1,745 research outputs found
Properties of the series solution for PainlevƩ I
We present some observations on the asymptotic behaviour of the coefficients in the Laurent series expansion of solutions of the first PainlevƩ equation. For the general solution, explicit recursive formulae for the Taylor expansion of the tau-function around a zero are given, which are natural extensions of analogous formulae for the elliptic sigma function, as given by Weierstrass. Numerical and exact results on the symmetric solution which is singular at the origin are also presented
Uso do mĆ©todo de graus-dia para estimar a data de diferenciaĆ§Ć£o da panĆcula de grupos de cultivares de arroz irrigado no Rio Grande do Sul.
bitstream/item/33519/1/documento-126.pd
The Evolution of the Galaxy Sizes in the NTT Deep Field: a Comparison with CDM Models
The sizes of the field galaxies with I<25 have been measured in the NTT Deep
Field. Intrinsic sizes have been obtained after deconvolution of the PSF with a
multigaussian method. The reliability of the method has been tested using both
simulated data and HST observations of the same field. The distribution of the
half light radii is peaked at r_{hl} 0.3 arcsec, in good agreement with that
derived from HST images at the same magnitude. An approximate morphological
classification has been obtained using the asymmetry and concentration
parameters. The intrinsic sizes of the galaxies are shown as a function of
their redshifts and absolute magnitudes using photometric redshifts derived
from the multicolor catalog. While the brighter galaxies with morphological
parameters typical of the normal spirals show a flat distribution in the range
r_{d}=1-6 kpc, the fainter population at 0.4<z<0.8 dominates at small sizes. To
explore the significance of this behaviour, an analytical rendition of the
standard CDM model for the disc size evolution has been computed. The model
showing the best fit to the local luminosity function and the Tully-Fisher
relation is able to reproduce at intermediate redshifts a size distribution in
general agreement with the observations, although it tends to underestimate the
number of galaxies fainter than M_B~ -19 with disk sizes r_d~ 1-2 kpc.Comment: 16 pages, 11 figures, ApJ in press, Dec 199
Permutable entire functions satisfying algebraic differential equations
It is shown that if two transcendental entire functions permute, and if one
of them satisfies an algebraic differential equation, then so does the other
one.Comment: 5 page
The Effects of Gas Dynamics, Cooling, Star Formation, and Numerical Resolution in Simulations of Cluster Formation
We present the analysis of a suite of simulations of a Virgo mass galaxy
cluster. Undertaken within the framework of standard cold dark matter
cosmology, these simulations were performed at differing resolutions and with
increasingly complex physical processes, with the goal of identifying the
effects of each on the evolution of the cluster. We focus on the cluster at the
present epoch and examine properties including the radial distributions of
density, temperature, entropy and velocity. We also map `observable' projected
properties such as the surface mass density, X-ray surface brightness and SZ
signature. We identify significant differences between the simulations, which
highlights the need for caution when comparing numerical simulations to
observations of galaxy clusters. While resolution affects the inner density
profile in dark matter simulations, the addition of a gaseous component,
especially one that cools and forms stars, affects the entire cluster. We
conclude that both resolution and included physical processes play an important
role in simulating the formation and evolution of galaxy clusters. Therefore,
physical inferences drawn from simulations that do not include a gaseous
component that can cool and form stars present a poor representation of
reality. (Abridged)Comment: Accepted for publication in the Astrophysical Journal. Several
changes from previous version, including new materia
Correlations Between Central Massive Objects And Their Host Galaxies: From Bulgeless Spirals to Ellipticals
Recent observations by Ferrarese et al. (2006) and Wehner et al. (2006)
reveal that a majority of galaxies contain a central massive object (CMO),
either a supermassive black hole (SMBH) or a compact stellar nucleus,
regardless of the galaxy mass or morphological type, and that there is a tight
relation between the masses of CMOs and those of the host galaxies. Several
recent studies show that feedback from black holes can successfully explain the
\msigma correlation in massive elliptical galaxies that contain SMBHs.
