Experimental Investigation of Cold-formed Steel Beam-column Sub-frames: Pilot Study

This paper presents the findings of an experimental investigation on the structural performance of bolted moment connections in cold-formed steel beam-column sub-frames. A total of eight tests with three different connection configurations in both internal and external columns were carried out. Double lipped C-sections back-to-back with hot rolled steel gusset plates of 10 mm and of 16 mm in two different shapes were tested; four bolts per member were used in the connections. Among the tests, three different modes of failure were identified and the measured moment resistances at the connections were found to vary from 36% to 97% of the measured moment capacities of the cold-formed steel sections, demonstrating that bolted moment connections between cold-formed steel members are structurally feasible and economical. Furthermore, structural members with double lipped C sections back-to-back are shown to be practical in constructing short to medium span portal frames with bolted moment connections through rational design

Cytomegalovirus-associated colitis mimicking necrotizing enterocolitis – A near miss diagnosis of neonatal colonic stricture

Although cytomegalovirus (CMV) is a common congenital infection in neonates, most patients are asymptomatic. Gastrointestinal manifestation is unusual. In this report, we described a newborn with perinatal CMV infection presented with symptoms mimicking necrotizing enterocolitis. We hope to alert clinicians about this possible diagnosis when managing newborn gastrointestinal diseases.published_or_final_versio

Electrospun Polymeric Membranes for Adhesion

With growing interest in detachable adhesives, new materials are explored such as the types that employ elastomers, thermoplastics, and pressuresensitive polymers [1]. Generally, these adhesives produce substantial shear adhesion strengths but are considerably difficult to detach from surfaces. Commercial high strength adhesives make use of chemical interactions such as glues and permanently attach two surfaces. Subsequently, fabrication of dry adhesives with anisotropic force distributions has the potential in several applications such as tapes, fasteners, treads of wall-climbing robots, spiderman\u27s suits, microelectronics, medical and space applications. High aspect ratio (AR) structures exhibit significant shear adhesion strength compared to ones with low AR(s) [2,3]. Electrospinning presents a versatile technique for fabricating nanofibers with significant AR [4,5]. Little has been done for fabricating dry adhesives, which are electrically insulating, and which possess significant shear adhesion strength with easy normal detachment. With use of electrospun nylon 6 nanofiber membrane, we report herein the fabrication of electrically insulating dry adhesives with high shear adhesion strength for strong shear binding-on but with substantial normal detachment strength (V) for easy normal lifting-off. With the aid of microscopy and microanalyses, we investigate the effects of the fiber diameter, fiber surface roughness, and thickness of membrane on their corresponding adhesion strengths

Polymer Fiber Arrays for Adhesion

The ability of geckos to adhere to vertical solid surfaces comes from their remarkable feet with millions of projections terminating in nanometer spatulae. In this paper, we present a simple yet robust method for fabricating directionally sensitive dry adhesives. By using electrospun nylon 6 nanofiber arrays, we create gecko-inspired dry adhesives, that are electrically insulating, and that show shear adhesion strength of 27 N/cm2 on a glass slide. This measured value is 270% that reported of gecko feet and 97-fold above normal adhesion strength of the same arrays. The data indicate a strong shear binding-on and easy normal lifting-off. Size and surface boundary of fibers both affect on the shear adhesion. This anisotropic strength distribution is attributed to enhanced shear adhesion strength with decreasing fiber diameter and an optimum performance of nanofiber arrays in the shear direction over a specific range of thicknesses

A Nano-Cheese-Cutter to Directly Measure Interfacial Adhesion of Freestanding Nano-Fibers

A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, “pull-off” occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation

Nitrate Anomaly in the Upper Nutricline in the Northern South China Sea - Evidence for Nitrogen Fixation

[1] Up to 2 μM of nitrate anomaly, N*, were found in the upper nutricline at the South East Asia Time-series Study (SEATS) site in the northern South China Sea (SCS). These concentrations were among the higher values reported in the Pacific and indicate the significant contribution of the remineralization of nitrogen-rich organic matter formed by nitrogen fixation to the nutrient dynamics of the area. The concentrations were systematically higher, by up to 2.5 μM, in the Fall through the early Spring, during the northeast monsoon, than in the Summer, suggesting that the impact of nitrogen fixation was higher during the former time period. This pattern is in phase with that of the atmospheric deposition of Asian dust to the northern SCS. The coherence is consistent with a coupling between nitrogen fixation and the availability of atmospherically derived iron

