Liquid Transport Due to Light Scattering

Using experiments and theory, we show that light scattering by inhomogeneities in the index of refraction of a fluid can drive a large-scale flow. The experiment uses a near-critical, phase-separated liquid, which experiences large fluctuations in its index of refraction. A laser beam traversing the liquid produces a large-scale deformation of the interface and can cause a liquid jet to form. We demonstrate that the deformation is produced by a scattering-induced flow by obtaining good agreements between the measured deformations and those calculated assuming this mechanism.Comment: 4 pages, 5 figures, submitted to Physical Review Letters v2: Edited based on comments from referee

Vasopressin/serotonin interactions in the anterior hypothalamus control aggressive behavior in golden hamsters

Studies in several species of rodents show that arginine vasopressin (AVP) acting through a V1A receptor facilitates offensive aggression, i.e., the initiation of attacks and bites, whereas serotonin (5-HT) acting through a 5-HT1B receptor inhibits aggressive responding. One area of the CNS that seems critical for the organization of aggressive behavior is the basolateral hypothalamus, particularly the anterior hypothalamic region. The present studies examine the neuroanatomical and neurochemical interaction between AVP and 5-HT at the level of the anterior hypothalamus (AH) in the control of offensive aggression in Syrian golden hamsters. First, specific V1A and 5-HT1B binding sites in the AH are shown by in vitro receptor autoradiography. The binding for each neurotransmitter colocalizes with a dense field of immunoreactive AVP and 5-HT fibers and putative terminals. Putative 5-HT synapses on AVP neurons in the area of the AH are identified by double-staining immunocytochemistry and laser scanning confocal microscopy. These morphological data predispose a functional interaction between AVP and 5-HT at the level of the AH. When tested for offensive aggression in a resident/intruder paradigm, resident hamsters treated with fluoxetine, a selective 5-HT reuptake inhibitor, have significantly longer latencies to bite and bite fewer times than vehicle-treated controls. Conversely, AVP microinjections into the AH significantly shorten the latency to bite and increase biting attacks. The action of microinjected AVP to increase offensive aggression is blocked by the pretreatment of hamsters with fluoxetine. These data suggest that 5-HT inhibits fighting, in part, by antagonizing the aggression-promoting action of the AVP system

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

Structure of laponite-styrene precursor dispersions for production of advanced polymer-clay nanocomposites

One method for production of polymer-clay nanocomposites involves dispersal of surface-modified clay in a polymerisable monomeric solvent, followed by fast in situ polymerisation. In order to tailor the properties of the final material we aim to control the dispersion state of the clay in the precursor solvent. Here, we study dispersions of surface-modified Laponite, a synthetic clay, in styrene via large-scale Monte-Carlo simulations and experimentally, using small angle X-ray and static light scattering. By tuning the effective interaction between simulated laponite particles we are able to reproduce the experimental scattering intensity patterns for this system, with good accuracy over a wide range of length scales. However, this agreement could only be obtained by introducing a permanent electrostatic dipole moment into the plane of each Laponite particle, which we explain in terms of the distribution of substituted metal atoms within each Laponite particle. This suggests that Laponite dispersions, and perhaps other clay suspensions, should display some of the structural characteristics of dipolar fluids. Our simulated structures show aggregation regimes ranging from networks of long chains to dense clusters of Laponite particles, and we also obtain some intriguing ‘globular’ clusters, similar to capsids. We see no indication of any ‘house-of-cards’ structures. The simulation that most closely matches experimental results indicates that gel-like networks are obtained in Laponite dispersions, which however appear optically clear and non-sedimenting over extended periods of time. This suggests it could be difficult to obtain truly isotropic equilibrium dispersion as a starting point for synthesis of advanced polymer-clay nanocomposites with controlled structures

Test methodologies for determining high temperature material properties of thin walled tubes

This report presents briefly the test methods used, within the in the EERA JPNM Pilot Project TASTE, for defining the tensile and creep material properties relevant to the integrity of nuclear fuel claddings. These properties are challenging to extract from thin walled tubes since the standard test methods use test specimen that require minimum material thicknesses in the order of 10 mm or more. In consequence the thin walled material properties are acquired through a number of testing techniques and evaluation methodologies suitable for the thin walled product form. In this report the different test methods and their data assessment requirements are briefly described. The test methods evaluated here comprises of sub-size (curved specimen) tensile testing (ST) of the cladding tube, micro specimen (dog-bone) tensile testing (MT), Small Punch testing (SP), Segmented Expanding Cone Mandrel tests (SCM), the ring tension (RT) and ring compression (RC) tests and internal pressure testing (IP).JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

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

Determination of high temperature material properties of 15-15Ti steel by small specimen techniques

This report presents the final results from the round robin test program on thin-walled cladding tubes in the EERA-JPNM pilot project TASTE. The test methods and assessment procedures used for the assessment of 15-15Ti steel are presented in a previous TASTE report 1. In this report the test results from different test types are assessed, compared and evaluated. The collation of results, mainly on tensile properties shows good agreement between tests methods. An open question remains if there is some anisotropy between the axial and the hoop direction of the tubes. Results from ring tension indicate lower strength values than the test performed in the axial direction. However, the ring tension calculated estimates do not take bending and friction into account. Tensile strength estimates from miniature Small punch tests samples (3 mm in diameter and 0.25 mm thick) indicate no anisotropy whereas tests on the full wall thickness (0.45 mm) with larger puncher balls indicate a reduction towards the INR measured tensile strength (Ring Tension) in the hoop direction. The ring compression test estimates based on calibration at room temperature by ENEA showed surprisingly good performance in estimating the tensile strength at higher temperatures despite the complex stress distribution for this type of test. The few tests performed for determining creep properties, i.e. small punch creep tests, were not successful in describing the expected creep properties. The SPC specimen (as was the case for some SP "tensile test") showed premature cracking at a very early stage of the test for the cold worked material. As a whole it seems that the different types of tests complement each other and together gives an overall picture of the strength and ductility of the tube material. The classical tests such as the ring compression test and the ring tension test gave good estimates on the hoop strength whereas the small punch tests seemingly give an estimate for the weaker direction.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes