20,711 research outputs found
Higher su(N) tensor products
We extend our recent results on ordinary su(N) tensor product multiplicities
to higher su(N) tensor products. Particular emphasis is put on four-point
couplings where the tensor product of four highest weight modules is
considered. The number of times the singlet occurs in the decomposition is the
associated multiplicity. In this framework, ordinary tensor products correspond
to three-point couplings. As in that case, the four-point multiplicity may be
expressed explicitly as a multiple sum measuring the discretised volume of a
convex polytope. This description extends to higher-point couplings as well. We
also address the problem of determining when a higher-point coupling exists,
i.e., when the associated multiplicity is non-vanishing. The solution is a set
of inequalities in the Dynkin labels.Comment: 17 pages, LaTe
Transplacental transmission of field and rescued strains of BTV-2 and BTV-8 in experimentally infected sheep
Transplacental transmission of bluetongue virus has been shown previously for the North European strain of serotype 8 (BTV-8) and for tissue culture or chicken egg-adapted vaccine strains but not for field strains of other serotypes. In this study, pregnant ewes (6 per group) were inoculated with either field or rescued strains of BTV-2 and BTV-8 in order to determine the ability of these viruses to cross the placental barrier. The field BTV-2 and BTV-8 strains was passaged once in Culicoides KC cells and once in mammalian cells. All virus inoculated sheep became infected and seroconverted against the different BTV strains used in this study. BTV RNA was detectable in the blood of all but two ewes for over 28Â days but infectious virus could only be detected in the blood for a much shorter period. Interestingly, transplacental transmission of BTV-2 (both field and rescued strains) was demonstrated at high efficiency (6 out of 13 lambs born to BTV-2 infected ewes) while only 1 lamb of 12 born to BTV-8 infected ewes showed evidence of in utero infection. In addition, evidence for horizontal transmission of BTV-2 between ewes was observed. As expected, the parental BTV-2 and BTV-8 viruses and the viruses rescued by reverse genetics showed very similar properties to each other. This study showed, for the first time, that transplacental transmission of BTV-2, which had been minimally passaged in cell culture, can occur; hence such transmission might be more frequent than previously thought
Formulating MEDLINE queries for article retrieval based on PubMed exemplars
Bibliographic search engines allow endless possibilities for building queries based on specific words or phrases in article titles and abstracts, indexing terms, and other attributes. Unfortunately, deciding which attributes to use in a methodologically sound query is a non-trivial process. In this paper, we describe a system to help with this task, given an example set of PubMed articles to retrieve and a corresponding set of articles to exclude. The system provides the users with unigram and bigram features from the title, abstract, MeSH terms, and MeSH qualifier terms in decreasing order of precision, given a recall threshold. From this information and their knowledge of the domain, users can formulate a query and evaluate its performance. We apply the system to the task of distinguishing original research articles of functional magnetic resonance imaging (fMRI) of sensorimotor function from fMRI studies of higher cognitive functions
On the Putative Detection of z>0 X-ray Absorption Features in the Spectrum of Markarian 421
In a series of papers, Nicastro et al. have reported the detection of z>0
OVII absorption features in the spectrum of Mrk421 obtained with the Chandra
Low Energy Transmission Grating Spectrometer (LETGS). We evaluate this result
in the context of a high quality spectrum of the same source obtained with the
Reflection Grating Spectrometer (RGS) on XMM-Newton. The data comprise over
955ks of usable exposure time and more than 26000 counts per 50 milliAngstrom
at 21.6 Angstroms. We concentrate on the spectrally clean region (21.3 < lambda
< 22.5 Angstroms) where sharp features due to the astrophysically abundant OVII
may reveal an intervening, warm--hot intergalactic medium (WHIM). We do not
confirm detection of any of the intervening systems claimed to date. Rather, we
detect only three unsurprising, astrophysically expected features down to the
Log(N_i)~14.6 (3 sigma) sensitivity level. Each of the two purported WHIM
features is rejected with a statistical confidence that exceeds that reported
for its initial detection. While we can not rule out the existence of fainter,
WHIM related features in these spectra, we suggest that previous discovery
claims were premature. A more recent paper by Williams et al. claims to have
demonstrated that the RGS data we analyze here do not have the resolution or
statistical quality required to confirm or deny the LETGS detections. We show
that our careful analysis resolves the issues encountered by Williams et al.
and recovers the full resolution and statistical quality of the RGS data. We
highlight the differences between our analysis and those published by Williams
et al. as this may explain our disparate conclusions.Comment: 19 pages/7 figures/4 tables. 060424 submitted to ApJ 060522
re-submitted following ApJ reques
X-Ray Emission from the Warm Hot Intergalactic Medium
The number of detected baryons in the Universe at z<0.5 is much smaller than
predicted by standard big bang nucleosynthesis and by the detailed observation
of the Lyman alpha forest at red-shift z=2. Hydrodynamical simulations indicate
that a large fraction of the baryons today is expected to be in a ``warm-hot''
(10^5-10^7K) filamentary gas, distributed in the intergalactic medium. This
gas, if it exists, should be observable only in the soft X-ray and UV bands.
