Thermocapillary effects in driven dewetting and self-assembly of pulsed laser-irradiated metallic films

In this paper the lubrication-type dynamical model is developed of a molten, pulsed laser-irradiated metallic film. The heat transfer problem that incorporates the absorbed heat from a single beam or interfering beams is solved analytically. Using this temperature field, we derive the 3D long-wave evolution PDE for the film height. To get insights into dynamics of dewetting, we study the 2D version of the evolution equation by means of a linear stability analysis and by numerical simulations. The stabilizing and destabilizing effects of various system parameters, such as the peak laser beam intensity, the film optical thickness, the Biot and Marangoni numbers, etc. are elucidated. It is observed that the film stability is promoted for such parameters variations that increase the heat production in the film. In the numerical simulations the impacts of different irradiation modes are investigated. In particular, we obtain that in the interference heating mode the spatially periodic irradiation results in a spatially periodic film rupture with the same, or nearly equal period. The 2D model qualitatively reproduces the results of the experimental observations of a film stability and spatial ordering of a re-solidified nanostructures

Instability and spatiotemporal rheochaos in a shear-thickening fluid model

We model a shear-thickening fluid that combines a tendency to form inhomogeneous, shear-banded flows with a slow relaxational dynamics for fluid microstructure. The interplay between these factors gives rich dynamics, with periodic regimes (oscillating bands, travelling bands, and more complex oscillations) and spatiotemporal rheochaos. These phenomena, arising from constitutive nonlinearity not inertia, can occur even when the steady-state flow curve is monotonic. Our model also shows rheochaos in a low-dimensional truncation where sharply defined shear bands cannot form

Detailed modeling and analysis of spacecraft plume/ionosphere interactions in low Earth orbit

Detailed direct simulation Monte Carlo/particle‐in‐cell simulations involving the interaction of spacecraft thruster plumes with the rarefied ambient ionosphere are presented for steady thruster firings in low Earth orbit (LEO). A nominal mass flow rate is used to prescribe the rocket exit conditions of a neutral propellant species for use in the simulations. The charge exchange interactions of the steady plume with the rarefied ionosphere are modeled using a direct simulation Monte Carlo/particle‐in‐cell methodology, allowing for a detailed assessment of nonequilibrium collisional and plasma‐related phenomena relevant for these conditions. Results are presented for both ram‐ and wake‐flow configurations, in which the thrusters are firing into (ram) or in the direction of (wake) the free stream ionosphere flow in LEO. The influence of the Earth's magnetic field on the development of the ion plume is also examined for three different field strengths: two limiting cases in which B →0 and B → ∞ , and the LEO case in which B =0.5 Gs. The magnetic field is found to have a substantial impact on the resulting neutral and ion plumes, and the gyroscopic motion of the magnetized ions results in a broadening of the ion energy distribution functions. The magnetic field model also incorporates a cross‐field diffusion mechanism which is shown to increase the current density sampled far from the thruster. Key Points Particle‐based model for plume/ionosphere interactions Charge‐exchange reactions modeled using detailed DCS/TCS data B ‐field has a strong influence on the development of plumesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106930/1/jgra50833.pd

Clinical assessment of gestational age in the newborn

The scoring method of Dubowitz et al. was used for the assessment of gestational age in 100 newborn Cape Colored infants. The accuracy of prediction of gestational age by this method was confirmed.Publishers' Versio

The distinction between gastric ulceration and carcinoma of the stomach : value of the erythrocyte sedimentation rate and the maximal acid output

CITATION: Bock, O. A. A. & Boyd, I. H. 1973. The distinction between gastric ulceration and carcinoma of the stomach : value of the erythrocyte sedimentation rate and the maximal acid output. South African Medical Journal, 47(29):1259-1260.The original publication is available at http://www.samj.org.zaThe erythrocyte sedimentation rate (ESR) is not a reliable criterion for distinguishing between gastric ulceration and carcinoma of the stomach. If the maximal acid output (MAO) = 0 mEq/h, the lesion is, with few exceptions, a carcinoma. Combining the ESR and MAO did not provide a more reliable criterion for distinguishing between gastric ulcer and carcinoma of the stomach, than when MAO alone is taken into consideration.Publisher’s versio

