45,609 research outputs found
Transition metal oxides using quantum Monte Carlo
The transition metal-oxygen bond appears prominently throughout chemistry and
solid-state physics. Many materials, from biomolecules to ferroelectrics to the
components of supernova remnants contain this bond in some form. Many of these
materials' properties strongly depend on fine details of the TM-O bond and
intricate correlation effects, which make accurate calculations of their
properties very challenging. We present quantum Monte Carlo, an explicitly
correlated class of methods, to improve the accuracy of electronic structure
calculations over more traditional methods like density functional theory. We
find that unlike s-p type bonding, the amount of hybridization of the d-p bond
in TM-O materials is strongly dependant on electronic correlation.Comment: 20 pages, 4 figures, to appear as a topical review in J. Physics:
Condensed Matte
Top-Antitop-Quark Production and Decay Properties at the Tevatron
At the Tevatron, the collider experiments CDF and DO have data sets at their
disposal that comprise a few thousand reconstructed top-antitop-quark pairs and
allow for precision measurements of the cross section as well as production and
decay properties. Besides comparing the measurements to standard model
predictions, these data sets open a window to physics beyond the standard
model. Dedicated analyses look for new heavy gauge bosons, fourth generation
quarks, and flavor-changing neutral currents. In this mini-review the current
status of these measurements is summarized.Comment: Mini-review to be submitted to Mod. Phys. Lett. A, was derived from
the proceedings of the 21st Rencontres de Blois: Windows on the Universe,
Blois, France, 21. - 27. June 2009. 19 pages. 2nd revision: correct a few
minor mistakes, update references
Ionic profiles close to dielectric discontinuities: Specific ion-surface interactions
We study, by incorporating short-range ion-surface interactions, ionic
profiles of electrolyte solutions close to a non-charged interface between two
dielectric media. In order to account for important correlation effects close
to the interface, the ionic profiles are calculated beyond mean-field theory,
using the loop expansion of the free energy. We show how it is possible to
overcome the well-known deficiency of the regular loop expansion close to the
dielectric jump, and treat the non-linear boundary conditions within the
framework of field theory. The ionic profiles are obtained analytically to
one-loop order in the free energy, and their dependence on different
ion-surface interactions is investigated. The Gibbs adsorption isotherm, as
well as the ionic profiles are used to calculate the surface tension, in
agreement with the reverse Hofmeister series. Consequently, from the
experimentally-measured surface tension, one can extract a single adhesivity
parameter, which can be used within our model to quantitatively predict hard to
measure ionic profiles.Comment: 14 pages, 6 figure
An ERTS-1 investigation for Lake Ontario and its basin
The author has identified the following significant results. Methods of manual, semi-automatic, and automatic (computer) data processing were evaluated, as were the requirements for spatial physiographic and limnological information. The coupling of specially processed ERTS data with simulation models of the watershed precipitation/runoff process provides potential for water resources management. Optimal and full use of the data requires a mix of data processing and analysis techniques, including single band editing, two band ratios, and multiband combinations. A combination of maximum likelihood ratio and near-IR/red band ratio processing was found to be particularly useful
Radiation from a charged particle-in-flight from a laminated medium to vacuum
The radiation from a charged particle-in-flight from a semi-infinite
laminated medium to vacuum and back,- from vacuum to the laminated medium, has
been investigated. Expressions for the spectral-angular distribution of
radiation energy in vacuum (at large distances from the boundary of laminated
medium) were obtained for both the cases with no limitations on the amplitude
and variation profile of the laminated medium permittivity. The results of
appropriate numerical calculations are presented and possible applications of
the obtained results are discussed.Comment: 8 pages, 6 figures, contribution to Proceedings of International
Symposium RREPS-2009, 07-11 September, 2009, Zvenigorod, Russi
Quantum Analogue Computing
We briefly review what a quantum computer is, what it promises to do for us,
and why it is so hard to build one. Among the first applications anticipated to
bear fruit is quantum simulation of quantum systems. While most quantum
computation is an extension of classical digital computation, quantum
simulation differs fundamentally in how the data is encoded in the quantum
computer. To perform a quantum simulation, the Hilbert space of the system to
be simulated is mapped directly onto the Hilbert space of the (logical) qubits
in the quantum computer. This type of direct correspondence is how data is
encoded in a classical analogue computer. There is no binary encoding, and
increasing precision becomes exponentially costly: an extra bit of precision
doubles the size of the computer. This has important consequences for both the
precision and error correction requirements of quantum simulation, and
significant open questions remain about its practicality. It also means that
the quantum version of analogue computers, continuous variable quantum
computers (CVQC) becomes an equally efficient architecture for quantum
simulation. Lessons from past use of classical analogue computers can help us
to build better quantum simulators in future.Comment: 10 pages, to appear in the Visions 2010 issue of Phil. Trans. Roy.
Soc.
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