Using the predictions of a particular hydrodynamic model, we simulated the
expected X-ray flux as a function of energy in the 0.1-2 keV band due to the
Warm-Hot Intergalactic Medium (WHIM), and compared it with the flux from local
and high red-shift diffuse components. Our results show that as much as 20% of
the total diffuse X-ray background (DXB) in the energy range 0.37-0.925keV
could be due to X-ray flux from the WHIM, 70% of which comes from filaments at
redshift z between 0.1 and 0.6. Simulations done using a FOV of 3', comparable
with that of Suzaku and Constellation-X, show that in more than 20% of the
observations we expect the WHIM flux to contribute to more than 20% of the DXB.
These simulations also show that in about 10% of all the observations a single
bright filament in the FOV accounts, alone, for more than 20% of the DXB flux.
Red-shifted oxygen lines should be clearly visible in these observations.Comment: 19 pages, 6 figure
Leucine supplementation differentially enhances pancreatic cancer growth in lean and overweight mice
Kristyn A Liu1†, Laura M Lashinger1†, Audrey J Rasmussen1†and Stephen D Hursting12*
Author Affiliations
1 Department of Nutritional Sciences, University of Texas at Austin, Austin, TX 78723, USA
2 Department of Molecular Carcinogenesis, University of Texas M.D. Anderson Cancer Center, 1808 Park Road 1c, Smithville, TX 78957, USABackground: The risk of pancreatic cancer, the 4th deadliest cancer for both men and women in the United States, is increased by obesity. Calorie restriction (CR) is a well-known dietary regimen that prevents or reverses obesity and suppresses tumorigenesis in a variety of animal models, at least in part via inhibition of mammalian target of rapamycin (mTOR) signaling. Branched-chain amino acids (BCAA), especially leucine, activate mTOR and enhance growth and proliferation of myocytes and epithelial cells, which is why leucine is a popular supplement among athletes. Leucine is also increasingly being used as a treatment for pancreatic cancer cachexia, but the effects of leucine supplementation on pancreatic tumor growth have not been elucidated. Results: Supplementation with leucine increased pancreatic tumor growth in both lean (104 ± 17 mm3 versus 46 ± 13 mm3; P <0.05) and overweight (367 ± 45 mm3 versus 230 ± 39 mm3; P <0.01) mice, but tumor enhancement was associated with different biological outcomes depending on the diet. In the lean mice, leucine increased phosphorylation of mTOR and downstream effector S6 ribosomal protein, but in the overweight mice, leucine reduced glucose clearance and thus increased the amount of circulating glucose available to the tumor. Conclusion: These findings show that leucine supplementation enhances tumor growth in both lean and overweight mice through diet-dependent effects in a murine model of pancreatic cancer, suggesting caution against the clinical use of leucine supplementation for the purposes of skeletal muscle enhancement in cachectic patients.Nutritional Science
Guidelines for physical weed control research: flame weeding, weed harrowing and intra-row cultivation
A prerequisite for good research is the use of appropriate methodology. In order to aggregate sound research methodology, this paper presents some tentative guidelines for physical weed control research in general, and flame weeding, weed harrowing and intra-row cultivation in particular. Issues include the adjustment and use of mechanical weeders and other equipment, the recording of impact factors that affect weeding performance, methods to assess effectiveness, the layout of treatment plots, and the conceptual models underlying the experimental designs (e.g. factorial comparison, dose response).
First of all, the research aims need to be clearly defined, an appropriate experimental design produced and statistical methods chosen accordingly. Suggestions on how to do this are given. For assessments, quantitative measures would be ideal, but as they require more resources, visual classification may in some cases be more feasible. The timing of assessment affects the results and their interpretation.
When describing the weeds and crops, one should list the crops and the most abundantly present weed species involved, giving their density and growth stages at the time of treatment. The location of the experimental field, soil type, soil moisture and amount of fertilization should be given, as well as weather conditions at the time of treatment.
The researcher should describe the weed control equipment and adjustments accurately, preferably according to the prevailing practice within the discipline. Things to record are e.g. gas pressure, burner properties, burner cover dimensions and LPG consumption in flame weeding; speed, angle of tines, number of passes and direction in weed harrowing.
The authors hope this paper will increase comparability among experiments, help less experienced scientists to prevent mistakes and essential omissions, and foster the advance of knowledge on non-chemical weed management
Magnetoinductive breathers in magnetic metamaterials
The existence and stability of discrete breathers (DBs) in one-dimensional
and two-dimensional magnetic metamaterials (MMs), which consist of periodic
arrangem ents (arrays) of split-ring resonators (SRRs), is investigated
numerically. We consider different configurations of the SRR arrays, which are
related to the relative orientation of the SRRs in the MM, both in one and two
spatial dimensions. In the latter case we also consider anisotropic MMs. Using
standard numerical methods we construct several types of linearly stable
breather excitations both in Hamiltonian and dissipative MMs (dissipative
breathers). The study of stability in both cases is performed using standard
Floquet analysi s. In both cases we found that the increase of dimensionality
from one to two spatial dimensions does not destroy the DBs, which may also
exist in the case of moderate anisotropy (in two dimensions). In dissipative
MMs, the dynamics is governed by a power balance between the mainly Ohmic
dissipation and driving by an alternating magnetic field. In that case it is
demonstrated that DB excitation locally alters the magnetic response of MMs
from paramagnetic to diamagnetic. Moreover, when the frequency of the applied
field approaches the SRR resonance frequency, the magnetic response of the MM
in the region of the DB excitation may even become negative (extreme
diamagnetic).Comment: 12 pages 15 figure
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