bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of intermolecular hydrogen bond on structural properties of phenylboronic acid: quantum chemical and X‐ray study
Authors: Cyrański Michał K. , Jezierska Aneta , Klimentowska Paulina , Panek Jarosław J. , Sporzyński Andrzej
Published: May 2008

The molecular structure and properties of phenylboronic acid were investigated experimentally using X‐ray structural analysis and spectroscopic methods. Infrared (IR) spectroscopy measurements were performed to assess the hydrogen bonding strength. The experimental part is enhanced by computational results concerning the geometrical and electronic structure. The molecular dimer (basic structural motif) was investigated on the basis of density functional theory (DFT) and Møller–Plesset second order (MP2) perturbation theory. The basis‐set superposition error (BSSE) was calculated to correct the binding energy. Atoms in molecules (AIM) and topological analysis of electron localization function (ELF) were applied to study the intermolecular hydrogen bond properties and localization pattern for the neighborhood of the boron atom. The anharmonicity of the hydrogen bond potential function was studied by solving the time‐independent Schrödinger equation. Potential energy distribution (PED) analysis of the normal modes was performed to identify the characteristic frequencies of the studied system. Subsequently, the interaction energy for the dimeric form was decomposed using the symmetry‐adapted perturbation theory (SAPT) scheme. Car–Parrinello molecular dynamics (CPMD) gave an insight into dynamical processes occurring in the phenylboronic acid dimerin vacuo. The hydrogen bridge protons in the phenylboronic acid are not shifted significantly toward the acceptor. Lower dimerization energy with respect to the carboxylic acid dimers is explained on the basis of the interaction energy decomposition as the effect of diminished induction term. The employment of SAPT and CPMD approaches is a step forward in the understanding of the physico‐chemical nature of the large family represented by the investigated compound. Copyright © 2008 John Wiley & Sons, Ltd.
H‐shaped (ABCDE type) quintopolymer via click reaction [3 + 2] strategy
Authors: Gungor Eda , Durmaz Hakan , Hizal Gurkan , Tunca Umit
Published: May 2008

H‐shaped quintopolymer containing different five blocks: poly(ε‐caprolactone) (PCL), polystyrene (PS), poly(ethylene glycol) (PEG), and poly(methyl methacrylate) (PMMA) as side chains and poly(tert‐butyl acrylate) (PtBA) as a main chain was simply prepared from a click reaction between azide end‐functionalized PCL‐PS‐PtBA 3‐miktoarm star terpolymer and PEG–PMMA‐block copolymer with alkyne at the junction point, using Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as a catalyst in DMF at room temperature for 20 h. The H‐shaped quintopolymer was obtained with a number–average molecular weight (Mn) around 32,000 and low polydispersity index (Mw/Mn) 1.20 as determined by GPC analysis in THF using PS standards. The click reaction efficiency was calculated to have 60% from 1H NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4459–4468, 2008
Stilbene‐containing polyactylenes: Molecular design, synthesis, and relationship between molecular structure and NLO properties
Authors: Su Xinyan , Xu Hongyao , Guo Quanzhen , Shi Guang , Yang Junyi , Song Yinglin , Liu Xiangyang
Published: May 2008

Polyacetylenes (P1–P4) containing different stilbene groups, [(CHC) PhCHCHPhR]n(ROCmH2m+1 (m = 4 (P1), 10 (P2), 16 (P3)), or NO2 (P4)) were designed and synthesized, respectively, using [Rh(nbd)Cl]2 as a catalyst. Their structures and properties were characterized and evaluated by FTIR, 1H‐NMR, 13C‐NMR, GPC, and UV, PL, respectively. The optical limiting and nonlinear optical properties were investigated by using a frequency doubled, Q‐switched, mode‐locked Continuum ns/ps Nd:YAG laser system and their optical limiting mechanism was discussed. It is surprising to see that the stilbene pendants endow the polyacetylenes with a high thermal stability (Td ≥ 270 °C), novel optical limiting properties and large third‐order nonlinear optical susceptibilities (up to 4.61 × 10−10 esu). The optical limiting mechanism is mainly originated from reverse saturable absorption of molecules. In addition, it is found that the polymer with electron accepted NO2 moiety exhibits better optical properties than that with electron donated alkoxy group because of larger π electron delocalization and dipolar effect. The strong interaction between stilbene pendants and the polyene main chain significantly results in red‐shift of fluorescence emitting peak. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4529–4541, 2008
Structural comparison of products from peroxide‐initiated grafting of vinylsilane and silane‐functionalized nitroxyl to hydrocarbon and polyolefin substrates
Authors: Weaver J. D. , Chowdhury A. K. , Mowery D. M. , Esseghir M. , Cogen J. M. , Chaudhary B. I.
Published: May 2008

