bluuebunny/crossref_metadata_2025 huggingface dataset:
Miscibility and rheological properties of poly(vinyl chloride)/styrene–acrylonitrile blends prepared by melt extrusion
Authors: Moon Hyun Sik , Choi Won Mook , Kim Mun Ho , Park O‐Ok
Published: January 2007

Styrene–acrylonitrile (SAN) with acrylonitrile (AN) concentrations of 11.6–26 wt % and α‐methylstyrene acrylonitrile (αMSAN) with a wide range of AN concentrations are miscible with poly(vinyl chloride) (PVC) through solution blending. Here we examine the rheological properties and miscibility of PVC/SAN and PVC/αMSAN blends prepared by melt extrusion for commercial applications. We have investigated the rheological properties of the blends with a rheometer and a melt indexer. The PVC/SAN and PVC/αMSAN blends have a low melting torque, a long degradation time, and a high melt index, and this means that they have better processability than pure PVC. The miscibility of the blends has been characterized with differential scanning calorimetry, dynamic mechanical thermal analysis, and advanced rheometrics expansion system analysis. The miscibility of the blends has also been characterized with scanning electron microscopy. The SAN series with AN concentrations of 24–31 wt % is immiscible with PVC by melt extrusion, whereas αMSAN with 31 wt % AN is miscible with PVC, even when they are blended by melt extrusion, because of the strong interaction between PVC and αMSAN. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Applicability of a Miniaturized Micro‐Separator/Classifier to Oil‐Water Separation
Authors: Ookawara S. , Ishikawa T. , Ogawa K.
Published: January 2007

The micro‐separator/classifier is miniaturized to approximately 1/2 size of the original device to examine its applicability to oil‐water separation. A small amount of oil with density of 930 kg/m3 is dispersed in water. The emulsion is fed into the curved microchannels and is discharged from the inner and outer branches that form the bifurcations. The lighter oil phase is collected from the outer branch. A possibility of simultaneous separation of heavier and lighter phases is brought about by the principle of lift‐force induced separation. The cut‐size and pressure loss are much smaller than those of existing hydrocyclones. Further, the miniaturized device attains smaller cut‐size compared with the larger original device applied to solid separation with larger density difference. The suitability of the device to numbering‐up methodology is argued based on the fact that the cut‐size is insensitive to total flow‐rate.
Investigation of the Mechanism of Action of Pyrogallol–Phloroglucinol Transhydroxylase by Using Putative Intermediates
Authors: Paizs Csaba , Bartlewski‐Hof Ulrike , Rétey János
Published: January 2007

Pyrogallol–phloroglucinol transhydroxylase from Pelobacter acidigallici, a molybdopterin‐containing enzyme, catalyzes a key reaction in the anaerobic degradation of aromatic compounds. In vitro, the enzymatic reaction requires 1,2,3,5‐tetrahydroxybenzene as a cocatalyst and the transhydroxylation occurs without exchange with hydroxy groups from water. To test our previous proposal that the transfer of the hydroxy group occurs via 2,4,6,3′,4′,5′‐hexahydroxydiphenyl ether as an intermediate, we synthesized this compound and investigated its properties. We also describe the synthesis and characterization of 3,4,5,3′,4′,5′‐hexahydroxydiphenyl ether. Both compounds could substitute for the cocatalyst in vitro. This indicates that the diphenyl ethers can intrude into the active site and initiate the catalytic cycle. Recently, the X‐ray crystal structure of the transhydroxylase (TH) was published16 and it supports the proposed mechanism of hydroxy‐group transfer.
Annelation of Benzimidazoles with α,β‐Acetylenic γ‐Hydroxyacid Nitriles and Hydrolytic Rearrangement of the Cycloadducts on Alumina
Authors: Trofimov Boris A. , Andriyankova Ludmila V. , Mal'kina Anastasiya G. , Belyaeva Kseniya V. , Nikitina Lina P. , Dyachenko Oleg A. , Kazheva Olga N. , Chekhlov Anatolii N. , Shilov Gennadii V. , Afonin Andrei V. , Ushakov Igor' A. , Baikalova Ludmila V.
Published: January 2007

1‐Substituted benzimidazoles are readily annelated regio‐ and stereoselectively with α,β‐acetylenic γ‐hydroxyacidnitriles under mild conditions (20–25 °C, no catalyst, no solvent) to form new polyfunctional condensed systems, 4‐cyanomethylene‐1,3‐oxazolobenzimidazoles (30–88 % yield). Unexpectedly, the latter, when chromatographed on neutral Al2O3 at room temperature, undergo a complex multi‐position hydrolytic rearrangement involving the cleavage of the imidazole ring to aminophenyl N‐substituted formamides with an aminodihydrofuran moiety in the aminophenylsubstituent, N‐(2‐{[5‐amino‐2,2‐dialkyl‐3(2H)‐furanylidene]amino}phenyl)‐N‐substituted formamides, a novel class of highly functionalized pharmacophoric compounds. The results contribute to the basic benzimidazole chemistry and provide for prospective families of drug candidates.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Cover Picture: Crystal Structures of Conformationally Locked Cyclitols: An Analysis of Hydrogen‐Bonded Architectures and their Implications in Crystal Engineering (Eur. J. Org. Chem. 3/2007)
Authors: Mehta Goverdhan , Sen Saikat , Ramesh Senaiar S.
Published: January 2007

The cover picture shows schematically, the manner in which a conformationally locked polycyclitol can be thought of as a LEGO® brick in the supramolecular world. This analogy manifests during the self‐assembling process by involvement of intermolecular H‐bond donors and acceptors engendered in preordained positions through the rigid trans‐decalin framework and intramolecular O–H···O hydrogen bonding between the 1,3‐diaxial OH groups. Details are discussed in the article by G. Mehta et al. on p. 423 ff.
Poly(Arylene Ether)s with Sulfonic Acid Groups on the Backbone and Pendant for Proton Exchange Membranes Used in PEMFC Applications
Authors: Tian S. H. , Shu D. , Wang S. J. , Xiao M. , Meng Y. Z.
Published: January 2007

Sulfonated poly(aryl ether) (SPAE) and sulfonated poly(fluorenyl ether ketone) (SPFEK) are synthesized by post‐sulfonation and direct polymerization from the sulfonated monomer, respectively. Flexible and smooth proton exchange membranes (PEM) are readily obtained from both polymers, by casting from their 5% solution in N, N′‐dimethylacetamide (DMAC) at 60 °C. The thermal stability, mechanical strength, and single cell performance of the as‐prepared SPAE and SPFEK membranes in a PEM fuel cell (PEMFC) are investigated. The SPAE membrane shows a water uptake of 45% at 80 °C and a proton conductivity of 1.02 × 10–2�S cm–1, which is close to that of Nafion® 115, whereas the SPFEK membrane shows a water uptake of 49% at 80 °C and a proton conductivity of 5.37 × 10–3�S cm–1. These membranes exhibit a higher mechanical strength, and very good hydrolytic and oxidative stabilities because of their specially designed molecular structures. A single cell evaluation experiment demonstrates the superior cell performance of SPAE compared to that of SPFEK and Nafion® 115. These polymers may be a promising proton membrane material for PEM fuel cell applications.
A density‐dependent elastoplastic hydro‐mechanical model for unsaturated compacted soils
Authors: Sun D. A. , Sheng D. C. , Cui H. B. , Sloan S. W.
Published: January 2007

This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd.
Trends in antidepressant overdoses
Authors: McKenzie Mary S. , McFarland Bentson H.
Published: January 2007

Background

Debate continues about antidepressants and suicide. However, there are few recent nation‐wide data about antidepressant overdoses. The purpose of this study was to describe United States trends from 1983 through 2003 in antidepressant overdoses as well as trends in health care utilization and mortality.

Methods

Data were obtained from the American Association of Poison Control Centers' (AAPPC) Toxic Exposure Surveillance System (TESS), the National Hospital Ambulatory Medical Care Survey (NHAMCS) of emergency departments, and the National Hospital Discharge Survey(NHDS).

Results

Antidepressant overdose reports rose dramatically in the United States (from 0.61 per 10 000 population in 1983 to 3.26 per 10 000 population in 2003) chiefly due to the rise in selective serotonin reuptake inhibitor (SSRI) ingestion. However, fatalities per antidepressant overdose report declined from 73 per 10 000 reported ingestions to 32 per 10 000 ingestions. Tricyclic antidepressant (TCA) overdoses had higher rates of hospitalization (78.7 vs. 64.7% hospitalized) and much higher fatality rates than did SSRI overdose reports (0.73 vs. 0.14% mortality). If the 55 977 SSRI overdoses in 2003 had represented TCA overdoses, then (other things being equal) approximately 410 fatalities would have been expected but only 106 people died. Emergency department visits associated with antidepressant overdose increased along with all emergency department visits. Hospitalization associated with antidepressant overdose increased in the early 1980s but then reached a plateau while overall hospitalizations declined.

Conclusions

The dramatic rise in United States antidepressant overdoses has not been reflected in antidepressant overdose fatalities nor in hospitalizations. If the marked increase in antidepressant overdoses in the United States had involved TCAs rather than SSRIs, then there would have been roughly 300 excess deaths annually. Copyright © 2007 John Wiley & Sons, Ltd.
Time‐resolved optically‐detected magnetic resonance of II–VI diluted‐magnetic‐semiconductor heterostructures
Authors: Ivanov V. Yu. , Godlewski M. , Yakovlev D. R. , Ryabchenko S. M. , Karczewski G. , Waag A.
Published: January 2007

Time‐resolved optically‐detected magnetic resonance (ODMR) technique was used to study spin dynamics of Mn2+ ions in (Zn,Mn)Se‐ and (Cd,Mn)Te‐based diluted magnetic semiconductor quantum wells. Times of spin–lattice relaxation have been measured directly from a dynamical shift of exciton luminescence lines after a pulsed impact of 60 GHz microwave radiation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Proton radiation effects in nitride lasers and light emitting diodes
Authors: Gonda Shun‐ichi , Tsutsumi Hiroyuki , Ito Yoshiumi , Mukai Takashi , Nagahama Shin‐ichi
Published: January 2007

