27,655 research outputs found
Barbaetis: A New Genus of Eastern Nearctic Mayflies (Ephemeroptera: Baetidae)
The new genus Barbaetis Waltz and McCafferty, and new species Barbaetis benfieldi Kennedy are described from larvae collected from the New River, Virginia. Barbaetis is easily told from Baetis by the presence of procoxal osmobranchia. Cladistics of B. benfieldi, related Pseudocloeon species, and the lutheri and pavidus complexes of Baetis are presented and indicate the need for further taxonomic revision. The habitat of B. benfieldi is described in terms of several ecological parameters. The new species demonstrates a univoltine life history with postembryonic development restricted to a short springtime period
Making the small oblique parameters large
We compute the oblique parameters, including the three new parameters ,
and introduced recently by the Montreal group, for the case of one
scalar multiplet of arbitrary weak isospin and weak hypercharge . We
show that, when the masses of the heaviest and lightest components of the
multiplet remain constant, but increases, the oblique parameter and
the three new oblique parameters increase like , while only
increases like . For large multiplets with masses not much higher than , the oblique parameters and may become much larger than
and .Comment: 9 pages, standard LATEX, 3 figures available from the authors, report
CMU-HEP93-17 and DOE-ER/40682-4
A Fast Algorithm for Simulating the Chordal Schramm-Loewner Evolution
The Schramm-Loewner evolution (SLE) can be simulated by dividing the time
interval into N subintervals and approximating the random conformal map of the
SLE by the composition of N random, but relatively simple, conformal maps. In
the usual implementation the time required to compute a single point on the SLE
curve is O(N). We give an algorithm for which the time to compute a single
point is O(N^p) with p<1. Simulations with kappa=8/3 and kappa=6 both give a
value of p of approximately 0.4.Comment: 17 pages, 10 figures. Version 2 revisions: added a paragraph to
introduction, added 5 references and corrected a few typo
Fast field-cycling NMR of cartilage : a way toward molecular imaging
Peer reviewedPublisher PD
Fabrication and properties of gallium phosphide variable colour displays
The unique properties of single-junction gallium phosphide devices incorporating both red and green radiative recombination centers were investigated in application to the fabrication of monolithic 5 x 7 displays capable of displaying symbolic and alphanumeric information in a multicolor format. A number of potentially suitable material preparation techniques were evaluated in terms of both material properties and device performance. Optimum results were obtained for double liquid-phase-epitaxial process in which an open-tube dipping technique was used for n-layer growth and a sealed tipping procedure for subsequent p-layer growth. It was demonstrated that to prepare devices exhibiting a satisfactory range of dominant wavelengths which can be perceived as distinct emission colors extending from the red through green region of the visible spectrum involves a compromise between the material properties necessary for efficient red emission and those considered optimum for efficient green emission
Particle Swarm Optimization and gravitational wave data analysis: Performance on a binary inspiral testbed
The detection and estimation of gravitational wave (GW) signals belonging to
a parameterized family of waveforms requires, in general, the numerical
maximization of a data-dependent function of the signal parameters. Due to
noise in the data, the function to be maximized is often highly multi-modal
with numerous local maxima. Searching for the global maximum then becomes
computationally expensive, which in turn can limit the scientific scope of the
search. Stochastic optimization is one possible approach to reducing
computational costs in such applications. We report results from a first
investigation of the Particle Swarm Optimization (PSO) method in this context.
The method is applied to a testbed motivated by the problem of detection and
estimation of a binary inspiral signal. Our results show that PSO works well in
the presence of high multi-modality, making it a viable candidate method for
further applications in GW data analysis.Comment: 13 pages, 5 figure
Field dependence of the temperature at the peak of the ZFC magnetization
The effect of an applied magnetic field on the temperature at the maximum of
the ZFC magnetization, , is studied using the recently obtained
analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for
the prefactor of the N\'{e}el relaxation time which allow one to precisely
calculate the prefactor in the N\'{e}el-Brown model and thus the blocking
temperature as a function of the coefficients of the Taylor series expansion of
the magnetocrystalline anisotropy. The present calculations indicate that even
a precise determination of the prefactor in the N\'{e}el-Brown theory, which
always predicts a monotonic decrease of the relaxation time with increasing
field, is insufficient to explain the effect of an applied magnetic field on
the temperature at the maximum of the ZFC magnetization. On the other hand, we
find that the non linear field-dependence of the magnetization along with the
magnetocrystalline anisotropy appears to be of crucial importance to the
existence of this maximum.Comment: 14 LaTex209 pages, 6 EPS figures. To appear in J. Phys.: Condensed
Matte
CPT- and B-Violation: The p-pbar Sector
The CPT symmetry of relativistic quantum field theory requires the total
lifetimes of particles and antiparticles be equal. Detection of pbar lifetime
shorter than tau_p > O(10^32) yr would signal breakdown of CPT invariance, in
combination with B-violation. The best current limit on tau_pbar, inferred from
cosmic ray measurements, is about one Myr, placing lower limits on
CPT-violating scales that depend on the exact mechanism. Paths to CPT breakdown
within and outside ordinary quantum mechanics are sketched. Many of the
limiting CPT-violating scales in pbar decay lie within the weak-to-Planck
range.Comment: 6 pages, LaTeX, .sty file included; based on contribution to CPT98
Conference; minor changes, accepted by Mod. Phys. Lett.
Solution of One-dimensional Dirac Equation via Poincare Map
We solve the general one-dimensional Dirac equation using a "Poincare Map"
approach which avoids any approximation to the spacial derivatives and reduces
the problem to a simple recursive relation which is very practical from the
numerical implementation point of view. To test the efficiency and rapid
convergence of this approach we apply it to a vector coupling Woods--Saxon
potential, which is exactly solvable. Comparison with available analytical
results is impressive and hence validates the accuracy and efficiency of this
method.Comment: 8 pages, 6 figures. Version to appear in EP
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