bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction of umu‐fhuA operon fusions to detect genotoxic potential by an antibody—cell surface reaction
Authors: Stubner Stephan , Schloter Michael , Moeck Gregory S. , Coulton J. W. , Ahne Fred , Hartmann Anton
Published: October 2006

For the environmental monitoring of genotoxic effects of chemicals, a new test system was developed using immunochemical detection of a cell surface reporter protein of Escherichia coli. A umu‐fhuA operon fusion was constructed on plasmid pST12, which is inducible via the SOS system by the mutagenic agent methyl‐methane‐sulfonate (MMS). The expression of the outer membrane protein FhuA as a reporter was detectable on the cell surface with a monoclonal anti‐FhuA antibody. Enzymelinked immunosorbent assay tests and immunofluorescence microscopy revealed that the operon fusion of PST12 led to specific and strong induction of the reporter protein FhuA after genotoxic treatment with MMS. © 1994 by John Wiley & Sons, Inc..
Studies on the water quality of river Ganga at Fatehgarh and Kannauj, U.P., India
Authors: Malik Abdul , Qadri Shafat A. , Musarrat Javed , Ahmad Masood
Published: October 2006

The comprehensive water quality studies on the River Ganga were undertaken at Fatehgarh and Kannauj (U.P.) during 1987–1990. The data revealed significant seasonal variations in the physicochemical and bacteriological properties of the river water. The remarkably high level of coliforms, fecal coliforms, and fecal streptococci reflects the poor quality of the water. Some of the Escherichia coli isolates from the test stretch also exhibited multiple drug resistance. These pollutants render the water unfit for drinking and bathing and may pose serious problems related to public health. © by John Wiley & Sons, Inc.
Comparison of gram positive and gram negative bacterial strains cloned with different types of luciferase genes in bioluminescence cytotoxicity tests
Authors: Lampinen Jorma , Virta Marko , Karp Matti
Published: October 2006

The bacterial bioluminescence assay is widely used to estimate chemical cytotoxicity. This assay is performed most often by using luminescent bacteria Vibrio fisheri NRRL‐B‐11177 (earlier cited as Photobacterium phosphoreum NRRL‐B‐11177) as a test organism. In this work we have used cloned gram(+) and gram(‐) bacterial strains for the evaluation of chemical toxicity. Two types of luciferase genes were used as reporter genes, one of which was ATP‐dependent eukaryotic luciferase from Pyrophorus plagiophthalamus and the other was FMN‐dependent bacterial luciferase from Vibrio harveyi. These cloned strains were used to evaluate the effects of differences in cell wall structures in the bioluminescence cytotoxicity test using small molecular weight toxic chemicals as model compounds. The strains were found to have remarkably similar behavior and sensitivity toward test toxicants regardless of rather different kinds of membrane structure. However, the eukaryotic luciferase was found in every aspect more useful in toxicity tests than bacterial luciferase mainly because of increased sensitivity and ease of operation. The general behavior of the light emission is described and several aspects affecting the usefulness of the strains are discussed. © by John Wiley & Sons, Inc.
Practical experiences with the biological early warning system “mosselmonitor”
Authors: de Zwart Dick , Kramer Kees J. M. , Jenner Henk A.
Published: October 2006

Biological early warning systems (BEWS) for water pollution involve organisms as sentinels for the quality of the environment. The organisms are usually fast in their response (minutes) to a multitude of pollutants. BEWS devices are very useful for continuous monitoring of (industrial) effluents, water intake, and river or seawater quality control.

The “Mosselmonitor” is a commercially available BEWS that uses the behavioral valve movement response of freshwater or marine mussels (e.g., Dreissena polymorpha or Mytilus edulis). As an indication of unfavorable conditions in the water, the closure of the shells, or a marked increase in the valve movement frequency, is automatically evaluated.

During the last few years the authors have gained practical experience with the Mosselmonitor in a number of field experiments. Examples of monitoring practice will be presented that involve the following monitoring situations:

–intake of drinking water from a river system;

–continuous monitoring of the rivers Rhine and Meuse, partly in combination with other BEWS devices and physicochemical monitoring;

–monitoring of industrial effluents in a tidal estuary; and

–control of cooling water chlorination for antifouling purposes.

In addition,

–the system has been used for toxicological laboratory studies on selected compounds.

© by John Wiley & Sons, Inc.
Microbial transformation of metolachlor
Authors: Liu D. , Maguire R. J. , Pacepavicius G. J. , Aoyama I. , Okamura H.
Published: October 2006

Metolachlor is an important selective herbicide used for the control of several annual grassy weeds and certain broad‐leafed weeds in corn, soybean, peanut, and other crops. It is the most heavily used agricultural pesticide in Ontario. There is, however, very little information in the open literature on the aquatic fate and persistence of metolachlor, a fact that hinders the assessment of its ultimate impact on the aquatic ecosystem. This study showed that metolachlor was very stable in natural water systems. No apparent biodegradation or biotransformation of metolachlor was observed in three test lake waters after an incubation period of 170 days. With a polynuclear aromatic hydrocarbon (PAH) degrading bacterial culture as the test organism, metolachlor was estimated to have an environmental persistence much greater than medium molecular weight PAHs. Thus the extensive herbicidal use of metolachlor may have a long‐lasting impact on Canadian aquatic ecosystems. The white rot fungus Phanerochaete chrysosporium was able to biotransform metolachlor. Based on the three identified metabolites, a tentative metabolic pathway of metolachlor biotransformation by P. chrysosporium was proposed, involving demethylation, hydroxylation, and hydrolytic dechlorination. © by John Wiley & Sons, Inc.
Coliphage association with coliform indicators: A case study—Brazil
Authors: Martins M. T. , El‐Shaarawi A. , Dutka B. J. , Pellizari V. H. , Alfredo G. , Ribeiro G. , Matsumoto E. F.
Published: October 2006

