2,043 research outputs found
The LHeC Detector
The Large Hadron Electron Collider (LHeC) is a proposed upgrade to the LHC,
to provide high energy, high luminosity electron-proton collisions to run
concurrently with Phase 2 of the LHC. The baseline design of a detector for the
LHeC is described, driven by the requirements from the projected physics
programme and including some preliminary results from first simulations.Comment: 6 pages, proceedings of parallel talk at Deep Inelastic Scattering
2013, 22-26 April 2013, Marseilles, Franc
A new detector for deep inelastic physics
The Large Hadron Electron Collider (LHeC) is a proposed upgrade to the LHC,
to provide high energy, high luminosity electron-proton and electron-ion
collisions to run concurrently with Phase 2 of the LHC. The key elements of the
LHeC detector and the requirements from the physics programme are outlined,
followed by a brief description of the baseline LHeC detector design.Comment: 3 pages, proceedings of poster at HEP-EPS 2013, July 18 - 24 2013,
Stockholm, Swede
Tribrid Inflation in Supergravity
We propose a novel class of F-term hybrid inflation models in supergravity
(SUGRA) where the -problem is resolved using either a Heisenberg symmetry
or a shift symmetry of the Kaehler potential. In addition to the inflaton and
the waterfall field, this class (referred to as tribrid inflation) contains a
third 'driving' field which contributes the large vacuum energy during
inflation by its F-term. In contrast to the ''standard'' hybrid scenario, it
has several attractive features due to the property of vanishing inflationary
superpotential (W_inf=0) during inflation. While the symmetries of the Kaehler
potential ensure a flat inflaton potential at tree-level, quantum corrections
induced by symmetry breaking terms in the superpotential generate a slope of
the potential and lead to a spectral tilt consistent with recent WMAP
observations.Comment: To appear in the proceedings of SUSY09; 5 page
r-Java 2.0: the nuclear physics
[Aims:] We present r-Java 2.0, a nucleosynthesis code for open use that
performs r-process calculations as well as a suite of other analysis tools.
[Methods:] Equipped with a straightforward graphical user interface, r-Java 2.0
is capable of; simulating nuclear statistical equilibrium (NSE), calculating
r-process abundances for a wide range of input parameters and astrophysical
environments, computing the mass fragmentation from neutron-induced fission as
well as the study of individual nucleosynthesis processes. [Results:] In this
paper we discuss enhancements made to this version of r-Java, paramount of
which is the ability to solve the full reaction network. The sophisticated
fission methodology incorporated into r-Java 2.0 which includes three fission
channels (beta-delayed, neutron-induced and spontaneous fission) as well as
computation of the mass fragmentation is compared to the upper limit on mass
fission approximation. The effects of including beta-delayed neutron emission
on r-process yield is studied. The role of coulomb interactions in NSE
abundances is shown to be significant, supporting previous findings. A
comparative analysis was undertaken during the development of r-Java 2.0
whereby we reproduced the results found in literature from three other
r-process codes. This code is capable of simulating the physical environment
of; the high-entropy wind around a proto-neutron star, the ejecta from a
neutron star merger or the relativistic ejecta from a quark nova. As well the
users of r-Java 2.0 are given the freedom to define a custom environment. This
software provides an even platform for comparison of different proposed
r-process sites and is available for download from the website of the
Quark-Nova Project: http://quarknova.ucalgary.ca/Comment: 26 pages, 18 figures, 1 tabl
Bioinformatics
Motivation: Chromatin immunoprecipitation (ChIP) is a powerful experimental approach to identify in vivo binding sites of sequence-specific transcription factors (TFs). These experiments are designed to specifically enrich DNA fragments that are bound to the TF. Tiling arrays have become more and more popular for the identification of these DNA fragments. However, many studies showed that only a fraction of the identified DNA fragments contains bona fide binding sites for the TF, suggesting that indirect binding mechanisms play a very important role. We explored the possibility that the lack of binding sites can also be explained by problems in identifying ChIP-enriched DNA fragments from the measured intensities. Results: We derived a physical model that explains some (but not all) variation of the measured probe intensities of Affymetrix tilling arrays. We used the physical model to estimate the probe-specific behavior and corrected for it. Subsequently, we developed a method to identify ChIP-enriched DNA fragments. We termed it physical model for tiling array analysis (PMT). We applied PMT to the data of ChIP-chip experiments interrogating chromosome 21 and 22 of the human genome for binding of the TFs MYC, SP1 and P53. Almost all regions recovered by PMT showed evidence for sequence-specific binding of the TFs
