5,165 research outputs found
Vortex Lattice in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} Well Above the First-Order Phase-Transition Boundary
Measurements of non-local in-plane resistance originating from transverse
vortex-vortex correlations have been performed on a
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} high-T_c superconductor in a magnetic field up
to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid
vortex lattice does exist over a broad portion of the magnetic field --
temperature (H-T) phase diagram, well above the first-order transition boundary
H_{FOT}(T). The results also provide evidence for the vortex lattice melting
and vortex liquid decoupling phase transitions, occurring above the H_{FOT}(T).Comment: 14 pages, 10 figure
Update on the Pyramid Scheme
We summarize recent work in which we attempt to make a consistent model of
LHC physics, from the Pyramid Scheme. The models share much with the NMSSM, in
particular, enhanced tree level contributions to the Higgs mass and a
preference for small tan {\beta}. There are 3 different singlet fields, and a
new strongly coupled gauge theory, so the constraints of perturbative
unification are quite different. We outline our general approach to the model,
which contains a Kahler potential for three of the low energy fields, which is
hard to calculate. Detailed calculations, based on approximations to the Kahler
potential, will be presented in a future publication.Comment: LaTeX 2e/ 9 page
The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches
Any search effort for gravitational waves (GW) using interferometric
detectors like LIGO needs to be able to identify if and when noise is coupling
into the detector's output signal. The Critical Coupling Likelihood (CCL)
method has been developed to characterize potential noise coupling and in the
future aid GW search efforts. By testing two hypotheses about pairs of
channels, CCL is able to identify undesirable coupled instrumental noise from
potential GW candidates. Our preliminary results show that CCL can associate up
to of observed artifacts with , to local noise sources,
while reducing the duty cycle of the instrument by . An approach
like CCL will become increasingly important as GW research moves into the
Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ
Too dense to go through: The importance of low-mass clusters for satellite quenching
We study the evolution of satellite galaxies in clusters of the C-EAGLE
simulations, a suite of 30 high-resolution cosmological hydrodynamical zoom-in
simulations based on the EAGLE code. We find that the majority of galaxies that
are quenched at ( 80) reached this state in a dense
environment (logM[M]13.5). At low redshift,
regardless of the final cluster mass, galaxies appear to reach their quenching
state in low mass clusters. Moreover, galaxies quenched inside the cluster that
they reside in at are the dominant population in low-mass clusters, while
galaxies quenched in a different halo dominate in the most massive clusters.
When looking at clusters at , their in-situ quenched population
dominates at all cluster masses. This suggests that galaxies are quenched
inside the first cluster they fall into. After galaxies cross the cluster's
they rapidly become quenched ( 1Gyr). Just a small fraction
of galaxies () is capable of retaining their gas for a longer
period of time, but after 4Gyr, almost all galaxies are quenched. This
phenomenon is related to ram pressure stripping and is produced when the
density of the intracluster medium reaches a threshold of
n (cm). These results suggest that
galaxies start a rapid-quenching phase shortly after their first infall inside
and that, by the time they reach , most of them are already
quenched.Comment: 14 pages, 8 figures, Submitted to MNRA
A first--order irreversible thermodynamic approach to a simple energy converter
Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
On the formation of hot Neptunes and super-Earths
The discovery of short-period Neptune-mass objects, now including the
remarkable system HD69830 (Lovis et al. 2006) with three Neptune analogues,
raises difficult questions about current formation models which may require a
global treatment of the protoplanetary disc. Several formation scenarios have
been proposed, where most combine the canonical oligarchic picture of core
accretion with type I migration (e.g. Terquem & Papaloizou 2007) and planetary
atmosphere physics (e.g. Alibert et al. 2006). To date, published studies have
considered only a small number of progenitors at late times. This leaves
unaddressed important questions about the global viability of the models. We
seek to determine whether the most natural model -- namely, taking the
canonical oligarchic picture of core accretion and introducing type I migration
-- can succeed in forming objects of 10 Earth masses and more in the innermost
parts of the disc. This problem is investigated using both traditional
semianalytic methods for modelling oligarchic growth as well as a new parallel
multi-zone N-body code designed specifically for treating planetary formation
problems with large dynamic range (McNeil & Nelson 2009). We find that it is
extremely difficult for oligarchic tidal migration models to reproduce the
observed distribution. Even under many variations of the typical parameters, we
form no objects of mass greater than 8 Earth masses. By comparison, it is
relatively straightforward to form icy super-Earths. We conclude that either
the initial conditions of the protoplanetary discs in short-period Neptune
systems were substantially different from the standard disc models we used, or
there is important physics yet to be understood.Comment: 19 pages, 18 figures. Final version accepted to MNRAS 30 September
200
No evidence of a hot Jupiter around HD 188753 A
The discovery of a short-period giant planet (a hot Jupiter) around the
primary component of the triple star system HD 188753 has often been considered
as an important observational evidence and as a serious challenge to
planet-formation theories. Following this discovery, we monitored HD 188753
during one year to better characterize the planetary orbit and the feasibility
of planet searches in close binaries and multiple star systems. We obtained
Doppler measurements of HD 188753 with the ELODIE spectrograph at the
Observatoire de Haute-Provence. We then extracted radial velocities for the two
brightest components of the system using our multi-order, two-dimensional
