Showing papers by "Shankar Narayanan published in 2014"

Nanoporous evaporative device for advanced electronics thermal management

Abstract: We report the design, fabrication and modeling of a thin film evaporation device for cooling of high performance electronic systems. The design uses a membrane with pore diameters of ~100 nm to pump liquid via capillarity to dissipate the high heat fluxes. Viscous losses are minimized by using a thin membrane (~200 nm) which is supported by a ridge structure that provides liquid supply channels. As a result, the external pumping requirements are low, enabling an integrated cooling device with a large coefficient of performance. By integrating the cooling solution directly into the substrate, the thermal resistance of the spreader and interface material are removed entirely. Pentane is used as the working fluid based on its dielectric properties, surface tension and latent heat of vaporization. We first developed a model to capture the heat and fluidic transport within the membrane and supporting ridge structure using conservation of mass, momentum and energy. Using the model, we conduct a parametric sweep of the ridge and membrane geometries to elucidate their influence on thermal performance. We then show how the temperature of hot spots can be managed with a customized cooling solution while independently managing the temperature of background heated regions through variation in the membrane porosity over a realizable range of 10 - 50%. This work provides design guidelines for the development of a high performance evaporator device capable of dissipating the extreme heat fluxes (> 1 kW/cm 2 ) required for next generation high power electronic devices.

Evaporative heat transfer system

Abstract: Evaporative heat transfer system. The system includes a substrate and a plurality of substantially parallel, spaced-apart ridges extending from the substrate forming vertical liquid manifolds therebetween. A nanoporous membrane is supported on the ridges and a pump delivers a dielectric fluid across the ridges. The fluid is drawn through the liquid manifolds via capillarity provided by the nanoporous membrane and evaporates to dissipate heat flux through the substrate. A preferred dielectric fluid is pentane. It is preferred that membrane porosity vary across the membrane to tailor thermal resistances to limit temperature rises.

Selection of Arginine-Rich Anti-Gold Antibodies Engineered for Plasmonic Colloid Self-Assembly

Abstract: Antibodies are affinity proteins with a wide spectrum of applications in analytical and therapeutic biology. Proteins showing specific recognition for a chosen molecular target can be isolated and their encoding sequence identified in vitro from a large and diverse library by phage display selection. In this work, we show that this standard biochemical technique rapidly yields a collection of antibody protein binders for an inorganic target of major technological importance: crystalline metallic gold surfaces. 21 distinct anti-gold antibody proteins emerged from a large random library of antibodies and were sequenced. The systematic statistical analysis of all the protein sequences reveals a strong occurrence of arginine in anti-gold antibodies, which corroborates recent molecular dynamics predictions on the crucial role of arginine in protein/gold interactions. Once tethered to small gold nanoparticles using histidine tag chemistry, the selected antibodies could drive the self-assembly of the colloids onto the surface of single crystalline gold platelets as a first step towards programmable protein-driven construction of complex plasmonic architectures. Electrodynamic simulations based on the Green Dyadic Method suggest that the antibody-driven assembly demonstrated here could be exploited to significantly modify the plasmonic modal properties of the gold platelets. Our work shows that molecular biology tools can be used to design the interaction between fully folded proteins and inorganic surfaces with potential applications in the bottom-up construction of plasmonic hybrid nanomaterials.

Selection of Arginine-Rich Anti-Gold Antibodies Engineered for Plasmonic Colloid Self-Assembly

Abstract: Antibodies are affinity proteins with a wide spectrum of applications in analytical and therapeutic biology. Proteins showing specific recognition for a chosen molecular target can be isolated and their encoding sequence identified in vitro from a large and diverse library by phage display selection. In this work, we show that this standard biochemical technique rapidly yields a collection of antibody protein binders for an inorganic target of major technological importance: crystalline metallic gold surfaces. 21 distinct anti-gold antibody proteins emerged from a large random library of antibodies and were sequenced. The systematic statistical analysis of all the protein sequences reveals a strong occurrence of arginine in anti-gold antibodies, which corroborates recent molecular dynamics predictions on the crucial role of arginine in protein/gold interactions. Once tethered to small gold nanoparticles using histidine tag chemistry, the selected antibodies could drive the self-assembly of the colloids onto the surface of single crystalline gold platelets as a first step towards programmable protein-driven construction of complex plasmonic architectures. Electrodynamic simulations based on the Green Dyadic Method suggest that the antibody-driven assembly demonstrated here could be exploited to significantly modify the plasmonic modal properties of the gold platelets. Our work shows that molecular biology tools can be used to design the interaction between fully folded proteins and inorganic surfaces with potential applications in the bottom-up construction of plasmonic hybrid nanomaterials.

Bi-directional porous media phase change heat exchanger

Abstract: Heat exchange structure A hydrophilic, thermally conductive porous medium includes nanostructures formed substantially uniformly throughout the porous medium providing a balance of capillary and viscous forces to self-regulate a liquid-vapor contact line A suitable porous medium is copper A method for making the structure is also disclosed