678 research outputs found
Order statistics and heavy-tail distributions for planetary perturbations on Oort cloud comets
This paper tackles important aspects of comets dynamics from a statistical
point of view. Existing methodology uses numerical integration for computing
planetary perturbations for simulating such dynamics. This operation is highly
computational. It is reasonable to wonder whenever statistical simulation of
the perturbations can be much more easy to handle. The first step for answering
such a question is to provide a statistical study of these perturbations in
order to catch their main features. The statistical tools used are order
statistics and heavy tail distributions. The study carried out indicated a
general pattern exhibited by the perturbations around the orbits of the
important planet. These characteristics were validated through statistical
testing and a theoretical study based on Opik theory.Comment: 9 pages, 12 figures, submitted for publication in Astronomy and
Astrophysic
Characterization of Neofabraea actinidiae and N. brasiliensis as causal agents of apple bull's-eye rot in southern Brazil.
The causal agents of apple bull?s-eye rot in southern Brazil have recently been described as Neofabraea actinidiae and N. brasiliensis. Isolates of both species were evaluated for response of mycelial growth index (MGI) to different temperatures, enzyme production, mycelial growth inhibition and effective concentrations (EC 50 and EC 100 ) of the fungicides tri fl umizole, pyrimethanil and thiophanate methyl, as well as aggres- siveness on fruits of "Fuji " hybrid and " Pink Lady " . There was signi ficantly lower mycelium growth in N. brasiliensis compared with N. actinidiae at all temperatures tested. Neither species grew at 3 and 32°C. There were minor differences in production of enzymes in the two species, with all N. brasiliensis isolates showing no production of pectolyase at pH 7. The lowest EC 50 and EC 100 values were observed with thiophanate methyl. In general, " Fuji " fruits were more susceptible to Neofabraea infection and had larger lesions, while N. brasiliensis isolates showed greater aggressiveness on " Fuji " hybrid and " Pink lady " fruits compared with N. actinidiae
Genetic Admixture and Gallbladder Disease in Mexican Americans
Gallbladder disease is a common source of morbidity in the Mexican American population. Genetic heritage has been proposed as a possible contributor, but evidence for this is limited. Because gallbladder disease has been associated with Native American heritage, genetic admixture may serve as a useful proxy for genetic susceptibility to the disease in epidemiologic studies. The objective of our study was to examine thepossibility that gallbladder disease is associated with greater Native American admixture in Mexican Americans. This study used data from the Hispanic Health and Nutrition Examination Survey and was based on 1,145 Mexican Americans who underwent gallbladder ultrasonography and provided usable phenotypic information. We used the GM and KM immunoglobulin antigen system to generate estimates of admixture proportions and compared these for individuals with and without gallbladder disease. Overall, the proportionate genetic contributions from European, Native American, and African ancestries in our sample were 0.575, 0.390, and 0.035, respectively. Admixture proportions did not differ between cases and noncases: Estimates of Native American admixture for the two groups were 0.359 and 0.396, respectively, but confidence intervals for estimates overlapped. This study found no evidence for the hypothesis that greater Native American admixture proportion is associated with higher prevalence of gallbladder disease in Mexican Americans. Reasons for the finding that Native American admixture proportions did not differ between cases and noncases are discussed. Improving our understanding of the measurement, use, and limitations of genetic admixture may increase its usefulness as an epidemiologic tool as well as its potential for contributing to our understanding of disease distributions across populations
Multi-axis fields boost SABRE hyperpolarization via new strategies
The inherently low signal-to-noise ratio of NMR and MRI is now being
addressed by hyperpolarization methods. For example, iridium-based catalysts
that reversibly bind both parahydrogen and ligands in solution can
hyperpolarize protons (SABRE) or heteronuclei (X-SABRE) on a wide variety of
ligands, using a complex interplay of spin dynamics and chemical exchange
processes, with common signal enhancements between . This does not
approach obvious theoretical limits, and further enhancement would be valuable
in many applications (such as imaging mM concentration species in vivo). Most
SABRE/X-SABRE implementations require far lower fields () than
standard magnetic resonance (>1T), and this gives an additional degree of
freedom: the ability to fully modulate fields in three dimensions. However,
this has been underexplored because the standard simplifying theoretical
assumptions in magnetic resonance need to be revisited. Here we take a
different approach, an evolutionary strategy algorithm for numerical
optimization, Multi-Axis Computer-aided HEteronuclear Transfer Enhancement for
SABRE (MACHETE-SABRE). We find nonintuitive but highly efficient multi-axial
pulse sequences which experimentally can produce a 10-fold improvement in
polarization over continuous excitation. This approach optimizes polarization
differently than traditional methods, thus gaining extra efficiency
Modulation of LISA free-fall orbits due to the Earth-Moon system
We calculate the effect of the Earth-Moon (EM) system on the free-fall motion
of LISA test masses. We show that the periodic gravitational pulling of the EM
system induces a resonance with fundamental frequency 1 yr^-1 and a series of
periodic perturbations with frequencies equal to integer harmonics of the
synodic month (9.92 10^-7 Hz). We then evaluate the effects of these
perturbations (up to the 6th harmonics) on the relative motions between each
test masses couple, finding that they range between 3mm and 10pm for the 2nd
and 6th harmonic, respectively. If we take the LISA sensitivity curve, as
extrapolated down to 10^-6 Hz, we obtain that a few harmonics of the EM system
can be detected in the Doppler data collected by the LISA space mission. This
suggests that the EM system gravitational near field could provide an absolute
calibration for the LISA sensitivity at very low frequencies.Comment: 15 pages, 5 figure
On the Stability of the Satellites of Asteroid 87 Sylvia
he triple asteroidal system (87) Sylvia is composed of a 280-km primary and
two small moonlets named Romulus and Remus (Marchis et al 2005). Sylvia is
located in the main asteroid belt. The satellites are in nearly equatorial
circular orbits around the primary. In the present work we study the stability
of the satellites Romulus and Remus, in order to identify the effects and the
contribution of each perturber. The results from the 3-body problem,
Sylvia-Romulus-Remus, show no significant variation of their orbital elements.
However, the inclinations of the satellites present a long period evolution,
when the Sun is included in the system. Such amplitude is amplified when
Jupiter is included. An analysis of these results show that Romulus and Remus
are librating in a secular resonance and their longitude of the nodes are
locked to each other. The satellites get caught in an evection resonance with
Jupiter. However, the orbital evolutions of the satellites became completely
stable when the oblateness of Sylvia is included in the simulations.Comment: 11 pages, 8 figures and 1 tabl
Pancreatic cancer in type 1 and young-onset diabetes: systematic review and meta-analysis
We conducted a systematic review of the risk of pancreatic cancer in people with type I and young-onset diabetes. In three cohort and six case–control studies, the relative risk for pancreatic cancer in people with (vs without) diabetes was 2.00 (95% confidence interval 1.37–3.01) based on 39 cases with diabetes
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