bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient hydrogeologic models for submarine flow in volcanic seamounts: 1. The Hawaiian Islands
Authors: Christiansen L. B. , Garven G.
Published: February 2004

Seamounts and volcanic islands are regions of the seafloor where pressure gradients, caused by temperature variations, are large enough to drive fluid flow. Compaction in surrounding sedimentary aprons, formed during mass wasting of these features, drives fluid flow as well. In seamount environments a complex flow pattern evolves as effects of compaction and free convection interact. We use transient finite element modeling to explore fluid flow and pore pressure in a volcanic edifice and its surrounding sedimentary apron to determine the hydrogeologic and pore pressure regime. Models are based on geophysical cross sections of the Hawaiian Islands and include the volcanic edifice, sedimentary apron, and underlying oceanic crust. Models simulate growth of the volcanic island, flexure of the oceanic crust due to loading, and formation of the sedimentary apron. High sedimentation rates of up to 1 mm/yr during volcanic building cause compaction in the sedimentary apron, and the weight of the edifice compacts the pelagic sediment beneath it; compaction‐driven flow dominates flow patterns. Excess pore pressures are highest during the beginning of volcanic construction and decline through the remainder of the simulation. As sedimentation decreases, compaction‐driven and buoyancy‐driven flow both control flow patterns. When sedimentation stops, pore pressure dissipates, and buoyancy‐driven flow dominates the flow regime. Pore pressure ratios indicate that under certain parameter conditions, pore pressure may exceed lithostatic, leading to unstable edifice conditions. Although fluid velocities are small (q < 0.5 cm/yr), the hydrologic regime has important implications for slope stability, volcanic spreading, sedimentation processes, and geochemical transport.
Temporal changes in P wave attenuation in the Loma Prieta rupture zone
Authors: Chun Kin‐Yip , Henderson Gary A. , Liu Jingsong
Published: February 2004

Clusters of recurring, nearly identical microearthquakes have been recorded near Loma Prieta, California. Such events make possible direct measurement of temporal changes in the attenuation operator t* along fixed paths under what are tantamount to laboratory conditions. Analysis of almost 10 years of P wave data following the 18 October 1989 Loma Prieta, California, main shock (M = 7.0) reveals a large‐amplitude t* increase within the first 3 weeks of the main shock. A gradual t* recovery toward its level prior to the main shock is seen in the years ensuing. The results point to changes in porosity and fluid saturation taking place in parts of the main shock source volume, stemming from coseismic crack opening and postseismic relaxation processes such as postseismic fluid flow into the cracks, crack healing, and rock compaction.
Different nutrient sources forcing increased productivity during eastern Mediterranean S1 sapropel formation as reflected by calcareous dinoflagellate cysts
Authors: Meier K. J. Sebastian , Zonneveld Karin A. F. , Kasten Sabine , Willems Helmut
Published: February 2004

Comparison of calcareous dinoflagellate cyst assemblages with Ba, Al, Mn, and Fe records from three sediment cores collected in the eastern Mediterranean Sea indicate that calcareous dinoflagellate cysts are generally resistant to postdepositional dissolution. Cyst association changes during and after sapropel S1 formation can therefore be closely related to variability in surface water productivity. Two groups of cysts are defined: those having highest abundances within the sapropelic and postsapropelic sediments. The temporal cyst distributions suggest increased freshwater input mainly from the Nile and a shallowing of the pycnocline as the most important processes increasing nutrient concentration in the photic zone, thus leading to increased productivity and organic carbon fluxes during sapropel formation. Furthermore, a general warming trend at the beginning of S1 formation and a slight salinity decrease are reconstructed.
Chronic bilateral otomycosis caused by Aspergillus niger
Authors: Mishra G. S. , Mehta Niral , Pal M.
Published: February 2004

Aspergillus niger, an opportunistic filamentous fungus, was identified as the cause of chronic bilateral otomycosis in a 46‐year‐old female patient who was unresponsive to different drugs. The patient showed signs of erythema, otalgia, itching, otorrhoea and presence of greyish black coloured mass in both the ear canals. The direct microscopical examination of the ear debris in potassium hydroxide preparations, Giemsa, phase contrast and Gram revealed many thin, branched septate hyphae, condia and conidiophores morphologically indistinguishable from Aspergillus spp. The histopathological section of the ear wax mass by haematoxylin and eosin and periodic acid‐Schiff techniques also showed similar fungal elements. The patient responded to 1% solution of mercurochrome. The use of mercurochrome in developing countries like India may be recommended to treat the fungal otitis in patients. We also emphasize that ‘Narayan’ stain should be routinely employed by microbiology and public health laboratories to study the morphology of pathogenic fungi.
Invasive fungal sinusitis due toBipolaris hawaiiensis
Authors: Castelnuovo P. , De Bernardi F. , Cavanna C. , Pagella F. , Bossolesi P. , Marone P. , Farina C.
Published: February 2004

A phaeohyphomycotic sinusitis due toBipolaris hawaiiensis, observed in an immunologically competent patient, is reported and a review of data from the literature is given. The patient was successfully treated by surgical drainage and amphotericin B.
Phylogenetic relationships among medically important yeasts based on sequences of mitochondrial large subunit ribosomal RNA gene
Authors: Yamada Y. , Makimura K. , Uchida K. , Yamaguchi H. , Osumi M.
Published: February 2004

