bluuebunny/crossref_metadata_2025_split huggingface dataset:
Repeated freeze–thaw events affect leaching losses of nitrogen and dissolved organic matter in a forest soil
Authors: Hentschel Kerstin , Borken Werner , Matzner Egbert 
Published: September 2008

AbstractFreezing and thawing may substantially influence the rates of C and N cycling in soils, and soil frost was proposed to induce NO$ _3^- $ losses with seepage from forest ecosystems. Here, we test the hypothesis that freezing and thawing triggers N and dissolved organic matter (DOM) release from a forest soil after thawing and that low freezing temperatures enhance the effect. Undisturbed soil columns were taken from a soil at a Norway spruce site either comprising only O horizons or O horizons + mineral soil horizons. The columns were subjected to three cycles of freezing and thawing at temperatures of –3°C, –8°C, and –13°C. The control columns were kept at constant +5°C. Following the frost events, the columns were irrigated for 20 d at a rate of 4 mm d–1. Percolates were analyzed for total N, mineral N, and dissolved organic carbon (DOC). The total amount of mineral N extracted from the O horizons in the control amounted to 8.6 g N m–2 during the experimental period of 170 d. Frost reduced the amount of mineral N leached from the soil columns with –8°C and –13°C being most effective. In these treatments, only 3.1 and 4.0 g N m–2 were extracted from the O horizons. Net nitrification was more negatively affected than net ammonification. Severe soil frost increased the release of DOC from the O horizons, but the effect was only observed in the first freeze–thaw cycle. We found no evidence for lysis of microorganisms after soil frost. Our experiment did not confirm the hypothesis that soil frost increases N mineralization after thawing. The total amount of additionally released DOC was rather low in relation to the expected annual fluxes.
Effects of experimental soil frost on the fine‐root system of mature Norway spruce
Authors: Gaul Dirk , Hertel Dietrich , Leuschner Christoph 
Published: September 2008

AbstractSoil‐frost events may influence the dynamics of fine roots and therefore affect root‐derived C fluxes to the soil. We studied the impact of soil frost on the fine‐root dynamics of Norway spruce (Picea abies [L.] Karst.) by a replicated snow‐removal experiment in a mature forest in SE Germany. Snow removal in the three treatment plots reduced soil temperature significantly with minima <–5.5°C in the O layer while the snow‐covered control plots never reached temperatures below the freezing point. Sequential soil coring in the O layer at the beginning and at the end of the soil‐frost period as well as after thawing revealed that the soil frost treatment increased fine‐root mortality by 29%. However, enhanced fine‐root production in the snow‐removal plots nearly compensated for the fine‐root losses caused by low temperatures. These findings were confirmed by minirhizotron observations in the O layer and the upper 25 cm of the mineral soil showing that relative fine‐root loss was by far higher in the snow‐removal plots than in the control plots. Compensatory fine‐root production in the snow‐removal plots exceeded fine‐root production in the control plots during a period of 8 weeks after the soil frost application by 39% in the O layer while it was similar in both plot types in the mineral soil. Sequential coring and minirhizotron observations led to substantially different fine root–longevity estimates for the soil frost period. However, in both cases, the snow‐removal treatment was characterized by a significant reduction in root longevity indicating a faster fine‐root turnover. As a consequence, experimental soil frost enhanced the C input to the soil via root death at our study site by approx. 42 g m–2 and stimulated the C investment towards the root system of the spruce trees due to a higher sink activity.
Repeated drying–rewetting cycles and their effects on the emission of CO2, N2O, NO, and CH4 in a forest soil
Authors: Muhr Jan , Goldberg Stefanie D. , Borken Werner , Gebauer Gerhard 
Published: September 2008

