bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Terrestrial Vegetation on Sediment-Forming Processes in Kettle Lakes of West-Central Minnesota
Authors: Almquist-Jacobson Heather , Almendinger James E. , Hobbie Sarah
Published: July 2006

The composition, magnetic characteristics, and pollen content of sediments from two small kettle lakes near the prairie-forest border in west-central Minnesota were used to infer changes in terrestrial vegetation, shoreline erosion, eolian inputs, carbonate deposition, and aquatic productivity. Several important changes in sediment stratigraphy coincide closely with changes in the terrestrial pollen assemblage. Accumulation rates of organic, inorganic, and carbonate sediment fractions as well as the concentration of magnetic particulates increased abruptly as prairie replaced pine forest, and decreased gradually throughout the subsequent transitions to oak scrub, and later, mixed woodland. Results suggest that by its mediation of wind exposure, local vegetation may affect (1) influx of eolian particulates, (2) erosion of shorelines, (3) water circulation, and (4) carbonate equilibria. In addition, low rates of accumulation of organic matter and increased humidicity during periods of conifer vegetation suggest that humic matter leached from forest soils may influence lake-water chemistry and reduce productivity. Changes in lake level caused by differential rates of evapotranspiration of the various vegetation types (conifer forest, deciduous hardwood forest, brush scrub, and prairie) could not be detected. Sediment-forming processes can therefore be altered by changes in local terrestrial vegetation through several mechanisms that are independent of changes in lake level.
Time Dependence of Magnetic Susceptibility of Soil Chronosequences on the California Coast
Authors: Singer M. J. , Fine P. , Verosub K. L. , Chadwick O. A.
Published: July 2006

As the age of the soils in a chronosequence on the California coast increases, the difference between the magnetic susceptibility of eluvial and illuvial horizons increases, and the residual susceptibility after extraction with citrate-bicarbonate-dithionite (CBD) decreases. Enhanced susceptibility results from the conversion of nonferrimagnetic minerals to secondary ferrimagnetic forms (most likely maghemite) and the preferential accumulation of inherited and pedogenic magnetic minerals. Little enhancement occurs for pedons younger than 40,000 yr. By 124,000 yr, most of the magnetic susceptibility can be attributed to forms soluble in CBD. Magnetic susceptibility appears to vary systematically over time for three chronosequences from areas with mean annual precipitation ranging from 650 to 1500 mm yr−1. Magnetic susceptibility enhancement may be a useful parameter for estimating soil age in certain climates.
Quantification of the Biogenic Silica Dissolution in Southern Ocean Sediments
Authors: Pichon Jean-Jacques , Bareille Gilles , Labracherie Monique , Labeyrie Laurent D. , Baudrimont Annick , Turon Jean-Louis
Published: July 2006

A transfer function has been established to quantify the dissolution of diatom silica in Southern Ocean sediments. The relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box-core tops, each representative of a modern diatom species sediment assemblage. The amount of dissolved silica was measured for each experiment. The resulting data set of species abundances (42 samples containing 32 diatom species and 2 silicoflagellate genera) was added to the modern data base of diatom species distributed over the Southern Ocean (124 core tops). Q-mode factor analysis individualizes four factors explaining 83% of the variance. The first three factors are controlled by surface water properties (mostly temperature). The fourth factor is the only one correlated with loss of silica in the reference samples (R = 0.900). We quantified the dissolution factor using this correlation: superficial sediments of the Southeast Indian Ocean are characterized, from low to high latitudes, by a decrease in silica loss by dissolution (from >50 to 10%) from the Subantarctic Zone (40°S) to around 55°S, followed by an increase of silica loss to values larger than 60% between 63° and 68°S. Application of the dissolution factor in two cores from the Southern Ocean (≈44° and 55°S) shows enhanced opal dissolution during the last glaciation, particularly during Emiliani's stage 3 (from 40,000 to 30,000 yr B.P.).
Childhood sexual abuse and risks for licit and illicit drug-related outcomes: a twin study
Authors: NELSON ELLIOT C. , HEATH ANDREW C. , LYNSKEY MICHAEL T. , BUCHOLZ KATHLEEN K. , MADDEN PAMELA A. F. , STATHAM DIXIE J. , MARTIN NICHOLAS G.
Published: July 2006

Background. This study examined the relationships between self-reported childhood sexual abuse (CSA) and drug-related outcomes in an Australian twin panel.

Method. A semi-structured psychiatric interview was conducted in 1996–2000 by telephone with young adult Australian twins (mean age 29·9 years). Data reported here are from 6050 twins who responded to both CSA and drug-related items.

Results. A history of CSA was associated with significant risk for subsequently occurring regular smoking and use of each illicit drug class. Further CSA-associated risk was found among regular users, for nicotine and alcohol dependence, and among illicit drug users, for abuse/dependence of most drug classes. In same-sex discordant pairs, significant risk for regular smoking and illicit drug use was found in twins with a history of CSA compared to their non-abused co-twins. Similar analyses for abuse/dependence found significant risk for opioids, any illicit drug, and any non-cannabis illicit drug. CSA was associated with significantly earlier drug use. Despite the association of CSA with risk for early-onset cannabis use and regular smoking, risks for illicit drug outcomes associated with CSA and with either form of early-onset use combine in near-additive fashion.

