Low-Reynolds number swimming in gels

Many microorganisms swim through gels, materials with nonzero zero-frequency elastic shear modulus, such as mucus. Biological gels are typically heterogeneous, containing both a structural scaffold (network) and a fluid solvent. We analyze the swimming of an infinite sheet undergoing transverse traveling wave deformations in the "two-fluid" model of a gel, which treats the network and solvent as two coupled elastic and viscous continuum phases. We show that geometric nonlinearities must be incorporated to obtain physically meaningful results. We identify a transition between regimes where the network deforms to follow solvent flows and where the network is stationary. Swimming speeds can be enhanced relative to Newtonian fluids when the network is stationary. Compressibility effects can also enhance swimming velocities. Finally, microscopic details of sheet-network interactions influence the boundary conditions between the sheet and network. The nature of these boundary conditions significantly impacts swimming speeds.Comment: 6 pages, 5 figures, submitted to EP

Effects of nicotine on microvascular responsiveness after nicotine satiety versus overnight nicotine abstinence

[no abstract available

Cosmic axion thermalization

Axions differ from the other cold dark matter candidates in that they form a degenerate Bose gas. It is shown that their huge quantum degeneracy and large correlation length cause cold dark matter axions to thermalize through gravitational self-interactions when the photon temperature reaches approximately 500 eV. When they thermalize, the axions form a Bose-Einstein condensate. Their thermalization occurs in a regime, herein called the `condensed regime', where the Boltzmann equation is not valid because the energy dispersion of the particles is smaller than their interaction rate. We derive analytical expressions for the thermalization rate of particles in the condensed regime, and check the validity of these expressions by numerical simulation of a toy model. We revisit axion cosmology in light of axion Bose-Einstein condensation. It is shown that axions are indistinguishable from ordinary cold dark matter on all scales of observational interest, except when they thermalize or rethermalize. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation as they go to the lowest energy state consistent with the total angular momentum they acquired by tidal torquing. This phenomenon explains the occurrence of caustic rings of dark matter in galactic halos. We find that photons may reach thermal contact with axions and investigate the implications of this possibility for the measurements of cosmological parameters.Comment: 38 pages, 1 figur

Thermal Cycling Stability of Silica Membranes for Gas Separation

Hydrogen is being seen as an alternative energy carrier to conventional hydrocarbons to reduce greenhouse gas emissions. High efficiency separation technologies to remove hydrogen from the greenhouse gas, carbon dioxide, are therefore in growing demand. Traditional thermodynamic separation systems utilise distillation, absorption and adsorption, but are limited in efficiency at compact scales. Molecular sieve silica (MSS) membranes can perform this separation as they have high permselectivity of hydrogen to carbon dioxide, but their stability under thermal cycling is not well reported. In this work we exposed a standard MSS membrane and a carbonised template MSS (CTMSS) membrane to thermal cycling from 100 to 450°C. The standard MSS and carbonised template CTMSS membranes both showed permselectivity of helium to nitrogen dropping from around 10 to 6 in the first set of cycles, remaining stable until the last test. The permselectivity drop was due to small micropore collapse, which occurred via structure movement during cycling. Simulating single stage membrane separation with a 50:50 molar feed of H2:CO2, H2 exiting the permeate stream would start at 79% and stabilise at 67%. Higher selectivity membranes showed less of a purity drop, indicating the margin at which to design a stable membrane separation unit for CO2 capture

Benefits of 8 weeks of High Intensity Training in healthy women: the Trion project

Aim High-intensity training (HIT) has recently been shown to be a suitable alternative time-saving strategy to improve athletic performance, cardiovascular fitness and muscle metabolism1. Nevertheless, women have rarely participated in studies investigating the efficacy of HIT2. Therefore, the aim of this study was to evaluate in moderately active women the effectiveness of an HIT intervention performed on a new device called Trion. Methods Before and after 8 weeks of HIT (3 time/week, 7reps x 30sec all-out interspersed with 2 min of active rest), in 35 healthy women volunteers (22.5±3.7 yy; BMI: 21.2±2.6), we measured maximal oxygen uptake (V’O2max), ventilatory threshold (VT), anaerobic performance, muscle structure, body composition, hematochemical (CHOLtot) and blood pressure profile at rest. The HIT workout was performed running on non-motorized curve treadmill and cycling on an competition bike mounted on an electromagnetic roller. Results Absolute and relative V’O2max significantly increased by 10% (p<.05); maximal power and power@VT increased by 7.2% and 6.3 % (p<.05), respectively; peak anaerobic performance significantly increased by 10% (p<.05). Large significant differences (p<.05) were identified for vastus lateralis thickness and pennation angle, +4.9% and +10.1%, respectively. Fat mass and CHOLtot decreased by 3.9% and 5.7% (p<.05), respectively. Conclusions Our results confirm the feasibility and effectiveness of HIT to improve exercise performance and health related parameters: HIT performed on Trion device was absolutely safe and well tolerated by the subjects. As confirmed in previous studies, our findings shows that exercise intensity, rather than duration, is the key factor in determining functional benefits. References 1Weston M, Effects of Low-Volume High-Intensity-Interval-Training (HIT) on Fitness in Adults: A Meta-Analysis of Controlled and Non-Controlled Trials Sports Med. 2014; 44(7): 1005–1017. 2Batacan, RB Jr. Effects of high-intensity-interval-training on cardiometabolic health: a systematic review and meta-analysis of intervention studies. Br J Sports Med. 2017 Mar;51(6):494-503

