7,721 research outputs found
Interstitial gas and density-segregation in vertically-vibrated granular media
We report experimental studies of the effect of interstitial gas on
mass-density-segregation in a vertically-vibrated mixture of equal-sized bronze
and glass spheres. Sufficiently strong vibration in the presence of
interstitial gas induces vertical segregation into sharply separated bronze and
glass layers. We find that the segregated steady state (i.e., bronze or glass
layer on top) is a sensitive function of gas pressure and viscosity, as well as
vibration frequency and amplitude. In particular, we identify distinct regimes
of behavior that characterize the change from bronze-on-top to glass-on-top
steady-state.Comment: 4 pages, 5 figures, submitted to PRL; accepted in PRE as rapid
communication, with revised text and reference
Feasibility of using teleradiology to improve tuberculosis screening and case management in a district hospital in Malawi.
Malawi has one of the world's highest rates of human immunodeficiency virus (HIV) infection (10.6%), and southern Malawi, where Thyolo district is located, bears the highest burden in the country (14.5%). Tuberculosis, common among HIV-infected people, requires radiologic diagnosis, yet Malawi has no radiologists in public service. This hinders rapid and accurate diagnosis and increases morbidity and mortality
THE EFFECT OF ANTAGONIST CONDITIONING CONTRACTIONS ON LOWER AND UPPER BODY POWER TESTS
This study assessed the effect of antagonist conditioning contractions (ACC) on lower and upper body power tests. Six subjects performed the bilateral countermovement jump and the supine medicine ball chest throw on a force platform in baseline conditions and after ACC. A repeated measures ANOVA was used to compare performance between the baseline conditions and the ACC condition. Analysis demonstrated no significant main effects for GRF (p = 0.41) or RFD (p = 0.55) for the countermovement jump. Additionally, there were no significant main effects for GRF (p = 0.85) or RFD (p = 0.95) for the medicine ball throw. This study demonstrated that maximal short term ACC do not enhance multi-joint power tests such as the countermovement jump and medicine ball throw
THE OSTEOGENIC POTENTIAL OF SUPERMAXIMAL SQUAT LOADS
This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the back squat at 3 different loads. Twelve subjects performed the back squat with 80%, 100%, and 120% of their 1 repetition maximum (RM) on a force platform. A two way repeated measures ANOVA revealed significant main effects for GRF for both the eccentric (p ≤ 0.001) and concentric (p ≤ 0.001) phases but no interaction between phase and GRF or RFD (p < 0.05). No significant main effects were found for RFD for the eccentric (p = 0.09) and concentric phases (p = 0.38). Post hoc analyses demonstrated that back squats at 120% produced the highest GRF in the eccentric and concentric conditions. Mean RFD was highest, and trending toward significance, during the eccentric phase at 100% of 1 RM condition
Volume fluctuations and compressibility of a vibrated granular gas
The volume fluctuations in the steady state reached by a vibrated granular
gas of hard particles confined by a movable piston on the top are investigated
by means of event driven simulations. Also, a compressibility factor, measuring
the response in volume of the system to a change in the mass of the piston, is
introduced and measured. From the second moment of the volume fluctuations and
the compressibility factor, an effective temperature is defined, by using the
same relation as obeyed by equilibrium molecular systems. The interpretation of
this effective temperature and its relationship with the granular temperature
of the gas, and also with the velocity fluctuations of the movable piston, is
discussed. It is found that the ratio of the temperature based on the volume
fluctuations to the temperature based on the piston kinetic energy, obeys
simple dependencies on the inelasticity and on the piston-particle mass ratio
Size segregation and convection
The size segregation of granular materials in a vibrating container is
investigated using Molecular Dynamics. We find that the rising of larger
particles is accompanied by the existence of convection cells even in the case
of the lowest possible frequencies. The convection can, however, also be
triggered by the larger particle itself. The possibility of rising through this
mechanism strongly depends on the depth of the larger particle.Comment: 7 pages, 4 figure
Explicit modelling of SOA formation from α-pinene photooxidation: sensitivity to vapour pressure estimation
The sensitivity of the formation of secondary organic aerosol (SOA) to the estimated vapour pressures of the condensable oxidation products is explored. A highly detailed reaction scheme was generated for α-pinene photooxidation using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). Vapour pressures (P^(vap)) were estimated with three
commonly used structure activity relationships. The values of P^(vap) were compared for the set of secondary species generated by GECKO-A to describe α-pinene oxidation. Discrepancies in the predicted vapour pressures were found to increase with the number of functional groups borne by the species. For semi-volatile organic compounds (i.e. organic species of interest for SOA formation), differences in the predicted Pvap range between a factor of 5 to 200 on average. The simulated SOA concentrations were compared to SOA observations in the Caltech chamber during three experiments performed under a range of NO_x conditions. While the model captures the qualitative features of SOA formation for the chamber experiments, SOA concentrations are systematically overestimated. For the conditions simulated, the modelled SOA speciation appears to be rather insensitive to the P^vap estimation method
Statistical characterization of the forces on spheres in an upflow of air
The dynamics of a sphere fluidized in a nearly-levitating upflow of air were
previously found to be identical to those of a Brownian particle in a
two-dimensional harmonic trap, consistent with a Langevin equation [Ojha {\it
et al.}, Nature {\bf 427}, 521 (2004)]. The random forcing, the drag, and the
trapping potential represent different aspects of the interaction of the sphere
with the air flow. In this paper we vary the experimental conditions for a
single sphere, and report on how the force terms in the Langevin equation scale
with air flow speed, sphere radius, sphere density, and system size. We also
report on the effective interaction potential between two spheres in an upflow
of air.Comment: 7 pages, experimen
A novel treatment of denuded areas in newborns: A report of 2 successful cases
Covering denuded areas in the extremes of life is challenging for the plastic surgeon. In newborns, this becomes a greater challenge because of the immaturity of all of their systems, making any injury a potential risk for death. We present in this case report a successful treatment of 2 cases covered with cultured autologous keratinocytes. In this procedure, a small skin biopsy is taken from the retroauricular area and the keratinocytes are cultured. After 5 days, a membrane with the cells cultured is applied covering the denuded area. We find the autologous keratinocyte method a suitable option for the treatment of denuded areas in newborns, without causing any additional morbidity and in a very short period of time. Copyright © 2015 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of The American Society of Plastic Surgeons. All rights reserved
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