Sequences of the mitochondrial large subunit ribosomal RNA (mtLsurRNA) gene of medically important yeasts were analysed. Sixteen strains of eight species including two varieties were subjected to sequencing. Sequencing enabled us to recognize the differences between all the species and varieties. Alignment analysis revealed that these sequences consisted of three clusters: the Candida albicans group, the C. glabrata group, and the basidiomycetous group. It is possible, therefore, that the mtLsurRNA gene is one of the targets not only for species identification but also for phylogenetic analysis of closely related yeasts. The dendrogram of each group, obtained from this gene, supports the previous study of yeasts based upon the chromosomal genes.
Pollen flow in the wildservice tree, Sorbus torminalis (L.) Crantz. I. Evaluating the paternity analysis procedure in continuous populations
Authors: Oddou‐Muratorio S. , Houot M.‐L. , Demesure‐Musch B. , Austerlitz F.
Published: February 2004

The joint development of polymorphic molecular markers and paternity analysis methods provides new approaches to investigate ongoing patterns of pollen flow in natural plant populations. However, paternity studies are hindered by false paternity assignment and the nondetection of true fathers. To gauge the risk of these two types of errors, we performed a simulation study to investigate the impact on paternity analysis of: (i) the assumed values for the size of the breeding male population (NBMP), and (ii) the rate of scoring error in genotype assessment. Our simulations were based on microsatellite data obtained from a natural population of the entomophilous wild service tree, Sorbus torminalis (L.) Crantz. We show that an accurate estimate of NBMP is required to minimize both types of errors, and we assess the reliability of a technique used to estimate NBMP based on parent–offspring genetic data. We then show that scoring errors in genotype assessment only slightly affect the assessment of paternity relationships, and conclude that it is generally better to neglect the scoring error rate in paternity analyses within a nonisolated population.
Patterns of spatial genetic structuring in a hydropsychid caddisfly (Cheumatopsyche sp. AV1) from southeastern Australia
Authors: Baker A. M. , Williams S. A. , Hughes J. M.
Published: February 2004

We assessed levels of mitochondrial genetic spatial structuring in the hydropsychid caddisfly Cheumatopsyche sp. AV1 in southeastern New South Wales, Australia. No significant spatial structuring was detected within or between catchments using analysis of molecular variance, and nested clade contingency analysis suggested no strong relationship between haplotypes and geographical location, at any clade level. However, tests for association among haplotypes incorporating geographical distance in the nested clade analysis, revealed patterns of historical range expansion and recent restricted gene flow. Most likely, population fragmentation preceded range expansion, although subsequent recontact and gene flow among the previously sundered populations has apparently obscured the geographical signature of the former fragmentation. Taken together, our analyses suggest that a number of populations fragmented during the Pleistocene evolved in isolation for a time and subsequently expanded into secondary contact. Since expansion, there has apparently been substantial (albeit somewhat restricted) dispersal and gene flow of adult female Cheumatopsyche sp. AV1, throughout the study area.
Strain‐specific regulation of intracellularWolbachiadensity in multiply infected insects
Authors: Mouton L. , Henri H. , Bouletreau M. , Vavre F.
Published: February 2004

Vertically transmitted symbionts suffer a severe reduction in numbers when they pass through host generations, resulting in genetic homogeneity or even clonality of their populations.Wolbachiaendosymbionts that induce cytoplasmic incompatibility in their hosts depart from this rule, because cytoplasmic incompatibility actively maintains multiple infection within hosts. Hosts and symbionts are thus probably under peculiar selective pressures that must shape the way intracellular bacterial populations are regulated. We studied the density and location ofWolbachiawithin adultLeptopilina heterotoma, a haplodiploid wasp that is parasitic onDrosophilaand that is naturally infected with threeWolbachiastrains, but for which we also obtained one simply infected and two doubly infected lines. Comparison of these four lines by quantitative polymerase chain reaction using a real‐time detection system showed that totalWolbachiadensity varies according to the infection status of individuals, while the specific density of eachWolbachiastrain remains constant regardless of the presence of other strains. This suggests thatWolbachiastrains do not compete with one another within the same host individual, and that a strain‐specific regulatory mechanism is operating. We discuss the regulatory mechanisms that are involved, and how this process might have evolved as a response to selective pressures acting on both partners.
Wirksamkeit und Nutzen eines 5‐FU‐/Salicylsäure‐haltigen Präparates in der Therapie vulgärer und plantarer Warzen – systematische Literaturübersicht und Metaanalyse
Authors: Zschocke Ina , Hartmann Armin , Schlöbe Andrea , Cummerow Ralf , Augustin Matthias
Published: February 2004

Hintergrund: 1) Salicylsäure (SA) und 5‐Fluorouracil (5‐FU) sind effektive Wirkstoffe in der Warzentherapie. 2) In Deutschland werden zunehmend Daten zum Nutzen und zur Wirtschaftlichkeit von Arzneimitteln auf dem Level I der Evidenz‐basierten Medizin benötigt.

Methoden: Evaluiert werden sollte die Wirksamkeit und der klinische Nutzen eines Arzneimittels mit 0,5 % 5‐FU und 10 % SA in der Therapie von a) vulgären und b) plantaren Warzen mittels: 1. Systematischer Literaturanalyse, 2. Metaanalyse der randomisiert‐kontrollierten Studien (RCTs).

