2,533 research outputs found
Infrared Surface Brightness Fluctuations of the Coma Elliptical NGC 4874 and the Value of the Hubble Constant
We have used the Keck I Telescope to measure K-band surface brightness
fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma
cluster. We use deep HST WFPC2 optical imaging to account for the contamination
due to faint globular clusters and improved analysis techniques to derive
measurements of the SBF apparent magnitude. Using a new SBF calibration which
accounts for the dependence of K-band SBFs on the integrated color of the
stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10
Mpc) for the Coma cluster. The resulting value of the Hubble constant is 71+/-8
km/s/Mpc, not including any systematic error in the HST Cepheid distance scale.Comment: ApJ Letters, in press. Uses emulateapj5.st
Existence and uniqueness of limit cycles in a class of second order ODE's with inseparable mixed terms
We prove a uniqueness result for limit cycles of the second order ODE . Under mild additional conditions, we
show that such a limit cycle attracts every non-constant solution. As a special
case, we prove limit cycle's uniqueness for an ODE studied in \cite{ETA} as a
model of pedestrians' walk. This paper is an extension to equations with a
non-linear of the results presented in \cite{S}
Bearings-Only Guidance in Cis-Lunar Rendezvous
The current plans of returning to the Moon involve rendezvous and docking/berthing operations
with a passive permanent station, whose targeted orbit is a Near Rectilinear Halo
Orbit. In this work a preliminary guidance algorithm for the close-range rendezvous phase
is proposed, based on a sample mission application, assuming the active chaser can measure
relative angles only to the target. The navigation performance is affected by the maneuvers
performed because their execution is necessary to make the problem observable. The relative
motion equations with third body perturbation are considered directly in the guidance
algorithm, with the additional aim of improving observability during the approach trajectory.
Numerical simulations are presented to validate the proposed methodology
The interplay between voluntary vaccination and reduction of risky behavior: a general behavior-implicit SIR model for vaccine preventable infections
The onset in the last 15 years of behavioral epidemiology has opened many new avenues for epidemiological modelers. In this manuscript we first review two classes of behavioral epidemiology models for vaccine preventable diseases, namely behaviour-implicit SIR models with prevalence-dependent vaccination (at birth and among older individuals), and prevalence-dependent contact rate.
Subsequently, we briefly propose a general framework of behaviorâdependent nonlinear and linear Forces of Infection (FoI) valid for a vast family of infectious diseases, and including delays and âepidemic memoryâ effects.
Finally and mainly, we develop a new general behavioral SIR model. This model combines the two aforementioned types of behavioral phenomena, previously considered only separately, into a single unified model for behavioral responses. The resulting model allows to develop a general phenomenological theory of the effects of behavioral responses within SIR models for endemic infections. In particular, the model allows to complete the picture about the complicate interplay between different behavioral responses acting on different epidemiological parameters in triggering sustained oscillations of vaccine coverage, risky behavior, and infection prevalence
Globular Clusters in Dense Clusters of Galaxies
Deep imaging data from the Keck II telescope are employed to study the
globular cluster (GC) populations in the cores of six rich Abell clusters. The
sample includes A754, A1644, A2124, A2147, A2151, and A2152, and spans the
redshift range z = 0.035-0.066. The clusters also range in morphology from
spiral-rich, irregular systems to centrally concentrated cD clusters rich in
early-type galaxies. Globular cluster specific frequencies S_N and luminosity
function dispersions are measured for a total of 9 galaxies in six central
fields. The measured values of S_N for the six brightest cluster galaxies
(BCGs) are all higher than typical values for giant ellipticals, in accord with
the known S_N-density correlations. The three non-BCGs analyzed also have
elevated values of S_N, confirming that central location is a primary factor.
The number of GCs per unit mass for these fields are consistent with those
found in an earlier sample, giving further evidence that GC number scales with
mass and that the S_N variations are due to a deficit of halo light, i.e., S_N
reflects mass-to-light ratio.
The discussion builds on an earlier suggestion that the GCs (both metal rich
and metal poor) around the central cluster galaxies were assembled at early
times, and that star formation halted prematurely in the central galaxies at
the epoch of cluster collapse. This is consistent with recent simulations of
BCG/cluster formation. The subsequent addition of luminous material through
cluster dynamical evolution can cause S_N to decrease, and we may be seeing the
first evidence of this. Finally, the GC luminosity function measurements are
used to constrain the relative distances of the three clusters that make up the
Hercules supercluster.Comment: Uses emulateapj.sty (included); 17 pages with 9 included PostScript
figures. Figures 1-6 are separate GIF images (so 15 figures total) available
from http://astro.caltech.edu/~jpb/clusters -- the full PostScript version of
the paper (20 pages; 2.2 Mb compressed) incorporating Figures 1-6 can also be
grabbed from this URL. Accepted for publication in A
Using flaming as an alternative method to vine suckering.
