Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges     

MJ Yoo  TA Fulton  HF Hess  RL Willett  LN Dunkleberger  RJ Chichester  LN Pfeiffer  KW West 《Science (New York, N.Y.)》1997,276(5312):579-582

A single-electron transistor scanning electrometer (SETSE)-a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron-has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/AlxGa1-xAs heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.  相似文献   

Crystallographic evidence for a free silylium ion     

Kim KC  Reed CA  Elliott DW  Mueller LJ  Tham F  Lin L  Lambert JB 《Science (New York, N.Y.)》2002,297(5582):825-827

Evidence for a three-coordinate silyl cation is provided by the crystal structure of [(Mes)3Si][H-CB11Me5Br6].C6H6 (where Mes is 2,4,6-trimethylphenyl). Free (Mes)3Si+ cations are well separated from the carborane anions and benzene solvate molecules. Ortho-methyl groups of the mesityl substituents shield the silicon atom from the close approach of nucleophiles, while remaining innocent as significant ligands themselves. The silicon center is three-coordinate and planar. The downfield 29Si nuclear magnetic resonance chemical shift in the solid state (226.7 parts per million) is almost identical to that in benzene solution and in "gas phase" calculations, indicating that three-coordination can be preserved in all phases.  相似文献   

DNA replication and traintracks     

Hayflick L 《Science (New York, N.Y.)》2002,296(5573):1611-1612

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Evidence that the M2 membrane-spanning region lines the ion channel pore of the nicotinic receptor   总被引：29，自引：0，他引：29  

R J Leonard  C G Labarca  P Charnet  N Davidson  H A Lester 《Science (New York, N.Y.)》1988,242(4885):1578-1581

Site-directed mutagenesis and expression in Xenopus oocytes were used to study acetylcholine receptors in which serine residues (i) were replaced by alanines (alpha, delta subunits) or (ii) replaced a phenylalanine (beta subunit) at a postulated polar site within the M2 transmembrane helix. As the number of serines decreased, there were decreases in the residence time and consequently the equilibrium binding affinity of QX-222, a quaternary ammonium anesthetic derivative thought to bind within the open channel. Receptors with three serine-to-alanine mutations also displayed a selective decrease in outward single-channel currents. Both the direction of this rectification and the voltage dependence of QX-222 blockade suggest that the residues mutated are within the aqueous pore of the receptor and near its cytoplasmic (inner) surface.  相似文献   

Functionally distinct NF-kappa B binding sites in the immunoglobulin kappa and IL-2 receptor alpha chain genes   总被引：47，自引：0，他引：47  

S L Cross  N F Halden  M J Lenardo  W J Leonard 《Science (New York, N.Y.)》1989,244(4903):466-469

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After-cooking darkening in oil-blanched French-fried potatoes     

W. W. Hawkins  Mary E. G. Chipman  Verna G. Leonard 《American Journal of Potato Research》1959,36(7):255-261

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Assessment of bioflocculant production by Bacillus sp. Gilbert, a marine bacterium isolated from the bottom sediment of Algoa Bay     

Nontembiso P  Sekelwa C  Leonard MV  Anthony OI 《Marine drugs》2011,9(7):1232-1242

The bioflocculant-producing potentials of a marine bacteria isolated from the bottom sediment of Algoa Bay was investigated using standard methods. The 16S rDNA sequence analysis revealed 98% similarity to that of Bacillus sp. HXG-C1 and the nucleotide sequence was deposited in GenBank as Bacillus sp. Gilbert with accession number {"type":"entrez-nucleotide","attrs":{"text":"HQ537128","term_id":"312064208","term_text":"HQ537128"}}HQ537128. Bioflocculant was optimally produced when sucrose (72% flocculating activity) and ammonium chloride (91% flocculating activity) were used as sole sources of carbon and nitrogen, respectively; an initial pH 6.2 of the production medium; and Mg²⁺ as cation. Chemical analysis of the purified bioflocculant revealed the compound to be a polysaccharide.  相似文献   

Correlation of the antinociceptive action and plasma concentration of fentanyl following intravenous administration in cats     

SA Robertson  WL Davies  PM Taylor  MJ Dixon 《Veterinary anaesthesia and analgesia》2002,29(2):94-94

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Lymphocystis disease in snapper (Pagrus auratus) from Spencer Gulf, South Australia     

PJK DURHAM  MJ ALLANSON  WG HUTCHINSON 《Australian veterinary journal》1996,74(4):312-313

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