Nitride laser diodes and light emitting diodes were irradiated with 200‐, 80‐ and 10‐MeV protons. The threshold current of violet laser diodes increased with increasing proton fluence to 1 × 1014 p/cm2. The increase in threshold current is considerably small compared with that of AlGaAs laser diodes. Proton energy dependence of the change of threshold current was a little bit different from that of GaN NIEL. Oscillation wavelength did not change before and after irradiation. The defect levels made by proton irradiation do not seem to be radiative recombination centers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correlation between optical and structural properties of (Al,Ga)N layers grown by MOCVD
Authors: Jahn Uwe , Jiang De‐Sheng , Ploog Klaus H. , Wang Xiaolan , Zhao Degang , Yang Hui
Published: January 2007

For both, (Al,Ga)N with low Al content grown on a GaN nucleation layer and (Al,Ga)N with high Al content gown on an AlN nucleation layer, the inhomogeneous distribution of the luminescence is linked to the distribution of defects, which may be due to inversion domains. In the former system, defect regions exhibit a much lower Al content than the nominal one leading to a splitting of the respective luminescence spectra. In the latter system, a domain‐like growth is observed with a pyramidal surface morphology and non‐radiative recombination within the domain boundaries. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A global observer for autonomous systems with bounded trajectories
Authors: Lei Hao , Wei Jianfeng , Lin Wei
Published: January 2007

The problem of global observer design for autonomous systems is investigated in this paper. A constructive approach is presented for the explicit design of global observers for completely observable systems whose solution trajectories are bounded from any initial condition. Since the bound of a solution trajectory depends on the initial condition and is thereforenot known a priori, the idea of universal control is employed to tune the observer gains on‐line, achieving global asymptotic convergence of the proposed high‐gain observer. Copyright © 2007 John Wiley & Sons, Ltd.
Anatomical study for an updated comprehension of clubfoot. Part II: Ligaments, tendons and muscles
Authors: Windisch Gunther , Anderhuber Friedrich , Haldi-Brändle Verena , Exner Gerhard Ulrich
Published: January 2007

Purpose

The aim of our study was to evaluate the pathological anatomy of the ligaments, tendons and muscles in clubfeet, and to show whether the dysbalance of shortened and elongated structures is an adaptive process or a primary factor inducing the misshaped bones and cartilagines.

Methods

Surgical exposure was performed on seven idiopathic clubfeet specimens, aborted between the 25th and 37th week of gestation and compared to two normal feet (27th and 36th week of gestation).

Results

The medial stabilisation system of the foot was found shortened, but all ligaments could be dissected. On the lateral side, the calcaneofibular ligament in particular was both ‘shortened’ and ‘elongated’, depending on the course of the fibres to the axis of motion in the subtalar and talocalcaneonavicular joint. The main difference to the normal feet was found in the thickened tendon of the tibialis posterior forming a bulbus before dividing into fascicules.

Conclusions

We presume the ossification disturbance of the calcaneus to be the primary fault. This disturbance will influence the reduction of the varus position, so ligaments and tendons will be conformed to the misshaped bones.
Localized convection cells in the presence of a vertical magnetic field
Authors: DAWES J. H. P.
Published: January 2007

Thermal convection in a horizontal fluid layer heated uniformly from below usually produces an array of convection cells of roughly equal amplitudes. In the presence of a vertical magnetic field, convection may instead occur in vigorous isolated cells separated by regions of strong magnetic field. An approximate model for two-dimensional solutions of this kind is constructed, using the limits of small magnetic diffusivity, large magnetic field strength and large thermal forcing.

The approximate model captures the essential physics of these localized states, enables the determination of unstable localized solutions and indicates the approximate region of parameter space where such solutions exist. Comparisons with fully nonlinear numerical simulations are made and reveal a power-law scaling describing the location of the saddle-node bifurcation in which the localized states disappear.
Pressure-dependent viscosity and interfacial instability in coupled ice–sediment flow
Authors: SCHOOF CHRISTIAN
Published: January 2007

We study an interfacial instability in the coupled flow of ice and subglacial sediment, both modelled as viscous media. Unlike other interfacial instabilities in coupled viscous flows at zero Reynolds number, the mechanism considered here does not rely on buoyancy or the effect of an upper free surface, but on the pressure-dependence of the sediment viscosity. Specifically, the instability relies on sediment rheology being such that, when sediment flows in simple shear, sediment flux increases with compressive normal stress at the ice–sediment interface when the velocity of the interface is kept constant. When ice moves over a shallow bump in the interface, it generates a higher compressive stress on the bump's upstream side than in its lee. If in addition the effective sediment viscosity is low compared with that of ice, interfacial velocity remains approximately constant, and this then implies that more sediment flows into the bump than out of it, causing it to grow. Modelling ice as a Newtonian material, we show that this mechanism works for a wide range of sediment rheologies, including the highly nonlinear shear-thinning ones typically thought most appropriate for the description of ‘nearly plastic’ sediment. The instabilities predicted are essentially two-dimensional, with infinite transverse wavelength, and a nonlinear model shows that growth is unbounded until cavitation occurs in the lee of evolving bumps on the interface. The instability mechanism does not seem to predict the formation of common glacial landforms, but may explain the formation of water-filled cavities on deformable glacier beds.
Equatorial wave attractors and inertial oscillations
Authors: MAAS LEO R. M. , HARLANDER UWE
Published: January 2007

