939 research outputs found
Characterization of structures in biofilms formed by a Pseudomonas fluorescens isolated from soil
<p>Abstract</p> <p>Background</p> <p>Microbial biofilms represent an incompletely understood, but fundamental mode of bacterial growth. These sessile communities typically consist of stratified, morphologically-distinct layers of extracellular material, where numerous metabolic processes occur simultaneously in close proximity. Limited reports on environmental isolates have revealed highly ordered, three-dimensional organization of the extracellular matrix, which may hold important implications for biofilm physiology <it>in vivo</it>.</p> <p>Results</p> <p>A <it>Pseudomonas </it>spp. isolated from a natural soil environment produced flocculent, nonmucoidal biofilms <it>in vitro </it>with unique structural features. These mature biofilms were made up of numerous viable bacteria, even after extended culture, and contained up to 50% of proteins and accumulated 3% (by dry weight) calcium, suggesting an important role for the divalent metal in biofilm formation. Ultrastructurally, the mature biofilms contained structural motifs consisting of dense, fibrillary clusters, nanofibers, and ordered, honeycomb-like chambers enveloped in thin sheets.</p> <p>Conclusion</p> <p>Mature biofilms contained living bacteria and were structurally, chemically, and physiologically heterogeneous. The principal architectural elements observed by electron microscopy may represent useful morphological clues for identifying bacterial biofilms <it>in vivo</it>. The complexity and reproducibility of the structural motifs observed in bacterial biofilms appear to be the result of organized assembly, suggesting that this environmental isolate may possess ecological advantages in its natural habitat.</p
Crossover between Thermally Assisted and Pure Quantum Tunneling in Molecular Magnet Mn12-Acetate
The crossover between thermally assisted and pure quantum tunneling has been
studied in single crystals of high spin (S=10) uniaxial molecular magnet Mn12
using micro-Hall-effect magnetometry. Magnetic hysteresis and relaxation
experiments have been used to investigate the energy levels that determine the
magnetization reversal as a function of magnetic field and temperature. These
experiments demonstrate that the crossover occurs in a narrow (0.1 K) or broad
(1 K) temperature interval depending on the magnitude of the field transverse
to the anisotropy axis.Comment: 5 pages, 4 figure
Systolic and Hyper-Systolic Algorithms for the Gravitational N-Body Problem, with an Application to Brownian Motion
A systolic algorithm rhythmically computes and passes data through a network
of processors. We investigate the performance of systolic algorithms for
implementing the gravitational N-body problem on distributed-memory computers.
Systolic algorithms minimize memory requirements by distributing the particles
between processors. We show that the performance of systolic routines can be
greatly enhanced by the use of non-blocking communication, which allows
particle coordinates to be communicated at the same time that force
calculations are being carried out. Hyper-systolic algorithms reduce the
communication complexity at the expense of increased memory demands. As an
example of an application requiring large N, we use the systolic algorithm to
carry out direct-summation simulations using 10^6 particles of the Brownian
motion of the supermassive black hole at the center of the Milky Way galaxy. We
predict a 3D random velocity of 0.4 km/s for the black hole.Comment: 33 pages, 10 postscript figure
Subsidizing Religious Participation through Groups: A Model of the “Megachurch” Strategy for Growth
Either despite or because of their non-traditional approach, megachurches have grown significantly in the United States since 1980. This paper models religious participation as an imperfect public good which, absent intervention, yields suboptimal participation by members from the church’s perspective. Megachurches address this problem in part by employing secular-based group activities to subsidize religious participation that then translates into an increase in the attendees’ religious investment. This strategy not only allows megachurches to attract and retain new members when many traditional churches are losing members but also results in higher levels of an individual’s religious capital. As a result, the megachurch may raise expectations of members’ levels of commitment and faith practices. Data from the FACT2000 survey provide evidence that megachurches employ groups more extensively than other churches, and this approach is consistent with a strategy to use groups to help subsidize individuals’ religious investment. Religious capital rises among members of megachurches relative to members of non-megachurches as a result of this strategy
The nature of late-type spiral galaxies: structural parameters, optical and near-infrared colour profiles, and dust extinction
We analyse V and H-band surface photometry of a sample of 18 Sb-Sd galaxies.
