5,371 research outputs found
Are classically singular spacetimes quantum mechanically singular as well?
Are the classical singularities of general relativistic spacetimes, normally
defined by the incompleteness of classical particle paths, still singular if
quantum mechanical particles are used instead? This is the question we will
attempt to answer for particles obeying the quantum mechanical wave equations
for scalar, null vector and spinor particles. The analysis will be restricted
to certain static general relativistic spacetimes that classically contain the
mildest true classical singularities, quasiregular singularities.Comment: 3 pages, no figures, submitted to the Proceedings of the Tenth Marcel
Grossmann Meeting on General Relativity, Rio de Janeiro, July 20-26, 200
Experimental Reexamination of Transverse Tensile Strength for IM7/8552 Tape-Laminate Composites
Due to the observed dependence of transverse-tensile strength, YT, on test geometry and specimen size, there is no consensus regarding a test method that can uniquely measure YT. This study reexamines characterization of YT by comparing results from established flexure tests with results from a new tensile test that exhibits consistent failure in the gage region. Additionally, the effects of surface preparation and direction of transverse fracture are investigated. Results show that YT is inversely proportional to specimen volume and surface roughness, and is insensitive to direction of transverse fracture. The relationship between specimen volume and YT is adequately captured by Weibull strength-scaling theory, except at the tails of the YT distributions. However, specimens exhibited microcracking prior to failure, which violates the weak-link assumptions of the Weibull theory. These findings highlight the challenges of using deterministic YT values in progressive damage analysis
Yang-Lee Theory for a Nonequilibrium Phase Transition
To analyze phase transitions in a nonequilibrium system we study its grand
canonical partition function as a function of complex fugacity. Real and
positive roots of the partition function mark phase transitions. This behavior,
first found by Yang and Lee under general conditions for equilibrium systems,
can also be applied to nonequilibrium phase transitions. We consider a
one-dimensional diffusion model with periodic boundary conditions. Depending on
the diffusion rates, we find real and positive roots and can distinguish two
regions of analyticity, which can identified with two different phases. In a
region of the parameter space both of these phases coexist. The condensation
point can be computed with high accuracy.Comment: 4 pages, accepted for publication in Phys.Rev.Let
Recent progress in high-output-voltage silicon solar cells
The status of the technology associated with the development of high output voltage silicon solar cells is reported. The energy conversion efficiency of a double diffusion process is compared to that of a single diffusion process. The efficiency of a 0.1 ohm/cm solar cell is characterized both before and after covering
Extraction of the coupling constant from NN scattering data
We reexamine Chew's method for extracting the coupling constant from
np differential cross section measurements. Values for this coupling are
extracted below 350 MeV, in the potential model region, and up to 1 GeV. The
analyses to 1~GeV have utilized 55 data sets. We compare these results to those
obtained via mapping techniques. We find that these two methods give
consistent results which are in agreement with previous Nijmegen
determinations.Comment: 12 pages of text plus 2 figures. Revtex file and postscript figures
available via anonymous FTP at ftp://clsaid.phys.vt.edu/pub/n
Extraction of radiative decay width for the non-strange partner of Theta^+
Using the results of the GRAAL collaboration on the \eta photoproduction from
the neutron target, we attempt to extract the partial radiative width of the
possible new nucleon resonance N^*(1675). The obtained estimates support this
resonance to be a very attractive candidate for the non-strange member of the
exotic antidecuplet of baryons -- a partner of the \Theta^+ pentaquark. Our
phenomenological value for the transition magnetic moment \mu(n^* n), appears
to be in good agreement with predictions of the Chiral Quark Soliton Model.Comment: 4 pages, v2 corresponds to the journal publicatio
Nucleon-Nucleon Optical Model for Energies to 3 GeV
Several nucleon-nucleon potentials, Paris, Nijmegen, Argonne, and those
derived by quantum inversion, which describe the NN interaction for T-lab below
300$ MeV are extended in their range of application as NN optical models.
Extensions are made in r-space using complex separable potentials definable
with a wide range of form factor options including those of boundary condition
models. We use the latest phase shift analyses SP00 (FA00, WI00) of Arndt et
al. from 300 MeV to 3 GeV to determine these extensions. The imaginary parts of
the optical model interactions account for loss of flux into direct or resonant
production processes. The optical potential approach is of particular value as
it permits one to visualize fusion, and subsequent fission, of nucleons when
T-lab above 2 GeV. We do so by calculating the scattering wave functions to
specify the energy and radial dependences of flux losses and of probability
distributions. Furthermore, half-off the energy shell t-matrices are presented
as they are readily deduced with this approach. Such t-matrices are required
for studies of few- and many-body nuclear reactions.Comment: Latex, 40 postscript pages including 17 figure
Larval morphology of genus Megacephala Latreille, 1802 (Coleoptera: Cicindelidae).
Die Larvalmerkmale der Gattung Megacephala Latreille werden beschrieben und ein Larvenbestimmungsschlüssel für 5 der 6 Untergattungen vorgelegt. Larven von Megacephala sind durch die Y-förmig Gularsutur (ein Merkmal aller Megacephalini) und das fehlende Doppelsklerit ventral am Prämentum charakterisiert. Nur die Untergattung Phaeoxantha besitzt einen gezähnelten Clypeus, den wahrscheinlich plesiomorphen Zustand dieses Merkmals im Verwandtschaftskreis. Die Untergattung Tetracha umfaßt mindestens zwei verschiedene Artengruppen, die sich durch ihre Chaetotaxie am Pronotum und Abdomen deutlich unterscheiden.A description of larval characters of the genus Megacephala Latreille and a larval key to five of the six subgenera are given. The most characteristic larval characters of Megacephala are the Y-shaped gular suture (known from all Megacephalini) and the lack of an oval double sclerite on the prementum. The anterior margin of the clypeus of the subgenus Phaeoxantha is serrated, which is probably the plesiomorphic character state. The subgenus Tetracha includes at least two distinct species groups, which are distinguished by the chaetotaxy of the pronotum and abdomen
Where are the missing members of the baryon antidecuplet?
We analyze what consequences has the observation of exotic pentaquark baryons
on the location of the non-exotic baryons belonging to the antidecuplet. We
suggest that there must be a new nucleon state at 1650-1690 MeV and a new Sigma
baryon at 1760-1810 MeV.Comment: 5 pages, 1 figure. Missing reference adde
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