Numerical Simulation of Droplet Impact on Patterned Surfaces

This work presents numerical simulation results for molten nickel and zirconia (YZS) droplets impacting on different microscale-patterned surfaces of silicon. The numerical simulation clearly showed the effect of surface roughness and solidification on the shape of the final splat, as well as the pore creation beneath the sprayed material. Simulations were performed using computational fluid dynamic software, SimDrop. The code uses a three-dimensional finite-difference algorithm solving the full Navier-Stokes equation, including heat transfer and phase change. A volume of fluid (VOF) tracking algorithm is used to track the droplet-free surface. Thermal contact resistance at the droplet-substrate interface is also included in the model. Specific attention is paid to the simulation of droplet impact under plasma spraying conditions. Droplet sizes ranged from 15 to 60 microns with initial velocities of 70-250 m/s. Substrate surfaces were patterned with regular arrays of cubes 1-3 μm high, spaced either 1 μm or 5 μm from each other. Different splat morphologies produced by simulations are compared with those obtained from the experiment conducted under the same impact and surface conditions. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Effect of Droplet Characteristics and Substrate Surface Topography on the Final Morphology of Plasma-Sprayed Zirconia Single Splats

The morphology of atmospheric plasma-sprayed yttria-stabilized zirconia single splats has been studied. Single splats of plasma-sprayed ZrO₂-7%Y₂O₃ powder have been collected on polished stainless steel substrates kept at three different temperatures (room temperature, 300 °C, and 600 °C). The effect of heating on the substrates’ surface topography was evaluated. The effects of spray process parameters such as substrate temperature, particle temperature, and velocity on the morphology of single splats was studied. Variation of splat shape with location within the footprint of plasma spray was investigated. Pore and microcrack formation, splashing behavior, splat/substrate, and splat/splat interfaces were analyzed. Splat morphology and diameter, satellite particles, and splashing behavior were recorded using both scanning electron microscopy and image analysis. Splat/substrate and splat/splat interfaces were studied from cross sections prepared by focused ion beam milling. Results showed primarily disk-shape morphology and no evidence of delamination along the splat/substrate interface at 600 °C substrate temperature. Overlapped splats showed evidence of melting (microwelding) at splat boundaries. Splat thickness was measured to be less than 1 μm for all spray conditions.     

Teravolt-per-meter beam and plasma fields from low-charge femtosecond electron beams

Recent initiatives in ultra-short, GeV electron beam generation have been aimed at achieving sub-femtosecond (fs) pulses capable of driving X-ray free-electron lasers (FELs) in single-spike mode. This scheme foresees the use of very low charge beams, which may allow existing FEL injectors to produce few-100 as pulses, with very high brightness. Towards this end, recent experiments at SLAC have produced ∼2 fs rms, low transverse emittance, 20 pC electron pulses. Here we examine the use of such pulses to excite plasma wakefields exceeding 1 TV/m, permitting a table-top TeV accelerator. We present a scheme for focusing the beam to very small dimensions, where the surface Coulomb fields are also at the TV/m level. These conditions access a new regime for high field for atomic physics, allowing frontier atomic physics experiments such as barrier suppression regime ionization. They also, critically, permit well-sub-fs plasma formation for subsequent wake excitation. We examine the use of such ultra-short beams for creating coherent sub-cycle IR radiation at unprecedented high power levels.     

RF properties of a X-band hybrid photoinjector

An INFN-LNF/UCLA/SAPIENZA collaboration is developing a hybrid photoinjector in X-band. A hybrid photoinjector is a novel high brightness electron source that couples a standing wave cell cavity (acting as an RF gun) directly to a multi-cell travelling-wave structure. This configuration offers a number of advantages over the split standing wave/travelling-wave system. Most notably the reflected RF transient is almost completely suppressed, thus eliminating the need for a circulator and the bunch lengthening effect that occurs in the drift section of the split system. These properties allow scaling of the device to higher field and frequencies, which should dramatically improve beam brightness. The RF coupling between the standing and the traveling wave sections is accomplished in the fourth cell encountered by the beam, with the SW section electrically coupled to it on-axis. This mode of coupling is particularly advantageous, as it is accompanied by a 90° phase shift in the accelerating field, resulting in strong velocity bunching effects on the beam that reverse the usual bunch lengthening induced after the gun exit in standard 1.6 cell photoinjectors. In this scenario, from the beam dynamics point of view, it is seen that device may produce ten's of femtosecond beams at ∼3.5 MeV and the emittance compensation dynamics remains manageable even in the presence of strong compression. We present here a survey of the device characteristics. In particular we show the results of the electromagnetic simulations, a beam dynamics analysis related to the temperature tuning of the SW and TW section, and a RF characterization using bead pull and scattering coefficient measurements of a device prototype.     

