Self-Assembled Two-Dimensional Surface Structures for Beam Shaping of GaN-Based Vertical-Injection Light-Emitting Diodes

Enhanced light extraction and beam shaping of GaN-based vertical-injection light-emitting diodes (VI-LEDs) employing biomimetic surface structures were demonstrated. The biomimetic surface structures were fabricated using self-assembled polystyrene nanospheres serving as a monolayer mask, and followed by anisotropic inductively coupled plasma reactive ion etching. The light output power of the VI-LEDs with the patterned structures exhibited an efficiency enhancement factor of 68% at a driving current of 350 mA, compared to those without any surface structures. The structures also resulted in a modified heart-shaped radiation pattern, which is preferable for backlight applications in flat panel displays.     

Synthesis of UV-curable silane-coupling agent as an adhesion promoter

In color filter industry, a problem was found that the adhesion strength between glass substrate and black matrix was largely decreased after ITO sputtering process. In order to solve this problem, a new UV-curable silane-coupling agent (UV-SCA) was synthesized to be an adhesion promoter, which was synthesized by the reaction between the hydroxyl group of bisphenol A epoxy diacrylate and the isocyanate group of 3-(isocyanatopropyl)-triethoxysilane. The adhesion strength between glass substrate and black film, which was prepared from the carbon black photo-resist with or without the addition of UV-SCA, was determined by a tensile/compression strength tester, and the effect of UV-SCA on the adhesion strength before and after ITO sputtering process was also discussed.     

Dual-Current Pump Module for Transient Improvement of Step-Down DC–DC Converters

This paper presents a novel dual-current pump module (DCPM) to improve the transient response of dc-dc converters. The DCPM operates only during transient to provide two additional current injections for step-up load and current drains for step-down load. Due to the two current pump paths, the current stress on the switches of the DCPM is also reduced. The measurement results show that the DCPM can enhance the dynamic recovery time of the buck dc-dc converter by more than an order.     

Visual representation of construction management data

Construction projects are associated with voluminous and often unstructured data sets, generated in support of construction management functions. Project managers face the challenge of making meaningful deductions from this data. A central contribution of this paper is that visual analytics can provide a means of analyzing data from various dimensions of a project to extract information in aid of decision making and helping to explain reasons for performance to date. Questions posed relate to the role of visual analytics in the execution and post-construction phases of a project, data representations and transformations of specific interest, and the kinds of visual representations and interactions that provide useful insights to management personnel, help explain performance, or assist with communication. Principles of designing effective visual analytics solutions for various construction management functions and applicable to the associated analytic reasoning tasks, data representations and transformations, and visual representations including relevant interaction features are described. Emphasis is placed on the choice of visual representations along with discussion of approaches for validating the usefulness of the visual analytics solutions proposed. The notion of context dimensions and performance dimensions for representing construction projects is introduced as part of the formulation of visual representation designs. To demonstrate the application of the concepts presented, data sets from two different projects were used to produce visual representations helpful for analytical reasoning about change order management data. A detailed assessment is given of several of the images presented in terms of strengths and weaknesses, and interaction features desired. The findings of the paper in terms of principles, concepts and lessons learned should prove helpful to those wishing to apply visual analytics to a broad range of construction management functions.     

Molecular structure and transport dynamics in Nafion and sulfonated poly(ether ether ketone ketone) membranes

An atomistic simulation technique is performed to investigate the molecular structure and transport dynamics inside a hydrated Nafion membrane and a hydrated sulfonated poly(ether ether ketone ketone) (SPEEKK) membrane. The simulation system consists of the representative fragments of the polymer electrolytes, hydronium ions and solvent molecules, such as water plus methanol molecules. Simulation results show that the hydrated SPEEKK has less phase separation among hydrophobic and hydrophilic regions in comparison with the Nafion. Those water channels formed in the SPEEKK are much narrower compared to those in the Nafion. These characteristics lead to a lower mobility of hydronium ions and water molecules and hence relatively lower diffusion coefficient of methanol in the SPEEKK. It results in the reduction of the methanol permeation problem in direct methanol fuel cells.     

Exploiting In-Zone Broadcasts for Cache Sharing in Mobile Ad Hoc Networks

The problem of cache sharing for supporting data access in mobile ad hoc networks is studied in this paper. The key to this problem is to discover a requested data item in an efficient manner. In the paper, we propose two caching protocols, IXP and DPIP, which distinguish themselves from the existing ones in that they fully exploit in-zone broadcasts to facilitate cache sharing operation. In particular, the DPIP protocol offers an implicit index push property, which is highly useful for enhancing cache hit ratio in the neighborhood of a data requester node. Moreover, our protocols also exploit the broadcasts to facilitate the design of a simple but efficient count-based cache replacement scheme. Performance study shows that the proposed protocols can significantly improve the performance of data access in a mobile ad hoc network.     

