Fish swimming kinematics in a turbulent wake: to spill or not to spill?

Due to the complex nature of fish-environment interactions, the effects of altered flow conditions on fish habitats and behaviour, particularly near obstructions, are not yet fully understood. Many hydro-engineering structures generate three-dimensional turbulent structures that differ in properties from naturally occurring ones, and are challenging to fish movement. Here, swimming stability and habitat usage of Nile tilapia (Oreochromis niloticus) were examined in the turbulent wake of a horizontally oriented cylinder (50 mm diameter, D) for a series of increasing cylinder Reynolds numbers (Red). Velocity statistics showed that the near wake downstream of the cylinder within a 2D distance had higher magnitudes of longitudinal, vertical and lateral velocity components as well as Reynolds stresses, turbulence intensity and turbulent kinetic energy than the remaining wake flow field. Flow accelerating over the cylinder top and underside generated two shear horizontal layers, where two coherent structures were formed due to the shear layer breakdown off the cylinder’s walls and alternating von Karman-type vortex shedding occurred in the wake of the cylinder. The eddy symmetry and vorticity off the cylinder’s edges was dependent on Red. The recorded total number of spills, defined as loss of balance, was inversely proportional to fish length and weight, and depended on proximity to the cylinder and the flume bed. Furthermore, the frequency of spills was closely linked to the orientation of vortices and magnitude of Reynolds stresses, suggesting that these parameters may govern the swimming stability of fishes. This information may be used to inform the design of fish-friendly obstacles including hydraulic structures and hydro turbines in riverine and estuarine systems

Dynamical Bonding Driving Mixed Valency in a Metal Boride

Samarium hexaboride is an anomaly, having many exotic and seemingly mutually incompatible properties. It was proposed to be a mixed-valent semiconductor, and later - a topological Kondo insulator, and yet has a Fermi surface despite being an insulator. We propose a new and unified understanding of SmB$_6$ centered on the hitherto unrecognized dynamical bonding effect: the coexistence of two Sm-B bonding modes within SmB$_6$, corresponding to different oxidation states of the Sm. The mixed valency arises in SmB$_6$ from thermal population of these distinct minima enabled by motion of B. Our model simultaneously explains the thermal valence fluctuations, appearance of magnetic Fermi surface, excess entropy at low temperatures, pressure-induced phase transitions, and related features in Raman spectra and their unexpected dependence on temperature and boron isotope

Modeling abstinence education effectiveness

Background: Controversy about the effectiveness of abstinence education has posed troubling dilemmas for everyone involved in this area of study. Strident statements about the lack of efficacy of abstinence education have approached the level of bitter ideology. One remedy to lessen this focus on ideology is to provide a broader analysis of program efforts. Method: This paper provides an innovative analysis of a community-based abstinence education program that encompassed multiple schools across several counties that includes thousands of students. The design addressed many deficits in published studies; it used hierarchical linear modeling to remedy the design flaws of a simple pretest-posttest analysis. Results: Pretests were the principal predictors of posttest scores. Gender was also a significant predictor of posttest scores. Age however was not a significant predictor. An interaction between gender and age was a significant predictor although a three-way interaction of gender x age x race was not. Conclusion: Implications for the findings are stated with recommendations for further research

Microrheology with optical tweezers: data analysis

We present a data analysis procedure that provides the solution to a long-standing issue in microrheology studies, i.e. the evaluation of the fluids' linear viscoelastic properties from the analysis of a finite set of experimental data, describing (for instance) the time-dependent mean-square displacement of suspended probe particles experiencing Brownian fluctuations. We report, for the first time in the literature, the linear viscoelastic response of an optically trapped bead suspended in a Newtonian fluid, over the entire range of experimentally accessible frequencies. The general validity of the proposed method makes it transferable to the majority of microrheology and rheology techniques

Judgements of Solomon: anxieties and defences of social workers involved in care proceedings

Evidence from focus group discussions with social workers in child care and child protection was collected for a research project exploring decision-making in care proceedings and seeking a better understanding of the causes of delay in the process. Here this material is used to examine social workers’ feelings about their work and to explore the anxieties they expressed. Isabel Menzies’s work on containing anxiety in institutions is used to provide a conceptual framework for thinking about the ways in which individuals’ unconscious defences against anxiety may affect the structure, policies and practices of the organization in which they work. It is suggested that this dimension needs to be taken into account in understanding difficulties which arise in putting policy into practice

New results on q-positivity

In this paper we discuss symmetrically self-dual spaces, which are simply real vector spaces with a symmetric bilinear form. Certain subsets of the space will be called q-positive, where q is the quadratic form induced by the original bilinear form. The notion of q-positivity generalizes the classical notion of the monotonicity of a subset of a product of a Banach space and its dual. Maximal q-positivity then generalizes maximal monotonicity. We discuss concepts generalizing the representations of monotone sets by convex functions, as well as the number of maximally q-positive extensions of a q-positive set. We also discuss symmetrically self-dual Banach spaces, in which we add a Banach space structure, giving new characterizations of maximal q-positivity. The paper finishes with two new examples.Comment: 18 page