Three different approximations to the axisymmetric small-disturbance dynamics of a uniformly rotating thin spherical shell are studied for the equatorial region assuming time-harmonic motion. The first is the standard β-plane model. The second is Stern's (Tellus, vol. 15, 1963, p. 246) homogeneous, equatorial β-plane model of inertial waves (that includes all Coriolis terms). The third is a version of Stern's equation extended to include uniform stratification. It is recalled that the boundary value problem (BVP) that governs the streamfunction of zonally symmetric waves in the meridional plane becomes separable only for special geometries. These separable BVPs allow us to make a connection between the streamfunction field and the underlying geometry of characteristics of the governing equation. In these cases characteristics are each seen to trace a purely periodic path. For most geometries, however, the BVP is non-separable and characteristics and therefore wave energy converge towards a limit cycle, referred to as an equatorial wave attractor. For Stern's model we compute exact solutions for wave attractor regimes. These solutions show that wave attractors correspond to singularities in the velocity field, indicating an infinite magnification of kinetic energy density along the attractor. The instability that arises occurs without the necessity of any ambient shear flow and is referred to as geometric instability.

For application to ocean and atmosphere, Stern's model is extended to include uniform stratification. Owing to the stratification, characteristics are trapped near the equator by turning surfaces. Characteristics approach either equatorial wave attractors, or point attractors situated at the intersections of turning surfaces and the bottom. At these locations, trapped inertia–gravity waves are perceived as near-inertial oscillations. It is shown that trapping of inertia–gravity waves occurs for any monochromatic frequency within the allowed range, while equatorial wave attractors exist in a denumerable, infinite set of finite-sized continuous frequency intervals. It is also shown that the separable Stern equation, obtained as an approximate equation for waves in a homogeneous fluid confined to the equatorial part of a spherical shell, gives an exact description for buoyancy waves in uniformly but radially stratified fluids in such shells.
Large-eddy simulation and experimental study of heat transfer, nitric oxide emissions and combustion instability in a swirled turbulent high-pressure burner
Authors: SCHMITT PATRICK , POINSOT T. , SCHUERMANS B. , GEIGLE K. P.
Published: January 2007

Nitric oxide formation in gas turbine combustion depends on four key factors: flame stabilization, heat transfer, fuel–air mixing and combustion instability. The design of modern gas turbine burners requires delicate compromises between fuel efficiency, emissions of oxides of nitrogen (NOx) and combustion stability. Burner designs allowing substantial NOx reduction are often prone to combustion oscillations. These oscillations also change the NOx fields. Being able to predict not only the main species field in a burner but also the pollutant and the oscillation levels is now a major challenge for combustion modelling. This must include a realistic treatment of unsteady acoustic phenomena (which create instabilities) and also of heat transfer mechanisms (convection and radiation) which control NOx generation.

In this work, large-eddy simulation (LES) is applied to a realistic gas turbine combustion chamber configuration where pure methane is injected through multiple holes in a cone-shaped burner. In addition to a non-reactive simulation, this article presents three reactive simulations and compares them to experimental results. The first reactive simulation neglects effects of cooling air on flame stabilization and heat losses by radiation and convection. The second reactive simulation shows how cooling air and heat transfer affect nitric oxide emissions. Finally, the third reactive simulation shows the effects of combustion instability on nitric oxide emissions. Additionally, the combustion instability is analysed in detail, including the evaluation of the terms in the acoustic energy equation and the identification of the mechanism driving the oscillation.

Results confirm that LES of gas turbine combustion requires not only an accurate chemical scheme and realistic heat transfer models but also a proper description of the acoustics in order to predict nitric oxide emissions and pressure oscillation levels simultaneously.
Shear-improved Smagorinsky model for large-eddy simulation of wall-bounded turbulent flows
Authors: LÉVÊQUE E. , TOSCHI F. , SHAO L. , BERTOGLIO J.-P.
Published: January 2007

A shear-improved Smagorinsky model is introduced based on results concerning mean-shear effects in wall-bounded turbulence. The Smagorinsky eddy-viscosity is modified asvT=(Csδ)2(|S|—|〈S〉|): the magnitude of the mean shear |〈S〉|is subtracted from the magnitude of the instantaneous resolved rate-of-strain tensor |S|;CSis the standard Smagorinsky constant and Δ denotes the grid spacing. This subgrid-scale model is tested in large-eddy simulations of plane-channel flows at Reynolds numbersReτ= 395 andReτ= 590. First comparisons with the dynamic Smagorinsky model and direct numerical simulations for mean velocity, turbulent kinetic energy and Reynolds stress profiles, are shown to be extremely satisfactory. The proposed model, in addition to being physically sound and consistent with the scale-by-scale energy budget of locally homogeneous shear turbulence, has a low computational cost and possesses a high potential for generalization to complex non-homogeneous turbulent flows.
Fast forward radiative transfer modeling of 4.3 μm nonlocal thermodynamic equilibrium effects for infrared temperature sounders
Authors: DeSouza‐Machado S. G. , Strow L. L. , Hannon S. E. , Motteler H. E. , Lopez‐Puertas M. , Funke B. , Edwards D. P.
Published: January 2007