Many microbiological tests are currently available for evaluating the suitability of water resources for human use. Cost, speed, simplicity, and the ability of the test to detect microbial contamination are some of the key factors involved in selecting the appropriate test. The performance of the test often depends on the nature of the tested water and hence it is necessary to evaluate the test under local conditions. This paper compares the performance of several microbiological tests on Brazilian waters. These tests include traditional coliform tests, and the presence/absence and coliphage tests.
Preliminary characterization of neurotoxic cyanobacteria blooms and strains from Finland
Authors: Sivonen K. , Himberg K. , Luukkainen R. , Niemelä S. I. , Poon G. K. , Codd G. A.
Published: October 2006

Two hundred fifteen cyanobacteria bloom samples collected from different parts of Finland were studied, 35 of which proved to be neurotoxic. Toxicity was determined by mouse bioassay. Anabaena species were present in all neurotoxic samples except one, in which Oscillatoria dominated. The presence of anatoxin‐a in the blooms and in the isolated strains was studied from freeze‐dried materials by gas chromatography/mass spectrometry. The simultaneous occurrence of neurotoxicity and hepatotoxicity in some samples was studied by high performance liquid chromatography and high performance thin layer chromatography. Thirteen out of 30 bloom samples contained anatoxin‐a. In the remaining samples, neurotoxicity was caused by unknown toxin(s). Strains producing anatoxin‐a were isolated from the genera Anabaena, Aphanizomenon, Oscillatoria, and Cylindrospermum. Anatoxin‐a content of the blooms varied from 12 to 4360 μg/g freeze‐dried material. Some strains were able to produce about three times as much anatoxin‐a as was detected in natural blooms. Simultaneous occurrence of neurotoxicity and hepatotoxicity was found in some samples as well as atypical toxic responses in mouse bioassay.
Production, detection, and quantification of cyanobacterial toxins
Authors: Codd G. A. , Brooks W. P. , Priestley I. M. , Poon G. K. , Bell S. G. , Fawell J. K.
Published: October 2006

Cyanobacterial blooms from several British freshwaters have been toxic by mouse bioassay each year since annual sampling began in 1981. Toxic blooms of Microcystis aeruginosa, Anabaena spp., Gloeotrichia echinulata, Oscillatoria spp., and Aphanizomenon flos‐aquae occur, with peptide toxin‐producing Microcystis and Anabaena being most often encountered. We are developing a range of detection and quantification methods for cyanobacterial peptide and alkaloid toxins to supplement the standard mouse bioassay. Both types of toxins can be readily assayed by high performance liquid chromatography, and we have developed facile high performance thin layer chromatographic procedures for their detection from natural blooms and laboratory cultures. We have also produced polyclonal and monoclonal antibodies for the assay of Microcystis toxins by enzyme‐linked immunosorbent assay and have developed in vitro fibroblast cytotoxicity assays for the toxins of Microcystis and other cyanobacteria.
Causes and extent of yield losses in cocoa progenies
Authors: Adomako B
Published: October 2006

Cocoa (Theobroma cacao) progenies in a field trial showed a mean yield loss of 10.3% due to unusable pods. This was equivalent to an annual loss of 98 kg ha−1 of dry beans, and 64.1% (62.8 kg ha−1), 30.5% (29.9 kg ha−1), 4.1% (4.0 kg ha−1) and 1.3% (1.4 kg ha−1) were due to black pods, immature ripe pods, rodent damage and other damage, respectively. Copyright © 2006 John Wiley & Sons, Ltd
The Bysl gene product, bystin, is essential for survival of mouse embryos
Authors: Aoki Rui , Suzuki Nao , Paria Bibhash C. , Sugihara Kazuhiro , Akama Tomoya O. , Raab Gerhard , Miyoshi Masaya , Nadano Daita , Fukuda Michiko N.
Published: October 2006

Human bystin is a cytoplasmic protein directly binding to trophinin, a cell adhesion molecule potentially involved in human embryo implantation. The present study shows that bystin is expressed in luminal and glandular epithelia in the mouse uterus at peri‐implantation stages. In fertilized embryos, bystin was not seen until blastocyst stage. Bystin expression started during hatching and increased in expanded blastocyst. However, bystin apparently disappeared from the blastocyst during implantation. After implantation bystin re‐appeared in the epiblast. Targeted disruption of the mouse bystin gene, Bysl, resulted in embryonic lethality shortly after implantation, indicating that bystin is essential for survival of mouse embryos.
Co‐expression of human ABCG5 and ABCG8 in insect cells generates an androstan stimulated membrane ATPase activity
Authors: Müller Marianna , Klein Izabella , Kopácsi Szilárd , Remaley Alan T. , Rajnavölgyi Éva , Sarkadi Balázs , Váradi András
Published: October 2006

