1,881 research outputs found
New and Old Tests of Cosmological Models and Evolution of Galaxies
We describe the classical cosmological tests, such as the Log-Log,
redshift-magnitude and angular diameter tests, and propose some new tests of
the evolution of galaxies and the universe. Most analyses of these tests treat
the problem in terms of a luminosity function and its evolution which can lead
to incorrect conclusions when dealing with high redshift sources. We develop a
proper treatment in three parts. In the first part we describe these tests
based on the isophotal values of the quantities such as flux, size or surface
brightness. We show the shortcomings of the simple point source approximation
based solely on the luminosity function and consideration of the flux limit. We
emphasize the multivariate nature of the problem and quantify the effects of
other selection biases due to the surface brightness and angular size
limitations. In these considerations the surface brightness profile plays a
critical role. In the second part we show that considerable simplification over
the complicated isophotal scheme is achieved if these test are carried out in
some sort of metric scheme, for example that suggested by Petrosian (1976).
This scheme, however, is limited to well resolved sources. Finally, we describe
the new tests, which use the data to a fuller extent than the isophotal or
metric based tests, and amount to simply counting the pixels or adding their
intensities as a function of the pixel surface brightness, instead of dealing
with surface brightness, sizes and fluxes of individual galaxies. We show that
the data analysis and its comparison with the theoretical models of the
distributions and evolution of galaxies has the simplicity of the metric test
and utilizes the data more fully than the isophotal test.Comment: 29 pages including 8 figures.
http://www-bigbang.stanford.edu/~vahe/papers/finals/newtest.ps. To appear in
ApJ, Oct. 199
Non-parametric mass reconstruction of A1689 from strong lensing data with SLAP
We present the mass distribution in the central area of the cluster A1689 by
fitting over 100 multiply lensed images with the non-parametric Strong Lensing
Analysis Package (SLAP, Diego et al. 2004). The surface mass distribution is
obtained in a robust way finding a total mass of 0.25E15 M_sun/h within a 70''
circle radius from the central peak. Our reconstructed density profile fits
well an NFW profile with small perturbations due to substructure and is
compatible with the more model dependent analysis of Broadhurst et al. (2004a)
based on the same data. Our estimated mass does not rely on any prior
information about the distribution of dark matter in the cluster. The peak of
the mass distribution falls very close to the central cD and there is
substructure near the center suggesting that the cluster is not fully relaxed.
We also examine the effect on the recovered mass when we include the
uncertainties in the redshift of the sources and in the original shape of the
sources. Using simulations designed to mimic the data, we identify some biases
in our reconstructed mass distribution. We find that the recovered mass is
biased toward lower masses beyond 1 arcmin (150 kpc) from the central cD and
that in the very center we may be affected by degeneracy problems. On the other
hand, we confirm that the reconstructed mass between 25'' and 70'' is a robust,
unbiased estimate of the true mass distribution and is compatible with an NFW
profile.Comment: 11 pages, 12 figures. MNRAS submitted. A full resolution of the paper
can be found in http://darwin.physics.upenn.edu/SLAP
Unavoidable Selection Effects in the Analysis of Faint Galaxies in the Hubble Deep Field: Probing the Cosmology and Merger History of Galaxies
(Abridged) We present a detailed analysis of the number count and photometric
redshift distribution of faint galaxies in the Hubble Deep Field (HDF), paying
a special attention to the selection effects including the cosmological dimming
of surface brightness of galaxies. We find a considerably different result from
previous studies ignoring the selection effects, and these effects should
therefore be taken into account in the analysis. We find that the model of pure
luminosity evolution (PLE) of galaxies in the Einstein-de Sitter (EdS) universe
predicts much smaller counts than those observed at faint magnitude limits by a
factor of more than 10, so that a very strong number evolution of galaxies with
\eta > 3-4 must be invoked to reproduce the I_{814} counts, when parametrized
as \phi^* \propto (1+z)^\eta. However we show that such a strong number
evolution under realistic merging processes of galaxies can not explain the
steep slope of the B_{450} and V_{606} counts, and it is seriously inconsistent
with their photometric redshift distribution. We find that these difficulties
still persist in an open universe with \Omega_0 > 0.2, but are resolved only
when we invoke a -dominated flat universe, after examining various
systematic uncertainties in modeling the formation and evolution of galaxies.
