12,804 research outputs found
A Monte Carlo Approach to Measure the Robustness of Boolean Networks
Emergence of robustness in biological networks is a paramount feature of
evolving organisms, but a study of this property in vivo, for any level of
representation such as Genetic, Metabolic, or Neuronal Networks, is a very hard
challenge. In the case of Genetic Networks, mathematical models have been used
in this context to provide insights on their robustness, but even in relatively
simple formulations, such as Boolean Networks (BN), it might not be feasible to
compute some measures for large system sizes. We describe in this work a Monte
Carlo approach to calculate the size of the largest basin of attraction of a
BN, which is intrinsically associated with its robustness, that can be used
regardless the network size. We show the stability of our method through
finite-size analysis and validate it with a full search on small networks.Comment: on 1st International Workshop on Robustness and Stability of
Biological Systems and Computational Solutions (WRSBS
Birth of Closed Strings and Death of Open Strings during Tachyon Condensation
The tremendous progress achieved through the study of black holes and branes
suggests that their time dependent generalizations called Spacelike branes
(S-branes) may prove similarly useful. An example of an established approach to
S-branes is to include a string boundary interaction and we first summarize
evidence for the death of open string degrees of freedom for the homogeneous
rolling tachyon on a decaying brane. Then, we review how to extract the flat
S-brane worldvolumes describing the homogeneous rolling tachyon and how large
deformations correspond to creation of lower dimensional strings and branes.
These S-brane worldvolumes are governed by S-brane actions which are on equal
footing to D-brane actions, since they are derived by imposing conformality on
the string worldsheet, as well as by analyzing fluctuations of time dependent
tachyon configurations. As further examples we generalize previous solutions of
the S-brane actions so as to describe multiple decaying and nucleating closed
fundamental strings. Conceptually S-brane actions are therefore different from
D-brane actions and can provide a description of time dependent strings/branes
and possibly their interactions.Comment: 15 pages, 7 eps figures; invited review for Modern Physics Letters A,
including new solutions for S-brane actions. v2 published version, minor
typos correcte
Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy
The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced
Explosive Nucleosynthesis in Axisymmetrically Deformed Type II Supernovae
Explosive nucleosynthesis under the axisymmetric explosion in Type II
supernova has been performed by means of two dimensional hydrodynamical
calculations. We have compared the results with the observations of SN 1987A.
Our chief findings are as follows: (1) is synthesized so much as to
explain the tail of the bolometric light curve of SN 1987A. We think this is
because the alpha-rich freezeout takes place more actively under the
axisymmetric explosion. (2) and tend to be overproduced
compared with the observations. However, this tendency relies strongly on the
progenitor's model.
We have also compared the abundance of each element in the mass number range
with the solar values. We have found three outstanding features. (1)
For the nuclei in the range , their abundances are insensitive to the
initial form of the shock wave. This insensitivity is favored since the
spherical calculations thus far can explain the solar system abundances in this
mass range. (2) There is an enhancement around A=45 in the axisymmetric
explosion compared with the spherical explosion fairly well. In particular,
, which is underproduced in the present spherical calculations, is
enhanced significantly. (3) In addition, there is an enhancement around A=65.
This tendency does not rely on the form of the mass cut but of the initial
shock wave. This enhancement may be the problem of the overproduction in this
mass range, although this effect would be relatively small since Type I
supernovae are chiefly responsible for this mass number range.Comment: 32 pages, 12 figures, LaTe
Nucleosynthesis in Type II Supernovae
Presupernova evolution and explosive nucleosynthesis in massive stars for
main-sequence masses from 13 to 70 are calculated. We
examine the dependence of the supernova yields on the stellar mass,
^{12}C(\alpha, \gamma) ^{16}O} rate, and explosion energy. The supernova
yields integrated over the initial mass function are compared with the solar
abundances.Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear
Physics A, Vol. A616 (1997
Constraints on Mass Spectrum of Fourth Generation Fermions and Higgs Bosons
We reanalyze constraints on the mass spectrum of the chiral fourth generation
fermions and the Higgs bosons for the standard model (SM4) and the two Higgs
doublet model (THDM). We find that the Higgs mass in the SM4 should be larger
than roughly the fourth generation up-type quark mass, while the light CP even
Higgs mass in the THDM can be smaller. Various mass spectra of the fourth
generation fermions and the Higgs bosons are allowed. The phenomenology of the
fourth generation models is still rich.Comment: 15 pages, 16 figures; some points clarified, references added, to
appear in Phys.Rev.