Ergebnisse: 1. Die Wirksamkeit der 5‐FU/SA‐Therapie wurde an insgesamt 625 Patienten (n = 8 RCTs) mit vulgären Warzen und an 101 Patienten (n = 4 RCTs) mit Plantarwarzen geprüft. Der Therapieeffekt über alle Studien betrug bei den Verrucae vulgares 63,4 % Response (komplette Abheilung) für 5‐FU/SA vs. 23,1 % für die 5‐FU‐freien Kontrollen. Bei den Plantarwarzen betrug die Response 63,0 % vs. 11,0 %. 2. Eine Metaanalyse über n = 7 RCTs an vulgären Warzen (n = 325 Patienten) ergab eine mittlere Risikodifferenz von 0,42 (KI 0,34 – 0,50, p < 0,05), somit signifikante Überlegenheit von 5‐FU/SA gegenüber SA. Ein vergleichbares Ergebnis fand sich auch für Plantarwarzen.

Schlußfolgerung: Die Kombination aus 5‐FU und SA stellt in der Therapie vulgärer und plantarer Warzen eine effektive und nützliche Therapie dar.
Feel the Information with VisPad: A Large Area Vibrotactile Device
Authors: Weissgerber Doanna , Bridgeman Bruce , Pang Alex
Published: February 2004

A new haptics design for visualizing data is constructed out of commodity massage pads and custom controllers and interfaces to a computer. It is an output device for information that can be transmitted to a user who sits on the pad. Two unique properties of the design are: (a) its large feedback area and (b) its passive nature, where unlike most current haptics devices, the user's hands are free to work on other things. To test how useful such a device is for visualizing data, we added the VisPad interface to our protein structure-alignment program (ProtAlign) and performed usability studies. The studies demonstrated that information could be perceived significantly faster utilizing our multi-modal presentation compared to vision-based graphical visualization alone.
Dynamic Query Tools for Time Series Data Sets: Timebox Widgets for Interactive Exploration
Authors: Hochheiser Harry , Shneiderman Ben
Published: February 2004

Timeboxes are rectangular widgets that can be used in direct-manipulation graphical user interfaces (GUIs) to specify query constraints on time series data sets. Timeboxes are used to specify simultaneously two sets of constraints: given a set of N time series profiles, a timebox covering time periods x1… x2 ( x1 ≤ x2) and values y1… y2 ( y1 ≤ y2) will retrieve only those n√N that have values y1 ≤ y2 during all times x1 ≤ x ≤ x2. TimeSearcher is an information visualization tool that combines timebox queries with overview displays, query-by-example facilities, and support for queries over multiple time-varying attributes. Query manipulation tools including pattern inversion and ‘leaders & laggards’ graphical bookmarks provide additional support for interactive exploration of data sets. Extensions to the basic timebox model that provide additional expressivity include variable time timeboxes, which can be used to express queries with variability in the time interval, and angular queries, which search for ranges of differentials, rather than absolute values. Analysis of the algorithmic requirements for providing dynamic query performance for timebox queries showed that a sequential search outperformed searches based on geometric indices. Design studies helped identify the strengths and weaknesses of the query tools. Extended case studies involving the analysis of two different types of data from molecular biology experiments provided valuable feedback and validated the utility of both the timebox model and the TimeSearcher tool. Timesearcher is available at http://www.cs.umd.edu/hcil/timesearcher
Representations of Time and Space
Authors: Greatbatch Ian
Published: February 2004

Donna Peuquet Published by Guildford Press, New York, 2002, 380 pp, ISBN 1572307730
A combined molecular dynamics+quantum mechanics method for investigation of dynamic effects on local surface structures
Authors: Herschend Björn , Baudin Micael , Hermansson Kersti
Published: February 2004

A combined molecular dynamics (MD)+quantum mechanics (QM) method for studying processes on ionic surfaces is presented. Through the combination of classical MD and ab initio embedded-cluster calculations, this method allows the modeling of surface processes involving both the structural and dynamic features of the substrate, even for large-scale systems. The embedding approach used to link the information from the MD simulation to the cluster calculation is presented, and rigorous tests have been carried out to ensure the feasibility of the method. The electrostatic potential and electron density resulting from our embedded-cluster model have been compared with periodic slab results, and confirm the satisfying quality of our embedding scheme as well as the importance of applying embedding in our combined MD+QM approach. We show that a highly accurate representation of the Madelung potential becomes a prerequisite when the embedded-cluster approach is applied to temperature-distorted surface snapshots from the MD simulation.
Low-lying electronic states of FeNC and FeCN: A theoretical journey into isomerization and quartet/sextet competition
Authors: DeYonker Nathan J. , Yamaguchi Yukio , Allen Wesley D. , Pak Chaeho , Schaefer Henry F. , Peterson Kirk A.
Published: February 2004