It has been demonstrated that peroxide‐initiated grafting of vinylsilanes to polyethylene results in a nonuniform distribution of silane groups on the polymer chain due to a chain‐transfer mechanism, leading to inefficient utilization of silane with respect to gel fraction in a crosslinked material. In this article, we demonstrate that grafting a nitroxyl free radical that contains a silane functional group gives a more uniform distribution of silane functionality. Model compounds were synthesized by grafting a silane‐functionalized TEMPO derivative and a vinylsilane to cyclooctane, and their structures were compared. The product grafted with vinyltriethoxysilane consisted of essentially all multigrafted product with an average of 2.26 silane grafts per cyclooctane molecule, which is in close agreement with published data, while the product of grafting the silane‐functional nitroxyl consisted of only the monografted species; no multigrafted product was detected. This confirms that grafting a silane‐functionalized nitroxyl occurs via bimolecular combination of free radicals that is not affected by chain‐transfer and suggests that the process may lead to more efficient utilization of silane as indicated by higher gel fraction for a given level of grafted silane. Synthetic work to prepare silane‐functionalized TEMPO derivatives and preliminary studies to graft them to polyolefins are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4542–4555, 2008
Hydrogen‐bond‐assisted syndiotactic‐specific radical polymerizations of N‐alkylacrylamides: The effect of the N‐substituents on the stereospecificities and unusual large hysteresis in the phase‐transition behavior of aqueous solution of syndiotactic poly(N‐n‐propylacrylamide)
Authors: Hirano Tomohiro , Nakamura Kimihiko , Kamikubo Takahiro , Ishii Satoshi , Tani Kanami , Mori Takeshi , Sato Tsuneyuki
Published: May 2008

The radical polymerizations of N‐alkylacrylamides, such as N‐methyl‐(NMAAm), N‐n‐propyl‐(NNPAAm), N‐benzyl‐(NBnAAm), and N‐(1‐phenylethyl)acrylamides (NPhEAAm), at low temperatures were investigated in the absence or presence of hexamethylphosphoramide (HMPA) and 3‐methyl‐3‐pentanol (3Me3PenOH), which induced the syndiotactic specificities in the radical polymerization of N‐isopropylacrylamide (NIPAAm). In the absence of the syndiotactic‐specificity inducers, the syndiotacticities of the obtained polymers gradually increased as the bulkiness of the N‐substituents increased. Both HMPA and 3Me3PenOH induced the syndiotactic specificities in the NNPAAm polymerizations as well as in the NIPAAm polymerizations. The addition of 3Me3PenOH into the polymerizations of NMAAm significantly induced the syndiotactic specificities, whereas the tacticities of the obtained polymers were hardly affected by adding HMPA. In the polymerizations of bulkier monomers, such as NBnAAm and NPhEAAm, HMPA worked as the syndiotactic specificity inducer at higher temperatures, whereas 3Me3PenOH hardly influenced the stereospecificity, regardless of the temperatures. The phase‐transition behaviors of the aqueous solutions of poly(NNPAAm)s were also investigated. It appeared that the poly (NNPAAm) with racemo dyad content of 70% exhibited unusual large hysteresis between the heating and cooling processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4575–4583, 2008
New Method for Prediction of the Gurney Energy of High Explosives
Authors: Keshavarz Mohammad Hossein
Published: June 2008

An empirical new correlation is used to calculate the Gurney velocity as an important parameter for the estimation of explosive energy output without considering the heat contents of explosives and detonation products. The number of nitrogen molecules as well as the ratios of oxygen to carbon and hydrogen to oxygen are the fundamental factors in the new method. The new correlation may be applied to any CaHbNcOd explosive, in which b is nonzero, at any loading density. The calculated Gurney velocity for both pure and explosive formulations shows good agreement with respect to measured values. Moreover, there is no need to use any assumed decomposition reaction.
Computational study of colipase interaction with lipid droplets and bile salt micelles
Authors: Kerfelec Brigitte , Allouche Maya , Colin Damien , Van Eyck Marie Hélène , Brasseur Robert , Thomas Annick
Published: May 2008

Colipase is a key element in the lipase‐catalyzed hydrolysis of dietary lipids. Although devoid of enzymatic activity, colipase promotes the pancreatic lipase activity in physiological intestinal conditions by anchoring the enzyme at the surface of lipid droplets. Analysis of structures of NMR colipase models and simulations of their interactions with various lipid aggregates, lipid droplet, and bile salt micelle, were carried out to determine and to map the lipid binding sites on colipase. We show that the micelle and the oil droplet bind to the same side of colipase 3D structure, mainly the hydrophobic fingers. Moreover, it appears that, although colipase has a single direction of interaction with a lipid interface, it does not bind in a specific way but rather oscillates between different positions. Indeed, different NMR models of colipase insert different fragments of sequence in the interface, either simultaneously or independently. This supports the idea that colipase finger plasticity may be crucial to adapt the lipase activity to different lipid aggregates. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Effect of mixed macromolecular crowding agents on protein folding
Authors: Zhou Huan‐Xiang
Published: May 2008

