Cardiovascular and Cerebral Hemodynamic Responses to Ego Depletion in a Pressurized Sporting Task

This study examined the effects of ego depletion on challenge and threat states and cerebral haemodynamic responses to a pressurized muscular endurance task requiring self-control. Following ethical approval, 58 participants (39 males, 19 females; Mage = 28 years, SD = 12) were randomly assigned to either an experimental or control group. Participants then completed self-report measures of trait anxiety and self-control. Next, the experimental group performed a written transcription task requiring self-control, while the control group transcribed the text normally. Finally, before the pressurized muscular endurance task, challenge and threat states were assessed using demand and resource evaluations and cardiovascular reactivity; while cerebral perfusion in Fp1 and Fp2 was assessed using near-infrared spectroscopy. The results supported the effectiveness of the self-control manipulation, with the experimental group transcribing fewer words, making more errors, and regulating their writing habits more than the control group. Although there were no differences between the groups in terms of muscular endurance performance or challenge and threat states, there was a significant interaction of time (pre vs. post) x group (experimental vs. control) in cerebral perfusion. These findings suggest that ego depletion might not influence challenge and threat states, but may lead to reduced cerebral perfusion. As such, cerebral perfusion may be a novel marker which could be used to assess ego depletion

Multiple Particle Tracking in a Fluidised Bed

Positron Emission Particle Tracking (PEPT) is a versatile method for following the motion of a single radioactive tracer particle in a fluidised bed. However, there are many applications in which it would be useful to be able to follow the motion of two or more particles simultaneously in cooperative motion. The tracers are labelled with different intensities of radiation and located by converging sequentially on centres of activity. Two 600&#;m polyethylene particles have been followed in a 15 cm diameter bed and their contact events studied

Magnetohydrodynamics and Plasma Cosmology

We study the linear magnetohydrodynamic (MHD) equations, both in the Newtonian and the general-relativistic limit, as regards a viscous magnetized fluid of finite conductivity and discuss instability criteria. In addition, we explore the excitation of cosmological perturbations in anisotropic spacetimes, in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m) and fast-magnetosonic modes, propagating normal to the magnetic field, can be excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X Meeting, IJTP Conference Serie

Study on solids translational and rotational motions in rotating cans

AbstractStudy on translational and rotational motion of solids is important in a wide range of engineering processes. However, rotational motion of solid particles in an opaque system has not been given much attention due to the lack of appropriate measurement methods. This paper presents a new technique, Multiple-Positron Emission Particle Tracking (Multiple-PEPT), to track both rotational and translational motions of a solid simultaneously. The sample study presented here is to track the rotation and translation of a cubed potato in a food can for optimising the canned food process. The results have demonstrated that the rotational and transitional motion of the cubed potato can be simultaneously tracked through mounting three small (200 microns) radioactive tracers on the cube corners. The rotation and translation of the cube can be reconstructed based on the trajectories of the three tracers. The translational and rotational motions of the potato particle are related to each other, and both the motions are greatly dependent on the solids fraction, the liquid viscosity and the density difference between the solid and liquid; but follow specific patterns

Stellar Mass Black Hole Binaries as ULXs

Ultraluminous X-ray sources (ULXs) with Lx > 10^{39} ergs/s have been discovered in great numbers in external galaxies with ROSAT, Chandra, and XMM. The central question regarding this important class of sources is whether they represent an extension in the luminosity function of binary X-ray sources containing neutron stars and stellar-mass black holes (BHs), or a new class of objects, e.g., systems containing intermediate-mass black holes (100-1000 Msun). We have carried out a theoretical study to test whether a large fraction of the ULXs, especially those in galaxies with recent star formation activity, can be explained with binary systems containing stellar-mass black holes. To this end, we have applied a unique set of binary evolution models for black-hole X-ray binaries, coupled to a binary population synthesis code, to model the ULXs observed in external galaxies. We find that for donor stars with initial masses >10 Msun the mass transfer driven by the normal nuclear evolution of the donor star is sufficient to potentially power most ULXs. This is the case during core hydrogen burning and, to an even more pronounced degree, while the donor star ascends the giant branch, though the latter phases lasts only ~5% of the main sequence phase. We show that with only a modest violation of the Eddington limit, e.g., a factor of ~10, both the numbers and properties of the majority of the ULXs can be reproduced. One of our conclusions is that if stellar-mass black-hole binaries account for a significant fraction of ULXs in star-forming galaxies, then the rate of formation of such systems is ~3 x 10^{-7} per year normalized to a core-collapse supernova rate of 0.01 per year.Comment: 15 pages, 12 figure

