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Metal-filled polymers containing micro-powders of highly conductive metals can serve as a starting material to fabricate complex metal structures using economic filament extrusion-based 3D printing and molding methods. We report our measurements of the thermal conductivity of copper samples prepared using these methods before and after a thermal treatment process. Sintering the samples at 980 ℃ leads to an order of magnitude improvement in thermal conductivity when compared with as-printed or as-molded samples. Thermal conductivity values of approximately 30 W/mK are achieved using commercially available polymer-copper composite filaments with a copper volume fraction of 0.4. Over-sintering the samples at 1080 ℃ further enhances the thermal conductivity by more than two folds, but it leads to uncontrolled shrinkage of the samples. The measured thermal conductivities show a modest decrease with increasing temperatures due to increased electron-phonon scattering rates. The experimental data agree well with the thermal conductivity models previously reported for sintered porous metal samples. The measured electrical conductivity, Young's modulus and yield strength of the present sintered samples are also reported.

Background - It has not been clarified whether the disparity in ischemic stroke outcome between populations is caused by ethnic and geographic differences or by variations in case mix. Propensity score matching (PSM) analysis can overcome some analytical problems but is rarely used in stroke outcome research. This study was to compare the ischemic stroke case-fatality between two PSM cohorts of Sweden and Korea. Methods - Prognostic variables related to baseline characteristics and stroke care were included in our PSM model. Then, we selected 7675 Swedish and 1220 Korean patients with ischemic stroke from each stroke registers and performed one-to-one matching based on propensity scores of each patient. Results - After PSM, all measured variables were well balanced in 1163 matched subjects, and the 90-day case-fatality was identical 6.2% (HR 0.997, 95%CI 0.905-1.099) in Sweden and Korea. Conclusions - No difference is found in the 90-day case-fatality in propensity score-matched Swedish and Korean patients with ischemic stroke.

© 2015 American Chemical Society. The deformation and rupture of axisymmetric liquid bridges being stretched between two fully wetted coaxial disks are studied experimentally and theoretically. We numerically solve the time-dependent Navier-Stokes equations while tracking the deformation of the liquid-air interface using the arbitrary Lagrangian-Eulerian (ALE) moving mesh method to fully account for the effects of inertia and viscous forces on bridge dynamics. The effects of the stretching velocity, liquid properties, and liquid volume on the dynamics of liquid bridges are systematically investigated to provide direct experimental validation of our numerical model for stretching velocities as high as 3 m/s. The Ohnesorge number (Oh) of liquid bridges is a primary factor governing the dynamics of liquid bridge rupture, especially the dependence of the rupture distance on the stretching velocity. The rupture distance generally increases with the stretching velocity, far in excess of the static stability limit. For bridges with low Ohnesorge numbers, however, the rupture distance stay nearly constant or decreases with the stretching velocity within certain velocity windows due to the relative rupture position switching and the thread shape change. Our work provides an experimentally validated modeling approach and experimental data to help establish foundation for systematic further studies and applications of liquid bridges.

A comparative study of oxidation methods to create Cu surfaces with controlled wettability is reported. Micro/nanostructures of Cu oxides are formed on Cu substrates using different chemical and thermal oxidation methods. The morphology and wetting characteristics of the resulting surfaces are characterized using atomic force microscopy, scanning electron microscopy, X-ray diffraction, and contact angle measurements. Chemical oxidation in alkali solutions can form uniform copper oxide layers with high roughness factors without causing thermal stress problems that often hamper thermal oxidation. By combining chemical oxidation with a hydrophobic coating, a wide range of wettability control is demonstrated from superhydrophilic (< 10°) to superhydrophobic (> 170°). Superhydrophilic CuO layers uniformly formed on Cu powder and Cu micropost wick surfaces lead to significant improvement in the capillary and heat transfer performance compared with comparable unoxidized Cu wicks. The present work motivates further studies to exploit the benefits of nanostructured Cu surfaces in various phase change heat transfer applications. © 2013 Taylor and Francis Group, LLC.