84 research outputs found
Real-time Realistic Rendering Of Nature Scenes With Dynamic Lighting
Rendering of natural scenes has interested the scientific community for a long time due to its numerous applications. The targeted goal is to create images that are similar to what a viewer can see in real life with his/her eyes. The main obstacle is complexity: nature scenes from real life contain a huge number of small details that are hard to model, take a lot of time to render and require a huge amount of memory unavailable in current computers. This complexity mainly comes from geometry and lighting. The goal of our research is to overcome this complexity and to achieve real-time rendering of nature scenes while providing visually convincing dynamic global illumination. Our work focuses on grass and trees as they are commonly visible in everyday life. We handle geometry and lighting complexities for grass to render millions of grass blades interactively with dynamic lighting. As for lighting complexity, we address real-time rendering of trees by proposing a lighting model that handles indirect lighting. Our work makes extensive use of the current generation of Graphics Processing Units (GPUs) to meet the real-time requirement and to leave the CPU free to carry out other tasks
Grizzly Bear Population Trend Estimated Using Genetic Detection
We use genetic detection data from natural bear rub sites to estimate annual rate of change for a threatened grizzly bear (Ursus arctos) population in the 33,300 km2 Northern Continental Divide Ecosystem (NCDE) in northwestern Montana, USA). Bear rubs were surveyed twice annually in 2004, 2009-2012 (3,580 – 4,805 rubs). We detected approximately 1/3 of the grizzly bear population annually. Using spatially explicit capturerecapture (SCR) models in a maximum likelihood framework, we estimate growth rate from the slope of a linear regression fit to the log of density estimates. To evaluate the usefulness of our estimates, we compare them to estimates of ? made using independent data from known-fate telemetry monitoring for our population. Total annual population rate of change was 1.056 (95% CI = 1.033-1.079). The large sample sizes generated by genetic detection provided information on variation in density and trend within the NCDE useful for designing monitoring and management strategies tailored to area-specific needs and priorities. Local rates of change within the NCDE were higher in areas of lower density and population expansion than in Glacier NP, the area with highest density. As density increased, the amount of space used by bears estimated by the SCR models, ?, decreased. Hair collection from natural bear rub sites was an efficient sampling approach able to generate precise estimates of annual growth rate from 2 years of data
Dual Massive Gravity
The linearized massive gravity in three dimensions, over any maximally
symmetric background, is known to be presented in a self-dual form as a first
order equation which encodes not only the massive Klein-Gordon type field
equation but also the supplementary transverse-traceless conditions. We
generalize this construction to higher dimensions. The appropriate dual
description in d dimensions, additionally to a (non-symmetric) tensor field
, involves an extra rank-(d-1) field equivalently represented by
the torsion rank-3 tensor. The symmetry condition for arises
on-shell as a consequence of the field equations. The action principle of the
dual theory is formulated. The focus has been made on four dimensions. Solving
one of the fields in terms of the other and putting back in the action one
obtains two other equivalent formulations of the theory in which the action is
quadratic in derivatives. In one of these representations the theory is
formulated entirely in terms of a rank-2 non-symmetric tensor .
This quadratic theory is not identical to the Fierz-Pauli theory and contains
the coupling between the symmetric and antisymmetric parts of .
Nevertheless, the only singularity in the propagator is the same as in the
Fierz-Pauli theory so that only the massive spin-2 particle is propagating. In
the other representation, the theory is formulated in terms of the torsion
rank-3 tensor only. We analyze the conditions which follow from the field
equations and show that they restrict to 5 degrees of freedom thus producing an
alternative description to the massive spin-2 particle. A generalization to
higher dimensions is suggested.Comment: 14 pages; v2: modifications in Appendix, more references adde
Warm H as a probe of massive accretion and feedback through shocks and turbulence across cosmic time
Galaxy formation depends on a complex interplay between gravitational
collapse, gas accretion, merging, and feedback processes. Yet, after many
decades of investigation, these concepts are poorly understood. This paper
presents the argument that warm H can be used as a tool to unlock some of
these mysteries. Turbulence, shocks and outflows, driven by star formation, AGN
activity or inflows, may prevent the rapid buildup of star formation in
galaxies. Central to our understanding of how gas is converted into stars is
the process by which gas can dissipate its mechanical energy through turbulence
and shocks in order to cool. H lines provide direct quantitative
measurements of kinetic energy dissipation in molecular gas in galaxies
throughout the Universe. Based on the detection of very powerful H lines
from z = 2 galaxies and proto-clusters at the detection limits of {\it
Spitzer}, we are confident that future far-IR and UV H observations will
provide a wealth of new information and insight into galaxy evolution to
high-z. Finally, at the very earliest epoch of star and galaxy formation, warm
H may also provide a unique glimpse of molecular gas collapse at 7 z
12 in massive dark matter (DM) halos on their way to forming the very first
galaxies. Such measurements are beyond the reach of existing and planned
observatories.Comment: Submitted as a science White Paper to the Astronomy and Astrophysics
Astro 2020 Decadal Survey call issued by the National Academies of Sciences,
Engineering and Medicine (March 11 2019
Myxomatous mitral valve degeneration: biochemical aspects and physiopathological considerations
peer reviewedMitral valve is a complex structure which is submitted to repeated mechanical constraints. In clinical practice, an increasing incidence of mitral insufficiency resulting from myxomatous degeneration is observed. Since myxomatous degeneration is also observed in defined genetic diseases of connective tissues, we propose the hypothesis that idiopathic mitral insufficiency might result from a minor alteration of the interstitial valvular cells and/or their interactions with their support. After a brief review of the role of the extracellular matrix in the heart, some histopathological and biochemical aspects of myxomatous degeneration are presented. Our data and those of the literature will be summarized and a physiopathological hypothesis proposed for myxomatous mitral valve degeneration
Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results
We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the
Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the
Spitzer Space Telescope in order to survey the agents of a galaxy's evolution
(SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of
diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies
of dust processes in the ISM. SAGE's point source sensitivity enables a
complete census of newly formed stars with masses >3 solar masses that will
determine the current star formation rate in the LMC. SAGE's detection of
evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify
the rate at which evolved stars inject mass into the ISM of the LMC. The
observing strategy includes two epochs in 2005, separated by three months, that
both mitigate instrumental artifacts and constrain source variability. The SAGE
data are non-proprietary. The data processing includes IRAC and MIPS pipelines
and a database for mining the point source catalogs, which will be released to
the community in support of Spitzer proposal cycles 4 and 5. We present initial
results on the epoch 1 data with a special focus on the N79 and N83 region. The
SAGE epoch 1 point source catalog has ~4 million sources. The point source
counts are highest for the IRAC 3.6 microns band and decrease dramatically
towards longer wavelengths consistent with the fact that stars dominate the
point source catalogs and that the dusty objects, e.g. young stellar objects
and dusty evolved stars that detected at the longer wavelengths, are rare in
comparison. We outline a strategy for identifying foreground MW stars, that may
comprise as much as 18% of the source list, and background galaxies, that may
comprise ~12% of the source list.Comment: Accepted by the Astronomical Journa
Spitzer survey of the Large Magellanic Cloud, surveying the agents of a galaxy's evolution (SAGE). IV. Dust properties in the interstellar medium
The goal of this paper is to present the results of a preliminary analysis of the extended infrared (IR) emission by dust in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). We combine Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and Infrared Astronomical Satellite (IRAS) data and correlate the infrared emission with gas tracers of H I, CO, and Hα. We present a global analysis of the infrared emission as well as detailed modeling of the spectral energy distribution (SED) of a few selected regions. Extended emission by dust associated with the neutral, molecular, and diffuse ionized phases of the ISM is detected at all IR bands from 3.6 μm to 160 μm. The relative abundance of the various dust species appears quite similar to that in the Milky Way (MW) in all the regions we have modeled. We construct maps of the temperature of large dust grains. The temperature map shows variations in the range 12.1-34.7 K, with a systematic gradient from the inner to outer regions, tracing the general distribution of massive stars and individual H II regions as well as showing warmer dust in the stellar bar. This map is used to derive the far-infrared (FIR) optical depth of large dust grains. We find two main departures in the LMC with respect to expectations based on the MW: (1) excess mid-infrared (MIR) emission near 70 μm, referred to as the 70 μm excess, and (2) departures from linear correlation between the FIR optical depth and the gas column density, which we refer to as FIR excess emission. The 70 μm excess increases gradually from the MW to the LMC to the Small Magellanic Cloud (SMC), suggesting evolution with decreasing metallicity. The excess is associated with the neutral and diffuse ionized gas, with the strongest excess region located in a loop structure next to 30 Dor. We show that the 70 μm excess can be explained by a modification of the size distribution of very small grains with respect to that in the MW, and a corresponding mass increase of ≃13% of the total dust mass in selected regions. The most likely explanation is that the 70 μm excess is due to the production of large very small grains (VSG) through erosion of larger grains in the diffuse medium. This FIR excess could be due to intrinsic variations of the dust/gas ratio, which would then vary from 4.6 to 2.3 times lower than the MW values across the LMC, but X_(CO) values derived from the IR emission would then be about three times lower than those derived from the Virial analysis of the CO data. We also investigate the possibility that the FIR excess is associated with an additional gas component undetected in the available gas tracers. Assuming a constant dust abundance in all ISM phases, the additional gas component would have twice the known H I mass. We show that it is plausible that the FIR excess is due to cold atomic gas that is optically thick in the 21 cm line, while the contribution by a pure H_2 phase with no CO emission remains a possible explanation
The Balloon-Borne Large Aperture Submillimeter Telescope (BLAST) 2005: A 10 deg^2 Survey of Star Formation in Cygnus X
We present Cygnus X in a new multi-wavelength perspective based on an
unbiased BLAST survey at 250, 350, and 500 micron, combined with rich datasets
for this well-studied region. Our primary goal is to investigate the early
stages of high mass star formation. We have detected 184 compact sources in
various stages of evolution across all three BLAST bands. From their
well-constrained spectral energy distributions, we obtain the physical
properties mass, surface density, bolometric luminosity, and dust temperature.
Some of the bright sources reaching 40 K contain well-known compact H II
regions. We relate these to other sources at earlier stages of evolution via
the energetics as deduced from their position in the luminosity-mass (L-M)
diagram. The BLAST spectral coverage, near the peak of the spectral energy
distribution of the dust, reveals fainter sources too cool (~ 10 K) to be seen
by earlier shorter-wavelength surveys like IRAS. We detect thermal emission
from infrared dark clouds and investigate the phenomenon of cold ``starless
cores" more generally. Spitzer images of these cold sources often show stellar
nurseries, but these potential sites for massive star formation are ``starless"
in the sense that to date there is no massive protostar in a vigorous accretion
phase. We discuss evolution in the context of the L-M diagram. Theory raises
some interesting possibilities: some cold massive compact sources might never
form a cluster containing massive stars; and clusters with massive stars might
not have an identifiable compact cold massive precursor.Comment: 42 pages, 31 Figures, 6 table
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