The present analysis revitalizes the practice of using faint number counts as
an important cosmological test, giving one of the arguments against the EdS
universe and suggests acceleration of the cosmic expansion by vacuum energy
density. While a modest number evolution of galaxies with \eta ~ 1 is still
necessary even in a Lambda-dominated universe, a stronger number evolution with
\eta > 1 is rejected from the HDF data, giving a strong constraint on the
merger history of galaxies.Comment: 24 pages, 15 figures, final version matching publication in ApJ. Some
references added. The complete ps file of Table 3 is available at
http://th.nao.ac.jp/~totani/images/paper/ty2000-table3.p
Response of selected plant and insect species to simulated solid rocket exhaust mixtures and to exhaust components from solid rocket fuels
The effects of solid rocket fuel (SRF) exhaust on selected plant and and insect species in the Merritt Island, Florida area was investigated in order to determine if the exhaust clouds generated by shuttle launches would adversely affect the native, plants of the Merritt Island Wildlife Refuge, the citrus production, or the beekeeping industry of the island. Conditions were simulated in greenhouse exposure chambers and field chambers constructed to model the ideal continuous stirred tank reactor. A plant exposure system was developed for dispensing and monitoring the two major chemicals in SRF exhaust, HCl and Al203, and for dispensing and monitoring SRF exhaust (controlled fuel burns). Plants native to Merritt Island, Florida were grown and used as test species. Dose-response relationships were determined for short term exposure of selected plant species to HCl, Al203, and mixtures of the two to SRF exhaust
A pneumatic power harvesting ankle-foot orthosis to prevent foot-drop
<p>Abstract</p> <p>Background</p> <p>A self-contained, self-controlled, pneumatic power harvesting ankle-foot orthosis (PhAFO) to manage foot-drop was developed and tested. Foot-drop is due to a disruption of the motor control pathway and may occur in numerous pathologies such as stroke, spinal cord injury, multiple sclerosis, and cerebral palsy. The objectives for the prototype PhAFO are to provide toe clearance during swing, permit free ankle motion during stance, and harvest the needed power with an underfoot bellow pump pressurized during the stance phase of walking.</p> <p>Methods</p> <p>The PhAFO was constructed from a two-part (tibia and foot) carbon composite structure with an articulating ankle joint. Ankle motion control was accomplished through a cam-follower locking mechanism actuated via a pneumatic circuit connected to the bellow pump and embedded in the foam sole. Biomechanical performance of the prototype orthosis was assessed during multiple trials of treadmill walking of an able-bodied control subject (n = 1). Motion capture and pressure measurements were used to investigate the effect of the PhAFO on lower limb joint behavior and the capacity of the bellow pump to repeatedly generate the required pneumatic pressure for toe clearance.</p> <p>Results</p> <p>Toe clearance during swing was successfully achieved during all trials; average clearance 44 ± 5 mm. Free ankle motion was observed during stance and plantarflexion was blocked during swing. In addition, the bellow component repeatedly generated an average of 169 kPa per step of pressure during ten minutes of walking.</p> <p>Conclusion</p> <p>This study demonstrated that fluid power could be harvested with a pneumatic circuit built into an AFO, and used to operate an actuated cam-lock mechanism that controls ankle-foot motion at specific periods of the gait cycle.</p
Theory of Spike Spiral Waves in a Reaction-Diffusion System
We discovered a new type of spiral wave solutions in reaction-diffusion
systems --- spike spiral wave, which significantly differs from spiral waves
observed in FitzHugh-Nagumo-type models. We present an asymptotic theory of
these waves in Gray-Scott model. We derive the kinematic relations describing
the shape of this spiral and find the dependence of its main parameters on the
control parameters. The theory does not rely on the specific features of
Gray-Scott model and thus is expected to be applicable to a broad range of
reaction-diffusion systems.Comment: 4 pages (REVTeX), 2 figures (postscript), submitted to Phys. Rev.
