Experimental study of anisotropy and non-coaxiality of granular solids

Previous experimental studies of anisotropy and non-coaxiality by using the hollow cylindrical apparatus are mainly focused on granular soils, which feature irregular particle shapes and non-uniform particle size distributions. This paper experimentally investigates these two characteristics on assemblages of particulate materials with regular particle shapes and uniform particle sizes. These assemblages are made from spherical, cylindrical and cubical particles, with an increasing order of particle angularity. Two types of loading paths in the hollow cylindrical apparatus are applied. One is the monotonic loading path with a range of fixed angles of major principal stress with respect to the horizontal bedding plan, used to investigate the anisotropy of materials. The other is the path of pure principal stress rotations, used to study the non-coaxiality. The experimental results indicate that these three materials exhibit a strong anisotropy and non-coaxiality. Their stress–strain responses are dependent on the orientation of major principal stress. The non-coaxiality is a function of stress ratio. In addition, there is a noticeable trend that these two characteristics are dependent on the angularity of particles. The more angular the particles are, the greater anisotropy and non-coaxiality take place

XAX: a multi-ton, multi-target detection system for dark matter, double beta decay and pp solar neutrinos

A multi-target detection system XAX, comprising concentric 10 ton targets of 136Xe and 129/131Xe, together with a geometrically similar or larger target of liquid Ar, is described. Each is configured as a two-phase scintillation/ionization TPC detector, enhanced by a full 4pi array of ultra-low radioactivity Quartz Photon Intensifying Detectors (QUPIDs) replacing the conventional photomultipliers for detection of scintillation light. It is shown that background levels in XAX can be reduced to the level required for dark matter particle (WIMP) mass measurement at a 10^-10 pb WIMP-nucleon cross section, with single-event sensitivity below 10^-11 pb. The use of multiple target elements allows for confirmation of the A^2 dependence of a coherent cross section, and the different Xe isotopes provide information on the spin-dependence of the dark matter interaction. The event rates observed by Xe and Ar would modulate annually with opposite phases from each other for WIMP mass >~100 GeV/c^2. The large target mass of 136Xe and high degree of background reduction allow neutrinoless double beta decay to be observed with lifetimes of 10^27-10^28 years, corresponding to the Majorana neutrino mass range 0.01-0.1 eV, the most likely range from observed neutrino mass differences. The use of a 136Xe-depleted 129/131Xe target will also allow measurement of the pp solar neutrino spectrum to a precision of 1-2%.Comment: 16 pages with 17 figure

Self-reported illness among Boston-area international travelers: A prospective study

This is the Accepted Manuscript version and was published in final edited form as: Travel Med Infect Dis. 2016 ; 14(6): 604–613. doi:10.1016/j.tmaid.2016.09.009.BACKGROUND: The Boston Area Travel Medicine Network surveyed travelers on travel-related health problems. METHODS: Travelers were recruited 2009-2011 during pre-travel consultation at three clinics. The investigation included pre-travel data, weekly during-travel diaries, and a post-travel questionnaire. We analyzed demographics, trip characteristics, health problems experienced, and assessed the relationship between influenza vaccination, influenza prevention advice, and respiratory symptoms. RESULTS:Of 987 enrolled travelers, 628 (64%) completed all surveys, of which 400 (64%) reported health problems during and/or after travel; median trip duration was 12 days. Diarrhea affected the most people during travel (172) while runny/stuffy nose affected the most people after travel (95). Of those with health problems during travel, 25% stopped or altered plans; 1% were hospitalized. After travel, 21% stopped planned activities, 23% sought physician or other health advice; one traveler was hospitalized. Travelers who received influenza vaccination and influenza prevention advice had lower rates of respiratory symptoms than those that received influenza prevention advice alone (18% vs 28%, P = 0.03). CONCLUSIONS:A large proportion of Boston-area travelers reported health problems despite pre-travel consultation, resulting in inconveniences. The combination of influenza prevention advice and influenza immunization was associated with fewer respiratory symptoms than those who received influenza prevention advice alone

Numerical Study of the Behaviour of Wall Shear Stress in Pulsatile Stenotic Flows

