106 research outputs found
Shock interactions, turbulence, and the origin of the stellar mass spectrum
Supersonic turbulence is an essential element in understanding how structure
within interstellar gas is created and shaped. In the context of star
formation, many computational studies show that the mass spectrum of density
and velocity fluctuations within dense clouds, as well as the distribution of
their angular momenta, trace their origin to the statistical and physical
properties of gas that is lashed with shock waves. In this article, we review
the observations, simulations, and theories of how turbulent-like processes can
account for structures we see in molecular clouds. We then compare traditional
ideas of supersonic turbulence with a simpler physical model involving the
effects of multiple shock waves and their interaction in the interstellar
medium. Planar intersecting shock waves produce dense filaments, and generate
vortex sheets that are essential to create the broad range of density and
velocity structure in clouds. As an example, the lower mass behaviour of the
stellar initial mass function can be traced to the tendency of a collection of
shock waves to build-up a log-normal density distribution (or column density).
Vorticity - which is essential to produce velocity structure over a very broad
range of length scales in shocked clouds - can also be generated by the passage
of curved shocks or intersecting planar shocks through such media. Two major
additional physical forces affect the structure of star forming gas - gravity
and feedback processes from young stars. Both of these can produce power-law
tails at the high mass end of the IMF.Comment: 20 pages, 5 figures, to appear in theme issue "Turbulent Mixing" of
the Philosophical Transactions of the Royal Society A, Snezhana I. Abarzhi,
Serge Gauthier, and Katepalli R. Sreenivasan (Guest Editors), accepted for
publicatio
Optimizing Taq Polymerase Concentration for Improved Signal-to-Noise in the Broad Range Detection of Low Abundance Bacteria
BACKGROUND:PCR in principle can detect a single target molecule in a reaction mixture. Contaminating bacterial DNA in reagents creates a practical limit on the use of PCR to detect dilute bacterial DNA in environmental or public health samples. The most pernicious source of contamination is microbial DNA in DNA polymerase preparations. Importantly, all commercial Taq polymerase preparations inevitably contain contaminating microbial DNA. Removal of DNA from an enzyme preparation is problematical. METHODOLOGY/PRINCIPAL FINDINGS:This report demonstrates that the background of contaminating DNA detected by quantitative PCR with broad host range primers can be decreased greater than 10-fold through the simple expedient of Taq enzyme dilution, without altering detection of target microbes in samples. The general method is: For any thermostable polymerase used for high-sensitivity detection, do a dilution series of the polymerase crossed with a dilution series of DNA or bacteria that work well with the test primers. For further work use the concentration of polymerase that gave the least signal in its negative control (H(2)O) while also not changing the threshold cycle for dilutions of spiked DNA or bacteria compared to higher concentrations of Taq polymerase. CONCLUSIONS/SIGNIFICANCE:It is clear from the studies shown in this report that a straightforward procedure of optimizing the Taq polymerase concentration achieved "treatment-free" attenuation of interference by contaminating bacterial DNA in Taq polymerase preparations. This procedure should facilitate detection and quantification with broad host range primers of a small number of bona fide bacteria (as few as one) in a sample
Obtaining Statistics of Turbulent Velocity from Astrophysical Spectral Line Data
Turbulence is a crucial component of dynamics of astrophysical fluids
dynamics, including those of ISM, clusters of galaxies and circumstellar
regions. Doppler shifted spectral lines provide a unique source of information
on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its
offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical
description of the spectral line statistics. Those techniques are well suited
for studies of supersonic turbulence. We stress that a great advantage of VCS
is that it does not necessary require good spatial resolution. Addressing the
studies of mildly supersonic and subsonic turbulence we discuss the criterion
that allows to determine whether a traditional tool for such a research,
namely, Velocity Centroids are dominated by density or velocity. We briefly
discuss the use of higher order correlations as the means to study
intermittency of turbulence. We discuss observational data available and
prospects of the field.Comment: 12 pages, Invited Talk, Penetrating Bars Through Masks of Cosmic
Dust, Pilanesberg National Park, South Afrika, 7 June-12 June 200
Enhancement of toxin- and virus-neutralizing capacity of single-domain antibody fragments by N-glycosylation
