10,215 research outputs found
Python I, II, and III CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies
We use Python I, II, and III cosmic microwave background anisotropy data to
constrain cosmogonies. We account for the Python beamwidth and calibration
uncertainties. We consider open and spatially-flat-Lambda cold dark matter
cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the range
0.1--1, baryonic-mass density parameter Omega_B in the range (0.005--0.029)
h^{-2}, and age of the universe t_0 in the range (10--20) Gyr. Marginalizing
over all parameters but Omega_0, the combined Python data favors an open
(spatially-flat-Lambda) model with Omega_0 simeq 0.2 (0.1). At the 2 sigma
confidence level model normalizations deduced from the combined Python data are
mostly consistent with those drawn from the DMR, UCSB South Pole 1994, ARGO,
MAX 4 and 5, White Dish, and SuZIE data sets.Comment: 20 pages, 7 figures, accepted by Ap
Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos
Ongoing accretion onto galactic disks has been recently theorized to progress
via the unstable cooling of the baryonic halo into condensed clouds. These
clouds have been identified as analogous to the High-Velocity Clouds (HVCs)
observed in HI in our Galaxy. Here we compare the distribution of HVCs observed
around our own Galaxy and extra-planar gas around the Andromeda galaxy to these
possible HVC analogs in a simulation of galaxy formation that naturally
generates these condensed clouds. We find a very good correspondence between
these observations and the simulation, in terms of number, angular size,
velocity distribution, overall flux and flux distribution of the clouds. We
show that condensed cloud accretion only accounts for ~ 0.2 M_solar / year of
the current overall Galactic accretion in the simulations. We also find that
the simulated halo clouds accelerate and become more massive as they fall
toward the disk. The parameter space of the simulated clouds is consistent with
all of the observed HVC complexes that have distance constraints, except the
Magellanic Stream which is known to have a different origin. We also find that
nearly half of these simulated halo clouds would be indistinguishable from
lower-velocity gas and that this effect is strongest further from the disk of
the galaxy, thus indicating a possible missing population of HVCs. These
results indicate that the majority of HVCs are consistent with being infalling,
condensed clouds that are a remnant of Galaxy formation.Comment: 10 pages, 6 figures, ApJ Accepted. Some changes to techniqu
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
Divergência genético-morfológica entre acessos de feijão caupi de porte semi-ereto e ereto.
O estudo da divergência é essencial para o melhoramento vegetal, pois possibilita a quantificação da variabilidade genética..
Popularização de ciência e tecnologia de alimentos na região sul do estado do Rio de Janeiro.
Internal kinematics of spiral galaxies in distant clusters III. Velocity fields from FORS2/MXU spectroscopy
(Abridged) We study the impact of cluster environment on the evolution of
spiral galaxies by examining their structure and kinematics. Rather than
two-dimensional rotation curves, we observe complete velocity fields by placing
three adjacent and parallel FORS2 MXU slits on each object, yielding several
emission and absorption lines. The gas velocity fields are reconstructed and
decomposed into circular rotation and irregular motions using kinemetry. To
quantify irregularities in the gas kinematics, we define three parameters:
sigma_{PA} (standard deviation of the kinematic position angle), Delta phi (the
average misalignment between kinematic and photometric position angles) and
k_{3,5} (squared sum of the higher order Fourier terms). Using local,
undistorted galaxies from SINGS, these can be used to establish the regularity
of the gas velocity fields. Here we present the analysis of 22 distant galaxies
in the MS0451.6-0305 field with 11 members at z=0.54. In this sample we find
both field (4 out of 8) and cluster (3 out of 4) galaxies with velocity fields
that are both irregular and asymmetric. We show that these fractions are
underestimates of the actual number of galaxies with irregular velocity fields.
The values of the (ir)regularity parameters for cluster galaxies are not very
different from those of the field galaxies, implying that there are isolated
field galaxies that are as distorted as the cluster members. None of the
deviations in our small sample correlate with photometric/structural properties
like luminosity or disk scale length in a significant way.
Our 3D-spectroscopic method successfully maps the velocity field of distant
galaxies, enabling the importance and efficiency of cluster specific
interactions to be assessed quantitatively.Comment: accepted for publication in A&A, high resolution version available at
http://www.astro.rug.nl/~kutdemir/papers
Extra dimensions in CERN LHC via mini-black holes: effective Kerr-Newman brane-world effects
We solve Einstein equations on the brane to derive the exact form of the
braneworld-corrected perturbations in Kerr-Newman singularities, using
Randall-Sundrum and Arkani-Hamed-Dimopoulos-Dvali (ADD) models. It is a
consequence of such models the possibility that Kerr-Newman mini-black holes
can be produced in LHC. We use this approach to derive a normalized correction
for the Schwarzschild Myers-Perry radius of a static -dimensional
mini-black hole, using more realistic approaches arising from Kerr-Newman
mini-black hole analysis. Besides, we prove that there are four Kerr-Newman
black hole horizons in braneworld scenario we use, although only the outer
horizon is relevant in the physical measurable processes. Parton cross sections
in LHC and Hawking temperature are also investigated as functions of Planck
mass (in the LHC range 1-10 TeV), mini-black hole mass and the number of large
extra dimensions in braneworld large extra-dimensional scenarios. In this case
a more realistic brane effect-corrected formalism can achieve more precisely
the effective extra-dimensional Planck mass and the number of large extra
dimensions -- in Arkani-Hamed-Dimopoulos-Dvali model -- or the size of the
warped extra dimension -- in Randall-Sundrum formalism.Comment: 11 pages, 23 figures, citations update
Poynting's theorem for planes waves at an interface: a scattering matrix approach
We apply the Poynting theorem to the scattering of monochromatic
electromagnetic planes waves with normal incidence to the interface of two
different media. We write this energy conservation theorem to introduce a
natural definition of the scattering matrix S. For the dielectric-dielectric
interface the balance equation lead us to the energy flux conservation which
express one of the properties of S: it is a unitary matrix. For the
dielectric-conductor interface the scattering matrix is no longer unitary due
to the presence of losses at the conductor. However, the dissipative term
appearing in the Poynting theorem can be interpreted as a single absorbing mode
at the conductor such that a whole S, satisfying flux conservation and
containing this absorbing mode, can be defined. This is a simplest version of a
model introduced in the current literature to describe losses in more complex
systems.Comment: 5 pages, 3 figures, submitted to Am. J. Phy
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