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Epicrates angulifer
Number of Pages: 4Integrative BiologyGeological Science
Baroclinic instability with variable gravity: A perturbation analysis
Solutions for a quasigeostrophic baroclinic stability problem in which gravity is a function of height were obtained. Curvature and horizontal shear of the basic state flow were omitted and the vertical and horizontal temperature gradients of the basic state were taken as constant. The effect of a variable dielectric body force, analogous to gravity, on baroclinic instability for the design of a spherical, baroclinic model for Spacelab was determined. Such modeling could not be performed in a laboratory on the Earth's surface because the body force could not be made strong enough to dominate terrestrial gravity. A consequence of the body force variation and the preceding assumptions was that the potential vorticity gradient of the basic state vanished. The problem was solved using a perturbation method. The solution gives results which are qualitatively similar to Eady's results for constant gravity; a short wavelength cutoff and a wavelength of maximum growth rate were observed. The averaged values of the basic state indicate that both the wavelength range of the instability and the growth rate at maximum instability are increased. Results indicate that the presence of the variable body force will not significantly alter the dynamics of the Spacelab experiment. The solutions are also relevant to other geophysical fluid flows where gravity is constant but the static stability or Brunt-Vaisala frequency is a function of height
Effects of heavy bosonic excitations on QED vacuum
We discuss the contribution of axion-like excitations (ALE) to the vacuum
birrefringence in the limit , where is the mass of
the excitation and the energy of test photons interacting with an
external (intense) magnetic field. The relevance of this term with respect to
the QED contribution depends on the ratio and, from present bounds on
the mass and the coupling constant , we find that in the present low
energy regime, it ranges from to suggesting an interesting
alternative to explore.Comment: References adde and section II rewritten. MPLA in pres
Coupled anharmonic oscillators: the Rayleigh-Ritz approach versus the collocation approach
For a system of coupled anharmonic oscillators we compare the convergence
rate of the variational collocation approach presented recently by Amore and
Fernandez (2010 Phys.Scr.81 045011) with the one obtained using the optimized
Rayleigh-Ritz (RR) method. The monotonic convergence of the RR method allows us
to obtain more accurate results at a lower computational cost.Comment: 7 pages, 1 figur
Robust ab initio calculation of condensed matter: transparent convergence through semicardinal multiresolution analysis
We present the first wavelet-based all-electron density-functional
calculations to include gradient corrections and the first in a solid. Direct
comparison shows this approach to be unique in providing systematic
``transparent'' convergence, convergence with a priori prediction of errors, to
beyond chemical (millihartree) accuracy. The method is ideal for exploration of
materials under novel conditions where there is little experience with how
traditional methods perform and for the development and use of chemically
accurate density functionals, which demand reliable access to such precision.Comment: 4 pages, 3 figures, 4 tables. Submitted to Phys. Rev. Lett. (updated
to include GGA
Analysis of Jovian decametric data: Study of radio emission mechanisms
The Voyager 1 and Voyager 2 Planetary Radio Astronomy Experiments (PRA) have produced the finest set of Jovian decametric radio emission data ever obtained. Jovian decametric L-burst and S-burst arcs were characterized and the data reconciled with models for the radio emission geometry and mechanisms. The first major results involve comparisons of the distribution of arc separations with longitudes. The identification and analyses of systematic variations in the PRA data have yielded interesting results, but only the most obvious features of the data were examined. Analyses of the PRA data were extended with the use of new 6-Sec formats that are more sensitive to the S-bursts
Investigating Galactic supernova remnant candidates with LOFAR
We investigate six supernova remnant (SNR) candidates --- G51.21+0.11,
G52.37-0.70, G53.07+0.49, G53.41+0.03, G53.84-0.75, and the possible shell
around G54.1-0.3 --- in the Galactic Plane using newly acquired LOw-Frequency
ARray (LOFAR) High-Band Antenna (HBA) observations, as well as archival
Westerbork Synthesis Radio Telescope (WSRT) and Very Large Array Galactic Plane
Survey (VGPS) mosaics. We find that G52.37-0.70, G53.84-0.75, and the possible
shell around pulsar wind nebula G54.1+0.3 are unlikely to be SNRs, while
G53.07+0.49 remains a candidate SNR. G51.21+0.11 has a spectral index of
, but lacks X-ray observations and as such requires further
investigation to confirm its nature. We confirm one candidate, G53.41+0.03, as
a new SNR because it has a shell-like morphology, a radio spectral index of
and it has the X-ray spectral characteristics of a
1000-8000 year old SNR. The X-ray analysis was performed using archival
XMM-Newton observations, which show that G53.41+0.03 has strong emission lines
and is best characterized by a non-equilibrium ionization model, consistent
with an SNR interpretation. Deep Arecibo radio telescope searches for a pulsar
associated with G53.41+0.03 resulted in no detection, but place stringent upper
limits on the flux density of such a source if it is beamed towards Earth.Comment: 9 pages, 4 figures, 1 tabl
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