1,542 research outputs found
Toward the next generation of research into small area effects on health : a synthesis of multilevel investigations published since July 1998.
To map out area effects on health research, this study had the following aims: (1) to inventory multilevel investigations of area effects on self rated health, cardiovascular diseases and risk factors, and mortality among adults; (2) to describe and critically discuss methodological approaches employed and results observed; and (3) to formulate selected recommendations for advancing the study of area effects on health. Overall, 86 studies were inventoried. Although several innovative methodological approaches and analytical designs were found, small areas are most often operationalised using administrative and statistical spatial units. Most studies used indicators of area socioeconomic status derived from censuses, and few provided information on the validity and reliability of measures of exposures. A consistent finding was that a significant portion of the variation in health is associated with area context independently of individual characteristics. Area effects on health, although significant in most studies, often depend on the health outcome studied, the measure of area exposure used, and the spatial scale at which associations are examined
Models linking production and comprehension
To what extent are linguistic representations shared between production and comprehension? What is the nature of the links between production and comprehension processes? In this chapter, we provide an introduction to those models that incorporate explicit assumptions about the degree of sharing and review some supporting evidence. We show that full sharing of representations is uncontroversial only for semantics and syntax, while there is mixed evidence over the degree of overlapping at the level of phonological and phonetic representations. We then propose a taxonomy of productionâcomprehension links, ranging from longâterm to fastâacting. To conclude, we advocate more explicit theorizing about the relationship between language production and language comprehension
The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
The first catalog of the RR Lyrae stars (RRLS) in the Galactic halo by the
QUEST Survey has been searched for significant overdensities that may be debris
from disrupted dwarf galaxies or globular clusters. Away from the major
overdensities, the distribution of these stars is adequately fit by a smooth
halo model, in which the flattening of the halo decreases with increasing
galactocentric distance (Preston et al 1991). This model was used to estimate
the ``background'' of RRLS on which the halo overdensities are overlaid. A
procedure was developed for recognizing groups of stars that constitute
significant overdensities with respect to this background. To test this
procedure, a Monte Carlo routine was used to make artificial RRLS surveys that
follow the smooth halo model, but with Poisson distributed noise in the numbers
of RRLS and, within limits, random variations in the positions and magnitudes
of the artificial stars. The artificial surveys created by this routine were
examined for significant groups in exactly the same way as the QUEST survey.
These calculations provided estimates of the frequencies with which random
fluctuations produce significant groups. In the QUEST survey, there are six
significant overdensities that contain six or more stars and several smaller
ones. The small ones and possibly one or two of the larger ones may be
artifacts of statistical fluctuations, and they need to be confirmed by
measurements of radial velocity and/or proper motion. The most prominent groups
are the northern stream from the Sagittarius dwarf spheroidal galaxy and a
large group in Virgo. Two other groups lie in the direction of the Monoceros
stream and at approximately the right distance for membership. Another group is
related to the globular cluster Palomar 5.Comment: Accepted for publication in the Astronomical Journa
Mojave remote sensing field experiment
The Mojave Remote Sensing Field Experiment (MFE), conducted in June 1988, involved acquisition of Thermal Infrared Multispectral Scanner (TIMS); C, L, and P-band polarimetric radar (AIRSAR) data; and simultaneous field observations at the Pisgah and Cima volcanic fields, and Lavic and Silver Lake Playas, Mojave Desert, California. A LANDSAT Thematic Mapper (TM) scene is also included in the MFE archive. TM-based reflectance and TIMS-based emissivity surface spectra were extracted for selected surfaces. Radiative transfer procedures were used to model the atmosphere and surface simultaneously, with the constraint that the spectra must be consistent with field-based spectral observations. AIRSAR data were calibrated to backscatter cross sections using corner reflectors deployed at target sites. Analyses of MFE data focus on extraction of reflectance, emissivity, and cross section for lava flows of various ages and degradation states. Results have relevance for the evolution of volcanic plains on Venus and Mars
Proteolytic cleavage of pertussis toxin S1 subunit is not essential for its activity in mammalian cells
BACKGROUND: Pertussis toxin (PT) is an exotoxin virulence factor produced by Bordetella pertussis, the causative agent of whooping cough. PT consists of an active subunit (S1) that ADP-ribosylates the alpha subunit of several mammalian G proteins, and a B oligomer (S2âS5) that binds glycoconjugate receptors on cells. PT appears to enter cells by endocytosis, and retrograde transport through the Golgi apparatus may be important for its cytotoxicity. A previous study demonstrated that proteolytic processing of S1 occurs after PT enters mammalian cells. We sought to determine whether this proteolytic processing of S1 is necessary for PT cytotoxicity. RESULTS: Protease inhibitor studies suggested that S1 processing may involve a metalloprotease, and processing does not involve furin, a mammalian cell protease that cleaves several other bacterial toxins. However, inhibitor studies showed a general lack of correlation of S1 processing with PT cellular activity. A combination of replacement, insertion and deletion mutations in the C-terminal region of S1, as well as mass spectrometry data, suggested that the cleavage site is located around residue 203â204, but that cleavage is not strongly sequence-dependent. Processing of S1 was abolished by each of 3 overlapping 8 residue deletions just downstream of the putative cleavage site, but not by smaller deletions in the same region. Processing of the various mutant forms of PT did not correlate with cellular activity of the toxin, nor with the ability of the bacteria producing them to infect the mouse respiratory tract. In addition, S1 processing was not detected in transfected cells expressing S1, even though S1 was fully active in these cells. CONCLUSIONS: S1 processing is not essential for the cellular activity of PT. This distinguishes it from the processing of various other bacterial toxins, which has been shown to be important for their cytotoxicity. S1 processing may be mediated primarily by a metalloprotease, but the cleavage site on S1 is not sequence-dependent and processing appears to depend on the general topology of the protein in that region, indicating that multiple proteases may contribute to this cleavage
Electron-phonon scattering at the intersection of two Landau levels
We predict a double-resonant feature in the magnetic field dependence of the
phonon-mediated longitudinal conductivity of a two-subband
quasi-two-dimensional electron system in a quantizing magnetic field. The two
sharp peaks in appear when the energy separation between two
Landau levels belonging to different size-quantization subbands is favorable
for acoustic-phonon transitions. One-phonon and two-phonon mechanisms of
electron conductivity are calculated and mutually compared. The phonon-mediated
interaction between the intersecting Landau levels is considered and no avoided
crossing is found at thermal equilibrium.Comment: 13 pages, 8 figure
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