620 research outputs found
Identification of a Protein in Several Borrelia Species which is Related to OspC of the Lyme Disease Spirochetes.
Using oligonucleotide probes which have previously been shown to be specific for the ospC gene found in the Lyme disease spirochete species Borrelia burgdorferi, B. garinii, and group VS461, we detected an ospC homolog in other Borrelia species including B. coriaceae, B. hermsii, B. anserina, B. turicatae, and B. parkeri. In contrast to the Lyme disease spirochetes, which carry the ospC gene on a 26-kb circular plasmid, we mapped the gene in other Borrelia species to linear plasmids which varied in size among the isolates tested. Some isolates carry multiple copies of the gene residing on linear plasmids of different sizes. The analyses conducted here also demonstrate that these Borrelia species contain a linear chromosome. Northern (RNA) blot analyses demonstrated that the gene is transcriptionally expressed in all species examined. High levels of transcriptional expression were observed in some B. hermsii isolates. Transcriptional start site analyses revealed that the length of the untranslated leader sequence was identical to that observed in the Lyme disease spirochete species. By Western blotting (immunoblotting) with antiserum (polyclonal) raised against the OspC protein of B. burgdorferi, we detected an immunoreactive protein of the same molecular weight as the OspC found in Lyme disease spirochete species. The results presented here demonstrate the presence of a protein that is genetically and antigenically related to OspC which is expressed in all species of the genus Borrelia tested
Brown dwarfs in the Hyades and beyond?
We have used both the Low-Resolution Imaging Spectrograph and the HIRES
echelle spectrograph on the Keck telescopes to obtain spectra of twelve
candidate members of the Hyades cluster identified by Leggett and Hawkins
(1988, 1989). All of the objects are chromospherically-active, late-type
M-dwarfs, with H equivalent widths varying from 1 to 30\AA. Based on
our measured radial velocities, the level of stellar activity and other
spectroscopic features, only one of the twelve stars has properties consistent
with cluster membership. We consider how this result affects estimates of the
luminosity and mass function of the Hyades cluster. Five of the eleven field
stars have weak K I 7665/7699\AA and CaH absorption as compared with M-dwarf
standards of the same spectral type, suggesting a lower surface gravity. Two of
these sources, LH0416+14 and LH0419+15, exhibit significant lithium 6708 \AA
absorption. Based partly on parallax measurements by the US Naval Observatory
(Harris et al, 1998), we identify all five as likely to be young, pre-main
sequence objects in or near the Taurus-Auriga association at distances of
between 150 and 250 parsecs. A comparison with theoretical models of pre-main
sequence stars indicates masses of less than 0.05 M.Comment: to appear in AJ, January 1999; 34 pages, (Latex format), including 10
embedded postscript figures and two table
On the determination of oxygen abundances in chromospherically active stars
We discuss oxygen abundances derived from [O I] 6300 and the O I triplet in
stars spanning a wide range in chromospheric activity level, and show that
these two indicators yield increasingly discrepant results with higher
chromospheric/coronal activity measures. While the forbidden and permitted
lines give fairly consistent results for solar-type disk dwarfs, spuriously
high O I triplet abundances are observed in young Hyades and Pleiades stars, as
well as in individual components of RS CVn binaries (up to 1.8 dex). The
distinct behaviour of the [O I]-based abundances which consistently remain
near-solar suggests that this phenomenon mostly results from large departures
from LTE affecting the O I triplet at high activity level that are currently
unaccounted for, but also possibly from a failure to adequately model the
atmospheres of K-type stars. These results suggest that some caution should be
exercised when interpreting oxygen abundances in active binaries or young open
cluster stars.Comment: 8 pages, accepted for publication in A&
The 10 Meter South Pole Telescope
The South Pole Telescope (SPT) is a 10 m diameter, wide-field, offset
Gregorian telescope with a 966-pixel, multi-color, millimeter-wave, bolometer
camera. It is located at the Amundsen-Scott South Pole station in Antarctica.
The design of the SPT emphasizes careful control of spillover and scattering,
to minimize noise and false signals due to ground pickup. The key initial
project is a large-area survey at wavelengths of 3, 2 and 1.3 mm, to detect
clusters of galaxies via the Sunyaev-Zeldovich effect and to measure the
small-scale angular power spectrum of the cosmic microwave background (CMB).
