Soft solution fluorine-free synthesis of anatase nanoparticles with tailored morphology

TiO₂ nanoparticles with tailored morphology have been synthesized under exceptionally soft conditions. The strategy is based on the use of a non-aqueous alcoholic reaction medium in which water traces, coming either from the air (atmospheric water) or from an ethanol–water azeotropic mixture (ethanol 96%), are incorporated in order to accelerate hydrolysis of the Ti–precursor. Moreover, organic surfactants have been used as capping agents so as to tailor crystal growth in certain preferential directions. Combinations of oleic acid and oleylamine, which lead to the formation of another surfactant, dioleamide, are employed instead of fluorine-based compounds, thus increasing the sustainability of the process. As a result, TiO₂ nanostructured hierarchical microspheres and individual nanoparticles with exposed high-energy facets can be obtained at atmospheric pressure and temperatures as low as 78 °C.     

Modification of the optical and structural properties of ZnO nanowires by low-energy Ar+ ion sputtering

The effects of low-energy (≤2 kV) Ar⁺ irradiation on the optical and structural properties of zinc oxide (ZnO) nanowires (NWs) grown by a simple and cost-effective low-temperature technique were investigated. Both photoluminescence spectra from ZnO NW-coated films and cathodoluminescence analysis of individual ZnO NWs demonstrated obvious evidences of ultraviolet/visible luminescent enhancement with respect to irradiation fluence. Annihilation of the thinner ZnO NWs after the ion bombardment was appreciated by means of high-resolution scanning electron microscopy and transmission electron microscopy (TEM), which results in an increasing NW mean diameter for increasing irradiation fluences. Corresponding structural analysis by TEM pointed out not only significant changes in the morphology but also in the microstructure of these NWs, revealing certain radiation-sensitive behavior. The possible mechanisms accounting for the decrease of the deep-level emissions in the NWs with the increasing irradiation fluences are discussed according to their structural modifications.     

Some microwave applications of BaSrTiO3 and high temperature superconductors

Abstract

The group at the University of Colorado has been working on the applications of BaSrTiO₃ and high temperature superconductors to microwave circuits and systems with support from Superconducting Core Technologies, NASA and ONR. This work has included the development of a voltage tunable oscillator, a phase shifter, and a voltage tunable phased array antenna system. An important aspect of this program is the lattice match between the high temperature superconductor and the ferroelectric materials which enables us to grow thin films of either material on each other. By choosing the appropriate barium stronium ratio we are able to obtain changes in the dielectric constant of 5 to 1 in bulk capacitors at 77 K, the liquid nitrogen boiling temperature. Phase shifts of a little less than 126° at 10 Ghz have been obtained by applying 5 volts on a one centimeter coplanar line. The proposed phased array systems should enable us to point the beam radiated from the antenna in an arbitrary direction using two control voltages of less than 50 volts. We believe this approach leads to the possibility of inexpensive electronically scannable antenna systems which could be used for mobile communications with satellites and cellular systems.     

Silver (Ag) as anode and cathode current collectors in high temperature planar solid oxide fuel cells

Planar electrolyte supported solid oxide fuel cells were operated at 900 °C with humidified H₂ for 200 h using silver mesh and paste for cathode current collection. Continuous potentiostatic tests at 0.7 V appeared to induce migration of Ag towards electrode-electrolyte interphase, while continuous OCV tests caused no mass transport. Similar SOFCs fueled by coal syngas at 850 °C using Ag for both anode and cathode current collection indicated little, if any, Ag migration; providing the possibility of employing Ag for 100 h laboratory scale tests using coal-derived syngas. Use of high temperature steam, carbon dioxide and carbon monoxide did not result in the formation of silver carbonates.     

Culture predicts Mexican Americans' college self-efficacy and college performance.