Conclusions. CSA is associated with risk for subsequently occurring regular smoking and illicit drug use and abuse/dependence. Risks for drug use are mildly attenuated with control for familial contributions; similar risks for abuse/dependence remain significant for opioids and for illicit drugs combined across classes. Although we found evidence of earlier onset drug use with CSA, risks associated with CSA and with early-onset use combine in a largely additive manner.
Unravelling Carbon Metabolism in Anaerobic Cellulolytic Bacteria
Authors: Desvaux Mickaël
Published: July 2006

Carbon metabolism in anaerobic cellulolytic bacteria has been investigated essentially in Clostridium thermocellum, Clostridium cellulolyticum, Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus. While cellulose depolymerization into soluble sugars by various cellulases is undoubtedly the first step in bacterial metabolisation of cellulose, it is not the only one to consider. Among anaerobic cellulolytic bacteria, C. cellulolyticum has been investigated metabolically the most in the past few years. Summarizing metabolic flux analyses in continuous culture using either cellobiose (a soluble cellodextrin resulting from cellulose hydrolysis) or cellulose (an insoluble biopolymer), this review aims to stress the importance of the insoluble nature of a carbon source on bacterial metabolism. Furthermore, some general and specific traits of anaerobic cellulolytic bacteria trends, namely, the importance and benefits of (i) cellodextrins with degree of polymerization higher than 2, (ii) intracellular phosphorolytic cleavage, (iii) glycogen cycling on cell bioenergetics, and (iv) carbon overflows in regulation of carbon metabolism, as well as detrimental effects of (i) soluble sugars and (ii) acidic environment on bacterial growth. Future directions for improving bacterial cellulose degradation are discussed.
On‐Line Measurement of Gas Production Rates
Authors: Cooney Michael , Maynard Nathan , Cannizzaro Christopher , Harris David
Published: July 2006

Gas evolution rates represent an important variable to track in biological and certain electrochemical processes. Accurate gas flow rate sensors exist for gas streams possessing a pressure head, such as when pressurized air or oxygen is delivered to a fermentation process. However, these devices impose pressure heads that can inhibit gas production and, therefore, yield false measurements. Examples of effected processes would include electrochemical production of a gas at the electrode (e.g., electrolysis) or anaerobic fermentation (e.g., anaerobic production of methane). In this work, we present an on‐line gas measurement technique that measures on‐line gas production from an anaerobic microbial process that is continuously fed simulated food waste over a 6‐month period. Commentary is given on the sensorapos;s accuracy and ease of use within the context of long‐term operation, ability to measure both low and high gas production rates, as well as its potential for process control and system‐health monitoring.
Kombinationsbehandlung von Psychotherapie und Pharmakotherapie
Authors: Klein Jan Philipp , Schweiger Ulrich , Hohagen Fritz
Published: July 2006

Zusammenfassung: Bei der Kombination von Psychotherapie und Pharmakotherapie sind Wechselwirkungen zu beachten. Psychopharmaka können den Verlauf der Psychotherapie begünstigen oder behindern. Benzodiazepine beispielsweise beeinträchtigen in Tierexperimenten und klinischen Studien den Lernerfolg. Bei einigen Störungen ist eine Pharmakotherapie in der Regel unerlässlich (Depression, Manie, Schizophrenie). Durch eine Kombination von Pharmakotherapie mit Psychotherapie kann die Rückfallrate gesenkt und die Remissionsrate erhöht werden. Bei anderen Störungen ist die Psychotherapie das Mittel der Wahl (Angst- und Zwangsstörungen). Eine Kombination mit Psychopharmaka kann den Therapieerfolg beschleunigen, besonders bei therapierefraktären Patienten oder sekundären Depressionen.
Mittelmeerfieber in Bayern
Authors: Wachsmuth Astrid C. , Vukovich Ruth. C. , Bäuml Josef , Zilker Thomas
Published: July 2006

Zusammenfassung: Die genetische Disposition für das Familiäre-Mittelmeer-Fieber (FMF) ist in mediterranen Gegenden weit verbreitet. Durch Migration wird die Erkrankung bei uns immer häufiger beobachtet. Das FMF manifestiert sich durch Fieber und Polyserositiden, sehr selten treten psychische Symptome auf. Wir berichten über Zwillingsschwestern tunesischer Abstammung, die während eines Urlaubs in Tunesien hohes Fieber, Schmerzen sowie ein stuporöses Bild mit Desorientiertheit und Wahn entwickelten. Unter medikamentöser Behandlung mit Colchizin remittierte die Erkrankung rasch. Die initial aufgrund des klinischen Bildes gestellte Verdachtsdiagnose eines FMF bestätigte sich durch Genotypisierung.
Die deutsche Version des NCCN Distress-Thermometers
Authors: Mehnert Anja , Müller Diana , Lehmann Claudia , Koch Uwe
Published: July 2006

