bluuebunny/crossref_metadata_2025 huggingface dataset:
Coexistence of 1,3-butadiene conformers in ionization energies and Dyson orbitals
Authors: Saha Saumitra , Wang Feng , Falzon Chantal T. , Brunger Michael J.
Published: September 2005

The minimum-energy structures on the torsional potential-energy surface of 1,3-butadiene have been studied quantum mechanically using a range of models including ab initio Hartree-Fock and second-order Møller-Plesset theories, outer valence Green’s function, and density-functional theory with a hybrid functional and statistical average orbital potential model in order to understand the binding-energy (ionization energy) spectra and orbital cross sections observed by experiments. The unique full geometry optimization process locates the s-trans-1,3-butadiene as the global minimum structure and the s-gauche-1,3-butadiene as the local minimum structure. The latter possesses the dihedral angle of the central carbon bond of 32.81° in agreement with the range of 30°–41° obtained by other theoretical models. Ionization energies in the outer valence space of the conformer pair have been obtained using Hartree-Fock, outer valence Green’s function, and density-functional (statistical average orbital potentials) models, respectively. The Hartree-Fock results indicate that electron correlation (and orbital relaxation) effects become more significant towards the inner shell. The spectroscopic pole strengths calculated in the Green’s function model are in the range of 0.85–0.91, suggesting that the independent particle picture is a good approximation in the present study. The binding energies from the density-functional (statisticaly averaged orbital potential) model are in good agreement with photoelectron spectroscopy, and the simulated Dyson orbitals in momentum space approximated by the density-functional orbitals using plane-wave impulse approximation agree well with those from experimental electron momentum spectroscopy. The coexistence of the conformer pair under the experimental conditions is supported by the approximated experimental binding-energy spectra due to the split conformer orbital energies, as well as the orbital momentum distributions of the mixed conformer pair observed in the orbital cross sections of electron momentum spectroscopy.
Structural characterizations and electronic properties of boron nitride nanotube crystalline bundles
Authors: Zheng Fawei , Zhou Gang , Hao Shaogang , Duan Wenhui
Published: September 2005

The structural characterizations and electronic properties of aligned armchair single-walled boron nitride nanotube (BNNT) bundles are theoretically investigated. In the spontaneous bundling process, the cylindrical shapes of bundled BNNTs are preserved all along, whereas their diameters expand, then shrink, and return back to the initial dimensions. Owing to the nonuniform distribution of positive and negative charges among BNNTs, the multipole interaction in bundles is completely dependent upon the chirality of each BNNT and the arrangement of bundled BNNTs. The effect of intertube coupling on the dispersions of BNNT bundles is demonstrated. Our systematical simulations might be helpful for the understanding of potential applications of BNNT bundles in the nanometer manufacturing techniques such as doping, adsorption, and derivative synthesis.
Effect of fluid-substrate attraction and pore geometry on fluid adsorption
Authors: Bohlen Holger , Schoen Martin
Published: September 2005

We employ grand canonical ensemble Monte Carlo simulations to investigate the impact of substrate curvature on the phase behavior of an adjacent fluid. The substrates consist of a periodic sequence of grooves in the x direction; the grooves are infinitely long in the y direction. The shape of the grooves is controlled by a parameter η. For η=0 the substrates are planar. If η=1, the grooves are wedge shaped. If η>1 the grooves become concave and in the limit η=∞ rectangular. The fluid-substrate potential representing a groove consists of two contributions, namely, that of the homogeneous substrate base corresponding to a semi-infinite solid and that of a finite piece of solid with nonplanar surfaces. Whereas the former contribution can be calculated analytically, the latter needs to be evaluated numerically. For very large values of η, that is in (almost) rectangular grooves, we observe capillary condensation of that portion of fluid located inside the grooves. As η decreases capillary condensation gives way to continuous filling. In all cases, a nearly planar film-gas interface eventually forms in the direction normal to the surface of the substrate base and outside the grooves if one increases the chemical potential sufficiently.
Electronic structure and properties of isoreticular metal-organic frameworks: The case of M-IRMOF1 (M=Zn, Cd, Be, Mg, and Ca)
Authors: Fuentes-Cabrera Miguel , Nicholson Donald M. , Sumpter Bobby G. , Widom Mike
Published: September 2005

We investigate the possibility of tailoring the electronic properties of isoreticular metal-organic materials by replacing the metal atom in the metal-organic cluster and by doping. The electronic structure of M-IRMOF1, where IRMOF1 stands for isoreticular metal-organic framework 1 and M=Be, Mg, Ca, Zn, and Cd, was examined using density-functional theory. The results show that these materials have similar band gaps (ca. 3.5eV) and a conduction band that is split into two bands, the lower of which has a width that varies with metal substitution. This variation prompted us to investigate whether doping with Al or Li could be used to tailor the electronic properties of the Zn-IRMOF1 and Be-IRMOF1 materials. It is shown that replacing one metal atom with Al can effectively be used to create IRMOFs with different metallic properties. On the other hand, adding Li produces structural changes that render this approach less suitable.
Picosecond IR-UV pump-probe spectroscopic study on the intramolecular vibrational energy redistribution of NH2 and CH stretching vibrations of jet-cooled aniline
Authors: Yamada Yuji , Okano Jun-ichi , Mikami Naohiko , Ebata Takayuki
Published: September 2005

