5,427 research outputs found
Family Unity, Family Health: How Family-Focused Immigration Reform Will Mean Better Health for Children and Families
This report builds on a body of evidence on the impact of immigration policy on communities, paying particular attention to the health and mental health of children and families.Using existing research, predictive quantitative analysis and data from a convenience survey and two focus groups, this reportshines a light on the consequences of a continued policy of detention and deportation on: physical health, mental health, educational and behavioral outcomes among children; adult health status and lifespan; and economic hardship and food access in households
`Sinking' in a bed of grains activated by shearing
We show how a weak force, , enables intruder motion through dense granular
materials subject to external mechanical excitations, in the present case
stepwise shearing. A force acts on a Teflon disc in a two dimensional system of
photoelastic discs. This force is much smaller than the smallest force needed
to move the disc without any external excitation. In a cycle, material +
intruder are sheared quasi-statically from to , and
then backwards to . During various cycle phases, fragile and jammed
states form. Net intruder motion, , occurs during fragile periods
generated by shear reversals. per cycle, e.g. the quasistatic rate
, is constant, linearly dependent on and . It vanishes as,
, with and ,
reflecting the stiffening of granular systems under shear as . The intruder motion induces large scale grain circulation. In the
intruder frame, this motion is a granular analogue to fluid flow past a
cylinder, where is the drag force exerted by the flow.Comment: 4 pages, 5 figures letter with supplementarie
Force and Mass Dynamics in Non-Newtonian Suspensions
Above a certain solid fraction, dense granular suspensions in water exhibit
non-Newtonian behavior, including impact-activated solidification. Although it
has been suggested that solidification depends on boundary interactions,
quantitative experiments on the boundary forces have not been reported. Using
high-speed video, tracer particles, and photoelastic boundaries, we determine
the impactor kinematics and the magnitude and timings of impactor-driven events
in the body and at the boundaries of cornstarch suspensions. We observe mass
shocks in the suspension during impact. The shockfront dynamics are strongly
correlated to those of the intruder. However, the total momentum associated
with this shock never approaches the initial impactor momentum. We also observe
a faster second front, associated with the propagation of pressure to the
boundaries of the suspension. The two fronts depend differently on the initial
impactor speed, , and the suspension packing fraction. The speed of the
pressure wave is at least an order of magnitude smaller than (linear)
ultrasound speeds obtained for much higher frequencies, pointing to complex
amplitude and frequency response of cornstarch suspensions to compressive
strains
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