227 research outputs found
Importance of the Initial Conditions for Star Formation - I. Cloud Evolution and Morphology
We present a detailed parameter study of collapsing turbulent cloud cores,
varying the initial density profile and the initial turbulent velocity field.
We systematically investigate the influence of different initial conditions on
the star formation process, mainly focusing on the fragmentation, the number of
formed stars, and the resulting mass distributions. Our study compares four
different density profiles (uniform, Bonnor-Ebert type, ,
and ), combined with six different supersonic turbulent
velocity fields (compressive, mixed, and solenoidal, initialised with two
different random seeds each) in three-dimensional simulations using the
adaptive-mesh refinement, hydrodynamics code FLASH. The simulations show that
density profiles with flat cores produce hundreds of low-mass stars, either
distributed throughout the entire cloud or found in subclusters, depending on
the initial turbulence. Concentrated density profiles always lead to the
formation of one high-mass star in the centre of the cloud and, if at all,
low-mass stars surrounding the central one. In uniform and Bonnor-Ebert type
density distributions, compressive initial turbulence leads to local collapse
about 25% earlier than solenoidal turbulence. However, central collapse in the
steep power-law profiles is too fast for the turbulence to have any significant
influence. We conclude that (I) the initial density profile and turbulence
mainly determine the cloud evolution and the formation of clusters, (II) the
initial mass function (IMF) is not universal for all setups, and (III) that
massive stars are much less likely to form in flat density distributions. The
IMFs obtained in the uniform and Bonnor-Ebert type density profiles are more
consistent with the observed IMF, but shifted to lower masses.Comment: 20 pages, MNRAS in pres
A semi-analytic model of the turbulent multi-phase interstellar medium
We present a semi-analytic model for the interstellar medium that considers
local processes and structures of turbulent star-forming gas. A volume element
of the interstellar medium is described as a multiphase system, comprising a
cold and a warm gas phase in effective (thermal plus turbulent) pressure
equilibrium, and a stellar component. Since turbulence has a critical impact on
the shape of the gaseous phases, on the production of molecular hydrogen and on
the formation of stars, the consistent treatment of turbulence energy -- the
kinetic energy of unresolved motions -- is an important new feature of our
model. Besides turbulence production by supernovae and by the cooling
instability, we also take into account the forcing by large scale motions.
We formulate a set of ordinary differential equations, which statistically
describes star formation and the exchange between the different budgets of mass
and energy in a region of the interstellar medium with given mean density,
size, metallicity and external turbulence forcing. By exploring the behaviour
of the solutions, we find equilibrium states, in which the star formation
efficiencies are consistent with observations. Kennicutt-Schmidt-like relations
naturally arise from the equilibrium solutions, while conventional star
formation models in numerical simulations impose such relations with observed
efficiency parameters as phenomenological calibrations.
Beyond the semi-analytic approach, a potential application is a complete
subgrid scale model of the unresolved multi-phase structure, star formation and
turbulence in simulations of galaxies or in cosmological simulations. The
formulation presented in this article combines various models focusing on
particular processes and yet can be adopted to specific applications, depending
on the range of resolved length scales.Comment: 25 pages, 22 figures, 1 table, accepted for publication by MNRA
Repetition, expectation, and the perception of time
Prior experience with a stimulus profoundly affects how it is processed, perceived, and acted upon. One striking finding is that repeated items seem to last for less time than novel or rare ones. This link between the processing of stimulus identity and the perception of stimulus duration has important implications for theories of timing, and for broader accounts of the organization, purpose, and neural basis of perception. Here, we examine the nature and basis of the repetition effect on subjective duration. Contrary to unitary accounts which equate repetition effects with implicit expectations about forthcoming stimuli, new work suggests that first-order repetition and second-order repetition?expectations differentially affect the perception of time. We survey emerging evidence from behavioural studies of time perception and neuroscientific studies of stimulus encoding which support this view, and outline key questions for the future
Community structure and microhabitat preferences of harpacticoid copepods in a tropical reef lagoon (Zanzibar Island, Tanzania)