AbstractProlonged summer droughts due to climate change are expected for this century, but little is known about the effects of drying and wetting on biogenic trace‐gas fluxes of forest soils. Here, the response of CO2, N2O, NO, and CH4 fluxes from temperate forest soils towards drying–wetting events has been investigated, using undisturbed soil columns from a Norway spruce forest in the “Fichtelgebirge”, Germany. Two different types of soil columns have been used for this study to quantify the contribution of organic and mineral horizons to the total fluxes: (1) organic horizons (O) and (2) organic and mineral soil horizons (O+M). Three drying–wetting treatments with different rewetting intensities (8, 20, and 50 mm of irrigation d–1) have been compared to a constantly moist control to estimate the influence of rainfall intensity under identical drying conditions and constant temperature (+15°C). Drought significantly reduced CO2, N2O, and NO fluxes in most cycles. Following rewetting, CO2 fluxes quickly recovered back to control level in the O columns but remained significantly reduced in the O+M columns with total CO2 fluxes from the drying–wetting treatment ranging approx. 80% of control fluxes. Fluxes of N2O and NO remained significantly reduced in both O and O+M columns even after rewetting, with cumulative fluxes from drying–wetting treatments ranging between 20% and 90% of the control fluxes, depending on gas and cycle. Fluxes of CH4 were small in all treatments and seem to play no significant role in this soil. No evidence for the release of additional gas fluxes due to drying–wetting was found. The intensity of rewetting had no significant effect on the CO2, N2O, NO, and CH4 fluxes, suggesting that the length of the drought period is more important for the emission of these gases. We can therefore not confirm earlier findings that fluxes of CO2, N2O, and NO during wetting of dry soil exceed the fluxes of constantly moist soil.
Anti‐Biofouling Properties of Polymers with a Carboxybetaine Moiety
Authors: Tada Susumu , Inaba Chika , Mizukami Kazuya , Fujishita Shigeto , Gemmei‐Ide Makoto , Kitano Hiromi , Mochizuki Akira , Tanaka Masaru , Matsunaga Takayuki 
Published: September 2008

AbstractThe resistance of random copolymers of BMA and CMB against biofouling was evaluated. The amount of proteins adsorbed onto the CMB copolymers was smaller than that onto other polymers (non‐ionic polymers and copolymers of ordinary ionic monomers and BMA) and decreased with an increase in the content of CMB residues. Furthermore, there was a dramatic decrease in the number of cells (platelets and fibroblasts) that adhered to the CMB copolymers compared with that to other polymers. In contrast with this, CMB copolymers were slightly perturbative to both complement and coagulation systems. However, the overall results suggest that zwitterionic moieties are effective for making polymer materials biocompatible due to their excellent anti‐biofouling property.magnified image
Synergistic Effect and Hierarchical Nanostructure Formation in Mixing Two Designer Lipid‐Like Peptide Surfactants Ac‐A6D‐OH and Ac‐A6K‐NH2
Authors: Khoe Ulung , Yang Yanlian , Zhang Shuguang 
Published: September 2008

AbstractWe here report the nanostructures from combinational self‐assembly of two designer lipid‐like peptides Ac‐A6D‐OH and Ac‐A6K‐NH2 using dynamic light scattering (DLS) and atomic force microscopy (AFM). The synergistic phenomenon is observed by measuring the critical aggregation concentrations (CACs) of these two mixed peptides, in different molar ratios by DLS. The nanoropes were observed in AFM images at a molar ratio of Ac‐A6D‐OH/Ac‐A6K‐NH2 = 1:1, and the thin film formation with aligned nanoropes is shown at a molar ratio of 2:1. The well aligned nanoropes at the molar ratio of Ac‐A6D‐OH/Ac‐A6K‐NH2 = 2:1 indicated the competition factor between the electrostatic repulsion according to DLVO theory and the hydrophobic interaction arising from the long side chains on lysine residues. This study will further our understanding for designing new nanomaterials based on designer lipid‐like peptide surfactants.magnified image
Polyurethanes Based on Castor Oil: Kinetics, Chemical, Mechanical and Thermal Properties
Authors: Hablot Elodie , Zheng Dan , Bouquey Michel , Avérous Luc 
Published: September 2008

AbstractPolyurethanes based on vegetable oil were synthesized with castor oil and toluene diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate, using dibutyltin dilaurate as a catalyst. The effects of the nature of the diisocyanate on the evolution of the kinetics, as well as the physical and mechanical properties and the thermal stability, of the different synthesized polyurethanes were investigated, and these complement data from the literature on equivalent systems. The polymerization kinetics, degree of swelling and mechanical properties were greatly affected by the diisocyanate nature, whereas the rheological properties and thermal stability were found to be similar for all polyurethanes.magnified image
Free‐Standing, Thermostable, Micrometer‐Scale Honeycomb Polymer Films and their Properties
Authors: Bormashenko Edward , Schechter Alex , Stanevsky Oleg , Stein Tamir , Balter Sagi , Musin Albina , Bormashenko Yelena , Pogreb Roman , Barkay Zahava , Aurbach Doron 
Published: September 2008