Single-domain antibody fragments (VHHs) have several beneficial properties as compared to conventional antibody fragments. However, their small size complicates their toxin- and virus-neutralizing capacity. We isolated 27 VHHs binding Escherichia coli heat-labile toxin and expressed these in Saccharomyces cerevisiae. The most potent neutralizing VHH (LT109) was N-glycosylated, resulting in a large increase in molecular mass. This suggests that N-glycosylation of LT109 improves its neutralizing capacity. Indeed, deglycosylation of LT109 decreased its neutralizing capacity three- to fivefold. We also studied the effect of glycosylation of two previously isolated VHHs on their ability to neutralize foot-and-mouth disease virus. For this purpose, these VHHs that lacked potential N-glycosylation sites were genetically fused to another VHH that was known to be glycosylated. The resulting fusion proteins were also N-glycosylated. They neutralized the virus at at least fourfold-lower VHH concentrations as compared to the single, non-glycosylated VHHs and at at least 50-fold-lower VHH concentrations as compared to their deglycosylated counterparts. Thus, we have shown that N-glycosylation of VHHs contributes to toxin- and virus-neutralizing capacity
Promotional Tone in Reviews of Menopausal Hormone Therapy After the Women's Health Initiative: An Analysis of Published Articles
Adriane Fugh-Berman and colleagues analyzed a selection of published opinion pieces on hormone therapy and show that there may be a connection between receiving industry funding for speaking, consulting, or research and the tone of such opinion pieces
UKPDS Outcomes Model 2: a new version of a model to simulate lifetime health outcomes of patients with type 2 diabetes mellitus using data from the 30Â year United Kingdom Prospective Diabetes Study: UKPDS 82
HIV Disclosure Anxiety:A Systematic Review and Theoretical Synthesis
HIV disclosure can help people living with HIV to access social support, enhance antiretroviral adherence, facilitate engagement in care and reduce unprotected sex. Given interpersonal risks associated with HIV disclosure, however, anxiety about sharing one’s status is common. To investigate anxiety about HIV disclosure in HIV-positive populations, we conducted a systematic review of qualitative and quantitative studies, with 119 studies included. The review demonstrated that perceived interpersonal risks are associated with HIV disclosure and outlined evidence of associations with anxiety, fear and worry. We present a new cognitive model of HIV disclosure anxiety adapted from clinical theories of health and social anxiety, consistent with evidence from the review. The model attempts to explain the development and maintenance of anxiety in individuals whose functioning is most affected by concerns about sharing their status. Implications for helping people living with HIV struggling with significant levels of anxiety about HIV disclosure are discussed. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10461-016-1453-3) contains supplementary material, which is available to authorized users
Effect of rennet on the composition, proteolysis and microstructure of reduced-fat Cheddar cheese during ripening
Clarity of task difficulty moderates the impact of the explicit achievement motive on physical effort in hand grip tasks
Stable personality dispositions, like motives, are often assumed to exert a direct, stable impact on behavior. This also applies to the explicit achievement motive, which is supposed to influence the behavior that individuals select and how strongly they engage in it. Drawing on motivational intensity theory, we demonstrated in two studies that explicit achievement motive strength only predicted exerted force in a hand grip task if task difficulty was unclear. If task difficulty was clear, explicit achievement motive strength did not influence exerted force. Our findings suggest that the availability of information about the difficulty of motive satisfaction moderates the impact of the explicit achievement motive on behavior
Wellbeing and resilience:Mechanisms of transmission of health and risk in parents with complex mental health problems and their offspring—The WARM Study
The WARM study is a longitudinal cohort study following infants of mothers with schizophrenia, bipolar disorder, depression and control from pregnancy to infant 1Â year of age.
Background:
Children of parents diagnosed with complex mental health problems including schizophrenia, bipolar disorder and depression, are at increased risk of developing mental health problems compared to the general population. Little is known regarding the early developmental trajectories of infants who are at ultra-high risk and in particular the balance of risk and protective factors expressed in the quality of early caregiver-interaction.
Methods/Design:
We are establishing a cohort of pregnant women with a lifetime diagnosis of schizophrenia, bipolar disorder, major depressive disorder and a non-psychiatric control group. Factors in the parents, the infant and the social environment will be evaluated at 1, 4, 16 and 52Â weeks in terms of evolution of very early indicators of developmental risk and resilience focusing on three possible environmental transmission mechanisms: stress, maternal caregiver representation, and caregiver-infant interaction.
Discussion:
The study will provide data on very early risk developmental status and associated psychosocial risk factors, which will be important for developing targeted preventive interventions for infants of parents with severe mental disorder
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