Zusammenfassung: Das NCCN Distress-Thermometer ist ein vom National Comprehensive Cancer Network (NCCN) entwickeltes Screeninginstrument zur Erfassung psychosozialer Belastungen bei onkologischen Patienten. Es besteht aus einer Skala von 0 bis 10 und einer Problemliste als Überweisungsschema zu entsprechenden professionellen Diensten. International wird ein Cut-off-Wert von 5 als Signal empfohlen, dass ein Patient auffällig belastet ist und Unterstützung benötigt. Die deutsche Adaptation erfolgte an einer Stichprobe von n = 475 Krebspatienten in der onkologischen Rehabilitation. Zur Validierung wurde die Hospital Anxiety and Depression Scale (HADS-D) und die Kurzform des Fragebogens zur Progredienzangst (PA-F 12) eingesetzt. Die Diskriminationsfähigkeit des Distress-Thermometers ist besonders zur Identifikation einer hohen Belastung (HADS Cut-off > 11) mit AUC-Werten von 0.71 bis 0.76 gut. Bei einem Cut-off-Wert von 5 im Distress-Thermometer zeigen sich bei moderater Belastung in den Merkmalen Angst und/oder Depressivität (HADS Cut-off > 8) eine Sensitivität bis 84 % und eine deutlich niedrigere Spezifität von bis zu 47 %. Bei einem HADS Cut-off > 11 und einem Cut-off-Wert von 5 im Distress-Thermometer liegen die Sensitivitätswerte bei bis zu 97 % und die Spezifitätswerte bei 41 %. Die Spezifität des Instruments ist in der deutschen Stichprobe niedriger als die in internationalen Studien gefundenen Werte, die Sensitivität ist entsprechend höher. Das NCCN Distress-Thermometer stellt aufgrund seiner hohen Akzeptanz, seiner Kürze und guten Praktikabilität im klinischen Alltag ein Screeninginstrument dar, das für den weiteren Einsatz in der onkologischen Versorgung empfohlen werden kann.
Relation between stress heterogeneity and aftershock rate in the rate‐and‐state model
Authors: Helmstetter Agnès , Shaw Bruce E.
Published: July 2006

We estimate the rate of aftershocks triggered by a heterogeneous stress change, using the rate‐and‐state model of Dieterich. We show that an exponential stress distribution Pτ(τ) ∼ exp(−τ/τ0) gives an Omori law decay of aftershocks with time ∼1/tp, with an exponent p = 1 − Aσn/τ0, where A is a parameter of the rate‐and‐state friction law and σn is the normal stress. Omori exponent p thus decreases if the stress “heterogeneity” τ0 decreases. We also invert the stress distribution Pτ(τ) from the seismicity rate R(t), assuming that the stress does not change with time. We apply this method to a synthetic stress map, using the (modified) scale invariant “k2” slip model (Herrero and Bernard). We generate synthetic aftershock catalogs from this stress change. The seismicity rate on the rupture area shows a huge increase at short times, even if the stress decreases on average. Aftershocks are clustered in the regions of low slip, but the spatial distribution is more diffuse than for a simple slip dislocation. Because the stress field is very heterogeneous, there are many patches of positive stress changes everywhere on the fault. This stochastic slip model gives a Gaussian stress distribution but nevertheless produces an aftershock rate which is very close to Omori's law, with an effective p ≤ 1, which increases slowly with time. We obtain a good estimation of the stress distribution for realistic catalogs when we constrain the shape of the distribution. However, there are probably other factors which also affect the temporal decay of aftershocks with time. In particular, heterogeneity of Aσn can also modify the parameters p and c of Omori's law. Finally, we show that stress shadows are very difficult to observe in a heterogeneous stress context.
Influence of flaws on joint spacing and saturation: Results of one‐dimensional mechanical modeling
Authors: Fischer Mark P. , Polansky Alan
Published: July 2006

In bedded sedimentary or mechanically anisotropic rocks, joints often occur in laterally persistent, parallel sets with distinctive spacing attributes. Three of those attributes include a positively skewed distribution of joint spacings, a positive correlation between median spacing and mechanical layer thickness, and the tendency for rocks to appear saturated with joints and to show a ratio of layer thickness to median joint spacing near one. We identify total applied strain, mechanical interaction, joint propagation velocity, and flaws as key variables in the progressive jointing process, and we use a one‐dimensional model of mechanically interacting joints to characterize the specific influence on joint spacing, of the number, sizes, and size distributions of flaws in rock. For a given flaw size distribution, the mode flaw size has no effect on spacing distribution shape, median spacing, or saturation. Layers with fewer flaws approach saturation more slowly and reach it with fewer joints and larger median joint spacing. The joint spacing distributions in these layers have variance and skewness that may be 1–3 orders of magnitude larger than in layers with greater numbers of flaws. Flaw size range affects the rate at which a jointing layer approaches saturation but not the number of joints at saturation. Resulting spacing distributions are similar, although narrow flaw size ranges tend to promote greater numbers of closely spaced joints. The skewness of a flaw size distribution affects the rate at which layers approach saturation, as well as the shape of the resulting joint spacing distribution at saturation. Negatively skewed flaw size distributions promote close joint spacing and create spacing distributions with greater variance and skewness.
Sensitivity analysis for mercury over Europe
Authors: Roustan Yelva , Bocquet Marc
Published: July 2006

