Publications

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Synthese par reaction de diphenylamine avec des iodures d'aryle en presence de K 2 CO 3 -18-crown-6 dans le dichloro-1,2 benzene

Zirconocene-coupling reactions of 6,6‘-bis[(trimethylsilyl)ethynyl]-2,2‘-bipyridine and 5,5‘-bis[(trimethylsilyl)ethynyl]-2,2‘-bipyridine give trimeric, zirconocene-containing macrocycles (3 and 4,...

D uring the next 25 years, world population is expected to increase by about 2.5 billion people, with most of this projected population growth expected to occur in developing countries. The food requirements in the developing world are expected to double by 2025. However, there has been a progressive decline in the annual rate of increase in cereal yield, so that at present, the annual rate of yield increase is below the rate of population increase. There are limited options for increasing the amount of land under cultivation for production of food crops without imposing undesirable environmental costs. Thus, the increased demand for food and fiber must be met primarily by increasing production on land already under cultivation. In addition to the limitations of intrinsic yield and available land, there is a significant water problem. Of the water that is available for use, about 70% is already used for agriculture.[*][1] Water systems are under severe strain in many parts of the world. Many rivers no longer flow all the way to the sea; 50% of the world's wetlands have disappeared; and many major groundwater aquifers are being mined unsustainably, with water tables in parts of Mexico, India, China, and North Africa declining by as much as 1 m per year. Approximately 40% of the world's food is produced from irrigated land,[†][2] and 10% is grown with water mined from aquifers. There is growing competition for water between cities and industry, with agriculture being the user of lowest value and last resort. Thus, the projected doubling of food production must largely take place on the same land area and using less water. More effective management of water requires a series of institutional and managerial changes in addition to a new generation of technical innovations that includes advances in genetic engineering of plants.[*][1] Photosynthetic carbon dioxide fixation by plants is associated with a large amount of water loss through transpiration. Thus, to prevent desiccation-induced growth arrest and injury, most plants require adequate soil moisture. The production of one pound of cotton by irrigated agriculture requires 17,000 pounds of water; production of a pound of rice requires about 4700 pounds of water.[‡][3] Recent advances in understanding the genetic control of drought tolerance offer new opportunities to develop crops that are less damaged by short periods of low soil moisture.[§][4] This might enable the use of less water for irrigation and reduce drought-induced yield reduction caused by the vagaries of weather in rain-fed agriculture. In addition, there is a promising opportunity to increase the average water use efficiency of agricultural systems by minimizing losses to pests and pathogens. Although many innovations in modifying plant water use are theoretically possible, one opportunity is related to the focus of this special issue of Science on plant pathology. It has been estimated that up to 40% of plant productivity in Africa and Asia, and about 20% in the developed world, is lost to pests and pathogens. Approximately one-third of the losses are due to viral, fungal, and bacterial pathogens, and the remainder is due to insects and nematodes. Much of the loss occurs after the plants are fully grown: a point at which most or all of the water required to grow a crop has been invested. Thus, reducing losses to pests and pathogens is equivalent to creating more land and more water. Most plants are resistant to most pests and pathogens. Knowledge of the mechanisms by which plants naturally resist pests and pathogens is rapidly increasing.[|][5] As knowledge about the molecular mechanisms for such resistance or susceptibility advances, it will become possible to transfer the genes responsible for resistance mechanisms from one species to another. The success of the genetically modified insect-resistant corn and cotton plants grown on a large scale in the United States provides a first example of the feasibility of the approach. Plants engineered for pest and pathogen resistance could be distributed without cost to subsistence farmers in the developing world by the International Crop Research Centers. The benefits of such developments would be substantial in terms of income and food for the poor, reduced demand for water, and limiting the expansion of land area under cultivation, all of which would also generate environmental benefits. [1]: #fn-1 [2]: #fn-2 [3]: #fn-3 [4]: #fn-4 [5]: #fn-5

Through calculation and analysis of the dynamic and electronic properties of 3d rocksalt transition metal carbides, we identify MnC as a novel material displaying ferromagnetic superconductivity mediated by minority-spin-triplet Cooper pairs.