Distance measures to compare real and ideal quantum processes

With growing success in experimental implementations it is critical to identify a "gold standard" for quantum information processing, a single measure of distance that can be used to compare and contrast different experiments. We enumerate a set of criteria such a distance measure must satisfy to be both experimentally and theoretically meaningful. We then assess a wide range of possible measures against these criteria, before making a recommendation as to the best measures to use in characterizing quantum information processing.Comment: 15 pages; this version in line with published versio

Discussion quality diffuses in the digital public square

Studies of online social influence have demonstrated that friends have important effects on many types of behavior in a wide variety of settings. However, we know much less about how influence works among relative strangers in digital public squares, despite important conversations happening in such spaces. We present the results of a study on large public Facebook pages where we randomly used two different methods--most recent and social feedback--to order comments on posts. We find that the social feedback condition results in higher quality viewed comments and response comments. After measuring the average quality of comments written by users before the study, we find that social feedback has a positive effect on response quality for both low and high quality commenters. We draw on a theoretical framework of social norms to explain this empirical result. In order to examine the influence mechanism further, we measure the similarity between comments viewed and written during the study, finding that similarity increases for the highest quality contributors under the social feedback condition. This suggests that, in addition to norms, some individuals may respond with increased relevance to high-quality comments.Comment: 10 pages, 6 figures, 2 table

Spacecraft plume interactions with the magnetosphere plasma environment in geostationary Earth orbit

Particle‐based kinetic simulations of steady and unsteady hydrazine chemical rocket plumes are presented in a study of plume interactions with the ambient magnetosphere in geostationary Earth orbit. The hydrazine chemical rocket plume expands into a near‐vacuum plasma environment, requiring the use of a combined direct simulation Monte Carlo/particle‐in‐cell methodology for the rarefied plasma conditions. Detailed total and differential cross sections are employed to characterize the charge exchange reactions between the neutral hydrazine plume mixture and the ambient hydrogen ions, and ion production is also modeled for photoionization processes. These ionization processes lead to an increase in local plasma density surrounding the spacecraft owing to a partial ionization of the relatively high‐density hydrazine plume. Results from the steady plume simulations indicate that the formation of the hydrazine ion plume are driven by several competing mechanisms, including (1) local depletion and (2) replenishing of ambient H+ ions by charge exchange and thermal motion of 1 keV H+ from the ambient reservoir, respectively, and (3) photoionization processes. The self‐consistent electrostatic field forces and the geostationary magnetic field have only a small influence on the dynamics of the ion plume. The unsteady plume simulations show a variation in neutral and ion plume dissipation times consistent with the variation in relative diffusion rates of the chemical species, with full H2 dissipation (below the ambient number density levels) approximately 33 s after a 2 s thruster burn.Key PointsSpacecraft hydrazine plume interacts with GEO via charge exchange and photoionization processesMagnetized hydrazine ion plumes envelop spacecraft, and neutral plumes convect downstreamIon and neutral plume dissipation times longer and species‐dependentPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135463/1/jgra52433_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135463/2/jgra52433.pd

Bounds on Heavy-to-Heavy Mesonic Form Factors

We provide upper and lower bounds on the form factors for B -> D, D^* by utilizing inclusive heavy quark effective theory sum rules. These bounds are calculated to leading order in Lambda_QCD/m_Q and alpha_s. The O(alpha_s^2 beta_0) corrections to the bounds at zero recoil are also presented. We compare our bounds with some of the form factor models used in the literature. All the models we investigated failed to fall within the bounds for the combination of form factors (omega^2 - 1)/(4 omega)|omega h_{A2}+h_{A3}|^2.Comment: 27 pages, 10 figure

The effect of composition on the mechanism of stress-corrosion cracking of titanium alloys in nitrogen tetroxide, and aqueous and hot- salt environments Annual summary report, 1 May 1967 - 30 Apr. 1968

Stress corrosion data for titanium alloys in aqueous, hot salt, and nitrogen dioxide environment