In hopes of promoting college success among Mexican Americans, researchers have identified factors related to their academic performance. A gap in the literature exists between the interactive role of acculturation, enculturation, and generation status in predicting college self-efficacy and college performance (grade-point average, or GPA). To fill this void, this study investigated the relation of demographic variables (e.g., age, gender, socioeconomic status) and cultural variables (e.g., acculturation, enculturation, generation status) on academic outcomes (e.g., college self-efficacy, college performance) among 408 Mexican-American college students. Results of a series of hierarchical regression analyses indicated socioeconomic status, generation status, enculturation, and acculturation had significant positive effects on college self-efficacy; socioeconomic status and the interaction of higher enculturation and first-generation status were positively and significantly related to GPA. Post-hoc analyses indicated college self-efficacy predicted college performance for students who were second generation and beyond. Implications for research and practice are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Strength Recovery in a High-Strength Steel During Multiple Weld Thermal Simulations

BlastAlloy 160 (BA160) is a low-carbon martensitic steel strengthened by copper and M₂C precipitates. Heat-affected zone (HAZ) microstructure evaluation of BA160 exhibited softening in samples subjected to the coarse-grained HAZ thermal simulations of this steel. This softening is partially attributed to dissolution of copper precipitates and metal carbides. After subjecting these coarse-grained HAZs to a second weld thermal cycle below the A _c1 temperature (at which austenite begins to form on heating), recovery of strength was observed. Atom-probe tomography and microhardness analyses correlated this strength recovery to re-precipitation of copper precipitates and metal carbides. A continuum model is proposed to rationalize strengthening and softening in the HAZ regions of BlastAlloy 160.     

Resilience and survivability in communication networks: Strategies,principles, and survey of disciplines

The Internet has become essential to all aspects of modern life, and thus the consequences of network disruption have become increasingly severe. It is widely recognised that the Internet is not sufficiently resilient, survivable, and dependable, and that significant research, development, and engineering is necessary to improve the situation. This paper provides an architectural framework for resilience and survivability in communication networks and provides a survey of the disciplines that resilience encompasses, along with significant past failures of the network infrastructure. A resilience strategy is presented to defend against, detect, and remediate challenges, a set of principles for designing resilient networks is presented, and techniques are described to analyse network resilience.     

Harmonizing agriculture and health sector actions to improve household nutrition: policy experiences from Afghanistan (2002–2007)

Coordination across sectors to address undernutrition with its varied underlying causes remains a challenge in developing countries. In Afghanistan, harmonization of health and agriculture policies and actions to reduce endemic undernutrition occurred during 2002-2007. This qualitative case study explores the forms of harmonization, enabling features and constraints in the policy process. We interviewed 57 stakeholders (39 central level, 18 provincial) involved in public nutrition or food security issues. Forms of harmonization included written policies, reseach, training and advocacy. Important features of the policy process included: policy entrepreneurs with operational and strategic capacity, consensus-building using a shared causal framework, working groups and strategic alliances. This case presents an interesting alternative to a national nutrition coordinating body, an approach that has met with mixed results, often due to the lack of authority, budget, and operational capacity of such a body to oversee ministries and enforce national nutrition objectives. Mid-level professionals mobilized into task forces achieved much with the support of national and international partners. This study highlights the importance of building capacity for sustaining change through local institutions.     

Microstructure and Thermoelectric Properties of Dense YB<Subscript>22</Subscript>C<Subscript>2</Subscript>N Samples Fabricated Through Spark Plasma Sintering

Dense samples of the higher boride YB₂₂C₂N have been fabricated through the spark plasma sintering (SPS) method with different sintering aids. YB₂₂C₂N is a representative of a series of newly discovered rare-earth borocarbonitrides, which may be the long-awaited n-type counterpart of boron carbide, “B₄C.” The effect of Si, SiC, Al, and TiC additions on the sintering process of YB₂₂C₂N has been studied. The best sintered bodies with densities higher than 90% of theoretical density were obtained by means of SPS at 1700°C. We show that the additive choice and pressure have an effect on grain size and density. An investigation of the effect of atmosphere on the sintering behavior has also been carried out. It was found that sinterability is enhanced under nitrogen atmosphere. Thermoelectric properties of the materials sintered with additives have been evaluated, and we discuss their dependences on the fabrication process route.