6,288 research outputs found
The cell cycle program of polypeptide labeling in Chlamydomonas reinhardtii
The cell cycle program of polypeptide labeling in syndhronous cultures of wild-type Chlamydomonas reinhardtii was analyzed by pulse-labeling cells with 35SO4 = or [3H]arginine at different cell cycle stages. Nearly 100 labeled membrane and soluble polypeptides were resolved and studied using one-dimensional sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis. The labeling experiments produced the following results. (a) Total 35SO4 = and [3H]arginine incorporation rates varied independently throughout the cell cycle. 35SO4 = incorporation was highest in the mid-light phase, while [3H]arginine incorporation peaked in the dark phase just before cell division. (b) The relative labeling rate for 20 of 100 polypeptides showed significant fluctuations (3-12 fold) during the cell cycle. The remaining polypeptides were labeled at a rate commensurate with total 35SO4 = or [3H]arginine incorporation. The polypeptides that showed significant fluctuations in relative labeling rates served as markers to identify cell cycle stages. (c) The effects of illumination conditions on the apparent cell cycle stage-specific labeling of polypeptides were tested. Shifting light-grown asynchronous cells to the dark had an immediate and pronounced effect on the pattern of polypeptide labeling, but shifting dark-phase syndhronous cells to the light had little effect. The apparent cell cycle variations in the labeling of ribulose 1,5-biphosphate (RUBP)-carboxylase were strongly influenced by illumination effects. (d) Pulse-chase experiments with light-grown asynchronous cells revealed little turnover or inter- conversion of labeled polypeptides within one cell generation, meaning that major polypeptides, whether labeled in a stage-specific manner or not, do not appear transiently in the cell cycle of actively dividing, light-grown cells. The cell cycle program of labeling was used to analyze effects of a temperature-sensitive cycle blocked (cb) mutant. A synchronous culture of ts10001 was shifted to restrictive temperature before its block point to prevent it from dividing. The mutant continued its cell cycle program of polypeptide labeling for over a cell generation, despite its inability to divide
Testing the diffusion hypothesis as a mechanism of self-healing in Disperse orange 11 doped in PMMA
In this work, we show that reversible photodegradation of Disperse Orange 11
doped in PMMA is not due to dye diffusion - a common phenomenon observed in
many dye-doped polymers. The change in linear absorbance due to
photodegradation of the material shows an isobestic point, which is consistent
with the formation of a quasi-stable damaged species. Spatially-resolved
amplified spontaneous emission and fluorescence, both related to the population
density, are measured by scanning the pump beam over a burn mark. A numerical
model of the time evolution of the population density due to diffusion is
inconsistent with the experimental data suggesting that diffusion is not
responsible.Comment: 5 pages, 6 figure
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Expression of the DNA mismatch repair proteins hMLH1 and hPMS2 in normal human tissues.
hMLH1 and hPMS2 are part of the DNA mismatch repair complex. Mutations in these genes have been linked to hereditary non-polyposis colon cancer; they also occur in a variety of sporadic cancers. Western blot analysis and immunohistochemistry demonstrated that hMLH1 and hPMS2 are widely expressed nuclear proteins with a distribution pattern very similar to that previously described for hMSH2. These observations showing similar localization of hMLH1 and hPMS2 with hMSH2 are consistent with the biochemical function of these proteins in DNA mismatch repair
X-ray Properties of Young Early Type Galaxies: II. Abundance Ratio in the Hot ISM
Using Chandra X-ray observations of young, post-merger elliptical galaxies,
we present X-ray characteristics of age-related observational results, by
comparing with typical old elliptical galaxies in terms of metal abundances in
the hot interstellar matter (ISM). While the absolute element abundances may be
uncertain because of unknown systematic errors and partly because of the
smaller amount of hot gas in young ellipticals, the relative abundance ratios
(e.g., the alpha-element to Fe ratio, most importantly Si/Fe ratio) can be
relatively well constrained. We find that in two young elliptical galaxies (NGC
720 and NGC 3923) the Si to Fe abundance ratio is super-solar (at a 99%
significance level), in contrast to typical old elliptical galaxies where the
Si to Fe abundance ratio is close to solar. Also the O/Mg ratio is close to
solar in the two young elliptical galaxies, as opposed to the sub-solar O/Mg
ratio reported in old elliptical galaxies. Both features appear to be less
significant outside the effective radius (roughly 30" for the galaxies under
study), consistent with the observations that confine to the centermost regions
