1,661 research outputs found
Inventory Behavior in Durable-Goods Manufacturing: The Target-Adjustment Model
macroeconomics,inventory behavior, durable-goods manufacturing
GROWTH AND MOVEMENT OF SMALLMOUTH BUFFALO, ICTIOBUS BUBALUS (RAFINESQUE), IN WATTS BAR RESERVOIR, TENNESSEE
The smallmouth buffalo fish, Ictiobus bubalus (Rafinesque), population of Watts Bar Reservoir, of the Tennessee River down stream from Oak Ridge National Laboratory, was investigated in order to describe its age distribution, growth rates, dispersion, and importance as an accumulator of radionuclides. Measurements and scale samples were taken from commercially-caught fish and fish caught in the ORNL tagging operations. Scale impressions were anaiyzed for age and growth phenomena. Dispersion of smallmouth buffalo was investigated by conventional of ging methods and by autoradiographic analyses of scales. Stable and radiochemicsl composition of scales was examined by spectrographic analysis, flame spectrophotometer and radiometric surveys. Calcium was the most abundance element in fish scales with at lease twenty-three other elements present in varying quantities. Fish scaless and bone were found to contain radionuclides of ruthenium, cesium, zirconium, zinc, and cobalt. Radiometric surveys of scales revealed the Watts Bar Reservoir smallmouth buffalo population was a relatively minor accumulator of radionuclides with only 0.08 per cent showing the presence of artificially produced radionuclides. Approximately 6 per cent of the Clinch River fish and 77 per cent of the White Oak Creek fish had accumulations. Limited data on dispersion were determined from conventional tags. Much more dispersion and life history data were determined from autoradiographic analyses of scales. These dispersion data were applied only to individuals because the number was too small for generalizations for the population as a whole. All normal scales containing radionuclide accumulations were found to produce identical autoradiographic patterns of concentric circles which were associated with growth of the fish in contaminated areas. This phenomenon was combined with conventional capture-recapture methods of population estimates in a proposed technique of population studies. A laboratory experiment showed that scales could be tagged with cesium-134, but this radionuclide was found to accumulate in much larger concentrations in the soft tissues than in the bony tissues. (C.H.
Cumulant expansion for ferrimagnetic spin (S_1, s_2) systems
We have generalized the application of cumulant expansion to ferrimagnetic
systems of large spins. We have derived the effective Hamiltonian in terms of
classical variables for a quantum ferrimagnet of large spins. A noninteracting
gas of ferrimagnetic molecules is studied systematically by cumulant expansion
to second order of () where is the exchange coupling in each
molecule, is the smaller spin () and is temperature. We have
observed fairly good results in the convergent regime of the expansion, i.e . We then extend our approach to a system of interacting ferrimagnetic
molecules. For one dimensional nearest neighbor interaction we have observed
that the correlation of more than two neighboring sites is negligible at
moderate and high temperature behavior. Thus the results of a single molecule
can be applied to the chain of interacting molecules for temperatures greater
than classical energy scale, i.e . Finally we will discuss the
effect of spin inhomogeneity on the accuracy of this method.Comment: 9 pages, 5 figures, 2 tables, submitted to PR
Random force in molecular dynamics with electronic friction
Originally conceived to describe thermal diffusion, the Langevin equation includes both a frictional drag and a random force, the latter representing thermal fluctuations first seen as Brownian motion. The random force is crucial for the diffusion problem as it explains why friction does not simply bring the system to a standstill. When using the Langevin equation to describe ballistic motion, the importance of the random force is less obvious and it is often omitted, for example, in theoretical treatments of hot ions and atoms interacting with metals. Here, friction results from electronic nonadiabaticity (electronic friction), and the random force arises from thermal electron–hole pairs. We show the consequences of omitting the random force in the dynamics of H-atom scattering from metals. We compare molecular dynamics simulations based on the Langevin equation to experimentally derived energy loss distributions. Despite the fact that the incidence energy is much larger than the thermal energy and the scattering time is only about 25 fs, the energy loss distribution fails to reproduce the experiment if the random force is neglected. Neglecting the random force is an even more severe approximation than freezing the positions of the metal atoms or modelling the lattice vibrations as a generalized Langevin oscillator. This behavior can be understood by considering analytic solutions to the Ornstein–Uhlenbeck process, where a ballistic particle experiencing friction decelerates under the influence of thermal fluctuations
Comparison of CT, PET, and PET/CT for Staging of Patients with Indolent Non-Hodgkin’s Lymphoma
The aim was to investigate the potential impact of positron emission tomography (PET)/computed tomography (CT) as compared to PET and CT on the staging of patients with indolent lymphoma.
