3,093 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
Design and advancement status of the Beam Expander Testing X-ray facility (BEaTriX)
The BEaTriX (Beam Expander Testing X-ray facility) project is an X-ray
apparatus under construction at INAF/OAB to generate a broad (200 x 60 mm2),
uniform and low-divergent X-ray beam within a small lab (6 x 15 m2). BEaTriX
will consist of an X-ray source in the focus a grazing incidence paraboloidal
mirror to obtain a parallel beam, followed by a crystal monochromation system
and by an asymmetrically-cut diffracting crystal to perform the beam expansion
to the desired size. Once completed, BEaTriX will be used to directly perform
the quality control of focusing modules of large X-ray optics such as those for
the ATHENA X-ray observatory, based on either Silicon Pore Optics (baseline) or
Slumped Glass Optics (alternative), and will thereby enable a direct quality
control of angular resolution and effective area on a number of mirror modules
in a short time, in full X-ray illumination and without being affected by the
finite distance of the X-ray source. However, since the individual mirror
modules for ATHENA will have an optical quality of 3-4 arcsec HEW or better,
BEaTriX is required to produce a broad beam with divergence below 1-2 arcsec,
and sufficient flux to quickly characterize the PSF of the module without being
significantly affected by statistical uncertainties. Therefore, the optical
components of BEaTriX have to be selected and/or manufactured with excellent
optical properties in order to guarantee the final performance of the system.
In this paper we report the final design of the facility and a detailed
performance simulation.Comment: Accepted paper, pre-print version. The finally published manuscript
can be downloaded from http://dx.doi.org/10.1117/12.223895
Characterization of a New Molecular Marker for Investigating Skate Population Genetics: Analysis of Three Mediterranean Skate Species (genus<i>Raja</i>) of Commercial Interest as a Test Case
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Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study
Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong
improvement both in sensitivity and angular resolution compared to all
instruments that have operated so far above 10 keV. The superb hard X-ray
imaging capability will be guaranteed by a mirror module of 100 electroformed
Nickel shells with a multilayer reflecting coating. Here we will describe the
technogical development and solutions adopted for the fabrication of the mirror
module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec
from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A,
terminated at the end of 2008, we have developed three engineering models with
two, two and three shells, respectively. The most critical aspects in the
development of the Simbol-X mirrors are i) the production of the 100 mandrels
with very good surface quality within the timeline of the mission; ii) the
replication of shells that must be very thin (a factor of 2 thinner than those
of XMM-Newton) and still have very good image quality up to 80 keV; iii) the
development of an integration process that allows us to integrate these very
thin mirrors maintaining their intrinsic good image quality. The Phase A study
has shown that we can fabricate the mandrels with the needed quality and that
we have developed a valid integration process. The shells that we have produced
so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and
effective area. However, we still need to make some improvements to reach the
requirements. We will briefly present these results and discuss the possible
improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International
Simbol-X Symposium", Paris, 2-5 december, 200
Incidence and predictors of heart failure hospitalization and death in permanent pacemaker patients: a single-centre experience over medium-term follow-up
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Inclusive social norms and nationals' positive intergroup orientations toward refugees: The moderating role of initial prejudice and intergroup contact
Research on the interplay between inclusive norms and intergroup contact on improving intergroup orientations has yielded conflicting results, suggesting either that an experience of personal contact is necessary to have a positive effect of inclusive norms or that such personal experience is not always necessary. To clarify this issue, across four studies ( N = 835), we investigated the influence of inclusive norms on positive intergroup orientations as a function of personal experiences of intergroup contact. Study 1 demonstrated that inclusive norms are more strongly correlated with experiences of personal contact with outgroups with whom opportunities of contact are more (i.e., immigrants) than less (i.e., refugees) frequent. Study 2 provided experimental evidence for this finding showing that inclusive norms increase prejudiced nationals’ willingness to engage in future contact with immigrants but not with refugees, suggesting that conformity to inclusive norms depends on varying contact opportunities with the outgroups. Studies 3 and 4 confirmed that prejudiced nationals conformed to inclusive norms specifically when experienced positive contact with a refugee (experimentally induced with the imagined contact paradigm), compared with no contact (Study 3) or negative contact (Study 4). We discuss the implications of these findings for research on intergroup contact, social influence, and intergroup relations.</p
Longitudinal tear protein changes correlate with ocular chronic gvhd development in allogeneic hematopoietic stem cell transplant patients
Ocular graft-versus-host disease (oGVHD) is a manifestation of chronic GVHD, frequently occurring in patients after allogeneic hematopoietic stem cell transplant (HSCT). We analyzed tear protein changes before and after allogeneic HSCT, and correlated their levels with the oGVHD development. This retrospective study included 102 patients, and data were recorded before the conditioning treatment, and after 3 to 6 months postoperatively. Tear protein analysis was performed with the Agilent-2100 Bioanalyzer on individual tears sampled by aspiration. Total protein (TP), Lysozyme-C (LYS-C), Lactoferrin (LACTO), Lipocalin-1 (LIPOC-1), Transferrin (TRANSF), Albumin (ALB), and Zinc-alpha-2-glycoprotein (ZAG-2) levels were retrieved and statistically analyzed. Following HSCT forty-three patients developed oGVHD. TP, LACTO, LYS-C, and ZAG-2 levels significantly decreased post-HSCT as compared to pre HSCT levels. In univariate analysis, TP, LACTO, and ZAG-2 decrease was associated with an increased development of oGVHD (OR = 4.49; 95% CI, 1.9 to 10.5; p < 0.001; OR = 3.08; 95% CI 1.3 to 7.6; p = 0.01; OR = 11.1; 95% CI 2.7 to 46.6; p < 0.001, respectively). TRANSF post-HSCT levels significantly increased (OR 15.7; 95% CI, 4.1 to 52.2; p = 0.0001). No pre-post-HSCT changes were shown in ALB and LIPOC-1 levels. Data suggest that TP content, LACTO, TRANSF, and ZAG-2 pre-post changes might be significant predictors of oGVHD development
The evolution of the orbit distance in the double averaged restricted 3-body problem with crossing singularities
We study the long term evolution of the distance between two Keplerian
confocal trajectories in the framework of the averaged restricted 3-body
problem. The bodies may represent the Sun, a solar system planet and an
asteroid. The secular evolution of the orbital elements of the asteroid is
computed by averaging the equations of motion over the mean anomalies of the
asteroid and the planet. When an orbit crossing with the planet occurs the
averaged equations become singular. However, it is possible to define piecewise
differentiable solutions by extending the averaged vector field beyond the
singularity from both sides of the orbit crossing set. In this paper we improve
the previous results, concerning in particular the singularity extraction
technique, and show that the extended vector fields are Lipschitz-continuous.
Moreover, we consider the distance between the Keplerian trajectories of the
small body and of the planet. Apart from exceptional cases, we can select a
sign for this distance so that it becomes an analytic map of the orbital
elements near to crossing configurations. We prove that the evolution of the
'signed' distance along the averaged vector field is more regular than that of
the elements in a neighborhood of crossing times. A comparison between averaged
and non-averaged evolutions and an application of these results are shown using
orbits of near-Earth asteroids.Comment: 29 pages, 8 figure
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