932 research outputs found
The Socio-Economic Value of the Shark-Diving Industry in Fiji
Based on a survey of divers, dive operators, resort managers, estimates business revenues from shark diving and related expenditures by area; tax revenues; and economic benefit to local communities
Quasars: What turns them off?
(Abridged) We explore the idea that the anti-hierarchical turn-off observed
in the quasar population arises from self-regulating feedback, via an outflow
mechanism. Using a detailed hydrodynamic simulation we calculate the luminosity
function of quasars down to a redshift of z=1 in a large, cosmologically
representative volume. Outflows are included explicitly by tracking halo
mergers and driving shocks into the surrounding intergalactic medium. Our
results are in excellent agreement with measurements of the spatial
distribution of quasars, and we detect an intriguing excess of galaxy-quasar
pairs at very short separations. We also reproduce the anti-hierarchical
turnoff in the quasar luminosity function, however, the magnitude of the
turn-off falls short of that observed as well as that predicted by analogous
semi-analytic models. The difference can be traced to the treatment of gas
heating within galaxies. The simulated galaxy cluster L_X-T relationship is
close to that observed for z~1 clusters, but the simulated galaxy groups at z=1
are significantly perturbed by quasar outflows, suggesting that measurements of
X-ray emission in high-redshift groups could well be a "smoking gun" for the
AGN heating hypothesis.Comment: 16 pages, 11 figures, submitted to ApJ, comments welcome
Measuring AGN Feedback with the Sunyaev-Zel'dovich Effect
One of the most important and poorly-understood issues in structure formation
is the role of outflows driven by active galactic nuclei (AGN). Using
large-scale cosmological simulations, we compute the impact of such outflows on
the small-scale distribution of the cosmic microwave background (CMB). Like
gravitationally-heated structures, AGN outflows induce CMB distortions both
through thermal motions and peculiar velocities, by processes known as the
thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, respectively. For AGN
outflows the thermal SZ effect is dominant, doubling the angular power spectrum
on arcminute scales. But the most distinct imprint of AGN feedback is a
substantial increase in the thermal SZ distortions around elliptical galaxies,
post-starburst ellipticals, and quasars, which is linearly proportional to the
outflow energy. While point source subtraction is difficult for quasars, we
show that by appropriately stacking microwave measurements around early-type
galaxies, the new generation of small-scale microwave telescopes will be able
to directly measure AGN feedback at the level important for current theoretical
models.Comment: 12 pages, 12 figures, submitted to ApJ (comments welcome
Treatment of neurocysticercosis with praziquantel
27 pacientes com neurocisticercose foram tratados com praziquantel, utilizado em doses progressivamente crescentes até alcançar 50 mg/kg/dia, por período de 21 dias, associado a dexametasona. Os doentes foram avaliados clínica e laboratorialmente durante o tratamento e, aqueles que completaram um ano de evolução, repetiram os testes imunofluorescência e ELISA neste período. Cefaléia foi o sintoma encontrado mais freqüentemente durante o tratamento, ocorrendo em 37% dos pacientes; 18,5% dos doentes apresentaram hipertensão intracraniana, um deles evoluindo para o óbito; 25,9% dos enfermos tiveram que suspender o praziquantel antes de completar o tratamento, devido ao surgimento de complicações importantes. Nos exames laboratoriais realizados no sétimo dia de tratamento, 33,3% dos pacientes apresentaram anormalidades, sendo leucocitose a mais freqüente. No período de um ano, 72,2% dos enfermos tiveram melhora do quadro clínico, enquanto os testes imunológicos tornaram-se não-reagentes no soro em 45,4% dos doentes e no LCR em 42,8%. Entretanto, nem sempre houve coincidência da melhora clínica com a apresentação dos testes imunológicos não-reagentes. No presente trabalho, não é possível afirmar que os testes imunológicos não-reagentes, assim como a melhora clínica dos pacientes, sejam conseqüentes à eficácia do tratamento com o praziquantel. Devido à grande freqüência e gravidade das complicações deste tratamento, os pacientes devem ser avaliados individualmente quanto aos riscos versus os benefícios dele.Twenty seven patients with neurocysticercosis were treated with praziquantel in progressive doses reaching 50 mg/kg/day associated with dexamethasone for 21 days. The patients were followed during and after treatment and those followed up for one year repeated their immunological tests (indirect immunofluorescence and ELISA) at this time. Headache was the most frequent symptom during the treatment, occurring on 37% of patients. During the treatment 18.5% of patients had intracranial hypertension and one died. One year after treatment 72.2% of patients who finished treatment improved. The immunological tests became negative in 45.4% of patients sera and 42.8% of cerebrospinal fluids. There was no correlation between the clinical evolution and immunological, testis. In this study it is not possible to afirm that both negative immunological tests and good clinical evolution were consequents to the efficacy of praziquantel treatment. Due to the great frequency and seriousness of this treatment complications, the patients with neurocysticercosis must be individually evaluated to know the risks and the benefits of the treatment with praziquantel
Estimating small angular scale CMB anisotropy with high resolution N-body simulations: weak lensing
We estimate the impact of weak lensing by strongly nonlinear cosmological
structures on the cosmic microwave background. Accurate calculation of large
multipoles requires N-body simulations and ray-tracing schemes with both
high spatial and temporal resolution. To this end we have developed a new code
that combines a gravitational Adaptive Particle-Particle, Particle-Mesh (AP3M)
solver with a weak lensing evaluation routine. The lensing deviations are
evaluated while structure evolves during the simulation so that all evolution
steps--rather than just a few outputs--are used in the lensing computations.
The new code also includes a ray-tracing procedure that avoids periodicity
effects in a universe that is modeled as a 3-D torus in the standard way.