Intramolecular vibrational energy redistribution (IVR) of the NH2 symmetric and asymmetric stretching vibrations of jet-cooled aniline has been investigated by picosecond time-resolved IR-UV pump-probe spectroscopy. A picosecond IR laser pulse excited the NH2 symmetric or asymmetric stretching vibration of aniline in the electronic ground state and the subsequent time evolutions of the excited level as well as redistributed levels were observed by a picosecond UV pulse. The IVR lifetimes for symmetric and asymmetric stretches were obtained to be 18 and 34ps, respectively. In addition, we obtained the direct evidence that IVR proceeds via two-step bath states; that is, the NH2 stretch energy first flows into the doorway state and the energy is further dissipated into dense bath states. The rate constants of the second step were estimated to be comparable to or slower than those of the first step IVR. The relaxation behavior was compared with that of IVR of the OH stretching vibration of phenol [Y. Yamada, T. Ebata, M. Kayano, and M. Mikami J. Chem. Phys. 120, 7400 (2004)]. We found that the second step IVR process of aniline is much slower than that of phenol, suggesting a large difference of the “doorway state↔the dense bath states” anharmonic coupling strength between the two molecules. We also observed IVR of the CH stretching vibrations, which showed much faster IVR behavior than that of the NH2 stretches. The fast relaxation is described by the interference effect, which is caused by the coherent excitation of the quasistationary states.
Phase properties and interaction force of acoustically interacting bubbles: A complementary study of the transition frequency
Authors: Ida Masato
Published: September 2005

The transition frequencies of multibubble systems in a sound field are reexamined to confirm their existence and further clarify their physical properties. We have recently suggested that a gas bubble interacting with a neighboring bubble in a sound field has up to three transition frequencies which invert the pulsation phase of the bubble, e.g., from in phase to out of phase with the driving sound [M. Ida, Phys. Lett. A 297, 210 (2002)]. The number is larger than that of the resonance frequencies of the double-bubble system, which also invert the pulsation phase of the bubbles. Namely, one of the three transition frequencies does not correspond to the resonance frequencies. We have furthermore suggested that the newly derived characteristic frequency plays a crucial role in the determination of the sign of the interaction force (the secondary Bjerknes force) acting between pulsating bubbles [M. Ida, Phys. Rev. E 67, 056617 (2003)]. More specifically, it has been shown that the height relation between the newly derived characteristic frequencies and the driving frequency determines the sign of the force, an interpretation which is different from the frequently cited explanation after Bjerknes that the resonance (or natural) frequencies of the interacting bubbles play a role in the determination of the sign. In the present paper, we attempt to resolve several points regarding the transition frequencies that had not been clarified in our previous papers. The results given are (1) further details of the characteristics of the transition frequencies, (2) the theoretical determination of the threshold distances for the appearance of the subtransition frequencies, (3) a simple understanding of the sign reversal of the interaction force, and (4) the clarification of several similarities and differences among the natural, resonance, and transition frequencies in double-bubble cases. The present effort enforces our claim that transition frequencies causing no resonance response exist in multibubble systems and thoroughly clarifies the physical effects of the transition frequencies and their roles in the sign reversal of the interaction force.
Experimental study of the structure of flow regions with negative turbulent kinetic energy production in confined three-dimensional shear flows with and without buoyancy
Authors: Liberzon A. , Lüthi B. , Guala M. , Kinzelbach W. , Tsinober A.
Published: September 2005

Regions of negative turbulent kinetic energy (TKE) production are observed and studied in two different flows, namely in turbulent thermal Rayleigh-Bénard convection in a cubic cell, and in a mechanically agitated shear flow in absence of buoyancy, with a main focus on the small scale structure of the flow. The experimental investigation is performed using three-dimensional (3D) particle tracking velocimetry, which allows for measuring the three velocity components and the full tensor of velocity derivatives in a finite 3D volume. The capability to compute the TKE production term in its complete form P=−⟨uiuj⟩Sij is crucial due to the three dimensionality of the flows. A comparative analysis of four different flow situations is performed in regions with positive and negative TKE production with and without buoyancy effects. In both, convective shear flow and shear flow without buoyancy, negative TKE production is associated with the unusual, more pronounced alignment of the velocity vector u with the first eigenvector λ1S of the mean rate-of-strain tensor, related to the stretching eigenvalue, Λ1S, in contrast to the positive TKE production associated with the alignment with the third eigenvector (i.e., related to the negative, compressing eigenvalue). In the negative TKE production region of convective flow we find (i) increased values for mean strain, (ii) increased values of the first contribution PΛ1 in the eigenframe of the mean rate-of-strain tensor, and decreased values of the vertical contribution to the production term in a fixed frame of reference, (iii) stronger anisotropy of u, (iv) higher levels of fluctuating strain s2 and enstrophy ω2, as well as (v) higher rates of their production, −sijsjkski and ωiωjsij, compared to the respective values in positive TKE production region. In the shear flow without buoyancy, all the mentioned quantities are lower in the negative TKE production region than in the positive TKE production region. From this we conclude that the inverse energy transfer in the shear flow case without buoyancy is associated with depletion of the field of velocity derivatives. This does not occur in the cubic Rayleigh-Bénard convection cell. In this flow, buoyancy is observed to have an effect on three levels: the field of velocity derivatives, velocity fluctuations, and the mean flow field. It is inferred that buoyancy is able to maintain a region with the negative TKE production by acting on all these levels simultaneously.
Crossover in growth exponent upon nanocrystallization of amorphous thin films
Authors: Gupta Mukul
Published: September 2005

