468 research outputs found
Functional Maps Representation on Product Manifolds
We consider the tasks of representing, analyzing and manipulating maps
between shapes. We model maps as densities over the product manifold of the
input shapes; these densities can be treated as scalar functions and therefore
are manipulable using the language of signal processing on manifolds. Being a
manifold itself, the product space endows the set of maps with a geometry of
its own, which we exploit to define map operations in the spectral domain; we
also derive relationships with other existing representations (soft maps and
functional maps). To apply these ideas in practice, we discretize product
manifolds and their Laplace--Beltrami operators, and we introduce localized
spectral analysis of the product manifold as a novel tool for map processing.
Our framework applies to maps defined between and across 2D and 3D shapes
without requiring special adjustment, and it can be implemented efficiently
with simple operations on sparse matrices.Comment: Accepted to Computer Graphics Foru
Direct perturbation theory on the shift of Electron Spin Resonance
We formulate a direct and systematic perturbation theory on the shift of the
main paramagnetic peak in Electron Spin Resonance, and derive a general
expression up to second order. It is applied to one-dimensional XXZ and
transverse Ising models in the high field limit, to obtain explicit results
including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE
A Hot Gap Around Jupiter's Orbit in the Solar Nebula
The Sun was an order of magnitude more luminous during the first few hundred
thousand years of its existence, due in part to the gravitational energy
released by material accreting from the Solar nebula. If Jupiter was already
near its present mass, the planet's tides opened an optically-thin gap in the
nebula. We show using Monte Carlo radiative transfer calculations that sunlight
absorbed by the nebula and re-radiated into the gap raised temperatures well
above the sublimation threshold for water ice, with potentially drastic
consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter
in size were vaporized within a single orbit if the planet was near its present
location during this early epoch. Dust particles lost their ice mantles, and
planetesimals were partially to fully devolatilized, depending on their size.
Scenarios in which Jupiter formed promptly, such as those involving a
gravitational instability of the massive early nebula, must cope with the high
temperatures. Enriching Jupiter in the noble gases through delivery trapped in
clathrate hydrates will be more difficult, but might be achieved by either
forming the planet much further from the star, or capturing planetesimals at
later epochs. The hot gap resulting from an early origin for Jupiter also would
affect the surface compositions of any primordial Trojan asteroids.Comment: 25 pages, 10 figures. ApJ in press. Discussion of Jupiter's volatile
enrichment revised in sec. 4.
Reliability of the CARE rule and the HEART score to rule out an acute coronary syndrome in non-traumatic chest pain patients
In patients consulting in the Emergency Department for chest pain, a HEART score †3 has been shown to rule out an acute coronary syndrome (ACS) with a low risk of major adverse cardiac event (MACE) occurrence. A negative CARE rule (†1) that stands for the first four elements of the HEART score may have similar rule-out reliability without troponin assay requirement. We aim to prospectively assess the performance of the CARE rule and of the HEART score to predict MACE in a chest pain population. Prospective two-center non-interventional study. Patients admitted to the ED for non-traumatic chest pain were included, and followed-up at 6 weeks. The main study endpoint was the 6-week rate of MACE (myocardial infarction, coronary angioplasty, coronary bypass, and sudden unexplained death). 641 patients were included, of whom 9.5% presented a MACE at 6 weeks. The CARE rule was negative for 31.2% of patients, and none presented a MACE during follow-up [0, 95% confidence interval: (0.0â1.9)]. The HEART score was †3 for 63.0% of patients, and none presented a MACE during follow-up [0% (0.0â0.9)]. With an incidence below 2% in the negative group, the CARE rule seemed able to safely rule out a MACE without any biological test for one-third of patients with chest pain and the HEART score for another third with a single troponin assay
Large-scale, multidirectional larval connectivity among coral reef fish populations in the Great Barrier Reef Marine Park
