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Zhenyu Zhang

Publications and source records attributed to Zhenyu Zhang.

35 records · Page 2Linked to original sources
PubMed2004

Direct extraction of the Eliashberg function for electron-phonon coupling: a case study of Be(10(-)10).

We propose a systematic procedure to directly extract the Eliashberg function for electron-phonon coupling from high-resolution angle-resolved photoemission measurement. The procedure is successfully applied to the Be(10(-)10) surface, providing new insights into electron-phonon coupling at this surface. The method is shown to be robust against imperfections in experimental data and suitable for wider applications.

Journal Article↗
PubMed2004

Adatom ascending at step edges and faceting on fcc metal (110) surfaces.

Using first-principles total-energy calculations, we show that an adatom can easily climb up at monatomic-layer-high steps on several representative fcc metal (110) surfaces via a place exchange mechanism. Inclusion of such novel adatom ascending processes in kinetic Monte Carlo simulations of Al(110) homoepitaxy as a prototypical model system can lead to the existence of an intriguing faceting instability, whose dynamical evolution and kinetic nature are explored in comparison with experimental observations.

Journal Article↗
PubMed2003

Electronic stability of magnetic Fe/Co superlattices with monatomic layer alternation.

We report a surprising observation that the growth of the [Fe(1 ML)/Co(1 ML)](n) superlattice of L1(0) structure on Cu(100) is stable only up to six atomic layers (n=3), which cannot be rationalized by stress arguments. Instead, first-principles calculations reveal a transition from the L1(0) to the B2 structure due to the effect of dimensionality on the stability of the electronic structure of the superlattice. Whereas the majority-spin electrons are energetically insensitive to the layer thickness, the minority-spin electrons induce the transition at n=3.

Journal Article↗
PubMed2003

Yeast V1-ATPase: affinity purification and structural features by electron microscopy.

V1-ATPase from the yeast Saccharomyces cerevisiae was purified via a FLAG affinity tag introduced into the N terminus of the G subunit. The preparation migrated as a single band in native gel electrophoresis and contained subunits ABCDEFGH (with subunit C present at substoichiometric amounts) as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The initial specific Ca-ATPase activity was approximately 6 micromol/min/mg. The structure of the yeast V1-ATPase was studied by electron microscopy of negatively stained and frozen hydrated samples. A 25-A resolution three-dimensional model of the complex was calculated from two-dimensional projections by the angular reconstitution technique. The model shows six elongated densities arranged in pseudo-3-fold symmetry around a large central cavity. At the top of the molecule, various protrusions can be seen. At the bottom of the complex, two large masses are visible that are connected to the main body of the molecule. Comparison of the yeast V1 structure with the structure of the intact V1V0-ATPase from bovine brain clathrin-coated vesicles (Wilkens, S., Vasilyeva, E., and Forgac, M. (1999) J. Biol. Chem. 274, 31804-31810) indicates that the structure of the isolated V1 from yeast is very similar to the structure of the V1 domain in the intact V-ATPase complex.

Chromatography, Affinity↗
PubMed2003

Surface phase transitions induced by electron mediated adatom-adatom interaction.

We propose that the indirect adatom-adatom interaction mediated by the conduction electrons of a metallic surface is responsible for the sqrt[3]xsqrt[3]<==>3x3 structural phase transitions observed in Sn/Ge (111) and Pb/Ge (111). When the indirect interaction overwhelms the local stress field imposed by the substrate registry, the system suffers a phonon instability, resulting in a structural phase transition in the adlayer. Our theory is capable of explaining all the salient features of the sqrt[3]xsqrt[3]<==>3x3 transitions observed in Sn/Ge (111) and Pb/Ge (111), and is in principle applicable to a wide class of systems whose surfaces are metallic before the transition.

Journal Article↗
PubMed2003

Nanocrystal formation and faceting instability in Al(110) homoepitaxy: true upward adatom diffusion at step edges and island corners.

Using atomic force microscopy and spot-profile analyzing low energy electron diffraction, we have observed the existence of a striking faceting instability in Al(110) homoepitaxy, characterized by the formation of nanocrystals with well-defined facets. These hut-shaped nanocrystals are over tenfold higher than the total film coverage, and coexist in a bimodal growth mode with much shallower and more populous surface mounds. We further use density functional theory calculations to elucidate the microscopic origin of the faceting instability, induced by surprisingly low activation barriers for adatom ascent at step edges and island corners.

Journal Article↗
PubMed2003

Functional characterization and expression analysis of members of the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase family from Drosophila melanogaster.