Thin films of Fe75Zr25 alloy were deposited by cosputtering of Fe and Zr targets using magnetron sputtering technique in the thickness range of 7–85nm. It was found that at a critical thickness of about 40nm, nanocrystallization of initially deposited amorphous phase takes place. A crossover occurs in the growth exponent (β) upon nanocrystallization giving a direct evidence for different growth behavior for amorphous and nanocrystalline phases.
Combustion velocities and propagation mechanisms of metastable interstitial composites
Authors: Bockmon B. S. , Pantoya M. L. , Son S. F. , Asay B. W. , Mang J. T.
Published: September 2005

Combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions. Pressures were also measured to provide detailed information about the reaction mechanism. Samples of three different fuel particle sizes (44, 80, and 121nm) were analyzed to determine the influence of particle size on combustion velocity. Bulk powder density was varied from approximately 5% to 10% of the theoretical maximum density (TMD). The combustion velocities ranged from approximately 600 to 1000m∕s. Results indicate that combustion velocities increase with decreasing particle size. Pressure measurements indicate that strong convective mechanisms are integral in flame propagation.
Extremum method: Inverse solution of the two-layer thermal wave problem
Authors: Nzodoum Fotsing J. L. , Gibkes J. , Pelzl J. , Bein B. K.
Published: September 2005

An inverse solution of the two-layer thermal wave problem has been derived, which allows us to determine the relevant thermal transport parameters, the thermal diffusion time and the thermal reflection coefficient, respectively, the ratio of the effusivities of the two layers, deduced from the relative minimum or maximum of the calibrated phase lags measured between the periodically modulated excitation of the thermal wave and the detected thermal response. Applying a functional transformation by multiplying the calibrated phase lags with the variable (1∕f1∕2)q, where f is the modulation frequency of excitation and q a positive or negative real number close to zero, the inversion method is extended to other values of the calibrated phase lags measured in the neighborhood of the phase minimum or maximum. The application potential of these two solution methods is studied by analyzing the phase lags measured as a function of frequency for two-layer systems of technological importance, e.g., different plasma-deposited hard coatings on tool steel, coated cutting tools after friction wear, and a sample of a shape memory alloy (NiTi) after mechanical surface treatment.
A neutron scattering study of rare-earth intermetallic compound La3Co29Si4B10
Authors: Zhang Heng , Campbell S. J. , Hofmann M. , Kennedy S. J.
Published: September 2005

A quaternary rare-earth intermetallic compound La3Co29Si4B10 has been synthesized and the crystal and magnetic structures are investigated by neutron diffraction over the temperature range of 7–300K. Rietveld refinements of the neutron diffraction patterns demonstrate that La3Co29Si4B10 is tetragonal and isostructural with Nd3Ni29Si4B10. The magnetic scattering indicates that the moments of the Co sublattice are collinear and lie in the basal plane. The mean magnetic moment for the Co atoms is μ∼0.5μB, or 13.6μB∕f.u., in agreement with the magnetization measurements.
Coulombic effects of electron-hole plasma in nitride-based nanostructures
Authors: Fedorov I. A. , Sokolov V. N. , Kim K. W. , Zavada J. M.
Published: September 2005

We study the Coulombic effects of electron-hole plasma on the ground and first excited energy levels and carrier wave functions in a GaN∕AlGaN quantum well (QW) structure. The coupled Schrödinger equations for electron and hole states are solved self-consistently in the Hartree-Fock approximation along with the Poisson equation. As expected, the decreasing QW width and increasing plasma density diminish the charge separation in the QW induced by the internal field, leading to the relatively reduced contribution of the Hartree interaction to the energy-level shift. In contrast, the calculation also demonstrates that the contribution of many-body effects becomes more pronounced. The resulting competition between the many-body and Hartree contributions causes a nonmonotonous dependence of the electron and hole energies on the plasma density at a given field. These findings are applied to explore the potential bistable behavior in the QW electroabsorption under near-band-edge photoexcitation.
Direct ordering and shape effects of FePt nanoparticles produced by nanoparticle beam technology
Authors: Chen J. S. , Tan C. Y. , Chow S. Y. , Liu B. , Chow G. M.
Published: September 2005

Partial chemically ordered FePt nanoparticles were produced by annealing the nanoparticles in transit through the furnace from the source to the substrate. The equiaxed or polyhedral morpohology of FePt nanoparticles can be produced by tuning the temperature of nanoparticle-forming chamber. The equiaxed FePt particles were amorphous whereas the polyhedral particles showed good crystallinity. Both FePt particle assemblies were superparamagnetic without on-line heating of particles. With on-line annealing, the assembled films showed ferromagnetic behavior. The coercivity of the polyhedral FePt particle assembly was about 600Oe, whereas that of equiaxed FePt particles was 450Oe. The larger coercivity was attributed to the increased particle size.
On the zigzag dynamics of freely moving axisymmetric bodies
Authors: Fernandes P. C. , Ern P. , Risso F. , Magnaudet J.
Published: September 2005

