6,422 research outputs found
A Search for Environmental Effects on Type Ia Supernovae
We use integrated colors and B and V absolute magnitudes of Type Ia supernova
(SN) host galaxies in order to search for environmental effects on the SN
optical properties. With the new sample of 44 SNe we confirm the conclusion by
Hamuy et al. (1996a) that bright events occur preferentially in young stellar
environments. We find also that the brightest SNe occur in the least luminous
galaxies, a possible indication that metal-poorer neighbourhoods produce the
more luminous events. The interpretation of these results is made difficult,
however, due to the fact that galaxies with younger stellar populations are
also lower in luminosity. In an attempt to remove this ambiguity we use models
for the line strengths in the absorption spectrum of five early-type galaxies,
in order to estimate metallicities and ages of the SN host galaxies. With the
addition of abundance estimates from nebular analysis of the emission spectra
of three spiral galaxies, we find possible further evidence that luminous SNe
are produced in metal-poor neighborhoods. Further spectroscopic observations of
the SN host galaxies will be necessary to test these results and assist in
disentangling the age/metallicity effects on Type Ia SNe.Comment: 14 pages, 5 figures, to appear in the September 2000 issue of The
Astronomical Journa
Lower Spectral Branches of a Particle Coupled to a Bose Field
The structure of the lower part (i.e. -away below the two-boson
threshold) spectrum of Fr\"ohlich's polaron Hamiltonian in the weak coupling
regime is obtained in spatial dimension . It contains a single polaron
branch defined for total momentum , where is a bounded domain, and, for any , a
manifold of polaron + one-boson states with boson momentum in a bounded
domain depending on . The polaron becomes unstable and dissolves into the
one boson manifold at the boundary of . The dispersion laws and
generalized eigenfunctions are calculated
ArgR is an essential local transcriptional regulator of the arcABC-operon in Streptococcus suis and crucial for biological fitness in acidic environment
Streptococcus suis is one of the most important pathogens in pigs and can also cause severe infections in humans. Despite its clinical relevance very little is known about the factors contributing to its virulence. Recently, we identified a new putative virulence factor in Streptococcus suis, the arginine deiminase system (ADS), an arginine catabolic enzyme system encoded by the arcABC-operon, which enables Streptococcus suis to survive in acidic environment. In this study, we focused on ArgR, an ADS associated regulator belonging to the ArgR/AhrC arginine repressor family. Using an argR knock-out strain we could show that ArgR is essential for arcABC-operon expression and necessary for the biological fitness of Streptococcus suis. By cDNA expression microarray analyses and quantitative real time RT-PCR we found that the arcABC-operon is the only gene cluster regulated by ArgR, which is in contrast to many other bacteria. Reporter gene analysis with gfp under the control of the arcABC promoter demonstrated that ArgR is able to activate the arcABC promoter. Electrophoretic mobility shift assays with fragments of the arcABC promoter and recombinant ArgR, and chromatin immunoprecipitation with antibodies directed against ArgR revealed that ArgR interacts with the arcABC promoter in vitro and in vivo by binding to a region from -147 to 72 bp upstream of the transcriptional start point. Overall our results show that in Streptococcus suis ArgR is an essential, system specific transcriptional regulator of the ADS directly interacting with the arcABC promoter in vivo
560 FUNCTIONAL CAPACITY, QUALITY OF LIFE AND COSTS IN OSTEOARTHRITIS (OA) PATIENTS WHO UNDERWENT TOTAL HIP OR KNEE REPLACEMENT SURGERY
Preferential depletion of a splenic marginal zone-like peripheral blood CD27+B220- memory B cell population in HIV-1 infected individuals
Coupling of hard dimers to dynamical lattices via random tensors
We study hard dimers on dynamical lattices in arbitrary dimensions using a
random tensor model. The set of lattices corresponds to triangulations of the
d-sphere and is selected by the large N limit. For small enough dimer
activities, the critical behavior of the continuum limit is the one of pure
random lattices. We find a negative critical activity where the universality
class is changed as dimers become critical, in a very similar way hard dimers
exhibit a Yang-Lee singularity on planar dynamical graphs. Critical exponents
are calculated exactly. An alternative description as a system of
`color-sensitive hard-core dimers' on random branched polymers is provided.Comment: 12 page
Humans versus robots: Converting golf putter trajectories for robotic guidance
Robotic devices are used to provide physical guidance when teaching different movements. To advance our knowledge of robotic guidance in training complex movements, this investigation tested different kinematic data filtering methods of individual’s golf putts to convert them into trajectories to be employed by a robot arm. The purpose of the current study was to identify a simple filtering method to aptly replicate participants’ individual golf putter trajectories which could be used by the robot to execute them with greater consistency and accuracy than their human counterpart.
Participants putted towards 3 targets where three-dimensional data of the putter’s head was filtered and then fitted by using one- or two-dimensions of the participant’s putter head trajectories. As expected, both filtering methods employed with the robot outperformed the human participants in ball endpoint accuracy and consistency. Further, after comparing the filtered to the human participants trajectories, the two-dimensional method best replicated the kinematic features of human participants natural putter trajectory, while the one-dimensional method failed to replicate participant’s backstroke position. This investigation indicates that a two-dimensional filtering method, using Y-forward and Z-vertical position data, can be used to create accurate, consistent, and smooth trajectories delivered by a robot arm
Statistical methods for analyzing immunosignatures
<p>Abstract</p> <p>Background</p> <p>Immunosignaturing is a new peptide microarray based technology for profiling of humoral immune responses. Despite new challenges, immunosignaturing gives us the opportunity to explore new and fundamentally different research questions. In addition to classifying samples based on disease status, the complex patterns and latent factors underlying immunosignatures, which we attempt to model, may have a diverse range of applications.</p> <p>Methods</p> <p>We investigate the utility of a number of statistical methods to determine model performance and address challenges inherent in analyzing immunosignatures. Some of these methods include exploratory and confirmatory factor analyses, classical significance testing, structural equation and mixture modeling.</p> <p>Results</p> <p>We demonstrate an ability to classify samples based on disease status and show that immunosignaturing is a very promising technology for screening and presymptomatic screening of disease. In addition, we are able to model complex patterns and latent factors underlying immunosignatures. These latent factors may serve as biomarkers for disease and may play a key role in a bioinformatic method for antibody discovery.</p> <p>Conclusion</p> <p>Based on this research, we lay out an analytic framework illustrating how immunosignatures may be useful as a general method for screening and presymptomatic screening of disease as well as antibody discovery.</p
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