Tailoring Electron‐Transfer Barriers for Zinc Oxide/C60 Fullerene Interfaces

The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C₆₀. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies.     

Biomimetic Bidirectional Switchable Adhesive Inspired by the Gecko

The gecko adhesive system has attracted significant attention since the discovery that van der Waals interactions, which are always present between surfaces, are predominantly responsible for their adhesion. The unique anisotropic frictional–adhesive capabilities of the gecko adhesive system originate from complex hierarchical structures and just as importantly, the anisotropic articulation of the structures. Here, by cleverly engineering asymmetric polymeric microstructures, a reusable switchable gecko‐like adhesive can be fabricated yielding steady high adhesion ( ≈ 1.25 N/cm²) and friction ( ≈ 2.8 N/cm²) forces when actuated for “gripping”, yet release easily with minimal adhesion ( ≈ 0.34 N/cm²) and friction (≈ 0.38 N/cm²) forces during detachment or “releasing”, over multiple attachment/detachment cycles, with a relatively small normal preload of 0.16 N/cm² to initiate the adhesion. These adhesives can also be used to reversibly suspend weights from vertical (e.g., walls), and horizontal (e.g., ceilings) surfaces by simultaneously and judiciously activating anisotropic friction and adhesion forces. This design opens the way for new gecko‐like adhesive surfaces and articulation mechanisms that do not rely on intensive nanofabrication in order to recover the anisotropic tribological property of gecko adhesive pads, albeit with lower adhesive forces compared to geckos.     

Oxidative microbial degradation of 2,4,6-trinitrotoluene via 3-methyl-4,6-dinitrocatechol

A novel pathway for biodegradation of 2,4,6-trinitrotoluene (TNT) was investigated where TNT was the sole carbon, nitrogen, and energy source. Results showed the ability of microorganismsto metabolize TNT through removal of a nitro-group, oxygenation of the aromatic ring, and production of a metabolite that is typically a precursor to oxygenolytic ring cleavage. Nitrite production was observed in active systems, and TNT degradation activity was repeatable and transferable. The metabolic intermediate, 3-methyl-4,6-dinitrocatechol, was positively identified through stable isotope mass spectrometry and tandem mass spectrometry. Experimentation with 14C-TNT showed >3% 14C-labeled CO2 in active systems after 30 d exposure to microorganisms. An increasing fraction of 14C-labeled material was associated with biomass with time, where 11.41 +/- 2.91% and 17.09 +/- 1.49% of 14C was associated with biomass in active systems after 20 and 30 d, respectively, as compared with 5.68 +/- 1.33% and 6.08 +/- 1.27% in inactive systems. Parallel degradation of TNT and production of organic metabolites and nitrite were observed in shake flasks constructed with soil from historically contaminated sites, indicating that the novel pathway identified herein is disturbed in the environment. Therefore, results presented provide evidence of a previously unreported pathway for oxidative degradation of TNT.     

Corrosion of high temprature alloys in the primary circuit helium of high temperature gas cooled reactors. – Part I: Theoretical background

The interaction of Ni and Fe-Ni base alloys with the reactive impurities H₂O, CO, H₂ and CH₄ in simulated cooling gas of the primary circuit of the High Temperature Gas Cooled Reactor (HTGR) causes corrosion effects that can significantly influence the mechanical properties. Apart from the formation of surface scales (oxides, carbides or mixed oxides/carbides), structural changes of the alloys are observed; depending on gas composition, gas supply rate and test temperature, carburization or decarburization can occur. In this report it is shown that an interpretation of the basic corrosion effects is possible on the basis of a modified stability diagram for chromium provided that - the kinetics of elementary gas metal reactions are incorporated in the expressions for carbon activity and oxygen partial pressure of the atmosphere and - the gradients of the potentials across the surface scales are taken into account. The interpretation allows the derivation of the corrosion behaviour of NiCr-base alloys in different HTGR helium compositions and enables the limits for the formation of protective chromia surface scales to be given. The influence of alloying elements other than chromium can be explained qualitatively. The results can be transferred to other reactive gas mixtures, which are characterized by an oxygen partial pressure near to the dissociation pressure of the scale forming oxides.     

Humanities computing 25 years later

This paper attempts to provide an overview of the development of humanities computing during the past twenty-five years. Mention is made of the major applications of the computer to humanities disciplines, and of the most important and representative projects across the world. Joseph Raben, professor emeritus at Queens College, The City University of New York, is founding editor of Computers and the Humanities. He is currently establishing an edited computer conference, SCHOLAR.     