Combining high resolution HST images with ground-based NIR observations, we
extract photometric profiles, which cover the whole disk and provide the
highest possible resolution. This is the first photometric study of late-type
spirals for which the stellar kinematics have been measured. For 10 out of the
18 galaxies, HST data in both F160W (H) and F606W (V) are available, and, for
those, we present colour maps and radial colour profiles at the resolution of
the Hubble Space Telescope.
Colours vary significantly from galaxy to galaxy, but tend to be highly
homogeneous within each galaxy, with smooth and flat colour profiles. Some of
the colour maps show jumps in the inner regions, likely due to dust. We
determine extinction-maps in an almost model-independent way using the V-H
colour map and the SAURON Mg b absorption line map of Ganda et al. (2007). The
maps show that A_V ranges from 0 to 2 mag, in the center from 0 to 1.5 mag, in
agreement with the models of Tuffs et al. (2004).
We describe the surface brightness profiles as the superposition of an
exponential disk and a Sersic bulge. The bulges are small (0.1-2.5 kpc), and
show a shape parameter n ranging from ~ 0.7 to 3, with a mean value smaller
than two: well below the value for the 'classical' de Vaucouleurs bulges. Most
galaxies (16 out of 18) show a central light excess above the Sersic fit to the
bulge, which can be interpreted as a nuclear cluster, as shown by previous
studies. We provide zero-order estimates for the magnitude of these components.
We discuss the correlations among the structural galaxy parameters and with
other relevant quantities (abridged).Comment: 28 pages, 12 figures and 7 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://www.astro.rug.nl/~peletier/ganda2009.pd
A Randomized Trial of Manual Phone Calls Versus Automated Text Messages for Peripheral Nerve Block Follow-Ups.
Mobile phone applications (apps) have been used for patient follow-up in the postoperative period, specifically to assess for complications and patient satisfaction. Few studies have evaluated their use in regional anesthesia. The objective of this study was to compare follow-up response rates using manual phone calls versus an automated patient outreach (APO) app for peripheral nerve block patients. We hypothesized that the response rate would be higher in the APO group. A mobile app, JeffAnesthesia, was developed, which sends notifications to patients to answer survey questions in the app. We randomly assigned patients who received peripheral nerve blocks for postoperative pain to either a manual phone call or an APO app group, with follow-up in each category occurring between postoperative days (POD) 14-21 and 90-100. In total, 60 patients were assigned to the phone call group and 60 patients to the APO app group. Between POD 14-21, 9 (15%) patients were reached in the manual phone call arm, and 16 (26.7%) patients were reached in the APO arm (p = 0.117). At POD 90-100, follow-up was successful with 5 (8.2%) in the manual phone call group vs. 3 (5.0%) patients in the APO app group (p = 0.300). Overall response rate was poor, with comparable response rates between groups. The APO method may reduce time spent by anesthesia staff on follow-up calls, but our data do not suggest this method improves response rates significantly. Further studies are needed to better understand the reasons for the poor response rate and strategies for improvement
The Third Gravitational Lensing Accuracy Testing (GREAT3) Challenge Handbook
The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third
in a series of image analysis challenges, with a goal of testing and
facilitating the development of methods for analyzing astronomical images that
will be used to measure weak gravitational lensing. This measurement requires
extremely precise estimation of very small galaxy shape distortions, in the
presence of far larger intrinsic galaxy shapes and distortions due to the
blurring kernel caused by the atmosphere, telescope optics, and instrumental
effects. The GREAT3 challenge is posed to the astronomy, machine learning, and
statistics communities, and includes tests of three specific effects that are
of immediate relevance to upcoming weak lensing surveys, two of which have
never been tested in a community challenge before. These effects include
realistically complex galaxy models based on high-resolution imaging from
space; spatially varying, physically-motivated blurring kernel; and combination
of multiple different exposures. To facilitate entry by people new to the
field, and for use as a diagnostic tool, the simulation software for the
challenge is publicly available, though the exact parameters used for the
challenge are blinded. Sample scripts to analyze the challenge data using
existing methods will also be provided. See http://great3challenge.info and
http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.Comment: 30 pages, 13 figures, submitted for publication, with minor edits
(v2) to address comments from the anonymous referee. Simulated data are
available for download and participants can find more information at
http://great3.projects.phys.ucl.ac.uk/leaderboard
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