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With a constant push to shrink size and elevate power density, the heat flux in GaN-based devices is drastically intensified, requiring effective cooling to control junction temperature. This work presents an embedded manifold microchannel cooling (EMMC) arrangement targeted at mitigating junction temperature, in which microchannels are directly etched in the GaN substrate to extract heat generated due to self-heating. The single-phase laminar flow of deionized water through near-junction microchannels has been investigated in a unit-cell mimicking a recently reported GaN power converter with EMMC arrangement. The effects of geometrical parameters of the manifold and microchannel, heat flux and flow rate on the thermal-hydraulic performance of the unit-cell model are thoroughly studied. High heat transfer coefficients in the order of 10(5) W/(m(2).K) associated with the near-junction microfluidic single-phase flow are acquired, which demonstrates the excellent heat extraction capability of EMMC applied to GaN-based devices. The unit-cell model in the prediction of the thermal performance of a large-scale EMMC multifinger GaN device is in good agreement with experiment and capable of providing detailed fluid flow and temperature distributions for design optimization. Furthermore, a capped diamond heat spreader is integrated with the EMMC GaN device to reduce junction thermal spreading resistance. It is shown that high die heat flux in the range 0.86-3.01 kW/cm(2) can be effectively removed for the 10-mu m-thick diamond capped GaN-on-SiC EMMC device within a junction temperature range 48-110 degrees C. This new EMMC arrangement complemented with capped diamond holds promise as an ultimate near-junction cooling solution that facilitates the implementation and development of high-power compact GaN-based devices.

We consider the effect that an upstream cylinder has on the effective inertial collection efficiency of a downstream cylinder. We consider an initially uniform distribution of particles moving past a cylindrical fiber in a potential crossflow and numerically calculate the resulting particle distribution far downstream of the fiber using finite differences. We then investigate the effect that the downstream distribution of particles has on the effective inertial collision efficiency of a downstream test cylinder oriented parallel to the first. We show that the effective collision efficiency of the test cylinder depends on its relative offset in the transverse direction (normal to the flow) with respect to the upstream cylinder. For relatively small offsets there is complete shielding, and no particles collide with the test cylinder. As the offset increases, a growing effective collision efficiency is observed leading to a significant enhancement relative to the collision efficiency of an isolated cylinder for intermediate offsets and Stokes numbers close to unity. Importantly, we observe relative gains in effective collision efficiency above 100% for a range of Stokes number and offset values. For larger offsets and Stokes numbers, the effect of the upstream cylinder on the effective collision efficiency of the test cylinder decreases and eventually becomes negligible. Detailed results are provided for Stokes drag acting on the particles and we also show that a non-linear drag has negligible effect on the observed trends for the conditions relevant to filtration systems. These results suggest that the arrangement of fibers has a substantial effect on inertial particle impaction even when neighboring fibers do not alter the flow field around each individual collector. Moreover, periodic arrangements with specific orientations with respect of the flow could lead to a significant enhancement of the inertial collision of particles on an array of collectors, thus contributing towards a better filtration performance.

In this study, artificial neural network (ANN) was used to predict forced convection heat transfer enhancement from microscale pin fin heat sinks under various operating conditions and at different geometries. Experimental data acquired from the literature were employed to train the ANN model. Different numbers of training cycles, layers, and neurons in the network were investigated to design an effective neural network. The performance of the trained network was tested using the mean squared error and the most accurate one was selected to predict the average Nusselt number. Mean absolute percentage errors between the ANN output and the experimental datapoints were calculated and compared with the existing correlations. This machine learning method offers significant improvement for thermal performance prediction and could be a reliable tool for determining convective heat transfer in microscale pin fin heat sinks.

(1) Background: Metal-on-metal (MoM) total hip arthroplasty (THA) and hip resurfacingarthroplasty (HRA) was presumed to provide superior functional outcomes compared to metal-onpolyethylene (MoP) THA. (2) Methods: We compared muscle mass, power, step test asymmetry, andpatient-reported outcomes between MoM THA/HRA and MoP THA. A total of 51 MoM THA/HRAsand 23 MoP THAs participated in the cross-sectional study at a mean of 6.5 (2.4–12.5) years postoperatively. Muscle mass was measured by Dual energy X-ray Absorption (DXA) scans and musclepower in a Leg Extensor Power Rig. Step test asymmetry was obtained with an Inertial MeasurementUnit (IMU). The patients completed the Harris Hip Score (HHS) and the Copenhagen Hip and GroinOutcome Score (HAGOS). (3) Results: The MoM THA/HRA group had a greater inter-limb differencein hip muscle mass compared to the MoP THA group (p = 0.02). Other inter-limb differences inmuscle mass and power were similar (p > 0.05). Muscle mass of the thigh and calf area and musclepower in both legs were higher in MoM THA/HRA compared to MoP THA (p < 0.009). Step test timeasymmetry when ascending was lower in MoM THA/HRA compared to MoP THA (p = 0.03). HHSand HAGOS scores were similar between groups (p > 0.05). (4) Conclusion: Overall, we could notverify the hypothesis that MoM THA/HRA contributes to superior functional outcomes compared toMoP THA.