Instability and dripping of electrified liquid films flowing down inverted substrates

We consider the gravity-driven flow of a perfect dielectric, viscous, thin liquid film, wetting a flat substrate inclined at a nonzero angle to the horizontal. The dynamics of the thin film is influenced by an electric field which is set up parallel to the substrate surface—this nonlocal physical mechanism has a linearly stabilizing effect on the interfacial dynamics. Our particular interest is in fluid films that are hanging from the underside of the substrate; these films may drip depending on physical parameters, and we investigate whether a sufficiently strong electric field can suppress such nonlinear phenomena. For a non-electrified flow, it was observed by Brun et al. [Phys. Fluids 27, 084107 (2015)] that the thresholds of linear absolute instability and dripping are reasonably close. In the present study, we incorporate an electric field and analyze the absolute and convective instabilities of a hierarchy of reduced-order models to predict the dripping limit in parameter space. The spatial stability results for the reduced-order models are verified by performing an impulse-response analysis with direct numerical simulations (DNS) of the Navier–Stokes equations coupled to the appropriate electrical equations. Guided by the results of the linear theory, we perform DNS on extended domains with inflow and outflow conditions (mimicking an experimental setup) to investigate the dripping limit for both non-electrified and electrified liquid films. For the latter, we find that the absolute instability threshold provides an order-of-magnitude estimate for the electric-field strength required to suppress dripping; the linear theory may thus be used to determine the feasibility of dripping suppression given a set of geometrical, fluid, and electrical parameters

Search for axion-like particles using a variable baseline photon regeneration technique

We report the first results of the GammeV experiment, a search for milli-eV mass particles with axion-like couplings to two photons. The search is performed using a "light shining through a wall" technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than 3.1x10^{-7} GeV^{-1} (3.5x10^{-7} GeV^{-1}) in the limit of massless particles.Comment: 5 pages, 4 figures. This is the version accepted by PRL and includes updated limit

Ground state magnetic dipole moment of 35K

The ground state magnetic moment of 35K has been measured using the technique of nuclear magnetic resonance on beta-emitting nuclei. The short-lived 35K nuclei were produced following the reaction of a 36Ar primary beam of energy 150 MeV/nucleon incident on a Be target. The spin polarization of the 35K nuclei produced at 2 degrees relative to the normal primary beam axis was confirmed. Together with the mirror nucleus 35S, the measurement represents the heaviest T = 3/2 mirror pair for which the spin expectation value has been obtained. A linear behavior of gp vs. gn has been demonstrated for the T = 3/2 known mirror moments and the slope and intercept are consistent with the previous analysis of T = 1/2 mirror pairs.Comment: 14 pages, 5 figure

A New Simulation Metric to Determine Safe Environments and Controllers for Systems with Unknown Dynamics

We consider the problem of extracting safe environments and controllers for reach-avoid objectives for systems with known state and control spaces, but unknown dynamics. In a given environment, a common approach is to synthesize a controller from an abstraction or a model of the system (potentially learned from data). However, in many situations, the relationship between the dynamics of the model and the \textit{actual system} is not known; and hence it is difficult to provide safety guarantees for the system. In such cases, the Standard Simulation Metric (SSM), defined as the worst-case norm distance between the model and the system output trajectories, can be used to modify a reach-avoid specification for the system into a more stringent specification for the abstraction. Nevertheless, the obtained distance, and hence the modified specification, can be quite conservative. This limits the set of environments for which a safe controller can be obtained. We propose SPEC, a specification-centric simulation metric, which overcomes these limitations by computing the distance using only the trajectories that violate the specification for the system. We show that modifying a reach-avoid specification with SPEC allows us to synthesize a safe controller for a larger set of environments compared to SSM. We also propose a probabilistic method to compute SPEC for a general class of systems. Case studies using simulators for quadrotors and autonomous cars illustrate the advantages of the proposed metric for determining safe environment sets and controllers.Comment: 22nd ACM International Conference on Hybrid Systems: Computation and Control (2019

