2,236 research outputs found
Bosonic stimulation of cold 1s excitons into a harmonic potential minimum in CuO
Density distribution of cold exciton clouds generated into a strain-induced
potential well by two-photon excitation in CuO is studied at 2 K. We find
that an anomalous spike, which can be interpreted as accumulation of the
excitons into the ground state, emerges at the potential minimum. The
accumulation can be due to stimulated scattering of cold excitons, mediated by
acoustic phonon emission. Possibility of the formation of the thermodynamic
Bose-Einstein condensate of paraexcitons has been discussed.Comment: Submitted to Solid State Communications on 17 December, 200
Toward a Deterministic Model of Planetary Formation VII: Eccentricity Distribution of Gas Giants
The ubiquity of planets and diversity of planetary systems reveal planet
formation encompass many complex and competing processes. In this series of
papers, we develop and upgrade a population synthesis model as a tool to
identify the dominant physical effects and to calibrate the range of physical
conditions. Recent planet searches leads to the discovery of many
multiple-planet systems. Any theoretical models of their origins must take into
account dynamical interaction between emerging protoplanets. Here, we introduce
a prescription to approximate the close encounters between multiple planets. We
apply this method to simulate the growth, migration, and dynamical interaction
of planetary systems. Our models show that in relatively massive disks, several
gas giants and rocky/icy planets emerge, migrate, and undergo dynamical
instability. Secular perturbation between planets leads to orbital crossings,
eccentricity excitation, and planetary ejection. In disks with modest masses,
two or less gas giants form with multiple super-Earths. Orbital stability in
these systems is generally maintained and they retain the kinematic structure
after gas in their natal disks is depleted. These results reproduce the
observed planetary mass-eccentricity and semimajor axis-eccentricity
correlations. They also suggest that emerging gas giants can scatter residual
cores to the outer disk regions. Subsequent in situ gas accretion onto these
cores can lead to the formation of distant (> 30AU) gas giants with nearly
circular orbits.Comment: 54 pages, 14 Figures; accepted for publication in Astrophysical
Journa
Formation of Hot Planets by a combination of planet scattering, tidal circularization, and Kozai mechanism
We have investigated the formation of close-in extrasolar giant planets
through a coupling effect of mutual scattering, Kozai mechanism, and tidal
circularization, by orbital integrations. We have carried out orbital
integrations of three planets with Jupiter-mass, directly including the effect
of tidal circularization. We have found that in about 30% runs close-in planets
are formed, which is much higher than suggested by previous studies. We have
found that Kozai mechanism by outer planets is responsible for the formation of
close-in planets. During the three-planet orbital crossing, the Kozai
excitation is repeated and the eccentricity is often increased secularly to
values close enough to unity for tidal circularization to transform the inner
planet to a close-in planet. Since a moderate eccentricity can remain for the
close-in planet, this mechanism may account for the observed close-in planets
with moderate eccentricities and without nearby secondary planets. Since these
planets also remain a broad range of orbital inclinations (even retrograde
ones), the contribution of this process would be clarified by more observations
of Rossiter-McLaughlin effects for transiting planets.Comment: 15 pages, 16 figures, Accepted for publication in Ap
Eccentricity Evolution of Extrasolar Multiple Planetary Systems due to the Depletion of Nascent Protostellar Disks
Most extrasolar planets are observed to have eccentricities much larger than
those in the solar system. Some of these planets have sibling planets, with
comparable masses, orbiting around the same host stars. In these multiple
planetary systems, eccentricity is modulated by the planets' mutual secular
interaction as a consequence of angular momentum exchange between them. For
mature planets, the eigenfrequencies of this modulation are determined by their
mass and semi-major axis ratios. But, prior to the disk depletion, self gravity
of the planets' nascent disks dominates the precession eigenfrequencies. We
examine here the initial evolution of young planets' eccentricity due to the
apsidal libration or circulation induced by both the secular interaction
between them and the self gravity of their nascent disks. We show that as the
latter effect declines adiabatically with disk depletion, the modulation
amplitude of the planets' relative phase of periapse is approximately invariant
despite the time-asymmetrical exchange of angular momentum between planets.
However, as the young planets' orbits pass through a state of secular
resonance, their mean eccentricities undergo systematic quantitative changes.
For applications, we analyze the eccentricity evolution of planets around
Upsilon Andromedae and HD168443 during the epoch of protostellar disk
depletion. We find that the disk depletion can change the planets' eccentricity
ratio. However, the relatively large amplitude of the planets' eccentricity
cannot be excited if all the planets had small initial eccentricities.Comment: 50 pages including 11 figures, submitted to Ap
Trypanosoma evansi ima gen sličan genu za oligosaharil-transferazu klona I protozoona Trypanosoma brucei rhodesiense.