Synthesis, characterization and properties of halogen-free flame retardant PMMA nanocomposites containing nitrogen/ silicon prepared from the Sol-Gel method

The investigation addresses the feasibility of preparing PMMA hybrid. MMA reacted with MA using AIBN initiator to form the copolymer in a free radical reaction. APTS was then reacted with the copolymer to synthesize the precursor, which has an OEt functional group and thus participates in the sol-gel reaction. HMMM and TEOS were added to the precursor to form networks with an organic-inorganic structure by the sol-gel method. FTIR was adopted to monitor the curing of the hybrid and NMR was employed to characterize the structure of the composites. The results demonstrate that the sol-gel reaction proceeded completely, and that networks had formed. SEM and EDS were applied to observe the morphology of nanocomposites and the particles were smaller than 100 nm. Accordingly, the nanocomposites had been successfully prepared. UV/vis spectroscopy was utilized to evaluate the transparency of nanocomposites and the results demonstrate that the composites have high transparency. Hence, the organic and inorganic phases are highly mutually compatible. TGA and LOI were applied to elucidate the thermal properties and flame retardance. The data indicate that the composites exhibited excellent thermal stability and flame retardance.     

Drying of Granular Ceramic Films: II, Drying Stress and Saturation Uniformity

Films composed of ceramic particles were observed during drying. The films were prepared from 20 vol% aqueous dispersions of α-alumina and α-quartz and were free of any organic binder. Conditions for uniform film saturation during drying were established by consideration of a liquid transport model and by direct observation of the drying films. Drying stresses were measured in situ by a substrate deflection method based on an optical interference technique. Simultaneous stress and weight measurements were used to determine stress as a function of saturation. The maximum stress occurred near 100% saturation and was approximately 2 and 1.1 MPa for films produced from 0.35-and 0.68-μm particles, respectively. The maximum stress decreased from 2 to 0.9 MPa for films produced from the 0.35-μm particles when 0.005 wt% surfactant was added to the slurry. The surfactant decreased the liquid surface tension from 72 to 32 dyn/cm. These observations are direct evidence of the effects of capillary tension on the state of stress in a ceramic body. Mechanical properties of the green ceramic films were estimated by use of a linear elastic fracture model. Knowledge of the critical cracking thickness and maximum stress in the film was used to estimate the fracture resistance of the granular film. The fracture resistance values are approximately 0.02 and 0.007 MPa·m^1/2 for films produced from alumina and silica, respectively. The difference in mechanical behavior of the silica and alumina films is similar to that expected by the difference in Hamaker constants between the two materials.     

Mechanical properties and morphology of crosslinked PP/PE blends and PP/PE/propylene–ethylene copolymer blends

Blending is an effective method for improving polymer properties. However, the problem of phase separation often occurs due to incompatibility of homopolymers, which deteriorates the physical properties of polyblends. In this study, isotactic polypropylene was blended with low-density polyethylene. Crosslinking agent and copolymers of propylene and ethylene (either random copolymer or block copolymer) were added to improve the interfacial adhesion of PP/LDPE blends. The tensile strength, heat deflection temperature, and impact strength of these modified PP/PE blends were investigated. The microstructures of polyblends have been studied to interpret the mechanical behavior through dynamic viscoelasticity, wide-angle X-ray diffraction, differential scanning calorimetry, picnometry, and scanning electron microscopy. The properties of crosslinked PP/PE blends were determined by the content of crosslinking agent and processing method. For the material blended by roll, a 2% concentration of peroxide corresponded to a maximum tensile strength and minimum impact strength. However, the mechanical strength of those products blended by extrusion monotonously decreased with increasing peroxide content because of serious degradation. The interfacial adhesion of PP/PE blends could be enhanced by adding random or block copolymer of propylene and ethylene, and the impact strength as well as ductility were greatly improved. Experimental data showed that the impact strength of PP/LDPE/random copolymer ternary blend could reach as high as 33.3 kg · cm/cm; however, its rigidity and tensile strength were inferior to those of PP/LDPE/block copolymer blend.     

Control of free-radical emulsion polymerization of methyl methacrylate by oxygen injection. II. Experimental study

Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.