With several levels of multireference and restricted open-shell single-reference electronic structure theory, optimum structures, relative energetics, and spectroscopic properties of the low-lying Δ6, Π6, Δ4, Π4, and Σ−4 states of linear FeNC and FeCN have been investigated using five contracted Gaussian basis sets ranging from Fe[10s8p3d], C/N[4s2p1d] to Fe[6s8p6d3f2g1h], C/N[6s5p4d3f2g]. Based on multireference configuration interaction (MRCISD+Q) results with a correlation-consistent polarized valence quadruple-zeta (cc-pVQZ) basis set, appended with core correlation and relativistic corrections, we propose the relative energies: Te(FeNC), Δ6(0)<6Π (2300 cm−1)<4Δ (2700 cm−1)<4Π (4200 cm−1)<4Σ−; and Te(FeCN), Δ6(0)<6Π (1800 cm−1)<4Δ (2500 cm−1)<4Π (2900 cm−1)<4Σ−. The Δ4 and Π6 states have massive multireference character, arising mostly from 11σ→12σ promotions, whereas the sextet states are dominated by single electronic configurations. The single-reference CCSDT-3 (coupled cluster singles and doubles with iterative partial triples) method appears to significantly overshoot the stabilization of the quartet states provided by both static and dynamical correlation. The Δ4,6 and Π4,6 states of both isomers are rather ionic, and all have dipole moments near 5 D. On the ground Δ6 surface, FeNC is predicted to lie 0.6 kcal mol−1 below FeCN, and the classical barrier for isocyanide/cyanide isomerization is about 6.5 kcal mol−1. Our data support the recent spectroscopic characterization by Lei and Dagdigian [J. Chem. Phys. 114, 2137 (2000)] of linear Δ6 FeNC as the first experimentally observed transition-metal monoisocyanide. Their assignments for the ground term symbol, isotopomeric rotational constants, and the Fe–N ω3 stretching frequency are confirmed; however, we find rather different structural parameters for Δ6 FeNC:re(Fe–N)=1.940 Å and r(N–C)=1.182 Å at the cc-pVQZ MRCISD+Q level. Our results also reveal that the observed band of FeNC originating at 27 236 cm−1 should have an analog in FeCN near 23 800 cm−1 of almost equal intensity. Therefore, both thermodynamic stability and absorption intensity factors favor the eventual observation of FeCN via a Π6←6Δ transition in the near-UV.
The rotational spectrum and theoretical study of a dinuclear complex, MnRe(CO)10
Authors: Tanjaroon Chakree , Keck Kristen S. , Kukolich Stephen G. , Palmer Michael H. , Guest Martyn F.
Published: February 2004

The first rotational spectrum of a dinuclear complex, MnRe(CO)10, has been obtained using a high-resolution pulsed beam microwave spectrometer. Sixty-four hyperfine components of the J=11→J′=12 and J=12→J′=13 rotational transitions were measured for two rhenium isotopomers. The B values obtained from the experiment are B=200.36871(18) MHz for the Re187 isotopomer and B=200.5561(10) MHz for the Re185 isotopomer. The measured rotational constants are in reasonably good agreement with the B values calculated from the x-ray diffraction structural data, and from theoretical calculations. The gas-phase Mn–Re bond distance is approximately 2.99 Å, and the calculated value is only slightly longer. The experimental quadrupole coupling constant for the manganese atom is eQqaa (55Mn)=−16.52(5) MHz, and the corresponding quadrupole coupling constants for the two rhenium isotopomers are eQqaa (187Re)=370.4(4) MHz and eQqaa (185Re)=390.9(6) MHz. The quadrupole coupling constants were also determined from a variety of theoretical calculations, with very large Gaussian orbital bases. The best estimates, at a nonrelativistic level, are eQqaa (55Mn)=0.68 MHz and eQqaa (187Re)=327.6 MHz with a 874 GTO basis set, but the results are very basis set dependent, especially the sign of the Mn quadrupole coupling. Very slight bending of angles MnCeqOeq and ReCeqOeq angles is found in the calculations.
Many-body potentials for aqueous Li+, Na+, Mg2+, and Al3+: Comparison of effective three-body potentials and polarizable models
Authors: Spångberg Daniel , Hermansson Kersti
Published: February 2004

Many-body potentials for the aqueous Li+, Na+, Mg2+, and Al3+ ions have been constructed from ab initio cluster calculations. Pure pair, effective pair, effective three-body, and effective polarizable models were created and used in subsequent molecular dynamics simulations. The structures of the first and second solvation shells were studied using radial distribution functions and angular-radial distribution functions. The effective three-body and polarizable potentials yield similar first-shell structures, while the contraction of the O–O distances between the first and second solvation shells is more pronounced with the polarizable potentials. The definition of the tilt angle of the water molecules around the ions is discussed. When a proper definition is used, it is found that for Li+, Mg2+, and Al3+ the water molecules prefer a trigonal orientation, but for Na+ a tetrahedral orientation (ion in lone-pair direction) is preferred. The self-diffusion coefficients for the water molecules and the ions were calculated; the ionic values follow the order obtained from experiment, although the simulated absolute values are smaller than experiment for Mg2+ and Al3+.
Influence of low temperature annealing on the micromagnetic structure of GaMnAs films
Authors: Pross Alexander , Bending Simon , Edmonds Kevin , Campion R. P. , Foxon C. T. , Gallagher Bryan
Published: February 2004

We have imaged the micromagnetic structure of 50 nm Ga0.91Mn0.09As films after different low-temperature anneals. Samples annealed in vacuum for 10 min display a very random domain structure with small (∼3–5 μm) domains. In contrast a sample which was further annealed in air for 50 h exhibited the highest Curie temperature and very large (∼100 μm) domains. Even within large domains we resolve magnetic disorder which has not been removed by the annealing procedure. Micron-sized regions near domain walls remain ferromagnetic well above TC in all the films, possibly indicating the presence of regions with above average Mn density or very small MnAs precipitates, which act as pinning centers and strongly influence the coercive fields of the films.
Intrusion and extrusion of water in hydrophobic mesopores
Authors: Lefevre B. , Saugey A. , Barrat J. L. , Bocquet L. , Charlaix E. , Gobin P. F. , Vigier G.
Published: February 2004