AbstractA method of manufacturing free‐standing, micrometer‐scale honeycomb polyetherimide films is reported for the first time. Films are manufactured with a dip‐coating technique under water‐assisted self‐assembly. It is shown that the addition of poly(organosilane/siloxane)s and poly(ethylene glycol) allows the formation of regular honeycomb patterns. The films demonstrated the high thermal stability inherent for polyetherimide. The wetting properties of films are reported. The presence of nanopores was revealed with SEM imaging of the films. The makeup of the films allows their use as asymmetric membranes for reverse osmosis and ultrafiltration.magnified image
Crystallization Kinetics and Hydrophilicity Improvement of Biodegradable Poly(butylene succinate) in its Miscible Blends with Poly(ethylene oxide)
Authors: Lu Jiaoming , Qiu Zhaobin , Yang Wantai 
Published: September 2008

AbstractThe spherulitic morphology and growth, overall isothermal crystallization kinetics and hydrophilicity of PBSU were investigated by POM, DSC and WCA measurements in its miscible blends with PEO. The Hoffman‐Lauritzen equation was employed to analyze the spherulitic growth rates of neat and blended PBSU, which show a crystallization regime transition between regime II and III. The overall crystallization rates of PBSU decreased with increasing crystallization temperature, regardless of blend composition, while the crystallization mechanism does not change. A significant improvement in the hydrophilicity of PBSU can be achieved by blending with different weight fractions of PEO, which may be essential for the practical application of PBSU/PEO blends.magnified image
An Improved Rapid Synthesis of Oligo(p‐benzamide) Block Copolymers
Authors: König Hannah M. , Kilbinger Andreas F. M. 
Published: September 2008

AbstractWe describe a new synthesis that allows the preparation of oligo(p‐benzamide)s up to the heptamer on solid support without the need of semi‐temporary amide N‐protective groups. With increase in length, the solubility of oligo(p‐benzamide)s reduces dramatically. Even the tetra(p‐benzamide) is not soluble in common organic solvents. Therefore, solution syntheses of oligomers beyond the tetramer are not feasible. As will be shown in this paper, solid supported synthesis allows the preparation of even longer oligomers (up to the heptamer) in good yields. The high dilution on the solid support is most likely responsible for their pseudo‐solution‐like reactivity and the prevention of aggregation. This procedure is a significant improvement of previous syntheses and an important tool for the rapid exploration of supramolecular rod–coil copolymers based on oligoaramides.magnified image
Molecular Simulation Via Connectivity‐altering Monte Carlo and Scale‐jumping Methods: Application to Amorphous Polystyrene
Authors: Mulder Tim , Harmandaris Vagelis A. , Lyulin Alexey V. , van der Vegt Nico F. A. , Michels M. A. J. 
Published: September 2008

AbstractWell‐equilibrated atactic‐polystyrene (aPS) samples are obtained through the end‐bridging Monte Carlo (EBMC) algorithm. A coarse‐grained (CG) description of aPS is used; monomers are represented by two CG beads. The algorithm produces correct polymer conformations on all length scales, beyond the size of the CG beads. The code is very efficient, even though the acceptance of 0.001–0.005% is approximately 10–100 times lower than in the original EB code for PE. Systems of aPS of the order of 5000 monomers (50 chains of 100 monomers on average) can be equilibrated on all length scales within a week, in a single‐processor run. The computer code is also adequate for simulations of other polymers that have the same regularity in their sequence of chemical groups and that are modeled at the same or at a coarser level of description.magnified image
Geometries and Electronic Structures of Co‐Oligomers and Co‐Polymers Based on Tricyclic Nonclassical Thiophene: A Theoretical Study
Authors: Fu Yangwu , Shen Wei , Li Ming 
Published: September 2008