Adjoint techniques are introduced to perform a sensitivity analysis for mercury over Europe, using a regional model. This approach differs from other techniques such as the direct and indirect approaches developed to compute sensitivities for air quality modeling. With gaseous elemental mercury lifetime being of order one year, global or hemispherical models are usually preferred to analyze its fate and transport. In an area‐limited domain, respective influences of incoming mercury and inner emissions fluxes have to be weighted. A local measurement depends on the potential ground emissions, the potential incoming mass from domain borders, and the potential initial content in mercury of the atmosphere. The sensitivities of the measurement to entire maps of emissions, boundary conditions, etc., are computed thanks to the adjoint method since other techniques do not allow to perform these computations directly. As an application to these methodological developments, we use the numerical transport model Polair3D. Quantitative sensitivity maps are provided for European Monitoring and Evaluation Program (EMEP) mercury monitoring stations. With the adjoint approach, sensitivities of a given country to other countries emissions are computed in a straightforward manner. The yearly average sensitivity of a measurement of gaseous elemental mercury to distant sources is shown to decrease like a power law r−2.4, where r is the distance to a source. It is eventually explained how the method developed here can be generalized to account for a more complex mercury chemistry and the modeling of oxidized species. In particular, sensitivities of dry and wet deposition fluxes of oxidized species are computed for one EMEP station.
Size of Rabbits consumed by Black Kites increased after a Rabbit epizootic
Authors: VILLAFUERTE R. , VIÑUELA J.
Published: July 2006

Rabbits are the staple prey for Black Kites in Matasgordas, south‐western Spain. Because of their poor predatory skills, it has been considered that most of the Rabbits consumed by Kites were young and affected by myxomatosis. After rabbit haemorrhagic disease (RHD) arrived in Spain, and since most of the Rabbits affected were adults, it was expected that the raptor would benefit with the incorporation of larger Rabbits in its diet. In concordance with that prediction, during the immediate three years before the arrival of RHD (1987–89), average size of Rabbits consumed by nestling Black Kites were similar and corresponded to the size of those Rabbits affected by myxomatosis. However, after RHD arrival in 1990, sizes of Rabbits consumed by Kites increased, corresponding to the age more frequently affected by RHD.
Vibrational energy relaxation of a diatomic molecule in a room-temperature ionic liquid
Authors: Shim Youngseon , Kim Hyung J.
Published: July 2006

Vibrational energy relaxation (VER) dynamics of a diatomic solute in ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI+PF6−) are studied via equilibrium and nonequilibrium molecular dynamics simulations. The time scale for VER is found to decrease markedly with the increasing solute dipole moment, consonant with many previous studies in polar solvents. A detailed analysis of nonequilibrium results shows that for a dipolar solute, dissipation of an excess solute vibrational energy occurs almost exclusively via the Lennard-Jones interactions between the solute and solvent, while an oscillatory energy exchange between the two is mainly controlled by their electrostatic interactions. Regardless of the anharmonicity of the solute vibrational potential, VER becomes accelerated as the initial vibrational energy increases. This is attributed primarily to the enhancement in variations of the solvent force on the solute bond, induced by large-amplitude solute vibrations. One interesting finding is that if a time variable scaled with the initial excitation energy is employed, dissipation dynamics of the excess vibrational energy of the dipolar solute tend to show a universal behavior irrespective of its initial vibrational state. Comparison with water and acetonitrile shows that overall characteristics of VER in EMI+PF6− are similar to those in acetonitrile, while relaxation in water is much faster than the two. It is also found that the Landau-Teller theory predictions for VER time scale obtained via equilibrium simulations of the solvent force autocorrelation function are in reasonable agreement with the nonequilibrium results.
Crystal nucleation in binary hard sphere mixtures: A Monte Carlo simulation study
Authors: Punnathanam S. , Monson P. A.
Published: July 2006

We present calculations of the nucleation barrier during crystallization in binary hard sphere mixtures under moderate degrees of supercooling using Monte Carlo simulations in the isothermal-isobaric semigrand ensemble in conjunction with an umbrella sampling technique. We study both additive and negatively nonadditive binary hard sphere systems. The solid-fluid phase diagrams of such systems show a rich variety of behavior, ranging from simple spindle shapes to the appearance of azeotropes and eutectics to the appearance of substitutionally ordered solid phase compounds. We investigate the effect of these types of phase behavior upon the nucleation barrier and the structure of the critical nucleus. We find that the underlying phase diagram has a significant effect on the mechanism of crystal nucleation. Our calculations indicate that fractionation of the species upon crystallization increases the difficulty of crystallization of fluid mixtures and in the absence of fractionation (azeotropic conditions) the nucleation barrier is comparable to pure fluids. We also calculate the barrier to nucleation of a substitutionally ordered compound solid. In such systems, which also show solid-solid phase separation, we find that the phase that nucleates is the one whose equilibrium composition is closer to the composition of the fluid phase.
Electronic, linear, and nonlinear optical properties of III-V indium compound semiconductors
Authors: Reshak Ali Hussain
Published: July 2006

We have made an extensive theoretical study of the electronic, linear, and nonlinear optical properties of the III-V indium compound semiconductors InX (X=P, As, and Sb) with the use of full potential linear augmented plane wave method. The results for the band structure, density of states, and the frequency-dependent linear and nonlinear optical responses are presented here and compared with available experimental data. Good agreement is found. Our calculations show that these compounds have similar electronic structures. The valence band maximum and the conduction band minimum are located at Γ resulting in a direct energy gap. The energy band gap of these compounds decreases when P is replaced by As and As by Sb. This can be attributed to the increase in bandwidth of the conduction bands. The linear and nonlinear optical spectra are analyzed and the origin of some of the peaks in the spectra is discussed in terms of the calculated electronic structure. The calculated linear optical properties show very good agreement with the available experimental data. We find that the intra-and interband contributions of the second-harmonic generation increase when moving from P to As to Sb. The smaller energy band gap compounds have larger values of χ123(2)(0) in agreement with the experimental measurements and other theoretical calculations.
String method in collective variables: Minimum free energy paths and isocommittor surfaces
Authors: Maragliano Luca , Fischer Alexander , Vanden-Eijnden Eric , Ciccotti Giovanni
Published: July 2006