The zigzag path of light flat cylinders rising freely in water at rest is investigated experimentally. The body dynamics are described in terms of the orientation of the cylinder axis relative to its path as a function of its aspect ratio and Reynolds number. We show that for thick bodies the inclinations of both the axis and the velocity oscillate almost in phase, whereas for thin bodies they are rather in quadrature. Most notably, for bodies of intermediate aspect ratio, the phase difference evolves continuously between these two limits when the body flatness changes. In contrast, this phase difference is nearly independent of the Reynolds number. Comparison with potential flow theory shows that these features can only be explained by taking into account vortical effects.
Scanning a photonic crystal slab nanocavity by condensation of xenon
Authors: Mosor S. , Hendrickson J. , Richards B. C. , Sweet J. , Khitrova G. , Gibbs H. M. , Yoshie T. , Scherer A. , Shchekin O. B. , Deppe D. G.
Published: September 2005

Allowing xenon or nitrogen gas to condense onto a photonic crystal slab nanocavity maintained at 10–20K results in shifts of the nanocavity mode wavelength by as much as 5nm(≅4meV). This occurs in spite of the fact that the mode defect is achieved by omitting three holes to form the spacer. This technique should be useful in changing the detuning between a single quantum dot transition and the nanocavity mode for cavity quantum electrodynamics experiments, such as mapping out a strong coupling anticrossing curve. Compared with temperature scanning, it has a much larger scan range and avoids phonon broadening.
Mobility enhancement of polycrystalline-Si thin-film transistors using nanowire channels by pattern-dependent metal-induced lateral crystallization
Authors: Wu Yung-Chun , Chang Ting-Chang , Liu Po-Tsun , Wu Yuan-Chun , Chou Cheng-Wei , Tu Chun-Hao , Lou Jen-Chung , Chang Chun-Yen
Published: September 2005

This work presents a method for enhancing the mobility of polycrystalline-Si (poly-Si) thin-film transistors (TFTs) by pattern-dependent metal-induced-lateral-crystallization (PDMILC) using nanowire channels. Experimental results indicate that the field-effect mobility of PDMILC TFT was enhanced as the channel width decreased, because the lateral length of the poly-Si grains increased. The PDMILC poly-Si TFT with ten nanowire channels (M10) had the greatest field-effect mobility, 109.34cm2∕Vs and the lowest subthreshold swing, 0.23V∕dec, at a gate length of 2μm. The field-effect mobility also increased as the gate length in the M10 PDMILC poly-Si TFT device declined, because the number of poly-Si grain-boundary defects was reduced.
Modulation of the high mobility two-dimensional electrons in Si∕SiGe using atomic-layer-deposited gate dielectric
Authors: Lai K. , Ye P. D. , Pan W. , Tsui D. C. , Lyon S. A. , Mühlberger M. , Schäffler F.
Published: September 2005

Metal-oxide-semiconductor field-effect-transistors using atomic-layer-deposited (ALD) Al2O3 as the gate dielectric are fabricated on the Si∕Si1−xGex heterostructures. The low-temperature carrier density of a two-dimensional electron system (2DES) in the strained Si quantum well can be controllably tuned from 2.5×1011to4.5×1011cm−2, virtually without any gate leakage current. Magnetotransport data show the homogeneous depletion of 2DES under gate biases. The characteristic of vertical modulation using ALD dielectric is shown to be better than that using Schottky barrier or the SiO2 dielectric formed by plasma-enhanced chemical-vapor-deposition.
Mapping of trap densities and energy levels in semiconductors using a lock-in infrared camera technique
Authors: Pohl Peter , Schmidt Jan , Bothe Karsten , Brendel Rolf
Published: September 2005

We examine nonrecombination active minority-carrier trapping centers in crystalline silicon using a lock-in infrared camera technique. Application of a simple trapping model to the injection-dependent lifetime data obtained from the infrared emission signal results in high-resolution mappings (spatial resolution=170μm) of the trap density and the energy level. Measurements on Czochralski-grown silicon wafers show striation-related inhomogeneities of the trap density and a very homogeneous distribution of energy levels.
Dual layer selective emitter
Authors: Chubb Donald L. , Wolford David S.
Published: September 2005

A selective emitter consisting of two layers separated by a vacuum is analyzed. The bottom layer consists of a selective emitting material such as a rare earth containing crystal on a metal substrate. The top layer, which blocks long wavelength radiation, is a window such as sapphire with a deposited metal film. As a result of reduced long wavelength emission, the theoretical analysis shows that the emitter efficiency can be increased by nearly a factor of 2.
Magnetic domain structure of wires studied by using the magneto-optical indicator film method
Authors: Kabanov Yu. , Zhukov A. , Zhukova V. , Gonzalez J.
Published: September 2005

Experimental studies of the magnetic domain structure of amorphous wires with positive (Fe-rich) and negative (Co-rich) magnetostriction by using the magneto-optical indicator film method have been performed. The following main results have been obtained. (i) Fe-rich wires possess unclosed 180° surface domain structures with magnetization perpendicular to the wire surface, i.e., without closure domains previously assumed for such materials. Such results have been attributed to the large magnetolastic anisotropy induced by the fabrication process. (ii) Domain structures of Co-rich wires consist of rather big (as-compared with Fe-rich wires) circular domains.
F
2
-laser digital etching of colloidal photonic crystals
Authors: Li J. , Herman P. R. , Kitaev V. , Wong S. , Ozin G. A.
Published: September 2005

