucleon-Nucleon Interaction
The phenomenon of shape coexistence is discussed within the self-consistent
Hartree-Fock method and the nuclear shell model. The occurrence of the
coexisting configurations with different intrinsic shapes is traced back to the
properties of the effective Hamiltonian.Comment: 40 pages (16 text, 24 figures). The file may also be retrieved at
http://csep2.phy.ornl.gov/theory_group/people/dean/shape_coex/shapes.htm
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