4,657 research outputs found
Marginal Fermi Liquid with a Two-Dimensional Patched Fermi Surface
We consider a model composed of Landau quasiparticle states with patched
Fermi surfaces (FS) sandwiched by states with flat FS to simulate the ``cold''
spot regions in cuprates. We calculate the one particle irreducible function
and the self-energy up to two-loop order. Using renormalization group arguments
we show that in the forward scattering channel the renormalized coupling
constant is never infrared stable due to the flat FS sectors. Furthemore we
show that the self-energy scales with energy as as , and thus the Fermi liquid state within each FS
patch is turned into a marginal Fermi liquid.Comment: 5 pages, 3 ps figure
Extrasolar Planets in Mean-Motion Resonance: Apses Alignment and Asymmetric Stationary Solutions
In recent years several pairs of extrasolar planets have been discovered in
the vicinity of mean-motion commensurabilities. In some cases, such as the
Gliese 876 system, the planets seem to be trapped in a stationary solution, the
system exhibiting a simultaneous libration of the resonant angle theta_1 = 2
lambda_2 - lambda_1 - varpi_1 and of the relative position of the pericenters.
In this paper we analyze the existence and location of these stable
solutions, for the 2/1 and 3/1 resonances, as function of the masses and
orbital elements of both planets. This is undertaken via an analytical model
for the resonant Hamiltonian function. The results are compared with those of
numerical simulations of the exact equations.
In the 2/1 commensurability, we show the existence of three principal
families of stationary solutions: (i) aligned orbits, in which theta_1 and
varpi_1 - varpi_2 both librate around zero, (ii) anti-aligned orbits, in which
theta_1=0 and the difference in pericenter is 180 degrees, and (iii) asymmetric
stationary solutions, where both the resonant angle and varpi_1 - varpi_2 are
constants with values different of 0 or 180 degrees. Each family exists in a
different domain of values of the mass ratio and eccentricities of both
planets. Similar results are also found in the 3/1 resonance.
We discuss the application of these results to the extrasolar planetary
systems and develop a chart of possible planetary orbits with apsidal
corotation. We estimate, also, the maximum planetary masses in order that the
stationary solutions are dynamically stable.Comment: 25 pages, 10 figures. Submitted to Ap
On planetary mass determination in the case of super-Earths orbiting active stars. The case of the CoRoT-7 system
This investigation uses the excellent HARPS radial velocity measurements of
CoRoT-7 to re-determine the planet masses and to explore techniques able to
determine mass and elements of planets discovered around active stars when the
relative variation of the radial velocity due to the star activity cannot be
considered as just noise and can exceed the variation due to the planets. The
main technique used here is a self-consistent version of the high-pass filter
used by Queloz et al. (2009) in the first mass determination of CoRoT-7b and
CoRoT-7c. The results are compared to those given by two alternative
techniques: (1) The approach proposed by Hatzes et al. (2010) using only those
nights in which 2 or 3 observations were done; (2) A pure Fourier analysis. In
all cases, the eccentricities are taken equal to zero as indicated by the study
of the tidal evolution of the system; the periods are also kept fixed at the
values given by Queloz et al. Only the observations done in the time interval
BJD 2,454,847 - 873 are used because they include many nights with multiple
observations; otherwise it is not possible to separate the effects of the
rotation fourth harmonic (5.91d = Prot/4) from the alias of the orbital period
of CoRoT-7b (0.853585 d). The results of the various approaches are combined to
give for the planet masses the values 8.0 \pm 1.2 MEarth for CoRoT-7b and 13.6
\pm 1.4 MEarth for CoRoT 7c. An estimation of the variation of the radial
velocity of the star due to its activity is also given.The results obtained
with 3 different approaches agree to give masses larger than those in previous
determinations. From the existing internal structure models they indicate that
CoRoT-7b is a much denser super-Earth. The bulk density is 11 \pm 3.5 g.cm-3 .
CoRoT-7b may be rocky with a large iron core.Comment: 12 pages, 11 figure
Initial pseudo-steady state & asymptotic KPZ universality in semiconductor on polymer deposition
The Kardar-Parisi-Zhang (KPZ) class is a paradigmatic example of universality
in nonequilibrium phenomena, but clear experimental evidences of asymptotic
2D-KPZ statistics are still very rare, and far less understanding stems from
its short-time behavior. We tackle such issues by analyzing surface
fluctuations of CdTe films deposited on polymeric substrates, based on a huge
spatio-temporal surface sampling acquired through atomic force microscopy. A
\textit{pseudo}-steady state (where average surface roughness and spatial
correlations stay constant in time) is observed at initial times, persisting up
to deposition of monolayers. This state results from a fine
balance between roughening and smoothening, as supported by a phenomenological
growth model. KPZ statistics arises at long times, thoroughly verified by
universal exponents, spatial covariance and several distributions. Recent
theoretical generalizations of the Family-Vicsek scaling and the emergence of
log-normal distributions during interface growth are experimentally confirmed.