the signatures of recent star formation in elliptical galaxies. Observed
differences between young and old elliptical galaxies can be explained by the
additional contribution from SNe II ejecta in the former. In young elliptical
galaxies, the later star formation associated with recent mergers would have a
dual effect, resulting both in galaxy scale winds - and therefore smaller
observed amounts of hot ISM - because of the additional SNII heating, and in
different metal abundances, because of the additional SNII yields.Comment: 21 pages, 4 color figures, ApJ in press, minor revisions for
referee's comments, a new figure adde
Curvature suppresses the Rayleigh-Taylor instability
The dynamics of a thin liquid film on the underside of a curved cylindrical
substrate is studied. The evolution of the liquid layer is investigated as the
film thickness and the radius of curvature of the substrate are varied. A
dimensionless parameter (a modified Bond number) that incorporates both
geometric parameters, gravity, and surface tension is identified, and allows
the observations to be classified according to three different flow regimes:
stable films, films with transient growth of perturbations followed by decay,
and unstable films. Experiments and theory confirm that, below a critical value
of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor
instability
Revisiting with Chandra the Scaling Relations of the X-ray Emission Components (Binaries, Nuclei and Hot Gas) of Early Type Galaxies
We have selected a sample of 30 normal (non-cD) early type galaxies, for all
of which optical spectroscopy is available, and which have been observed with
Chandra to a depth such to insure the detection of bright low-mass X-ray
binaries (LMXBs) with Lx>1e38 erg/s. This sample includes a larger fraction of
gas-poor galaxies than previously studied samples, and covers a wide range of
stellar luminosity, velocity dispersion, GC specific frequency, and stellar
age. We derive X-ray luminosities (or upper limits) from the different
significant X-ray components of these galaxies: nuclei, detected and undetected
LMXBs, coronally active binaries (ABs), cataclysmic variables (CVs), and hot
gas. The ABs and CVs contribution is estimated from the Lx-LK scaling relation
of M31 and M32. The contribution of undetected LMXBs is estimated both by
fitting the spectra of the unresolved X-ray emission and by extrapolating the
LMXB X-ray luminosity function. The results for the nuclei are consistent with
those discussed by Pellegrini (2010). We derive a revised scaling relation
between the integrated X-ray luminosity of LMXBs in a galaxy and the LK
luminosity of the host galaxy: Lx(LMXB)/LK ~ 1e29 erg s-1 LK-1 with 50% 1sigma
rms; moreover, we also obtain a tighter LX(LMXB)/LK - SN relation than
previously published. We revisit the relations between hot gas content and
other galaxy parameters. finding a steeper LX(gas)-LK relation with larger
scatter than reported in the literature. We find a positive correlation between
the luminosity and temperature of the hot ISM, significantly tighter than
reported by earlier studies.[abridged
Habitat Use and Population Densities of Rain Forest Chameleons in the East Usambara Mountains of Tanzania [poster]
Conclusions: Chamaeleo dilepis and Ri. brevicaudatus are absent from forest at this elevation (852-1103m), while K. matschiei, K. vosseleri, K. tenuis, and R. spinosus are relatively scarce in the forest. Trioceros deremensis and R. temporalis are common, but density varies greatly. The endemic and scarce K. matschiei and K. vosseleri may be of concern given their scarcity in forest habitat. Density estimates in other habitat types are needed to determine status. For accurate density estimates, it is important to consider seasonal variation in density and animals too high to be observed in surveys
Using Crowdsourced Vehicle Braking Data to Identify Roadway Hazards
Modern vehicles know more about the road conditions than transportation agencies. Enhanced vehicle data that provides information on “close calls” such as hard braking events or road conditions during winter such as wheel slips and traction control will be critical for improving safety and traffic operations. This research applied conflict analyses techniques to process approximately 1.5 million hard braking events that occurred in the state of Indiana over a period of one week in August 2019. The study looked at work zones, signalized intersections, interchanges and entry/exit ramps. Qualitative spatial frequency analysis of hard-braking events on the interstate demonstrated the ability to quickly identify temporary and long-term construction zones that warrant further investigation to improve geometry and advance warning signs. The study concludes by recommending the frequency of hard-braking events across different interstate routes to identify roadway locations that have abnormally high numbers of “close calls” for further engineering assessment
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