We present experimental and theoretical results on intrusion-extrusion cycles of water in hydrophobic mesoporous materials, characterized by independent cylindrical pores. The intrusion, which takes place above the bulk saturation pressure, can be well described using a macroscopic capillary model. Once the material is saturated with water, extrusion takes place upon reduction of the externally applied pressure. Our results for the extrusion pressure can only be understood by assuming that the limiting extrusion mechanism is the nucleation of a vapor bubble inside the pores. A comparison of calculated and experimental nucleation pressures shows that a proper inclusion of line tension effects is necessary to account for the observed values of nucleation barriers. Negative line tensions of order 10−11 J m−1 are found for our system, in reasonable agreement with other experimental estimates of this quantity.
Extended rotational diffusion and orientational relaxation of symmetric top molecules in a strong dc electric field: Second-rank orientational correlation functions
Authors: Titov S. V. , Déjardin P. M. , Kalmykov Yu. P.
Published: February 2004

Second-rank orientational correlation functions (pertaining to Kerr effect relaxation and Raman scattering) are obtained using the extended rotational diffusion (J-diffusion) model of symmetric top polar molecules in a strong constant external field. It is shown that the shape of the molecule noticeably affects all second-rank correlation functions and relaxation times in the rare collision limit. In the opposite limit of frequent collisions, the quantities of interest are shown to be shape independent as a consequence of vanishingly small inertial effects. An interpolation formula for the orientation relaxation times in the intermediate regime between the rare and frequent collision limits is also given.
Zero-voltage conductance of short gold nanowires
Authors: Zhuang Min , Ernzerhof Matthias
Published: February 2004

Using the Landauer formula, the conductance of short gold wires is studied. The required electronic structure calculations are performed with a self-consistent tight-binding method. We consider gold wires of single-atom diameter with a variable number (N=1,…,5) of atoms. Depending on N, we find considerable conductance variations with one conductance quantum being the upper limit. The results are confirmed by means of Friedel’s sum rule. Tip-shaped clusters are used to provide the contact–wire interfaces and the relation between various tip structures and the conductance is discussed. Our predictions about the conductance variations agree qualitatively with new experimental results [R. H. M. Smit et al., Phys. Rev. Lett. 91, 076805-1 (2003)].
Functionalization of carbon nanotubes using phenosafranin
Authors: Curran S. A. , Ellis A. V. , Vijayaraghavan A. , Ajayan P. M.
Published: February 2004

Spectroscopic analysis and atomic force microscopy (AFM) phase imaging studies show self-assembly of phenosafranin (PSF) to multiwalled carbon nanotubes (MWNTs). The shift in absorption spectra is associated with charge transfer of valence electrons from PSF to electron accepting sites on the MWNTs. The Raman-active disorder modes are used to fingerprint PSF attachment to MWNTs via defect states. AFM phase imaging was used to obtain a molecular topographic visual confirmation of PSF attached to the MWNT.
Low viscosity contrast fingering in a rotating Hele-Shaw cell
Authors: Alvarez-Lacalle E. , Ortı́n J. , Casademunt J.
Published: February 2004

We study the fingering instability of a circular interface between two immiscible liquids in a radial Hele-Shaw cell. The cell rotates around its vertical symmetry axis, and the instability is driven by the density difference between the two fluids. This kind of driving allows studying the interfacial dynamics in the particularly interesting case of an interface separating two liquids of comparable viscosity. An accurate experimental study of the number of fingers emerging from the instability reveals a slight but systematic dependence of the linear dispersion relation on the gap spacing. We show that this result is related to a modification of the interface boundary condition which incorporates stresses originated from normal velocity gradients. The early nonlinear regime shows nearly no competition between the outgrowing fingers, characteristic of low viscosity contrast flows. We perform experiments in a wide range of experimental parameters, under conditions of mass conservation (no injection), and characterize the resulting patterns by data collapses of two characteristic lengths: the radius of gyration of the pattern and the interface stretching. Deep in the nonlinear regime, the fingers which grow radially outwards stretch and become gradually thinner, to a point that the fingers pinch and emit drops. We show that the amount of liquid emitted in the first generation of drops is a constant independent of the experimental parameters. Further on there is a sharp reduction of the amount of liquid centrifugated, punctuated by periods of no observable centrifugation.
Molecular dynamics simulations of acetonitrile/dimethyl sulfoxide liquid mixtures
Authors: Bernardi Edson , Stassen Hubert
Published: February 2004

Binary liquid mixtures of dimethyl sulfoxide and acetonitrile at the three molar fractions 0.25, 0.50, and 0.75 have been investigated by molecular dynamics computer simulations. Thermodynamic states corresponding to liquid–vapor coexistence at a temperature of 298 K were considered. Intermolecular interactions were described by potential models of the site–site (12-6) Lennard–Jones plus Coulomb type that have been developed for the description of the pure liquids. Dimethyl sulfoxide has been represented by four interactions sites and acetonitrile by a three- as well as a six-site potential model. We have calculated thermodynamic properties and the intermolecular pair distribution functions. Intermolecular interaction energies indicate deviations from the behavior of ideal mixtures. The local mole fraction analysis demonstrates that dimethyl sulfoxide is preferentially solvated by acetonitrile and that the first solvation shell surrounding acetonitrile molecules is significantly enriched by dimethyl sulfoxide. The nonideal behavior in the mixtures is not affected by the choice of the three- or the six-site potential model for acetonitrile. Orientational correlations of dipole vectors within the first solvation shells indicate that the relative molecular orientations found in pure acetonitrile and dimethyl sulfoxide are maintained in the mixtures. Parallel and antiparallel dipole–dipole configurations determine first shell acetonitrile–dimethyl sulfoxide configurations. Dynamical features of the mixtures are discussed in terms of diffusion constants and orientational correlation times as obtained from the time correlation functions for linear velocities and molecular dipole moments, respectively. Computed relaxation times indicate faster reorientational motion for dimethyl sulfoxide if acetonitrile is added. In contrast, the orientational dynamics of acetonitrile becomes stronger correlated upon dilution with dimethyl sulfoxide. The diffusion coefficients for both compounds follow this tendency.
The yield strength of thin copper films on Kapton
Authors: Yu Denis Y. W. , Spaepen Frans
Published: February 2004