In cells, proteins fold and unfold in the presence of macromolecules with various sizes and shapes. Recent experiments by Liang and coworkers (J Biol Chem 2004;279:55109–55116; J Mol Biol 2006;364:469–482) show that protein refolding is enhanced by a mixture of two different crowding agents relative to the individual crowding agents and an optimal mixing ratio exists. Here, we present a theory that predicts the existence of an optimal mixing ratio. The theory is based on models for calculating the changes in the chemical potentials of the folded and unfolded states by a mixture of crowders. The existence of an optimal mixing ratio results from the dependences of these chemical‐potential changes on crowder sizes and concentrations, which can be argued to be quite general. We further predict that, for any crowding agent, the stabilizing effect can be optimized both by varying the molecular weight and the mixing ratio of two species with different molecular weights. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Molecular strategies for protein stabilization: The case of a trehalose/maltose‐binding protein from Thermus thermophilus
Authors: Scirè Andrea , Marabotti Anna , Aurilia Vincenzo , Staiano Maria , Ringhieri Paola , Iozzino Luisa , Crescenzo Roberta , Tanfani Fabio , D'Auria Sabato
Published: May 2008

The trehalose/maltose‐binding protein (MalE1) is one component of trehalose and maltose uptake system in the thermophilic organism Thermus thermophilus. MalE1 is a monomeric 48 kDa protein predominantly organized in α‐helix conformation with a minor content of β‐structure. In this work, we used Fourier‐infrared spectroscopy and in silico methodologies for investigating the structural stability properties of MalE1. The protein was studied in the absence and in the presence of maltose as well as in the absence and in the presence of SDS at different p2H values (neutral p2H and at p2H 9.8). In the absence of SDS, the results pointed out a high thermostability of the MalE1 α‐helices, maintained also at basic p2H values. However, the obtained data also showed that at high temperatures the MalE1 β‐sheets underwent to structural rearrangements that were totally reversible when the temperature was lowered. At room temperature, the addition of SDS to the protein solution slightly modified the MalE1 secondary structure content by decreasing the protein thermostability. The infrared data, corroborated by molecular dynamics simulation experiments performed on the structure of MalE1, indicated that the protein hydrophobic interactions have an important role in the MalE1 high thermostability. Finally, the results obtained on MalE1 are also discussed in comparison with the data on similar thermostable proteins already studied in our laboratories. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Effects of uniaxial stress on the magnetic properties of thin films and GMR sensors prepared on polyimide substrates
Authors: Özkaya Berkem , Saranu Srinivasa Rao , Mohanan Senthilnathan , Herr Ulrich
Published: June 2008

The effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo‐spin‐valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (∼1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in‐plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto‐optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in‐plane four‐point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (Hext), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Complex oxide scintillators: Material defects and scintillation performance
Authors: Nikl M. , Laguta V. V. , Vedda A.
Published: June 2008

An overview of recognized structural defects, impurities and related trapping levels and their role in the scintillation mechanism is provided and discussed in single crystal materials belonging to tungstate, Ce‐ or Pr‐doped aluminum perovskite, garnet and finally to Ce‐doped silicate scintillators. New achievements and open problems in deeper understanding of electron and hole self‐trapping phenomena and of the nature of defects in the crystal structure and their ability to localize migrating charge carriers are indicated. Fast optical ceramics and nanocomposite materials are pointed out as possible future advanced scintillators. Such novel technologies can in principle explore materials which are not available in the bulk single crystal form, but their figure‐of‐merit is dramatically dependent on the surface‐interface defect states and related trapping and nonradiative recombination phenomena. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band‐structure calculations and electron momentum densities of AgCl and AgBr
Authors: Rathor A. , Arora G. , Ahuja B. L.
Published: June 2008

We report the band‐structure calculations and the first ever electron momentum densities of AgCl and AgBr. Isotropic Compton profiles of these compounds are measured at an intermediate resolution using a 20 Ci 137Cs Compton spectrometer. We have computed Compton profiles, energy bands, density of states and charge density using Hartree–Fock and density‐functional theories. It is seen that the Hartree–Fock theory‐based Compton line shapes are in a better agreement with the measurements. In addition, we have also derived the energy bands and density of states using the full‐potential linearized augmented plane‐wave method. The Compton data is also analyzed at the equal‐valence‐electron‐density scale. The present data shows that AgBr is more covalent than AgCl, which is in agreement with the present Mulliken's population analysis, valence charge densities and other available ionicity trends. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DC characteristics of AlGaN/GaN high electron mobility transistors
Authors: Inada Masaki , Nakajima Akira , Piao Guanxi , Shimizu Mitsuaki , Yano Yoshiki , Ubukata Akinori
Published: June 2008

The dependence of DC operating characteristics on the device dimensions in AlGaN/GaN HEMTs is systematically obtained varying the device parameters in relatively wide range. The maximum transconductance gm,max and the maximum drain current ID,max depend on both the source‐gate distance LSG and the gate length LG rather than LG only, and proportional to (LSG+LG)–0.5, which is different from the case of the GaAs or Si FET model. Influence of the source‐gate distance LSG on the DC characteristics of AlGaN/GaN high electron mobility transistors is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier‐density‐dependent increase and suppression of optical gain in T‐shaped quantum‐wire lasers
Authors: Yoshita Masahiro , Okano Makoto , Ihara Toshiyuki , Akiyama Hidefumi , Huai Ping , Ogawa Tetsuo , Pfeiffer Loren N. , West Ken W.
Published: June 2008