We report on digital etching of silica colloidal photonic crystals by employing a pulsed deep-ultraviolet F2 laser at 157nm wavelength. When the laser fluence is above a microsphere-size-dependent threshold and within an appropriate fluence window, colloidal crystals can be etched in a digitized fashion, whereby a single microsphere layer can be removed upon exposure to a single laser pulse. Alternatively, single spheres or lines of spheres can be selectively ejected by patterning the laser beam. The results demonstrate a fast, noncontact, straightforward, and cost-effective approach for engineering extrinsic defects into colloidal photonic crystals.
Thermal Metamorphism of Primitive Meteorites—XII. The Enstatite Chondrites Revisited
Authors: Wang Ming-Sheng , Lipschutz Michael E.
Published: September 2005

Environmental Context.The first Solar System material condensed 4.567 billion years ago, rapidly forming planetesimals—solid bodies that might combine to form planets (accretion) or survive as asteroidal meteorites. Earth’s main accretion ended within the next 30 million years, but subsequent high temperatures essentially erased evidence of this history. However, heating in these early episodes produced effects uniquely recorded by 14 volatile trace elements. The volatile element composition of chondritic meteorites, whose parent material formed closest to Earth, may thus provide important information about early planetesimal evolution. Abstract.We report data for 14 trace and ultratrace elements—Au, Co, Sb, Ga, Rb, Ag, Cs, Te, Zn, Cd, Bi, Tl, In (ordered by increasing putative nebular volatility)—in 13 enstatite (E) chondrites recovered from Antarctica and two E inclusions in the Kaidun polymict breccia that fell in 1980. These data, determined by radiochemical neutron activation analysis (RNAA), essentially double the amount of information known for E chondrites, whose parent materials formed closest to the Sun in the chondrite-forming nebular region. We discuss here the data for all 29 samples studied. The meteoritic suite studied here includes both representatives of previously rare types—like high-iron EH3 and EH5 individuals—but also unique individuals and previously unknown low-iron, EL3, chondrites. Prior hypothetical assertions by others are corrected by the new data. Volatile element contents of EL3 and EH3 chondrites are variable, but comparable, like those of type 3 ordinary chondrites (i.e. H3, L3, and LL3). Volatile element contents of EH4 chondrites are at least as high as those of the E3 types, in contrast to the lower contents of H4, L4, and LL4 types. Compositionally, E3,4 chondrites reflect only nebular condensation and/or accretion processes. Volatiles in E5 and E6 chondrites—whether of EH, EL or unique ones—are depleted relative to cosmic (i.e. CI1) or E3,4 chondrite abundances. The evidence indicates that E5,6 chondrites compositionally reflect vaporization and loss of volatiles during open-system, thermal metamorphism of their parent(s); this may have been the terrestrial environment during Earth’s formation from early planetesimals. Compositional differences between Antarctic E5,6 chondrites and contemporary falls probably do not reflect weathering during the long residence of these chondrites in Antarctica. They might reflect differences in the starting compositions and/or metamorphic conditions in the parent(s).
High Throughput Determination of BTEX by a One-Step Fluorescence Polarization Immunoassay
Authors: Eremin Sergei A. , Knopp Dietmar , Niessner Reinhard , Hong Ji Youn , Park Song-Ja , Choi Myung Ja
Published: September 2005

Environmental Context.Benzene, toluene, ethylbenzene, and xylenes (BTEX) are used as solvents in paints and coatings and are constituents of petroleum products. BTEX can contaminate air, water or soil and is toxic; benzene, in particular, is a recognized human carcinogen. Most existing methods for detecting BTEX are time-consuming, complicated and very expensive for routine screening. A rapid immunoassay of BTEX is presented that greatly simplifies environmental monitoring of water contamination. Abstract.For the rapid screening of BTEX (benzene, toluene, ethylbenzene, xylenes), a fluorescence polarization immunoassay (FPIA) was developed using the fluorescence polarization analyzer Abbott TDx. Several fluorescence-labelled tracers were synthesized by binding ethylenediamine fluorescein thiocarbamyl (EDF) to various substituted phenylcarboxylic acids. The binding of 27 tracers with two antisera that can be considered as class-specific for BTEX was investigated to select optimal tracer–antibody pairs. Significant differences were found in binding, titer, sensitivity, and assay kinetics. A best pair of anti-BTEX antiserum and EDF-labelled p-tolylacetic acid tracer was selected for FPIA. To simplify the method, an immunocomplex single reagent was prepared to detect BTEX by a one-step FPIA. One-step FPIA is a rapid homogeneous type of immunoassay that has only one pipetting step, does not need separation of free and bound analyte and can be performed at room temperature. The within-run coefficient of variation was ranged between 3.4% and 5.7%. Furthermore, if the measurement can be done at constant temperature, standards for every assay run are unnecessary. Cross-reactivity studies of petroleum compounds and a BTEX mixture indicated that p-xylene was most reactive with a limit of detection (LOD) of 0.22 µg mL−1 in 50 µL of sample. The LOD for toluene and benzene was 2.1 and 11 µg mL−1 respectively. The immunocomplex single reagent has proven to be significantly more stable than the corresponding solutions of antibody and tracer.
Surfactants in South East Asian Aerosols
Authors: Latif Mohd Talib , Brimblecombe Peter , Ramli Nor Azam , Sentian Justin , Sukhapan Jariya , Sulaiman Norela
Published: September 2005

