Putting hydrodynamic interactions to work: tagged particle separation

Separation of magnetically tagged cells is performed by attaching markers to a subset of cells in suspension and applying fields to pull from them in a variety of ways. The magnetic force is proportional to the field gradient, and the hydrodynamic interactions play only a passive, adverse role. Here we propose using a homogeneous rotating magnetic field only to make tagged particles rotate, and then performing the actual separation by means of hydrodynamic interactions, which thus play an active role. The method, which we explore here theoretically and by means of numerical simulations, lends itself naturally to sorting on large scales.Comment: Version accepted for publication - Europhysics Letter

Effect of Control Mode and Test Rate on the Measured Fracture Toughness of Advanced Ceramics

The effects of control mode and test rate on the measured fracture toughness of ceramics were evaluated by using chevron-notched flexure specimens in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% (statistically insignificant) variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or crack mouth opening displacement (CMOD) control gave approx. 5% (statistically significant) variation over a very wide range of rates (1 to 80 m/m/s), with the measurements being a function of rate. However, the rate effect was eliminated by use of dry nitrogen, implying a stress corrosion effect rather than a stability effect. With the use of a nitrogen environment during strain controlled tests, fracture toughness values were within about 1% over a wide range of rates (1 to 80 micons/m/s). CMOD or strain control did allow stable crack extension well past maximum force, and thus is preferred for energy calculations. The effort is being used to confirm recommendations in ASTM Test Method C1421 on fracture toughness measurement

Effects of Aqueous Solutions on the Slow Crack Growth of Soda-Lime-Silicate Glass

The slow crack growth (SCG) parameters of soda-lime-silicate were measured in distilled and saltwater of various concentrations in order to determine if the presence of salt and the contaminate formation of a weak sodium film affects stress corrosion susceptibility. Past research indicates that solvents affect the rate of crack growth; however, the effects of salt have not been studied. The results indicate a small but statistically significant effect on the SCG parameters A and n at high concentrations; however, for typical engineering purposes, the effect can be ignored

Effect of Control Mode and Test Rate on Fracture Toughness of Advanced Ceramics

The effects of control mode and rate on the fracture toughness of ceramics were measured by using chevron-notched flexure specimen in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or CMOD control gave ~5% variation over a very wide range of rates, with the measurements being a function of rate. However, the effect was eliminated by use of dry nitrogen, implying a stress corrosion effect rather than a stability effect. With the use of nitrogen for strain control, fracture toughness values were within about 1% over a wide range of rates (1 to 80 /s). CMOD or strain control did allow stable crack extension well past maximum load, and thus is preferred for energy calculations. The effort is being used to confirm recommendations in ASTM International standard C1421 on fracture toughness measurement

Investigating routes toward atomic layer deposition of silicon carbide: Ab initio screening of potential silicon and carbon precursors

Silicon carbide (SiC) is a promising material for electronics due to its hardness, and ability to carry high currents and high operating temperature. SiC films are currently deposited using chemical vapor deposition (CVD) at high temperatures 1500–1600 °C. However, there is a need to deposit SiC-based films on the surface of high aspect ratio features at low temperatures. One of the most precise thin film deposition techniques on high-aspect-ratio surfaces that operates at low temperatures is atomic layer deposition (ALD). However, there are currently no known methods for ALD of SiC. Herein, the authors present a first-principles thermodynamic analysis so as to screen different precursor combinations for SiC thin films. The authors do this by calculating the Gibbs energy ΔGΔG of the reaction using density functional theory and including the effects of pressure and temperature. This theoretical model was validated for existing chemical reactions in CVD of SiC at 1000 °C. The precursors disilane (Si2H6), silane (SiH4), or monochlorosilane (SiH3Cl) with ethyne (C2H2), carbontetrachloride (CCl4), or trichloromethane (CHCl3) were predicted to be the most promising for ALD of SiC at 400 °C

Veterinary Conduct and Animal Welfare

This paper is a lecture presented to the same Association but fifteen years later: the 131st Annual Congress in 1984. This second presentation contemplates two points: First, it tries to indicate how this criticism has gradually emerged and a historical outline is put forth of the development of veterinary medicine, a differentiation being made between a mythical, a technical, and a critical approach. Second, a discussion of how veterinarians have to associate themselves with this criticism in their professional conduct is presented. This discussion is necessary for two reasons. Veterinarians have increasingly become aware that they bear a professional responsibility not only for animal health but also for animal welfare; and, veterinarians are expected to give their views in concrete situations

Temporally disordered Ising models

We present a study of the influence of different types of disorder on systems in the Ising universality class by employing both a dynamical field theory approach and extensive Monte Carlo simulations. We reproduce some well known results for the case of quenched disorder (random temperature and random field), and analyze the effect of four different types of time-dependent disorder scarcely studied so far in the literature. Some of them are of obvious experimental and theoretical relevance (as for example, globally fluctuating temperatures or random fields). All the predictions coming from our field theoretical analysis are fully confirmed by extensive simulations in two and three dimensions, and novel qualitatively different, non-Ising transitions are reported. Possible experimental setups designed to explore the described phenomenologies are also briefly discussed.Comment: Submitted to Phys. Rev. E. Rapid Comm. 4 page

Single Color Centers Implanted in Diamond Nanostructures

The development of materials processing techniques for optical diamond nanostructures containing a single color center is an important problem in quantum science and technology. In this work, we present the combination of ion implantation and top-down diamond nanofabrication in two scenarios: diamond nanopillars and diamond nanowires. The first device consists of a 'shallow' implant (~20nm) to generate Nitrogen-vacancy (NV) color centers near the top surface of the diamond crystal. Individual NV centers are then isolated mechanically by dry etching a regular array of nanopillars in the diamond surface. Photon anti-bunching measurements indicate that a high yield (>10%) of the devices contain a single NV center. The second device demonstrates 'deep' (~1\mu m) implantation of individual NV centers into pre-fabricated diamond nanowire. The high single photon flux of the nanowire geometry, combined with the low background fluorescence of the ultrapure diamond, allows us to sustain strong photon anti-bunching even at high pump powers.Comment: 20 pages, 7 figure