Larval dispersal is the key process by which populations of most marine fishes and invertebrates are connected and replenished. Advances in larval tagging and genetics have enhanced our capacity to track larval dispersal, assess scales of population connectivity, and quantify larval exchange among no-take marine reserves and fished areas. Recent studies have found that reserves can be a significant source of recruits for populations up to 40 km away, but the scale and direction of larval connectivity across larger seascapes remain unknown. Here, we apply genetic parentage analysis to investigate larval dispersal patterns for two exploited coral reef groupers (Plectropomus maculatus and Plectropomus leopardus) within and among three clusters of reefs separated by 60-220 km within the Great Barrier Reef Marine Park, Australia. A total of 69 juvenile P. maculatus and 17 juvenile P. leopardus (representing 6% and 9% of the total juveniles sampled, respectively) were genetically assigned to parent individuals on reefs within the study area. We identified both short-distance larval dispersal within regions (200 m to 50 km) and long-distance, multidirectional dispersal of up to similar to 250 km among regions. Dispersal strength declined significantly with distance, with best-fit dispersal kernels estimating median dispersal distances of similar to 110 km for P. maculatus and similar to 190 km for P. leopardus. Larval exchange among reefs demonstrates that established reserves form a highly connected network and contribute larvae for the replenishment of fished reefs at multiple spatial scales. Our findings highlight the potential for long-distance dispersal in an important group of reef fishes, and provide further evidence that effectively protected reserves can yield recruitment and sustainability benefits for exploited fish populations
Electron Irradiation and Thermal Processing of Mixed-ices of Potential Relevance to Jupiter Trojan Asteroids
In this work we explore the chemistry that occurs during the irradiation of ice mixtures on planetary surfaces, with the goal of linking the presence of specific chemical compounds to their formation locations in the solar system and subsequent processing by later migration inward. We focus on the outer solar system and the chemical differences for ice mixtures inside and outside the stability line for H_2S. We perform a set of experiments to explore the hypothesis advanced by Wong & Brown that links the color bimodality in Jupiter's Trojans to the presence of H_2S in the surface of their precursors. Non-thermal (10 keV electron irradiation) and thermally driven chemistry of CH_3OHâNH_3âH_2O ("without H_2S") and H_2SâCH_3OHâNH_3âH_2O ("with H_2S") ices were examined. Mid-IR analyses of ice and mass spectrometry monitoring of the volatiles released during heating show a rich chemistry in both of the ice mixtures. The "with H_2S" mixture experiment shows a rapid consumption of H_2S molecules and production of OCS molecules after a few hours of irradiation. The heating of the irradiated "with H_2S" mixture to temperatures above 120 K leads to the appearance of new infrared bands that we provisionally assign to SO_2 and CS. We show that radiolysis products are stable under the temperature and irradiation conditions of Jupiter Trojan asteroids. This makes them suitable target molecules for potential future missions as well as telescope observations with a high signal-to-noise ratio. We also suggest the consideration of sulfur chemistry in the theoretical modeling aimed at understanding the chemical composition of Trojans and KOBs
Complex organosulfur molecules on comet 67P: Evidence from the ROSINA measurements and insights from laboratory simulations.
The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard the Rosetta mission revolutionized our understanding of cometary material composition. One of Rosetta's key findings is the complexity of the composition of comet 67P/Churyumov-Gerasimenko. Here, we used ROSINA data to analyze dust particles that were volatilized during a dust event in September 2016 and report the detection of large organosulfur species and an increase in the abundances of sulfurous species previously detected in the coma. Our data support the presence of complex sulfur-bearing organics on the surface of the comet. In addition, we conducted laboratory simulations that show that this material may have formed from chemical reactions that were initiated by the irradiation of mixed ices containing H2S. Our findings highlight the importance of sulfur chemistry in cometary and precometary materials and the possibility of characterizing organosulfur materials in other comets and small icy bodies using the James Webb Space Telescope
Preface
No AbstractPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38319/1/1687_ftp.pd
Electron Spin Resonance in S=1/2 antiferromagnetic chains
A systematic field-theory approach to Electron Spin Resonance (ESR) in the
quantum antiferromagnetic chain at low temperature (compared to the
exchange coupling ) is developed. In particular, effects of a transverse
staggered field and an exchange anisotropy (including a dipolar
interaction) on the ESR lineshape are discussed. In the lowest order
of perturbation theory, the linewidth is given as and
, respectively. In the case of a transverse staggered
field, the perturbative expansion diverges at lower temperature;
non-perturbative effects at very low temperature are discussed using exact
results on the sine-Gordon field theory. We also compare our field-theory
results with the predictions of Kubo-Tomita theory for the high-temperature
regime, and discuss the crossover between the two regimes. It is argued that a
naive application of the standard Kubo-Tomita theory to the
Dzyaloshinskii-Moriya interaction gives an incorrect result. A rigorous and
exact identity on the polarization dependence is derived for certain class of
anisotropy, and compared with the field-theory results.Comment: 53 pages in REVTEX, 7 figures in EPS included; revised version with
missing references and correction
- âŠ