These results confirm that high vacuum vapor deposition of CdTe constitutes a
genuine 2D-KPZ system, and expand our knowledge about possible
substrate-induced short-time behaviors.Comment: 13 pages, 8 figures, 2 table
Sorption of Cr(III) from aqueous solutions by spent brewery grain
Two types of spent brewery grains were tested for Cr(III) uptake from aqueous solutions: not treated
spent grains (NTSG), obtained by abundant washing of spent grain obtained from a Portuguese
brewing industry with distilled water, and treated spent grain (TSG), prepared by treating NTSG with
NaOH 0.5 M for four hours followed by washing with distilled water.
Both materials were mixed with chromium solutions (50 and 100 mg Cr(III)/L), varying medium pH
from 3 to 5. Maximum metal uptake occurred at pH 5. Langmuir isotherm model well describes
Cr(III) biosorption by NTSG and TSG. The maximum uptake capacity obtained was 17.84 mg
Cr(III)/g NTSG and 13.87 mg Cr(III)/g TSG. Considering that Langmuir constant, b, reflecting the
affinity between the sorbent and the sorbate is lower for NTSG (0.0749 L/mg) it is possible to
conclude that the alkalis treatment does not improve spent grain uptake capacity for Cr(III).Fundação para a CiĂȘncia e a Tecnologia (FCT) - PRAXIS XXI/BD/15945/98
Cr(III) removal and recovery from Saccharomyces cerevisiae
Heavy metal recovery from biosorbents is of major importance in the assessment of competitiveness of biosorption processes. Several
desorption agents (H2SO4, HNO3, HCl, CH3COOH and EDTA) were tested for the selection of the optimal elution conditions for Cr(III)
recovery from Saccharomyces cerevisiae cells.
Sorption time was optimised as it plays an important role in the sorptionâdesorption process, being shown that a 30 min sorption period is
the best option to ensure metal removal from solution and good recovery from biosorbent. The optimal contact time with desorption agents
was also studied, as long exposures to these ones may cause cell damage, affecting biosorbent metal uptake capacity in subsequent sorption
cycles.
Each eluant was analysed in terms of its desorption capacity and its effect on the biomass metal uptake capacity in multiple
sorptionâdesorption cycles. Considering the effectiveness of chromium desorption from loaded biomass, it was possible to conclude that
H2SO4 (pHâ1) was the most effective eluant tested, accomplishing the highest Cr(III) recovery from S. cerevisiae in three consecutive
sorption/desorption cycles.
Regarding the damage caused by acid treatment on S. cerevisiae cells, assessed by the reduction on metal uptake capacity after elution,
it was possible to observe that sulphuric acid was the most harmful eluant causing long term negative effects in metal uptake. By the time
the experiments were interrupted (nearly 26 h of continuous cycles) biomass uptake capacity was reduced to about 77% of the value reached
before acid treatment.Fundação para a CiĂȘncia e a Tecnologia (FCT) â PRAXIS XXI/BD/15945/98
Dynamics of two planets in co-orbital motion
We study the stability regions and families of periodic orbits of two planets
locked in a co-orbital configuration. We consider different ratios of planetary
masses and orbital eccentricities, also we assume that both planets share the
same orbital plane. Initially we perform numerical simulations over a grid of
osculating initial conditions to map the regions of stable/chaotic motion and
identify equilibrium solutions. These results are later analyzed in more detail
using a semi-analytical model. Apart from the well known quasi-satellite (QS)
orbits and the classical equilibrium Lagrangian points L4 and L5, we also find
a new regime of asymmetric periodic solutions. For low eccentricities these are
located at , where \sigma is
the difference in mean longitudes and \Delta\omega is the difference in
longitudes of pericenter. The position of these Anti-Lagrangian solutions
changes with the mass ratio and the orbital eccentricities, and are found for
eccentricities as high as ~ 0.7. Finally, we also applied a slow mass variation
to one of the planets, and analyzed its effect on an initially asymmetric
periodic orbit. We found that the resonant solution is preserved as long as the
mass variation is adiabatic, with practically no change in the equilibrium
values of the angles.Comment: 9 pages, 11 figure
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