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The advancement of liquid phase electron/ion beam induced deposition has enabled an effective direct-write approach for functional nanostructure synthesis with the possibility of three-dimensional control of morphology. For formation of a metallic solid phase, the process employs ambient temperature, beam-guided, electrochemical reduction of precursor cations, resulting in rapid formation of structures, but with challenges for retention of resolution achievable via slower electron beam approaches. The possibility of spatial control of redox pathways via the use of water–ammonia solvents has opened avenues for improved nanostructure resolution without sacrificing the growth rate. In particular, ammonia enables "electrochemical lensing" in which a tightly confined and highly reducing environment is created locally to enable high resolution, rapid beam-directed nanostructure growth. We demonstrate this unique approach to high resolution synthesis through a combination of analysis and experiment. [ABSTRACT FROM AUTHOR]

This paper presents a complete set of coupled equations that govern the bubble transport in three-dimensional gravity driven flow. The model accounts for bubbles growth or shrinkage due to pressure and temperature changes as well as for multiple gas diffusion in and out of the bubbles but neglects bubble coalescence, break-up, and nucleation. The model applies to glass melting furnaces but it could be extended to other two-phase flow applications such as metal and polymer processings, passive cooling systems, and two-phase flow around naval surface ship. Governing equations are given for the key variables which are, in the present case, (1) the refining agent concentration, (2) the gas species dissolved in the liquid phase, and (3) the bubble radius, gas molar fraction, and density function. The method of solution is discussed and based on the modified method of characteristics.

This paper presents a simple, experimentally validated approach to analyze the transient formation of a foam layer produced by injecting gas bubbles in a foaming solution. Based on experimental observations, three different regimes in the transient growth of the foam have been identified as a function of the superficial gas velocity. A model based on the mass conservation equation for the gas phase in the foam combined with three different models for the average porosity is proposed. It is shown that for practical calculations a constant average porosity equal to 0.82 can be used. The model predictions show very good agreement with experimental data for low superficial gas velocity and provide an upper limit of the foam thickness for intermediate and large superficial gas velocities. The paper discusses the physical mechanisms that may occur during the foam formation and the effects of the superficial gas velocity on the foam dynamics. The present analysis speculates several mechanisms for the bursting of the bubbles at the top of the foams and proposes the framework for more fundamental and detailed studies.

This paper presents an approach for predicting the thickness of isothermal foams produced by blowing gas in a liquid solution under steady-state conditions. The governing equation for the transient foam thickness has been non-dimensionalized, and two dimensionless numbers have been identified to describe the formation and stability of this type of foam: \Pi_1 = {Re}/{Fr} and \Pi_2 = Ca H_{\infty}/r_0. Physical interpretation of the dimensionless numbers has been proposed, a power-law type relation has been assumed between \Pi_1 and \Pi_2 (i.e., \Pi_2=K \Pi^n_1). Experimental data available in the literature have been used to determine the empirical parameters of the correlation K and n. The experimental conditions cover a wide range of viscosity, density, surface tension, gas superficial velocity, and average bubble radius. The model is valid for foams formed from high viscosity liquids bubbled with nitrogen, air, helium, hydrogen, and argon injected through single, multi-orifice nozzles or porous medium. Comparison between the correlation developed and the experimental data yields reasonable agreements (within 35% error), given the broadness of the bubble radius distribution around the mean value, the uncertainty of the experimental data and of the thermophysical properties. Predictions have been found to be very sensitive to the average bubble radius. A more refined model is still needed which should be supported by a careful experimental studies. Finally, suggestions are given to extend the present work to foams generated from low viscosity solutions.

The objective of this paper is to present an engineering model based on fundamentally sound but simplified treatment of mass diffusion phenomena for practical predictions of the effective diffusion coefficient of gases through closed-cell foams. A special attention was paid to stating all assumptions and simplifications that define the range of applicability of the proposed model. The model developed is based on the electrical circuit analogy, and on the first principles. The analysis suggests that the effective diffusion coefficient through the foam can be expressed as a product of the geometric factor and the gas diffusion coefficient through the foam membrane. Validation against experimental data available in the literature gives satisfactory results. Discrepancies between the model predictions and experimental data have been observed for gases with high solubility in the condensed phase for which Henry's law does not apply. Finally, further experimental data concerning both the foam morphology and the diffusion coefficient in the membrane are needed to fully validate the model.