Environmental Context.Surfactants are present in all atmospheric aerosols with potential effects on surface tension, cloud droplets and even human health. They appear to be anionic and associated with yellow aqueous extracts, suggesting a humic-like character. These surfactants are probably derived from the oxidation of combustion-generated soot (from vehicles and forest fires).
Abstract.The concentration of surfactants in aerosols was determined at several sites in South East Asia, Bangi, Penang and Kota Kinabalu in Malaysia and Bangkok, Thailand, as methylene blue active substances (MBAS) and ethyl violet active substances (EVAS) for anionic surfactants and disulphine blue active substances (DBAS) for cationic surfactants. The methodology used is based on the formation of extractable ion-association complexes of surfactants and dye in organic solvents followed by spectrometric measurement of the intensity of the extracted coloured complex. Results showed surfactants in aerosols are mostly in the anionic form as MBAS and EVAS, and higher in aerosols collected in congested areas, especially in times of forest fires. Concentrations are in the range of 34.6 to 285.0 pmol m−3 for MBAS and 129.9 to 932.2 pmol m−3 for EVAS. Several different types of soot and humic acid seem possible sources of surfactants in atmospheric aerosols. Laboratory experiments suggested that combustion products, especially from motor vehicles, are important primary sources of surfactants in aerosols. There is also some laboratory evidence that there are secondary sources for these surfactants in aerosols, possibly humic-like substances (HULIS) from the oxidation and photochemical reaction of soots and humic acid.
Unexpected Beneficial Effects of Arsenic on Corn Roots Grown in Culture
Authors: Evans Grant , Evans Julyette , Redman Andrea , Johnson Nancy , Foust Richard D.
Published: September 2005

Environmental Context. Phytoremediation, the process of using plants to remove metals from contaminated soils, shows promise as a low-technology method for economically removing arsenic, and other toxic metals, from soil. Arsenic transport studies in vascular plants have examined how arsenic is taken up, chemically modified, and transported from roots to other parts of the plant. No studies, to our knowledge, have examined the effect of low-level doses of arsenic on the roots themselves. This paper shows, for the first time, that arsenic at low levels may beneficially affect root development.
Abstract. Corn (Zea mays) roots were grown in culture on modified Strullu–Roman medium in two separate experiments. Roots were exposed to one of four treatments combining arsenic (100 µg L−1 or 0.0 µg L−1) and phosphorous (4.8 mg L−1 or 0.0 mg L−1). The cultures were allowed to grow for 18 days or 21 days before they were used for quantitative measurement of root mass, root length, number of branches, and branch length. Results indicate roots grown in medium lacking phosphate but containing arsenic were longer and had greater mass than roots grown in medium with only phosphate. The data presented here suggest that arsenic at low levels might be beneficial for root development.
Arsenosugar Metabolism Not Unique to the Sheep of North Ronaldsay
Authors: Martin Simon J. , Newcombe Chris , Raab Andrea , Feldmann Jörg
Published: September 2005

Environmental Context. Seaweed is enjoying a revival in farming practice, in particular by organic farmers. However, seaweed accumulates arsenic, and these arsenic compounds can enter the food chain. It is known that the arsenic is present mainly as arsenosugars, but the metabolism of these compounds by ruminants needs clarification. Abstract. Here we describe a feeding trial with Blackface sheep conducted on an organic farm in Kintyre (Scotland), which aims to prove that the metabolism of arsenic, acquired from the consumption of seaweed, is not unique to the North Ronaldsay sheep, which are adapted to a seaweed diet. Results show that the trial sheep supplemented their diet with, on average, 20 ± 9% Laminaria digitata when given the choice. The daily arsenic intake varied greatly from sheep to sheep but on average, the sheep consumed 65 μg kg−1 b.w. Total arsenic concentrations in urine, as measured by inductively coupled plasma-mass spectrometry (ICP-MS) (m/z 75) also show significant differences between the trial and control group (P < 0.0001). HPLC coupled with ICP-MS in parallel with electrospray ionization-mass spectrometry (ES-MS) for detection was used for the identification of arsenic metabolites in urine samples. Dimethylarsinic acid (DMAV) is the main metabolite in the control group as well as in the trial group. In addition, arsenic metabolites previously only found in the urine of North Ronaldsay sheep were successfully identified in the urine of the trial group of the seaweed-eating Blackface sheep: dimethylarsinoyl acetic acid (DMAA) and its thio-analogue dimethylarsinothioyl acetic acid (DMAAS) as well as the monosulfide of DMAV, DMAS. However, the poor chromatographic recovery indicates that the urine contains arsenic species, which do not elute under the conditions tested.
Commonalities in Metabolism of Arsenicals
Authors: Adair Blakely M. , Waters Stephen B. , Devesa Vicenta , Drobna Zuzana , Styblo Miroslav , Thomas David J.
Published: September 2005

