Ultrasonic wave propagation in compounds containing ordered vacancies

The compounds HgTe, Hg(_5)In(_2)□Te(_8), Hg(_3)In(_2)□Te(_6) and Hg(_5)Ga(_2)□Te(_8), Hg(_3)Ga(_2)□Te(_6) constitute a series in which the concentration of vacancies, sited regularly on the lattice, increases progressively from zero. To assess the effect of such vacancies on the mechanical properties, the propagation of 10MHz ultrasonic waves in single crystal samples of each compound has been studied over the temperature range 77 K to room temperature. The large single crystals required for the ultrasonic experiements have been grown, using a modified Bridgman technique, from stoichiometric melts. Single crystal grains within each boule produced, have been identified by the use of polishing, etching and back reflection x-ray techniques. Back reflection x-ray photographs have been used primarily to establish the Laue group of Hg(_3)In(_2)□Te(_6), Hg(_3)Ga(_2)□Te(_6) and Hg(_5)Ga(_2)□ Te(_8), which are shown to be cubic, and to align the samples in the specific direction required by the theory of ultrasonic wave propagation in solids; the│110│axis in a cubic material. The lattice parameter of each of these compounds has been found using Debye-Scherrer powder photographs each of which exhibits a superlattice imposed on the zincblende pattern of lines, because of this Hg(_5)In(_2)□Te(_8)(Hg(_5)Ga(_2)□Te(_8) was indexed using a 2 x 2 x 2 unit cell and Hg(_3)In(_2)□Te(_6)(Hg(_3)Ga(_2)□Te(_6) using 3 x 3 x 3 unit cell. An order-disorder transformation has been observed in quenched samples of the semiconducting compound Hg(_3)In(_2)□Te(_6); extinction of the superlattice lines indicates that a change from an ordered to a disordered state is complete above 595 ± 5 K. This effect has been further investigated by making resistivity, Hall voltage, thermoelectric power and differential thermal analysis measurements through the temperature region of the transition. In each case the order-disorder transformation had a marked effect on the results, especially in the transition region. The elastic constants of each compound have been determined from measurements of the ultrasonic velocity made by the pulse echo technique. These constants show a regular trend through each series, namely that the stiffness decreases as the vacancy concentration increases. In particular, there is a linear relationship between the reduced compressibility and the vacancy concentration. The elastic constants are also used to determine the anisotropy ratio, the Cauchy relationship and those parameters which can be related to interatomic binding such as the force constants of Bern's model, ionicity (Potters relationship) and Debye temperature. Finally, the elastic constant data in conjunction with the mathematical theory for wave propagation in cubic crystals enabled the phase velocity surfaces, and the particle displacement and energy flux vectors to be determined. Attenuation measurements - made over the same temperature range as the elastic constant data - exhibit Bordoni-type relaxation peaks on a background which is probably dominated by a resonance type loss mechanism associated with pinned dislocations. The peaks which occur in the compounds HgTe, Hg(_5)In(_2)□Te(_8) and Hg(_3)In(_2)□Te(_6) are consistent with dislocation motion on the (111) and (110) slip planes. In this series of compounds the activation energies for kink formation and the Peierls stresses, calculated on the basis of the kink nucleation theory, show that dislocation motion becomes easier with increased vacancy concentration and takes place more readily on the (111) slip planes

Prevention work with children disaffected from school: Findings from the evaluation of two innovative community-based projects

Purpose - To report on findings from the evaluation of two innovative community-based prevention projects in the UK targeted at children disaffected from school, one involving football the other horticulture. Design/methodology/ approach - Qualitative inquiry focusing on three areas: "theories of change" underpinning the projects; referral and operational processes; inter-agency partnerships. Main methods were: an interactive event for 50 practitioners; semi-structured interviews with project staff, project participants and other stakeholders; review of project documentation; observations. Findings - Both the projects evaluated had clear and plausible "theories of change". Referral processes were effective. Strong variations in "dosage" and length of project involvement appeared to be linked to differences in the effectiveness of the two projects. Research limitations/implications - The principal limitation to the research was the lack of case monitoring and outcome data that prevented any quantitative assessment of the projects. Further research is needed to establish the long-term impact of this kind of targeted prevention work. Practical implications - Prevention work targeted at children disaffected from school needs to be underpinned by clear "theories of change". Effective work requires good relationships with referring schools, the delivery of multi-faceted interventions and interventions to be of an adequate length. Originality/value - The focus on "theories of change" or mechanisms is an original contribution to the prevention literature. The paper will be valuable for those working in drug action teams and local authorities in planning prevention work for young people. The two projects were highly innovative in involving pupils in two very different activities - football and horticulture. © Emerald Group Publishing Limited

