26 research outputs found
Direct evidence of the dependence of surface state density on the size of SnO2 nanoparticles observed by scanning tunneling spectroscopy
No full textIn this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles.
The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the
band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental
evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases,
and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles
Evidence of band bending flattening of 10 nm polycrystalline SnO2
No full textWe developed a model for n-type metal-oxide semiconductors, which allows one to calculate the density of charged surface states on
nanostructured grains, once the Schottky barrier height is known.We characterised structurally and electrically two sets of polycrystalline
SnO2 films with average grain radius of 30 and 10 nm. The purpose of this experiment was to observe the flattening of the bandbending
and the corresponding decrease in the density of charged surface states which are, in turn, responsible for the pinning of the Fermi level.
Finally, we highlighted how this phenomenon affects the characteristics of the films as gas sensors
STM and XPS characterisation of vacuum annealed nanocrystalline WO3 films
No full textScanning tunnelling microscopy and X-ray Photoelectron Spectroscopy were conducted on magnetron sputtered WO3 thin films, following a sequence of ultra high vacuum anneals from 100 degrees C to 900 degrees C. Annealing from 100 degrees C to 400 degrees C induced an upward surface band bending of about 0.3 eV, attributed to the oxygen migration from the bulk to the surface, but no changes in the surface topography. Chemical changes occurred from 600 degrees C to 800 degrees C, associated with the formation of secondary oxide species. STM imaging showed that the film surface consists of amorphous particles 35 nm in size up to 600 degrees C, while higher temperatures resulted in an increase in particle size. Crystallisation of the nanoparticles started to occur after annealing at 600 degrees C. The implications in terms of gas sensing are discussed. (c) 2007 Elsevier B.V. All rights reserved
On TGG Ability for Transforming UML 2 Sequence Diagrams with Imbricate Combined Fragments to π-Calculus Specifications
No full textAbstractThis paper describes a way based on operational semantics of π-calculus and uses TGG tool to formalize sequence diagrams to establish formal verification through model transformations. Our transformation uses basic interactions and combined fragments with the operator Alt, Opt and Par. We argue that TGG rules can be more easily used and they become more understandable. The transformation feasibility is illustrated on a scenario of phone system
Photo-induced unpinning of Fermi level in WO3
No full textAtomic force and high resolution scanning tunneling analyses were carried out on
nanostructured WO3 films. It turned out that the band gap measured by scanning tunneling
spectroscopy at surface is lower than the band gap reported in the literature. This effect is
attributed to the high density of surface states in this material, which allows tunneling into
these states. Such a high density of surface states pins the Fermi level resulting in modest
surface activity at room temperature. Photo activation of WO3 results in unpinning of the
Fermi level and thereby in higher chemical activity at surface
Stylistic Study of Purple Hibiscus
No full textThis paper did a linguistic-stylistic study of the novel with emphasis on determining how the author manipulated language to create aesthetic patterns and values. Using the notion projection method in selecting data from the texts, a linguistic model like the Transformational Generative Grammar (TGG) was applied in the analysis of certain aspects of identified literary language. The TGG features were used to describe foregrounding, hypotactic, paratactic, code-mixing and code switching rhetorical patterns and fragmentary structures. This not only showed the inter-relationship among literature, languages, linguistics and stylistics but revealed the literary artists (un) conscious ability to manipulate language
Molecular mechanism of sequence-dependent stability of RecA filament
No full textA is a DNA-dependent ATPase and mediates homologous recombination by first forming a filament on a single-stranded (ss) DNA. RecA binds preferentially to TGG repeat sequence, which resembles the recombination hot spot Chi (5'-GCTGGTGG-3') and is the most frequent pattern (GTG) of the codon usage in Escherichia coli. Because of the highly dynamic nature of RecA filament formation, which consists of filament nucleation, growth and shrinkage, we need experimental approaches that can resolve each of these processes separately to gain detailed insights into the molecular mechanism of sequence preference. By using a single-molecule fluorescence assay, we examined the effect of sequence on individual stages of nucleation, monomer binding and dissociation. We found that RecA does not recognize the Chi sequence as a nucleation site. In contrast, we observed that it is the reduced monomer dissociation that mainly determines the high filament stability on TGG repeats. This sequence dependence of monomer dissociation is well-correlated with that of ATP hydrolysis, suggesting that DNA sequence dictates filament stability through modulation of ATP hydrolysis.BN/BionanoscienceApplied Science
RecA filament maintains structural integrity using ATP-driven internal dynamics
No full textAt the core of homologous DNA repair, RecA catalyzes the strand exchange reaction. This process is initiated by a RecA loading protein, which nucleates clusters of RecA proteins on single-stranded DNA. Each cluster grows to cover the single-stranded DNA but may leave 1- to 2-nucleotide (nt) gaps between the clusters due to three different structural phases of the nucleoprotein filaments. It remains to be revealed how RecA proteins eliminate the gaps to make a seamless kilobase-long filament. We develop a single-molecule fluorescence assay to observe the novel internal dynamics of the RecA filament. We directly observe the structural phases of individual RecA filaments and find that RecA proteins move their positions along the substrate DNA to change the phase of the filament. This reorganization process, which is a prerequisite step for interjoining of two adjacent clusters, requires adenosine triphosphate hydrolysis and is tightly regulated by the recombination hotspot, Chi. Furthermore, RecA proteins recognize and self-align to a 3-nt-period sequence pattern of TGG. This sequence-dependent phase bias may help the RecA filament to maintain structural integrity within the kilobase-long filament for accurate homology search and strand exchange reaction.BN/Cees Dekker LabBN/Chirlmin Joo La
Small molecules blocking the entry of severe acute respiratory syndrome coronavirus into host cells
No full textSevere acute respiratory syndrome coronavirus (SARS-CoV) is the pathogen of SARS, which caused a global panic in 2003. We describe here the screening of Chinese herbal medicine-based, novel small molecules that bind avidly with the surface spike protein of SARS-CoV and thus can interfere with the entry of the virus to its host cells. We achieved this by using a two-step screening method consisting of frontal affinity chromatography-mass spectrometry coupled with a viral infection assay based on a human immunodeficiency virus (HIV)-luc/SARS pseudotyped virus. Two small molecules, tetra-O-galloyl-beta-D-glucose (TGG) and luteolin, were identified, whose anti-SARS-CoV activities were confirmed by using a wild-type SARS-CoV infection system. TGG exhibits prominent anti-SARS-CoV activity with a 50% effective concentration of 4.5 microM and a selective index of 240.0. The two-step screening method described here yielded several small molecules that can be used for developing new classes of anti-SARS-CoV drugs and is potentially useful for the high-throughput screening of drugs inhibiting the entry of HIV, hepatitis C virus, and other insidious viruses into their host cells.link_to_OA_fulltex