A computational technique is proposed which combines the string method with a sampling technique to determine minimum free energy paths. The technique only requires to compute the mean force and another conditional expectation locally along the string, and therefore can be applied even if the number of collective variables kept in the free energy calculation is large. This is in contrast with other free energy sampling techniques which aim at mapping the full free energy landscape and whose cost increases exponentially with the number of collective variables kept in the free energy. Provided that the number of collective variables is large enough, the new technique captures the mechanism of transition in that it allows to determine the committor function for the reaction and, in particular, the transition state region. The new technique is illustrated on the example of alanine dipeptide, in which we compute the minimum free energy path for the isomerization transition using either two or four dihedral angles as collective variables. It is shown that the mechanism of transition can be captured using the four dihedral angles, but it cannot be captured using only two of them.
Liquid-vapor isotopic fractionation factors of diatomic fluids: A direct comparison between molecular simulation and experiment
Authors: Chialvo Ariel A. , Horita Juske
Published: July 2006

Liquid-vapor fractionation factors of molecular fluids are studied by molecular-based simulation, Gibbs ensemble Monte Carlo, and isothermal-isochoric molecular dynamics of realistic models for N2, O2, and CO. The temperature dependence of the fractionation factors for N15N14∕N214, N215∕N214, O18O16∕O216, O218∕O216, C13O16∕C12O16, and C12O18∕C12O16 along the vapor-liquid coexistence curves as predicted by simulation is compared with the existing experimental data to assess the accuracy of ℏ2-order Kirkwood-Wigner free energy expansion for specific model parametrizations. Predictions of the fractionation factors for other isotopologue pairs, including O18O17∕O216, O16O17∕O216, and O217∕O216, as well as tests of some approximations behind the microscopic interpretation of the fractionation factors are also given.
Static and dynamic critical behavior of a symmetrical binary fluid: A computer simulation
Authors: Das Subir K. , Horbach Jürgen , Binder Kurt , Fisher Michael E. , Sengers Jan V.
Published: July 2006

A symmetrical binary, A+B Lennard-Jones mixture is studied by a combination of semi-grand-canonical Monte Carlo (SGMC) and molecular dynamics (MD) methods near a liquid-liquid critical temperature Tc. Choosing equal chemical potentials for the two species, the SGMC switches identities (A→B→A) to generate well-equilibrated configurations of the system on the coexistence curve for TTc. A finite-size scaling analysis of the concentration susceptibility above Tc and of the order parameter below Tc is performed, varying the number of particles from N=400 to 12 800. The data are fully compatible with the expected critical exponents of the three-dimensional Ising universality class. The equilibrium configurations from the SGMC runs are used as initial states for microcanonical MD runs, from which transport coefficients are extracted. Self-diffusion coefficients are obtained from the Einstein relation, while the interdiffusion coefficient and the shear viscosity are estimated from Green-Kubo expressions. As expected, the self-diffusion constant does not display a detectable critical anomaly. With appropriate finite-size scaling analysis, we show that the simulation data for the shear viscosity and the mutual diffusion constant are quite consistent both with the theoretically predicted behavior, including the critical exponents and amplitudes, and with the most accurate experimental evidence.
Ab initio studies on (H2O)14− clusters: Existence of surface and interior-bound extra electrons
Authors: Khan Arshad
Published: July 2006

A recent paper by Turi et al. [Science 309, 914 (2005)] suggests that the anionic water clusters smaller than (H2O)45− (at a low temperature) will only have surface-bound extra electrons and no internally bound electrons. Accordingly, (H2O)14− cluster isomers should only have surface-bound extra electrons. The ab initio results presented here, however, suggest that the (H2O)14− cluster isomers can have two distinct types of isomers with almost the same energy. The one type of isomer (type 1) has all the non-H-bonding H atoms (NHB H) directed outward and surface-bound extra electron while the other type (type 2) has a number of NHB H atoms directed toward cavity and has an interior-bound electron, and thus, contradicts the earlier quantum simulation results of Turi et al.
Simulated surface potentials at the vapor-water interface for the KCl aqueous electrolyte solution
Authors: Wick Collin D. , Dang Liem X. , Jungwirth Pavel
Published: July 2006

Classical molecular dynamics simulations with polarizable potential models were carried out to quantitatively determine the effects of KCl salt concentrations on the electrostatic surface potentials of the vapor-liquid interface of water. To the best of our knowledge, the present work is the first calculation of the aqueous electrolyte surface potentials. Results showed that increased salt concentration enhanced the electrostatic surface potentials, in agreement with the corresponding experimental measurements. Furthermore, the decomposition of the potential drop into contributions due to static charges and induced dipoles showed a very strong effect (an increase of ∼1V per 1M) due to the double layers formed by KCl. However, this was mostly negated by the negative contribution from induced dipoles, resulting in a relatively small overall increase (∼0.05V per 1M) with increased salt concentration.
Matrix effects on the optical response of silver nanoclusters
Authors: Conus F. , Rodrigues V. , Lecoultre S. , Rydlo A. , Félix C.
Published: July 2006