Results from our new simulations are compared with previous ones based on
Particle-Mesh simulations. We also systematically investigate the impact of box
volume, resolution, and ray-tracing directions on the variance of the computed
power spectra. We find that a box size of Mpc is sufficient to
provide a robust estimate of the weak lensing angular power spectrum in the
-interval (2,000--7,000). For a reaslistic cosmological model the power
takes on values of a few in this
interval, which suggests that a future detection is feasible and may explain
the excess power at high in the BIMA and CBI observations.Comment: 49 pages, 13 figures, accepted for publication in Ap
The Role of Heating and Enrichment in Galaxy Formation
We show that the winds identified with high-redshift low-mass galaxies may
strongly affect the formation of stars in more massive galaxies that form
later. With 3D realizations of a simple linear growth model we track gas
shocking, metal enrichment, and cooling, together with dark halo formation. We
show that outflows typically strip baryonic material out of collapsing
intermediate mass halos, suppressing star formation. More massive halos can
trap the heated gas but collapse late, leading to a broad bimodal redshift
distribution, with a larger characteristic mass associated with the lower
redshift peak. This scenario accounts for the observed bell-shaped luminosity
function of early type galaxies, explains the small number of Milky Way
satellite galaxies relative to Cold Dark Matter models predictions, and
provides a possible explanation for the lack of metal poor G-dwarfs in the
solar neighborhood and the more general lack of low-metallicity stars in
massive galaxies relative to ``closed-box'' models of chemical enrichment.
Intergalactic medium heating from outflows should produce spectral distortions
in the cosmic microwave background that will be measurable with the next
generation of experiments.Comment: 19 pages, 12 figures, accepted to ApJ, models refined and minor
revisions mad
Measuring the three-dimensional shear from simulation data, with applications to weak gravitational lensing
We have developed a new three-dimensional algorithm, based on the standard
PM method, for computing deflections due to weak gravitational lensing. We
compare the results of this method with those of the two-dimensional planar
approach, and rigorously outline the conditions under which the two approaches
are equivalent. Our new algorithm uses a Fast Fourier Transform convolution
method for speed, and has a variable softening feature to provide a realistic
interpretation of the large-scale structure in a simulation. The output values
of the code are compared with those from the Ewald summation method, which we
describe and develop in detail. With an optimal choice of the high frequency
filtering in the Fourier convolution, the maximum errors, when using only a
single particle, are about 7 per cent, with an rms error less than 2 per cent.
For ensembles of particles, used in typical -body simulations, the rms
errors are typically 0.3 per cent. We describe how the output from the
algorithm can be used to generate distributions of magnification, source
ellipticity, shear and convergence for large-scale structure.Comment: 22 pages, latex, 11 figure
Efeito da reutilização de implantes de progesterona sobre o momento e número de ovulações em ovelhas.
Resumo: Em um programa de manejo reprodutivo ovino, as vantagens do uso da inseminação artificial dependem do controle do estro e da ovulação. Os métodos mais utilizados para a indução e sincronização de estro e estimulação do crescimento folicular em ovelhas envolvem progesterona e a administração de gonadotrofina sérica da égua gestante (Menchaca & Rubianes, 2004). O objetivo do presente trabalho foi avaliar o efeito da reutilização de implantes de progesterona sobre o momento e número de ovulações de ovelhas. [Effect of reuse the implants of progesterone on the moment and number of ovulations in sheep]
The violation of the Hund's rule in semiconductor artificial atoms
The unrestricted Pople-Nesbet approach for real atoms is adapted to quantum
dots, the man-made artificial atoms, under applied magnetic field. Gaussian
basis sets are used instead of the exact single-particle orbitals in the
construction of the appropriated Slater determinants. Both system chemical
potential and charging energy are calculated, as also the expected values for
total and z-component in spin states. We have verified the validity of the
energy shell structure as well as the Hund's rule state population at zero
magnetic field. Above given fields, we have observed a violation of the Hund's
rule by the suppression of triplets and quartets states at the 1p energy shell,
taken as an example. We also compare our present results with those obtained
using the LS-coupling scheme for low electronic occupations. We have focused
our attention to ground-state properties for GaAs quantum dots populated up to
forty electrons.Comment: 5 pages, 2 figures, submitted to Semic. Sci. Techno
Weak gravitational lensing in the standard Cold Dark Matter model, using an algorithm for three-dimensional shear
We investigate the effects of weak gravitational lensing in the standard Cold
Dark Matter cosmology, using an algorithm which evaluates the shear in three
dimensions. The algorithm has the advantage of variable softening for the
particles, and our method allows the appropriate angular diameter distances to
be applied to every evaluation location within each three-dimensional
simulation box. We investigate the importance of shear in the distance-redshift
relation, and find it to be very small. We also establish clearly defined
values for the smoothness parameter in the relation, finding its value to be at
least 0.88 at all redshifts in our simulations. From our results, obtained by
linking the simulation boxes back to source redshifts of 4, we are able to
observe the formation of structure in terms of the computed shear, and also
note that the major contributions to the shear come from a very broad range of
redshifts. We show the probability distributions for the magnification, source
ellipticity and convergence, and also describe the relationships amongst these
quantities for a range of source redshifts. We find a broad range of
magnifications and ellipticities; for sources at a redshift of 4, 97{1/2}% of
all lines of sight show magnifications up to 1.3 and ellipticities up to 0.195.
There is clear evidence that the magnification is not linear in the
convergence, as might be expected for weak lensing, but contains contributions
from higher order terms in both the convergence and the shear.Comment: 14 pages, LaTeX, 15 figures include
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