不同组分Zn1-xCdxTe<110>单晶产生THz辐射的研究

本文介绍了不同组分的Zn1-xCdxTe〈110〉单晶产生THz辐射的特性.通过实验我们得到了不同组分的Zn1-xCdxTe〈110〉单晶产生THz辐射的效率与晶体中Cd所占组分的关系.发现当Cd的组分x=0.05时,晶体产生THz辐射的效率最好.通过研究晶体对THz辐射的吸收和实验中晶体的相位匹配条件,我们发现晶体的相位匹配是影响THz辐射产生效率的主要因素.     

Medium-scale carbon nanotube thin-film integrated circuits on flexible plastic substrates

The ability to form integrated circuits on flexible sheets of plastic enables attributes (for example conformal and flexible formats and lightweight and shock resistant construction) in electronic devices that are difficult or impossible to achieve with technologies that use semiconductor wafers or glass plates as substrates. Organic small-molecule and polymer-based materials represent the most widely explored types of semiconductors for such flexible circuitry. Although these materials and those that use films or nanostructures of inorganics have promise for certain applications, existing demonstrations of them in circuits on plastic indicate modest performance characteristics that might restrict the application possibilities. Here we report implementations of a comparatively high-performance carbon-based semiconductor consisting of sub-monolayer, random networks of single-walled carbon nanotubes to yield small- to medium-scale integrated digital circuits, composed of up to nearly 100 transistors on plastic substrates. Transistors in these integrated circuits have excellent properties: mobilities as high as 80 cm(2) V(-1) s(-1), subthreshold slopes as low as 140 m V dec(-1), operating voltages less than 5 V together with deterministic control over the threshold voltages, on/off ratios as high as 10(5), switching speeds in the kilohertz range even for coarse (approximately 100-microm) device geometries, and good mechanical flexibility-all with levels of uniformity and reproducibility that enable high-yield fabrication of integrated circuits. Theoretical calculations, in contexts ranging from heterogeneous percolative transport through the networks to compact models for the transistors to circuit level simulations, provide quantitative and predictive understanding of these systems. Taken together, these results suggest that sub-monolayer films of single-walled carbon nanotubes are attractive materials for flexible integrated circuits, with many potential areas of application in consumer and other areas of electronics.     

An allylic ketyl radical intermediate in clostridial amino-acid fermentation

The human pathogenic bacterium Clostridium difficile thrives by the fermentation of l-leucine to ammonia, CO(2), 3-methylbutanoate and 4-methylpentanoate under anaerobic conditions. The reductive branch to 4-methylpentanoate proceeds by means of the dehydration of (R)-2-hydroxy-4-methylpentanoyl-CoA to 4-methylpent-2-enoyl-CoA, which is chemically the most demanding step. Ketyl radicals have been proposed to mediate this reaction catalysed by an iron-sulphur-cluster-containing dehydratase, which requires activation by ATP-dependent electron transfer from a second iron-sulphur protein functionally similar to the iron protein of nitrogenase. Here we identify a kinetically competent product-related allylic ketyl radical bound to the enzyme by electron paramagnetic resonance spectroscopy employing isotope-labelled (R)-2-hydroxy-4-methylpentanoyl-CoA species. We also found that the enzyme generated the stabilized pentadienoyl ketyl radical from the substrate analogue 2-hydroxypent-4-enoyl-CoA, supporting the proposed mechanism. Our results imply that also other 2-hydroxyacyl-CoA dehydratases and the related benzoyl-CoA reductases-present in anaerobically living bacteria-employ ketyl radical intermediates. The absence of radical generators such as coenzyme B12, S-adenosylmethionine or oxygen makes these enzymes unprecedented in biochemistry.     

Molecular identification of a retinal cell type that responds to upward motion

The retina contains complex circuits of neurons that extract salient information from visual inputs. Signals from photoreceptors are processed by retinal interneurons, integrated by retinal ganglion cells (RGCs) and sent to the brain by RGC axons. Distinct types of RGC respond to different visual features, such as increases or decreases in light intensity (ON and OFF cells, respectively), colour or moving objects. Thus, RGCs comprise a set of parallel pathways from the eye to the brain. The identification of molecular markers for RGC subsets will facilitate attempts to correlate their structure with their function, assess their synaptic inputs and targets, and study their diversification. Here we show, by means of a transgenic marking method, that junctional adhesion molecule B (JAM-B) marks a previously unrecognized class of OFF RGCs in mice. These cells have asymmetric dendritic arbors aligned in a dorsal-to-ventral direction across the retina. Their receptive fields are also asymmetric and respond selectively to stimuli moving in a soma-to-dendrite direction; because the lens reverses the image of the world on the retina, these cells detect upward motion in the visual field. Thus, JAM-B identifies a unique population of RGCs in which structure corresponds remarkably to function.     