Retrieval algorithms for downlooking infrared sounders typically avoid using channels from the 4.3 μm CO2 region that probe the mid‐ and upper‐atmosphere due to very high altitude Non Local Thermodynamic Equilibrium (NLTE) emission, which can add as much as 10 K to the measured daytime brightness temperatures (BT). In this paper we report a fast radiative transfer model for a nadir sounding instrument (AIRS) that includes the effects of NLTE, allowing the retrieval algorithm to use many short wave CO2 channels for upper‐air soundings. Model biases and standard deviations are very similar for both day and night. This work allows an infrared sounder to probe the upper atmosphere much more completely using only short wave 4.3–4.5 μm channels.
VHF radar investigations on the role of mechanical oscillator effect in exciting convectively generated gravity waves
Authors: Kumar Karanam Kishore
Published: January 2007

The present communication reports experimental verification of one of the existing generating mechanisms of convectively generated gravity waves (CGW), viz., mechanical oscillator effect. Two deep convective systems are chosen for the present study. Continuous observations of vertical velocities provided an opportunity to study the spectra of CGW above the deep convection using wavelet analysis. Mechanical oscillator effect is examined by observing the oscillations of the vertical velocities in the mid troposphere. The present analysis showed time localized mid tropospheric peak vertical velocity oscillations at two distinct time periods. The resultant oscillation due to the interaction of these two oscillations is observed in the lower stratosphere, which is an exciting result from the present study. As there are very few observational evidences in support of mechanical oscillator effect, the present results are of importance for gravity wave community.
Does dust from Patagonia reach the sub‐Antarctic Atlantic Ocean?
Authors: Gassó Santiago , Stein Ariel F.
Published: January 2007

Although emission of dust from the Patagonia desert is shown by global aerosol models, there is conflicting observational evidence of dust activity in the region. Because dust from Patagonia into the Southern Ocean (SO) may play a role in regulating phytoplankton activity, it is necessary to confirm whether there is dust activity and if so, how far the dust travels into the SO. We used a combination of surface visibility, satellite measurements (MODIS and OMI) and transport model (HYSPLIT) to track and report for the first time a dust event originating in Patagonia. We show that the dust reached the free troposphere in the Sub‐Antarctic Atlantic Ocean. Although the dust emission was significant, cloudiness and dilution of the plume resulted in difficult conditions to track dust in the SW Atlantic. We show that the use of any single tool (i.e., MODIS or OMI) is not enough to track the dust and only an integrated approach of satellite and modeling tools can achieve a consistent description. As a result, current platforms used for dust detection are probably underestimating aerosol loading in the area
CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada
Authors: Clark Ian D. , Henderson Lori , Chappellaz Jérôme , Fisher David , Koerner Roy , Worthy Douglas E. J. , Kotzer Tom , Norman Ann‐Lise , Barnola Jean‐Marc
Published: January 2007

Firn air and ice have been sampled and analyzed for trace gases (CO2, N2O, CH4, and CO) and isotopes (14C, 13C, and 18O of CO2; 3H of ice) at 3 m intervals from the surface to the depth of closure at 60 m on the Devon Island Ice Cap, a low‐elevation permanent glacier in the Canadian Arctic Islands, to investigate firn diffusion and the effects of summer melting. The 14CO2 profile from the permeable firn includes the 1963 thermonuclear peak at a depth of 53.9 ± 1.5 m. The twofold increase and rapid decay that characterize the recent atmospheric history for 14CO2 provide a robust atmospheric scenario that is used with a firn air diffusion model to inversely construct the firn diffusivity profile. The results show a permeable but essentially nondiffusive zone from 50 to 60 m depth. A firn‐ice age profile was produced from density measurements, and accumulation rates were calibrated with the depth of the 1963 thermonuclear 3H peak. The average ages for CO2 in the sampled firn air profile were determined by a new method based on the rate of 18O exchange between CO2 and the ice matrix. Calibrated with the 1963 peak for thermonuclear 14CO2, a 21.2‐year reaction halftime is calculated for exchange taking place at the firn temperature of −22.8°C on Devon. This gives an average age of 54.9 (+6.0/−12.0) years for firn air at 60 m depth in 140‐year‐old ice. Thus CO2 has a mean age 85 years younger than associated ice at the point of occlusion. The measured in firn air provides no indication of alteration by summer melting, which is attributed to a high degree of convective and diffusive flushing of the upper firn as shown by diffusion modeling. This suggests that ice sheets with summer melt layers can reliably preserve atmospheric trace gas signals.
Nutrient Limitation and Stoichiometry of Carnivorous Plants
Authors: Ellison A. M.
Published: January 2007

Abstract: The cost‐benefit model for the evolution of carnivorous plants posits a trade‐off between photosynthetic costs associated with carnivorous structures and photosynthetic benefits accrued through additional nutrient acquisition. The model predicts that carnivory is expected to evolve if its marginal benefits exceed its marginal costs. Further, the model predicts that when nutrients are scarce but neither light nor water is limiting, carnivorous plants should have an energetic advantage in competition with non‐carnivorous plants. Since the publication of the cost‐benefit model over 20 years ago, marginal photosynthetic costs of carnivory have been demonstrated but marginal photosynthetic benefits have not. A review of published data and results of ongoing research show that nitrogen, phosphorus, and potassium often (co‐)limit growth of carnivorous plants and that photosynthetic nutrient use efficiency is 20 ‐ 50 % of that of non‐carnivorous plants. Assessments of stoichiometric relationships among limiting nutrients, scaling of leaf mass with photosynthesis and nutrient content, and photosynthetic nutrient use efficiency all suggest that carnivorous plants are at an energetic disadvantage relative to non‐carnivorous plants in similar habitats. Overall, current data support some of the predictions of the cost‐benefit model, fail to support others, and still others remain untested and merit future research. Rather than being an optimal solution to an adaptive problem, botanical carnivory may represent a set of limited responses constrained by both phylogenetic history and environmental stress.
Hydrodynamic chains and the classification of their Poisson brackets
Authors: Pavlov Maxim V.
Published: January 2007

