Solvothermal synthesis,nanostructural characterization and gas cryo-adsorption studies in a metal–organic framework (IRMOF-1) material

A nanoporous metal–organic framework material, exhibiting an IRMOF-1 type crystalline structure, was prepared by following a direct solvothermal synthesis approach, using zinc nitrate and terephthalic acid as precursors and dimethylformamide as solvent, combined with supercritical CO₂ activation and vacuum outgassing procedures. A series of advanced characterization methods were employed, including scanning electron microscopy, Fourier-transform infrared radiation spectroscopy and X-ray diffraction, in order to study the morphology, surface chemistry and structure of the IRMOF-1 material directly upon its synthesis. Porosity properties, such as Brunauer–Emmet–Teller (BET) specific area (～520 m²/g) and micropore volume (～0.2 cm³/g), were calculated for the activated sample based on N₂ gas sorption data collected at 77 K. The H₂ storage performance was preliminary assessed by low-pressure (0–1 bar) H₂ gas adsorption and desorption measurements at 77 K. The activated IRMOF-1 material of this study demonstrated a fully reversible H₂ sorption behavior combined with an adequate gravimetric H₂ uptake relative to its BET specific area, thus achieving a value of ～1 wt.% under close-to-atmospheric pressure conditions.     

Effects of ion irradiation in metallic glasses

Application of metallic glasses as structural materials has been limited by their poor ductility. To overcome brittle failure, nanocrystals are intentionally introduced to stabilize the glasses. In this study, we report on the application of ion irradiation to induce nanocrystalization in a Cu₅₀Zr₄₅Ti₅ (CZT) alloy. Transmission electron microcopy, microindentation and nanoindentation have been used to characterize the CZT alloy irradiated with 140 keV He ions at room temperature. Hardness enhancement was observed near the projected range of the He ions, coinciding with the formation of nanocrystals. Such microstructural changes, however, were not observed in the near surface region, where the electronic stopping process is dominant.     

Foraging theory for autonomous vehicle speed choice

We consider the optimal control design of an abstract autonomous vehicle (AAV). The AAV searches an area for tasks that are detected with a probability that depends on vehicle speed, and each detected task can be processed or ignored. Both searching and processing are costly, but processing also returns rewards that quantify designer preferences. We generalize results from the analysis of animal foraging behavior to model the AAV. Then, using a performance metric common in behavioral ecology, we explicitly find the optimal speed and task processing choice policy for a version of the AAV problem. Finally, in simulation, we show how parameter estimation can be used to determine the optimal controller online when density of task types is unknown.     

Determination of longitudinal dispersion coefficient and net advection in the tidal hudson river with a large-scale,high resolution SF6 tracer release experiment

Physical processes such as advection, dispersion, and air-water gas exchange play important roles in determining the movement and change in concentration of contaminants discharged into rivers. In the following, we report results from a large-scale SF6 tracer release experiment conducted in the tidal Hudson Riverto examine longitudinal dispersion and net advection. SF6 was injected into the Hudson River near Newburgh, NY, and surveyed for 13 days using a new, fully automated, high-resolution SF6 sampling and analysis system. Net down river advection of the water body originally tagged with SF6 was slow, averaging mean displacement rates of about 0.5 +/- 0.2 km d(-1). In contrast, spreading of the tracer was driven by tidal movement, causing rapid mixing of the water up and down river. By examining the change in the second moment of the tracer distribution with time, we determined the mean longitudinal dispersion coefficient to be 70.1 +/- 4.3 m2 s(-1). Temporal evolution of the SF6 inventory indicates an average gas transfer velocity over the period of the experiment of 6.5 +/- 0.5 cm h(-1) (1.56 +/- 0.12 m d(-1)). Vertical profiles show that mixing into the bottom layers of the river, in places reaching more than 53 m, seemed to be rapid.     

Novel tubing microreactor for monitoring chemical reactions

There is an expanding interest in small-scale methods to evaluate catalysts and chemical reactions at a variety of conditions, ranging up to 6.9 MPa (1000 psig) and 300 degrees C. Multiwell parallel batch techniques are most commonly applied in high-throughput screening systems. In contrast, we describe here a rapid, serial, highly controllable method based on LC-type steel tubing rated for high pressures. The tube, containing a variety of flowing ingredients, such as carrier solvents, catalyst formulations, and reactants, is self-heated ohmically using electrical current from a power supply monitored and regulated with a precision of 0.01%. An array of voltage taps arranged along its length serves to sense the real-time temperature profile of the tube. Reactions are seen as temperature pulses progressing through the reactor, in zones of 200 microL each, and tracked with a temperature precision of 0.1 degrees C. A unique pressure controller was devised to maintain constant reactor pressures despite effluent viscosity fluctuations due to polymerization. Several chemical reaction systems have been characterized to date, including decomposition reactions of di-tert-butyl peroxide, polymerizations of styrene, formation of polyethylene from ethylene, and copolymerization of ethylene with 1-octene. For ethylene polymerization, the amount of mass of polymer formed is proportional to the responses observed.     

Growth of InGaN HBTs by MOCVD

The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD) are studied. Atomic-force microscopy (AFM) images of p⁺InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures, the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch.     

Autonomic correlates of attention-deficit/hyperactivity disorder and oppositional defiant disorder in preschool children.

Numerous studies have revealed autonomic underarousal in conduct-disordered adolescents and antisocial adults. It is unknown, however, whether similar autonomic markers are present in at-risk preschoolers. In this study, the authors compared autonomic profiles of 4- to 6-year-old children with attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD; n = 18) with those of age-matched controls (n = 20). Children with ADHD and ODD exhibited fewer electrodermal responses and lengthened cardiac preejection periods at baseline and during reward. Although group differences were not found in baseline respiratory sinus arrhythmia, heart rate changes among ADHD and ODD participants were mediated exclusively by parasympathetic withdrawal, with no independent sympathetic contribution. Heart rate changes among controls were mediated by both autonomic branches. These results suggest that at-risk preschoolers are autonomically similar to older externalizing children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Student Perceptions of Asynchronous Computer-Mediated Communication in Face-to-Face Courses

While there are many distance education studies of student satisfaction or perceptions of CMC, studies on residential student perceptions of CMC are rare. A paper survey was administered to 105 residential graduate and undergraduate students at a midwestern U.S. university. Results indicated that the majority of students preferred face-to-face discussion over CMC for most tasks; however, CMC was preferred overall for simple learning tasks. Content analyses of student responses to open-ended questions revealed that some students perceived face-to-face discussion to be faster, easier, and more convenient, while others perceived that CMC saves time and is more convenient. A discriminant analysis revealed several important factors that predicted those who preferred CMC for discussion. Students further commented that they would learn better from CMC if their instructors were more involved with and enthusiastic about CMC. Speed and convenience appear to be more important to students than whether discussion is face-to-face or CMC .     

Management of complexity in enterprise integration projects by the PERA methodology

The issue of the presentation and management of complexity is one of the most important aspects of the development and use of enterprise reference architectures and their associated methodologies. There is a limit to the degree of detail that any level of decision-making can comprehend adequately. As the breadth of vision of a decision expands the degree of detail must be correspondingly reduced. It is thus impossible to present every detail of any real world problem. The presentation has to be based on the principle of minimal complexity at any point. Therefore, the formalism of an enterprise reference architecture needs only to capture the most important factors at each stage of complexity. A hierarchical approach is thus inevitable. This article proposes a four-level formalism as a hierarchical model for use in further studies on the presentation of complexity management. These four levels include architectural, interface, design tool and semantic methods. The impact of complexity management on workflow design for enterprise integration is also discussed.