Rational design of HIV vaccine and microbicides: report of the EUROPRISE annual conference
EUROPRISE is a Network of Excellence sponsored from 2007 to 2011 by the European Commission within the 6th Framework Program. The Network encompasses a wide portfolio of activities ranging from an integrated research program in the field of HIV vaccines and microbicides to training, dissemination and advocacy. The research program covers the whole pipeline of vaccine and microbicide development from discovery to early clinical trials. The Network is composed of 58 partners representing more than 65 institutions from 13 European countries; it also includes three major pharmaceutical companies (GlaxoSmithKline, Novartis and Sanofi-Pasteur) involved in HIV microbicide and vaccine research. The Network displays a dedicated and informative web page: http://www.europrise.org. Finally, a distinguishing trait of EUROPRISE is its PhD School of students from across Europe, a unique example in the world of science aimed at spreading excellence through training
Genome-Wide DNA Methylation Profiling in Early Stage I Lung Adenocarcinoma Reveals Predictive Aberrant Methylation in the Promoter Region of the Long Noncoding RNA PLUT: An Exploratory Study
Introduction: Surgical procedure is the treatment of choice in early stage I lung adenocarcinoma. However, a considerable number of patients experience recurrence within the first 2 years after complete resection. Suitable prognostic biomarkers that identify patients at high risk of recurrence (who may probably benefit from adjuvant treatment) are still not available. This study aimed at identifying methylation markers for early recurrence that may become important tools for the development of new treatment modalities. Methods: Genome-wide DNA methylation profiling was performed on 30 stage I lung adenocarcinomas, comparing 14 patients with early metastatic recurrence with 16 patients with a long-term relapse-free survival period using methylated-CpG-immunoprecipitation followed by high-throughput next-generation sequencing. The differentially methylated regions between the two subgroups were validated for their prognostic value in two independent cohorts using the MassCLEAVE assay, a high-resolution quantitative methylation analysis. Results: Unsupervised clustering of patients in the discovery cohort on the basis of differentially methylated regions identified patients with shorter relapse-free survival (hazard ratio: 2.23; 95% confidence interval: 0.66-7.53; p = 0.03). In two validation cohorts, promoter hypermethylation of the long noncoding RNA PLUT was significantly associated with shorter relapse-free survival (hazard ratio: 0.54; 95% confidence interval: 0.31-0.93; p < 0.026) and could be reported as an independent prognostic factor in the multivariate Cox regression analysis. Conclusions: Promoter hypermethylation of the long noncoding RNA PLUT is predictive in patients with early stage I adenocarcinoma at high risk for early recurrence. Further studies are needed to validate its role in carcinogenesis and its use as a biomarker to facilitate patient selection and risk stratification
A Novel Liquid Multi-Phytonutrient Supplement Demonstrates DNA-Protective Effects
This study explored the DNA protective (anti-mutagenic) effects of an oral, liquid, multi-phytonutrient dietary supplement containing a proprietary blend of fruits, vegetables and aloe vera concentrated components in addition to a proprietary catechin complex from green tea (VIBE Cardiac & Life, Eniva Nutraceuticals, Anoka, MN; herein described as “VIBE”). This study tested the hypothesis that VIBE would reduce DNA damage in skin cells exposed to UVR. Human epidermal cells, from the cell line A431NS, were treated with 0% (control), 0.125%, 0.5%, 1% and 2% VIBE, and then exposed to 240 J/m2 UVR. The amount of DNA damage was assessed using the COMET assay. At each concentration tested, a significantly smaller amount of DNA damage was measured by the COMET assay for the VIBE treated cells compared to the control cells exposed to UVR without VIBE. The dose response curves showed a maximal response at 0.5% VIBE with a threefold reduction in COMET tail density compared to the control samples without VIBE (p < 0.001). Additional research is warranted in human clinical trials to further explore the results of this study which demonstrated the DNA protective and anti-mutagenic effects of VIBE for human skin cells exposed to UVR-induced DNA damage
Associations of plasma fibrinogen assays, C-reactive protein and interleukin-6 with previous myocardial infarction