AbstractThe geometries and electronic properties of four copolymers based on tricyclic nonclassical thiophene were studied using DFT at the B3LYP/6‐31G(d) level. Bond lengths and their alternation, electron densities at BCPs, NICS, and WBIs were analyzed and correlated with the energy gap. The results show that the degree of conjugation increases upon main chain extension. The energy gap decreased steadily with increasing degree of polymerization. Conjugation is stronger in the central than in the outer section. The results suggest that the narrow HOMO/LUMO separation of tricyclic nonclassical thiophenes can be carried over to their co‐polymers by using them as building blocks for the co‐polymers.magnified image
Synthesis and NMR elucidation of novel penta‐cycloundecane amine derivatives as potential antituberculosis agents
Authors: Onajole Oluseye K. , Govender Thavendran , Makatini Maya , Kruger Hendrik G. 
Published: September 2008

AbstractThe synthesis and NMR elucidation of five novel penta‐cycloundecane amine derivatives are reported. These compounds are potential antituberculosis agents. The 1H and 13C spectra showed major overlapping of methine signals of the cage skeleton making it extremely difficult to elucidate these compounds. The overlapping occurs as a result of the additions made to the carbonyl carbon (C‐8/C‐11) of the cage. The two‐dimensional NMR technique proved to be a useful tool in overcoming this problem. All compounds reported are meso compounds thereby not only simplifying the NMR structure elucidation, but also making it indeed possible. Copyright © 2008 John Wiley & Sons, Ltd.
NMR spectroscopic elucidation of the structure and stereochemistry of tricyclic 3‐styrylpyrazolines
Authors: Tóth Gábor , Simon András , Jenei Attila , Jekő József , Lévai Albert 
Published: September 2008

AbstractDiastereomeric mixtures of tricyclic 3‐styrylpyrazolines have been prepared by the reaction of 3‐cynnamylidenechroman‐4‐ones and their 1‐thio analogs with hydrazine in hot acetic acid or propionic acid solutions. The diastereomeric mixtures were separated by column chromatography to obtain the pure diastereomers. The elucidation of their structure and stereochemistry and complete 1H and 13C assignments have been performed by a combination of various one‐ and two‐dimensional NMR experiments. Copyright © 2008 John Wiley & Sons, Ltd.
Hydrolytic Degradation and Monomer Recovery of Poly(butylene succinate) and Poly(butylene succinate/adipate) in the Melt
Authors: Tsuji Hideto , Yamamura Yoshiko , Ono Tomoyuki , Saeki Takashi , Daimon Hiroyuki , Fujie Koichi 
Published: September 2008

AbstractAliphatic dicarboxylic acid/aliphatic diol‐derived polyesters, poly(butylene succinate) and poly(butylene succinate/adipate), have been hydrolytically degraded in the melt in high‐temperature and high‐pressure water over a wide temperature range of 180–300 °C for periods of up to 30 min. The formation/decomposition of succinic acid (SA), adipic acid (AA), and butane‐1,4‐diol (BD), plus the molecular weight change of PBS and PBSA were then investigated. SA and AA were recovered at maximum yields of 65–80%, whereas BD was recovered at a maximum yield of only 30%, probably because of its decomposition. The obtained results were compared with those reported for aliphatic hydroxycarboxylic acid‐derived polyesters and aromatic dicarboxylic acid/aliphatic diol‐derived polyesters.magnified image
Discrete modelling of time‐dependent rockfill behaviour
Authors: Silvani Claire , Désoyer Thierry , Bonelli Stéphane 
Published: September 2008

AbstractThis modelling study deals with the time‐dependent behaviour of rockfill media, which is of particular interest during the life of rockfill dams. Breakage of rock blocks and crack propagation are the main processes responsible for rockfill creep and collapse. The modelling procedure presented here is performed on two scales: on the rock block scale, where the grain is taken to be an assembly of rigid particles initially endowed with cohesive bonds, and on the rockfill scale, which is taken to involve a set of breakable grains interacting via contact and friction processes. The grain breakage process is described in term of a thermodynamically consistent damage interface model, where the damage is a gradual delayed process. This model was implemented in a non‐smooth contact dynamics code. The effects of the main parameters involved were analysed by performing numerical studies. The ability of the model to predict the creep behaviour of rockfill media is confirmed by presenting several simulations. Copyright © 2008 John Wiley & Sons, Ltd.
Fast solvers with block‐diagonal preconditioners for linear FEM–BEM coupling
Authors: Funken Stefan A. , Stephan Ernst P. 
Published: September 2008