Carrier‐density dependence of the optical‐gain spectra were studied for an undoped T‐shaped quantum‐wire (T wire) laser by optical pumping at 4 K. The gain appeared at a low excitation power of 3 mW corresponding to the carrier density of about 3 × 105 cm–1 in the T wire. As the carrier density was increased, the peak gain increased, but it reached a maximum value of about 1 × 104 cm–1 at the carrier density of 1 × 106 cm–1 and then decreased hereafter. This peculiar gain evolution dependent on the carrier density was not explained by a simple free‐electron model, which suggests significant contributions of the enhanced Coulomb interactions to the optical gain in the T‐wire laser. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural, optical, and electrical characterizations of epitaxial lifted‐off InGaAs/InAlAs metamorphic heterostructures bonded on AlN ceramic substrates
Authors: Jeong Y. , Shindo M. , Takita H. , Akabori M. , Suzuki T.
Published: June 2008

We investigated epitaxial lift‐off (ELO) of In0.57Ga0.43As/In0.56Al0.44As metamorphic high electron mobility heterostructures and their van der Waals bonding (VWB) on AlN ceramic substrates. Structural, optical, and electrical characterizations were carried out for samples obtained by ELO and VWB, in comparison with on‐wafer counterparts before ELO. We confirmed a strain release after ELO and VWB from xray diffraction, and observed a consequent photoluminescence energy shift. The ELO samples exhibit very high electron mobilities owing to the high indium contents and successful ELO and VWB processes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Attribute control charts using generalized zero‐inflated Poisson distribution
Authors: Chen Nan , Zhou Shiyu , Chang Tzyy‐Shuh , Huang Howard
Published: June 2008

This paper presents a control charting technique to monitor attribute data based on a generalized zero‐inflated Poisson (GZIP) distribution, which is an extension of ZIP distribution. GZIP distribution is very flexible in modeling complicated behaviors of the data. Both the technique of fitting the GZIP model and the technique of designing control charts to monitor the attribute data based on the estimated GZIP model are developed. Simulation studies and real industrial applications illustrate that the proposed GZIP control chart is very flexible and advantageous over many existing attribute control charts. Copyright © 2008 John Wiley & Sons, Ltd.
Gaussian approximation of exponential type orbitals based on B functions
Authors: Pinchon Didier , Hoggan Philip E.
Published: May 2008

This work gives new, highly accurate optimized gaussian series expansions for the B functions used in molecular quantum mechanics. These functions are generally chosen because of their compact Fourier transform, following Shavitt. The inverse Laplace transform in the square root of the variable is used for Gauss quadrature in this work. Two procedures for obtaining accurate gaussian expansions have been compared for the required extended precision arithmetic. The first is based on Gaussian quadratures and the second on direct optimization. Both use the Maple computer algebra system. Numerical results are tabulated and compared with previous work. Special cases are found to agree before pushing the optimization technique further. The optimal gaussian expansions of B functions obtained in this work are available for reference. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Molecular properties calculations using the q‐integral method
Authors: de Oliveira Heibbe C. B. , Esteves Cristiano S. , Gargano Ricardo , Chaer Do Nascimento Marco A. , Malbouisson Luiz A. C. , Mundim Kleber C.
Published: May 2008

The q‐Integral method, based on the q‐Exponential function, has been recently introduced as an alternative approach to calculate the two‐electron integrals which appear in ab initio atomic and molecular quantum mechanical calculations. The advantage of this procedure is that the CPU time for calculating of two‐electron integrals is substantially reduced when compared with the usual one. The objective of this work is to investigate the accuracy of the q‐Integrals as a function of the internuclear distance for molecular systems. To this purpose we employed the q‐Integrals to construct the potential energy surface (PES) for the H2 molecule and used the PES to determine the rovibrational levels and spectroscopic constants of the molecule, which are properties very sensitive to the form of the PES. The results obtained are in good agreement with the ones obtained through the standard procedure of calculating the two‐electron integrals, implying that the q‐Integral method is accurate enough to be used in any molecular quantum mechanical calculation. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
Measuring the 13C content of soil‐respired CO2 using a novel open chamber system
Authors: Midwood Andrew J. , Thornton Barry , Millard Pete
Published: June 2008

Carbon dioxide respired by soils comes from both autotrophic and heterotrophic respiration. 13C has proved useful in differentiating between these two sources, but requires the collection and analysis of CO2 efflux from the soil. We have developed a novel, open chamber system which allows for the accurate and precise quantification of the δ13C of soil‐respired CO2. The chamber was tested using online analyses, by configuring a GasBench II and continuous flow isotope ratio mass spectrometer, to measure the δ13C of the chamber air every 120 s. CO2 of known δ13C value was passed through a column of sand and, using the chamber, the CO2 concentration stabilized rapidly, but 60 min was required before the δ13C value was stable and identical to the cylinder gas (−33.3‰). Changing the chamber CO2 concentration between 200 and 900 µmol.mol−1 did not affect the measured δ13C of the efflux. Measuring the δ13C of the CO2 efflux from soil cores in the laboratory gave a spread of ±2‰, attributed to heterogeneity in the soil organic matter and roots. Lateral air movement through dry sand led to a change in the δ13C of the surface efflux of up to 8‰. The chamber was used to measure small transient changes (±2‰) in the δ13C of soil‐respired CO2 from a peaty podzol after gradual heating from 12 to 35°C over 12 h. Finally, soil‐respired CO2 was partitioned in a labelling study and the contribution of autotrophic and heterotrophic respiration to the total efflux determined. Potential applications for the chamber in the study of soil respiration are discussed. Copyright © 2008 John Wiley & Sons, Ltd.
The gas‐phase interactions of TEMPO radicals with Fe+ ions
Authors: Kazazić Snježana P. , Klasinc Leo , Rožman Marko , Srzić Dunja
Published: June 2008