Suckering is the process of removing the suckers that grapevine trunks put out in the
spring. Suckering by hand is costly and time consuming and requires constant bending down, getting
up and making repetitive motions. The mechanical removal of suckers with rotating scourges can
damage the vine plants. Chemical suckering is a limiting factor for wine grape growers interested in
sustainable and/or organic agriculture. The aim of this research was to test flaming as an alternative
method to vine suckering. A three-year experiment was conducted on a 10-year-old Sangiovese
vine (775 Paulsen rootstock). The treatments consisted of flame suckering at different phenological
stages, hand-suckering and a no-suckered control. Data on the number of suckers, grape yield
components, and grape composition were collected and analysed. The results showed that flaming
significantly reduced the initial number of suckers. This effect on the suckers was highest when
the main productive shoots of the vines were at the 18-19 BBCH growth stage. Flame-suckering
did not affect grape yield components and grape composition. Future studies could investigate the
simultaneous use of flaming for both suckering and weed control
Aids and surgery
HIV constitutes one of the most difficult challenges facing the healthcare profession today. It is estimated that HIV infects over 40 million people in the world and 14 million have died from the disease so far. The objective of the study was to evaluate the outcome of treatment of HIV-related surgical conditions, estimating the morbidity and mortality of surgical intervention cross infection risks to surgical equipes and analysing preventive strategies to HIV perioperative transmission
UGC 3995: A Close Pair of Spiral Galaxies
UGC 3995 is a close pair of spiral galaxies whose eastern component hosts a
Seyfert 2 nucleus. We present a detailed analysis of this system using long
slit spectroscopy and narrow (\ha + \nii) as well as broad band (B, R) imaging
and an archive WFPC2 image. The component galaxies reveal surprisingly small
signs of interaction considering their spatial proximity and almost identical
recession velocities, as the bright filament is probably an optical illusion
due to the superposition of the bar of the Seyfert galaxy and of the spiral
arms of the companion. The broad band morphology, a B--R color map, and a
continuum-subtracted \ha + \nii image demonstrate that the western component
UGC 3995B is in front of the Seyfert-hosting component UGC 3995A, partly
obscuring its western side. The small radial velocity difference leaves the
relative motion of the two galaxies largely unconstrained. The observed lack of
major tidal deformations, along with some morphological peculiarities, suggests
that the galaxies are proximate in space but may have recently approached each
other on the plane of the sky. The geometry of the system and the radial
velocity curve at P. A. = 106 suggest that the encounter may be retrograde or,
alternatively, prograde before perigalacticon. The partial overlap of the two
galaxies allows us to estimate the optical thickness of the disk of component
B. We derive an extinction = 0.18 visual magnitudes in the infra-arms parts of
the foreground galaxy disk, and >= 1-1.5 visual magnitudes in correspondence of
the spiral arms.Comment: Accepted for publication in the Astronomical Journal (June 1999
issue
Cognitive ability and risk for substance misuse in men : genetic and environmental correlations in a longitudinal nation-wide family study.
Aims. To investigate the association between cognitive ability in late adolescence and
subsequent substance misuse-related events in men, and to study the underlying genetic and
environmental correlations. Design. A population-based longitudinal study with three
different family-based designs. Cox proportional hazards models were conducted to
investigate the association at the individual level. Bivariate quantitative genetic modeling in
(1) full brothers and maternal half-brothers, (2) full brothers reared together and apart, and (3)
monozygotic and dizygotic twin brothers was used to estimate genetic and environmental
correlations. Setting. Register-based study in Sweden.
Participants. The full sample included 1,402,333 Swedish men born 1958-1991 and
conscripted at mean age 18.2 (SD=0.5) years. 1,361,066 men who had no substance misuse
events before cognitive assessment at mandatory military conscription were included in the
Cox regression models with a follow-up time of up to 35.6 years. Measures. Cognitive ability
was assessed at conscription with the Swedish Enlistment Battery. Substance misuse events
included alcohol and drug related court convictions, medical treatments, and deaths, available
from governmental registries Findings. Lower cognitive ability in late adolescence predicted
an increased risk for substance misuse events (hazard ratio [HR] for a 1-stanine unit decrease
in cognitive ability: 1.29, 95% CI: 1.29-1.30). The association was somewhat attenuated
within clusters of full brothers (HR=1.21, 95% CI: 1.20-1.23). Quantitative genetic analyses
indicated that the association was primarily due to genetic influences; the genetic correlations
ranged between -.39 (95% CI: -.45, -.34) and -.52 (-.55, -.48) in the three different designs.
Conclusions. Our findings from different family designs indicate that shared genetic
influences underlie the association between low cognitive ability and subsequent risk for
substance misuse events.The Academy of FinlandThe Swedish Research Council for Health, Working Life and Welfare.The Swedish Research CouncilThe Swedish Research Council through the Swedish Initiative for Research on Microdata in the Social And Medical Sciences (SIMSAM)Manuscrip
Redshift-Distance Survey of Early-type Galaxies. I. Sample Selection, Properties and Completeness
This is the first in a series of papers describing the recently completed
all-sky redshift-distance survey of nearby early-type galaxies (ENEAR) carried
out for peculiar velocity analysis. The sample is divided into two parts and
consists of 1607 elliptical and lenticular galaxies with cz < 7000 km/s and
with blue magnitudes brighter than m_B=14.5 (ENEARm), and of galaxies in
clusters (ENEARc). Galaxy distances based on the Dn-sigma and Fundamental Plane
(FP) relations are now available for 1359 and 1107 ENEARm galaxies,
respectively, with roughly 80% based on new data gathered by our group. The
Dn-sigma and FP template distance relations are derived by combining 569 and
431 galaxies in 28 clusters, respectively, of which about 60% are based on our
new measurements. The ENEARm redshift-distance survey extends the earlier work
of the 7S and the recent Tully-Fisher surveys sampling a comparable volume. In
subsequent papers of this series we intend to use the ENEAR sample by itself or
in combination with the SFI Tully-Fisher survey to analyze the properties of
the local peculiar velocity field and to test how sensitive the results are to
different sampling and to the distance indicators. We also anticipate that the
homogeneous database assembled will be used for a variety of other applications
and serve as a benchmark for similar studies at high-redshift.Comment: 43 pages, 15 figures, submitted to the Astronomical Journa
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