Engagement of MHC class I-specific inhibitory receptors regulates natural killer (NK) cell development and function. Using both new and previously characterized anti-Ly49 monoclonal antibodies, we comprehensively determined expression and co-expression frequencies of four Ly49 receptors by NK cells from MHC-congenic, MHC class I-deficient, and Ly49A-transgenic mice to study mechanisms that shape the inhibitory Ly49 repertoire. All Ly49 receptors were expressed on partially overlapping subsets. Significantly, in the absence of class I MHC, several receptor pairs were co-expressed more frequently than predicted from a purely random expression model, indicating that biases independent of MHC class I underlie receptor co-expression in some cases. MHC interactions were found to inhibit Ly49 co-expression variably depending on the MHC allele and the receptor pair examined. These data extend previous evidence that interactions with MHC shape the repertoire. It was previously proposed that developing NK cells express Ly49 receptors sequentially and cumulatively, until self-MHC specific receptors are expressed and inhibit new receptor expression. Fulfilling a major prediction of this model, we found that class I recognition by a Ly49A transgene expressed by all developing NK cells equivalently inhibited expression of endogenous self-specific and nonself-specific Ly49 receptors.

We report the discovery of a light echo (LE) from the Type Ia supernova (SN) 2006X in the nearby galaxy M100. The presence of the LE is supported by analysis of both the Advanced Camera for Surveys (ACS) images taken with the {\it Hubble Space Telescope (HST)} at $\sim$300 d after maximum brightness and the Keck optical spectrum obtained at a similar phase. In the image procedure, both the radial-profile analysis and the point-spread-function (PSF) subtraction method resolve significant excess emission at 2--5 ACS pixels ($\sim0.05''-0.13''$) from the center. In particular, the PSF-subtracted ACS images distinctly appear to have an extended, ring-like echo. Due to limitations of the image resolution, we cannot confirm any structure or flux within 2 ACS pixels from the SN. The late-time spectrum of SN 2006X can be reasonably fit with two components: a nebular spectrum of a normal SN Ia and a synthetic LE spectrum. Both image and spectral analysis show a rather blue color for the emission of the LE, suggestive of a small average grain size for the scattering dust. Using the Cepheid distance to M100 of 15.2 Mpc, we find that the dust illuminated by the resolved LE is $\sim$27--170 pc from the SN. The echo inferred from the nebular spectrum appears to be more luminous than that resolved in the images (at the $\sim2\sigma$ level), perhaps suggesting the presence of an inner echo at $<$2 ACS pixels ($\sim0.05''$). It is not clear, however, whether this possible local echo was produced by a distinct dust component (i.e., the local circumstellar dust) or by a continuous, larger distribution of dust as with the outer component. Nevertheless, our detection of a significant echo in SN 2006X confirms that this supernova was produced in a dusty environment having unusual dust properties.

A hydrogen sensor has been developed for in situ measurements of the concentration of hydrogen in aqueous solutions at elevated temperatures. The sensor was based on an electrochemical cell employing an yttria‐stabilized zirconia (9% ) solid electrolyte, a (in air) reference electrode, and a noble metal working electrode (Pt or Pd) covered with a polytetrafluorene‐ethyl membrane. The response of the sensor to hydrogen has been examined in gas mixtures and aqueous solutions at temperatures as high as 300°C, and for hydrogen concentrations ranging from 0.001 to 100% or to mol/kg, respectively. The sensor displayed rapid responses to changes in concentration of hydrogen in both gas mixtures and aqueous solutions. Linear relationships with Nernstian slopes (2.303RT/2F) were observed between the measured potential of the sensor and the logarithm of the hydrogen concentration. Oxygen in solution had little effect on the potential of the sensor when the concentration of oxygen was lower than that of hydrogen, while there was a significant change in the potential with oxygen concentration in gas mixtures. The potential of the sensor was not affected by the pH of the solution.