We report absorption spectra for Ag7, Ag9, and Ag11 in an argon matrix grown at a temperature of 28K and compare them with previous spectra of the same species measured in matrices of argon grown at lower temperatures as well as in neon matrices. We discuss the discrepancies in the light of the matrix crystallinity and show that this leads to an understanding of the influence of the matrix on the optical response of small clusters.
Real space Hartree-Fock configuration interaction method for complex lateral quantum dot molecules
Authors: Abolfath Ramin M. , Hawrylak Pawel
Published: July 2006

We present unrestricted Hartree-Fock method coupled with configuration interaction (CI) method (URHF-CI) suitable for the calculation of ground and excited states of large number of electrons localized by complex gate potentials in quasi-two-dimensional quantum dot molecules. The method employs real space finite difference method, incorporating strong magnetic field, for calculating single particle states. The Hartree-Fock method is employed for the calculation of direct and exchange interaction contributions to the ground state energy. The effects of correlations are included in energies and directly in the many-particle wave functions via CI method using a limited set of excitations above the Fermi level. The URHF-CI method and its performance are illustrated on the example of ten electrons confined in a two-dimensional quantum dot molecule.
Spin-polarized transport in magnetically assembled carbon nanotube spin valves
Authors: Thamankar R. , Niyogi S. , Yoo B. Y. , Rheem Y. W. , Myung N. V. , Haddon R. C. , Kawakami R. K.
Published: July 2006

Spin polarized transport over 5μm long carbon nanotubes (CNTs) is observed in magnetically assembled spin valves with electrochemically deposited ferromagnetic (FM) electrodes. An annealing procedure is developed to produce stable devices with highly transmissive FM/CNT contacts. The devices exhibit magnetoresistance (MR) with magnitudes up to 4%, and the sign of MR is consistently negative. The temperature dependence is investigated and MR is observed up to 14K. Bias dependence is also investigated, with MR persisting up to ∼300mV.
Vertical GaP nanowires arranged at atomic steps on Si(111) substrates
Authors: Tateno K. , Hibino H. , Gotoh H. , Nakano H.
Published: July 2006

We report vertical GaP nanowires self-arranged in lines formed from Au islands that were initially arranged at single-layer steps on Si(111) substrates. These Au islands are spontaneously arranged by controlling the deposition. There are three aspects to the growth of vertical GaP wires: the cosupply of TMGa and PH3, two growths at different temperatures, and a low PH3 flow rate. The grown wires are quite ordered in lines of several micrometers. Electrical measurement confirmed selective current flow at the wires and we confirmed photoluminescence from the wires. This bottom-up technique is promising for nano-hetero-device integration on Si circuits.
One-step synthesis and enhanced blue emission of carbon-encapsulated single-crystalline ZnSe nanoparticles
Authors: Geng B. Y. , Du Q. B. , Liu X. W. , Ma J. Z. , Wei X. W. , Zhang L. D.
Published: July 2006

Carbon-encapsulated ZnSe nanoparticles with diameters about 50nm were synthesized by noncatalytic one-step thermal evaporation method. The ZnSe cores have a wurtzite crystal structure. The as-synthesized products are uniform and composed of single-crystalline ZnSe nanoparticles enwrapped with polycrystalline graphite layers. The photoluminescence measurement of the carbon-encapsulated nanoparticles shows that the blue emission enhances dramatically compared with the naked ZnSe nanoparticles. This synthetic strategy might exploit a favorable route to synthesize carbon-encapsulated semiconductor nanostructures, which are potentially important for optoelectronic nanodevices.
Effect of two-step growth on the heteroepitaxial growth of InSb thin film on Si (001) substrate: A transmission electron microscopy study
Authors: Kim Y. H. , Lee J. Y. , Noh Y. G. , Kim M. D. , Kwon Y. J. , Oh J. E. , Gronsky R.
Published: July 2006

InSb thin films were grown on Si (001) substrate via both conventional one-step growth and two-step growth methods by molecular beam epitaxy. The effect of two-step growth was investigated by transmission electron microscopy. A lot of planar defects and surface steps were observed in the InSb thin film directly grown on buffer layer. The crystalline quality of the InSb thin film was improved when it was grown via two-step growth. The low-temperature InSb initiation layer of two-step growth relieved a misfit strain by generating 90° misfit dislocations and obstructed the propagation of defects by trapping at the interface.
Characterization and photoluminescence properties of aluminum borate nanorods doped with Eu
Authors: Lin J. , Huang Y. , Zhang J. , Song H. S. , Elssfah E. M. , Liu S. J. , Luo J. J. , Ding X. X. , Qi S. R. , Tang C. C.
Published: July 2006

Aluminum borate (Al18B4O33) nanorods doped with Eu3+ and Eu2+ were synthesized via a simple calcination method. Both nanorods are of straight morphology and smooth surface, with the average diameter of ∼80nm. The structural and compositional characteristics have been investigated by x-ray diffraction, infrared spectra, and various microscopy techniques. A possible growth mechanism was proposed for the synthesis of the doped Al18B4O33 nanorods. Photoluminescence measurements indicate that Al18B4O33:Eu3+ nanorods exhibit emission peaks at 590, 595, 612, and 617nm, and Al18B4O33:Eu2+ nanorods display a broad green emission band centered at ∼540nm.
Organization of the Integrin LFA-1 in Nanoclusters Regulates Its Activity
Authors: Cambi Alessandra , Joosten Ben , Koopman Marjolein , de Lange Frank , Beeren Inge , Torensma Ruurd , Fransen Jack A. , Garcia-Parajó Maria , van Leeuwen Frank N. , Figdor Carl G.
Published: July 2006