cAMP signalling in mushroom bodies modulates temperature preference behaviour in Drosophila

Homoiotherms, for example mammals, regulate their body temperature with physiological responses such as a change of metabolic rate and sweating. In contrast, the body temperature of poikilotherms, for example Drosophila, is the result of heat exchange with the surrounding environment as a result of the large ratio of surface area to volume of their bodies. Accordingly, these animals must instinctively move to places with an environmental temperature as close as possible to their genetically determined desired temperature. The temperature that Drosophila instinctively prefers has a function equivalent to the 'set point' temperature in mammals. Although various temperature-gated TRP channels have been discovered, molecular and cellular components in Drosophila brain responsible for determining the desired temperature remain unknown. We identified these components by performing a large-scale genetic screen of temperature preference behaviour (TPB) in Drosophila. In parallel, we mapped areas of the Drosophila brain controlling TPB by targeted inactivation of neurons with tetanus toxin and a potassium channel (Kir2.1) driven with various brain-specific GAL4s. Here we show that mushroom bodies (MBs) and the cyclic AMP-cAMP-dependent protein kinase A (cAMP-PKA) pathway are essential for controlling TPB. Furthermore, targeted expression of cAMP-PKA pathway components in only the MB was sufficient to rescue abnormal TPB of the corresponding mutants. Preferred temperatures were affected by the level of cAMP and PKA activity in the MBs in various PKA pathway mutants.     

TMEM16A confers receptor-activated calcium-dependent chloride conductance

Calcium (Ca(2+))-activated chloride channels are fundamental mediators in numerous physiological processes including transepithelial secretion, cardiac and neuronal excitation, sensory transduction, smooth muscle contraction and fertilization. Despite their physiological importance, their molecular identity has remained largely unknown. Here we show that transmembrane protein 16A (TMEM16A, which we also call anoctamin 1 (ANO1)) is a bona fide Ca(2+)-activated chloride channel that is activated by intracellular Ca(2+) and Ca(2+)-mobilizing stimuli. With eight putative transmembrane domains and no apparent similarity to previously characterized channels, ANO1 defines a new family of ionic channels. The biophysical properties as well as the pharmacological profile of ANO1 are in full agreement with native Ca(2+)-activated chloride currents. ANO1 is expressed in various secretory epithelia, the retina and sensory neurons. Furthermore, knockdown of mouse Ano1 markedly reduced native Ca(2+)-activated chloride currents as well as saliva production in mice. We conclude that ANO1 is a candidate Ca(2+)-activated chloride channel that mediates receptor-activated chloride currents in diverse physiological processes.     

An analytical solution for VOCs emission from multiple sources/sinks in buildings

An analytical solution is presented to describe the emission/sorption of volatile organic compounds （VOCs） from/on multiple single-layer materials coexisting in buildings. The diffusion of VOCs within each material is described by a transient diffusion equation. All diffusion equations are coupled with each other through the equation of mass conservation in the air. The analytical solution is validated by the experimental data in literature. Compared to the one-material case, the coexistence of multiple materials may decrease the emission rate of VOCs from each material. The smaller the diffusion coefficient is, the more the emission rate decreases. Whether a material is a source or a sink in the case of multiple materials coexisting is not affected by the diffusion coefficient. For the case of multiple materials with different partition coefficients, a material with a high partition coefficient may become a sink. This may promote the emission of VOCs from other materials.     

Optimization of Casting Process for Heat and Abrasion Resistant Large Gray Iron Castings

Numerical simulations were used to optimize the casting design and conditions for large cast iron castings for marine engines, Simulations of the mold filling and solidification sequences were used to analyze the problems of previous casting conditions with marked improvements for large cylinder liner parts, The amount and positions of chills were optimized to improve the mechanical properties and to minimize the shrinkage and micro porosity in the castings. Ultra sonic testing, penetration testing, and mechanical property testing show no defects in the castings with the productivity significantly increased.