Non-Linear/Non-Commutative Non-Abelian Monopoles
Using recently proposed non-linearly realized supersymmetry in non-Abelian
gauge theory corrected to the order (alpha')^2, we derive the non-linear BPS
equations in the background B-field for the U(2) monopoles and instantons. We
show that these non-Abelian non-linear BPS equations coincide with the
non-commutative anti-self-dual equations via the Seiberg-Witten map.Comment: 9 pages, LaTe
Nucleosynthesis Basics and Applications to Supernovae
This review concentrates on nucleosynthesis processes in general and their
applications to massive stars and supernovae. A brief initial introduction is
given to the physics in astrophysical plasmas which governs composition
changes. We present the basic equations for thermonuclear reaction rates and
nuclear reaction networks. The required nuclear physics input for reaction
rates is discussed, i.e. cross sections for nuclear reactions,
photodisintegrations, electron and positron captures, neutrino captures,
inelastic neutrino scattering, and beta-decay half-lives. We examine especially
the present state of uncertainties in predicting thermonuclear reaction rates,
while the status of experiments is discussed by others in this volume (see M.
Wiescher). It follows a brief review of hydrostatic burning stages in stellar
evolution before discussing the fate of massive stars, i.e. the nucleosynthesis
in type II supernova explosions (SNe II). Except for SNe Ia, which are
explained by exploding white dwarfs in binary stellar systems (which will not
be discussed here), all other supernova types seem to be linked to the
gravitational collapse of massive stars (M8M) at the end of their
hydrostatic evolution. SN1987A, the first type II supernova for which the
progenitor star was known, is used as an example for nucleosynthesis
calculations. Finally, we discuss the production of heavy elements in the
r-process up to Th and U and its possible connection to supernovae.Comment: 52 pages, 20 figures, uses cupconf.sty (included); to appear in
"Nuclear and Particle Astrophysics", eds. J. Hirsch., D. Page, Cambridge
University Pres
Effects of heat-treatments on electrical properties of boron-doped silicon crystals
The effects of heat-treatments around 1000°Cand subsequent annealing on the electrical properties of boron-doped
silicon have been studied by electrical conductivity, Hall effect, and deep-level transient spectroscopy measurements. The
high-temperature heat-treatments always induced net densities of donors. Four recovery stages, stages I-IV, of heat-treatment-
induced donors were observed on isochronal annealing up to 400°C Conductivity changes in these stages can be explained
as described below by the reactions of interstitial iron (Fei), its pair (Fe1Bs)with substitutional boron (Bs), and two
unknown donors (D1, D2). That is, stage I (25°-100°C):
D1→sink and Fei + Bs→FeiBs, stage II (100°-150°C):
FeiBs→Fei + Bs, stage III (200°-250°C):D2→sink, stage IV (250°-350°C)Fei→precipitation. Heat-treatments in an oxygen
atmosphere greatly reduced the introduction of Fei and FeiBs in comparison with an argon atmosphere and mainly introduced
D1 and D2 donors. The density of D2 was dependent on the heat-treatment temperature, while that of D1 showed almost
no dependence. In stage I, D, was annihilated by first-order kinetics with an activation energy of 0.8 eV. It was indicated
that DI and D2 have no relations to iron, copper, oxygen, nor carbon. Though their origins are still unidentified, there
may be some interstitial impurities. In stage IV, Fei is suggested to precipitate at oxygen precipitates and dislocation loops
formed by high-temperature heat-treatments. As to the application to iron gettering in the device fabrication process, it is
proposed that annealing around 300°C is most suitable as the final heat-treatment step to remove iron and related defects
from active regions of devices.
Silicon wafers receive complex heat-treatments at various.</p
A note on the coupling of the techni-dilaton to the weak bosons
In this note, we study the coupling of the techni-dilaton to the weak bosons.
We consider two cases: (1) The dilaton directly couples to the weak bosons
similarly to the SM. (2) The coupling in question is effectively induced only
through the techni-fermion loops. In both cases, we find that the coupling is
essentially determined by the mass-squared of the weak bosons over the dilaton
decay constant.Comment: 3 pages, 2 figures; minor changes, a reference added, to appear in
PR
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