Mutations in the ATP‐binding cassette (ABC) proteins ABCG5 or ABCG8 cause sitosterolemia, a condition with increased accumulation of plant sterols. Upon high level expression of the ABCG5 and ABCG8 proteins in baculovirus‐Sf9 cell expression system we found a distinct, vanadate sensitive ATPase activity in isolated membrane preparations only when the two proteins were co‐expressed. This ATPase activity was significantly stimulated by the addition of certain androgen hormones and analogs, and was effectively inhibited by progesterone. Our results provide a new aspect of biochemical and functional characterization of the ABCG5/ABCG8 proteins and their possible involvement in steroid hormone transport or regulation.
Disposition of plasma creatinine in non-azotaemic and moderately azotaemic cats
Authors: Le Garreres Alain , Laroute Valérie , De La Farge France , Boudet Karine G , Lefebvre Hervé P
Published: October 2006

The objectives of this study were to compare assay methods for plasma creatinine (Pl-creat) in cats and to describe the disposition of creatinine and iohexol in 12 healthy and moderately azotaemic cats. Exogenous creatinine and iohexol were injected simultaneously by intravenous bolus, and repeated blood samples were taken to determine the pharmacokinetic parameters of each marker. Pl-creat was assayed by high-performance liquid chromatography (HPLC), Jaffé and enzymatic methods. The enzymatic method was shown to be more reliable than the Jaffé method. Two stereoisomers, exo- and endo-iohexol were identified. The plasma clearance of creatinine (2.3±0.66 ml/min/kg) was significantly higher ( P<0.001) than that of exo-iohexol (1.7±0.40 ml/min/kg). The volume of distribution (447±97 ml/kg) and elimination half-life (181±77 min) of creatinine were also higher ( P<0.001) than those of exo- and endo-iohexol. The estimated daily endogenous production of creatinine was 65±23 mg/kg. None of the pharmacokinetic parameters was changed by the azotaemic status of the animals.
Interannual variability of newly formed Labrador Sea Water from 1994 to 2005
Authors: Avsic Tom , Karstensen Johannes , Send Uwe , Fischer Jürgen
Published: October 2006

Mooring records collected in the central Labrador Sea are evaluated regarding the variability of the hydrographic properties of newly formed Labrador Sea Water (LSW) between 1994 and 2005. This time series is longer and of significantly higher temporal resolution than any discussed before in the context of decreasing convection activity. For the upper 1500 m depth range two distinct warming periods are identified from 1997 to 1999 and from 2003 to 2005 leading to a substantial temperature increase of 0.6°C over the recent decade. The time series of LSW source water properties suggest that ocean transport of heat and freshwater anomalies play a significant role in determining the ultimate convection depth. In 2005 the LSW temperature and salinity had reached high values comparable to those from the early 1970's, shortly after the passage of the Great Salinity Anomaly.
Cloud fraction errors for trade wind cumuli from EOS‐Terra instruments
Authors: Zhao Guangyu , Di Girolamo Larry
Published: October 2006

Errors in the standard cloud fraction products produced by the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi‐angle Imaging SpectroRadiometer (MISR) on EOS‐Terra were examined using 15 m resolution data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Relative to 124 ASTER scenes containing only trade wind cumuli and having an average cloud fraction of 0.08, MODIS and MISR overestimated cloud fraction by 0.18 and 0.36, respectively. For non‐sunglint scenes, MODIS and MISR overestimated cloud fractions by 0.02 and 0.24, respectively. Systematic dependences in the MODIS and MISR cloud fractions with ASTER cloud fraction were observed. Large RMS errors in MODIS and MISR cloud fractions were observed because of variations in the spatial distribution of clouds, suggesting it may be difficult to decouple long‐term changes in cloud fraction from satellites from true changes in the spatial distribution of clouds.
Mechanisms of conduit plug formation: Implications for vulcanian explosions
Authors: Diller K. , Clarke A. B. , Voight B. , Neri A.
Published: October 2006

We explore physical mechanisms controlling formation of a confining conduit plug using 1D, steady‐state numerical models of magma ascent. Model results for the well‐documented 1997 Vulcanian explosions at Soufrière Hills volcano were compared against subsurface conditions constrained by geophysical and petrologic analysis. We suggest that, if magma is permeable and overpressured and rock surrounding the conduit is permeable, degassing occurs both vertically and through conduit walls. This outgassing creates a region of low‐vesicularity, dense magma near the surface (magma plug) which eventually seals the conduit and promotes system overpressure. Driving pressure increases with increasing magma flow rate, hindering volatile exsolution and shifting open‐system degassing to shallower levels of the conduit. As a result, increasing magma flow rate for a fixed conduit width creates a vertically thinner plug and increases the magnitude and vertical extent of conduit overpressure. Plug thickness and density are also controlled by magma and edifice permeability.
Investigating multi‐polarization GPR wave transmission through thin layers: Implications for vertical fracture characterization
Authors: Tsoflias Georgios P. , Hoch Anthony
Published: October 2006

