Thickness of the rim of an expanding lamella near the splash threshold

The evolution of the ejected liquid sheet, or lamella, created after impact of a liquid drop onto a solid surface is studied using high-speed video in order to observe the detailed time evolution of the thickness of the rim of the lamella. Since it has been suggested that splashing behavior is set at very early times after impact, we study early times up to D-0/U-0, where D-0 and U-0 are the diameter and speed of the impacting drop, respectively, for different liquid viscosities and impact speeds below the splashing threshold. Within the regime of our experiments, our results are not consistent with the idea that the lamella rim grows similar to the boundary layer thickness. Rather, we find that the rim thickness is always much larger than the boundary layer thickness, and that the rim thickness decreases with increasing impact speed. For lower impact speeds, the increase in the rim thickness is consistent with a root t response over the limited time range available, but the dependence is not simply proportional to root nu, where nu is the kinematic viscosity, and there is a strong dependence of the rim thickness on the impact speed U-0. Scaling of the rim height using a balance of inertial and surface tension forces provides some collapse of the data at lower impact speeds. We also observe an unusual plateau behavior in thickness versus time at higher impact speeds as we approach the splash threshold. (C) 2010 American Institute of Physics. [doi:10.1063/1.3313360

Electrical and radiation characteristics of semilarge photoconductive terahertz emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry

NEUTRON SPECTRA MEASUREMENTS

Thermal neutron spectra were measured with timeof-flight techniques. Spectra were obtained for pure water and for a nearly homogeneous subcritical assembly where the ratio of themal absorption to high energy scattering cross section was t 125, 150, 175 0.3. For each medium, spectra were measured at 298 and 586 K. The experimental results are presented and compared with calculated theoretical spectra The agreement between theory and experiment is excellent for the multiplying media. On the basis of this agreement, one concludes that chemical binding effects in light water play a negligible role in determining the equllibrium neutron spectrum in water assemblies. (auth

Modeling the potential impact of changing access rates to specialist treatment for alcohol dependence for local authorities in England: The Specialist Treatment for Alcohol Model (STreAM)

OBJECTIVE: We modeled the impact of changing Specialist Treatment Access Rates to different treatment pathways on the future prevalence of alcohol dependence, treatment outcomes, service capacity, costs, and mortality. METHOD: Local Authority numbers and the prevalence of people "potentially in need of assessment for and treatment in specialist services for alcohol dependence" (PINASTFAD) are estimated by mild, moderate, severe, and complex needs. Administrative data were used to estimate the Specialist Treatment Access Rate per PINASTFAD person and classify 22 different treatment pathways. Other model inputs include natural remission, relapse after treatment, service costs, and mortality rates. "What-if" analyses assess changes to Specialist Treatment Access Rates and treatment pathways. Model outputs include the numbers and prevalence of people who are PINASTFAD, numbers treated by 22 pathways, outcomes (successful completion with abstinence, successfully moderated nonproblematic drinking, re-treatment within 6 months, dropout, transfer, custody), mortality rates, capacity requirements (numbers in contact with community services or staying in residential or inpatient places), total treatment costs, and general health care savings. Five scenarios illustrate functionality: (a) no change, (b) achieve access rates at the 70th percentile nationally, (c) increase access by 25%, (d) increase access to Scotland rate, and (e) reduce access by 25%. RESULTS: At baseline, 14,581 people are PINASTFAD (2.43% of adults) and the Specialist Treatment Access Rate is 10.84%. The 5-year impact of scenarios on PINASTFAD numbers (vs. no change) are (B) reduced by 191 (-1.3%), (C) reduced by 477 (-3.3%), (D) reduced by almost 2,800 (-19.2%), and (E) increased by 533 (+3.6%). The relative impact is similar for other outputs. CONCLUSIONS: Decision makers can estimate the potential impact of changing Specialist Treatment Access Rates for alcohol dependence

Heliospheric Transport of Neutron-Decay Protons

We report on new simulations of the transport of energetic protons originating from the decay of energetic neutrons produced in solar flares. Because the neutrons are fast-moving but insensitive to the solar wind magnetic field, the decay protons are produced over a wide region of space, and they should be detectable by current instruments over a broad range of longitudes for many hours after a sufficiently large gamma-ray flare. Spacecraft closer to the Sun are expected to see orders-of magnitude higher intensities than those at the Earth-Sun distance. The current solar cycle should present an excellent opportunity to observe neutron-decay protons with multiple spacecraft over different heliographic longitudes and distances from the Sun.Comment: 12 pages, 4 figures, to be published in special issue of Solar Physic

The Basics of Water Waves Theory for Analogue Gravity

This chapter gives an introduction to the connection between the physics of water waves and analogue gravity. Only a basic knowledge of fluid mechanics is assumed as a prerequisite.Comment: 36 pages. Lecture Notes for the IX SIGRAV School on "Analogue Gravity", Como (Italy), May 201