Solar Resource Estimation Using a Radiative Transfer with Shading (RTS) Model

A combination of falling technology prices and government financial incentives has led to the rapid expansion of the solar microgeneration industry in the UK and around the world. With conditions for investment becoming more favourable, viability appraisal is now of great interest to potential investors ranging from individuals to large companies and authorities. A methodology to predict solar resource available to solar technologies in urban areas is presented that combines a radiative transfer simulation with shading derived from digital surface model (DSM) data. The radiative transfer simulation includes water vapour, ozone, clouds and surface albedo determined from MODIS satellite products along with aerosol properties that are derived from the GLOMAP model. A DSM is used to calculate the height of near-by obstacles and the horizon from each point of interest to establish when the site is in shade during a year. The site-level radiance field is adjusted by elements in shade and integrated over the view hemisphere of the photovoltaic (PV) panels to take into account panel tilt. Modelled annual global radiation (Wh/m2/a) estimations are validated using power output data from 17 sites across four major UK cities (Bristol, Cambridge, Leeds and Sheffield) and show good agreement with -3.68% and +2.62% mean percentage error under assumed performance ratio conversions of 0.75 and 0.8 respectively. The results are compared to the outputs of both Esri ArcGIS and PVGIS, the first of which predicted annual global radiation with -15.97% and -20.78% mean percentage error with the latter returning +3.34% and +10.23% mean percentage error for the 0.75 and 0.8 performance ratios

A Map-Reduce Parallel Approach to Automatic Synthesis of Control Software

Many Control Systems are indeed Software Based Control Systems, i.e. control systems whose controller consists of control software running on a microcontroller device. This motivates investigation on Formal Model Based Design approaches for automatic synthesis of control software. Available algorithms and tools (e.g., QKS) may require weeks or even months of computation to synthesize control software for large-size systems. This motivates search for parallel algorithms for control software synthesis. In this paper, we present a Map-Reduce style parallel algorithm for control software synthesis when the controlled system (plant) is modeled as discrete time linear hybrid system. Furthermore we present an MPI-based implementation PQKS of our algorithm. To the best of our knowledge, this is the first parallel approach for control software synthesis. We experimentally show effectiveness of PQKS on two classical control synthesis problems: the inverted pendulum and the multi-input buck DC/DC converter. Experiments show that PQKS efficiency is above 65%. As an example, PQKS requires about 16 hours to complete the synthesis of control software for the pendulum on a cluster with 60 processors, instead of the 25 days needed by the sequential algorithm in QKS.Comment: To be submitted to TACAS 2013. arXiv admin note: substantial text overlap with arXiv:1207.4474, arXiv:1207.409

Does mode of administration affect health-related quality-of-life outcomes after stroke?

Telephone interviews and postal surveys may be a resource-efficient way of assessing health-related quality-of-life post-stroke, if they produce data equivalent to face-to-face interviews. This study explored whether telephone interviews and postal surveys of the Stroke and Aphasia Quality of Life Scale (SAQOL-39g) yielded similar results to face-to-face interviews. Participants included people with aphasia and comprised two groups: group one (n =22) were 3-6 months post-stroke; group two (n =26) were ≥1 year post-stroke. They completed either a face-to-face and a telephone interview or a face-to-face interview and a postal survey of the SAQOL-39g. Response rates were higher for group two (87%) than for group one (72-77%). There were no significant differences between respondents and non-respondents on demographics, co-morbidities, stroke severity, or communication impairment. Concordance between face-to-face and telephone administrations (.90-.98) was excellent; and very good-excellent between face-to-face and postal administrations (.84-.96), although scores in postal administrations were lower (significant for psychosocial domain and overall SAQOL-39g in group two). These findings suggest that the SAQOL-39g yields similar results in different modes of administration. Researchers and clinicians may employ alternative modes, particularly in the longer term post-stroke, in order to reduce costs or facilitate clients with access difficulties

Probing shell structure and shape changes in neutron-rich sulfur isotopes through transient-field g factor measurements on fast radioactive beams of 38S and 40S

The shell structure underlying shape changes in neutron-rich nuclei near N=28 has been investigated by a novel application of the transient field technique to measure the first-excited state g factors in 38S and 40S produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The g factor of deformed 40S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.Comment: 10 pages, 6 figures, accepted in PR

Shell structure underlying the evolution of quadrupole collectivity in S-38 and S-40 probed by transient-field g-factor measurements on fast radioactive beams

The shell structure underlying shape changes in neutron-rich nuclei between N=20 and N=28 has been investigated by a novel application of the transient field technique to measure the first-excited state g factors in S-38 and S-40 produced as fast radioactive beams. Details of the new methodology are presented. In both S-38 and S-40 there is a fine balance between the proton and neutron contributions to the magnetic moments. Shell model calculations which describe the level schemes and quadrupole properties of these nuclei also give a satisfactory explanation of the g factors. In S-38 the g factor is extremely sensitive to the occupation of the neutron p3/2 orbit above the N=28 shell gap as occupation of this orbit strongly affects the proton configuration. The g factor of deformed S-40 does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.Comment: 10 pages, 36 figures, accepted for publication in Physical Review