137,882 research outputs found
Catalysts for electrochemical generation of oxygen
An effort was made to study the effects of cation and anion additions on oxygen evolution kinetics on platinum and the inhibitive or catalytic nature of the additions. The kinetics and mechanism of oxygen evolution on planitum metal in hydrofluoric and sulfuric acids, including the effects of foreign anions, were examined. The LEED-Auger-thin layer electrochemical system was developed for the examination of electrocatalytic surfaces. Samples for electrocatalytic LEED-Auger studies were prepared and examined
Wilson-t'Hooft Loops in Finite-Temperature Non-commutative Dipole Field Theory from Dual Supergravity
We first study the temporal Wilson loop in the finite-temperature
non-commutative dipole field theory from the string/gauge correspondence. The
associated dual supergravity background is constructed from the near-horizon
geometry of near-extremal D-branes, after applying T-duality and smeared twist.
We investigate the string configuration therein and find that while the
temperature produces a maximum distance in the interquark distance
the dipole in there could produce a minimum distance . The quark
boundary pair therefore could be found only if their distance is between
and . We also show that, beyond a critical temperature the
quark pair becomes totally free due to screening by thermal bath. We next study
the spatial Wilson loop and find the confining nature in the zero temperature
3D and 4D non-supersymmetry dipole gauge theory. The string tension of the
linear confinement potential is obtained and found to be a decreasing function
of the dipole field. We also investigate the associated t'Hooft loop and
determine the corresponding monopole anti-monopole potential. The conventional
screening of magnetic charge which indicates the confinement of the electric
charge is replaced by a strong repulsive however. Finally, we show that the
dual string which is rotating along the dipole deformed will behave as a
static one without dipole field, which has no minimum distance and has larger
energy than a static one with dipole field. We discuss the phase transition
between these string solutions.Comment: Latex, 22 pages, 8 figures, add several comment
Extraction and parsing of herbarium specimen data: Exploring the use of the Dublin core application profile framework
Herbaria around the world house millions of plant specimens; botanists and other researchers value these resources as ingredients in biodiversity research. Even when the specimen sheets are digitized and made available online, the critical information about the specimen stored on the sheet are not in a usable (i.e., machine-processible) form. This paper describes a current research and development project that is designing and testing high-throughput workflows that combine machine- and human-processes to extract and parse the specimen label data. The primary focus of the paper is the metadata needs for the workflow and the creation of the structured metadata records describing the plant specimen. In the project, we are exploring the use of the new Dublin Core Metadata Initiative framework for application profiles. First articulated as the Singapore Framework for Dublin Core Application Profiles in 2007, the use of this framework is in its infancy. The promises of this framework for maximum interoperability and for documenting the use of metadata for maximum reusability, and for supporting metadata applications that are in conformance with Web architectural principles provide the incentive to explore and add implementation experience regarding this new framework
Electrochemical generation of oxygen. 1: The effects of anions and cations on hydrogen chemisorption and anodic oxide film formation on platinum electrode. 2: The effects of anions and cations on oxygen generation on platinum electrode
The effects were studied of anions and cations on hydrogen chemisorption and anodic oxide film formation on Pt by linear sweep voltammetry, and on oxygen generation on Pt by potentiostatic overpotential measurement. The hydrogen chemisorption and anodic oxide film formation regions are greatly influenced by anion adsorption. In acids, the strongly bound hydrogen occurs at more cathodic potential when chloride and sulfate are present. Sulfate affects the initial phase of oxide film formation by produced fine structure while chloride retards the oxide-film formation. In alkaline solutions, both strongly and weakly bound hydrogen are influenced by iodide, cyanide, and barium and calcium cations. These ions also influence the oxide film formation. Factors considered to explain these effects are discussed. The Tafel slope for oxygen generation was found to be independent on the oxide thickness and the presence of cations or anions. The catalytic activity indicated by the exchange current density was observed decreasing with increasing oxide layer thickness, only a minor dependence on the addition of certain cations and anions was found
Life Tables of Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae): with a Mathematical Invalidation for Applying the Jackknife Technique to the Net Reproductive Rate
Life table data for the melon fly, Bactrocera cucurbitae (Coquillett), reared on cucumber (Cucumis sativus L.) were collected under laboratory and simulated field conditions. Means and standard errors of life table parameters were estimated for two replicates using the jackknife technique. At 25ºC, the intrinsic rates of increase (_r_) found for the two replicates were 0.1354 and 0.1002 day-1, and the net reproductive rates (_R_~0~) were 206.3 and 66.0 offspring, respectively. When the cucumbers kept under simulated field conditions were covered with leaves, the _r_ and _R_~0~ for the two replicates were 0.0935 and 0.0909 day-1, 17.5 and 11.4 offspring, respectively. However, when similar cucumbers were left uncovered, the _r_ and _R_~0~ for the two replicates were 0.1043 and 0.0904 day-1, and 27.7 and 10.1 offspring, respectively. Our results revealed that considerable variability between replicates in both laboratory and field conditions is possible; this variability should be taken into consideration in data collection and application of life tables. Mathematical analysis has demonstrated that applying the jackknife technique results in unrealistic pseudo-_R_~0~ and overestimation of its variance. We suggest that the jackknife technique should not be used for the estimation of variability of _R_~0~
An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
The new BABAR data on the pion-photon transition form factor arouses people's
new interests on the determination of pion distribution amplitude. To explain
the data, we take both the leading valence quark state's and the non-valence
quark states' contributions into consideration, where the valence quark part up
to next-to-leading order is presented and the non-valence quark part is
estimated by a phenomenological model based on its limiting behavior at both
and . Our results show that to be consistent with the
new BABAR data at large region, a broader other than the asymptotic-like
pion distribution amplitude should be adopted. The broadness of the pion
distribution amplitude is controlled by a parameter . It has been found that
the new BABAR data at low and high energy regions can be explained
simultaneously by setting to be around 0.60, in which the pion distribution
amplitude is closed to the Chernyak-Zhitnitsky form.Comment: 19 pages, 6 figures, 2 tables. Slightly changed, references updated.
To be published in Phys.Rev.
Single-Walled Carbon Nanotubes as Shadow Masks for Nanogap Fabrication
We describe a technique for fabricating nanometer-scale gaps in Pt wires on
insulating substrates, using individual single-walled carbon nanotubes as
shadow masks during metal deposition. More than 80% of the devices display
current-voltage dependencies characteristic of direct electron tunneling. Fits
to the current-voltage data yield gap widths in the 0.8-2.3 nm range for these
devices, dimensions that are well suited for single-molecule transport
measurements
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