Recent data has shown that there are strong indications that the putative oligosaccharyl transferase genes from Trypanosoma brucei rhodesiense were conserved within the family Trypanosomatidae. Based on these findings, the study endeavored to determine if Trypanosoma evansi also possessed putative oligosaccharyl transferase (OST) clone I previously documented in Trypanosoma brucei rhodesiense. Using the DNA hybridization method (Southern blot analyses), genomic DNAs of Trypanosoma brucei rhodesiense and Trypanosoma evansi were processed using the same set of restriction enzymes and subsequently hybridized by the same set of DNA probes designed from the reported nucleotide sequence of Trypanosoma brucei rhodesiense putative oligosaccharyl transferase clone I. The results exhibited that Trypanosoma evansi also contains a gene similar to the reported Trypanosoma brucei rhodesiense putative OST gene clone I, as shown by the successful hybridization of the DNA probes to their complementary nucleotide sequences in the genome of the Trypanosoma evansi species. In addition, the data also showed that Trypanosoma brucei rhodesiense and Trypanosoma evansi genomes shared some common restriction sites and loci within the genome of each individual parasite species.Nedavna istraživanja pokazala su da su geni za oligosaharil transferazu protozoona Trypanosoma brucei rhodesiense vrlo dobro sačuvani unutar porodice Trypanosomatidae. Cilj istraživanja bio je otkriti je li ista pojava karakteristična za gen za oligosaharil transferazu klona I protozoona Trypanosoma evansi. Genomske DNA vrste Trypanosoma brucei rhodesiense i vrste Trypanosoma evansi bile su pretražene hibridizacijom DNA (Southern Blot analizom) rabeći istu skupinu restrikcijskih enzima kao i iste probe za hibridizaciju DNA pripravljene na temelju objavljenog slijeda nukleotida za oligosaharil-transferazu klona I protozoona Trypanosoma brucei rhodesiense. Rezultati su pokazali da Trypanosoma evansi također sadrži gen koji je vrlo sličan genu za oligosaharil-transferazu protozoona Trypanosoma brucei rhodesiense, što je dokazano uspješnom hibridizacijom DNA proba s komplementarnim nukleotidnim slijedovima u genomu vrste Trypanosoma evansi. Istraživanje je pokazalo da Trypanosoma brucei rhodesiense i Trypanosoma evansi dijele i zajednička restrikcijska mjesta
Entropy, time irreversibility and Schroedinger equation in a primarily discrete space-time
In this paper we show that the existence of a primarily discrete space-time
may be a fruitful assumption from which we may develop a new approach of
statistical thermodynamics in pre-relativistic conditions. The discreetness of
space-time structure is determined by a condition that mimics the Heisenberg
uncertainty relations and the motion in this space-time model is chosen as
simple as possible. From these two assumptions we define a path-entropy that
measures the number of closed paths associated with a given energy of the
system preparation. This entropy has a dynamical character and depends on the
time interval on which we count the paths. We show that it exists an
like-equilibrium condition for which the path-entropy corresponds exactly to
the usual thermodynamic entropy and, more generally, the usual statistical
thermodynamics is reobtained. This result derived without using the Gibbs
ensemble method shows that the standard thermodynamics is consistent with a
motion that is time-irreversible at a microscopic level. From this change of
paradigm it becomes easy to derive a . A comparison with the
traditional Boltzmann approach is presented. We also show how our approach can
be implemented in order to describe reversible processes. By considering a
process defined simultaneously by initial and final conditions a well defined
stochastic process is introduced and we are able to derive a Schroedinger
equation, an example of time reversible equation.Comment: latex versio
Radiation Yield and Radicals Produced in Irradiated Poly (Butylene Succinate)
The main chemical effects of ionizing irradiation on polymers are crosslinking and chain scission. Both processes occur simultaneously and their yields determine the final results of processing. The radiation yield of crosslinking could be determined by several methods depending on the characteristics of the material and properties of the gel. Radiation parameters of gelation, such as gelation dose and ratio of scission yield to crosslinking yield, as well as their values were estimated. In this study, those parameters depend on the amount of Trimethallyl isocyanurate (TMAIC) in Poly(butylene succinate) (PBS), molecular weight of PBS, and irradiation condition. In the absence of TMAIC, higher molecular weight of PBS required less energy to start gelation process compare to lower molecular weight of PBS. While in the presence of TMAIC all of the PBS samples require similar energy to start gelation process. The existence of macroradicals were observed by Electron Spin Resonance measurements. The result showed that the spectra consisted of signals derived from radicals on carbon nearby carbonyl, and signals derived from radicals on carbon reside between two similar carbon on polymer, both of radicals lead to crosslinking
Dynamical Shakeup of Planetary Systems II. N-body simulations of Solar System terrestrial planet formation induced by secular resonance sweeping
We revisit the "dynamical shakeup" model of Solar System terrestrial planet
formation, wherein the whole process is driven by the sweeping of Jupiter's
secular resonance as the gas disk is removed. Using a large number of 0.5
Gyr-long N-body simulations, we investigate the different outcomes produced by
such a scenario. We confirm that in contrast to existing models, secular
resonance sweeping combined with tidal damping by the disk gas can reproduce
the low eccentricities and inclinations, and high radial mass concentration, of
the Solar System terrestrial planets. At the same time, this also drives the
final assemblage of the planets on a timescale of several tens of millions of
years, an order of magnitude faster than inferred from previous numerical
simulations which neglected these effects, but possibly in better agreement
with timescales inferred from cosmochemical data. In addition, we find that
significant delivery of water-rich material from the outer Asteroid Belt is a
natural byproduct.Comment: To appear in Ap
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