The gas‐phase ligation of the 2,2,6,6‐tetramethylpiperidyl‐1‐oxide (TEMPO) radical (1) and its 4‐hydroxy derivative (2) with Fe+ ions in a 3 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer was investigated. Triple ligation may occur: the first ligation produces a transient species prone to either charge exchange or a stable second ligation; the third ligand adds slowly, with fragmentation. 1 and 2 differ in that 1 binds exclusively at the nitroxyl oxygen while 2 also binds at the OH site after the loss of a H‐radical. Calculations combined with steric considerations support such a mechanism for 2. The site and the mechanism of the important side reaction of 1 that involves OH addition from a water impurity to yield an FeR species remain unexplained. Copyright © 2008 John Wiley & Sons, Ltd.
Environmental flow methodologies to protect fisheries resources in human‐modified large lowland rivers
Authors: Huckstorf Volker , Lewin Wolf‐Christian , Wolter Christian
Published: May 2008

The flow regimes of temperate large lowland rivers are manipulated to provide various services for society. Most water policy decisions are based on economic considerations, with little or no consideration toward fish conservation and fisheries. The prerequisite for a stronger implementation of these interests in water policy decisions is the development of appropriate tools for assessing the adequate flow needed to protect fish diversity and fisheries resources.

From the 1970s onwards, environmental flow methodologies (EFMs) have been developed primarily to protect endangered fish species and to maintain fisheries resources in human‐modified rivers. Until now, their application had mainly been restricted to small upland rivers and headwater streams. Here, we investigate the applicability of commonly used EFMs for predicting and quantifying the consequences of flow manipulation on fish and fisheries of regulated large lowland rivers.

Among the range of environmental flow methods currently available, habitat simulation methods are promising tools to assess adequate flow and to quantify the consequences of flow manipulation on the temporal and spatial availability of littoral habitats important for fish. However, habitat simulation methods may be effective only with those fish species whose recruitment is influenced by the availability of those habitats. To increase prediction accuracy, habitat simulation methods have to be linked to population dynamic models. More research is needed to improve understanding of the mechanisms controlling the dynamics of populations and assemblages in regulated large lowland rivers. Copyright © 2008 John Wiley & Sons, Ltd.
Quantifying channel planform and physical habitat dynamics on a large braided river using satellite data—the Brahmaputra, India
Authors: Boruah Sanchita , Gilvear David , Hunter Peter , Sharma Nayan
Published: May 2008

This paper presents the results of a trialling of the use of Indian Remote Sensing (IRS) satellite imagery for mapping the geomorphology and physical habitat of the Brahmaputra River in Assam, India. The study was undertaken on a 110 km reach as the river emerges out of the Himalayas; a reach with a complex braid pattern and high levels of channel instability. Image analysis on four sets of IRS data encompassing a period of 13 years (1990–2002) was undertaken to detect basic changes in the extent and pattern of low flow channels, vegetated islands, exposed sand bars and floodplain vegetation. Simple unsupervised classification techniques were applied to the images. The water surface of the low flow braided channel network, however was mapped more accurately using the GROW facility within ENVI 4.1; a technique based upon mapping areas within a given number of standard deviations in terms of pixel values within a training area. Subsequent to this unsupervised classification of the water surface area allowed classification of the water in to three water types based on depth and separation of isolated pools and backwaters from the channels conveying flow. Overall classification accuracies of 82.5% were achieved in relation to mapping physical habitat; varying between 86 and 95% for the four different dates. Analysis of the nature of channel planform and habitat change showed that there has been a 3.7% increase in the active channel area consisting of exposed sediment and water within the river corridor. This substantiated a general awareness of an increase in the width and reduction in depth of the Brahmaputra River over the last few decades. The analysis also depicts the occurrence of a major avulsion and the highly dynamic nature of the braided channel network and sand bars.

Overall the study demonstrated that simple classification methods when applied to satellite data, capturing imagery in the visible and near infra‐red, can be used to measure important changes in the geomorphology and physical habitats that make up the fluvial system of the Brahmaputra River. The approach may also be more widely applicable to large river systems comprising a mosaic of water, exposed sediment and spectrally different vegetation communities. Copyright © 2008 John Wiley & Sons, Ltd.
The relationships between benthic macroinvertebrates and biotic and abiotic environmental characteristics downstream of the Yahagi Dam, Central Japan, and the State Change Caused by inflow from a Tributary
Authors: Takao Akira , Kawaguchi Yôichi , Minagawa Tomoko , Kayaba Yuichi , Morimoto Yukihiro
Published: May 2008

Anthropogenic modifications have disrupted aquatic ecosystems by modification of the flow regime and transport of sediment. The impacts of dams are believed to be very large, but, despite the abundance of dams in monsoonal Asia, great scientific uncertainty still exists about the effect of dams on macroinvertebrates. Therefore, we studied macroinvertebrate assemblages at three reaches (downstream of a dam, downstream of a confluence and on a tributary) of the Yahagi River, central Japan, to confirm the impact of long‐term impoundment on the relationships between macroinvertebrate assemblages and biotic and abiotic environmental factors and also the role of a major tributary in community shift.

