Self-optimizing, highly surface-active layered metal dichalcogenide catalysts for hydrogen evolution

Low-cost, layered transition-metal dichalcogenides (MX_2) based on molybdenum and tungsten have attracted substantial interest as alternative catalysts for the hydrogen evolution reaction (HER). These materials have high intrinsic per-site HER activity; however, a significant challenge is the limited density of active sites, which are concentrated at the layer edges. Here we unravel electronic factors underlying catalytic activity on MX_2 surfaces, and leverage the understanding to report group-5 MX_2 (H-TaS_2 and H-NbS_2) electrocatalysts whose performance instead mainly derives from highly active basal-plane sites, as suggested by our first-principles calculations and performance comparisons with edge-active counterparts. Beyond high catalytic activity, they are found to exhibit an unusual ability to optimize their morphology for enhanced charge transfer and accessibility of active sites as the HER proceeds, offering a practical advantage for scalable processing. The catalysts reach 10 mA cm^(−2) current density at an overpotential of ∼50–60 mV with a loading of 10–55 μg cm^(−2), surpassing other reported MX2 candidates without any performance-enhancing additives

Cation insertion to break the activity/stability relationship for highly active oxygen evolution reaction catalyst

The production of hydrogen at a large scale by the environmentally-friendly electrolysis process is currently hampered by the slow kinetics of the oxygen evolution reaction (OER). We report a solid electrocatalyst α-Li2IrO3 which upon oxidation/delithiation chemically reacts with water to form a hydrated birnessite phase, the OER activity of which is five times greater than its non-reacted counterpart. This reaction enlists a bulk redox process during which hydrated potassium ions from the alkaline electrolyte are inserted into the structure while water is oxidized and oxygen evolved. This singular charge balance process for which the electrocatalyst is solid but the reaction is homogeneous in nature allows stabilizing the surface of the catalyst while ensuring stable OER performances, thus breaking the activity/stability tradeoff normally encountered for OER catalysts

Achieving developability of a polygonal surface by minimum deformation: a study of global and local optimization approaches

Surface developability is required in a variety of applications in product design, such as clothing, ship hulls, automobile parts, etc. However, most current geometric modeling systems using polygonal surfaces ignore this important intrinsic geometric property. This paper investigates the problem of how to minimally deform a polygonal surface to attain developability, or the so-called developability-by-deformation problem. In our study, this problem is first formulated as a global constrained optimization problem and a penalty-function-based numerical solution is proposed for solving this global optimization problem. Next, as an alternative to the global optimization approach, which usually requires lengthy computing time, we present an iterative solution based on a local optimization criterion that achieves near real-time computing speed

Fast energy-based surface wrinkle modeling

This paper presents an energy-based approach that models the distinct wrinkle shapes to represent the different material properties of non-rigid objects at an interactive speed. Our approach is a curve driven technique, where the surface wrinkles are generated by deforming the given mesh surface according to the shape change of a governing curve on the surface. An energy function is defined on the governing curve to indicate flexure properties. By minimizing the energy function, our approach offers the ability to mimic desirable and pleasing wrinkle shapes corresponding to the given material properties. We then propagate the wrinkle shape of the governing curve on the given mesh surface in the influence region. The final surface wrinkles interpolate the governing curve and are attenuated while they gradually move close to the boundary of the influence region to achieve the smoothness. Consequently, this results in the fast manipulation for complex wrinkle shapes with material properties. The most common problem of physically based simulation, the speed bottleneck, is avoided in our approach. In one word, our approach provides an efficient and useful interactive tool to model realistic wrinkles on non-rigid objects. (c) 2005 Elsevier Ltd. All rights reserved

Exploiting computerized adaptive testing for self-directed learning

Self-directed learning enables learners to take responsibility for and to design their own learning-related activities. Frequent assessments facilitate self-directed learners to monitor learning regularly. Often, quizzes with multiple-choice (MC), true-false, or fill-in-the-gap items are a quick way of gathering information on the strengths and weakness of learners. Although with limitations, such kinds of items can assess both low-level (e.g., fact recall and comprehension) and high-level (e.g., application, analysis, and evaluation) thinking and are particularly suitable for online computerized testing, largely because they can be scored by computers. This chapter starts with an introduction to traditional paper-and-pencil testing, followed by computer-based testing, and six commonly used test delivery models. Then, key features, underlying measurement theory, major steps, and constructions of computerized adaptive testing, are described. This chapter ends with some concluding remarks and discussion of future developments of CAT

Effect of clomiphene citrate on human spermatozoal motility and fertilizing capacity in vitro

The effect of clomiphene citrate (CC) at various concentrations (0.005, 0.05, 0.5, 5, and 50 μg/ml) on the in vitro motility and fertilizing capacity of human spermatozoa was studied. Spermatozoa collected from 14 normal men were washed in modified Krebs-Ringer solution (Biggers, Whitten and Whittingham [BWW] medium) and incubated with CC for 5 hours, the period required for spermatozoal capacitation. The percent motilities of spermatozoa were recorded at 0 and 5 hours during incubation with CC. After incubation, the spermatozoa were washed with BWW medium to remove CC before insemination of the zona-free hamster ova. CC caused a significant dose-dependent decrease in the penetration of denuded hamster ova in comparison with the control (P<0.05). Significant depressive effect on spermatozoal motility was observed with CC at 0.05 μg/ml or higher concentrations (P<0.05). These results indicate that (1) CC decreases human spermatozoal fertilizing capacity in vitro and (2) the inhibitory effect on fertilizing capacity could be due to the sperm-immobilizing activity of CC.link_to_subscribed_fulltex

Minimum area convex packing of two convex polygons

Given two convex polygons P and Q in the plane that are free to translate and rotate, a convex packing of them is the convex hull of a placement of P and a placement of Q whose interiors do not intersect. A minimum area convex packing of P and Q is one whose area is minimized. The problem of designing a deterministic algorithm for finding a minimum area convex packing of two convex polygons has remained open. We address this problem by first studying the contact configurations between P and Q and their algebraic structures. Crucial geometric and algebraic properties on the area function are then derived and analyzed which enable us to successfully discretize the search space. This discretization, together with a delicate algorithmic design and careful complexity analysis, allows us to develop an efficient O((n + m)nm) time deterministic algorithm for finding a true minimum area convex packing of P and Q, where n and m are the numbers of vertices of P and Q, respectively