1,017 research outputs found
Finite-temperature scalar fields and the cosmological constant in an Einstein universe
We study the back reaction effect of massless minimally coupled scalar field
at finite temperatures in the background of Einstein universe. Substituting for
the vacuum expectation value of the components of the energy-momentum tensor on
the RHS of the Einstein equation, we deduce a relationship between the radius
of the universe and its temperature. This relationship exhibit a maximum
temperature, below the Planck scale, at which the system changes its behaviour
drastically. The results are compared with the case of a conformally coupled
field. An investigation into the values of the cosmological constant exhibit a
remarkable difference between the conformally coupled case and the minimally
coupled one.Comment: 7 pages, 2 figure
A Coloring Algorithm for Disambiguating Graph and Map Drawings
Drawings of non-planar graphs always result in edge crossings. When there are
many edges crossing at small angles, it is often difficult to follow these
edges, because of the multiple visual paths resulted from the crossings that
slow down eye movements. In this paper we propose an algorithm that
disambiguates the edges with automatic selection of distinctive colors. Our
proposed algorithm computes a near optimal color assignment of a dual collision
graph, using a novel branch-and-bound procedure applied to a space
decomposition of the color gamut. We give examples demonstrating the
effectiveness of this approach in clarifying drawings of real world graphs and
maps
A First-Quantized Formalism for Cosmological Particle Production
We show that the amount of particle production in an arbitrary cosmological
background can be determined using only the late-time positive-frequency modes.
We don't refer to modes at early times, so there is no need for a Bogolubov
transformation. We also show that particle production can be extracted from the
Feynman propagator in an auxiliary spacetime. This provides a first-quantized
formalism for computing particle production which, unlike conventional
Bogolubov transformations, may be amenable to a string-theoretic
generalization.Comment: 18 pages, LaTeX; v2: significantly revised for clarity; conclusions
unchange
Localized surface states in HTSC: Alternative mechanism of zero-bias conductance peaks
It is shown that the quasiparticle states localized in the vicinity of
surface imperfections of atomic size can be responsible for the zero-bias
tunneling conductance peaks in high-Tc superconductors. The contribution from
these states can be easily separated from other mechanisms using their
qualitatively different response on an external magnetic field.Comment: REVTeX, 4 pages, 2 figs; to be published in PR
Theoretical approach and impact of correlations on the critical packet generation rate in traffic dynamics on complex networks
Using the formalism of the biased random walk in random uncorrelated networks
with arbitrary degree distributions, we develop theoretical approach to the
critical packet generation rate in traffic based on routing strategy with local
information. We explain microscopic origins of the transition from the flow to
the jammed phase and discuss how the node neighbourhood topology affects the
transport capacity in uncorrelated and correlated networks.Comment: 6 pages, 5 figure
Residual cognitive deficits 50 years after lead poisoning during childhood
The long term neurobehavioural consequences of childhood lead poisoning are not known. In this study adult subjects with a documented history of lead poisoning before age 4 and matched controls were examined with an abbreviated battery of neuropsychological tests including measures of attention, reasoning, memory, motor speed, and current mood. The subjects exposed to lead were inferior to controls on almost all of the cognitive tasks. This pattern of widespread deficits resembles that found in children evaluated at the time of acute exposure to lead rather than the more circumscribed pattern typically seen in adults exposed to lead. Despite having completed as many years of schooling as controls, the subjects exposed to lead were lower in lifetime occupational status. Within the exposed group, performance on the neuropsychological battery and occupational status were related, consistent with the presumed impact of limitations in neuropsychological functioning on everyday life. The results suggest that many subjects exposed to lead suffered acute encephalopathy in childhood which resolved into a chronic subclinical encephalopathy with associated cognitive dysfunction still evident in adulthood. These findings lend support to efforts to limit exposure to lead in childhood
Influence of impurity scattering on tunneling conductance in normal metal- d -wave superconductor junctions
Tunneling conductance spectra between a normal metal / d-wave superconductor
junction under the presence of bulk impurities in the superconductor are
studied. The quasiclassical theory has been applied to calculate the spatial
variation of the pair potential and the effect of impurity scattering has been
introduced by t-matrix approximation. The magnitude of a subdominant s-wave
component at the interface is shown to robust against the impurity scattering
while that for a subdominant -wave component is largely suppressed with
the increase of the impurity scattering rate. The zero-bias conductance peak
due to the zero-energy Andreev bound states is significantly broadened for the
case of Born limit impurity compared with that of unitary limit impurity.Comment: 14 pages, 5 figure
CO adsorption on neutral iridium clusters
The adsorption of carbon monoxide on neutral iridium clusters in the size
range of n = 3 to 21 atoms is investigated with infrared multiple photon
dissociation spectroscopy. For each cluster size only a single v(CO) band is
present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1
(n = 18) which can be attributed to an atop binding geometry. This behaviour is
compared to the CO binding geometries on clusters of other group 9 and 10
transition metals as well as to that on extended surfaces. The preference of Ir
for atop binding is rationalized by relativistic effects on the electronic
structure of the later 5d metals
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