Large-scale Inference of Competing Endogenous {RNA} Networks with Sparse Partial Correlation
The bacterial composition within the Sarracenia purpurea model system: local scale differences and the relationship with the other members of the food web
The leaves of the carnivorous pitcher plant, Sarracenia purpurea, contain a microscopic aquatic food web that is considered a model system in ecological research. The species identity of the intermediate and top trophic level of this food web, as well the detritivore midge, are highly similar across the native geographic range of S. purpurea and, in some cases, appear to have co-evolved with the plant. However, until recently, the identity, geographic variation, and diversity of the bacteria in the bottom trophic level of this food web have remained largely unknown. This study investigated bacterial community composition inside the leaves of S. purpurea to address: 1) variation in bacterial communities at the beginning of succession at the local scale in different areas of the plant’s native geographic range (southern and mid-regional sites) and 2) the impacts of bacterial consumers and other members of the aquatic food web (i.e., insects) on bacterial community structure. Communities from six leaves (one leaf per plant) from New York and Florida study sites were analyzed using 16S ribosomal RNA gene cloning. Each pitcher within each site had a distinct community; however, there was more overlap in bacterial composition within each site than when communities were compared across sites. In contrast, the identity of protozoans and metazoans in this community were similar in species identity both within a site and between the two sites, but abundances differed. Our results indicate that, at least during the beginning of succession, there is no strong selection for bacterial taxa and that there is no core group of bacteria required by the plant to start the decomposition of trapped insects. Co-evolution between the plant and bacteria appears to not have occurred as it has for other members of this community
Finite element simulation of sintering of metal-bonded grinding wheels
The grinding wheel properties porosity, particle distribution and the grain holding force influence the surface roughness of the machined workpiece and the performance of the grinding process. These properties of a grinding wheel are in turn defined during tool production. However, the adaptation of the properties of a grinding wheel to the specific grinding task is currently based on empirical knowledge and experience. Understanding the interdependencies from the initial manufacturing to the final grinding results is the key to achieve the target-oriented generation of the grinding wheel properties for the grinding task at hand. With regard to the large number of powder particles for the manufacturing of metal-bonded grinding wheels, an analytical investigation of the powder metallurgical processes is not suitable. Numerical simulations offer a cost and time saving alternative to provide information on the sintering behavior and gain knowledge on the acting mechanism. In this article the sintering of a metal-bonded diamond grinding wheel is modelled and the obtained results are connected to material properties of the resulting grinding layer
Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream
The X-ray binary system GX301-2 consists of a neutron star in an eccentric
orbit accreting from the massive early-type star WRAY 977. It has previously
been shown that the X-ray orbital light curve is consistent with existence of a
gas stream flowing out from Wray 977 in addition to its strong stellar wind.
Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer (RXTE)/
All-Sky-Monitor (ASM) and pointed observations by the RXTE/ Proportional
Counter Array (PCA) over the past decade are analyzed. We analyze both the flux
and column density dependence on orbital phase. The wind and stream dynamics
are calculated for various system inclinations, companion rotation rates and
wind velocities, as well as parametrized by the stream width and density. These
calculations are used as inputs to determine both the expected accretion
luminosity and the column density along the line-of-sight to the neutron star.
The model luminosity and column density are compared to observed flux and
column density vs. orbital phase, to constrain the properties of the stellar
wind and the gas stream. We find that the change between bright and medium
intensity levels is primarily due to decreased mass loss in the stellar wind,
but the change between medium and dim intensity levels is primarily due to
decreased stream density. The mass-loss rate in the stream exceeds that in the
stellar wind by a factor of 2.5. The quality of the model fits is significantly
better for lower inclinations, favoring a mass for WRAY 977 of 53 to 62 Msun.Comment: 19 pages, 6 figure
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