Environmental Context. Health effects associated with inorganic arsenic include various cancers and increased risk of diabetes. Millions of people in Bangladesh and India are at risk through use of contaminated drinking water. When humans ingest inorganic arsenic, it is rapidly converted to methylated metabolites. Although this methylation process is largely understood, the metabolism of other arsenicals (e.g. arsenosugars to dimethylarsenic) is very unclear. Connections among pathways for metabolism of various arsenicals are now being elucidated. Commonalities and differences in these pathways may be important determinants of the risk associated with exposure to these agents. Abstract. Elucidating the pathway of inorganic arsenic metabolism shows that some of methylated arsenicals formed as intermediates and products are reactive and toxic species. Hence, methylated arsenicals likely mediate at least some of the toxic and carcinogenic effects associated with exposure to arsenic. Trimethylarsonium compounds and arsenosugars are two other classes of arsenicals to which humans are routinely exposed and there is evidence that both classes are metabolized to produce methylated arsenicals. Here, we review evidence for production of methylated metabolism and consider the challenges posed in unraveling a complex web for metabolism of arsenicals in humans.
Environmental Contamination of Arsenic and its Toxicological Impact on Humans
Authors: Ng Jack C.
Published: September 2005

Environmental Context. Tens of millions of people in developing countries are being exposed to excessive levels of arsenic in their drinking water, and this contamination is widely regarded as the largest current calamity of chemical poisoning in the world. However, arsenic can exist in many chemical forms, and these vary widely in solubility, toxicity, and in bioavailability. Therefore, it is critical to be able to measure arsenic speciation accurately and reliably in order to understand its toxicity and design effective measures of remedial action. Abstract. Inorganic arsenic compounds are known carcinogens. The human epidemiologic evidence of arsenic-induced skin, lung, and bladder cancers is strong. However, the evidence of arsenic carcinogenicity in animals is very limited. Lack of a suitable animal model until recent years has inhibited studies of the mechanism of arsenic carcinogenesis. The toxicity and bioavailability of arsenic depend on its solubility and chemical forms. Therefore, it is critical to be able to measure arsenic speciation accurately and reliably. However, speciation of arsenic in more complex matrices remains a real challenge. There are tens of millions of people who are being exposed to excessive levels of arsenic in the drinking water alone. The source of contamination is mainly of natural origin and the mass poisoning is occurring worldwide, particularly in developing countries. Chronic arsenicosis resulting in cancer and non-cancer diseases will impact significantly on the public health systems in their respective countries. Effective watershed management and remediation technologies in addition to medical treatment are urgently needed in order to avoid what has been regarded as the largest calamity of chemical poisoning in the world.
Heterotrophic bacterial production in the lower Murray River, south-eastern Australia
Authors: Rees Gavin N. , Beattie Gillian , Bowen Patricia M. , Hart Barry T.
Published: September 2005

Bacterial production is important in aquatic carbon cycles because it represents a key component whereby dissolved and particulate carbon can be recycled back into food webs. Despite its acknowledged importance, few studies have examined bacterial production in lowland rivers. Since studies have suggested bacterial production is closely related to some carbon pools, we anticipated this to be the case in the Murray River, but that the timing and type of carbon inputs in the Murray River may lead to bacterial dynamics that differ from studies from other sites. Bacterial abundance and production were measured at three contrasting sites of the lowland Murray River, south-eastern Australia, over an 18-month period. Bacterial abundance varied across the three sites on the Murray River and was correlated with chlorophyll a concentrations but not with temperature, nutrients, particulate organic carbon and dissolved organic carbon concentrations. Bacterial production also varied across the sites. Lowest production was at the site most immediately downstream of a large reservoir, with production generally ranging from 0.88 to 8.00 μg C L−1 h−1. Bacterial production in a reach within a large forest ranged from 4.00 to 17.38 μg C L−1 h−1. Production at the reach furthest downstream ranged from 1.04 to 23.50 μg C L−1 h−1. Bacterial production in the Murray River was generally greater than in the European River Spree, reaches of the Meuse and Rhine without immediate impacts from major urban centres and the Amazon River, but was similar to the concentration measured in the Mississippi and Hudson Rivers. Bacterial production was closely correlated with chlorophyll a concentration and total phosphorus, but not with temperature, dissolved organic carbon, particulate organic carbon or inorganic nitrogen. Despite the differences in production and respiration measured at different sites across the Murray River, bacterial growth efficiency was very similar at the three sites. Bacterial populations in the Murray River appear to be influenced by reach-specific conditions rather than broad-scale drivers such as temperature, carbon and nutrient concentrations.
Increasing codend mesh openings: an appropriate strategy for improving the selectivity of penaeid fishing gears in an Australian estuary?
Authors: Macbeth William G. , Broadhurst Matt K. , Millar Russell B. , Smith Stephen D. A.
Published: September 2005

This study investigates the effects of increasing the lateral mesh openings in codends on the size and species selectivity of lagoon and river seines and a stow net used to target penaeid prawns (eastern king (Penaeus plebejus), school (Metapenaeus macleayi) and greasyback prawns (M. bennettae)) in Wallis Lake, New South Wales, Australia. Compared with conventional codends made from 36-mm diamond-shaped mesh, new designs made from 25- and 29-mm mesh hung on the bar (i.e. square-shaped mesh) significantly reduced the catches of non-target fish (by between 58 and 95%) and improved size selection for the targeted penaeids in the stow net and lagoon seine. In contrast, owing to gear-specific operational characteristics such as a slower hauling speed, there were few detectable effects of altering mesh openings in the codend of the river seine. The results are discussed in terms of the differences in the gears used and their particular selection mechanisms. We conclude that, pending further trials, codends made from a mesh size approaching 29 mm, hung on the bar, would provide appropriate size- and species-selection for Wallis Lake stow nets and lagoon seines. Further research is required, however, to examine the utility of operational changes to river seines and/or alterations to mesh size and configuration in the wings and body to improve selectivity.
Quantifying percentage cover of subtidal organisms on rocky coasts: a comparison of the costs and benefits of standard methods
Authors: Drummond S. P. , Connell S. D.
Published: September 2005