PET/CTs from 45 patients with indolent lymphoma undergoing staging or restaging were studied. Clinical follow-up, additional imaging, and histology served as the gold standard.
PET/CT correctly diagnosed 92 nodal regions as positive for lymphomatous involvement and 458 as disease free vs 68 and 449 for PET and 64 and 459 for CT, respectively. The respective sensitivities, specificities, and accuracies were 99%, 100%, and 99.8% for PET/CT, 68%, 97.5%, and 92.2% for PET, and 70%, 100%, and 94.7% for CT. PET/CT performed significantly better than PET (p < 0.001 for sensitivity, specificity, and accuracy) and CT (p < 0.001 for sensitivity and accuracy). PET/CT also correctly identified significantly more extra-nodal lesions (22) than CT (14) and PET (nine).
PET/CT provides significantly more accurate information compared to PET and CT for the staging and re-staging of patients with indolent lymphoma
Recommended from our members
Inflation and Taxes in a Growing Economy with Debt and Equity Finance
Our tax system was designed for an economy with little or no inflation. The current paper shows that inflation causes capricious changes in the effective rate of tax on capital income and therefore in the real net rate of return that savers receive. This is not only a temporary disequilibrium effect but one which persists in steady-state equilibrium. Unlike earlier papers by Feldstein and by Green and Sheshinski, the current study recognizes that firms finance investment by both debt and equity in a ratio that depends on the tax rates and on the rate of inflation.Economic
From transition magnetic moments to majorana neutrino masses
It is well known that a majorana mass induces a (small) transition magnetic
moment. The converse is also true; in this paper we estimate the loop
contribution of transition magnetic moments to the
neutrino mass matrix . We show that for hierarchical
neutrino masses, the contribution of to can
exceed the experimental value of .Comment: 9 pages, final version (improved notation, some mention of the
dimension 5 mass operator
Statics and dynamics of weakly coupled antiferromagnetic spin-1/2 ladders in a magnetic field
We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work
is motivated by recent experiments on the compound (C5H12N)2CuBr4 (BPCB). We
use a combination of numerical and analytical methods, in particular the
density matrix renormalization group (DMRG) technique, to explore the phase
diagram and the excitation spectra of such a system. We give detailed results
on the temperature dependence of the magnetization and the specific heat, and
the magnetic field dependence of the nuclear magnetic resonance (NMR)
relaxation rate of single ladders. For coupled ladders, treating the weak
interladder coupling within a mean-field or quantum Monte Carlo approach, we
compute the transition temperature of triplet condensation and its
corresponding antiferromagnetic order parameter. Existing experimental
measurements are discussed and compared to our theoretical results. Furthermore
we compute, using time dependent DMRG, the dynamical correlations of a single
spin ladder. Our results allow to directly describe the inelastic neutron
scattering cross section up to high energies. We focus on the evolution of the
spectra with the magnetic field and compare their behavior for different
couplings. The characteristic features of the spectra are interpreted using
different analytical approaches such as the mapping onto a spin chain, a
Luttinger liquid (LL) or onto a t-J model. For values of parameters for which
such measurements exist, we compare our results to inelastic neutron scattering
experiments on the compound BPCB and find excellent agreement. We make
additional predictions for the high energy part of the spectrum that are
potentially testable in future experiments.Comment: 35 pages, 26 figure
Study of chirally motivated low-energy optical potentials
The optical potential in the nuclear medium is evaluated self
consistently from a free-space matrix constructed within a
coupled-channel chiral approach to the low-energy data. The
chiral-model parameters are fitted to a select subset of the low-energy data
{\it plus} the atomic data throughout the periodic table. The resulting
attractive optical potentials are relatively `shallow', with central
depth of the real part about 55 MeV, for a fairly reasonable reproduction of
the atomic data with . Relatively `deep' attractive
potentials of depth about 180 MeV, which result in other phenomenological
approaches with , are ruled out within chirally
motivated models. Different physical data input is required to distinguish
between shallow and deep optical potentials. The ()
reaction could provide such a test, with exclusive rates differing by over a
factor of three for the two classes of potentials. Finally, forward ()
differential cross sections for the production of relatively narrow deeply
bound {\it nuclear} states are evaluated for deep optical
potentials, yielding values considerably lower than those estimated before.Comment: 22 pages, 3 figures, minor revisions, Nucl. Phys. A in pres
- …