This paper presents a numerical study of pulsatile flow through an axisymmetric stenosed artery. Numerical calculations of the incompressible Navier-Stokes equations were carried out in an axisymmetric geometry to investigate how the wall shear stress (WSS) is affected by varying levels of stenosis contractions and pulse periods (reduced velocity). It is found that the distribution and strength of the WSS is closely correlated with the position of the vortex ring formed at the stenosis. Each vortex ring generates high WSS at the stenosis walls and this high WSS propagate downstream with the vortex ring. As the vortex ring convects downstream, it loses its strength due to viscous effects and WSS decreases in magnitude. In general, the strength of the vortex ring increases with increasing stenosis levels which leads to higher WSS values on the walls. The effect of smaller pulse period is to reduce the distance between the vortex rings, thus increasing the spatial variation of WSS along the stenosed artery

Hydrogels that listen to cells:a review of cell-responsive strategies in biomaterial design for tissue regeneration

The past decade has seen a decided move from static and passive biomaterials to biodegradable, dynamic, and stimuli responsive materials in the laboratory and the clinic. Recent advances towards the rational design of synthetic cell-responsive hydrogels-biomaterials that respond locally to cells or tissues without the input of an artificial stimulus-have provided new strategies and insights on the use of artificial environments for tissue engineering and regenerative medicine. These materials can often approximate responsive functions of a cell's complex natural extracellular environment, and must respond to the small and specific stimuli provided within the vicinity of a cell or tissue. In the current literature, there are three main cell-based stimuli that can be harnessed to create responsive hydrogels: (1) enzymes (2) mechanical force and (3) metabolites/small molecules. Degradable bonds, dynamic covalent bonds, and non-covalent or supramolecular interactions are used to provide responsive architectures that enable features ranging from cell selective infiltration to control of stem-cell differentiation. The growing ability to spatiotemporally control the behavior of cells and tissue with rationally designed responsive materials has the ability to allow control and autonomy to future generations of materials for tissue regeneration, in addition to providing understanding and mimicry of the dynamic and complex cellular niche

Global three-dimensional flow of a neutron superfluid in a spherical shell in a neutron star

We integrate for the first time the hydrodynamic Hall-Vinen-Bekarevich-Khalatnikov equations of motion of a $^{1}S_{0}$-paired neutron superfluid in a rotating spherical shell, using a pseudospectral collocation algorithm coupled with a time-split fractional scheme. Numerical instabilities are smoothed by spectral filtering. Three numerical experiments are conducted, with the following results. (i) When the inner and outer spheres are put into steady differential rotation, the viscous torque exerted on the spheres oscillates quasiperiodically and persistently (after an initial transient). The fractional oscillation amplitude ($\sim 10^{-2}$) increases with the angular shear and decreases with the gap width. (ii) When the outer sphere is accelerated impulsively after an interval of steady differential rotation, the torque increases suddenly, relaxes exponentially, then oscillates persistently as in (i). The relaxation time-scale is determined principally by the angular velocity jump, whereas the oscillation amplitude is determined principally by the gap width. (iii) When the mutual friction force changes suddenly from Hall-Vinen to Gorter-Mellink form, as happens when a rectilinear array of quantized Feynman-Onsager vortices is destabilized by a counterflow to form a reconnecting vortex tangle, the relaxation time-scale is reduced by a factor of $\sim 3$ compared to (ii), and the system reaches a stationary state where the torque oscillates with fractional amplitude $\sim 10^{-3}$ about a constant mean value. Preliminary scalings are computed for observable quantities like angular velocity and acceleration as functions of Reynolds number, angular shear, and gap width. The results are applied to the timing irregularities (e.g., glitches and timing noise) observed in radio pulsars.Comment: 6 figures, 23 pages. Accepted for publication in Astrophysical Journa

Experimental investigation of flow and segregation behaviour of bulk solids in silos under high gravity conditions

Many researchers have investigated the flow and segregation behaviour in model scale experimental silos at normal gravity conditions. However it is known that the stresses experienced by the bulk solid in industrial silos are high when compared to model silos. Therefore it is important to understand the effect of stress level on flow and segregation behaviour and establish the scaling laws governing this behaviour. The objective of this paper is to understand the effect of gravity on the flow and segregation behaviour of bulk solids in a silo centrifuge model. The materials used were two mixtures composed of Polyamide and glass beads. The discharge of two bi-disperse bulk solids in a silo centrifuge model were recorded under accelerations ranging from 1g to 15g. The velocity distribution during discharge was evaluated using Particle Image Velocimetry (PIV) techniques and the concentration distribution of large and small particles were obtained by imaging processing techniques. The flow and segregation behaviour at high gravities were then quantified and compared with the empirical equations available in the literature