We investigate the controls governing the response of ground‐penetrating radar (GPR) wave transmission through thin layers in order to explore the use of variable polarization GPR signals for remote characterization of fracture aperture and fluid‐fill. We employ an experimental setting that provides controlled observations of the effects of thin‐layer properties to the transmitted GPR wavefield. GPR signals of variable polarization, variable angle of incidence, and variable frequency are transmitted through an air‐ and water‐filled layer of variable thickness. We observe that at high angles of incidence, variable polarization GPR signals display characteristic and quantifiable phase and amplitude responses that are related to thin‐layer properties. The GPR data are in agreement to analytical solutions of plane‐wave oblique‐incidence transmission through layered media. We conclude that multi‐polarization GPR observations can be exploited to determine fracture properties. This work has implications in the remote determination of fractured formation anisotropic properties, such as fluid‐flow.
Relationship between Region 2 field‐aligned current and the ring current: Model results
Authors: Zheng Y. , Lui A. T. Y. , Fok M.‐C. , Anderson B. J. , Brandt P. C. , Immel T. J. , Mitchell D. G.
Published: October 2006

Detailed investigations on the relationship between the ring current and Region 2 field‐aligned currents (FACs) have been tenuous. Using the Comprehensive Ring Current Model (CRCM), we first studied their relationship for two GEM storm events (22 April 2001 and 21 October 2001) through model and data comparison. The simulated Region 2 FACs for two different magnetic storm events capture major characteristics of the Iridium measurements, and the simulated ENA flux has a reasonable agreement with the IMAGE/HENA data. We then examined the effects of polar cap potential drop, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 FACs, and the relationship between Region 2 FACs and the ring current, either through one of the two GEM events or the 12 August 2000 storm. It is shown that an increase in polar cap potential, ionospheric conductivity, or plasma sheet density generally results in an increase in Region 2 FACs' intensity, but Region 2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. The CRCM run in the Tsyganenko 2004 magnetic field model for storm times (T04S), which includes a partial ring current, produces the dawn‐dusk asymmetry in Region 2 FACs during geomagnetically active times, as reported by Anderson et al. (2005): more intense currents flow into the ionosphere around dusk, compared to those that flow out of the ionosphere around dawn, and the dusk currents shift further equatorward than do the dawn currents.
Morphology of the near‐terminator Martian ionosphere: A comparison of models and data
Authors: Fox J. L. , Yeager Katherine E.
Published: October 2006

We have constructed low and high solar activity models of the Martian thermosphere/ionosphere for solar zenith angles from 60 to 90° in 5 degree increments. The solar fluxes that we have adopted are those from the Solar 2000 v2.22 models of Tobiska (2004), without enhancements of the soft X‐ray fluxes. The background neutral density and temperature profiles are similar to those that we have recently presented (Fox, 2004). We compute the density profiles for 14 ions and nine neutral species. For all the models, we present altitude profiles of the photoionization rates, electron impact ionization rates, total ion production rates, and the predicted electron density profiles. Each model exhibits both an F1 peak and an E peak, although the latter usually appears as a shoulder, rather than as a separate peak. The altitudes of the model peaks are found to be slightly too high. We fit the model peak densities to the equation nmax,χi = A(cos χ)k, where, for an ideal Chapman layer, A is the value of the subsolar peak density, nmax,0i, and the exponent k is 0.5. We compare the behavior of the model electron density profiles to that of a theoretical Chapman layer and to the values of A and k obtained by fitting the Mars Global Surveyor (MGS) radio science electron density profiles for occultation seasons 1, 2, and 4. We also compare our results to those of previous investigators who have analyzed data from earlier Mars missions and those from MGS and from the Mars Express spacecraft. We find that our model best fit values of k for the F1 peak and those derived from the MGS data are less than the Chapman value of 0.5. We note, however, that the use of spherical geometry alone reduces the value of k below the Chapman value for large solar zenith angles, but the deviation from the experimental values also indicates that there are changes in the neutral atmosphere as the terminator is approached. Our peak densities and predicted subsolar peak densities for both the F1 and E peaks are somewhat smaller than those derived from the data. This is attributed to the use of the S2K v2.22 solar flux models, rather than the S2K v1.24 models or those from Hinteregger (1981). We also evaluate the neutral, ion, and plasma pressure scale heights at the peaks, 33 km above the peaks and at 250 km for all the models. We find that the solar activity variation of our peak densities are in substantial agreement with those determined by other investigators. We argue that the peaks near 90° solar zenith angle are above the photochemical equilibrium region and fitting these peaks to a Chapman profile is therefore inappropriate.
Implementation of imaging Thomson scattering on the Omega Laser
Authors: Ross J. S. , Froula D. H. , Mackinnon A. J. , Sorce C. , Meezan N. , Glenzer S. H. , Armstrong W. , Bahr R. , Huff R. , Thorp K.
Published: October 2006

Imaging Thomson scattering has been implemented on the Omega Laser facility at the Laboratory for Laser Energetics, University of Rochester [J. M. Soures et al., Laser and Particle Beams 11, 317 (1993)]. Using a high-resolution spectrometer and an intensified charge-coupled device, the electron temperature profile, ranging from 1.5to3keV, was measured along the axis of a CH gas-filled hohlraum. The system integrates over 200ps a region 2mm in length and has a spatial resolution of 50μm and a spectral resolution of 0.027nm. Data obtained from this diagnostic are compared to hydrodynamic simulations.
Characterization of scintillators for lost alpha diagnostics on burning plasma experiments
Authors: Nishiura M. , Kubo N. , Hirouchi T. , Ido T. , Nagasaka T. , Mutoh T. , Matsuyama S. , Isobe M. , Okamoto A. , Shinto K. , Kitajima S. , Sasao M. , Nakatsuka M. , Fujioka K.
Published: October 2006