Background: The association of plasma fibrinogen with myocardial infarction (MI) may (like that of C-reactive protein, CRP) be a marker of subclinical inflammation, mediated by cytokines such as interleukin-6 (IL-6). There are well- recognized discrepancies between commonly performed fibrinogen assays. Increased ratio of clottable fibrinogen to intact fibrinogen (measured by a recently developed immunoassay) has been proposed as a measure of hyperfunctional fibrinogen, and is elevated in acute MI.<br/> Objective: To compare the associations of intact fibrinogen and four routine fibrinogen assays (two von Clauss assays; one prothrombin-time derived; and one immunonephelometric) in a case-control study of previous MI. Patients/methods: Cases (n = 399) were recruited 3-9 months after their event; 413 controls were age- and sex-matched from the case-control study local population. Intact fibrinogen was measured in 50% of subjects. Results: All routine fibrinogen assays showed high intercorrelations (r = 0.82-0.93) and significant (P lt 0.0001) increased mean levels in cases vs. controls. These four routine assays correlated only moderately with intact fibrinogen (r = 0.45-0.62), while intact fibrinogen showed only a small, nonsignificant increase in cases vs. controls. Consequently, the ratio of each of the four routine assays to the intact fibrinogen assay was significantly higher (P lt 0.0003) in cases vs. controls. Each fibrinogen assay correlated with plasma levels of CRP and IL-6 (which were also elevated in cases vs. controls). Each routine fibrinogen assay remained significantly elevated in cases vs. controls after further adjustment for C-reactive protein and interleukin-6. Conclusions: These data provide evidence for acquired, increased hyperfunctional plasma fibrinogen in MI survivors, which is not associated with markers of inflammatory reactions. The causes and significance of these results remain to be established in prospective studies
Fucoxantin: A Treasure from the Sea
The World Health Organization (WHO) estimates that 2.3 billion people will be overweight and 700 million obese in 2015. The reasons for this disastrous trend are attributed to the global tendency toward the reduced magnitude of exercise and physical activity and the increased dietary intake of fats, sugars and calories with reduced amount of vitamins and minerals. To prevent life-style-related diseases, like Metabolic Syndrome (MS), researchers’ attention is increasingly focusing on some of the so called “functional foods” which may be useful for their prevention and treatment. One of these functional ingredients is fucoxanthin (FX), a characteristic carotenoid present in edible brown seaweeds, such as Undaria pinnatifida (Wakame), Hijikia fusiformis (Hijiki), Laminaria japonica (Ma-Kombu) and Sargassum fulvellum. The increasing popularity of this molecule is certainly due to its anti-obesity effect, primarily detected by murine studies. These works revealed FX mediated induction of uncoupling protein-1 (UCP-1) in abdominal white adipose tissue (WAT) mitochondria, leading to the oxidation of fatty acids and heat production in WAT. Beyond this important role, in recent studies FX has shown a great antioxidant activity, anti-cancer, anti-diabetic and anti-photoaging properties. The aim of this review is to highlight the main effects of FX on human health
Polyphenol Content and Modulatory Activities of Some Tropical Dietary Plant Extracts on the Oxidant Activities of Neutrophils and Myeloperoxidase
Young leaves of Manihot esculenta Crantz (Euphorbiaceae), Abelmoschus esculentus (Malvaceae), Hibiscus acetosella (Malvaceae) and Pteridium aquilinum (Dennstaedtiaceae) are currently consumed as green vegetables by peoples in sub-Saharan Africa, Latin America, Asia and their migrants living in Western Europe. Sub-Saharan peoples use Manihot, Abelmoschus and Hibiscus also in the folk medicine to alleviate fever and pain, in the treatment of conjunctivitis, rheumatism, hemorrhoid, abscesses, ... The present study investigates the effects of aqueous extracts of those plants on the production of reactive oxygen species (ROS) and the release of myeloperoxidase (MPO) by equine neutrophils activated with phorbol 12-myristate 13-acetate (PMA). The ROS production was measured by lucigenin-enhanced chemiluminescence (CL), and the release of total MPO by an ELISA method. The study also investigates the effect of the extracts on the activity of MPO by studying its nitration activity on tyrosine and by using a new technique called SIEFED (Specific Immunological Extraction Followed by Enzymatic Detection) that allows studying the direct interaction of compounds with the enzyme. In all experiments, the aqueous extracts of the plants developed concentration-dependent inhibitory effects. A moderate heat treatment did not significantly modify the inhibitory capacity of the extracts in comparison to not heated ones. Total polyphenol and flavonoid contents were determined with an HPLC-UV/DAD analysis and a spectroscopic method using Folin-Ciocalteu reagent. Some polyphenols with well-known antioxidant activities (caffeic acid, chlorogenic acid, hyperoside, rosmarinic acid and rutin) were found in the extracts and may partly explain the inhibitory activities observed. The role of those dietary and medicinal plants in the treatment of ROS-dependent inflammatory diseases could have new considerations for health
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