3,014 research outputs found
3-D Simulations of Protostellar Jets in Stratified Ambient Media
We present fully three-dimensional hydrodynamical simulations of radiative
cooling jets propagating into stratified isothermal ambient media with
power-law density and pressure distributions. The parameters used are mainly
suitable for protostellar jets but results applicable to extragalactic jets are
also presented. Comparisons are made with previous simulations of jets through
homogeneous media. We find that for radiative cooling jets propagating into
regions where the ambient medium has an increasing density (and pressure)
gradient, the ambient gas tends to compress the cold, low-pressure cocoon of
shocked material that surrounds the beam and destroy the bow shock-like
structure at the head. The compressing medium collimates the jet and promotes
the development of Kelvin-Helmholtz instabilities which cause beam focusing,
wiggling and the formation of internal traveling shocks,
, via pinching along the beam. This remarkably resembles the structure of
some observed systems (e.g. Haro 6-5B northern and HH 24G jets). These effects
are larger for jets with smaller density ratio between jet and environment
(tested for =1, 3, and 10) and larger Mach number
(tested for 12 and 24, where is the jet velocity and the
ambient sound speed). In an ambient medium of decreasing density (and
pressure), the beam is poorly collimated and relaxes, becoming faint. This
could explain ''invisible'' jet sections, like the gap between the parent
source and collimated beam (e.g., in HH30 jet). Although, on average, jets
propagating into an increasing (decreasing) density environment are decelerated
(accelerated) by the increasing (decreasing) ram pressure of the ambient
medium, we find that their propagation velocities have an oscillating pattern.Comment: 33 pp, LaTeX file, 13 figures upon request. To appear in the
Astrophys. J., vol 471, nov. 10t
Correlation between nucleotide composition and folding energy of coding sequences with special attention to wobble bases
Background: The secondary structure and complexity of mRNA influences its
accessibility to regulatory molecules (proteins, micro-RNAs), its stability and
its level of expression. The mobile elements of the RNA sequence, the wobble
bases, are expected to regulate the formation of structures encompassing coding
sequences.
Results: The sequence/folding energy (FE) relationship was studied by
statistical, bioinformatic methods in 90 CDS containing 26,370 codons. I found
that the FE (dG) associated with coding sequences is significant and negative
(407 kcal/1000 bases, mean +/- S.E.M.) indicating that these sequences are able
to form structures. However, the FE has only a small free component, less than
10% of the total. The contribution of the 1st and 3rd codon bases to the FE is
larger than the contribution of the 2nd (central) bases. It is possible to
achieve a ~ 4-fold change in FE by altering the wobble bases in synonymous
codons. The sequence/FE relationship can be described with a simple algorithm,
and the total FE can be predicted solely from the sequence composition of the
nucleic acid. The contributions of different synonymous codons to the FE are
additive and one codon cannot replace another. The accumulated contributions of
synonymous codons of an amino acid to the total folding energy of an mRNA is
strongly correlated to the relative amount of that amino acid in the translated
protein.
Conclusion: Synonymous codons are not interchangable with regard to their
role in determining the mRNA FE and the relative amounts of amino acids in the
translated protein, even if they are indistinguishable in respect of amino acid
coding.Comment: 14 pages including 6 figures and 1 tabl
Chemical equilibration and thermal dilepton production from the quark gluon plasma at finite baryon density
The chemical equilibration of a highly unsaturated quark-gluon plasma has
been studied at finite baryon density. It is found that in the presence of
small amount of baryon density, the chemical equilibration for gluon becomes
slower and the temperature decreases less steeply as compared to the baryon
free plasma. As a result, the space time integrated yield of dilepton is
enhanced if the initial temperature of the plasma is held fixed. Even at a
fixed initial energy density, the suppression of the dilepton yields at higher
baryo-chemical potential is compensated, to a large extent, by the slow cooling
of the plasma.Comment: Latex, 19 pages, 8 postscript figures. To appear in Phys. Rev.