Infinite component Poisson brackets of the Dubrovin-Novikov type [Sov. Math. Dokl. 27, 665–669 (1983)] are considered. The corresponding Jacobi identity is significantly simplified in the Liouville coordinates since the skew-symmetry condition is automatically satisfied. The concept of M Poisson bracket connected with hydrodynamic chains is introduced. Then the Jacobi identity is a nonlinear system of equations in partial derivatives which can be completely integrated. In such a case, a classification of infinite component Poisson brackets of the Dubrovin-Novikov type can be obtained. Two simplest examples, M=0 and M=1, are considered. Also infinite component Poisson brackets of the Ferapontov [Am. Math. Soc. Transl. 170, 38–58 (1995)] type can be simplified in the Liouville coordinates. The Jacobi identity for infinite component Poisson brackets of the Ferapontov-Mokhov type [Russ. Math. Surveys 45, 218–219 (1990)] is presented in the Liouville coordinates
Volume magnetostriction of Fe81(Ga1−xGex)19 alloys
Authors: Gao Fang , Jiang Chengbao , Liu Jinghua , Xu Huibin
Published: January 2007

Linear and volume magnetostrictions were investigated in the as-cast Fe81Ga19 and Ge doped Fe81(Ga1−xGex)19 (x=0.1, 0.2, and 0.3) alloys by measuring the change in length along the three-dimensional directions of the samples. For as-cast Fe81Ga19 alloy, when the applied field was lower than about 0.3T, the linear magnetostriction was positive along the direction of the field, but became negative in another two orthogonal directions normal to the applied field. Volume expansion was observed along all the three directions at the applied field over 0.3T. Due to the contribution of the volume expansion, namely, volume magnetostriction, the longitudinal magnetostriction increased from 27ppm at 0.3Tto47ppm at 2.0T. The saturation of volume magnetostriction was absent at 2T and should be higher with further increasing field. Not only the linear magnetostriction but also the volume magnetostriction can be drastically enhanced by doping Ga in Fe. The same phenomena were observed in Fe81(Ga1−xGex)19 alloys. The as-cast Fe81Ga19 alloy exhibits mainly a disordered bcc A2 phase, and the Ge doped Fe81Ga19 alloys keep the A2 structure with a smaller lattice constant.
Structural and magnetic characterization of oleic acid and oleylamine-capped gold nanoparticles
Authors: de la Presa P. , Multigner M. , de la Venta J. , García M. A. , Ruiz-González M. L.
Published: January 2007

In this work the study of oleic acid and oleylamine-capped gold nanoparticles is presented. The structural characterization of the sample shows 6.7 nm gold nanoparticles with a narrow size distribution. The experimental optical absorption spectrum has a maximum at 2.35 eV. The calculated optical absorption spectrum is shifted and narrower than the experimental one, indicating that the oleic acid and oleylamine do not merely passivate the metallic nanoparticles but modify its electronic structure. These gold nanoparticles show in addition a kind of magnetic order similar to other organic passivated gold nanoparticles as thiol-capped gold nanoparticles. Although the magnetic interactions seem to be weaker than in thiol-capped ones, the magnetic behavior looks similar to that, i.e., an invariant temperature dependence of the magnetization from 5 to 300 K and a noticeable coercive field. We analyze the influence of the organic layer bonding the nanoparticles on the magnetic behavior.
Versatile and compact capacitive dilatometer
Authors: Schmiedeshoff G. M. , Lounsbury A. W. , Luna D. J. , Tracy S. J. , Schramm A. J. , Tozer S. W. , Correa V. F. , Hannahs S. T. , Murphy T. P. , Palm E. C. , Lacerda A. H. , Bud’ko S. L. , Canfield P. C. , Smith J. L. , Lashley J. C. , Cooley J. C.
Published: January 2007

We describe the design, construction, calibration, and operation of a relatively simple differential capacitive dilatometer suitable for measurements of thermal expansion and magnetostriction from 300 to below 1K with a low-temperature resolution of about 0.05Å. The design is characterized by an open architecture permitting measurements on small samples with a variety of shapes. Dilatometers of this design have operated successfully with a commercial physical property measurement system, with several types of cryogenic refrigeration systems, in vacuum, in helium exchange gas, and while immersed in liquid helium (magnetostriction only) to temperatures of 30mK and in magnetic fields to 45T.
Small Si clusters on surfaces of carbon nanotubes
Authors: Meng Lijun , Zhang Kaiwang , Stocks G. Malcolm , Zhong Jianxin
Published: January 2007

Structures of small Si clusters, Sin, on surfaces of carbon nanotubes have been studied by molecular dynamics simulation. We show that the lowest-energy structures of Sin are three-dimensional clusters rather than thin Si sheets covering the surface of a nanotube. As n increases from 10 to 30, Sin undergoes structural transitions from a tentlike structure (with nanotube surface as its base) to a cagelike structure (without interior atoms) and further to a spherical compact structure (with interior atoms). Our results are different from the structures of small Si clusters found in a free space without Si-nanotube interaction.
Role of heterostructures and multiple magnetic phases in the low-field magnetization of Fe–Cr giant magnetoresistive multilayers
Authors: Patel R. S. , Majumdar A. K. , Nigam A. K. , Temple D. , Pace C.
Published: January 2007

