392 research outputs found
Enhancement of parametric pumping due to Andreev reflection
We report properties of parametric electron pumping in the presence of a
superconducting lead. Due to a constructive interference between the direct
reflection and the multiple Andreev reflection, the pumped current is greatly
enhanced. For both quantum point contacts and double barrier structures at
resonance, we obtain exact solutions in the weak pumping regime showing that
, which should be compared with the result of conductance
. Numerical results are also provided for the strong pumping
regime showing interesting Andreev assisted pumping behaviour
Universal quantized spin-Hall conductance fluctuation in graphene
We report a theoretical investigation of quantized spin-Hall conductance
fluctuation of graphene devices in the diffusive regime. Two graphene models
that exhibit quantized spin-Hall effect (QSHE) are analyzed. Model-I is with
unitary symmetry under an external magnetic field but with zero
spin-orbit interaction, . Model-II is with symplectic symmetry where
B=0 but . Extensive numerical calculations indicate that the two
models have exactly the same universal QSHE conductance fluctuation value
regardless of the symmetry. Qualitatively different from the
conventional charge and spin universal conductance distributions, in the
presence of edge states the spin-Hall conductance shows an one-sided log-normal
distribution rather than a Gaussian distribution. Our results strongly suggest
that the quantized spin-Hall conductance fluctuation belongs to a new
universality class
Nonlinear transport theory for hybrid normal-superconducting devices
We report a theory for analyzing nonlinear DC transport properties of
mesoscopic or nanoscopic normal-superconducting (N-S) systems. Special
attention was paid such that our theory satisfies gauge invariance. At the
linear transport regime and the sub-gap region where the familiar scattering
matrix theory has been developed, we provide confirmation that our theory and
the scattering matrix theory are equivalent. At the nonlinear regime, however,
our theory allows the investigation of a number of important problems: for N-S
hybrid systems we have derived the general nonlinear current-voltage
characteristics in terms of the scattering Green's function, the second order
nonlinear conductance at the weakly nonlinear regime, and nonequilibrium charge
pile-up in the device which defines the electrochemical capacitance
coefficients
Analysing Railway Safety with Systems Thinking
Railway system is a socio-technical system because the operation of such system also
heavily relies on the management of human activities and operating procedures in the organisation, as well as the execution of technical subsystems. Safety of these systems therefore is more than just about engineering their technical subsystems. The latest approach from systems engineering considers that an accident is due to inadequate controlled interactions in the system and is usually a dynamic event chain started from the activation of a hazard and culminated in a complex process of sequential and concurrent events until the system is eventually out of control. Meanwhile the analysis of these systems’s safety becomes much harder when simply applying the traditional techniques of safety assessment. It is because, first of all, a social-technical system consists of a lot of complex and
non-linear interactions, traditional techniques show their limits when analysing complex systems. And secondly, the safety of a social-technical system requires a system perspective, which should take all the behaviours (desired and undesired but predicted) of a system as a whole in the context of its environment. To capture the information needed, the models for these analyses (i.e., fault tree and FMEA table) will become too complex to have a systemic view of each individual causal factor. In this paper, we proposed an approach based on system thinking and system dynamics to analyse the safety of a social-technical system. The case study of a tram accident is simple enough for the purpose of demonstrating its feasibility and benefits. The comparison with fault tree analysis was conducted, but it was not for the evaluation of our approach. The real evaluation comes from the extensive
applications in real world
Engineering Klebsiella sp. 601 multicopper oxidase enhances the catalytic efficiency towards phenolic substrates
<p>Abstract</p> <p>Background</p> <p>Structural comparison between bacterial CueO and fungal laccases has suggested that a charged residue Glu (E106) in CueO replaces the corresponding residue Phe in fungal laccases at the gate of the tunnel connecting type II copper to the protein surface and an extra α-helix (L351-G378) near the type I copper site covers the substrate binding pocket and might compromise the electron transfer from substrate to type I copper. To test this hypothesis, several mutants were made in <it>Klebsiella sp</it>. 601 multicopper oxidase, which is highly homologous to <it>E. coli </it>CueO with a similarity of 90% and an identity of 78%.