6,968 research outputs found
Fermions in the pseudoparticle approach
The pseudoparticle approach is a numerical technique to compute path
integrals without discretizing spacetime. The basic idea is to integrate over
those field configurations, which can be represented by a sum of a fixed number
of localized building blocks (pseudoparticles). In a couple of previous papers
we have successfully applied the pseudoparticle approach to pure SU(2)
Yang-Mills theory. In this work we discuss how to incorporate fermionic fields
in the pseudoparticle approach. To test our method, we compute the phase
diagram of the 1+1-dimensional Gross-Neveu model in the large-N limit.Comment: 11 pages, 10 figure
A Detailed Study of Giants and Horizontal Branch Stars in M68: Atmospheric Parameters and Chemical Abundances
In this paper, we present a detailed high-resolution spectroscopic study of
post main sequence stars in the Globular Cluster M68. Our sample, which covers
a range of 4000 K in , and 3.5 dex in , is comprised of
members from the red giant, red horizontal, and blue horizontal branch, making
this the first high-resolution globular cluster study covering such a large
evolutionary and parameter space. Initially, atmospheric parameters were
determined using photometric as well as spectroscopic methods, both of which
resulted in unphysical and unexpected , , , and
[Fe/H] combinations. We therefore developed a hybrid approach that addresses
most of these problems, and yields atmospheric parameters that agree well with
other measurements in the literature. Furthermore, our derived stellar
metallicities are consistent across all evolutionary stages, with
[Fe/H] = 2.42 ( = 0.14) from 25 stars. Chemical
abundances obtained using our methodology also agree with previous studies and
bear all the hallmarks of globular clusters, such as a Na-O anti-correlation,
constant Ca abundances, and mild -process enrichment.Comment: Accepted to the Astronomical Journa
Structure of smectic defect cores: an X-ray study of 8CB liquid crystal ultra-thin films
We study the structure of very thin liquid crystal films frustrated by
antagonistic anchorings in the smectic phase. In a cylindrical geometry, the
structure is dominated by the defects for film thicknesses smaller than 150 nm
and the detailed topology of the defects cores can be revealed by x-ray
diffraction. They appear to be split in half tube-shaped Rotating Grain
Boundaries (RGB). We determine the RGB spatial extension and evaluate its
energy per unit line. Both are significantly larger than the ones usually
proposed in the literatureComment: 4 page
Signature of Electronic Correlations in the Optical Conductivity of the Doped Semiconductor Si:P
Electronic transport in highly doped but still insulating silicon at low
temperatures is dominated by hopping between localized states; it serves as a
model system of a disordered solid for which the electronic interaction can be
investigated. We have studied the frequency-dependent conductivity of
phosphorus-doped silicon in the THz frequency range (30 GHz to 3 THz) at low
temperatures K. The crossover in the optical conductivity from a
linear to a quadratic frequency dependence as predicted by Efros and Shklovskii
is observed qualitatively; however, the simple model does not lead to a
quantitative agreement. Covering a large range of donor concentration, our
temperature- and frequency-dependent investigations reveal that electronic
correlation effects between the localized states play an important and complex
role at low temperatures. In particular we find a super-linear frequency
dependence of the conductivity that highlights the influence of the density of
states, i.e. the Coulomb gap, on the optical conductivity. When approaching the
metal-to-insulator transition by increasing doping concentration, the
dielectric constant and the localization length exhibit critical behavior.Comment: 9 pages, 8 figures, 1 tabl
Extracting Atoms on Demand with Lasers
We propose a scheme that allows to coherently extract cold atoms from a
reservoir in a deterministic way. The transfer is achieved by means of
radiation pulses coupling two atomic states which are object to different
trapping conditions. A particular realization is proposed, where one state has
zero magnetic moment and is confined by a dipole trap, whereas the other state
with non-vanishing magnetic moment is confined by a steep microtrap potential.