Four Surber samples and associated physical measurements (depth, velocity and substrate composition) were taken from four study sites (riffles) at each study reach during the period from 10 to 21 February 2004. Drifting materials (zooplankton, POM and bedload sediment) and periphyton were also sampled. Significant differences were found in the macroinvertebrate fauna of these different reaches. Faunal distributions downstream of the dam were severely altered, with high macroinvertebrate abundance and low taxa richness in contrast to those in the tributary. The two‐way indicator species analysis (TWINSPAN) classification clearly distinguished these samples from the others. Based on nonmetric multidimensional scaling (NMS) ordination and correlation analysis (environmental variables vs. NMS axis score), these differences in community structure reflected changes in substrate composition and quantity and quality of suspended and benthic FPOMs. Our observations suggest that while dam‐derived zooplankton and reduced sediment transport had a great impact on the fauna, the tributary inflow, with a catchment size of less than 20% of that above the dam, acted as a major source of sediment input and facilitated macroinvertebrate community recovery. Copyright © 2008 John Wiley & Sons, Ltd.
Trophic gradients in a large‐river Delta: ecological structure determined by connectivity gradients in the Danube Delta (Romania)
Authors: Coops Hugo , Buijse Laura L. , Buijse Anthonie D. (Tom) , Constantinescu Adrian , Covaliov Silviu , Hanganu Jenica , Ibelings Bas W. , Menting Geert , Navodaru Ion , Oosterberg Willem , Staras Mircea , Török Liliana
Published: May 2008

There are over 300 lakes interconnected by riverbranches and man‐made canals in the Danube Delta (Romania). A multidisciplinary survey of these riverine lakes situated in large wetland complexes was made comprising hydrological modelling, remote sensing and monitoring of water quality, plankton, aquatic vegetation and fish communities. Between‐lake differences in water quality and aquatic vegetation cover were inferred from satellite image. Based on channel and lake dimensions, hydrological characteristics of the lakes in the delta were determined: hydrological distance from a riverbranch, residence time and impact of reed water. Water‐quality and biotic parameters (phyto‐ and zooplankton, submerged plants and fish) were sampled in a comparative survey in June 1997–1999 in subsets of the lakes. In a follow‐up study in 2001–2002, seasonality of aquatic vegetation and fish were recorded.

A clear distinction was found in three lake types: (1) inflow lakes at short distance to the river, with a high flushing rate, high load of suspended minerals but low chlorophyll concentrations, high cover of floating and submerged vegetation and dominance of eurytopic fish; (2) large, relatively deep lakes with moderately long residence time, high Potamogeton‐cover that collapses during summer, and dominated by eurytopic fish; (3) smaller, isolated lakes at the longest distance from the river, with long residence time, of which the water quality is strongly influenced by water flows through large floating reedbeds (‘blackwater’), with a high vegetation cover of Ceratophyllum demersum and Nitellopsis obtusa throughout the summer and a limnophilic fish community tolerant for low oxygen conditions.

Aquatic vegetation showed a clear seasonality related to the interaction between plant development and light conditions. Seasonal changes in fish distribution within the system merely followed the vegetation trends in different lakes and the conditions in the river channels.

Past trends in the trophic gradient are discussed in the context of hydromorphological modifications in the Delta. There is a high potential for restoring natural processes owing to the high connectivity and large scale of the system. Copyright © 2008 John Wiley & Sons, Ltd.
Florida river flow patterns and the Atlantic multidecadal oscillation
Authors: Kelly Martin H. , Gore James A.
Published: May 2008

A major step in developing legislatively mandated ecological flows for watercourses in Florida, USA is the selection of an appropriate baseline flow period. Recently climatologists have established a link between multidecadal periods of warming and cooling of the Atlantic Ocean (the Atlantic Multidecadal Oscillation (AMO)) and rainfall patterns across much of North America. During an AMO warm period (pre‐1970), much of North America received less than average rainfall, while during a multidecadal cool period (post‐1970), much of North America experienced above normal rainfall. There are exceptions to this general trend with some areas of North America showing an opposite relationship with the AMO. Peninsular Florida is one of these exceptions. While analysing flows on a number of rivers in south–central Florida, we observed a step rather than a monotonic trend in flows consistent with a switch from a warm multidecadal period to a cool multidecadal period. We examined river flows at all gaging sites throughout Florida and the southeast United States that had flow records of 60 years or more. Three river flow patterns were clearly discerned: a Southern River Flow Pattern (SRP) where flows are seasonally greatest during the summer months (June–September); a Northern River Flow Pattern (NRP) where flows are seasonally greatest in the spring and a Bimodal River Flow Pattern (BRP) with distinct peaks in rainfall and flow both in spring and summer. Those rivers with a BRP occur in a band that stretches diagonally from the northeast corner of Florida (St. Marys River) and runs in a southwest direction to the big bend area of the state near the mouth of the Suwannee River. Rivers to the north of this line exhibit the NRP, while rivers to the south of this line exhibit the SRP. Rivers with the SRP exhibited consistently lower flows during the AMO cool period and consistently higher flows during the AMO warm period. Differences in flow volumes between multidecadal periods averaged 30% in SRP rivers. Rivers with a NRP showed an opposite trend. Most convincingly, rivers with the BRP exhibited both trends, the spring mode responded similarly to the northern rivers while the summer mode followed the southern river trend. These results have important implications not only for the establishment of ecological flows, but also for water supply planning and development, flood control and stream ecology in general, since there are considerable differences in the magnitude of flows that should naturally be expected between multidecadal periods. Relatively large decreases and increases in flow are attributable to rainfall differences between multidecadal periods. Copyright © 2008 John Wiley & Sons, Ltd.
Increased growth and distribution of Ephemerella aurivillii (Ephemeroptera) after hydropower regulation of the Aurland catchment in Western Norway
Authors: Raddum Gunnar G. , Fjellheim Arne , Velle Gaute
Published: May 2008