This study compares the cost (time and funds) and benefits (precision and accuracy) of methods commonly used to estimate percentage cover of sessile marine organisms. We applied nine methods to morphological groups of benthic algae and broad taxonomic groups of sessile invertebrates; including varying the intensity of sampling (25 v. 50 v. 100 point-intercepts), random v. regular arrays, in situ v. laboratory v. photographic sampling v. computer digitising. We detected little to no difference in estimates of percentage cover among methods, indicating that accuracy is unlikely to be an important issue that distinguishes methods. Precision was generally unaffected by the intensity of sampling within quadrats (25 v. 50 v. 100 point-intercepts) or between environments (in situ v. on photographs v. within the laboratory) and appeared to be of secondary concern to decisions about replication. Computer digitising (estimates of surface area of each taxon) provided the least precise estimates and did not justify the additional laboratory time required to process them. Depending on whether field expenses or laboratory expenses are of the greatest concern, the techniques that permit the greatest coverage of area (greatest replication) are likely to produce the most representative (accurate) and reliable (precise) estimates.
Trophic shifts in three subtropical Australian halfbeaks (Teleostei:Hemiramphidae)
Authors: Tibbetts Ian R. , Carseldine Lee
Published: September 2005

To elucidate the trophic status of hemiramphids, the diets of three species from subtropical south-east Queensland were investigated. All undergo a marked ontogenetic trophic shift from an animal to plant diet, which occurred between 50 and 70 mm standard length (Ls) for Arrhamphus sclerolepis krefftii (freshwater) and between 80 and 110 mm Ls for both Hyporhamphus regularis ardelio and H. quoyi (both marine). After the ontogenetic shift, the diet of A. sclerolepis krefftii is dominated by filamentous algae, whereas the diet of the two marine species is dominated by Zostera capricorni. The two marine species feed mainly during the day, with gut fullness dropping markedly after dusk. Neither showed evidence of a diel trophic shift between herbivory and carnivory that has been reported for other hemiramphids. The lack of diel trophic switching in these subtropical hemiramphids may suggest that latitudinal effects on daylength and/or water temperature may influence the extent to which hemiramphids switch periodically to animal prey from an otherwise essentially herbivorous diet in order to balance their nutrient requirements.
Specific amplification of mt-COI gene of the invasive gastropod Maoricolpus roseus in planktonic samples reveals a free-living larval life-history stage
Authors: Gunasekera Rasanthi M. , Patil Jawahar G. , McEnnulty Felicity R. , Bax Nicholas J.
Published: September 2005

The New Zealand screwshell Maoricolpus roseus was unintentionally introduced to south-eastern Tasmania in the 1920s. It has colonised more habitat than any other high-impact benthic marine pest in Australia and its wide temperature and depth tolerance makes further spread likely. We developed three sets of genetic probes, each targeting a unique region in the mitochondrial COI locus, for the rapid detection of this species in mixed plankton samples. In particular, we wanted to know whether this species has a planktonic life-history stage that could lead to its dispersal in ships’ ballast water. All probe sets were tested against as many closely related species as could be obtained and the reaction conditions were optimised for maximum sensitivity and specificity of M. roseus. Plankton samples collected in the Derwent Estuary between August 2003 and June 2004 were tested with the probes using a nested polymerase chain reaction. Maoricolpus roseus was detected in the plankton samples especially in the spring–summer period. The presence of M. roseus in the plankton and water available for ships’ ballast indicates that the risk of this species being spread by shipping needs to be managed.
A plausible model for the digital response of p53 to DNA damage
Authors: Ma Lan , Wagner John , Rice John Jeremy , Hu Wenwei , Levine Arnold J. , Stolovitzky Gustavo A.
Published: September 2005

Recent observations show that the single-cell response of p53 to ionizing radiation (IR) is “digital” in that it is the number of oscillations rather than the amplitude of p53 that shows dependence on the radiation dose. We present a model of this phenomenon. In our model, double-strand break (DSB) sites induced by IR interact with a limiting pool of DNA repair proteins, forming DSB–protein complexes at DNA damage foci. The persisting complexes are sensed by ataxia telangiectasia mutated (ATM), a protein kinase that activates p53 once it is phosphorylated by DNA damage. The ATM-sensing module switches on or off the downstream p53 oscillator, consisting of a feedback loop formed by p53 and its negative regulator, Mdm2. In agreement with experiments, our simulations show that by assuming stochasticity in the initial number of DSBs and the DNA repair process, p53 and Mdm2 exhibit a coordinated oscillatory dynamics upon IR stimulation in single cells, with a stochastic number of oscillations whose mean increases with IR dose. The damped oscillations previously observed in cell populations can be explained as the aggregate behavior of single cells.