The characteristics of light output by ion beam irradiations under high ion fluxes have been measured for three kinds of scintillators: ZnS:Ag deposited on the glass plate, Y3Al5O12:Ce powder stiffened with a binder, and Y3Al5O12:Ce ceramics sintered at high temperature. The ion beam flux in the range from 1012to1013ions∕(cm2s) is irradiated to simulate the burning plasma experiments. The decrease of light output has been observed by long time ion irradiation. The deterioration of ZnS:Ag deposited scintillator is most serious. The deterioration has been improved for the scintillators of Y3Al5O12:Ce with a binder and that sintered. Their applications to ITER lost alpha diagnostics are discussed.
Diagnostics for studying the dynamics of wire array Z pinches
Authors: Bland S. N. , Bott S. C. , Hall G. N. , Lebedev S. V. , Suzuki F. , Ampleford D. J. , Palmer J. B. A. , Pikuz S. A. , Shelkovenko T. A.
Published: October 2006

The evolution of a wire array Z pinch encompasses a huge range of conditions—with spatial dimensions varying from micrometers to centimeters, densities from solid metal through plasmas of 1015–1022e−cm−3, and temperatures from sub-eV to many 100eV. We present a summary of the diagnostics developed and used at the Imperial College MAGPIE facility to study the formation and dynamics of plasma in wire array Z pinches, describing the plasma conditions for which they are useful, their various limitations, and some of the novel diagnostic techniques applied.
Simultaneous measurements of ion and electron currents using a novel compact electrostatic end-loss-current detector
Authors: Hirata M. , Miyake Y. , Cho T. , Kohagura J. , Numakura T. , Shimizu K. , Ito M. , Kiminami S. , Morimoto N. , Hirai K. , Yamagishi T. , Miyata Y. , Nakashima Y. , Miyoshi S. , Ogura K. , Kondoh T. , Kariya T.
Published: October 2006

For the purpose of end-loss-ion and -electron analyses in open-field plasmas, a compact-sized electrostatic end-loss-current detector is proposed on the basis of a self-collection principle for suppressing the effects of secondary-electron emission from a metal collector. For employing this specific method, it is worth noting that no further additional magnetic systems except the ambient open-ended magnetic fields are required in the detector operation. This characteristic property provides a compactness of the total detection system and availability for its use in plasma confinement devices without disturbing plasma-confining magnetic fields. The detector consists of a set of parallel metal plates with respect to lines of ambient magnetic forces of a plasma device for analyzing incident ion currents along with a grid for shielding the collector against strays due to the metal-plate biasing. The characterization experiments are carried out by the use of a test-ion-beam line along with an additional use of a Helmholtz coil system for the formation of open magnetic fields similar to those in the GAMMA 10 end region. The applications of the developed end-loss-current detector in the GAMMA 10 plasma experiments are demonstrated under the conditions with simultaneous incidence of energetic electrons produced by electron-cyclotron heatings for end-loss-plugging potential formation.
Simulation of sheet-shaped lithium beam probe performance for two-dimensional edge plasma measurement
Authors: Tsuchiya H. , Morisaki T. , Komori A. , Motojima O.
Published: October 2006

A sheet-shaped thermal lithium beam probe has been developed for two-dimensional density measurements in the edge region of the torus plasma. A numerical simulation was carried out to confirm the validity of the diagnostics for fast and transient phenomena such as edge localized modes or blobs, etc., where the velocity of blobs is faster than that of the probe beam. It was found in the simulation that the density of the blob itself is reconstructed to be low and unexpected ghosts appear in the reconstructed density profile near the blob, if the conventional reconstruction method is employed. These results invite our attention to the numerical errors in the density reconstruction process. On the other hand, the errors can be corrected by using the simulation results.
Variational principles for eigenvalues of the Klein–Gordon equation
Authors: Langer Matthias , Tretter Christiane
Published: October 2006

In this paper variational principles for eigenvalues of an abstract model of the Klein–Gordon equation with electromagnetic potential are established. They are used to characterize and estimate eigenvalues in cases where the essential spectrum has a gap around 0, even in the presence of complex eigenvalues. As a consequence, a comparison between eigenvalues of the Klein–Gordon equation in Rd and eigenvalues of certain Schrödinger operators is obtained. The results are illustrated on examples including the Klein–Gordon equation with Coulomb and square-well potential.
Effects of neutral-beam excited states on charge-exchange emission cross sections
Authors: Bespamyatnov I. O. , Rowan W. L. , Granetz R. S. , Beals D. F.
Published: October 2006

Charge-exchange recombination spectroscopy can be used as a diagnostic for local densities of fully stripped impurities. For example, impurity profiles are valuable for transport studies. A major impediment to analysis is the availability of cross sections which relate the observed spectroscopic emission to the impurity densities. In this work, this impediment is removed for boron ions. Emission cross sections for B+4 states excited by charge exchange between beams of neutrals and fully stripped B+5 impurities in high density plasmas are computed for beams with multiple energy components. We show that even the low-energy neutral beam components make significant contributions to the emission for high-density plasmas which are commonly generated in the laboratory. Excited states as high as n=3 are important. This implies that a detailed description of the beam components including density, excited state population, and penetration is required for prediction of intensities of spectral lines excited by diagnostic neutral beams in high-density plasmas. Plasma experiments performed on the Alcator C-Mod tokamak will be described which clearly show the efficacy of our analysis method. This technique can be extended to species other than boron.
Visible spectrometer at the Compact Toroid Injection Experiment and the Alcator C-Mod tokamak for Doppler width and shift measurements
Authors: Graf A. , Howard S. , Horton R. , Hwang D. , May M. , Beiersdorfer P. , Terry J.
Published: October 2006