Understanding the Antiproliferative Activity of Plant Extracts

Many plants possess medicinal properties. Some, such as the Pacific yew, have yielded chemotherapeutic drugs (taxanes). Scientists report that other extracts such as the leaves of Calendula officinalis (marigold), Vinca rosea (periwinkle), Viscum cruciatum (mistletoe), and Rosmarinus officinalis (rosemary) have anti-tumor activity. In most cases, the chemical components responsible for antiproliferative activity have not been identified and it is unclear if any individual components are as effective in isolation as they are in the context of the whole extract. Furthermore, in most cases, there are no data indicating whether these extracts have synergistic effects or cause negative reactions when used with other drugs. We are using HeLa (adenocarcinoma), RAW 264.7 (leukemia), HepG2 (hepatoma), MDA-MB-231 (adenocarcinoma), and human foreskin fibroblasts (HFF, non-tumorigenic) to test the antiproliferative activity of several plant extracts. We identified five extracts, grapeseed, guava, yew, juniper berry, and Vinca, that slow the growth of all five cell lines in a dose-dependent manner. We are using a variety of methods to understand the mechanism by which these extracts are blocking cell growth

The effects of acute exposure to prolonged sitting, with and without interruption, on vascular function among adults: a meta-analysis

Background Exposure to acute prolonged sitting can result in vascular dysfunction, particularly within the legs. This vascular dysfunction, assessed using flow-mediated dilation (FMD), is likely the consequence of decreased blood flow-induced shear stress. With mixed success, several sitting interruption strategies have been trialled to preserve vascular function. Objectives The objectives of this meta-analysis were to (1) assess the effects of acute prolonged sitting exposure on vascular function in the upper- and lower-limb arteries, and (2) evaluate the effectiveness of sitting interruption strategies in preserving vascular function. Sub-group analyses were conducted to determine whether artery location or interruption modality explain heterogeneity. Data Sources Electronic databases (PubMed, Web of Science, SPORTDiscus, and Google Scholar) were searched from inception to January 2020. Reference lists of eligible studies and relevant reviews were also checked. Study Selection Inclusion criteria for objective (1) were: (i) FMD% was assessed pre- and post-sitting; (ii) studies were either randomised-controlled, randomised-crossover, or quasi-experimental trials; (iii) the sitting period was ≥ 1 h; and (iv) participants were healthy non-smoking adults (≥ 18 years), and free of vascular-acting medication and disease at the time of testing. Additional inclusion criteria for objective (2) were: (i) the interruption strategy must have been during the sitting period; (ii) there was a control (uninterrupted sitting) group/arm; and (iii) the interruption strategy must have involved the participants actively moving their lower- or upper-limbs. Appraisal and Synthesis Methods One thousand eight hundred and two articles were identified, of which 17 (22 trials, n = 269) met inclusion criteria for objective (1). Of those 17 articles, 6 studies (9 trials, n = 127) met the inclusion criteria for objective (2). Weighted mean differences (WMD), 95% confidence intervals (95% CI), and standardised mean difference (SMD) were calculated for all trials using random-effects meta-analysis modelling. SMD was used to determine the magnitude of effect, where < 0.2, 0.2, 0.5, and 0.8 was defined as trivial, small, moderate, and large respectively. Results (1) Random-effects modelling showed uninterrupted bouts of prolonged sitting resulted in a significant decrease in FMD% (WMD = − 2.12%, 95% CI − 2.66 to − 1.59, SMD = 0.84). Subgroup analysis revealed reductions in lower- but not upper-limb FMD%. (2) Random-effects modelling showed that interrupting bouts of sitting resulted in a significantly higher FMD% compared to uninterrupted sitting (WMD = 1.91%, 95% CI 0.40 to 3.42, SMD = 0.57). Subgroup analyses failed to identify an optimum interruption strategy but revealed moderate non-significant effects for aerobic interventions (WMD = 2.17%, 95% CI − 0.34 to 4.67, SMD = 0.69) and simple resistance activities (WMD = 2.40%, 95% CI − 0.08 to 4.88, SMD = 0.55) and a trivial effect for standing interruptions (WMD = 0.24%, 95% CI − 0.90 to 1.38, SMD = 0.16). Conclusions Exposure to acute prolonged sitting leads to significant vascular dysfunction in arteries of the lower, but not upper, limbs. The limited available data indicate that vascular dysfunction can be prevented by regularly interrupting sitting, particularly with aerobic or simple resistance activities