Here we report the cloning and functional characterization of eight members of the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase gene family from Drosophila melanogaster (polypeptide GalNAc transferase = pgant1-8). Full-length cDNAs were isolated from a Drosophila embryonic library based on homology to known ppGaNTases. Alignments with characterized mammalian isoforms revealed strong sequence similarities between certain fly and mammalian isoforms, highlighting putative orthologues between the species. In vitro activity assays demonstrated biochemical transferase activity for each gene, with three isoforms requiring glycosylated substrates. Comparison of the activities of Drosophila and mammalian orthologues revealed conservation of substrate preferences against a panel of peptide and glycopeptide substrates. Furthermore, Edman degradation analysis demonstrated that preferred sites of GalNac addition were also conserved between certain fly and mammalian orthologues. Semi-quantitative PCR amplification of Drosophila cDNA revealed expression of most isoforms at each developmental stage, with some isoforms being less abundant at certain stages relative to others. In situ hybridization to Drosophila embryos revealed specific staining of pgant5 and pgant6 in the salivary glands and pgant5 in the developing hindgut. Additionally, pgant5 and pgant6 expression within the egg chamber was restricted to the follicle cells, cells known to be involved in egg formation and subsequent embryonic patterning. The characterization reported here provides additional insight into the use of this model system to dissect the biological role of this enzyme family in vivo during both fly and mammalian development.

Amino Acid Sequence↗
PubMed2002

Self-assembly of nanometer-scale magnetic dots with narrow size distributions on an insulating substrate.

The self-assembly of iron dots on the insulating surface of NaCl(001) is investigated experimentally and theoretically. Under proper growth conditions, nanometer-scale magnetic iron dots with remarkably narrow size distributions can be achieved in the absence of a wetting layer. Furthermore, both the vertical and lateral sizes of the dots can be tuned with the iron dosage without introducing apparent size broadening, even though the clustering is clearly in the strong coarsening regime. These observations are interpreted using a phenomenological mean-field theory, in which a coverage-dependent optimal dot size is selected by strain-mediated dot-dot interactions.

Journal Article↗
PubMed2002

Island shape selection in Pt(111) submonolayer homoepitaxy with or without CO as an adsorbate.

The microscopic selection mechanisms of single-layer island shapes in Pt(111) homoepitaxy with or without minute amounts of CO adsorbate have been investigated theoretically. For clean growth, only triangular islands of a fixed orientation are obtained within a wide range of growth temperatures, with the orientation uniquely determined by a disparity in the rates of atom supply to an island corner site from the two island edges defining the corner. This novel picture is further corroborated by growth predictions in the presence of CO, whose preferential decoration of one type of the island edges reverses the intrinsic rate disparity for atom supply, thereby inverting the island orientation.

Journal Article↗
PubMed2002

Spontaneous assembly of perfectly ordered identical-size nanocluster arrays.

A method, by which periodic two-dimensional arrays of identical metal clusters of nanometer size and spacing could be spontaneously obtained by taking advantage of surface mediated clustering, is reported. The versatility of the method is demonstrated for a broad range of metals on Si(111)-(7 x 7) substrates. In situ scanning tunneling microscopy analysis of In clusters, combined with first-principles total energy calculations, unveils unique initial-stage atomic structures of the surface-supported clusters and the vital steps that lead to the success of this method. A strong interaction between the clusters and the surface holds the key to the observed cluster sizes.

Journal Article↗
PubMed2002

Application of the biological conjugate between antibody and colloid Au nanoparticles as analyte to inductively coupled plasma mass spectrometry.

This paper describes the study of atomization of nanoparticles by inductively coupled plasma mass spectrometry (ICPMS) and developes a novel nonisotopic immunoassay by coupling sandwich-type immunoreaction to ICPMS. The goat-anti-rabbit immunoglobulin G (IgG) labeled with colloidal gold nanoparticles served as an analyte in ICPMS for the indirect measurement of rabbit-anti-human IgG. Matrix effect studies showed the gold signal was not sensitive to the organic matrix. A relatively good correlation (r2 = 0.9528) between the proposed method and enzyme-linked immunosorbent assay has been obtained. The method may have significant potential as an important ICPMS-based nonisotopic immnoassay method for the simultaneous determination of biologic analytes of interest by labeling different kinds of inorganic nanoparticles.

Animals↗
PubMed2002

Development of a gas sensor utilizing chemiluminescence on nanosized titanium dioxide.

A gas-sensing mode based on chemiluminescence generated on the surface of nanosized materials is proposed in the present work. Seven nanosized materials were tested, and chemiluminescence was detected from six of them during the catalytic oxidation of organic vapors in air. The luminescence characteristics of ethanol and acetone vapors passing through the surface of TiO2 chosen were studied with a chemiluminescence-based detection system. The linear range of chemiluminescence intensity versus concentration of organic compounds is 40-400 microg/mL for ethanol and 20-200 microg/mL for acetone dissolved in water, respectively. X-ray powder diffraction and Raman spectrometry were used to investigate the changes in catalytic activity of TiO2 after a 60-h reaction at 380 degrees C. The results showed that the carbon deposited on the surface of TiO2, decreasing the catalytic activity, but can be removed in air by controlling the temperature at 500 degrees C for 3 h. Regenerability and no consumption of sensor substrate signify the long lifetime of the gas sensor.