A novel Doppler spectrometer is currently being used for ion or neutral velocity and temperature measurements on the Alcator C-Mod tokamak. The spectrometer has an f∕# of ∼3.1 and is appropriate for visible light (3500–6700Å). The linewidth from a line emitting calibration source has been measured to be as small as 0.4Å. The ultimate time resolution is line brightness light limited and on the order of milliseconds. A new photon efficient charge coupled device detector is being used at C-Mod. Time resolution is achieved by moving the camera during a plasma discharge in a perpendicular direction through the dispersion plane of the spectrometer, causing a vertical streaking across the camera face. Initial results from C-Mod as well as previous measurements from the Compact Toroid Injection Experiment are presented.
Fabry-Pérot interferometry for microplasma diagnostics
Authors: Hojo H. , Mase A.
Published: October 2006

A new method for determining the electron density of a thin plasma by means of Fabry-Pérot interferometry is proposed. The interferometer consists of two plasma layers and dielectric material surrounded by two plasma layers. The transmittance of electromagnetic waves across the interferometer is calculated, and Fabry-Pérot resonances are demonstrated. It is shown that the electron density can be determined from the measurement of the Fabry-Pérot resonance frequencies. This method can also be applied to the measurement of conduction electron density in semiconductor films.
The role of negative ions on the Jeans instability in a complex plasma in the presence of nonthermal positive ions
Authors: Roy Banamali , Sarkar Susmita , Khan Manoranjan , Gupta M. R.
Published: October 2006

The role of negative ions on Jeans instability in the presence of nonthermal positive ions has been investigated in this paper. Electrons and negative ions are considered Boltzmann-distributed, while the positive ions follow nonthermal velocity distribution. A negatively charged dust component is modeled by continuity and momentum equations. The linear dispersion relation shows that the presence of negative ions reduces the critical value of the nonthermal parameter acr, which consequently increases the unstable region and hence pronounces the Jeans instability. The growth rate of this Jeans instability decreases with the increasing negative ion temperature.
High resolution photoemission spectroscopy: Evidence for strong chemical interaction between Mg and 3,4,9,10-perylene-tetracarboxylic dianhydride
Authors: Gavrila G. , Zahn D. R. T. , Braun W.
Published: October 2006

The interface formation between Mg and 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) was investigated by high resolution soft x-ray photoemission spectroscopy. The interface chemistry was obtained after fitting the core level spectra as a function of Mg thickness. At the initial stage of deposition, a strong chemical interaction between Mg and the single bonded oxygen atoms of PTCDA is observed leading to the formation of MgO and a modified organic molecule. Based on the experimental evidence, the molecular structure of the modified molecule is proposed. Moreover, the changes observed in the measured C1s core level spectra are supported by density functional theory calculations.
Dipole trapped spheromak in a prolate flux conserver
Authors: Brown M. R. , Cothran C. D. , Fung J. , Chang M. , Horwitz J. , Schaffer M. J. , Leuer J. , Belova E. V.
Published: October 2006

This paper reports the observation and characterization of a spheromak formed in the Swarthmore Spheromak Experiment (SSX, [M. R. Brown, Phys. Plasmas 6, 1717 (1999)]) and trapped in a simple dipole magnetic field. The spheromak is studied in a prolate (tilt unstable) 0.4m diameter, 0.6m length copper flux conserver in SSX. This plasma does not tilt, despite the prolate flux conserver. The spheromak is characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), ion Doppler spectroscopy for Ti and flow, and interferometry for ne. Three-dimensional magnetohydrodynamics simulations of this configuration verify its gross sta-bility.
Self-focusing, Raman, and modulation instability of shaped relativistic laser pulse in plasmas
Authors: Lin Hai , Zha Xuejun , Li Ruxin , Chen Li-Ming , Xu Zhizhan
Published: October 2006

The interaction of shaped laser pulses with plasmas is studied in a strict theoretical framework without adopting the slow-varying envelope approximation (SVEA). Any physical quantities involved in the interaction are denoted as a summation of different real quantities of respective phases. The relationships among the phases of those real quantities and their moduli are strictly analyzed. Such strict analyses lead to a more exact equation set for the three-dimensional envelope of the laser pulse, which is not based on SVEA. Based on this equation set, self-focusing, Raman, and modulation instabilities could be discussed in a unified framework. The solutions of this equation set for the laser envelope reveal many possible multicolor laser modes in plasmas. The energy and the shape of a pulse determine its propagation through plasmas in a multicolor mode or in a monochromic mode. A global growth rate is introduced to measure the speed of the transition from the monochromic mode in vacuum to a possible mode in plasmas.
Carrier recombination near threading dislocations in GaN epilayers by low voltage cathodoluminescence
Authors: Pauc N. , Phillips M. R. , Aimez V. , Drouin D.
Published: October 2006

