12,323 research outputs found
The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution
Post-common-envelope binaries (PCEBs) have been frequently used to
observationally constrain models of close-compact-binary evolution, in
particular common-envelope (CE) evolution. However, recent surveys have
detected PCEBs consisting of a white dwarf (WD) exclusively with an M dwarf
companion. Thus, we have been essentially blind with respect to PCEBs with more
massive companions. Recently, the second PCEB consisting of a WD and a G-type
companion, the spectacularly self-lensing binary KOI-3278, has been identified.
This system is different from typical PCEBs not only because of the G-type
companion, but also because of its long orbital period. Here we investigate
whether the existence of KOI-3278 provides new observational constraints on
theories of CE evolution. We reconstruct its evolutionary history and predict
its future using BSE, clarifying the proper use of the binding energy parameter
in this code. We find that a small amount of recombination energy, or any other
source of extra energy, is required to reconstruct the evolutionary history of
KOI-3278. Using BSE we derive progenitor system parameters of M1,i = 2.450
Msun, M2,i = 1.034 Msun, and Porb,i ~ 1300 d. We also find that in ~9 Gyr the
system will go through a second CE phase leaving behind a double WD, consisting
of a C/O WD and a He WD with masses of 0.636 Msun and 0.332 Msun, respectively.
After IK Peg, KOI-3278 is the second PCEB that clearly requires an extra source
of energy, beyond that of orbital energy, to contribute to the CE ejection.
Both systems are special in that they have long orbital periods and massive
secondaries. This may also indicate that the CE efficiency increases with
secondary mass.Comment: Accepted for publication in A&A Letters, 4 pages, 2 figure
Finite-Size Scaling of the Level Compressibility at the Anderson Transition
We compute the number level variance and the level
compressibility from high precision data for the Anderson model of
localization and show that they can be used in order to estimate the critical
properties at the metal-insulator transition by means of finite-size scaling.
With , , and denoting, respectively, system size, disorder strength,
and the average number of levels in units of the mean level spacing, we find
that both and the integrated obey finite-size scaling.
The high precision data was obtained for an anisotropic three-dimensional
Anderson model with disorder given by a box distribution of width . We
compute the critical exponent as and the critical
disorder as in agreement with previous
transfer-matrix studies in the anisotropic model. Furthermore, we find
at the metal-insulator transition in very close
agreement with previous results.Comment: Revised version of paper, to be published: Eur. Phys. J. B (2002
Transport properties near the Anderson transition
The electronic transport properties in the presence of a temperature gradient
in disordered systems near the metal-insulator transition [MIT] are considered.
The d.c. conductivity , the thermoelectric power , the thermal
conductivity and the Lorenz number are calculated for the
three-dimensional Anderson model of localization using the
Chester-Thellung-Kubo-Greenwood formulation of linear response. We show that
, S, K and can be scaled to one-parameter scaling curves with a
single scaling paramter .Comment: 4 pages, 4 EPS figures, uses annalen.cls style [included]; presented
at Localization 1999, to appear in Annalen der Physik [supplement
Phase diagram of the three-dimensional Anderson model of localization with random hopping
We examine the localization properties of the three-dimensional (3D) Anderson
Hamiltonian with off-diagonal disorder using the transfer-matrix method (TMM)
and finite-size scaling (FSS). The nearest-neighbor hopping elements are chosen
randomly according to . We find that the
off-diagonal disorder is not strong enough to localize all states in the
spectrum in contradistinction to the usual case of diagonal disorder. Thus for
any off-diagonal disorder, there exist extended states and, consequently, the
TMM converges very slowly. From the TMM results we compute critical exponents
of the metal-insulator transitions (MIT), the mobility edge , and study
the energy-disorder phase diagram.Comment: 4 pages, 5 EPS figures, uses annalen.cls style [included]; presented
at Localization 1999, to appear in Annalen der Physik [supplement
Thermoelectric Transport Properties in Disordered Systems Near the Anderson Transition
We study the thermoelectric transport properties in the three-dimensional
Anderson model of localization near the metal-insulator transition [MIT]. In
particular, we investigate the dependence of the thermoelectric power S, the
thermal conductivity K, and the Lorenz number L_0 on temperature T. We first