Submicrometric lipobead-based fluorescence sensors for chloride ion measurements in aqueous solution

This paper describes the preparation and optimization of the analytical properties of fluorescence-based submicrometric chloride ion sensing lipobeads. Fluorescence sensing lipobeads are polystyrene nanoparticles that are coated with a phospholipid membrane that contains a fluorescent indicator for a targeted analyte. In this study, the halide-specific fluorescence dye, lucigenin, was immobilized into the phospholipid membrane of the lipobeads to enable chloride ion detection. The fluorescence intensity of lucigenin decreases with increasing chloride ion concentration due to dynamic quenching. Lipobeads that contained only lucigenin were ineffective as chloride ion sensors due to poor partition of the water-soluble lucigenin molecules into the phospholipid membrane and high leakage rate of immobilized lucigenin molecules to the aqueous solution. To stabilize the chloride ion sensing lipobeads we coimmobilized hexadecanesulfonate molecules into the phospholipid membrane. The formation of ion pairs between hexadecanesulfonate and lucigenin decreased the hydrophilicity of the dye, increased its partition rate into the membrane, increased the brightness of the particles, and significantly decreased the leakage rate of the hydrophobic ion pair from the membrane to the solution. To further improve their chloride ion sensitivity, we also immobilized the chloride ionophore [9] mercuracarborand-3 into the lipobead membrane. The study resulted in a unique submicrometric chloride ion sensor, which is suitable for chloride ion measurements in biological fluids.     

Homeland security

Trends & Controversies this issue grows out of a panel discussion at the 2005 AAAI Spring Symposium on Al Technologies and Homeland Security, held at Stanford University in March 2005. Robert Popp, who gave the keynote speech at the symposium, describes a DARPA initiative for dealing with the 21st-century strategic threat triad: failed states, global terrorism, and weapons of mass destruction proliferation. George Cybenko presents a philosophical/strategic viewpoint on national security. K.A. Taipale discusses policy implications of using trusted systems for counterterrorism security and how risk management, decision heuristics, and the presumption of innocence relate to such systems. Latanya Sweeney proposes privacy-aware technology (selective revelation) that allows data about people to be shared for surveillance purposes while protecting their privacy. Paul Rosenzweig points out two major changes in privacy protection in the post-9/11 era: the broadening of the approach to generating privacy policy/rules from a purely top-down process to one that includes a bottom-up component in which privacy is protected through institutional oversight, and a change from a focus on rules to a focus on results. These five articles present a snapshot of the complex interactions between information security and privacy. A comprehensive understanding of such interactions is critical for developing solutions, whether they are technological solutions, political solutions, or both.     

Some implicit common factors in diverse methods of psychotherapy.

This article is a republication of a classic paper in which Rosenzweig introduced the concept of common factors in psychotherapy. This seminal idea-which refers to the finding that all forms of psychotherapy seem to share, to some degree, a small number of effective change ingredients-remains highly influential in psychotherapy integration today. Rosenzweig reviewed the data presented by then current forms of psychotherapy and argued that the theories that describe the change principles in each psychotherapy are inadequate to capture those deeper common factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Damping-limited modulation bandwidths up to 40 GHz in undoped short-cavity In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers

We demonstrate record direct modulation bandwidths from MBE-grown In/sub 0.35/Ga/sub 0.65/As-GaAs multiple-quantum-well lasers with undoped active regions and with the upper and lower cladding layers grown at different growth temperatures. Short-cavity ridge waveguide lasers achieve CW direct modulation bandwidths up to 40 GHz for 6/spl times/130 /spl mu/m/sup 2/ devices at a bias current of 155 mA, which is the damping limit for this structure. We further demonstrate large-signal digital modulation up to 20 Gb/s (limited by the measurement setup) and linewidth enhancement factors of 1.4 at the lasing wavelength at threshold of /spl sim/1.1 /spl mu/m for these devices.     

Fluorescence-based zinc ion sensor for zinc ion release from pancreatic cells

In this paper, we describe the synthesis and characterization of analytical properties of fluorescence-based zinc ion-sensing glass slides and their application in monitoring zinc ion release from beta pancreatic cells in cell cultures. To fabricate the sensors, the zinc ion indicator ZnAF-2 {6-[N-[N',N'-bis(2-pyridinylmethyl)-2-aminoethyl]amino-3',6'-dihydroxyspiro[isobenzofuran-1(3H),9'-[9H]xanthene]-3-one} was modified to include a sufficiently long linking aliphatic chain with a terminal carboxyl functional group. The recently synthesized ZnAF-2 zinc ion indicator provided high zinc ion selectivity in physiological solutions containing millimolar levels of calcium and other possible interfering cations. The carboxyl-modified ZnAF-2 was conjugated to the activated surface of glass slides, which then served as zinc ion sensors. It was possible to grow pancreatic cells directly on the zinc-sensing glass slide or on a membrane placed on these glass slides. The sensors were used to monitor zinc ion release events from glucose-stimulated pancreatic cells. The study showed that the zinc ion sensors responded effectively to the release of zinc ions from pancreatic cells at the nanomolar level with high selectivity and rapid subsecond response time.