Investigating the Effect of a High Fat Meal and Prolonged Sitting on Executive Function: A Pilot Study [Astract only]

Prolonged periods of sitting have been shown to reduce cerebral blood flow and autoregulation, which may subsequently impair executive function. Similarly, the consumption of a high-fat diet can negatively impact cerebral perfusion. However, whether prolonged sitting combined with a high fat meal additionally impairs both executive function and cerebral perfusion is unknown. PURPOSE: To investigate the effects of consuming a high-fat meal followed by 3 hours of prolonged sitting on executive function and cerebral perfusion. METHODS: Five young healthy males (Age: 22.8 ± 2.9 yrs; stature 177.7 ± 6.4 cm; mass 78.9 ± 14.3 kg), from a target of 18, were recruited. Following familiarisation, participants completed two randomised sessions of 3 hours of prolonged sitting following the consumption of a high-fat (HF) and low-fat (LF) meal. Each visit was separated by a minimum of 2 and maximum of 7 days. Participants completed a Stroop test (containing both congruent and incongruent trials) and trail-making test (TMT) both pre- and post- sitting period. The TMT consists of two parts, A and B. Continuous wave near-infrared spectroscopy (cw-NIRS) was used to measure cerebral perfusion at AF4 both before (baseline) and throughout each trial. Data was analyzed using two-way repeated measures analysis of variance. Alpha was set at P < 0.1 a priori for preliminary analyses. RESULTS: There were no significant differences between or within trials for completion time for Stroop and TMT part A. Completion time for TMT part B was significantly (p = 0.078, d = 2.2) faster in the low-fat condition compared to HF condition (16.4 ± 4 s vs. 21.6 ± 0.7 s). There were no significant differences in cerebral perfusion between or within groups (p = 0.201). CONCLUSIONS: These preliminary findings suggest that the consumption of a high-fat meal may negatively impact core executive functions measured by TMT Part B, namely working memory and task-switching ability. However, cerebral perfusion, as measured by cw-NIRS, failed to identify a mechanism. This may be a consequence of limited statistical power given the sample size, or uncertainties regarding the sensitivity of cw-NIRS when measuring cerebral perfusion

The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae

We present the results of a 10.5 yr, volume limited (28 Mpc) search for supernova (SN) progenitor stars. We compile all SNe discovered within this volume (132, of which 27% are type Ia) and determine the relative rates of each sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%) and II-L (3%). Twenty II-P SNe have high quality optical or near-IR pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies (distance, metallicity and extinction) and determine masses and upper mass estimates using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass is consistent with current estimates for white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations. Red supergiants in the Local Group have masses up to 25Msol and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 Msol. We term this discrepancy the "red supergiant problem" and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. Low luminosity SNe with low 56Ni production seem to arise from explosions of low mass progenitors near the mass threshold for core-collapse. (abridged).Comment: 37 pages, 9 figs, accepted for publication in MNRA

Open Questions in GRB Physics

Open questions in GRB physics are summarized as of 2011, including classification, progenitor, central engine, ejecta composition, energy dissipation and particle acceleration mechanism, radiation mechanism, long term engine activity, external shock afterglow physics, origin of high energy emission, and cosmological setting. Prospects of addressing some of these problems with the upcoming Chinese-French GRB mission, SVOM, are outlined.Comment: 27 pages. To appear in a special issue of Comptes Rendus Physique "GRB studies in the SVOM era", Eds. F. Daigne, G. Dubu