</p> <p>Results</p> <p>The E106F mutant gave smaller <it>K</it><sub><it>m </it></sub>(2.4-7fold) and <it>k</it><sub><it>cat </it></sub>(1-4.4 fold) values for all three substrates DMP, ABTS and SGZ as compared with those for the wild-type enzyme. Its slightly larger <it>k</it><sub><it>cat</it></sub><it>/K</it><sub><it>m </it></sub>values for three substrates mainly come from the decreased <it>K</it><sub><it>m</it></sub>. Deleting α-helix (L351-G378) resulted in the formation of inactive inclusion body when the mutant <sup>Δ</sup>α351-378 was expressed in <it>E. coli</it>. Another mutant α351-380M was then made <it>via </it>substitution of seven amino acid residues in the α-helix (L351-G378) region. The α351-380M mutant was active, and displayed a far-UV CD spectrum markedly different from that for wild-type enzyme. Kinetic studies showed the α351-380M mutant gave very low <it>K</it><sub><it>m </it></sub>values for DMP, ABTS and SGZ, 4.5-, 1.9- and 7-fold less than those for the wild type. In addition, <it>k</it><sub><it>cat</it></sub><it>/K</it><sub><it>m </it></sub>values were increased, 9.4-fold for DMP, similar for ABTS and 3-fold for SGZ.</p> <p>Conclusion</p> <p>The Glu residue at position 106 appears not to be the only factor affecting the copper binding, and it may also play a role in maintaining enzyme conformation. The α-helix (L351-G378) may not only block access to the type I copper site but also play a role in substrate specificities of bacterial MCOs. The α351-380M mutant catalyzing oxidation of the phenolic substrate DMP effectively would be very useful in green chemistry.</p
mTreeIllustrator: A Mixed-Initiative Framework for Visual Exploratory Analysis of Multidimensional Hierarchical Data
Multidimensional hierarchical (mTree) data are very common in daily life and scientific research. However, mTree data exploration is a laborious and time-consuming process due to its structural complexity and large dimension combination space. To address this problem, we present mTreeIllustrator, a mixed-initiative framework for exploratory analysis of multidimensional hierarchical data with faceted visualizations. First, we propose a recommendation pipeline for the automatic selection and visual representation of important subspaces of mTree data. Furthermore, we design a visual framework and an interaction schema to couple automatic recommendations with human specifications to facilitate progressive exploratory analysis. Comparative experiments and user studies demonstrate the usability and effectiveness of our framework
Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies
Fine powders of micron- and submicron-sized particles of undoped Cu2O
semiconductor, with three different sizes and morphologies have been
synthesized by different chemical processes. These samples include nanospheres
200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm.
They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5
K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The
other two polyhedron samples synthesized in different runs by the same process
are found to show different magnetic properties. One of them exhibits weak
ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g
at T = 5 K, while the other is paramagnetic. The total magnetic moment
estimated from the detected impurity concentration of Fe, Co, and Ni, is too
small to account for the observed magnetism by one to two orders of magnitude.
Calculations by the density functional theory (DFT) reveal that cation
vacancies in the Cu2O lattice are one of the possible causes of induced
magnetic moments. The results further predict that the defect-induced magnetic
moments favour a ferromagnetically coupled ground state if the local
concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible
scenario to explain the observed magnetic properties. The limitations of the
investigations in the present work, in particular in the theoretical
calculations, are discussed and possible areas for further study are suggested.Comment: 20 pages, 5 figures 2 tables, submitted to J Phys Condense Matte
Identification of the forensically important flies (Diptera: Muscidae) based on cytochrome oxidase subunit I (COI) gene in China
Accurate species identification is a crucial step in forensic entomology, as the insect collected on a corpse can provide useful information for estimation of postmortem interval (PMI). However, morphological distinction may on occasion be impossible to the adult flies and nymphs of the same genus. DNA-based method can be used as a supplemental means of morphological method. In this study, 31 forensically important Muscidae flies were collected from 15 locations in 11 provinces of China, and a 272 base pair region of the mitochondrial cytochrome oxidase subunit I (COI) gene was sequenced. The monophyletic branches of the phylogenetic tree revealed that this marker is suitable for discrimination between these five species of four genera of Muscidae. The genetic variations found on COI can be applied not only to identify the forensically important species, but also to understand the taxonomic positions of the sarcophagine species. In addition, this research will be instrumental for implementation of the Chinese Muscidae database.Keywords: Forensic science, forensic entomology, Muscidae, cytochrome oxidase subunit I (COI), species identificatio
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