Let
Pleasant and unpleasant odour-face combinations influence face and odour perception: An event-related potential study.
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Odours alter evaluations of concurrent visual stimuli. However, neural mechanisms underlying the effects of
congruent and incongruent odours on facial expression perception are not clear. Moreover, the influence of
emotional faces on odour perception is not established. We investigated the effects of one pleasant and one
unpleasant odour paired with happy and disgusted faces, on subjective ratings and ERP responses to faces.
Participants rated the pleasantness of happy and disgusted faces that appeared during 3 s pleasant or unpleasant
odour pulses, or without odour. Odour pleasantness and intensity ratings were recorded in each trial.
EEG was recorded continuously using a 128-channel system.
Happy and disgusted faces paired with pleasant and unpleasant odour were rated as more or less pleasant,
respectively, compared to the same faces presented in the other odour conditions. Odours were rated as more
pleasant when paired with happy faces, and unpleasant odour was rated more intense when paired with disgusted
faces. Unpleasant odour paired with disgusted faces also decreased inspiration. Odour-face interactions
were evident in the N200 and N400 components.
Our results reveal bi-directional effects of odours and faces, and suggest that odour-face interactions may be
represented in ERP components. Pairings of unpleasant odour and disgusted faces resulted in stronger hedonic
ratings, ERP changes, increased odour intensity ratings and respiratory adjustment. This finding likely represents
heightened adaptive responses to multimodal unpleasant stimuli, prompting appropriate behaviour in the presence
of danger
Construction of an isotropic cellular automaton for a reaction-diffusion equation by means of a random walk
We propose a new method to construct an isotropic cellular automaton
corresponding to a reaction-diffusion equation. The method consists of
replacing the diffusion term and the reaction term of the reaction-diffusion
equation with a random walk of microscopic particles and a discrete vector
field which defines the time evolution of the particles. The cellular automaton
thus obtained can retain isotropy and therefore reproduces the patterns found
in the numerical solutions of the reaction-diffusion equation. As a specific
example, we apply the method to the Belousov-Zhabotinsky reaction in excitable
media
Size-selective nanoparticle growth on few-layer graphene films
We observe that gold atoms deposited by physical vapor deposition onto few
layer graphenes condense upon annealing to form nanoparticles with an average
diameter that is determined by the graphene film thickness. The data are well
described by a theoretical model in which the electrostatic interactions
arising from charge transfer between the graphene and the gold particle limit
the size of the growing nanoparticles. The model predicts a nanoparticle size
distribution characterized by a mean diameter D that follows a scaling law D
proportional to m^(1/3), where m is the number of carbon layers in the few
layer graphene film.Comment: 15 pages, 4 figure
Adaptive response and enlargement of dynamic range
Many membrane channels and receptors exhibit adaptive, or desensitized,
response to a strong sustained input stimulus, often supported by protein
activity-dependent inactivation. Adaptive response is thought to be related to
various cellular functions such as homeostasis and enlargement of dynamic range
by background compensation. Here we study the quantitative relation between
adaptive response and background compensation within a modeling framework. We
show that any particular type of adaptive response is neither sufficient nor
necessary for adaptive enlargement of dynamic range. In particular a precise
adaptive response, where system activity is maintained at a constant level at
steady state, does not ensure a large dynamic range neither in input signal nor
in system output. A general mechanism for input dynamic range enlargement can
come about from the activity-dependent modulation of protein responsiveness by
multiple biochemical modification, regardless of the type of adaptive response
it induces. Therefore hierarchical biochemical processes such as methylation
and phosphorylation are natural candidates to induce this property in signaling
systems.Comment: Corrected typos, minor text revision
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