Zero-field-cooled (ZFC) and field-cooled (FC) magnetizations along with ac magnetization versus temperature and M-H loop measurements are reported for two series of ion beam sputtered Fe–Cr giant magnetoresistive (GMR) (maximum of 33%) multilayers where the interface roughness is different. The ZFC and FC magnetization data follow different curves below an irreversibility temperature (Tirr). The FC data show a T3∕2 thermal demagnetization behavior at lower temperatures with a very small spin-wave stiffness constant but they go as 1∕T at higher temperatures (above Tirr). The ZFC data show maxima at Tm(H), from which we find the glass transition temperature Tg using the de Almeida and Thouless plot. ac magnetization versus T also shows broad peaks roughly near the same Tg. This behavior is interpreted in terms of the coexistence of spin-glass∕superparamagnetic, FM and AF phases. Most of the above exotic low-field features are absent in molecular beam epitaxy grown Fe–Cr multilayers (GMR >50%) with very smooth interfaces. The relatively rough interfaces in the present sputtered samples give rise to frustrations of Fe and Cr moments, leading to spin-glass-like behavior.
Relativistic density functional calculations using two-spinor minimax finite-element method and linear combination of atomic orbitals for ZnO, CdO, HgO, UubO and Cu2, Ag2, Au2, Rg2
Authors: Kullie O. , Zhang H. , Kolb J. , Kolb D.
Published: January 2007

In previous work the authors have presented a highly accurate two-spinor fully relativistic solution of the two-center Coulomb problem utilizing the finite-element method (FEM) and furthermore developed a relativistic minimax two-spinor linear combination of atomic orbitals (LCAO). In the present paper the authors present Dirac-Fock-Slater (DFS-) density functional calculations for two-atomic molecules up to super heavy systems using the fully nonlinear minimax FEM and the minimax LCAO in its linearized approximation (linear approximation to relativistic minimax). The FEM gives highly accurate benchmark results for the DFS functional. Especially considering molecules with up to super heavy atoms such as UubO and Rg2, the authors found that LCAO fails to give the correct systematic trends. The accurate FEM results shed a new light on the quality of the DFS-density functional.
Field emission of electrons from a Cs-doped single carbon nanotube of known chiral indices
Authors: Zhao Gongpu , Zhang Qi , Zhang Han , Yang Guang , Zhou Otto , Qin Lu-Chang , Tang Jie
Published: January 2007

The authors report the effects of Cs doping on the field emission properties of a five-shell single carbon nanotube. The chiral indices of each shell of this carbon nanotube have been determined using nanobeam electron diffraction, which has four semiconducting shells and one metallic shell in the middle. From the Fowler-Nordheim plots, a reduction from 4.8to3.8eV has been observed in the work function of the single carbon nanotube before and after Cs doping.
General reconstruction formulas for analyzer-based computed tomography
Authors: Nesterets Ya. I. , Gureyev T. E. , Wilkins S. W.
Published: January 2007

General formulas are derived for computed tomography reconstruction in analyzer-based imaging. Two image acquisition geometries are investigated. In the first geometry, which is widely used, the rotation axis of the object is perpendicular to that of the analyzer crystal. In the second geometry, in which the rotation axes are parallel, the reconstruction formulas are shown to be significantly simpler and more stable with respect to noise in experimental data.
Structural short-range order of the β-Ti phase in bulk Ti–Fe–(Sn) nanoeutectic composites
Authors: Das J. , Eckert J. , Theissmann R.
Published: January 2007

The authors report lattice distortion and “ω-like” structural short-range order (SRO) of the β-Ti phase in a Ti–Fe–(Sn) bulk nanoeutectic composite prepared by slow cooling from the melt. The nanoeuetctic phases are chemically homogeneous, but the addition of Sn releases the local lattice strain, modifies the structural SRO, and prevents the formation of stacking faults in the body centered cubic (bcc) β-Ti phase resulting in improved plastic deformability. The elastic properties and the structural SRO of the β-Ti phase are proposed to be important parameters for developing advanced high strength, ductile Ti-base nanocomposite alloys.
Interaction of low-energy electrons with the purine bases, nucleosides, and nucleotides of DNA
Authors: Winstead Carl , McKoy Vincent
Published: January 2007

The authors report results from computational studies of the interaction of low-energy electrons with the purine bases of DNA, adenine and guanine, as well as with the associated nucleosides, deoxyadenosine and deoxyguanosine, and the nucleotide deoxyadenosine monophosphate. Their calculations focus on the characterization of the π* shape resonances associated with the bases and also provide general information on the scattering of slow electrons by these targets. Results are obtained for adenine and guanine both with and without inclusion of polarization effects, and the resonance energy shifts observed due to polarization are used to predict π* resonance energies in associated nucleosides and nucleotides, for which static-exchange calculations were carried out. They observe slight shifts between the resonance energies in the isolated bases and those in the nucleosides.
Stability diagram and effect of initial density stratification for a two-layer system in a supercritical fluid
Authors: Boutrouft K. , Amiroudine S. , Ambari A.
Published: January 2007