The Aurland watershed has been regulated for hydropower since the establishment of a series of power plants during the period 1970–1983. This resulted in a strong reduction of the flow in the river Vassbygdelvi, the inlet river to lake Vassbygdvatn. In the downstream river Aurland, the flow has varied, but from 2000 the intention has been to simulate pre‐regulation winter flow as far as possible. The temperature in the river Vassbygdelvi has increased from about 1500 degree‐days per year before regulation to above 2000 degree‐days after regulation. In the river Aurland the thermal regime, expressed as degree‐days per year, was more or less unchanged, but a small reduction in the summer temperature and a corresponding increase during other periods was observed. The mayfly Ephemerella aurivillii (Bengtsson) was not recorded in Vassbygdelvi prior to regulation, but became abundant in the river after. Full‐grown larvae were recorded 1–2 months earlier in the river Vassbygdelvi than in the river Aurland after regulation. E. aurivillii has a 1‐year life cycle with imagos present in June–August. Young larvae occurred from June to early September. It is concluded that larvae of E. aurivillii could not complete their life cycle within 1 year before regulation in the river Vassbygdelvi, due to low temperature. The study demonstrates how temperature can regulate the distribution of a species with a strict 1‐year life cycle. Copyright © 2008 John Wiley & Sons, Ltd.
Hydraulic resistance of some selected vegetation in open channel Flows
Authors: Rhee Dong Sop , Woo Hyoseop , Kwon Bo Ae , Ahn Hong Kyu
Published: May 2008

Vegetation in rivers has important roles in improving and restoring river environment. Other than it adds high aesthetic value to revetments, that it can be used as a levee protection in environmental friendly way. In open channel hydraulics, vegetation often causes changes in the flow resistance, usually resulting in the increase of flood stage. Both experimental and numerical researches have been conducted on flow resistance of vegetation in open channels, however, the researches were based mostly on the vegetation found in the region where the researches were conducted, and this restricts the generality of the results.

In this study, three Korean natural vegetations, Zoysia matrella (Korean zoysia), Pennisetum alopecuroides (L.) Spreng. (Korean native vegetation) and Phragmites communis Trin. (Korean reed) were used in flume tests on the effect of vegetation in the channel on flow resistance. ‘n‐VR’ retardance curves were developed for each grass. All the grasses were tested under unmown conditions. Z. matrella was tested under fully submerged condition and other two were tested under both submerged and un‐submerged conditions.

Resistance coefficient, expressed as Manning's n, converged to about 0.027 (total roughness) for Z. matrella as VR increased. Resistance coefficients for other plants were found affected by the states of the plants, that is, whether they were ‘green’ or ‘dormant’. Generally, resistance coefficients are higher when plants are ‘green’ than when they are ‘dormant’. This is because the resistance coefficient is influenced by the leaf elements of vegetation on the river flow in addition to the stem of vegetation. The interaction between the bending part of vegetation and the water surface can also increase the resistance coefficient. In terms of water depth, P. communis Trin were found more affected on the resistance coefficients compared to Z. matrella and P. alopecuroides (L.) Spreng. Copyright © 2008 John Wiley & Sons, Ltd.
Inducing dendrite formation using an Atomic Force Microscope tip
Authors: Zhang Gengxin , Weeks Brandon L.
Published: June 2008

Atomic force microscope (AFM) tip‐induced nucleation, and dendrite growth of vapor deposited PETN films on Si (100) have been investigated at room temperature. The AFM tip induces a change from smooth and flat morphology to islands and dendrites, which is owing to the lowering and vanishing of 2‐D nucleation barrier at the tip contact area; this action gives rise to the formation of large islands in the scanned area and dendrite growth along the scanning boundary. SCANNING 30: 228–231, 2008. © 2008 Wiley Periodicals, Inc.
Reuptake of L‐DOPA‐derived extracellular DA in the striatum of a rodent model of Parkinson's disease via norepinephrine transporter
Authors: Arai Akira , Tomiyama Masahiko , Kannari Kazuya , Kimura Tamaki , Suzuki Chieko , Watanabe Mitsunori , Kawarabayashi Takeshi , Shen Huo , Shoji Mikio
Published: May 2008