AbstractThe purpose of this paper is to present optimal preconditioned iterative methods to solve indefinite linear systems of equations arising from symmetric coupling of finite elements and boundary elements. This is a block‐diagonal preconditioner together with a conjugate residual method and a preconditioned inner–outer iteration. We prove the efficiency of these methods by showing that the number of iterations to preserve a given accuracy is bounded independent of the number of unknowns. Numerical examples underline the efficiency of these methods. Copyright © 2008 John Wiley & Sons, Ltd.
A model for interface cracks in layered orthotropic solids: Convergence of modal decomposition using the interaction integral method
Authors: Merzbacher M. J. , Horst P. 
Published: September 2008

AbstractThe mode‐partitioning problem for bimaterial interfaces is still not resolved by the classical fracture mechanics approach in a satisfactory manner. Stress oscillations and overlapping crack faces are a direct consequence of the rigorous solution of the elastic boundary value problem, if the constitutive law changes discontinuously across the interface. Conversely, continuously varying material properties, also referred to as functionally graded materials (FGM), avoid these physically not admissible drawbacks. In this case the crack tip fields are of the same nature as those known from homogeneous materials. Therefore, the well‐established stress intensity factor concept can be used without any changes. Following this motivation an FGM‐interface model for delaminated composite beam structures was developed and its characteristics with respect to the modal decomposition of the crack tip fields were investigated. The considered beam structures consisted of two orthotropic layers, each of a different material. The spatial variation of the material properties in the interface region was modeled by a tanh ‐function introducing one transition parameter that controlled the FGM‐gradient. Four load cases were analyzed for each structural configuration: either a unit normal force or a unit bending moment was imposed on each end of the split beam. Thus, any load case can be simply reconstructed from the presented results by means of superposition. The stress intensity factors for modes I and II were then evaluated using an interaction integral method along with the finite element method. The corresponding results are given depending on the mesh density of the interface region, the integration domain and the transition parameter. In this manner, the influence of the transition parameter on the mode ratio and on the convergence behavior of the modal decomposition scheme with respect to its integration domain was identified. Finally, the ability of the FGM‐interface model to represent bimaterial interfaces while still maintaining the advantages of crack analysis in homogeneous materials was highlighted. Copyright © 2008 John Wiley & Sons, Ltd.
Application of the X‐FEM to the fracture of piezoelectric materials
Authors: Béchet E. , Scherzer M. , Kuna M. 
Published: September 2008

AbstractThis paper presents an application of the extended finite element method (X‐FEM) to the analysis of fracture in piezoelectric materials. These materials are increasingly used in actuators and sensors. New applications can be found as constituents of smart composites for adaptive electromechanical structures. Under in service loading, phenomena of crack initiation and propagation may occur due to high electromechanical field concentrations. In the past few years, the X‐FEM has been applied mostly to model cracks in structural materials. The present paper focuses at first on the definition of new enrichment functions suitable for cracks in piezoelectric structures. At second, generalized domain integrals are used for the determination of crack tip parameters. The approach is based on specific asymptotic crack tip solutions, derived for piezoelectric materials. We present convergence results in the energy norm and for the stress intensity factors, in various settings. Copyright © 2008 John Wiley & Sons, Ltd.
SPH with the multiple boundary tangent method
Authors: Yildiz M. , Rook R. A. , Suleman A. 
Published: September 2008

AbstractIn this article, we present an improved solid boundary treatment formulation for the smoothed particle hydrodynamics (SPH) method. Benchmark simulations using previously reported boundary treatments can suffer from particle penetration and may produce results that numerically blow up near solid boundaries. As well, current SPH boundary approaches do not properly treat curved boundaries in complicated flow domains. These drawbacks have been remedied in a new boundary treatment method presented in this article, called the multiple boundary tangent (MBT) approach. In this article we present two important benchmark problems to validate the developed algorithm and show that the multiple boundary tangent treatment produces results that agree with known numerical and experimental solutions. The two benchmark problems chosen are the lid‐driven cavity problem, and flow over a cylinder. The SPH solutions using the MBT approach and the results from literature are in very good agreement. These solutions involved solid boundaries, but the approach presented herein should be extendable to time‐evolving, free‐surface boundaries. Copyright © 2008 John Wiley & Sons, Ltd.