A numerical study of the stability in a two-layer system filled with a single pure supercritical fluid subjected to an initial temperature difference is performed. The very large compressibility and the very low heat diffusivity of near-critical fluids lead to a Rayleigh-Taylor-like gravitational instability of the heat diffusion layer. This instability is similar to the one of two miscible fluids where molecular species diffusion coefficient is replaced by the heat diffusion coefficient. Our numerical results are consistent with respect to the dispersion relation derived by Duff et al. [Phys. Fluids 5, 417 (1962)] for a system of two incompressible miscible fluids (argon-bromine mixture falling into helium or air). It has also been shown that when the thickness of the lower layer becomes smaller than the heat diffusion length based on the maximum growth rate, the system is stable [Phys. Fluids 17, 054102 (2005)]. A linear stability diagram has been established as a function of three parameters: the thickness of the lower layer, the density difference between the two layers and the distance to the critical point. When the critical point is approached, the high initial stratification (due to the high compressibility) of this Rayleigh-Taylor-like configuration has seen the effect of stabilizing the system.
Enhanced charge mobility in a molecular hole transporter via addition of redox inactive ionic dopant: Implication to dye-sensitized solar cells
Authors: Snaith Henry J. , Grätzel Michael
Published: January 2007

Upon the addition of lithium salts to the hole-transporter matrix, 2,2′,7,7′-tetrakis(N,N-di-p-methoxypheny-amine)-9,9′-spirobifluorene (spiro-MeOTAD), the authors observe a 100-fold increase in conductivity through spiro-MeOTAD within a TiO2 mesoporous network. The authors demonstrate this to be a bulk effect and not due to improved injection at the electrodes. By testing “hole-only” diodes of pure spiro-MeOTAD and those doped with lithium salts, the authors calculate that the hole mobility increases from 1.6×10−4to1.6×10−3cm2∕Vs. The authors discuss the possible mechanisms for this significant enhancement in charge mobility and its implication to the dye-sensitized solar cell operation.
Identification of oxygen and zinc vacancy optical signals in ZnO
Authors: Børseth T. Moe , Svensson B. G. , Kuznetsov A. Yu. , Klason P. , Zhao Q. X. , Willander M.
Published: January 2007

Photoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In particular, annealing in O2 results in a DBE at 2.35±0.05eV, whereas annealing in the presence of metallic Zn results in DBE at 2.53±0.05eV. The authors attribute the former band to zinc vacancy (VZn) related defects and the latter to oxygen vacancy (VO) related defects. Additional confirmation for the VO and VZn peak identification comes from the observation that the effect is reversible when O- and Zn-rich annealing conditions are switched. After annealing in the presence of ZnO powder, there is no indication for the VZn- or VO-related bands, but the authors observe a low intensity yellow luminescence band peaking at 2.17eV, probably related to Li, a common impurity in hydrothermally grown ZnO.
Electrical properties of Ohmic contacts to ZnSe nanowires and their application to nanowire-based photodetection
Authors: Salfi J. , Philipose U. , de Sousa C. F. , Aouba S. , Ruda H. E.
Published: January 2007

Multilayer Ti∕Au contacts were fabricated on individual, unintentionally doped zinc selenide nanowires with 80nm nominal diameter. Four-terminal contact structures were used to independently measure current-voltage characteristics of contacts and nanowires. Specific contact resistivity of Ti∕Au contacts is 0.024Ωcm2 and intrinsic resistivity of the nanowires is approximately 1Ωcm. The authors have also measured the spectral photocurrent responsivity of a ZnSe nanowire with 2.0V bias across Ti∕Au electrodes, which exhibits a turnon for wavelengths shorter than 470nm and reaches 22A∕W for optical excitation at 400nm.
Photorefractive effect in relaxor ferroelectric 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystal
Authors: He Chongjun , Zhou Zhongxiang , Liu Dajun , Zhao Xiangyong , Luo Haosu
Published: January 2007

The photorefractive properties of 0.62Pb(Mg1∕3Nb2∕3)O3–0.38PbTiO3 single crystals have been investigated by the two-wave mixing experiment. The maximal gain coefficient is 5.4cm−1, the effective trap density is 1.2×1016cm−3, and the normalized photorefractive response time under 1W∕cm2 illumination is 1.5s at a wavelength of 632.8nm. The dominant charge carrier was identified as holes from the direction of two-wave mixing energy transfer.
Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN∕GaN heterostructures using capacitance deep level optical spectroscopy
Authors: Armstrong A. , Chakraborty A. , Speck J. S. , DenBaars S. P. , Mishra U. K. , Ringel S. A.
Published: January 2007

Deep levels were observed using capacitance deep level optical spectroscopy (DLOS) in an AlGaN∕GaN heterostructure equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AlGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AlGaN- and GaN-related defects, and the latter emphasizes defects residing in the GaN. A band gap state at Ec−3.85eV was unambiguously identified with the AlGaN region, and deep levels at Ec−2.64eV and Ec−3.30eV were associated with the GaN layers. Both the AlGaN and GaN layers exhibited additional deep levels with large lattice relaxation. The influence of deep levels on the two-dimensional electron gas sheet charge was estimated using a lighted capacitance-voltage method.