Thin films of copper, with thickness between 0.1 and 3 μm, were vapor-deposited on 12.7 or 7.6-μm-thick polyimide (Kapton) substrates. They were tested in a microtensile tester in which the strain is measured by optical diffraction from a microlithographically applied grid. The Young modulus is independent of film thickness and is about 20% below the value calculated from single-crystal elastic constants. The yield stress depends strongly on the film thickness and is fit by σy=116+355(t)−0.473, where t is the thickness in μm and σy is in MPa. The microstructure of the films was studied by focused ion-beam microscopy. The grains are heavily twinned and the microstructural lengths (grain size, twin spacing, twin width) depend only weakly on the film thickness. A substantial part of the yield stress is therefore attributable to an effect of the film thickness, such as that predicted by strain gradient plasticity theory. The lower limit and some estimates of the thickness contribution to the yield stress are calculated. The estimated characteristic length of strain gradient plasticity theory is 0.6 μm for these materials.
Dissociation of hydrogen fluoride in HF(H2O)7
Authors: Kuo Jer-Lai , Klein Michael L.
Published: February 2004

We have previously demonstrated that H-bond arrangement has a significant influence on the energetics, structure and chemistry of water clusters [J.-L. Kuo, C. V. Ciobanu, I. Shavitt, L. Ojamäe, and S. J. Singer, J. Chem. Phys., 118, 3583 (2003)]. In this work, the effect of H-bond orientation on the dissociation of hydrogen fluoride with seven water molecules is studied by means of graph theory and high level ab initio methods. It is found that cubic structures of HF(H2O)7 are more stable than structures of other topologies reported in the literature. Electronic calculations on all possible H-bond orientations of cubie–HF(H2O)7 show that ionized structures are energetically more favorable than nonionized ones. This is an indication that seven water molecules might be capable of ionizing hydrogen fluoride.
Differential, partial and total electron impact ionization cross sections for SF6
Authors: Pal Satyendra , Kumar J. , Märk T. D.
Published: February 2004

Single and double differential ionization cross sections for the production of ions resulting from dissociative, single and double ionization of SF6 by electron impact have been calculated using a semiempirical formulation based on the Jain–Khare approach. In addition, triple differential cross sections have been obtained for some of the doubly charged fragment ions at an incident electron energy of 100, 150, and 200 eV, respectively, and a fixed scattering angle of 30°. As no previous data seem to exist for differential cross sections we have derived from these differential cross sections corresponding partial and total ionization cross sections from threshold up to 900 eV and compared those with the available theoretical and experimental data.
Effects of surfactant micelles on viscosity and conductivity of poly(ethylene glycol) solutions
Authors: Wang Shun-Cheng , Wei Tzu-Chien , Chen Wun-Bin , Tsao Heng-Kwong
Published: February 2004

The neutral polymer–micelle interaction is investigated for various surfactants by viscometry and electrical conductometry. In order to exclude the well-known necklace scenario, we consider aqueous solutions of low molecular weight poly(ethylene glycol) (2–20)×103, whose radial size is comparable to or smaller than micelles. The single-tail surfactants consist of anionic, cationic, and nonionic head groups. It is found that the viscosity of the polymer solution may be increased several times by micelles if weak attraction between a polymer segment and a surfactant exists, ε<kBT. Similarly, ion migration in polymer solutions may be significantly hindered by cooperative interactions between polymers and micelles. Even though ε is small, the interaction energy between a macromolecule and a micelle can be a few kBT due to many contacts, and thus leads to polymer adsorption on micelles’ surfaces. The rapid growth of the viscosity with surfactant concentration is therefore attributed to the considerable cross links among micelles and polymers (transient network). In addition to substantial alteration of the transport properties, this weak interaction also influences the onset point of thermodynamic instability associated with polymer–surfactant solutions. The examples include the decrease of critical aggregation concentration for ionic surfactant and clouding point for nonionic surfactant due to PEG addition.
Comment on “Comment on ‘Constant temperature molecular dynamics simulations by means of a stochastic collision model. II. The harmonic oscillator’ [J. Chem. Phys. 104, 3732 (1996)]” [J. Chem. Phys. 106, 1646 (1997)]
Authors: Kast Stefan M.
Published: February 2004

An argument brought forward by Sholl and Fichthorn [J. Chem. Phys. 106, 1646 (1997)] against the stochastic collision-based constant temperature algorithm for molecular dynamics simulations developed by Kast et al. [J. Chem. Phys 100, 566 (1994); 104, 3732 (1996)] is refuted. It is demonstrated that the large temperature fluctuations noted by Sholl and Fichthorn are due to improperly chosen initial conditions within their formulation of the algorithm. With the original form or by suitable initialization of their variant no deficient behavior is observed.
The 1 2A1, 1 2B2, and 1 2A2 states of the SO2+ ion studied using multiconfiguration second-order perturbation theory
Authors: Li Wen-Zuo , Huang Ming-Bao , Chen Bo-Zhen
Published: February 2004