calculate the T dependence of the chemical potential from the number density of
electrons at the MIT using averaged density of state obtained by
diagonalization. Without any additional approximation, we determine from the
chemical potential the behavior of S, K and L_0 at low T as the MIT is
approached. We find that the d.c. conductivity and K decrease to zero at the
MIT as T -> 0 and show that S does not diverge. Both S and L_0 become
temperature independent at the MIT and depend only on the critical behavior of
the conductivity.Comment: 11 pages, 10 eps figures, coded with the EPJ macro package, submitted
to EPJ
White dwarf masses in cataclysmic variables
The white dwarf (WD) mass distribution of cataclysmic variables (CVs) has
recently been found to dramatically disagree with the predictions of the
standard CV formation model. The high mean WD mass among CVs is not imprinted
in the currently observed sample of CV progenitors and cannot be attributed to
selection effects. Two possibilities have been put forward: either the WD grows
in mass during CV evolution, or in a significant fraction of cases, CV
formation is preceded by a (short) phase of thermal time-scale mass transfer
(TTMT) in which the WD gains a sufficient amount of mass. We investigate if
either of these two scenarios can bring theoretical predictions and
observations into agreement. We employed binary population synthesis models to
simulate the present intrinsic CV population. We incorporated aspects specific
to CV evolution such as an appropriate mass-radius relation of the donor star
and a more detailed prescription for the critical mass ratio for dynamically
unstable mass transfer. We also implemented a previously suggested wind from
the surface of the WD during TTMT and tested the idea of WD mass growth during
the CV phase by arbitrarily changing the accretion efficiency. We compare the
model predictions with the characteristics of CVs derived from observed
samples. We find that mass growth of the WDs in CVs fails to reproduce the
observed WD mass distribution. In the case of TTMT, we are able to produce a
large number of massive WDs if we assume significant mass loss from the surface
of the WD during the TTMT phase. However, the model still produces too many CVs
with helium WDs. Moreover, the donor stars are evolved in many of these
post-TTMT CVs, which contradicts the observations. We conclude that in our
current framework of CV evolution neither TTMT nor WD mass growth can fully
explain either the observed WD mass or the period distribution in CVs.Comment: 15 pages, 7 figures, 1 table, accepted for publication in A&A.
Replaced and added a reference, corrected typo
An exact-diagonalization study of rare events in disordered conductors
We determine the statistical properties of wave functions in disordered
quantum systems by exact diagonalization of one-, two- and quasi-one
dimensional tight-binding Hamiltonians. In the quasi-one dimensional case we
find that the tails of the distribution of wave-function amplitudes are
described by the non-linear sigma-model. In two dimensions, the tails of the
distribution function are consistent with a recent prediction based on a direct
optimal fluctuation method.Comment: 13 pages, 5 figure
Residual Action of Slow Release Systemic Insecticides on \u3ci\u3eRhopalosiphum Padi\u3c/i\u3e (Homoptera: Aphididae) on Wheat
Slow release formulations of acephate and carbofuran encapsulated in pearl corn starch or corn flour granules were applied to the soil at seeding time of potted \u27Caldwell\u27 wheat in the laboratory. Dosages of these insecticides were adjusted to a standard of IO kg/ha of a 10 10 granular formulation of carbofuran. The residual action of these insecticide treatments against Rhopalosiphum padi were compared with those obtained with that of carbofuran 150 at corresponding dosages and foliar sprays of solutions of acephate (25 10 EC) at 0.2 10 and carbofuran (4F) at 1.25 10, applied 12 d after seedling emergence. The residual action of carbofuran 150, which controlled R. padi since seedling emergence, lasted 28.5 d. The slow release granular formulations of carbofuran began to provide control (\u3e 50 10 aphid mortality) on days 13.3 and 17.9 after seeding. They controlled the insect until days 31.6 and 35.5 after seeding. The two corresponding granular formulations of acephate began to provide control on days 15.0 and 17.0 after seeding and con trolled the aphids until days 31.5 and 32.8 after seeding. The foliar sprays of acephate and carbofuran provided control for 18.3 and 36.2 d from application, respectively. The slow release granular formulations provided control of R. padi, an important vector of barley yellow dwarf virus, during early. stages of wheat development
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