Synchrotron x-ray imaging visualization study of capillary-induced flow and critical heat flux on surfaces with engineered micropillars

Over the last several decades, phenomena related to critical heat flux (CHF) on structured surfaces have received a large amount of attention from the research community. The purpose of such research has been to enhance the safety and efficiency of a variety of thermal systems. A number of theories have been put forward to explain the key CHF enhancement mechanisms on structured surfaces. However, these theories have not been confirmed experimentally because of limitations in the available visualization techniques and the complexity of the phenomena. To overcome these limitations and elucidate the CHF enhancement mechanism on the structured surfaces, we introduce synchrotron x-ray imaging with high spatial (similar to 2 mu m) and temporal (similar to 20,000 Hz) resolutions. This technique has enabled us to confirm that capillary-induced flow is the key CHF enhancement mechanism on structured surfaces.11Ysciescopu

DNA Guided Self-Assembly of Nanocrystals for Optoelectronic Devices /

While inherent properties of nanocrystals have been actively investigated within the last decade, control over positioning and ordering of nanomaterials at multiple length scales has been difficult to achieve. In the research shown here, DNA is used in conjunction with metal and semiconductor nanocrystals to facilitate their assembly at precise locations on a substrate with potential for programmable ordering. The inimitable ability of DNA to binding through stable, specific, and reversible molecular recognition has allowed the creation of nanocrystal assemblies through extraordinary control over spatial location and crystallization. We first show an inexpensive printing method that enables repeated patterning of large area arrays of nanoscale materials by AFM and fluorescence microscopy. DNA strands were patterned with 50nm resolution by a soft-lithographic subtraction printing process and DNA hybridization was used to direct the assembly of 10nm gold nanoparticles to create ordered two-dimensional nanoparticle arrays. This technique was further modified to demonstrate methods to generate patterned nanocrystal superlattices. Electron microscopy and fourier transformation analysis were used to investigate the role of chemical and geometrical confinement on interparticle DNA hybridization and particle packing and obtaining long-range order. Using similar strategies, we also demonstrate the generation of highly ordered 3-D body-centered-cubic (BCC) superlattices of gold nanocrystals at desired areas on a surface through specific DNA interactions. In this work, controlled film thicknesses from 20nm to 100nm could be easily obtained by varying initial gold nanoparticle concentrations and particles remained ordered in the z-direction as well. These gold nanoparticle studies were then applied toward producing 3D thin film arrays of quantum dots (QDs) For this, successful aqueous phase transfer of CdTe QDs for DNA conjugation was first demonstrated. Next, the DNA conjugated CdTe QDs were assembled on TiO₂ films to fabricate ITO/TiO₂/DNA-CdTe/Au thin film devices which were then tested by current-voltage measurements. We demonstrate that producing close packed arrays as opposed to disordered ones significantly improves film formation with less defects. By tuning the QD size and film thicknesses, the correlation between Voc and Jsc values was investigated to show the possibility of charge transport through DNA-QDs assembly for the application of optoelectronic device

Effects of wettability on droplet movement in a V-shaped groove

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BALLU2: A Safe and Affordable Buoyancy Assisted Biped.

This work presents the first full disclosure of BALLU, Buoyancy Assisted Lightweight Legged Unit, and describes the advantages and challenges of its concept, the hardware design of a new implementation (BALLU2), a motion analysis, and a data-driven walking controller. BALLU is a robot that never falls down due to the buoyancy provided by a set of helium balloons attached to the lightweight body, which solves many issues that hinder current robots from operating close to humans. The advantages gained also lead to the platforms distinct difficulties caused by severe nonlinearities and external forces such as buoyancy and drag. The paper describes the nonconventional characteristics of BALLU as a legged robot and then gives an analysis of its unique behavior. Based on the analysis, a data-driven approach is proposed to achieve non-teleoperated walking: a statistical process using Spearman Correlation Coefficient is proposed to form low-dimensional state vectors from the simulation data, and an artificial neural network-based controller is trained on the same data. The controller is tested both on simulation and on real-world hardware. Its performance is assessed by observing the robots limit cycles and trajectories in the Cartesian coordinate. The controller generates periodic walking sequences in simulation as well as on the real-world robot even without additional transfer learning. It is also shown that the controller can deal with unseen conditions during the training phase. The resulting behavior not only shows the robustness of the controller but also implies that the proposed statistical process effectively extracts a state vector that is low-dimensional yet contains the essential information of the high-dimensional dynamics of BALLUs walking

Electrospun calcium doped lithium titanate nanofibers as anode materials for high-performance lithium-ion batteries

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