2,287 research outputs found
Prediksi Evolusi Diameter Aorta Berdasarkan Sinyal Trombus dari Magnetic Resonance Images pada Small Abdominal Aortic Aneurysms
Mempelajari gambar T1 dan T2 dari hasil pemeriksaan MR Imaging terhadap adanya trombus pada pasien
Small Abdominal Aortic Aneurysms (SAAA) untuk mengetahui apakah sinyal trombus bisa dihubungkan dengan evolusi
pembesaran diameter aorta, dan kemudian bisa memprediksi risiko pecahnya dinding aorta. Data diperoleh dari 16
pasien dengan SAAA. Gambar MR diperoleh dari Imager 3T (Trio TIM, Siemens Medical Solution, Jerman). Dalam
protokol penelitian kami, gambar yang diambil adalah studi anatomi, gambar cine-MR, gambar T1/T2, gambar aliran
darah, dan gambar setelah injeksi contrast agents. Manual tracing dilakukan untuk menentukan luas permukaan Aorta
dan luas permukaan luminal guna menentukan luas permukaan trombus. Maksimum diameter aorta secara otomatis
didapat dari manual tracing pada gambar T1. Parameter digunakan untuk mempelajari sinyal trombus adalah mean,
median, standar deviasi, skewness dan kurtosis. Setiap parameter dihitung pada area thrombus, dan sinyal di otot
digunakan untuk menormalisasikannya. Setelah itu, semua parameter akan dibandingkan dengan evolusi dari diameter
aorta. Ditemukan 13 dari 16 pasien dengan SAAA memiliki trombus. Namun tidak ada korelasi antara sinyal trombus
dengan evolusi dari diameter aorta (r sering kali kurang dari 0,3). Tapi beberapa parameter menunjukkan hubungan
antara sinyal thrombus dan diameter maksimum (mean (r = 0318)), median (r = 0,318), skewness (r = 0304)) atau
dengan evolusi diameter maksimum (mean (r = 0512)). Dapat disimpulkan bahwa perbandingan kategori trombus yang
kami kalkulasikan secara matematik dengan kategori thrombus secara visualisasi mencapai 81% tingkat kesesuaian, tapi
kita tidak bisa menggunakan sinyal trombus sendiri sebagai parameter untuk memprediksi evolusi dari diameter aorta
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
COSMOS: A Hybrid N-Body/Hydrodynamics Code for Cosmological Problems
We describe a new hybrid N-body/hydrodynamical code based on the
particle-mesh (PM) method and the piecewise-parabolic method (PPM) for use in
solving problems related to the evolution of large-scale structure, galaxy
clusters, and individual galaxies. The code, named COSMOS, possesses several
new features which distinguish it from other PM-PPM codes. In particular, to
solve the Poisson equation we have written a new multigrid solver which can
determine the gravitational potential of isolated matter distributions and
which properly takes into account the finite-volume discretization required by
PPM. All components of the code are constructed to work with a nonuniform mesh,
preserving second-order spatial differences. The PPM code uses vacuum boundary
conditions for isolated problems, preventing inflows when appropriate. The PM
code uses a second-order variable-timestep time integration scheme. Radiative
cooling and cosmological expansion terms are included. COSMOS has been
implemented for parallel computers using the Parallel Virtual Machine (PVM)
library, and it features a modular design which simplifies the addition of new
physics and the configuration of the code for different types of problems. We
discuss the equations solved by COSMOS and describe the algorithms used, with
emphasis on these features. We also discuss the results of tests we have
performed to establish that COSMOS works and to determine its range of
validity.Comment: 43 pages, 14 figures, submitted to ApJS and revised according to
referee's comment
Constraining the Galaxy's dark halo with RAVE stars
We use the kinematics of giant stars that lie within kpc of the plane to measure the vertical profile of mass density near the
Sun. We find that the dark mass contained within the isodensity surface of the
dark halo that passes through the Sun
(), and the surface density within
kpc of the plane () are almost
independent of the (oblate) halo's axis ratio . If the halo is spherical, 46
per cent of the radial force on the Sun is provided by baryons, and only 4.3
per cent of the Galaxy's mass is baryonic. If the halo is flattened, the
baryons contribute even less strongly to the local radial force and to the
Galaxy's mass. The dark-matter density at the location of the Sun is
.
When combined with other literature results we find hints for a mildly oblate
dark halo with . Our value for the dark mass within the solar
radius is larger than that predicted by cosmological dark-matter-only
simulations but in good agreement with simulations once the effects of baryonic
infall are taken into account. Our mass models consist of three
double-exponential discs, an oblate bulge and a Navarro-Frenk-White dark-matter
halo, and we model the dynamics of the RAVE stars in the corresponding
gravitational fields by finding distribution functions that
depend on three action integrals. Statistical errors are completely swamped by
systematic uncertainties, the most important of which are the distance to the
stars in the photometric and spectroscopic samples and the solar distance to
the Galactic centre. Systematics other than the flattening of the dark halo
yield overall uncertainties per cent.Comment: 20 pages, 17 figures, accepted for publication in MNRA
Single-lined Spectroscopic Binary Star Candidates in the RAVE Survey
Repeated spectroscopic observations of stars in the Radial Velocity
Experiment (RAVE) database are used to identify and examine single-lined binary
(SB1) candidates. The RAVE latest internal database (VDR3) includes radial
velocities, atmospheric and other parameters for approximately quarter million
of different stars with little less than 300,000 observations. In the sample of
~20,000 stars observed more than once, 1333 stars with variable radial
velocities were identified. Most of them are believed to be SB1 candidates. The
fraction of SB1 candidates among stars with several observations is between 10%
and 15% which is the lower limit for binarity among RAVE stars. Due to the
distribution of time spans between the re-observation that is biased towards
relatively short timescales (days to weeks), the periods of the identified SB1
candidates are most likely in the same range. Because of the RAVE's narrow
magnitude range most of the dwarf candidates belong to the thin Galactic disk
while the giants are part of the thick disk with distances extending to up to a
few kpc. The comparison of the list of SB1 candidates to the VSX catalog of
variable stars yielded several pulsating variables among the giant population
with the radial velocity variations of up to few tens of km/s. There are 26
matches between the catalog of spectroscopic binary orbits (SB9) and the whole
RAVE sample for which the given periastron time and the time of RAVE
observation were close enough to yield a reliable comparison. RAVE measurements
of radial velocities of known spectroscopic binaries are consistent with their
published radial velocity curves.Comment: 10 pages, 7 figures, accepted for publication in A
Potenciais regiões produtoras de morango durante a primavera e verão e riscos de ocorrência de geada na produção de inverno no estado do Rio Grande do Sul.