A computational model of binding thermodynamics: The design of cyclin-dependent kinase 2 inhibitors

The cyclin-dependent protein kinases are important targets in drug discovery because of their role in cell cycle regulation. In this computational study, we have applied a continuum solvent model to study the interactions between cyclin-dependent kinase 2 (CDK2) and analogues of the clinically tested anticancer agent flavopiridol. The continuum solvent model uses Coulomb's law to account for direct electrostatic interactions, solves the Poisson equation to obtain the electrostatic contributions to solvation energy, and calculates scaled solvent-accessible surface area to account for hydrophobic interactions. The computed free energy of binding gauges the strength of protein-ligand interactions. Our model was first validated through a study on the binding of a number of flavopiridol derivatives to CDK2, and its ability to identify potent inhibitors was observed. The model was then used to aid in the design of novel CDK2 inhibitors with the aid of a computational sensitivity analysis. Some of these hypothetical structures could be significantly more potent than the lead compound flavopiridol. We applied two approaches to gain insights into designing selective inhibitors. One relied on the comparative analysis of the binding pocket for several hundred protein kinases to identify the parts of a lead compound whose modifications might lead to selective compounds. The other was based on building and using homology models for energy calculations. The homology models appear to be able to classify ligand potency into groups but cannot yet give reliable quantitative results

Charge optimization of the interface between protein kinases and their ligands

Abstract: Examining the potential for electrostatic complementarity between a ligand and a receptor is a useful technique for rational drug design, and can demonstrate how a system prioritizes interactions when allowed to optimize its charge distribution. In this computational study, we implemented the previously developed, continuum solvent-based charge optimization theory with a simple, quadratic programming algorithm and the UHBD Poisson-Boltzmann solver. This method allows one to compute the best set of point charges for a ligand or ligand region based on the ligand and receptor shape, and the receptor partial charges, by optimizing the binding free energy obtained from a continuumsolvent model. We applied charge optimization to a fragment of the heat-stable protein kinase inhibitor (PKI) of protein kinase A (PKA), to three flavopiridol inhibitors of CDK2, and to cyclin A which interacts with CDK2 to regulate the cell cycle. We found that a combination of global (involving every charge) and local (involving only charges in a local region) optimization can give useful hints for designing better inhibitors. Although some parts of an inhibitor may already contribute significantly to binding, we found that they could still be the most important targets for modifications to obtain stronger binders. In studying the binding of flavopiridol inhibitors to CDK2, comparable binding affinity could be obtained regardless of whether the net charges of the inhibitors were constrained to Ϫ2, Ϫ1, 0, 1, or 2 during the optimization. This provides flexibility in inhibitor design when a certain net charge of the inhibitor is desired in addition to strong binding affinity. For the study of the PKA-PKI and CDK2-cyclin A interfaces, we identified residues whose charge distributions are already close to optimal and those whose charge distributions could be refined to further improve binding

Demonstration of an air-slot mode-gap confined photonic crystal slab nanocavity with ultrasmall mode volumes

We demonstrate experimentally an air-slot mode-gap photonic crystal cavity with quality factor of 15,000 and modal volume of 0.02 cubic wavelengths, based on the design of an air-slot in a width-modulated line-defect in a photonic crystal slab. The origin of the high Q air-slot cavity mode is the mode-gap effect from the slotted photonic crystal waveguide mode with negative dispersion. The high Q cavities with ultrasmall mode volume are important for applications such as cavity quantum electrodynamics, nonlinear optics and optical sensing.Comment: 12 pages, 4 figure

Model-Independent Determination of the WIMP Mass from Direct Dark Matter Detection Data

Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for Dark Matter. We develop a model-independent method for determining the mass $m_\chi$ of the WIMP by using data (i.e., measured recoil energies) of direct detection experiments. Our method is independent of the as yet unknown WIMP density near the Earth, of the form of the WIMP velocity distribution, as well as of the WIMP-nucleus cross section. However, it requires positive signals from at least two detectors with different target nuclei. In a background-free environment, $m_\chi \sim 50$ GeV could in principle be determined with an error of $\sim 35$ with only $2 \times 50$ events; in practice upper and lower limits on the recoil energy of signal events, imposed to reduce backgrounds, can increase the error. The method also loses precision if $m_\chi$ significantly exceeds the mass of the heaviest target nucleus used.Comment: 30 pages, 15 figures, typos fixed, one reference adde