The authors present a low voltage cathodoluminescence (CL) study of as grown GaN and GaN:Si epilayers on sapphire. At 1kV they resolve individual threading dislocations on the sample surface at low temperature (5K), which appear as correlated dark spots. Analysis of CL intensity profiles across individual dislocation cores provides a direct measurement of the exciton and minority carrier diffusion lengths. Using this approach at 5K, an exciton diffusion length of 62±28nm was found for GaN:Si (∼3×1018cm−3) compared with 81±20nm for a nominally undoped n-type GaN (∼1×1016cm−3).
Theoretical prediction of noble-gas compounds: Ng–Pd–Ng and Ng–Pt–Ng
Authors: Taketsugu Yuriko , Taketsugu Tetsuya , Noro Takeshi
Published: October 2006

Following our recent study on Ng–Pt–Ng (Ng=Ar,Kr,Xe) [J. Chem. Phys. 123, 204321 (2005)], the binding of noble-gas atoms with Pd atom has been investigated by the ab initio coupled cluster CCSD(T) method with counterpoise corrections, including relativistic effects. It is shown that two Ng atoms bind with Pd atom in linear geometry due to the s-dσ hybridization in Pd where the second Ng atom attaches with much larger binding energy than the first. The binding energies are evaluated as 4.0, 10.2, and 21.5kcal∕mol for Ar–Pd–Ar, Kr–Pd–Kr, and Xe–Pd–Xe, respectively, relative to the dissociation limit, Pd (S1)+2Ng. In the hybrid Ng complexes, the binding energies for XePd and Ng (=Ar,Kr) are evaluated as 4.0 and 6.9kcal∕mol for XePd–Ar and XePd–Kr, respectively. The fundamental frequencies and low-lying vibrational-rotational energy levels are determined for each compound by the variational method, based on the three-dimensional near-equilibrium potential energy surface. Results of vibrational-rotational analyses for Ng–Pt–Ng (Ng=Ar,Kr,Xe) and Xe–Pt–Ng (Ng=He,Ne,Ar,Kr) compounds are also given.
Effects of a guide field on the evolution of a current sheet
Authors: Tsai C. L. , Lee L. C. , Wu B. H.
Published: October 2006

The evolution of an initial current sheet is studied by using the set of one-dimensional (1D) magnetohydrodynamic equations. In a simulation of the 1D Riemann problem along the z direction, the initial magnetic field is chosen as B(z)=−Bx0tanh(z∕δ)x̂+Byŷ+Bzẑ, where Bx0 denotes the antiparallel component and By is called the guide field of current sheet. For the By=0 case, a pair of slow shocks is formed and propagates away from the current sheet. For By≠0 (even for a very small By), it is found that a pair of slow shocks and an additional pair of time-dependent intermediate shocks (TDISs) are formed. TDISs are not present in the By=0 case, indicating that the case with By=0 is a singular case. In this paper, an attempt is made to reconcile the By=0 case with small nonzero By cases by examining the early time evolution of TDISs and slow shocks. The early current evolutions for the By=0 case and for small By cases are found to be very similar. For By≠0 cases, the plasma density and pressure are found to increase and the magnetic field decreases across TDISs. The dependence of current sheet evolution on initial By (or ϕ∞) and the plasma beta β∞ and also examined, where ϕ∞=tan−1(By∕Bx0) is the initial angle beteween the tangential magnetic field and the x axis, and the subscript ∞ denotes the location far from the current sheet. The rotation angle (Δϕ) of tangential magnetic field across TDIS develops gradually with time and reaches the final value Δϕfinal=90°−ϕ∞. For small By (ϕ∞→0), it is found that the time reaching the final state is very long. Both pressure and temperature downstream of the slow shock decrease with ϕ∞, and increase with plasma beta β∞. With a decreasing ϕ∞ or an increasing β∞, the Alfvén Mach number (MA=Vn1∕VA) associated with slow shocks increases, and the amount of magnetic energy converted into kinetic energy also increases.
Response to “Comment on ‘Kinetic theory of the stability of the inhomogeneous plasmas with transverse inhomogeneous electric field’ ” [Phys. Plasmas 13, 104703 (2006)]
Authors: Mikhailenko Vladimir S.
Published: October 2006

The statement about the existence of the inhomogeneous energy density driven instability, claimed in the series of papers by Ganguli et al. is grounded on the invalid theory and misunderstanding of the experimental data.
Theoretical treatments of ultrafast electron transfer from adsorbed dye molecule to semiconductor nanocrystalline surface
Authors: Liang Kuo Kan , Lin Chih-Kai , Chang Huan-Cheng , Hayashi Michitoshi , Lin Sheng Hsien
Published: October 2006

In studying ultrafast electron transfer from a dye molecule to a nanosized semiconductor particle, pump-probe experiments are commonly used. In this system the electron transfer (ET) rate is faster than vibrational relaxation so that the ET rate should be described by a single-level rate constant and the probing signal (often in the form of time-resolved spectra) contains the contribution from the dynamics of both population and coherence (i.e., wave packet). In this paper, we shall present the theoretical treatments for femtosecond time-resolved pump-probe experiment and the dynamics of population and coherence by the density matrix method, and the calculation of single-level ET rate constant involved in a pump-probe experiment. As an application, we show the theoretical results using parameters extracted from experiments on a specific dye/semiconductor system.
Large-eddy simulation of sheared interfacial flow
Authors: Reboux S. , Sagaut P. , Lakehal D.
Published: October 2006