The recent application of inkjet printing to fabrication of three-dimensional, multilayer and multimaterial parts has tested the limits of conventional printing-based additive manufacturing techniques. The novel method presented here, termed as additive manufacturing via microarray deposition (AMMD), expands the allowable range of physical properties of printed fluids to include important, high-viscosity production materials (e.g., polyurethane resins). AMMD relies on a piezoelectrically driven ultrasonic print-head that generates continuous streams of droplets from 45 [micro]m orifices while operating in the 0.5-3.0 MHz frequency range. The device is composed of a bulk ceramic piezoelectric transducer for ultrasound generation, a reservoir for the material to be printed, and a silicon micromachined array of liquid horn structures, which make up the ejection nozzles. Unique to this new printing technique are the high frequency of operation, use of fluid cavity resonances to assist ejection, and acoustic wave focusing to generate the pressure gradient required to form and eject droplets. We present the initial characterization of a micromachined print-head for deposition of fluids that cannot be used with conventional printing-based rapid prototyping techniques. Glycerol-water mixtures with a range of properties (surface tensions of ~58-73 mN/m and viscosities of O. 7-380 mN s/me) were used as representative printing fluids for most investigations. Sustained ejection was observed in all cases. In addition, successful ejection of a urethane-based photopolymer resin (surface tension of ~25-30 mN/ m and viscosity of 900-3000 mN s / m2) was achieved in short duration bursts. Peaks in the ejection quality were found to correspond to predicted device resonances. Based on these results, we have demonstrated the printing of fluids that fall well outside of the accepted range for the previously introduced printing indicator The micromachined ultrasonic print-head achieves sustained printing of fluids up to 380 mN s/me, far above the typical printable range. [DOI: 10.1115/1.4001551] Keywords: inkjet printing, additive manufacturing, rapid prototyping

The scanning mass spectrometry (SMS) probe is a new electrospray ion source. Motivated by the need for untargeted chemical imaging of dynamic events in solution, we have exploited an approach to electrospray ionization (ESI) that allows continuous sampling from a highly localized volume (~picoliters) in a liquid environment, softly ionizes molecules in the sample to render them amenable for mass spectrometric analysis, and sends the ions to the mass spectrometer. The key underlying concepts for our approach are (1) treating the electrospray capillary inlet as a chemical scanning probe and (2) locating the electrospray point as close as possible to the sampling point, thus providing the shortest response time possible. This approach enables chemical monitoring or imaging of submerged interfaces, providing access to details of spatial heterogeneity and temporal changes within liquid samples. It also permits direct access to liquid/liquid interfaces for ESI-MS analysis. In this letter we report the first demonstrations of these capabilities of the SMS probe and describe some of the probe's basic characteristics. 10.1021/ac902102x

An innovative heat sink design aimed at meeting both the hot spot and large background heat flux requirements of next generation integrated circuits is presented. The heat sink design utilizes two separate unmixed fluids to meet the cooling requirements of the chip with one fluid acting as a fluidic spreader dedicated to cooling the hot spots only, while the second fluid serves as both a coolant for the background heat fluxes and an on-chip regenerator for the hot spot fluid. In this paper the conceptual heat sink design is presented and its theoretical capabilities are explored through optimization calculations and computational fluid dynamics simulations. It has been shown that through close coupling of the two thermal fluids the proposed hybrid heat sink can theoretically remove hot spot heat fluxes on the order of 1 kW/[cm.sup.2] and background heat fluxes up to 100 W/[cm.sup.2] in one compact and efficient package. Additionally, it has been shown that the F2/S2 design can handle these thermal loads with a relatively small pressure drop penalty, within the realm of existing micropump technologies. Finally, the feasibility of the F2/S2 design was demonstrated experimentally by modifying a commercially available, air-cooled aluminum heat sink to accommodate an integrated hot spot cooling system and fluidic spreader. The results of these experiments, where the prototype heat sink was able to remove hot spot heat fluxes of up to 365 W/[cm.sup.2] and background heat fluxes of up to 20 W/[cm.sup.2], are reported. [DOI: 10.1115/1.3104029] Keywords: hot spots, liquid cooling