The data will be used to characterize the primordial matter power spectrum and
to place constraints on the equation of state of dark energy. A
second-generation camera will measure the polarization of the CMB, potentially
leading to constraints on the neutrino mass and the energy scale of inflation.Comment: 47 pages, 14 figures, updated to match version to be published in
PASP 123 903 (May, 2011
Electrode Polarization Effects in Broadband Dielectric Spectroscopy
In the present work, we provide broadband dielectric spectra showing strong
electrode polarization effects for various materials, belonging to very
different material classes. This includes both ionic and electronic conductors
as, e.g., salt solutions, ionic liquids, human blood, and
colossal-dielectric-constant materials. These data are intended to provide a
broad data base enabling a critical test of the validity of phenomenological
and microscopic models for electrode polarization. In the present work, the
results are analyzed using a simple phenomenological equivalent-circuit
description, involving a distributed parallel RC circuit element for the
modeling of the weakly conducting regions close to the electrodes. Excellent
fits of the experimental data are achieved in this way, demonstrating the
universal applicability of this approach. In the investigated ionically
conducting materials, we find the universal appearance of a second dispersion
region due to electrode polarization, which is only revealed if measuring down
to sufficiently low frequencies. This indicates the presence of a second
charge-transport process in ionic conductors with blocking electrodes.Comment: 9 pages, 6 figures, experimental data are provided in electronic form
(see "Data Conservancy"
Toward a first-principles integrated simulation of tokamak edge plasmas
Performance of the ITER is anticipated to be highly sensitive to the edge plasma condition. The edge pedestal in ITER needs to be predicted from an integrated simulation of the necessary first-principles, multi-scale physics codes. The mission of the SciDAC Fusion Simulation Project (FSP) Prototype Center for Plasma Edge Simulation (CPES) is to deliver such a code integration framework by (1) building new kinetic codes XGC0 and XGC1, which can simulate the edge pedestal buildup; (2) using and improving the existing MHD codes ELITE, M3D-OMP, M3D-MPP and NIMROD, for study of large-scale edge instabilities called Edge Localized Modes (ELMs); and (3) integrating the codes into a framework using cutting-edge computer science technology. Collaborative effort among physics, computer science, and applied mathematics within CPES has created the first working version of the End-to-end Framework for Fusion Integrated Simulation (EFFIS), which can be used to study the pedestal-ELM cycles
A Theoretical Analysis of How Segmentation of Dynamic Visualizations Optimizes Students' Learning
This article reviews studies investigating segmentation of dynamic visualizations (i.e., showing dynamic visualizations in pieces with pauses in between) and discusses two not mutually exclusive processes that might underlie the effectiveness of segmentation. First, cognitive activities needed for dealing with the transience of dynamic visualizations impose extraneous cognitive load, which may hinder learning. Segmentation may reduce the negative effect of this load by dividing animations into smaller units of information and providing pauses between segments that give students time for the necessary cognitive activities after each of those units of information. Second, event segmentation theory states that people mentally segment dynamic visualizations during perception (i.e., divide the information shown in pieces). Segmentation of dynamic visualisation could cue relevant segments to students, which may aid them in perceiving the structure underlying the process or procedure shown
The XMM-LSS survey: the Class 1 cluster sample over the initial 5 square degrees and its cosmological modelling
We present a sample of 29 galaxy clusters from the XMM-LSS survey over an
area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which
represent about half of the X-ray clusters identified in the region, follow
well defined X-ray selection criteria and are all spectroscopically confirmed.
For all clusters, we provide X-ray luminosities and temperatures as well as
masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the
objects being groups with a temperature below 2 keV. Our L-T(z) relation points
toward self-similar evolution, but does not exclude other physically plausible
models. Assuming that cluster scaling laws follow self-similar evolution, our
number density estimates up to z=1 are compatible with the predictions of the
concordance cosmology and with the findings of previous ROSAT surveys. Our well
monitored selection function allowed us to demonstrate that the inclusion of
selection effects is essential for the correct determination of the evolution
of the L-T relation, which may explain the contradictory results from previous
studies. Extensive simulations show that extending the survey area to 10deg2
has the potential to exclude the non-evolution hypothesis, but that constraints
on more refined ICM models will probably be limited by the large intrinsic
dispersion of the L-T relation. We further demonstrate that increasing the
dispersion in the scaling laws increases the number of detectable clusters,
hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and
T(M,z)] in the cosmological interpretation of the cluster number counts. We
provide useful empirical formulae for the cluster mass-flux and mass-count-rate
relations as well as a comparison between the XMM-LSS mass sensitivity and that
of forthcoming SZ surveys.Comment: Accepted for publication by MNRAS. Full resolution images as well as
additional cluster data are available through a dedicated database at
http://l3sdb.in2p3.fr:8080/l3sdb
Collaboration scripts - a conceptual analysis
This article presents a conceptual analysis of collaboration scripts used in face-to-face and computer-mediated collaborative learning. Collaboration scripts are scaffolds that aim to improve collaboration through structuring the interactive processes between two or more learning partners. Collaboration scripts consist of at least five components: (a) learning objectives, (b) type of activities, (c) sequencing, (d) role distribution, and (e) type of representation. These components serve as a basis for comparing prototypical collaboration script approaches for face-to-face vs. computer-mediated learning. As our analysis reveals, collaboration scripts for face-to-face learning often focus on supporting collaborators in engaging in activities that are specifically related to individual knowledge acquisition. Scripts for computer-mediated collaboration are typically concerned with facilitating communicative-coordinative processes that occur among group members. The two lines of research can be consolidated to facilitate the design of collaboration scripts, which both support participation and coordination, as well as induce learning activities closely related to individual knowledge acquisition and metacognition. In addition, research on collaboration scripts needs to consider the learners’ internal collaboration scripts as a further determinant of collaboration behavior. The article closes with the presentation of a conceptual framework incorporating both external and internal collaboration scripts
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