Knudsen gas provides nanobubble stability

We provide a model for the remarkable stability of surface nanobubbles to bulk dissolution. The key to the solution is that the gas in a nanobubble is of Knudsen type. This leads to the generation of a bulk liquid flow which effectively forces the diffusive gas to remain local. Our model predicts the presence of a vertical water jet immediately above a nanobubble, with an estimated speed of $\sim3.3\,\mathrm{m/s}$, in good agreement with our experimental atomic force microscopy measurement of $\sim2.7\,\mathrm{m/s}$. In addition, our model also predicts an upper bound for the size of nanobubbles, which is consistent with the available experimental data

Generation of Busulfan Chimeric Mice for the Analysis of T Cell Population Dynamics

This protocol was developed to generate chimeric mice in which T lymphocytes could be stratified by age on the basis of congenic marker expression. The conditioning drug busulfan is used to ablate host haematopoietic stem cells while leaving the peripheral immune system intact. Busulfan treatment is followed by bone marrow transplantation (BMT), with T-cell depleted donor bone marrow bearing a different congenic marker (CD45.2) to that of the host mouse (CD45.1). New cell production post-BMT can thus be tracked by measuring the fraction of CD45.2^{+} cells over time within a population of interest (Hogan et al., 2015; Gossel et al., 2017)

Surface bubble nucleation phase space

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobised silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this phase space, occurring for gas concentrations of approximately 100-110%. Below the nanobubble phase we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.Comment: 4 pages, 4 figure

Kinetics and mechanism of the interconversion of inverse bicontinuous cubic mesophases

This paper describes time-resolved x-ray diffraction data monitoring the transformation of one inverse bicontinuous cubic mesophase into another, in a hydrated lipid system. The first section of the paper describes a mechanism for the transformation that conserves the topology of the bilayer, based on the work of Charvolin and Sadoc, Fogden and Hyde, and Benedicto and O'Brien in this area. We show a pictorial representation of this mechanism, in terms of both the water channels and the lipid bilayer. The second section describes the experimental results obtained. The system under investigation was 2:1 lauric acid: dilauroylphosphatidylcholine at a hydration of 50% water by weight. A pressure-jump was used to induce a phase transition from the gyroid (Q(II)(G)) to the diamond (Q(II)(D)) bicontinuous cubic mesophase, which was monitored by time-resolved x-ray diffraction. The lattice parameter of both mesophases was found to decrease slightly throughout the transformation, but at the stage where the Q(II)(D) phase first appeared, the ratio of lattice parameters of the two phases was found to be approximately constant for all pressure-jump experiments. The value is consistent with a topology-preserving mechanism. However, the polydomain nature of our sample prevents us from confirming that the specific pathway is that described in the first section of the paper. Our data also reveal signals from two different intermediate structures, one of which we have identified as the inverse hexagonal (H-II) mesophase. We suggest that it plays a role in the transfer of water during the transformation. The rate of the phase transition was found to increase with both temperature and pressure-jump amplitude, and its time scale varied from the order of seconds to minutes, depending on the conditions employed

Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety

Peer reviewedPublisher PD

Age is not just a number: Naive T cells increase their ability to persist in the circulation over time

The processes regulating peripheral naive T-cell numbers and clonal diversity remain poorly understood. Conceptually, homeostatic mechanisms must fall into the broad categories of neutral (simple random birth-death models), competition (regulation of cell numbers through quorum-sensing, perhaps via limiting shared resources), adaptation (involving cell-intrinsic changes in homeostatic fitness, defined as net growth rate over time), or selection (involving the loss or outgrowth of cell populations deriving from intercellular variation in fitness). There may also be stably maintained heterogeneity within the naive T-cell pool. To distinguish between these mechanisms, we confront very general models of these processes with an array of experimental data, both new and published. While reduced competition for homeostatic stimuli may impact cell survival or proliferation in neonates or under moderate to severe lymphopenia, we show that the only mechanism capable of explaining multiple, independent experimental studies of naive CD4+ and CD8+ T-cell homeostasis in mice from young adulthood into old age is one of adaptation, in which cells act independently and accrue a survival or proliferative advantage continuously with their post-thymic age. However, aged naive T cells may also be functionally impaired, and so the accumulation of older cells via 'conditioning through experience' may contribute to reduced immune responsiveness in the elderly