PENGARUH TINGKAT PENDIDIKAN DAN PEKERJAAN TERHADAP ORAL HYGIENE PADA IBU HAMIL DI RSUD MEURAXA BANDA ACEH
ABSTRAKNama: Muhammad AdriansyahProgram Studi: Kedokteran GigiJudul:Pengaruh Tingkat Pendidikan dan Pekerjaan Terhadap Oral Hygiene pada Ibu Hamil di RSUD Meuraxa Banda AcehPendidikan adalah faktor sosial ekonomi yang mempengaruhi status kesehatan. Pekerjaan dihubungkan dengan tingkat pendidikan dan penghasilan, dimana pekerjaan membutuhkan latar belakang pendidikan yang tinggi, dan penghasilan dimana seseorang mempunyai penghasilan lebih besar maka akan mampu memenuhi kebutuhan dalam menjaga kesehatan gigi dan mulut. Selama masa kehamilan, wanita mengalami beberapa perubahan fisiologis yang menyebabkan terjadinya perubahan hormonal. Perubahan fisiologis juga berdampak pada perubahan menjaga kesehatan gigi dan mulut, sehingga wanita hamil lebih rentan terkena masalah gigi dan mulut. Tujuan penelitian ini adalah untuk mengetahui pengaruh tingkat pendidikan dan pekerjaan terhadap oral hygiene pada ibu hamil di RSUD Meuraxa Banda Aceh. Jenis penelitian ini bersifat analitik dengan metode cross sectional untuk melihat hubungan antar dua variabel. Penelitian ini melibatkan 48 subjek yang memenuhi kriteria inklusi. Subjek penelitian mengisi kuisioner yang diberikan serta diperiksa tingkat kebersihan rongga mulutnya. Data dianalisis dengan SPSS menggunakan Korelasi Spearman. Hasil uji menunjukkan ada pengaruh yang signifikan antara tingkat pendidikan (
Forming Disoriented Chiral Condensates through Fluctuations
Using the influence functional formalism, classical equations of motion for
the O(N) model are derived in the presence of a heat bath, in both the
symmetric phase as well as the phase of spontaneously broken symmetry. The heat
bath leads to dissipation and fluctuation terms in the classical equations of
motion, which are explicitly computed to lowest order in perturbation theory.
In the broken phase these terms are found to be large for the sigma field, even
at zero temperature, due to the decay process sigma -> pi pi, while they are
small for the pi fields at temperatures below T_c = 160 MeV. It is shown that
in large volumes the presence of dissipation and fluctuations suppresses the
formation of disoriented chiral condensates (DCC's). In small volumes, however,
fluctuations become sufficiently large to induce the formation of DCC's even if
chiral symmetry has not been restored in the initial stage of the system's
evolution.Comment: 34 pages, 11 figures, ReVTeX, eps-, aps-, psfig-style files require
Jets and the shaping of the giant bipolar envelope of the planetary nebula KjPn 8
A hydrodynamic model involving cooling gas in the stagnation region of a
collimated outflow is proposed for the formation of the giant parsec-scale
bipolar envelope that surrounds the planetary nebula KjPn 8. Analytical
calculations and numerical simulations are presented to evaluate the model. The
envelope is considered to consist mainly of environmental gas swept-up by
shocks driven by an episodic, collimated, bipolar outflow. In this model, which
we call the ``free stagnation knot'' mechanism, the swept-up ambient gas
located in the stagnation region of the bow-shock cools to produce a high
density knot. This knot moves along with the bow-shock. When the central
outflow ceases, pressurization of the interior of the envelope stops and its
expansion slows down. The stagnation knot, however, has sufficient momentum to
propagate freely further along the axis, producing a distinct nose at the end
of the lobe. The model is found to successfully reproduce the peculiar shape
and global kinematics of the giant bipolar envelope of KjPn 8.Comment: 20 pages + 8 figures (in 1 tar-file 0.67 Mb
Percolation of strings and the first RHIC data on multiplicity and tranverse momentum distributions
The dependence of the multiplicity on the number of collisions and the
transverse momentum distribution for central and peripheral Au-Au collisions
are studied in the model of percolation of strings relative to the experimental
conditions at RHIC. The comparison with the first RHIC data shows a good
agreement.Comment: RevTeX, 11 pages, 4 eps figures included using epsfi
Transverse momentum distributions and their forward- backward correlations in the percolating colour string approach
The forward-backward correlations in the distributions, which present a
clear signature of non-linear effects in particle production, are studied in
the model of percolating colour strings. Quantitative predictions are given for
these correlations at SPS, RHIC and LHC energies. Interaction of strings also
naturally explains the flattening of distributions and increase of
with energy and atomic number for nuclear collisionsComment: 6 pages in LaTex, 3 figures in Postscrip
Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim
Multicolor (BVRI) light curves of the eclipsing classical nova V Per are
presented, and a total of twelve new eclipse timings are measured for the
system. When combined with previous eclipse timings from the literature, these
timings yield a revised ephemeris for the times of mid-eclipse given by HJD =
2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a
parameter-fitting model that assumes four sources of luminosity: a white dwarf
primary star, a main-sequence secondary star, a flared accretion disk with a
rim, and a bright spot at the intersection of the mass-transfer stream and the
disk periphery. A matrix of model solutions are computed, covering an extensive
range of plausible parameter values. The solution matrix is then explored to
determine the optimum values for the fitting parameters and their associated
errors. For models that treat the accretion disk as a flat structure without a
rim, optimum fits require that the disk have a flat temperature profile.
Although models with a truncated inner disk (R_in >> R_wd) result in a steeper
temperature profile, steady-state models with a temperature profile
characterized by T(r) \propto r^{-3/4} are found only for models with a
significant disk rim. A comparison of the observed brightness and color at
mid-eclipse with the photometric properties of the best-fitting model suggests
that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine
pages, including 9 figures. V2 - updated to include additional references and
related discussion to previous work overlooked in the original version, and
to correct a typo in the ephemeris given in the abstract. V3 - Minor typos
corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 -
An error in equation (9) has been corrected. The results presented in the
paper were not affected, as all computations were made using the correct
formulation of this equatio
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