The 1 2A1, 1 2B2, and 1 2A2 electronic states of the SO2+ ion have been studied using multiconfiguration second-order perturbation theory (CASPT2) and two contracted atomic natural orbital basis sets, S[6s4p3d1f]/O[5s3p2d1f] (ANO-L) and S[4s3p2d]/O[3s2p1d] (ANO-S), and the three states were considered to correspond to the observed X̃, B̃, and Ã states, respectively, in the previous experimental and theoretical studies. Based on the CASPT2/ANO-L adiabatic excitation energy calculations, the X̃, Ã, and B̃ states of SO2+ are assigned to 1 2A1, 1 2B2, and 1 2A2, respectively, and our assignments of the Ã and B̃ states are contrary to the previous assignments (Ã to A22 and B̃ to B22). The CASPT2/ANO-L energetic calculations also indicate that the 1 2A1, 1 2B2, and 1 2A2 states are, respectively, the ground, first excited, and second excited states at the ground-state (1 2A1) geometry of the ion and at the geometry of the ground-state SO2 molecule. Based on the CASPT2/ANO-L results for the geometries, we realize that the experimental geometries (determined by assuming the bond lengths to be the same as the neutral ground state of SO2) were not accurate. The CASPT2/ANO-S calculations for the potential energy curves as functions of the OSO angle confirm that the 1 2B2 and 1 2A2 states are the results of the Renner–Teller effect in the degenerate Πg2 state at the linear geometry, and it is clearly shown that the 1 2B2 curve, as the lower component of the Renner splitting, lies below the 1 2A2 curve. The UB3LYP/cc-pVTZ adiabatic excitation energy calculations support the assignments (Ã to B22 and B̃ to A22) based on the CASPT2/ANO-L calculations.
Simulating the effect of surfactant structure on bending moduli of monolayers
Authors: Rekvig Live , Hafskjold Bjørn , Smit Berend
Published: February 2004

We have used dissipative particle dynamics to simulate amphiphilic monolayers on the interface between oil and water. An ultralow interfacial tension is imposed by means of Monte Carlo to resemble the amphiphilic films that separate oil and water regions in microemulsions. We calculate the bending modulus by analyzing the undulation spectrum. By varying the surfactant chain length and topology we investigate the effect of surfactant structure and composition of the monolayer on the bending moduli. We find that increasing the thickness has a larger effect than increasing the density of the layer. This follows from the observations that at a given interfacial tension, the bending modulus increases with chain length and is larger for linear than branched surfactants. The increase with chain length is approximately linear, which is slower than the theoretical predictions at a fixed area. We also investigated a binary mixture of short and long surfactants compared to pure layers of the same average chain length. We find a roughly linear decrease in bending modulus with mole fraction of short surfactants. Furthermore, the mixed film has a lower bending modulus than the corresponding pure film for all mole fractions. Linking the bending moduli to the structure of the surfactants is an important step in predicting the stability of microemulsions.
Sodium diffusion through amorphous silica surfaces: A molecular dynamics study
Authors: Rarivomanantsoa Michaël , Jund Philippe , Jullien Rémi
Published: February 2004

We have studied the diffusion inside the silica network of sodium atoms initially located outside the surfaces of an amorphous silica film. We have focused our attention on structural and dynamical quantities, and we have found that the local environment of the sodium atoms is close to the local environment of the sodium atoms inside bulk sodo-silicate glasses obtained by quench. This is in agreement with recent experimental results.
Bond-selective photodissociation of partially deuterated ammonia molecules: Photodissociations of vibrationally excited NHD2 in the 5νNH state and NH2D in the 5νND state
Authors: Akagi Hiroshi , Yokoyama Keiichi , Yokoyama Atsushi
Published: February 2004

Ultraviolet photodissociation of NHD2 excited to the fourth overtone state of the NH stretching mode (5νNH) and NH2D excited to that of the ND stretching mode (5νND) has been investigated by using a crossed laser and molecular beams method. Branching ratio between the NH and ND bond dissociations has been determined by utilizing a (2+1) resonance enhanced multiphoton ionization scheme of H and D atoms. For the photolysis of NHD2 in the 5νNH state, the NH dissociation cross section is 5.1±1.4 times as large as the ND dissociation cross section per bond. On the other hand, for the photolysis of NH2D in the 5νND state, the ratio of the NH dissociation cross section per bond to the ND dissociation cross section decreases to 0.68±0.16. In comparison with the branching ratios for the photolysis of vibrationally unexcited NH2D and NHD2 [Koda and Back, Can. J. Chem. 55, 1380 (1977)], the present results indicate that the excitation of the NH stretching mode enhances the NH dissociation with ca. two times larger NH/ND branching ratio, whereas the excitation of the ND stretching mode results in the preferential ND dissociation with ca. 3–4 times larger ND/NH branching ratio than that for the vibrational ground states. The mechanism of the bond-selective enhancement has been discussed in terms of the energetics and dynamics of wave packet.
On the growth and shape of sodium taurodeoxycholate micellar aggregates: A spin-label and quasielastic light scattering investigation
Authors: D’Archivio Angelo Antonio , Galantini Luciano , Panatta Alberto , Tettamanti Enzo
Published: February 2004