The β2-integrin LFA-1 facilitates extravasation of monocytes (MOs) into the underlying tissues, where MOs can differentiate into dendritic cells (DCs). Although DCs express LFA-1, unlike MOs, they cannot bind to ICAM-1. We hypothesized that an altered integrin organization on the DC plasma membrane might cause this effect and investigated the relationship between membrane organization and function of LFA-1 on MOs and DCs. High-resolution mapping of LFA-1 surface distribution revealed that on MOs LFA-1 function is associated with a distribution in well-defined nanoclusters (100–150-nm diameter). Interestingly, a fraction of these nanoclusters contains primed LFA-1 molecules expressing the specific activation-dependent L16-epitope. Live imaging of MO–T-cell conjugates showed that only these primed nanoclusters are dynamically recruited to the cellular interface forming micrometer-sized assemblies engaged in ligand binding and linked to talin. We conclude that besides affinity regulation, LFA-1 function is controlled by at least three different avidity patterns: random distributed inactive molecules, well-defined ligand-independent proactive nanoclusters, and ligand-triggered micrometer-sized macroclusters.
Yeast-to-Hyphal Transition Triggers Formin-dependent Golgi Localization to the Growing Tip inCandida albicans
Authors: Rida Padmashree C.G. , Nishikawa Akiko , Won Gena Y. , Dean Neta
Published: July 2006

Rapid and long-distance secretion of membrane components is critical for hyphal formation in filamentous fungi, but the mechanisms responsible for polarized trafficking are not well understood. Here, we demonstrate that in Candida albicans, the majority of the Golgi complex is redistributed to the distal region during hyphal formation. Randomly distributed Golgi puncta in yeast cells cluster toward the growing tip during hyphal formation, remain associated with the distal portion of the filament during its extension, and are almost absent from the cell body. This restricted Golgi localization pattern is distinct from other organelles, including the endoplasmic reticulum, vacuole and mitochondria, which remain distributed throughout the cell body and hypha. Hyphal-induced positioning of the Golgi and the maintenance of its structural integrity requires actin cytoskeleton, but not microtubules. Absence of the formin Bni1 causes a hyphal-specific dispersal of the Golgi into a haze of finely dispersed vesicles with a sedimentation density no different from that of normal Golgi. These results demonstrate the existence of a hyphal-specific, Bni1-dependent cue for Golgi integrity and positioning at the distal portion of the hyphal tip, and suggest that filamentous fungi have evolved a novel strategy for polarized secretion, involving a redistribution of the Golgi to the growing tip.
Fta2, an Essential Fission Yeast Kinetochore Component, Interacts Closely with the Conserved Mal2 Protein
Authors: Kerres Anne , Jakopec Visnja , Beuter Christoph , Karig Inga , Pöhlmann Jennifer , Pidoux Alison , Allshire Robin , Fleig Ursula
Published: July 2006

The fission yeast multiprotein-component Sim4 complex plays a fundamental role in the assembly of a functional kinetochore. It affects centromere association of the histone H3 variant CENP-A as well as kinetochore association of the DASH complex. Here, multicopy suppressor analysis of a mutant version of the Sim4 complex component Mal2 identified the essential Fta2 kinetochore protein, which is required for bipolar chromosome attachment. Kinetochore localization of Mal2 and Fta2 depends on each other, and overexpression of one protein can rescue the phenotype of the mutant version of the other protein. fta2 mal2 double mutants were inviable, implying that the two proteins have an overlapping function. This close interaction with Fta2 is not shared by other Sim4 complex components, indicating the existence of functional subgroups within this complex. The Sim4 complex seems to be assembled in a hierarchical way, because Fta2 is localized correctly in a sim4 mutant. However, Fta2 kinetochore localization is reduced in a spc7 mutant. Spc7, a suppressor of the EB1 family member Mal3, is part of the conserved Ndc80–MIND–Spc7 kinetochore complex.
Rapid adaptive divergence of life-history traits in response to abiotic stress within a natural population of a parthenogenetic nematode
Authors: Doroszuk Agnieszka , Wojewodzic Marcin W , Kammenga Jan E
Published: July 2006

Sexual reproduction is acknowledged to facilitate adaptation to novel environments while asexual eukaryotes are often regarded as having low adaptive potential. This view has been challenged in a number of studies, but the adaptive potential of asexual populations in the field is poorly documented. We investigated the response of natural populations of the parthenogenetic nematodeAcrobeloides nanusto imposed divergent selective pressures. For this purpose, we employed a replicated evolution experiment in the field. After 20 years of evolution under abiotic stress and control conditions, life-history traits were assessed in reaction norm- and reciprocal transplant experiments. Both these experiments indicated adaptive divergence within the population ofA. nanus. Namely, the transplant experiment demonstrated that in the stressed soil environment, body growth rate was more reduced in the nematodes originating from the control treatment. In the reaction norm experiment, survival and reproduction were higher under test conditions corresponding to the native environment of the nematodes. The differences in the analysed traits are discussed in the context of life-history theory. Overall, our results strongly support high adaptive potential ofA. nanusand suggest that population structure and distribution of asexual species is shaped by local adaptation events.
Acetylcholinesterase genes within the Diptera: takeover and loss in true flies
Authors: Huchard Elise , Martinez Michel , Alout Haoues , Douzery Emmanuel J.P , Lutfalla Georges , Berthomieu Arnaud , Berticat Claire , Raymond Michel , Weill Mylène
Published: July 2006