We show that in this setup a predetermined number of atoms can be transferred
from a reservoir, a Bose-Einstein condensate, into the collective quantum state
of the steep trap with high efficiency in the parameter regime of present
experiments.Comment: 11 pages, 8 figure
Two-photon absorption spectroscopy of stilbene and phenanthrene: Excited-state analysis and comparison with ethylene and toluene
The following article appeared in The Journal of Chemical Physics 146, 174102 (2017); doi: 10.1063/1.498204 and may be found at http://doi.org/10.1063/1.4982045Two-photon absorption (2PA) spectra of several prototypical molecules (ethylene, toluene, trans- and cis-stilbene, and phenanthrene) are computed using the equation-of-motion coupled-cluster method with single and double substitutions. The states giving rise to the largest 2PA cross sections are analyzed in terms of their orbital character and symmetry-based selection rules. The brightest 2PAtransitions correspond to Rydberg-like states from fully symmetric irreducible representations. Symmetry selection rules dictate that totally symmetric transitions typically have the largest 2PA cross sections for an orientationally averaged sample when there is no resonance enhancement via one-photon accessible intermediate states. Transition dipole arguments suggest that the strongest transitions also involve the most delocalized orbitals, including Rydberg states, for which the relative transition intensities can be rationalized in terms of atomic selection rules. Analysis of the 2PA transitions provides a foundation for predicting relative 2PA cross sections of conjugated molecules based on simple symmetry and molecular orbital arguments
Key impact of an uncommon plasmid on bacillus amyloliquefaciens subsp. plantarum S499 developmental traits and lipopeptide production
The rhizobacterium Bacillus amyloliquefaciens subsp. plantarum S499 (S499) is particularly efficient in terms of the production of cyclic lipopeptides, which are responsible for the high level of plant disease protection provided by this strain. Sequencing of the S499 genome has highlighted genetic differences and similarities with the closely related rhizobacterium B. amyloliquefaciens subsp. plantarum FZB42 (FZB42). More specifically, a rare 8008 bp plasmid (pS499) harboring a rap-phr cassette constitutes a major distinctive element between S499 and FZB42. By curing this plasmid, we demonstrated that its presence is crucial for preserving the typical physiology of S499 cells. Indeed, the growth rate and extracellular proteolytic activity were significantly affected in the cured strain (S499 P-). Furthermore, pS499 made a significant contribution to the regulation of cyclic lipopeptide production. Surfactins and fengycins were produced in higher quantities by S499 P-, whereas lower amounts of iturins were detected. In line with the increase in surfactin release, bacterial motility improved after curing, whereas the ability to form biofilm was reduced in vitro. The antagonistic effect against phytopathogenic fungi was also limited for S499 P-, most probably due to the reduction of iturin production. With the exception of this last aspect, S499 P- behavior fell between that of S499 and FZB42, suggesting a role for the plasmid in shaping some of the phenotypic differences observed in the two strains. © 2017 Molinatto, Franzil, Steels, Puopolo, Pertot and Ongena
The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation
We present a comprehensive catalog of high signal-to-noise spectra obtained
with the DEIMOS spectrograph on the Keck II telescope for a sample of
F850LP<22.43 (AB) field spheroidal (E+S0s; 163) and bulge dominated disk (61)
galaxies in the redshift range 0.2<z<1.2. We examine the zero point, tilt and
scatter of the Fundamental Plane (FP) as a function of redshift and
morphological properties, carefully accounting for luminosity-dependent biases
via Montecarlo simulations. The evolution of the overall FP can be represented
by a mean change in effective mass-to-light ratio given by <d \log (M/L_{\rm
B})/dz>=-0.72^{+0.07}_{-0.05}\pm0.04. However, this evolution depends
significantly on the dynamical mass, being slower for larger masses as reported
in a previous letter. In addition, we separately show the intrinsic scatter of
the FP increases with redshift as d(rms(M/L_{\rm B}))/dz=0.040\pm0.015.
Although these trends are consistent with single burst populations which formed
at for high mass spheroidals and z_{f}~1.2 for lower mass systems, a
more realistic picture is that most of the stellar mass formed in all systems
at z>2 with subsequent activity continuing to lower redshifts (z<1.2). The
fraction of stellar mass formed at recent times depend strongly on galactic
mass, ranging from <1% for masses above 10^{11.5} M_{\odot} to 20-40% below
10^{11} M_{\odot}. Independent support for recent activity is provided by
spectroscopic ([\ion{O}{2}] emission, H\delta) and photometric (blue cores and
broad-band colors) diagnostics. Via the analysis of a large sample with many
independent diagnostics, we are able to reconcile previously disparate
interpretations of the assembly history of field spheroidals. [Abridged]Comment: 26 pages including 24 figures, submitted to ApJ. Complete and compact
version with full resolution images available at
http://www.astro.ucla.edu/~ttreu/ms.pd
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