William A. Hunt (1903–1986).

William A. Hunt was one of our country's early scientist-clinicians. He began his career with study of a psychology that was a meld of Titchener's structuralism and Harvard's functionalism and completed it 50 years later in the field of health psychology. Hunt spent all but a few of those 50 years as a full-time teacher, at schools that included Dartmouth College, Connecticut College for Women, and Northwestern University. While doing his dissertation, he had mastered and used the structuralist's experimental method of introspection, applying it to the study of human emotion, specifically the James-Lange theory. In 1941, Hunt entered the Navy. He discerned that the screening for military duty of some 15 million women and men required an approach suited to the rapid, albeit individual, screening of large numbers of such personnel. His teaming up with a psychiatrist, Cecil Wittson, led to their joint development of a screening interview lasting one to two minutes that, with continued refinement, proved remarkably effective. Their goals as the mental health specialists participating in the medical examination conducted at this intake station were twofold: (a) to improve the efficiency of the Navy by removing those neuropsychiatric high-risk recruits who were potential psychiatric casualties if they continued in the Navy and (b) by such removal, to save these recruits the disastrous personal experience of subsequent breakdown during military duty. In his own still active research in the 1960s and 1970s Hunt continued to apply the same methods he earlier had used (in his Navy research) to the judgmental processes clinical psychologists used to identify psychological test responses that were pathognomonic of schizophrenia, mental retardation, and related forms of psychopathology. Hunt remained, until his death at age 82, an active scientist-clinician. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modified spontaneous emission in oligo (p-phenylene vinylene) planar microcavities

This paper reports on the photoluminescence properties of phenylene vinylene oligomers films (OPV) the emission of which was modified by microcavity effect. Films with 4 and 6 vinyl groups (respectively denoted OPV-4 and OPV-6) were investigated. A strong blue luminescence at 470 nm is observed for OPV-4. OPV-6 shows an emission spectrum quite similar to that of poly phenylene vinylene (PPV). Photoluminescence excitation measurements (PLE) give similar behaviors for the two samples and do not show any change in the shape of the spectra. Ageing under UV irradiation (380 nm) of the unencapsulated OPV-4 layers was evidenced by an exponential decrease of the photoluminescence intensity of about 40% after 3 h a continuous illumination. OPV-6 samples, aged on shelf, for weeks does only show a small decrease (15%) of the PL level over more than 7 h under continuous UV irradiation. Microcavity related effects were observed by inserting the films between two mirrors. These are generally a TiO₂/SiO₂ distributed Bragg reflectors (DBR) as bottom mirror and a Ag film as top mirror. However best results were obtained with two dielectric DBR. As expected, a strong enhancement of the emission at the cavity resonance and pronounced angular effects (emission peaking in the direction normal to the surface of the device) were observed. The importance of the position of the emitting material within the microcavity is evidenced with a thin tris(8-hydroxy) quinoline aluminum (Alq) embedded in SiO₂ with various cavity configurations.     

WorkSpace and the study of Chagas' disease

Chagas' disease afflicts more than 18 million people throughout South and Central America. Some areas of North America have also seen an increased incidence in recent years. The Trypanosoma cruzi (T. cruzi) parasite, which causes the disease, is most often transmitted by Triatomid bugs living in close proximity to humans. The T. cruzi parasite depends heavily on a small molecule called trypanothione to protect itself against damage from free radicals produced during normal metabolism. The concentration of trypanothione in the cell is carefully maintained by an enzyme called trypanothione reductase (TR). Drugs that inhibit TR should cause the parasite to die. Human cells have a similar enzyme-substrate pair: glutathione and glutathione reductase (GR). Fortunately, the enzyme GR differs electrostatically from TR, so there is hope of developing a drug that will be safe for human cells. The molecular structures of both TR and GR are known from ongoing X-ray crystallography studies. Both enzymes are dimers, that is, they consist of two equivalent domains, each having its own active site (the place where glutathione or trypanothione binds). One surprising feature of this system is a long tunnel passing through the center of the dimer and connecting the active sites of the two domains. While this is a naturally interesting feature to explore in a VR environment, the goal of the research is to evaluate the binding ability of particular drugs. For purposes of early testing, we chose chlorpromazine, an antidepressant drug. Large doses of the drug are known to kill the parasite, but are also toxic to the human host. It is possible that minor structural changes to this molecule would improve the selectivity and potency of the drug. For purposes of testing our VR environment, we present only a token calculation on chlorpromazine