54,603 research outputs found
T-Shape Molecular Heat Pump
We report on the first molecular device of heat pump modeled by a T-shape
Frenkel-Kontorova lattice. The system is a three-terminal device with the
important feature that the heat can be pumped from the low-temperature region
to the high-temperature region through the third terminal. The pumping action
is achieved by applying a stochastic external force that periodically modulates
the atomic temperature. The temperature, the frequency and the system size
dependence of heat pump are briefly discussed.Comment: 6 figure
On the Helix-coil Transition in Alanine-based Polypeptides in Gas Phase
Using multicanonical simulations, the authors study the effect of charged end
groups on helix formation in alanine based polypeptides. They confirm earlier
reports that neutral polyalanine exhibits a pronounced helix-coil transition in
gas phase simulations. Introducing a charged Lys+ at the C terminal stabilizes
the helix and leads to a higher transition temperature. On the other hand,
adding the Lys+ at the N terminal inhibits helix formation. Instead, a more
globular structure was found. These results are in agreement with recent
experiments on alanine based polypeptides in gas phase. They indicate that
present force fields describe accurately the intramolecular interactions in
proteins
Can the Bump be Observed in the Early Afterglow of GRBS with X-Ray Line Emission Features?
Extremely powerful emission lines are observed in the X-ray afterglow of
several GRBs. The energy contained in the illuminating continuum which is
responsible for the line production exceeds 10 erg, much higher than
that of the collimated GRBs. It constrains the models which explain the
production of X-ray emission lines. In this paper, We argue that this energy
can come from a continuous postburst outflow. Focusing on a central engine of
highly magnetized millisecond pulsar or magnetar we find that afterglow can be
affected by the illuminating continuum, and therefore a distinct achromatic
bump may be observed in the early afterglow lightcurves. With the luminosity of
the continuous outflow which produces the line emission, we define the upper
limit of the time when the bump feature appears. We argue that the reason why
the achromatic bumps have not been detected so far is that the bumps should
appear at the time too early to be observed.Comment: 13 pags, 2 tables, appear in v603 n1 pt1 ApJ March 1, 2004 issu
Data Unfolding with Wiener-SVD Method
Data unfolding is a common analysis technique used in HEP data analysis.
Inspired by the deconvolution technique in the digital signal processing, a new
unfolding technique based on the SVD technique and the well-known Wiener filter
is introduced. The Wiener-SVD unfolding approach achieves the unfolding by
maximizing the signal to noise ratios in the effective frequency domain given
expectations of signal and noise and is free from regularization parameter.
Through a couple examples, the pros and cons of the Wiener-SVD approach as well
as the nature of the unfolded results are discussed.Comment: 26 pages, 12 figures, match the accepted version by JINS
Spectrum of low-lying configurations with negative parity
Spectrum of low-lying five-quark configurations with strangeness quantum
number and negative parity is studied in three kinds of constituent
quark models, namely the one gluon exchange, Goldstone Boson exchange, and
instanton-induced hyperfine interaction models, respectively. Our numerical
results show that the lowest energy states in all the three employed models are
lying at 1800 MeV, about 200 MeV lower than predictions of various
quenched three-quark models. In addition, it is very interesting that the state
with the lowest energy in one gluon exchange model is with spin 3/2, but 1/2 in
the other two models.Comment: Version published in Phys. Rev.
Simulation Subsumption or Déjà vu on the Web
Simulation unification is a special kind of unification adapted to retrieving semi-structured data on the Web. This article introduces simulation subsumption, or containment, that is, query subsumption under simulation unification. Simulation subsumption is crucial in general for query optimization, in particular for optimizing pattern-based search engines, and for the termination of recursive rule-based web languages such as the XML and RDF query language Xcerpt. This paper first motivates and formalizes simulation subsumption. Then, it establishes decidability of simulation subsumption for advanced query patterns featuring descendant constructs, regular expressions, negative subterms (or subterm exclusions), and multiple variable occurrences. Finally, we show that subsumption between two query terms can be decided in O(n!n) where n is the sum of the sizes of both query terms
- …