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This study examined physical stability of spray freeze dried (SFD) bovine serum albumin (BSA) solids produced using the radio frequency (RF)-assisted drying technique. BSA formulations were prepared with varying concentrations of trehalose and mannitol, using an excipient-free formulation as control. These formulations were produced using either traditional ultrasonic spray freeze drying (SFD) or RF-assisted ultrasonic spray freeze drying (RFSFD). The dried formulations were then characterized using Karl Fischer moisture content measurement, powder X-ray diffraction (PXRD), size exclusion chromatography (SEC), and solid-state hydrogen/deuterium exchange with mass spectrometry (ssHDX-MS). Moisture content did not have a good correlation with the physical stability of the formulations measured by SEC. ssHDX-MS metrics such as deconvoluted peak areas of the deuterated samples showed a satisfactory correlation (R2 = 0.914) with the SEC stability data. RFSFD improved the stability of formulations with 20 mg/ml of trehalose and no mannitol, and had similar stability with all other formulations as compared to SFD. This study demonstrated that RFSFD technique can significantly reduce the duration of primary drying cycle from 48.0 h to 27.5 h while maintaining or improving protein physical stability as compared to traditional lyophilization. [ABSTRACT FROM AUTHOR]

A hierarchical manifold microchannel heat sink array is fabricated and experimentally characterized for uniform heat flux dissipation over a footprint area of 5 mm × 5 mm. A 3 × 3 array of heat sinks is fabricated into the silicon substrate containing the heaters for direct intrachip cooling, eliminating the thermal resistances typically associated with the attachment of a separate heat sink. The heat sinks are fed in parallel using a hierarchical manifold distributor that delivers flow to each of the heat sinks. Each heat sink contains a bank of high-aspect-ratio microchannels; five different channel geometries with nominal widths of 15 μm and 33 μm and nominal depths between 150 μm and 470 μm are tested. The thermal and hydraulic performance of each heat sink array geometry is evaluated using HFE-7100 as the working fluid, for mass fluxes ranging from 600 kg/m 2  s to 2100 kg/m 2  s at a constant inlet temperature of 59 °C. To simulate heat generation from electronics devices, a uniform background heat flux is generated with thin-film serpentine heaters fabricated on the silicon substrate opposite the channels; temperature sensors placed across the substrate provide spatially resolved surface temperature measurements. Experiments are also conducted with simultaneous background and hotspot heat generation; the hotspot heat flux is produced by a discrete 200 μm × 200 μm hotspot heater. Heat fluxes up to 1020 W/cm 2 are dissipated under uniform heating conditions at chip temperatures less than 69 °C above the fluid inlet and at pressure drops less than 120 kPa. Heat sinks with wider channels yield higher wetted-area heat transfer coefficients, but not necessarily the lowest thermal resistance; for a fixed channel depth, samples with narrower channels have increased total wetted areas owing to the smaller fin pitches. During simultaneous background and hotspot heating conditions, background heat fluxes up to 900 W/cm 2 and hotspot fluxes up to 2700 W/cm 2 are dissipated. The hotspot temperature increases linearly with hotspot heat flux; at hotspot heat fluxes of 2700 W/cm 2 , the hotspot experiences a temperature rise of 16 °C above the average chip temperature. [ABSTRACT FROM AUTHOR]

High-heat-flux removal is necessary for next-generation microelectronic systems to operate more reliably and efficiently. Extremely high heat removal rates are achieved in this work using a hierarchical manifold microchannel heat sink array. The microchannels are imbedded directly into the heated substrate to reduce the parasitic thermal resistances due to contact and conduction resistances. Discretizing the chip footprint area into multiple smaller heat sink elements with high-aspect-ratio microchannels ensures shortened effective fluid flow lengths. Phase change of high fluid mass fluxes can thus be accommodated in micron-scale channels while keeping pressure drops low compared to traditional, microchannel heat sinks. A thermal test vehicle, with all flow distribution components heterogeneously integrated, is fabricated to demonstrate this enhanced thermal and hydraulic performance. The 5 mm × 5 mm silicon chip area, with resistive heaters and local temperature sensors fabricated directly on the opposite face, is cooled by a 3 × 3 array of microchannel heat sinks that are fed with coolant using a hierarchical manifold distributor. Using the engineered dielectric liquid HFE-7100 as the working fluid, experimental results are presented for channel mass fluxes of 1300, 2100, and 2900 kg/m 2 s and channel cross sections with nominal widths of 15 μm and nominal depths of 35 μm, 150 μm, and 300 μm. Maximum heat flux dissipation is shown to increase with mass flux and channel depth and the heat sink with 15 μm × 300 μm channels is shown to dissipate base heat fluxes up to 910 W/cm 2 at pressure drops of less than 162 kPa and chip temperature rise under 47 °C relative to the fluid inlet temperature. [ABSTRACT FROM AUTHOR]

Abstract: Effects of uncertainties in gas damping models, geometry and mechanical properties on the dynamics of micro-electro-mechanical systems (MEMS) capacitive switch are studied. A sample of typical capacitive switches has been fabricated and characterized at Purdue University. High-fidelity simulations of gas damping on planar microbeams are developed and verified under relevant conditions. This and other gas damping models are then applied to study the dynamics of a single closing event for switches with experimentally measured properties. It has been demonstrated that although all damping models considered predict similar damping quality factor and agree well for predictions of closing time, the models differ by a factor of two and more in predicting the impact velocity and acceleration at contact. Implications of parameter uncertainties on the key reliability-related parameters such as the pull-in voltage, closing time and impact velocity are discussed. A notable effect of uncertainty is that the nominal switch, i.e. the switch with the average properties, does not actuate at the mean actuation voltage. Additionally, the device-to-device variability leads to significant differences in dynamics. For example, the mean impact velocity for switches actuated under the 90%-actuation voltage (about 150V), i.e. the voltage required to actuate 90% of the sample, is about 129cm/s and increases to 173cm/s for the 99%-actuation voltage (of about 173V). Response surfaces of impact velocity and closing time to five input variables were constructed using the Smolyak sparse grid algorithm. The sensitivity analysis showed that impact velocity is most sensitive to the damping coefficient whereas the closing time is most affected by the geometric parameters such as gap and beam thickness. [Copyright &y& Elsevier]