Electron spin resonance (ESR) and quasielastic laser scattering (QELS) measurements have been carried out on sodium taurodeoxycholate (NaTDC) micellar aqueous solutions. Computer simulation of the ESR line shape has been used to quantitatively analyze the rotational dynamics of the cholestan-spin label (CSL) dissolved by the NaTDC micellar aggregates as a function of temperature and NaCl concentration. The local reorientation of CSL has been accounted for motionally-averaged g- and A-tensors assuming fast oscillation around the spin-probe long molecular axis. The overall Brownian tumbling of CSL-micelle complexes has been modeled by an axially symmetric rotational tensor. Good agreement with experimental spectra is obtained. Best-fit rotational parameters and QELS data suggest that, in the circumstance of large aggregation, NaTDC micelles have cylindrical shape and micellar growth occurs along the cylinder axis.
Origin of charge trapping in germanium nanocrystal embedded SiO2 system: Role of interfacial traps?
Authors: Kan E. W. H. , Choi W. K. , Chim W. K. , Fitzgerald E. A. , Antoniadis D. A.
Published: February 2004

Wet thermal oxidations of polycrystalline Si0.54Ge0.46 films at 600 °C for 30 and 50 min were carried out. A stable mixed oxide was obtained for films that were oxidized for 50 min. For film oxidized for 30 min, however, a mixed oxide with Ge nanocrystallites embedded in the oxide matrix was obtained. A trilayer gate stack structure that consisted of tunnel oxide/oxidized polycrystalline Si0.54Ge0.46/rf sputtered SiO2 layers was fabricated. We found that with a 30 min oxidized middle layer, annealing the structure in N2 ambient results in the formation of germanium nanocrystals and the annealed structure exhibits memory effect. For a trilayer structure with middle layer oxidized for 50 min, annealing in N2 showed no nanocrystal formation and also no memory effect. Annealing the structures with 30 or 50 min oxidized middle layer in forming gas ambient resulted in nanocrystals embedded in the oxide matrix but no memory effect. This suggests that the charge storage mechanism for the trilayer structure is closely related to the interfacial traps of the nanocrystals.
Optical transitions and upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses
Authors: Yang Jianhu , Zhang Liyan , Wen Lei , Dai Shixun , Hu Lili , Jiang Zhonghong
Published: February 2004

Er 3+ -doped halide modified tellurite glasses were synthesized by conventional melting and quenching method. The Judd–Ofelt analysis was performed on the absorption spectra and the transition probabilities, excited state lifetimes, and the branching ratios were calculated and discussed. The intense infrared and visible fluorescence spectra under 980 nm excitation were obtained. Strong upconversion signal was observed at pumping power as low as 30 mW in the glasses with halide ions. The upconversion mechanisms and power dependent intensities were discussed, which showed two-photon process are involved for the green and red emissions. The decay times of the emitting states and the corresponding quantum efficiency were determined and explained.
Composition and orientation dependence of electrical properties of epitaxial Pb(ZrxTi1−x)O3 thin films grown using metalorganic chemical vapor deposition
Authors: Oikawa Takahiro , Aratani Masanori , Funakubo Hiroshi , Saito Keisuke , Mizuhira Manabu
Published: February 2004

The composition dependence and orientation anisotropy of the dielectric and ferroelectric properties of epitaxial Pb(ZrxTi1−x)O3 (PZT) thin films grown using metalorganic chemical vapor deposition were investigated. {100}-, {110}-, and {111}-oriented PZT films were ascertained to have been grown on (100)c, (110)c, and (111)cSrRuO3//SrTiO3 substrates, respectively. The relative dielectric constant reached a maximum near x=0.5, around the morphotropic phase boundary (MPB) composition, irrespective of film orientation, with the {111}-oriented film showing the largest value. Well-saturated hysteresis loops were observed for all films, and abrupt saturation of the remanent polarization (Pr) and coercive field (Ec) values were observed when the value of x was small, irrespective of film orientation. The Ec value reached a minimum around the composition for {110}- and {111}-oriented films but not for {100}-oriented ones. The saturated polarization (Psat) and Pr values for the {111}-oriented film reached a maximum around the MPB composition, while attaining a minimum for films with other orientations. The ratio of Pr to Psat decreased near the MPB composition regardless of film orientation. These results suggest that the electrical properties of epitaxial PZT thin films strongly depend on both of the composition and orientation of the films.
Oscillator-amplifier free electron laser devices with stable output power
Authors: Dattoli G. , Giannessi L. , Ottaviani P. L.
Published: February 2004

We propose a free electron laser oscillator-amplifier device, in which the modulating section is provided by an optical-klystron oscillator. We show that this configuration ensures a stable output power of the amplifier section.
Optical studies of metallodielectric photonic crystals: Bismuth and gallium infiltrated opals
Authors: Kamaev V. , Kozhevnikov V. , Vardeny Z. V. , Landon P. B. , Zakhidov A. A.
Published: February 2004

We have fabricated three-dimensional metallodielectric photonic crystals that consist of bismuth and gallium metals infiltrated into porous synthetic opals that have 300 nm diam silica balls. The specular reflectivity was measured in a broad spectral range from 0.3 to 25 μm using a variety of light sources, detectors and spectrometers. In addition to broadening of the original Bragg stop bands in the visible spectral range that give rise to iridescence colors, we also found a dramatic decrease of reflectivity in the visible/near-infrared spectral range. For frequencies below a cut-off frequency in the mid-infrared range the reflectivity increases to its normal bulk value in the respective metal, as predicted by theory and fitted by a model calculation.