3,028 research outputs found
Do Historically Black Colleges and Universities Enhance the College Attendance of African American Youths?
Recently, Historically Black Colleges and Universities (HBCUs) have become the center of intense policy debates. Do HBCUs enhance the college attendance of African American youths? Previous research has been inconclusive. Among other improvements, our study adjusts for the relative availability of HBCU enrollment opportunities in each state. We find that African Americans are more likely to choose HBCUs over other colleges if more HBCU openings are available. However, more HBCU openings don\u27t increase overall African American enrollment. As we have shown elsewhere, attendance at an HBCU does enhance African American students\u27 college graduation rates
Systematic Review of the Exposure Assessment and Epidemiology of High-Frequency Voltage Transients
Conclusions of epidemiological studies describing adverse health effects as a result of exposure to electromagnetic fields are not unanimous and often contradictory. It has been proposed that an explanation could be that high frequency voltage transients (dirty electricity [DE]) which are superimposed on 50/60Hz fields, but are generally not measured, is the real causal agent. DE has been linked to many different health and wellbeing effects, and on the basis of this an industry selling measurement and filtering equipment is growing. We reviewed the available peer-reviewed evidence for DE as a causal agent for adverse human health effects.A literature search was performed in the Cochrane Library, PubMed, Web of Science, Google Scholar and additional publications were obtained from reference lists and from the grey literature. This search resulted in 25 publications; 16 included primary epidemiological and/or exposure data. All studies were reviewed by both authors independently, and including a re-review of studies included in a review of data available up to July 31 2009 by one of the authors. DE has been measured differently in different studies and comparison data are not available. There is no evidence for 50 Graham/Stetzer (G/S) units as a safety threshold being anything more than arbitrary. The epidemiological evidence on human health effects of DE is primarily based on, often re-used, case descriptions. Quantitative evidence relies on self-reporting in non-blinded interventions, ecological associations, and one cross-sectional cohort study of cancer risk which does not point to DE as the causal agent. The available evidence for DE as an exposure affecting human health at present does not stand up to scientific scrutiny
Emergence Characteristics of Several Annual Weeds
No other event in the life cycle of weeds affects scouting and management timing as greatly as weed emergence. The timing and intensity of weed emergence affect everything from the effectiveness of burndown herbicides and preplant tillage, to timing of postplant tillage and herbicide application, to competitiveness of weeds that escape control, to seed production by surviving plants, to eventually population shifts. Given the importance of weed emergence to all forms of weed management, it seems logical that we should give greater attention to understanding and predicting weed emergence as affected by environmental factors, weed species, and management practices
Recommended from our members
Electromagnetic Characteristics of a Horizontal Wire Above a Dissipative Earth - Part 1: Propagation of Transmission-line and Fast-wave Modes
Stellar Crowding and the Science Case for Extremely Large Telescopes
We present a study of the effect of crowding on stellar photometry. We
develop an analytical model through which we are able to predict the error in
magnitude and color for a given star for any combination of telescope
resolution, stellar luminosity function, background surface brightness, and
distance. We test our predictions with Monte Carlo simulations of the LMC
globular cluster NGC 1835, for resolutions corresponding to a seeing-limited
telescope, the , and an AO-corrected 30-m (near diffraction limited)
telescope. Our analytically predicted magnitude errors agree with the
simulation results to within 20%. The analytical model also predicts that
errors in color are strongly affected by the correlation of crowding--induced
photometric errors between bands as is seen in the simulations. Using
additional Monte Carlo simulations and our analytical crowding model, we
investigate the photometric accuracy which 30-m and 100-m Extremely Large
Telescopes (ELTs) will be able to achieve at distances extending to the Virgo
cluster. We argue that for stellar populations work, ELTs quickly become
crowding-limited, suggesting that low--Strehl AO systems may be sufficient for
this type of science.Comment: 25 pages, 19 figures in 35 separate files, Astronomical Journal,
accepte
Evolution of the leukotoxin promoter in genus Mannheimia
<b>Background</b>: The <i>Mannheimia</i> species encompass a wide variety of bacterial lifestyles, including opportunistic pathogens and commensals of the ruminant respiratory tract, commensals of the ovine rumen, and pathogens of the ruminant integument. Here we present a scenario for the evolution of the leukotoxin promoter among representatives of the five species within genus <i>Mannheimia</i>. We also consider how the evolution of the leukotoxin operon fits with the evolution and maintenance of virulence.