It has recently been reported that the synaptic acetylcholinesterase (AChE) in mosquitoes is encoded by theace-1gene, distinct and divergent from theace-2gene, which performs this function inDrosophila. This is an unprecedented situation within the Diptera order because bothacegenes derive from an old duplication and are present in most insects and arthropods. Nevertheless,Drosophilapossesses only theace-2gene. Thus, a secondary loss occurred during the evolution of Diptera, implying a vital function switch from one gene (ace-1) to the other (ace-2). We sampled 78 species, representing 50 families (27% of the Dipteran families) spread over all major subdivisions of the Diptera, and looked forace-1andace-2by systematic PCR screening to determine which taxonomic groups within the Diptera have this gene change. We show that this loss probably extends to all true flies (or Cyclorrhapha), a large monophyletic group of the Diptera. We also show thatace-2plays a non-detectable role in the synaptic AChE in a lower Diptera species, suggesting that it has non-synaptic functions. A relative molecular evolution rate test showed that the intensity of purifying selection onace-2sequences is constant across the Diptera, irrespective of the presence or absence oface-1, confirming the evolutionary importance of non-synaptic functions for this gene. We discuss the evolutionary scenarios for the takeover oface-2and the loss oface-1, taking into account our limited knowledge of non-synaptic functions ofacegenes and some specific adaptations of true flies.
Developmental response to cold stress in cranial morphology of
Rattus
: implications for the interpretation of climatic adaptation in fossil hominins
Authors: Rae Todd C , Viðarsdóttir Una Strand , Jeffery Nathan , Steegmann A. Theodore
Published: July 2006

Adaptation to climate occupies a central position in biological anthropology. The demonstrable relationship between temperature and morphology in extant primates (including humans) forms the basis of the interpretation of the Pleistocene hominin
Homo neanderthalensis
as a cold-adapted species. There are contradictory signals, however, in the pattern of primate craniofacial changes associated with climatic conditions.

To determine the direction and extent of craniofacial change associated with temperature, and to understand the proximate mechanisms underlying cold adaptations in vertebrates in general, dry crania from previous experiments on cold- and warm-reared rats were investigated using computed tomography scanning and three-dimensional digitization of cranial landmarks. Aspects of internal and external cranial morphology were compared using standard statistical and geometric morphometric techniques.

The results suggest that the developmental response to cold stress produces subtle but significant changes in facial shape, and a relative decrease in the volume of the maxillary sinuses (and nasal cavity), both of which are independent of the size of the skull or postcranium. These changes are consistent with comparative studies of temperate climate primates, but contradict previous interpretations of cranial morphology of Pleistocene Hominini.
A small-angle neutron scattering study of fine-scale NbC precipitation kinetics in the α-Fe–Nb–C system
Authors: Perrard F. , Deschamps A. , Bley F. , Donnadieu P. , Maugis P.
Published: July 2006

The fine-scale precipitation of NbC in ferrite has been quantitatively characterized in the temperature range 873–1073 K for two alloy compositions, containing respectively 800 p.p.m. Nb and 400 p.p.m. Nb (by weight). Transmission electron microscopy (TEM) has revealed that the precipitates are located on dislocations, and have a plate-like morphology with an average aspect ratio between 2 and 3. Small-angle neutron scattering (SANS) has been systematically used to determine the precipitation kinetics. The validity of the quantitative SANS measurements of size and volume fraction has been assessed by TEM image analysis and chemical dissolution experiments. The precipitation kinetics is observed to depend strongly on temperature but to be similar for the two alloy compositions. From the measurements, it is inferred that precipitate nucleation is extremely rapid, in relation to the nature of the nucleation sites. A time–temperature transformation diagram is built from the kinetic data, showing a maximum reaction rate between 973 and 1073 K.
GENEFP: a full-profile fitting program for X-ray powder patterns using the genetic algorithm
Authors: Feng Zhen Jie , Dong Cheng
Published: July 2006

GENEFPis a full-profile fitting program, employing a fundamental-parameters method, for Cu-target X-ray powder patterns. In this program, the Le Bail method is used to determine integrated intensities and the genetic algorithm is used to search for the proper fundamental parameters. When some parameters, such as the grain size, have large uncertainties, the genetic algorithm has an advantage over conventional least-squares methods in finding the global extremum.
Reciprocal-space mapping for simultaneous determination of texture and stress in thin films
Authors: Šimek Daniel , Kužel Radomír , Rafaja David
Published: July 2006

A method of reciprocal-space mapping followed by Rietveld-type refinement of the maps has been developed and tested for strongly textured thin films with fibre texture. The method is particularly useful for simultaneous analysis of stress and texture, especially in non-cubic materials. It could also be used for the analysis of other parameters, like film thickness, microstrain and domain size. Both of the extreme elastic models (Voigt/Reuss) have been adopted for the case of the fibre texture often present in thin films. The method allows estimation of residual stresses even for very strong [001] texture in hexagonal materials with angular half-widths of a few degrees. The procedure of two-dimensional reciprocal-space map fitting is described in detail; simulations are presented and discussed. The method can be applied to multiphase materials, as long as the assumptions of the elastic models (Voigt/Reuss) are valid in the multiphase film.