Single crystalline ZnSe nanowires grown by molecular beam epitaxy technique viaAucatalyzed vapor-liquid-solid reaction showed interesting growth phenomena. Au catalysts initially reacted with the substrate to from binary AuGa2 alloy droplets. The growth direction ZnSe nanowires was mainly determined by the sizes of AuGa2 catalysts. The L-S interface structure at the tip of the NW was the most critical factor influencing the NW growth direction. The size-dependent growth direction of ZnSe nanowires was interpreted based on the estimation of the surface and interface energies of ZnSe nuclei.

No abstract

We report molecular-beam epitaxy growth of single crystalline ZnSe nanowires with uniform diameters (∼10 nm) on GaP(111) substrates. The growth process was based on the Au-catalyzed vapor-liquid-solid deposition. As determined by electron microdiffraction and high-resolution transmission electron microscopy, ZnSe nanowires grew generally along the 〈110〉 and 〈112〉 directions with the orientation relationship of (111)ZnSe wire//(111)GaP and 〈11̄0〉ZnSe wire//〈11̄0〉GaP. The dominant defects were found to be twins at the interface between the substrate and the nanowires along the (111) plane.

This paper reports the first part of a project that aims to develop a knowledge extraction and knowledge discovery system that extracts causal knowledge from textual databases. In this initial study, we develop a method to identify and extract cause-effect information that is explicitly expressed in medical abstracts in the Medline database. A set of graphical patterns were constructed that indicate the presence of a causal relation in sentences, and which part of the sentence represents the cause and which part represents the effect. The patterns are matched with the syntactic parse trees of sentences, and the parts of the parse tree that match with the slots in the patterns are extracted as the cause or the effect.

A progress report is given of an extension of the density functional formalism to include long-range interactions such as van der Waals or dispersion forces. This is done by proving a general expression for the so-called exchange-correlation energy to contain and to describe such interactions just as well as any other treatment. The proper long-range forms of the interactions are derived explicitly in the cases of two neutral atoms, an atom outside a metal surface, and two parallel metal surfaces. The long-standing problem of treating the attractive and repulsive forces on the same footing in this way gets a solution. For practical calculations, an approximate form, based on an analysis in the weakly inhomogeneous limit and on a limiting form of the three-point function given by Rapcewicz and Ashcroft, is proposed and applied to some prototype cases. 0 1995 John Wiley & Sons, Inc.well-known R -6 form of London [4]. The asymptotic z p 3 form of the interaction potential between a neutral atom and a surface was first identified by , with subsequent refined treatments of the atom and surface polarizabilities [6,7]. For the interaction between solid bodies, general formulas have been derived [S], which for flat sur-

A high incidence of sensitization to Blomia tropicalis, the predominant house dust mite species in tropical regions, is strongly associated with allergic diseases in Singapore, Malaysia, and Brazil. IgE binding to the group 5 allergen, Blo t 5, is found to be the most prevalent among all B. tropicalis allergens. The NMR structure of Blo t 5 determined represents a novel helical bundle structure consisting of three antiparallel α-helices. Based on the structure and sequence alignment with other known group 5 dust mite allergens, surface-exposed charged residues have been identified for site-directed mutagenesis and IgE binding assays. Four charged residues, Glu76, Asp81, Glu86, and Glu91 at around the turn region connecting helices α2 and α3 have been identified to be involved in the IgE binding. Using overlapping peptides, we have confirmed that these charged residues are located on a major putative linear IgE epitope of Blo t 5 from residues 76–91 comprising the sequence ELKRTDLNILERFNYE. Triple and quadruple mutants have been generated and found to exhibit significantly lower IgE binding and reduced responses in skin prick tests. The mutants induced similar PBMC proliferation as the wild-type protein but with reduced Th2:Th1 cytokines ratio. Mass screening on a quadruple mutant showed a 40% reduction in IgE binding in 35 of 42 sera of atopic individuals. Findings in this study further stressed the importance of surface-charged residues on IgE binding and have implications in the cross-reactivity and use of Blo t 5 mutants as a hypoallergen for immunotherapy.

Plants use a highly evolved immune system to exhibit defense response against microbial infections. The plant TIR domain, together with the nucleotide-binding (NB) domain and/or a LRR region, forms a type of molecule, named resistance (R) proteins, that interact with microbial effector proteins and elicit hypersensitive responses against infection. Here, we report the first crystal structure of a plant TIR domain from Arabidopsis thaliana (AtTIR) solved at a resolution of 2.0 Å . The structure consists of five b-strands forming a parallel b-sheet at the core of the protein. The b-strands are connected by a series of a-helices and the overall fold mimics closely that of other mammalian and bacterial TIR domains. However, the region of the aD-helix reveals significant differences when compared with other TIR structures, especially the aD3-helix that corresponds to an insertion only present in plant TIR domains. Available mutagenesis data suggest that several conserved and exposed residues in this region are involved in the plant TIR signaling function.

Type III secretion systems (T3SSs) are adopted by pathogenic bacteria for the transport of effector proteins into host cells through the translocon pore composed of major and minor translocator proteins. Both translocators require a dedicated chaperone for solubility. Despite tremendous efforts in the past, structural information regarding the chaperone-translocator complex and the topology of the translocon pore have remained elusive. Here, we report the crystal structure of the major translocator, AopB, from Aeromonas hydrophila AH-1 in complex with its chaperone, AcrH. Overall, the structure revealed unique interactions between the various interfaces of AopB and AcrH, with the N-terminal "molecular anchor" of AopB crossing into the "N-terminal arm" of AcrH. AopB adopts a novel fold, and its transmembrane regions form two pairs of helical hairpins. From these structural studies and associated cellular assays, we deduced the topology of the assembled T3SS translocon; both termini remain extracellular after membrane insertion.