<b>Results</b>: The alignment of the intergenic regions upstream of the leukotoxin genes showed significant sequence and positional conservation over a 225-bp stretch immediately proximal to the transcriptional start site of the <i>lktC</i> gene among all <i>Mannheimia</i> strains. However, in the course of the <i>Mannheimia</i> genome evolution, the acquisition of individual noncoding regions upstream of the conserved promoter region has occurred. The rate of evolution estimated branch by branch suggests that the conserved promoter may be affected to different extents by the types of natural selection that potentially operate in regulatory regions. Tandem repeats upstream of the core promoter were confined to <i>M. haemolytica</i> with a strong association between the sequence of the repeat units, the number of repeat units per promoter, and the phylogenetic history of this species.
<b>Conclusion</b>: The mode of evolution of the intergenic regions upstream of the leukotoxin genes appears to be highly dependent on the lifestyle of the bacterium. Transition from avirulence to virulence has occurred at least once in <i>M. haemolytica</i> with some evolutionary success of bovine serotype A1/A6 strains. Our analysis suggests that changes in <i>cis</i>-regulatory systems have contributed to the derived virulence phenotype by allowing phase-variable expression of the leukotoxin protein. We propose models for how phase shifting and the associated virulence could facilitate transmission to the nasopharynx of new hosts
Societal Adaptation to Decadal Climate Variability in the United States
The search for evidence of decadal climatic variability (DCV) has a very long history. In the past decade, a research community has coalesced around a series of roughly biennial workshops that have emphasized description of past DCV events; their causes and their teleconnections responsible for droughts, floods, and warm and cold spells around the world; and recently, the predictability of DCV events. Researchers studying climate change put great emphasis on prospective impacts, but the DCV community has yet to do so. To begin rectifying this deficiency, a short but ambitious workshop was convened in Waikoloa, near Kona, Hawaii, from 26-28 April 2007. This workshop, sponsored by the Center for Research on the Changing Earth System (CRCES), NOAA, the U.S. Geological Survey, and the U.S. Army Corps of Engineers, brought together climatologists and sectoral specialists representing agriculture, water resources, economics, the insurance industry, and developing country interests
Clinical Practice Guidelines for Antimicrobial Prophylaxis in Surgery
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140217/1/sur.2013.9999.pd
Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols
The
mechanism for the iridium–BINAP catalyzed dehydrogenative
decarbonylation of primary alcohols with the liberation of molecular
hydrogen and carbon monoxide was studied experimentally and computationally.
The reaction takes place by tandem catalysis through two catalytic
cycles involving dehydrogenation of the alcohol and decarbonylation
of the resulting aldehyde. The square planar complex IrCl(CO)(<i>rac</i>-BINAP) was isolated from the reaction between [Ir(cod)Cl]<sub>2</sub>, <i>rac</i>-BINAP, and benzyl alcohol. The complex
was catalytically active and applied in the study of the individual
steps in the catalytic cycles. One carbon monoxide ligand was shown
to remain coordinated to iridium throughout the reaction, and release
of carbon monoxide was suggested to occur from a dicarbonyl complex.
IrH<sub>2</sub>Cl(CO)(<i>rac</i>-BINAP) was also synthesized
and detected in the dehydrogenation of benzyl alcohol. In the same
experiment, IrHCl<sub>2</sub>(CO)(<i>rac</i>-BINAP) was
detected from the release of HCl in the dehydrogenation and subsequent
reaction with IrCl(CO)(<i>rac</i>-BINAP). This indicated
a substitution of chloride with the alcohol to form a square planar
iridium alkoxo complex that could undergo a β-hydride elimination.
A KIE of 1.0 was determined for the decarbonylation and 1.42 for the
overall reaction. Electron rich benzyl alcohols were converted faster
than electron poor alcohols, but no electronic effect was found when
comparing aldehydes of different electronic character. The lack of
electronic and kinetic isotope effects implies a rate-determining
phosphine dissociation for the decarbonylation of aldehydes
Условия формирования и проблемы функционирования крупных диверсифицированных производственно-корпоративных структур в Украине
У статті розглянуто умови формування та функціонування, а також історія розвитку великих диверсифікованих виробничо-корпоративних структур в Україні. Пропонуються підходи оцінки результативності процесу диверсифікації з використанням різних методик. Визначено, що в даний час оцінка результативності процесу диверсифікації можлива лише непрямими математичними методами.В статье рассмотрены условия формирования и функционирования, а также история развития крупных диверсифицированных производственно-корпоративных структур в Украине. Предлагаются подходы оценки результативности процесса диверсификации с использованием разных методик. Определено, что в настоящее время оценка результативности процесса диверсификации возможна лишь косвенными математическими методами.In the article address the formation and functioning of the conditions, as well as story development of large industrial and corporate structures, becoming diversification in Ukraine. Proposes approaches assessing impact of the process of diversification, using of different methods. Proved that the current performance assessment process of diversification can only be indirect mathematical methods
- …