Large-eddy simulations (LES) of a turbulent interfacial gas-liquid flows are described in this paper. The variational multiscale approach (VMS) introduced by Hughes for single-phase flows is systematically assessed against direct numerical simulation (DNS) data obtained at a shear Reynolds number Re⋆=171, and compared to LES results obtained with the Smagorinsky model, modified by a near-interface turbulence decay treatment. The models are incorporated in the same pseudospectral DNS solver built within the boundary fitting method used by Fulgosi et al. for air-water flow. The LES are performed for physical conditions allowing low interface deformations that fall in the range of capillary waves of wave slope ak=0.01. The LES results show that both the modified Smagorinsky model and the VMS are capable to predict the boundary layer structure in the gas side, including the decay process, and to cope with the anisotropy of turbulence in the liquid blockage layer underneath the interface. Higher-order turbulence statistics, including the transfer of energy between the normal stresses is also well predicted by both approaches, but qualitatively the VMS results remain overall better than the modified Smagorinsky model. The study has demonstrated that the key to the prediction of the energy transfer mechanism is in the proper prediction of the fluctuating pressure field, which has been found out of reach of any of the LES methodologies. The superiority of the VMS is demonstrated through the analysis of the subgrid transport and exchange terms in the resolved kinetic energy, where it is indeed shown to be self-adaptive with regard to the eddy viscosity. Although VMS is shown to be sensitive to filter scale partition and model constant, the optimal setting can be easily translated in the interface tracking/finite-volume context, which makes it very useful for practical purposes. An important point is that the VMS approach yields very satisfactory results without the need for prescribing an ad-hoc damping function and the required distance to the interface.
Frequency-selective response of FitzHugh-Nagumo neuron networks via changing random edges
Authors: Zhao Gang , Hou Zhonghuai , Xin Houwen
Published: October 2006

We consider a network of FitzHugh-Nagumo neurons; each neuron is subjected to a subthreshold periodic signal and independent Gaussian white noise. The firing pattern of the mean field changes from an internal-scale dominant pattern to an external-scale dominant one when more and more edges are added into the network. We find numerically that (a) this transition is more sensitive to random edges than to regular edges, and (b) there is a saturation length for random edges beyond which the transition is no longer sharpened. The influence of network size is also investigated.
Computing stationary free-surface shapes in microfluidics
Authors: Schindler Michael , Talkner Peter , Hänggi Peter
Published: October 2006

A finite-element algorithm for computing free-surface flows driven by arbitrary body forces is presented. The algorithm is primarily designed for the microfluidic parameter range where (i) the Reynolds number is small and (ii) force-driven pressure and flow fields compete with the surface tension for the shape of a stationary free surface. The free surface shape is represented by the boundaries of finite elements that move according to the stress applied by the adjacent fluid. Additionally, the surface tends to minimize its free energy and by that adapts its curvature to balance the normal stress at the surface. The numerical approach consists of the iteration of two alternating steps: The solution of a fluidic problem in a prescribed domain with slip boundary conditions at the free surface and a consecutive update of the domain driven by the previously determined pressure and velocity fields. For a Stokes problem the first step is linear, whereas the second step involves the nonlinear free-surface boundary condition. This algorithm is justified both by physical and mathematical arguments. It is tested in two dimensions for two cases that can be solved analytically. The magnitude of the errors is discussed in dependence on the approximation order of the finite elements and on a step-width parameter of the algorithm. Moreover, the algorithm is shown to be robust in the sense that convergence is reached also from initial forms that strongly deviate from the final shape. The presented algorithm does not require a remeshing of the used grid at the boundary. This advantage is achieved by a built-in mechanism that causes a smooth change from the behavior of a free surface to that of a rubber blanket if the boundary mesh becomes irregular. As a side effect, the element sides building up the free surface in two dimensions all approach equal lengths. The presented variational derivation of the boundary condition corroborates the numerical finding that a second-order approximation of the velocity also necessitates a second-order approximation for the free surface discretization.
Nanowire-based multiple quantum dot memory
Authors: Nilsson Henrik A. , Thelander Claes , Fröberg Linus E. , Wagner Jakob B. , Samuelson Lars
Published: October 2006

The authors propose and demonstrate an alternative memory concept in which a storage island is connected to a nanowire containing a stack of nine InAs quantum dots, each separated by thin InP tunnel barriers. Transport through the quantum dot structure is suppressed for a particular biasing window due to misalignment of the energy levels. This leads to hysteresis in the charging/discharging of the storage island. The memory operates for temperatures up to around 150K and has write times down to at least 15ns. A comparison is made to a nanowire memory based on a single, thick InP barrier.
Production of a microbeam of slow highly charged ions with a tapered glass capillary
Authors: Ikeda Tokihiro , Kanai Yasuyuki , Kojima Takao M. , Iwai Yoshio , Kambara Tadashi , Yamazaki Yasunori , Hoshino Masamitsu , Nebiki Takuya , Narusawa Tadashi
Published: October 2006

The authors have developed a method to produce a microbeam of slow highly charged ions based on a self-organized charge-up inside a tapered glass capillary. A transmission of 8keV Ar8+ beam through the capillary 5cm long with 800∕24μm inlet/outlet inner diameters was observed stably for more than 1200s. The transmitted beam had the same size as the outlet with a beam density enhancement of approximately 10 and a divergence of ±5mrad. The initial beam was guided through a capillary tilted by as large as ±100mrad, and it still kept the incident charge.