Magneto-transport in periodic and quasiperiodic arrays of mesoscopic rings

We study theoretically the transmission properties of serially connected mesoscopic rings threaded by a magnetic flux. Within a tight-binding formalism we derive exact analytical results for the transmission through periodic and quasiperiodic Fibonacci arrays of rings of two different sizes. The role played by the number of scatterers in each arm of the ring is analyzed in some detail. The behavior of the transmission coefficient at a particular value of the energy of the incident electron is studied as a function of the magnetic flux (and vice versa) for both the periodic and quasiperiodic arrays of rings having different number of atoms in the arms. We find interesting resonance properties at specific values of the flux, as well as a power-law decay in the transmission coefficient as the number of rings increases, when the magnetic field is switched off. For the quasiperiodic Fibonacci sequence we discuss various features of the transmission characteristics as functions of energy and flux, including one special case where, at a special value of the energy and in the absence of any magnetic field, the transmittivity changes periodically as a function of the system size.Comment: 9 pages with 7 .eps figures included, submitted to PR

Points in Mental Space: an Interdisciplinary Study of Imagery in Movement Creation

As part of a programme of research that is developing tools to enhance choreographic practice, an interdisciplinary team of cognitive scientists, neuroscientists and dance professionals collaborated on two studies examining the mental representations used to support movement creation. We studied choreographer Wayne McGregor’s approach to movement creation through tasking, in which he asks dancers to create movement in response to task instructions that require a great deal of mental imagery and decision making. In our first experiment, we used experience sampling methods (self-report scales and reports about the current focus of thought) with the full company of Wayne McGregor | Random Dance to describe what the dancers report thinking about while creating movement, and to establish how their experiences change as a function of different task conditions. In particular, we contrasted a conventional ‘active’ condition (where dancers are free to move around) with a ‘static’ condition (where they have to create movement mentally, without moving), because all neuroimaging studies of dance require participants to lie motionless within a scanner. We adapted the static mode from Experiment 1 for the neuroimaging session in Experiment 2. Here we recorded the brain activity of an experienced dancer from Wayne McGregor | Random Dance while she mentally undertook movement creation tasks similar to those used in our experience sampling experiment. Both studies involved imagery tasks of a primarily spatial-praxic nature (involving an imagined object or volume that could be approached and manipulated) and imagery that focused on content invoking emotional narratives. In the first study, the dancers’ awareness was focused more than they had anticipated upon conceptual rather than physical or bodily aspects. The very act of reflecting on, and categorising, their experiences provided the dancers with insights about their mental habits during innovative movement creation. Such insights provide conditions under which habits can be recognised and then altered to adopt alternative points in mental space from which to create movement material. Providing the dancers and McGregor with a means to communicate more productively about the properties of the task-based instructions has been acknowledged by the company to be of clear benefit and a useful addition to their working process. In the second study we assessed the feasibility of using fMRI to study the neural underpinnings of choreographing movement tasks. The experiment enabled us to compare brain activity in imagery and movement creation. The data raise some key questions Points in Mental Space 3 concerning the mental context in which such thinking occurs and, given the clear limitations of the current fMRI and experience sampling work, how future research might usefully be directed. Taken together, these two exploratory studies indicate that the experiential and neural attributes of imagery during movement creation are open to systematic investigation: innovative movement creation can start from alternative points in mental, as well as physical, space. This enables us to look forward to establishing with greater precision how tasks that challenge dancers in different ways may affect mental and neural processes and how variation in imagery use across dancers might contribute to the variety of movement creation that they produce. Notably, the act of reflecting on the experience of movement creation also offers some practical leverage to help dancers develop a wider range of strategies for innovation. These findings are being used to contribute to further work informing the development of personal, notebook-like, Choreographic Thinking Tools

From chemical gardens to chemobrionics

Chemical gardens in laboratory chemistries ranging from silicates to polyoxometalates, in applications ranging from corrosion products to the hydration of Portland cement, and in natural settings ranging from hydrothermal vents in the ocean depths to brinicles beneath sea ice. In many chemical-garden experiments, the structure forms as a solid seed of a soluble ionic compound dissolves in a solution containing another reactive ion. In general any alkali silicate solution can be used due to their high solubility at high pH. The cation should not precipitate with the counterion of the metal salt used as seed. A main property of seed chemical-garden experiments is that initially, when the fluid is not moving under buoyancy or osmosis, the delivery of the inner reactant is diffusion controlled. Another experimental technique that isolates one aspect of chemical-garden formation is to produce precipitation membranes between different aqueous solutions by introducing the two solutions on either side of an inert carrier matrix. Chemical gardens may be grown upon injection of solutions into a so-called Hele-Shaw cell, a quasi-two-dimensional reactor consisting in two parallel plates separated by a small gap