489 research outputs found
A single sub-km Kuiper Belt object from a stellar Occultation in archival data
The Kuiper belt is a remnant of the primordial Solar System. Measurements of
its size distribution constrain its accretion and collisional history, and the
importance of material strength of Kuiper belt objects (KBOs). Small, sub-km
sized, KBOs elude direct detection, but the signature of their occultations of
background stars should be detectable. Observations at both optical and X-ray
wavelengths claim to have detected such occultations, but their implied KBO
abundances are inconsistent with each other and far exceed theoretical
expectations. Here, we report an analysis of archival data that reveals an
occultation by a body with a 500 m radius at a distance of 45 AU. The
probability of this event to occur due to random statistical fluctuations
within our data set is about 2%. Our survey yields a surface density of KBOs
with radii larger than 250 m of 2.1^{+4.8}_{-1.7} x 10^7 deg^{-2}, ruling out
inferred surface densities from previous claimed detections by more than 5
sigma. The fact that we detected only one event, firmly shows a deficit of
sub-km sized KBOs compared to a population extrapolated from objects with r>50
km. This implies that sub-km sized KBOs are undergoing collisional erosion,
just like debris disks observed around other stars.Comment: To appear in Nature on December 17, 2009. Under press embargo until
1800 hours London time on 16 December. 19 pages; 7 figure
The stone pine, Pinus pinea L., a new highly rewarding host for the invasive Leptoglossus occidentalis
Research ArticleThe invasive seed bug Leptoglossus occidentalis, a species native to Western North America, is of major
concern for the producers of stone pine seeds in the Mediterranean countries. The large size of these edible
seeds and their nutritive content may represent a pull factor for the seed bug. Cone and seed traits of three
main Mediterranean pine species: P. pinea, P. pinaster, and P. halepensis, were evaluated. Preference trials
with cone-bearing branches, individual cones and seeds were conducted to test host preference among the
three host species.
Considering the kernel size, stone pine seeds provide 4 to 13 times more reward than P. pinaster and P. halepensis
seeds, respectively, but also needed a greater effort to be reached as measured by coat thickness. Still,
the benefit/cost ratio was higher on P. pinea. Individual seeds and cones of P. pinea were 2 to 3 times more
consumed than those of the two other pine species. However, branch preference trials did not reveal any
difference in bug visits. Moreover, adults manifested strong group behaviour on branches, frequently dissociating
into two persisting groups. The implications of these results for P. pinea producing areas are discussedinfo:eu-repo/semantics/publishedVersio
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
Deep Learning for Brain Tumor Segmentation in Radiosurgery: Prospective Clinical Evaluation
Stereotactic radiosurgery is a minimally-invasive treatment option for a
large number of patients with intracranial tumors. As part of the therapy
treatment, accurate delineation of brain tumors is of great importance.
However, slice-by-slice manual segmentation on T1c MRI could be time-consuming
(especially for multiple metastases) and subjective. In our work, we compared
several deep convolutional networks architectures and training procedures and
evaluated the best model in a radiation therapy department for three types of
brain tumors: meningiomas, schwannomas and multiple brain metastases. The
developed semiautomatic segmentation system accelerates the contouring process
by 2.2 times on average and increases inter-rater agreement from 92.0% to
96.5%
Coronary artery bypass surgery in high-risk patients
BACKGROUND: In high-risk coronary artery bypass patients; off-pump versus on-pump surgical strategies still remain a matter of debate, regarding which method results in a lower incidence of perioperative mortality and morbidity. We describe our experience in the treatment of high-risk coronary artery patients and compare patients assigned to on-pump and off-pump surgery. METHODS: From March 2002 to July 2004, 86 patients with EuroSCOREs > 5 underwent myocardial revascularization with or without cardiopulmonary bypass. Patients were assigned to off-pump surgery (40) or on-pump surgery (46) based on coronary anatomy coupled with the likelihood of achieving complete revascularization. RESULTS: Those patients undergoing off-pump surgery had significantly poorer left ventricular function than those undergoing on-pump surgery (28.6 ± 5.8% vs. 40.5 ± 7.4%, respectively, p < 0.05) and also had higher Euroscore values (7.26 ± 1.4 vs. 12.1 ± 1.8, respectively, p < 0.05). Differences between the two groups were nonsignificant with regard to number of grafts per patient, mean duration of surgery, anesthesia and operating room time, length of stay intensive care unit (ICU) and rate of postoperative atrial fibrillation CONCLUSION: Utilization of off-pump coronary artery bypass graft (CABG) does not confer significant clinical advantages in all high-risk patients. This review suggest that off-pump coronary revascularization may represent an alternative approach for treatment of patients with Euroscore ℠10 and left ventricular function †30%
State transition and flaring activity of IGR J17464-3213/H1743-322 with SPI/INTEGRAL telescope
IGR J17464-3213, already known as the HEAO-1 transient source H1743-322, has
been detected during a state transition by the SPI/INTEGRAL telescope. We
describe the spectral evolution and flaring activity of IGR
J17464-3213/H1743-322 from 2003 March 21 to 2003 April 22. During the first
part, the source followed a continuous spectral softening, with the peak of the
spectral energy distribution shifting from 100 keV down to a few keV. However
the thermal disk and the hard X-ray components had a similar intensity,
indicating that the source was in an intermediate state throughout our
observations and evolving toward the soft state. In the second part of our
observations, the ASM/RXTE and SPI/INTEGRAL light curve showed a strong flaring
activity. Two flare events lasting about 1 day each have been detected with SPI
and are probably due to instabilities in the accretion disk associated with the
state transition. During these flares, the low (1.5-12 keV) and high (20-200
keV) energy fluxes monitored with ASM/RXTE and SPI/INTEGRAL, are correlated and
the spectral shape (above 20 keV) remains unchanged while the luminosity
increases by a factor greater than 2.Comment: 26 pages, 7 figures, accepted for publication in Astrophysical
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