Traditional vs non-motorized curve treadmill: differences in energetic requirements

Previous studies suggest that exercise performed on curve surface treadmill (CT) can increase energy expenditure more than exercise performed on a traditional motorized treadmill (MT). However, to date, there are no data about energy cost that confirm this hypothesis. Thus, the purpose of the study is to analyze the physiological requirements of walking and running on a CT as compared to a traditional MT. 26 subjects (11M + 15W) (24.1±3.4yy; 64.7±11.2kg; 171.1±8.6cm) performed preferred walking speed test and running ramp test to exhaustion on both treadmill in two separated sessions. The gross energy cost of walking (Cw) is greater (p<.05) in CT than in MT (3.79±0.35 j/m/kg, 2.43±0.38 j/m/kg, respectively). The gross energy cost of running (Cr) is greater (p<.05) in CT than in MT (5.05±1.67 j/m/kg, 4.09±0.70 j/m/kg, respectively). Moreover, MT allows to reach higher speeds than CT (MT:15.5±1.7 km/h, CT:13.9±1.4 km/h, p<.05) with lower peak blood lactate concentrations (MT: 8.98±2.43 mmol/L, CT: 10.75±2.76 mmol/L, p<.05). Our data confirm that i) the Cw, matched for speed, is greater in CT than MT; ii) the Cr, analyzed during incremental ramp test, is greater in CT than MT; iii) during the ramp test, for the same metabolic load, the mechanical load is lower in the CT compared to MT. The increased physical effort is due to the greater frictional characteristics and force generation requirements inherent with the use of a CT

The H.E.S.S. II GRB Program

Gamma-ray bursts (GRBs) are some of the most energetic and exotic events in the Universe, however their behaviour at the highest energies (>10 GeV) is largely unknown. Although the Fermi-LAT space telescope has detected several GRBs in this energy range, it is limited by the relatively small collection area of the instrument. The H.E.S.S. experiment has now entered its second phase by adding a fifth telescope of 600 m$^{2}$ mirror area to the centre of the array. This new telescope increases the energy range of the array, allowing it to probe the sub-100 GeV range while maintaining the large collection area of ground based gamma-ray observatories, essential to probing short-term variability at these energies. We will present a description of the GRB observation scheme used by the H.E.S.S. experiment, summarising the behaviour and performance of the rapid GRB repointing system, the conditions under which potential GRB repointings are made and the data analysis scheme used for these observations.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherland

Quasinormal Modes of Dirty Black Holes

Quasinormal mode (QNM) gravitational radiation from black holes is expected to be observed in a few years. A perturbative formula is derived for the shifts in both the real and the imaginary part of the QNM frequencies away from those of an idealized isolated black hole. The formulation provides a tool for understanding how the astrophysical environment surrounding a black hole, e.g., a massive accretion disk, affects the QNM spectrum of gravitational waves. We show, in a simple model, that the perturbed QNM spectrum can have interesting features.Comment: 4 pages. Published in PR

V’O2 kinetics in response to High-Intensity-Interval Training (HIT) and isoinertial resistance training (IRT) in older, healthy men

High intensity exercise training (HIT) accelerates V’O2 kinetics (VO2k) in older subjects. It is controversial whether IRT may elicit the same adaptation. We explored the effect of HIT and IRT on VO2k and muscle deoxygenation during moderate intensity exercise in older, healthy men. 12 men (68 yy ± 4) were exposed to 8 weeks (3 times a week) of: i) HIT, and, after 4 months, ii) IRT performed with an isoinertial YoYo. Before and after training we measured: i) V’O2 peak (V’O2p); ii) breath-by-breath V’O2 and fractional muscle O2 extraction (∆HHb) of vastus lateralis by quantitative NIRS during step-exercise transitions of moderate intensity. VO2k was modeled by means of a double - exponential function to obtain the time constant (Tau) of its primary component. The normalized ∆HHb to ∆V’O2 ratio (∆HHb/∆V’O2) was calculated as and index of the matching between muscular O2 delivery (VO2m) and uptake (QaO2). V’O2p increased after HIT (29.9 mL min-1 kg-1 ± 4.3 - 32.6 mL min-1 kg-1± 6.0, p<0.05); it was not affected by IRT. Tau decreased after HIT (26.97 s ± 5.54 - 19.63 s ± 4.31, p<0.05); it did not change after IRT. Peak ∆HHb/∆V’O2 was smaller after HIT (1.83 ± 0.63 - 1.23 ± 0.37, p<0.05); it was not affected by IRT. 8 weeks of HIT accelerated V’O2k and improved the matching between QaO2 and VO2m. IRT did not lead to any improvement of ∆HHb/∆V’O2 and left V’O2k unchanged. Results suggest that the acceleration of V’O2k was mainly due to the improved matching of VO2m to QaO2