However, puzzles remain in spirals or dwarf spheroids that do not appear to
have black holes but instead harbor a compact central stellar cluster. Here we
use three-dimensional, smoothed particle hydrodynamics simulations of isolated
galaxies to study the formation and evolution of CMOs in bulgeless disk
galaxies, and simulations of merging galaxies to study the transition of the
CMO--host mass relation from late-type bulgeless spirals to early-type
ellipticals. Our results suggest that the observed correlations may be
established primarily by the depletion of gas in the central region by
accretion and star-formation, and may hold for all galaxy types. A systematic
search for CMOs in the nuclei of bulgeless disk galaxies would offer a test of
this conclusion. (Abridged)Comment: 11 pages, 8 figures, accepted to Ap
Gravitational Collapse in Turbulent Molecular Clouds. I. Gasdynamical Turbulence
Observed molecular clouds often appear to have very low star formation
efficiencies and lifetimes an order of magnitude longer than their free-fall
times. Their support is attributed to the random supersonic motions observed in
them. We study the support of molecular clouds against gravitational collapse
by supersonic, gas dynamical turbulence using direct numerical simulation.
Computations with two different algorithms are compared: a particle-based,
Lagrangian method (SPH), and a grid-based, Eulerian, second-order method
(ZEUS). The effects of both algorithm and resolution can be studied with this
method. We find that, under typical molecular cloud conditions, global collapse
can indeed be prevented, but density enhancements caused by strong shocks
nevertheless become gravitationally unstable and collapse into dense cores and,
presumably, stars. The occurance and efficiency of local collapse decreases as
the driving wave length decreases and the driving strength increases. It
appears that local collapse can only be prevented entirely with unrealistically
short wave length driving, but observed core formation rates can be reproduced
with more realistic driving. At high collapse rates, cores are formed on short
time scales in coherent structures with high efficiency, while at low collapse
rates they are scattered randomly throughout the region and exhibit
considerable age spread. We suggest that this naturally explains the observed
distinction between isolated and clustered star formation.Comment: Minor revisions in response to referee, thirteen figures, accepted to
Astrophys.
Aircraft engine with inter-turbine engine frame supported counter rotating low pressure turbine rotors
An aircraft gas turbine engine assembly includes an inter-turbine frame axially located between high and low pressure turbines. Low pressure turbine has counter rotating low pressure inner and outer rotors with low pressure inner and outer shafts which are at least in part rotatably disposed co-axially within a high pressure rotor. Inter-turbine frame includes radially spaced apart radially outer first and inner second structural rings disposed co-axially about a centerline and connected by a plurality of circumferentially spaced apart struts. Forward and aft sump members having forward and aft central bores are fixedly joined to axially spaced apart forward and aft portions of the inter-turbine frame. Low pressure inner and outer rotors are rotatably supported by a second turbine frame bearing mounted in aft central bore of aft sump member. A mount for connecting the engine to an aircraft is located on first structural ring
Semi-Analytical Models for the Formation of Disk Galaxies: I. Constraints from the Tully-Fisher Relation
We present new semi-analytical models for the formation of disk galaxies with
the purpose of investigating the origin of the near-infrared Tully-Fisher (TF)
relation. The models assume that disks are formed by cooling of the baryons
inside dark halos with realistic density profiles, and that the baryons
conserve their specific angular momentum. Only gas with densities above the
critical density given by Toomre's stability criterion is considered eligible
for star formation, and a simple recipe for supernovae feedback is included. We
emphasize the importance of extracting the proper luminosity and velocity
measures from the models, something that has often been ignored in the past.
The observed K-band TF relation has a slope that is steeper than simple
predictions based on dynamical arguments suggest. Taking the stability related
star formation threshold densities into account steepens the TF relation,
decreases its scatter, and yields gas mass fractions that are in excellent
agreement with observations. In order for the TF slope to be as steep as
observed, further physics are required. We argue that the characteristics of
the observed near-infrared TF relation do not reflect systematic variations in
stellar populations, or cosmological initial conditions, but are governed by
feedback. Finally we show that our models provide a natural explanation for the
small amount of scatter that makes the TF relation useful as a cosmological
distance indicator.Comment: 20 pages, 10 figures. Accepted for publication in Ap
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