To determine the role of norepinephrine transporter in reuptake of L‐DOPA‐derived extracellular DA in the DA‐denervated Parkinsonian striatum, we examined extracellular DA levels in the striatum of 6‐hydroxyDA‐lesioned rats that received L‐DOPA (50 mg/kg with 12.5 mg/kg of benserazide) and L‐DOPA plus desipramine (25 mg/kg), a selective norepinephrine reuptake inhibitor, using in vivo microdialysis. The pretreatment with desipramine increased levels of extracellular DA derived from administrated L‐DOPA in the DA‐denervated striatum. This study provides evidence that L‐DOPA‐derived DA is taken up by the norepinephrine transporter, instead of the dopamine transporter, in the striatum with dopaminergic denervation. This result suggests that the norepinephrine transporter could be a promising target in the treatment for Parkinson's disease. Synapse 62:632–635, 2008. © 2008 Wiley‐Liss, Inc.
Oxidative stress, DNA damage, and antioxidant enzyme activity induced by hexavalent chromium in Sprague‐Dawley rats
Authors: Patlolla Anita K. , Barnes Constance , Yedjou Clement , Velma V. R. , Tchounwou Paul B.
Published: May 2008

Chromium is a widespread industrial compound. The soluble hexavalent chromium Cr (VI) is an environmental contaminant widely recognized as carcinogen, mutagen, and teratogen toward humans and animals. The fate of chromium in the environment is dependent on its oxidation state. The reduction of Cr (VI) to Cr (III) results in the formation of reactive intermediates leading to oxidative tissue damage and cellular injury. In the present investigation, Potassium dichromate was given intraperitoneally to Sprague‐Dawley rats for 5 days with the doses of 2.5, 5.0, 7.5, and 10 mg/kg body weight per day. Oxidative stress including the level of reactive oxygen species (ROS), the extent of lipid peroxidation and the activity of antioxidant enzymes in both liver and kidney was determined. DNA damage in peripheral blood lymphocytes was determined by single‐cell gel electrophoresis (comet assay). The results indicated that administration of Cr (VI) had caused a significant increase of ROS level in both liver and kidney after 5 days of exposure, accompanied with a dose‐dependent increase in superoxide dismutase and catalase activities. The malondialdehyde content in liver and kidney was elevated as compared with the control animals. Dose‐ and time‐dependent effects were observed on DNA damage after 24, 48, 72, and 96 h posttreatment. The results obtained from the present study showed that Cr (VI) could induce dose‐ and time‐dependent effects on DNA damage, both liver and kidney show defense against chromium‐induced oxidative stress by enhancing their antioxidant enzyme activity. However, liver was found to exhibit more antioxidant defense than the kidney. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2009.
Balanced association algorithm for IEEE 802.11 extended service areas
Authors: Ekici O. , Yongacoglu A.
Published: May 2008

Most wireless local area network performance estimations are done with the assumption of uniformly distributed (UD) users. In practice, however, stations (STAs) are distributed unevenly among access points (APs) in an extended service area, causing congested hot‐spots (HS) and under‐utilized APs. Considering a typical network is made up of multiple APs, having some nodes carrying excessive loads degrades the overall network performance. The system performance can be improved by associating STAs efficiently throughout the network, in a sense sharing the network resources fairly among APs and thus relieving congestion. The association algorithm currently employed in IEEE 802.11 systems, that is specifically designed for residential and small office environments, takes into account signal strength as the only parameter and associates STAs to the closest (in signal strength sense) AP, ignoring its load. Novel user association algorithms are required to solve the problems commonly seen in corporate network environments spanning multiple APs, namely congestion relief and resource sharing. In this work, a distributed and online association algorithm is proposed that demonstrates improved average throughput performance, a balanced load distribution as well as fairness across the network compared to the conventional algorithm. Copyright © 2008 John Wiley & Sons, Ltd.
Polyglycerol esters: Optimization and techno‐economic evaluation
Authors: Garti N. , Aserin A. , Zaidman B.
Published: June 2008

Optimization of the two‐step reaction for preparation of polygly‐cerol esters of fatty acids from the industrial point of view has been studied. Parameters such as nature of the alkaline catalyst, tempera‐ture and time of the reaction have been examined. It was found that the polymerization process needs 260–280 C in the presence of inert gas and 2.5 mol % of NaOH as catalyst. The esterification can be accomplished in the absence of additional catalyst and temperatures as low as 230 C. A simulation model of a chemical plant has been used for evaluation of cost of the production of such emulsifiers.
A Sharpened Nuclearity Condition and the Uniqueness of the Vacuum in QFT
Authors: Dybalski Wojciech
Published: May 2008

It is shown that only one vacuum state can be prepared with a finite amount of energy and it appears, in particular, as a limit of physical states under large timelike translations in any theory which satisfies a phase space condition proposed in this work. This new criterion, related to the concept of additivity of energy over isolated subsystems, is verified in massive free field theory. The analysis entails very detailed results about the momentum transfer of local operators in this model.