Journal Article↗
PubMed2002

New dsDNA binding unnatural oligopeptides with pyrimidine selectivity.

Solid phase peptide library screening followed by extension of a lead recognition element for binding to a dsDNA sequence (NF binding site of IL6) using solution phase screening, delivered a new DNA binding peptide, Ac-Arg-Ual-Sar-Chi-Chi-Tal-Arg-CONH2. In the present research, the contribution of the different amino acid side chains to the binding strength of the peptide to dsDNA was investigated using an ethidium bromide displacement test. Based on these results, the lead structure was optimized by deconvolution. Eight new unnatural amino acids were evaluated at two positions of the heptapeptide replacing the Ual-Sar fragment. The strongest dsDNA binding was observed using ([(3-chlorophenyl)methyl]amino)acetic acid (Cbg) and beta-cyclohexyl-l-alanine (Cha) respectively, at those two positions. A 10-fold increase in affinity compared to the Ual-Sar sequence was obtained. Further enhancement of dsDNA binding was obtained with hybrid molecules linking the newly developed peptide fragment to an acridine derivative with a flexible spacer. This resulted in ligands with affinities in the microM range for the dsDNA target (K(d) of 2.1 x 10(-6) M). DNase I footprinting with the newly developed oligopeptide motifs showed the presence of a pronounced pyrimidine specificity, while conjugation to an intercalator seems to redirect the interaction to mixed sequences. This way, new unnatural oligopeptide motifs and hybrid molecules have been developed endowed with different sequence selectivities. The results demonstrate that the unnatural peptide library approach combined with subsequent modification of selected amino acid positions, is very suited for the discovery of novel sequence-specific dsDNA binding ligands.

Amino Acids↗
PubMed2002

Development of a chemiluminescence ethanol sensor based on nanosized ZrO2.

Chemiluminescence was observed on introducing ethanol vapor to the surface of nanosized ZrO2 and this effect could be utilized to design a sensor for trace ethanol detection. The term cataluminescence (CTL) was used to describe this kind of chemiluminescence because the luminescence is generated by the catalytic oxidation of organic vapors on the solid surface. The proposed sensor showed high sensitivity to ethanol at 195 degrees C. The stability of the gas sensor was demonstrated by continuous reaction with ethanol for 100 h. Quantitative analysis was performed at an optimum wavelength of 460 +/- 10 nm. The chemiluminescence intensity was proportional to the concentration of ethanol from 1.6 to 160 microg ml(-1), with a detection limit of 0.6 microg ml(-1) (signal-to-noise ratio = 3:1). The mechanism of the chemiluminescence reaction is discussed and the results show that one of the possible luminescent intermediates is acetaldehyde. The chemiluminescence on nanosized ZrO2 observed in this work demonstrates the possibility of developing new nanomaterials for low-temperature cataluminescence detection.

Journal Article↗
PubMed2002

Influence of abnormal cervical pap smear undertaken during pregnancy to the outcome of the pregnancy.

OBJECTIVE: To investigate the influence of abnormal cervical pap smear undertaken in pregnancy to the outcome of the pregnancy. METHODS: A total of 1 069 primipara deliveried in Beijing Chaoyang hospital from Jan 1999 to May 2001 were reviewed, furthermore we compared the group of normal pap smear (group A) with the group of abnormal pap smear (group B), and analysed the difference of the complications during pregnancy, methods of delivery, the first stage of labor, fetal distress and the outcome of the cervical pap smear postpartum. RESULTS: The incidence of premature rupture of the membranes and fetal distress in group B, which were 39.39% and 30.30%, respectively, were significantly higher than that of group A, which were 5.21% and 15.25%, respectively (P < 0.01). There was no statistical difference in premature delivery, the ratio of cesarean section and the first stage of labor which were 3.38% and 3.03%, 44.11% and 30.30%, 7.3 h and 7.7 h, respectively (P > 0.05). The regression rate for patients with abnormal cervical pap smear postpartum was 62%. CONCLUSIONS: The outcomes of the pregnancy such as premature rupture of the membranes and fetal distress were affected by the abnormal cervical pap smear undertaken during pregnancy. It is important to undergo routine cervical pap smear examination during pregnancy.

Female↗
PubMed2001

Quantitative determination of the metastability of flat Ag overlayers on GaAs(110).

Atomically flat ultrathin Ag films on GaAs(110) can be formed through a kinetic pathway. However, such films are metastable and will transform to 3D islands upon high temperature annealing. Using scanning tunneling microscopy, we have measured quantitatively the layer-resolved metastability of flat Ag overlayers as they evolve toward their stable state, and deduced the corresponding kinetic barrier the system has to overcome in reaching the stable state. These results indicate that the metastability of the Ag overlayer is defined by the quantum nature of the conduction electrons confined within the overlayer.

Journal Article↗