387 research outputs found
Internal stresses in steel plate generated by shape memory alloy inserts
Neutron strain scanning was employed to investigate the internal stress fields in steel plate coupons with embedded prestrained superelastic NiTi shape memory alloy inserts. Strain fields in steel were evaluated at T = 21 °C and 130 °C on virgin coupons as well as on mechanically and thermally fatigued coupons. Internal stress fields were evaluated by direct calculation of principal stress components from the experimentally measured lattice strains as well as by employing an inverse finite element modeling approach. It is shown that if the NiTi inserts are embedded into the elastic steel matrix following a carefully designed technological procedure, the internal stress fields vary with temperature in a reproducible and predictable way. It is estimated that this mechanism of internal stress generation can be safely applied in the temperature range from −20 °C to 150 °C and is relatively resistant to thermal and mechanical fatigue. The predictability and fatigue endurance of the mechanism are of essential importance for the development of future smart metal matrix composites or smart structures with embedded shape memory alloy components
Between supply and demand: the limits to participatory development in South Africa
Much of the focus in the literature on participatory development has been on the
demand side and on the extent to which citizens succeed in pressuring the state to
deliver basic services. Less attention has been focused on the supply side of participatory
development, namely on how state institutions give effect to development policies.
Post-Apartheid South Africa is replete with policies and legislation supporting participatory
processes and yet in practice this has seldom lived up to the ideals espoused.
This article examines the delivery of public housing in poor communities in three
municipalities in South Africa and argues that there is a mismatch between how the
formulators of policy understand participation and how it is interpreted by beneficiary
communities and local officials. It concludes that considerably more attention needs to
be focused on why officials fail to translate national policies into action if participatory
democracy is to attain any legitimacy in the population at large.Web of Scienc
Stretching and squeezing of sessile dielectric drops by the optical radiation pressure
We study numerically the deformation of sessile dielectric drops immersed in
a second fluid when submitted to the optical radiation pressure of a continuous
Gaussian laser wave. Both drop stretching and drop squeezing are investigated
at steady state where capillary effects balance the optical radiation pressure.
A boundary integral method is implemented to solve the axisymmetric Stokes flow
in the two fluids. In the stretching case, we find that the drop shape goes
from prolate to near-conical for increasing optical radiation pressure whatever
the drop to beam radius ratio and the refractive index contrast between the two
fluids. The semi-angle of the cone at equilibrium decreases with the drop to
beam radius ratio and is weakly influenced by the index contrast. Above a
threshold value of the radiation pressure, these "optical cones" become
unstable and a disruption is observed. Conversely, when optically squeezed, the
drop shifts from an oblate to a concave shape leading to the formation of a
stable "optical torus". These findings extend the electrohydrodynamics approach
of drop deformation to the much less investigated "optical domain" and reveal
the openings offered by laser waves to actively manipulate droplets at the
micrometer scale
Laser microfluidics: fluid actuation by light
The development of microfluidic devices is still hindered by the lack of
robust fundamental building blocks that constitute any fluidic system. An
attractive approach is optical actuation because light field interaction is
contactless and dynamically reconfigurable, and solutions have been anticipated
through the use of optical forces to manipulate microparticles in flows.
Following the concept of an 'optical chip' advanced from the optical actuation
of suspensions, we propose in this survey new routes to extend this concept to
microfluidic two-phase flows. First, we investigate the destabilization of
fluid interfaces by the optical radiation pressure and the formation of liquid
jets. We analyze the droplet shedding from the jet tip and the continuous
transport in laser-sustained liquid channels. In the second part, we
investigate a dissipative light-flow interaction mechanism consisting in
heating locally two immiscible fluids to produce thermocapillary stresses along
their interface. This opto-capillary coupling is implemented in adequate
microchannel geometries to manipulate two-phase flows and propose a contactless
optical toolbox including valves, droplet sorters and switches, droplet
dividers or droplet mergers. Finally, we discuss radiation pressure and
opto-capillary effects in the context of the 'optical chip' where flows,
channels and operating functions would all be performed optically on the same
device
Specific Activation of Estrogen Receptor Alpha and Beta Enhances Male Sexual Behavior and Neuroplasticity in Male Japanese Quail
Two subtypes of estrogen receptors (ER), ERα and ERβ, have been identified in humans and numerous vertebrates, including the Japanese quail. We investigated in this species the specific role(s) of each receptor in the activation of male sexual behavior and the underlying estrogen-dependent neural plasticity. Castrated male Japanese quail received empty (CX) or testosterone-filled (T) implants or were daily injected with the ER general agonist diethylstilbestrol (DES), the ERα-specific agonist PPT, the ERβ-specific agonist DPN or the vehicle, propylene glycol. Three days after receiving the first treatment, subjects were alternatively tested for appetitive (rhythmic cloacal sphincter movements, RCSM) and consummatory aspects (copulatory behavior) of male sexual behavior. 24 hours after the last behavioral testing, brains were collected and analyzed for aromatase expression and vasotocinergic innervation in the medial preoptic nucleus. The expression of RCSM was activated by T and to a lesser extent by DES and PPT but not by the ERβagonist DPN. In parallel, T fully restored the complete sequence of copulation, DES was partially active and the specific activation of ERα or ERβ only resulted in a very low frequency of mount attempts in few subjects. T increased the volume of the medial preoptic nucleus as measured by the dense cluster of aromatase-immunoreactive cells and the density of the vasotocinergic innervation within this nucleus. DES had only a weak action on vasotocinergic fibers and the two specific ER agonists did not affect these neural responses. Simultaneous activation of both receptors or treatments with higher doses may be required to fully activate sexual behavior and the associated neurochemical events
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