13,265 research outputs found
Local Volume Effects in the Generalized Pseudopotential Theory
The generalized pseudopotential theory (GPT) is a powerful method for
deriving real-space transferable interatomic potentials. Using a coarse-grained
electronic structure, one can explicitly calculate the pair ion-ion and
multi-ion interactions in simple and transition metals. Whilst successful in
determining bulk properties, in central force metals the GPT fails to describe
crystal defects for which there is a significant local volume change. A
previous paper [PhysRevLett.66.3036 (1991)] found that by allowing the GPT
total energy to depend upon some spatially-averaged local electron density, the
energetics of vacancies and surfaces could be calculated within experimental
ranges. In this paper, we develop the formalism further by explicitly
calculating the forces and stress tensor associated with this total energy. We
call this scheme the adaptive GPT (aGPT) and it is capable of both molecular
dynamics and molecular statics. We apply the aGPT to vacancy formation and
divacancy binding in hcp Mg and also calculate the local electron density
corrections to the bulk elastic constants and phonon dispersion for which there
is refinement over the baseline GPT treatment.Comment: 11 pages, 6 figure
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3-5-man chess: Maximals and mzugs
This article reports the combined results of several initiatives in creating and surveying complete suites of endgame tables (EGTs) to the Depth to Mate (DTM) and Depth to Conversion (DTC) metrics. Data on percentage results, maximals and mutual zugzwangs, mzugs, has been filed and made available on the web, as have the DTM EGTs
The pulsed air gust generator Final report
Wind tunnel simulation of jet pulsing apparatus for controlled gust
Heavy Quark Lifetimes, Mixing and CP Violation
This paper emphasizes four topics that represent some of the year's
highlights in heavy quark physics. First of all, a review is given of charm
lifetime measurements and how they lead to better understanding of the
mechanisms of charm decay. Secondly, the CLEO collaboration's new search for
charm mixing is reported, which significantly extends the search for new
physics in that sector. Thirdly, important updates in Bs mixing are summarized,
which result in a new limit on the mass difference, and which further constrain
the unitarity triangle. Finally, the first efforts to measure CP violation in
the B system are discussed. Results are shown for the CDF and ALEPH
measurements of sin(2beta), as well as the CLEO branching fraction measurements
of B-->Kpi,pipi, which have implications for future measurements of alpha.Comment: 25 pages, 15 figures. Talk given at the XIX International Symposium
on Lepton and Photon Interactions, Stanford University, August 9-14, 199
Bargmann representations for deformed harmonic oscillators
Generalizing the case of the usual harmonic oscillator, we look for Bargmann
representations corresponding to deformed harmonic oscillators. Deformed
harmonic oscillator algebras are generated by four operators
and the unity 1 such as , and . We discuss the conditions of existence of
a scalar product expressed with a true integral on the space spanned by the
eigenstates of (or ). We give various examples, in particular we
consider functions that are linear combinations of , and
unity and that correspond to q-oscillators with Fock-representations or with
non-Fock-representations.Comment: 23 pages, Late
The irrationality of a number theoretical series
Denote by the sum of the -th powers of the divisors of ,
and let . We prove that Schinzel's
conjecture H implies that is irrational, and give an unconditional proof
for the case
Pacific Hake, Merluccius productus, Autecology: A Timely Review
Pacific hake, Merluccius productus, the most abundant groundfish in the California Current Large Marine Ecosystem
(CCLME), is a species of both commercial significance, supporting a large international fishery, and ecological importance, connecting other species as both predator and prey. Coastal Pacific hake migrations are characterized by movements between northern summer feeding areas and southern winter spawning areas, with variations in annual abundance, distribution, and the extent of these movements
associated with varying climate-ocean conditions. In general, warm (cool) years with enhanced (reduced) stratification and poleward (equatorward) transport are
often related to good (poor) recruitment, increased (decreased) northward distribution, and reduced (enhanced) growth. However, the classic periodic pattern of annual migration and distribution may no longer be fully representative. Based on recent advances in the understanding of climate-ocean variability off the U.S. west
coast, we hypothesize that the annual movements of Pacific hake are more responsive to climate-ocean variability than previously thought, and further, that changes observed in Pacific hake distributions may reflect long-term changes in climate-ocean conditions in the CCLME. Therefore, an updated
model of these relations is key to effective monitoring and management of this stock, as well as to devising scenarios of future change in the CCLME as a result of climate
variations. The current state of knowledge of the relationship between the Pacific hake and its environment is reviewed, highlighting emerging ideas compared to those of the past, and priorities for future research are suggested
Determination of the critical current density in the d-wave superconductor YBCO under applied magnetic fields by nodal tunneling
We have studied nodal tunneling into YBa2Cu3O7-x (YBCO) films under magnetic
fields. The films' orientation was such that the CuO2 planes were perpendicular
to the surface with the a and b axis at 450 form the normal. The magnetic field
was applied parallel to the surface and perpendicular to the CuO2 planes. The
Zero Bias Conductance Peak (ZBCP) characteristic of nodal tunneling splits
under the effect of surface currents produced by the applied fields. Measuring
this splitting under different field conditions, zero field cooled and field
cooled, reveals that these currents have different origins. By comparing the
field cooled ZBCP splitting to that taken in decreasing fields we deduce a
value of the Bean critical current superfluid velocity, and calculate a Bean
critical current density of up to 3*10^7 A/cm2 at low temperatures. This
tunneling method for the determination of critical currents under magnetic
fields has serious advantages over the conventional one, as it avoids having to
make high current contacts to the sample.Comment: 8 pages, 2 figure
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