bitstream/item/31530/1/comunicado-229.pd
Weighing the local dark matter with RAVE red clump stars
We determine the Galactic potential in the solar neigbourhood from RAVE
observations. We select red clump stars for which accurate distances, radial
velocities, and metallicities have been measured. Combined with data from the
2MASS and UCAC catalogues, we build a sample of 4600 red clump stars within a
cylinder of 500 pc radius oriented in the direction of the South Galactic Pole,
in the range of 200 pc to 2000 pc distances. We deduce the vertical force and
the total mass density distribution up to 2 kpc away from the Galactic plane by
fitting a distribution function depending explicitly on three isolating
integrals of the motion in a separable potential locally representing the
Galactic one with four free parameters. Because of the deep extension of our
sample, we can determine nearly independently the dark matter mass density and
the baryonic disc surface mass density. We find (i) at 1kpc Kz/(2piG) = 68.5 pm
1.0 Msun/pc2, and (ii) at 2 kpc Kz/(2piG) = 96.9 pm 2.2 Msun/pc2. Assuming the
solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density
rhoDM (z=0) = 0.0143 pm 0.0011Msun pc3 = 0.542 pm 0.042 Gev/cm3 and the
baryonic surface mass density Sigma = 44.4 pm 4.1 Msun/pc2 . Our results are in
agreement with previously published Kz determinations up to 1 kpc, while the
extension to 2 kpc shows some evidence for an unexpectedly large amount of dark
matter. A flattening of the dark halo of order 0.8 can produce such a high
local density in combination with a circular velocity of 240 km/s . Another
explanation, allowing for a lower circular velocity, could be the presence of a
secondary dark component, a very thick disc resulting either from the deposit
of dark matter from the accretion of multiple small dwarf galaxies, or from the
presence of an effective phantom thick disc in the context of effective
galactic-scale modifications of gravity.Comment: 14 pages, 13 figures, accepted to Astronomy and Astrophysic
Single photon emitters based on Ni/Si related defects in single crystalline diamond
We present investigations on single Ni/Si related color centers produced via
ion implantation into single crystalline type IIa CVD diamond. Testing
different ion dose combinations we show that there is an upper limit for both
the Ni and the Si dose 10^12/cm^2 and 10^10/cm^2 resp.) due to creation of
excess fluorescent background. We demonstrate creation of Ni/Si related centers
showing emission in the spectral range between 767nm and 775nm and narrow
line-widths of 2nm FWHM at room temperature. Measurements of the intensity
auto-correlation functions prove single-photon emission. The investigated color
centers can be coarsely divided into two groups: Drawing from photon statistics
and the degree of polarization in excitation and emission we find that some
color centers behave as two-level, single-dipole systems whereas other centers
exhibit three levels and contributions from two orthogonal dipoles. In
addition, some color centers feature stable and bright emission with saturation
count rates up to 78kcounts/s whereas others show fluctuating count rates and
three-level blinking.Comment: 7 pages, submitted to Applied Physics B, revised versio
Kinematic modelling of the Milky Way using the RAVE and GCS stellar surveys
We investigate the kinematic parameters of the Milky Way disc using the RAVE
and GCS stellar surveys. We do this by fitting a kinematic model to the data
taking the selection function of the data into account. For stars in the GCS we
use all phase-space coordinates, but for RAVE stars we use only . Using MCMC technique, we investigate the full posterior distributions
of the parameters given the data. We investigate the `age-velocity dispersion'
relation for the three kinematic components
(), the radial dependence of the velocity
dispersions, the Solar peculiar motion (), the
circular speed at the Sun and the fall of mean azimuthal motion with
height above the mid-plane. We confirm that the Besan\c{c}on-style Gaussian
model accurately fits the GCS data, but fails to match the details of the more
spatially extended RAVE survey. In particular, the Shu distribution function
(DF) handles non-circular orbits more accurately and provides a better fit to
the kinematic data. The Gaussian distribution function not only fits the data
poorly but systematically underestimates the fall of velocity dispersion with
radius. We find that correlations exist between a number of parameters, which
highlights the importance of doing joint fits. The large size of the RAVE
survey, allows us to get precise values for most parameters. However, large
systematic uncertainties remain, especially in and . We
find that, for an extended sample of stars, is underestimated by as
much as if the vertical dependence of the mean azimuthal motion is
neglected. Using a simple model for vertical dependence of kinematics, we find
that it is possible to match the Sgr A* proper motion without any need for
being larger than that estimated locally by surveys like GCS.Comment: 27 pages, 13 figures, accepted for publication in Ap
- …