Experimental and first-principles theoretical studies on Ag-doped cuprous oxide as photocathode in photoelectrochemical splitting of water

Nanostructured thin films of undoped and Ag-doped cuprous oxide were deposited on indium tin oxide-coated glass substrate using simple spray pyrolysis method for their use as photocathode in photoelectrochemical (PEC) cell for solar energy based water splitting. Combination of experiments and first-principles density functional theory based calculations was used to determine and understand the effect of Ag substitution on electronic structure and PEC performance. Thin films were characterized using XRD, FE-SEM, UV–Vis spectroscopy and PEC measurements. The results of DFT calculations show that the top of valence band and bottom of conduction band of undoped Cu₂O lie at Г point of brillouin zone, respectively, suggesting that pure Cu₂O is a direct band gap material. Minimal changes appear in the band gap and band gap energies in the Ag-doped Cu₂O system, keeping it still a direct band gap material. A defect band appearance can be seen between ?4 and ?5 eV in the valence band consisting mainly of Ag 4d states and can be explained by a stronger interaction between the Ag 4d and O 2p, due to the larger Ag size. Ag-doped samples exhibit improved conductivity and fourfold increase in photocurrent density with respect to undoped samples.     

A conformal mapping‐based approach for fast two‐dimensional FEM electrostatic analysis of MEMS devices

In this paper, a methodology is proposed for expediting the coupled electro‐mechanical two‐dimensional finite element modeling of electrostatically actuated MEMS. The proposed methodology eliminates the need for repeated finite element meshing and subsequent electrostatic modeling of the device during mechanical deformation. We achieve this by mapping the deformed electrostatic domain to the reference undeformed domain ‘conformally’. A ‘conformal’ map preserves the form of the Laplace equation and the boundary conditions; thus the electrostatic problem is solved only once in the undeformed electrostatic domain. The conformal map itself is generated through the solution of the same Laplace equation on the undeformed geometry and with displacement boundary conditions dictated by the movement of the mechanical domain. The proposed methodology is demonstrated through its application to the modeling of three MEMS devices with varying length‐to‐gap ratios, multiple dielectrics and complicated geometries. The accuracy of the proposed methodology is confirmed through comparisons of its results with results obtained using the conventional finite element solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Improving Domain-Specific Language Reuse with Software Product Line Techniques

Developing a domain-specific language (DSL) or a composition of DSLs to model a system concern, such as deploying and configuring software components to meet real-time scheduling constraints, is time consuming. Ideally, developers should be able to reuse DSLs and DSL compositions across projects to amortize development effort. Reusing DSLs is hard, however, because they're often designed to precisely describe a single domain or concern. A new approach uses techniques from software product lines (SPLs) to improve the reusability of a DSL, DSL composition, or supporting tool by providing traceability of language concepts to DSL design. A case study of four DSLs demonstrates the need for—and benefits of—applying SPL reuse techniques to DSLs.     

Synthesis and characterization of mechanically strong carboxymethyl cellulose–gelatin–hydroxyapatite nanocomposite for load-bearing orthopedic application

Novel three-dimensional hybrid polymer–hydroxyapatite nanocomposites have been developed as load-bearing synthetic bone graft through in situ mineralization process, using natural polymers carboxymethyl cellulose (CMC) and gelatin (Gel) as matrix. This process is simple and does not involve any chemical cross-linker. Detailed structural and physicochemical characterization of the samples disclosed that incorporation of gelatin with CMC assists the formation of CMC-Gel polymeric network of new conformational structure through non-covalent interactions (H-bond). The formation of hydroxyapatite (HA) in this polymeric network was occurred in such a fashion that the HA serves as bridging molecule which strengthen the polymeric network more and formed a mechanically strong three-dimensional CMC-Gel-HA nanocomposite. The synthesized CMC-Gel-HA nanocomposites have compressive strength and modulus in the range of 40–86 MPa and 0.4–1.2 GPa, respectively, analogous to human cancellous as well as cortical bone. In vitro cell interaction of the synthesized nanocomposites with osteoblast-like MG-63 cells has been evaluated. Results showed that synthesized CMC-Gel-HA nanocomposite promote cells for high alkaline phosphatase activity and extracellular mineralization. Extracellular mineralization ability of nanocomposite was investigated by alizarin red staining and von Kossa staining. Biodegradable nature and bone apatite formation ability of CMC-Gel-HA nanocomposite under simulated physiological environment were investigated by different characterization processes. Results indicated that the synthesized CMC-Gel-HA nanocomposite has great potential to be used as regenerative bone graft in major load-bearing region.     

Diamond coatings for micro end mills: Enabling the dry machining of aluminum at the micro-scale

We show that thin diamond coatings can dramatically enhance the performance of micrometer-scale cutting tools. We present a new approach for coating 300 μm diameter tungsten carbide (WC) micro end mills using a tailored seeding method and hot filament chemical vapor deposition (HFCVD) to obtain uniform, conformal, and continuous diamond coatings less than 2 μm in both thickness and grain size. The performance of the uncoated and coated tools has been evaluated by dry machining channels in 6061-T6 aluminum. The test results demonstrate far lower tool wear and breakage, much lower adhesion of aluminum to the tool, and significantly lower cutting forces for the coated tools. The coatings achieve a more predictable surface finish and enable dry machining at high speeds (40,000 rpm) with little or no burr formation. The improved performance of the coated tools is a result of the superior tribological properties of fine-grained diamond against aluminum, specifically low friction, low adhesion, and low wear of the film. Since the coating allows machining without lubricants and essentially eliminates metal burrs, this approach can reduce the environmental impact of micro-machining processes and offers greatly improved performance for micro and meso-scale manufacturing applications.     

Characterization of Microscale Wear in a Polysilicon-Based MEMS Device Using AFM and PEEM–NEXAFS Spectromicroscopy

Mechanisms of microscale wear in silicon-based microelectromechanical systems (MEMS) are elucidated by studying a polysilicon nanotractor, a device specifically designed to conduct friction and wear tests under controlled conditions. Photoelectron emission microscopy (PEEM) was combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM) to quantitatively probe chemical changes and structural modification, respectively, in the wear track of the nanotractor. The ability of PEEM–NEXAFS to spatially map chemical variations in the near-surface region of samples at high lateral spatial resolution is unparalleled and therefore ideally suited for this study. The results show that it is possible to detect microscopic chemical changes using PEEM–NEXAFS, specifically, oxidation at the sliding interface of a MEMS device. We observe that wear induces oxidation of the polysilicon at the immediate contact interface, and the spectra are consistent with those from amorphous SiO₂. The oxidation is correlated with gouging and debris build-up in the wear track, as measured by AFM and scanning electron microscopy (SEM).