7,897 research outputs found
Forming a Primordial Star in a Relic HII Region
There has been considerable theoretical debate over whether photoionization
and supernova feedback from the first Population III stars facilitate or
suppress the formation of the next generation of stars. We present results from
an Eulerian adaptive mesh refinement simulation demonstrating the formation of
a primordial star within a region ionized by an earlier nearby star. Despite
the higher temperatures of the ionized gas and its flow out of the dark matter
potential wells, this second star formed within 23 million years of its
neighbor's death. The enhanced electron fraction within the HII region
catalyzes rapid molecular hydrogen formation that leads to faster cooling in
the subsequent star forming halos than in the first halos. This "second
generation" primordial protostar has a much lower accretion rate because,
unlike the first protostar, it forms in a rotationally supported disk of
approx. 10-100 solar masses. This is primarily due to the much higher angular
momentum of the halo in which the second star forms. In contrast to previously
published scenarios, such configurations may allow binaries or multiple systems
of lower mass stars to form. These first high resolution calculations offer
insight into the impact of feedback upon subsequent populations of stars and
clearly demonstrate how primordial chemistry promotes the formation of
subsequent generations of stars even in the presence of the entropy injected by
the first stars into the IGM.Comment: 4 pages, 2 figures. Some revisions, including enhanced discussion of
angular momentum issues. Asrophysical Journal, accepte
The Formation of Population III Binaries from Cosmological Initial Conditions
Previous high resolution cosmological simulations predict the first stars to
appear in the early universe to be very massive and to form in isolation. Here
we discuss a cosmological simulation in which the central 50 solar mass clump
breaks up into two cores, having a mass ratio of two to one, with one fragment
collapsing to densities of 10^{-8} g/cc. The second fragment, at a distance of
800 astronomical units, is also optically thick to its own cooling radiation
from molecular hydrogen lines, but is still able to cool via collision-induced
emission. The two dense peaks will continue to accrete from the surrounding
cold gas reservoir over a period of 10^5 years and will likely form a binary
star system.Comment: Accepted by Science, first published online on July 9, 2009 in
Science Express. 16 pages, 4 figures, includes supporting online materia
Evidence for contact delocalization in atomic scale friction
We analyze an advanced two-spring model with an ultra-low effective tip mass
to predict nontrivial and physically rich 'fine structure' in the atomic
stick-slip motion in Friction Force Microscopy (FFM) experiments. We
demonstrate that this fine structure is present in recent, puzzling
experiments. This shows that the tip apex can be completely or partially
delocalized, thus shedding new light on what is measured in FFM and, possibly,
what can happen with the asperities that establish the contact between
macroscopic sliding bodies.Comment: 4 pages text and 3 figure
First Stars III Conference Summary
The understanding of the formation, life, and death of Population III stars,
as well as the impact that these objects had on later generations of structure
formation, is one of the foremost issues in modern cosmological research and
has been an active area of research during the past several years. We summarize
the results presented at "First Stars III," a conference sponsored by Los
Alamos National Laboratory, the Kavli Institute for Particle Astrophysics and
Cosmology, and the Joint Institute for Nuclear Astrophysics. This conference,
the third in a series, took place in July 2007 at the La Fonda Hotel in Santa
Fe, New Mexico, U.S.A.Comment: 11 pages, no figures; Conference summary for First Stars III, which
was held in Santa Fe, NM on July 15-20, 2007. To appear in "Proceedings of
First Stars III," Eds. Brian W. O'Shea, Alexander Heger & Tom Abe
Effects of a feeding strategy to increase intramuscular fat content of pork under the conditions of organic farming
In an ongoing study, the effect of the implementation of a specific feeding strategy using a high portion of home-grown grain legumes on the intramuscular fat (IMF) content of pork, is assessed under different conditions on organic farms in Germany and Austria. Preliminary results indicate that variation in the IMF content seems to be higher between farms than between treatments within each farm
Ultrasound-guided trans-rectal high-intensity focused ultrasound (HIFU) for advanced cervical cancer ablation is feasible: a case report.
High-intensity focused ultrasound (HIFU) is an ablative treatment undergoing assessment for the treatment of benign and malignant disease. We describe the first reported intracavitary HIFU ablation for recurrent, unresectable and symptomatic cervical cancer.A 38 year old woman receiving palliative chemotherapy for metastatic cervical adenocarcinoma was offered ablative treatment from an intracavitary trans-rectal HIFU device (Sonablate® 500). Pre-treatment symptoms included vaginal bleeding and discharge that were sufficient to impede her quality of life. No peri-procedural adverse events occurred. Symptoms resolved completely immediately post-procedure, reappeared at 7 days, increasing to pre-procedural levels by day 30.This first time experience of intracavitary cervical HIFU suggests that it is feasible for palliation of advanced cervical cancer, with no early evidence of unexpected toxicity. Ethical approval had also been granted for the use of per-vaginal access if appropriate. This route, alone or in combination with the rectal route, may provide increased accessibility in future patients with a redesigned device more suited to trans-vaginal ablations.Intracavitary HIFU is a potentially safe procedure for the treatment of cervical cancer and able to provide symptomatic improvement in the palliative setting
Direct multiscale coupling of a transport code to gyrokinetic turbulence codes
Direct coupling between a transport solver and local, nonlinear gyrokinetic
calculations using the multiscale gyrokinetic code TRINITY [M. Barnes, Ph.D.
thesis, arxiv:0901.2868] is described. The coupling of the microscopic and
macroscopic physics is done within the framework of multiscale gyrokinetic
theory, of which we present the assumptions and key results. An assumption of
scale separation in space and time allows for the simulation of turbulence in
small regions of the space-time grid, which are embedded in a coarse grid on
which the transport equations are implicitly evolved. This leads to a reduction
in computational expense of several orders of magnitude, making
first-principles simulations of the full fusion device volume over the
confinement time feasible on current computing resources. Numerical results
from TRINITY simulations are presented and compared with experimental data from
JET and ASDEX Upgrade plasmas.Comment: 12 pages, 13 figures, invited paper for 2009 APS-DPP meeting,
submitted to Phys. Plasma
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