correlation algorithm, TODCOR. Our observations and analysis do not confirm the
existence of the short-period giant planet previously reported around HD 188753
A. Monte Carlo simulations show that we had both the precision and the temporal
sampling required to detect a planetary signal like the one quoted. From our
failure to detect the presumed planet around HD 188753 A and from the available
data on HD 188753, we conclude that there is currently no convincing evidence
of a close-in giant planet around HD 188753 A.Comment: 8 pages, 3 figures, accepted for publication in A&A. Corrected typos
and minor mistake
Nonlinear software sensor for monitoring genetic regulation processes with noise and modeling errors
Nonlinear control techniques by means of a software sensor that are commonly
used in chemical engineering could be also applied to genetic regulation
processes. We provide here a realistic formulation of this procedure by
introducing an additive white Gaussian noise, which is usually found in
experimental data. Besides, we include model errors, meaning that we assume we
do not know the nonlinear regulation function of the process. In order to
illustrate this procedure, we employ the Goodwin dynamics of the concentrations
[B.C. Goodwin, Temporal Oscillations in Cells, (Academic Press, New York,
1963)] in the simple form recently applied to single gene systems and some
operon cases [H. De Jong, J. Comp. Biol. 9, 67 (2002)], which involves the
dynamics of the mRNA, given protein, and metabolite concentrations. Further, we
present results for a three gene case in co-regulated sets of transcription
units as they occur in prokaryotes. However, instead of considering their full
dynamics, we use only the data of the metabolites and a designed software
sensor. We also show, more generally, that it is possible to rebuild the
complete set of nonmeasured concentrations despite the uncertainties in the
regulation function or, even more, in the case of not knowing the mRNA
dynamics. In addition, the rebuilding of concentrations is not affected by the
perturbation due to the additive white Gaussian noise and also we managed to
filter the noisy output of the biological systemComment: 21 pages, 7 figures; also selected in vjbio of August 2005; this
version corrects a misorder in the last three references of the published
versio
Antimicrobial and Antibiofilm Activity of Synergistic Combinations of a Commercially Available Small Compound Library With Colistin Against Pseudomonas aeruginosa
Biofilm-associated Pseudomonas aeruginosa infections remain a significant clinical challenge since the conventional antibiotic treatment or combination therapies are largely ineffective; and new approaches are needed. To circumvent the major challenges associated with discovery of new antimicrobials, we have screened a library of compounds that are commercially available and approved by the FDA (Prestwick Chemical Library) against P. aeruginosa for effective antimicrobial and anti-biofilm activity. A preliminary screen of the Prestwick Chemical Library alone did not yield any repositionable candidates, but in a screen of combinations with a fixed sub-inhibitory concentration of the antibiotic colistin we observed 10 drugs whose bacterial inhibiting activity was reproducibly enhanced, seven of which were enhanced by more than 50%. We performed checkerboard assays of these seven drugs in combination with colistin against planktonic cells, and analysis of their interactions over the complete combination matrix using the Zero Interaction Potency (ZIP) model revealed interactions that varied from highly synergistic to completely antagonistic. Of these, five combinations that showed synergism were down-selected and tested against preformed biofilms of P. aeruginosa. Two of the five combinations were active against preformed biofilms of both laboratory and clinical strain of P. aeruginosa, resulting in a 2-log reduction in culturable cells. In summary, we have identified synergistic combinations of five commercially available, FDA-approved drugs and colistin that show antimicrobial activity against planktonic P. aeruginosa (Clomiphene Citrate, Mitoxantrone Dihydrochloride, Methyl Benzethonium Chloride, Benzethonium Chloride, and Auranofin) as well as two combinations (Auranofin and Clomiphene Citrate) with colistin that show antibiofilm activity
Possible Disintegrating Short-Period Super-Mercury Orbiting KIC 12557548
We report here on the discovery of stellar occultations, observed with
Kepler, that recur periodically at 15.685 hour intervals, but which vary in
depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star
that is apparently being occulted is KIC 12557548, a K dwarf with T_eff = 4400
K and V = 16. Because the eclipse depths are highly variable, they cannot be
due solely to transits of a single planet with a fixed size. We discuss but
dismiss a scenario involving a binary giant planet whose mutual orbit plane
precesses, bringing one of the planets into and out of a grazing transit. We
also briefly consider an eclipsing binary, that either orbits KIC 12557548 in a
hierarchical triple configuration or is nearby on the sky, but we find such a
scenario inadequate to reproduce the observations. We come down in favor of an
explanation that involves macroscopic particles escaping the atmosphere of a
slowly disintegrating planet not much larger than Mercury. The particles could
take the form of micron-sized pyroxene or aluminum oxide dust grains. The
planetary surface is hot enough to sublimate and create a high-Z atmosphere;
this atmosphere may be loaded with dust via cloud condensation or explosive
volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind,
dragging dust grains with it. We infer a mass loss rate from the observations
of order 1 M_E/Gyr, with a dust-to-gas ratio possibly of order unity. For our
fiducial 0.1 M_E planet, the evaporation timescale may be ~0.2 Gyr. Smaller
mass planets are disfavored because they evaporate still more quickly, as are
larger mass planets because they have surface gravities too strong to sustain
outflows with the requisite mass-loss rates. The occultation profile evinces an
ingress-egress asymmetry that could reflect a comet-like dust tail trailing the
planet; we present simulations of such a tail.Comment: 14 pages, 7 figures; submitted to ApJ, January 10, 2012; accepted
March 21, 201
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