bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Conformational Properties of Partially Alkylated Methylene‐Bridged Resorc[4]arenes – Study of the “Flip‐Flop” Inversion
Authors: Dvořáková Hana , Štursa Jan , Čajan Michal , Moravcová Jitka 
Published: August 2006

AbstractThe deprotection of resorc[4]arene octaisopropyl ether 5 by boron trichloride in dichloromethane has been found to give a parent resorc[4]arene, 1, as well as a mixture of partially alkylated derivatives, 6, 7, 8 and 9, the ratio of which depended on the conditions used. The conformational behaviour of the prepared alkyl ethers was studied with temperature‐dependent 1H NMR spectroscopy and quantum chemical calculations. It was found that the compounds 6, 7 and 8 interconvert between two possible identical crown conformations (flip‐flop inversion). The activation free energy ΔG‡ values for this process, obtained by NMR, strongly depends on the number of hydroxy groups in the molecule; an increase in their number generally increases the values of ΔG‡. The flip‐flop inversion was not observed in the cases of fully deprotected 1 and monoisopropyl resorc[4]arenes 9, which are soluble only in polar solvents, inconvenient for the formation of a hydrogen bonding system. Molecular modelling studies revealed that the flip‐flop inversion proceeds via the consecutive rotation of two adjacent rings, leading to a transition state with deformed chair geometry. Subsequent rotation of the remaining two units leads to the formation of the second crown conformer. The calculated heights of the energy barriers correspond well with those obtained by NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Life cycle impact assessment of various treatment scenarios for sulfur hexafluoride (SF6) used as an insulating gas
Authors: Shiojiri K. , Yamasaki A. , Fujii M. , Kiyono F. , Yanagisawa Y. 
Published: August 2006

AbstractA life cycle environmental impact assessment was conducted for sulfur hexafluoride (SF6) used as an insulating gas in electrical devices. Eight scenarios with a variety of SF6 treatment processes were considered. For each scenario, the life cycle power consumption was determined and an inventory analysis of pollutants and toxic materials was conducted. The scenarios were compared in terms of their life cycle environmental impacts, such as power consumption, global warming, acidification, eutrophication, generation of photochemical oxidants, and generation of substances toxic to human health. The power consumption is significantly reduced by the use of a gaseous mixture of SF6 and nitrogen in comparison to when pure SF6 is used, because the power consumption required for producing SF6, which is the major power consumption process, can be reduced according to the amount of SF6 replaced by nitrogen. On the other hand, larger amounts of the pollutants associated with the transportation process will be generated for the scenarios using gaseous mixtures with smaller SF6 contents in the insulating gas. The reuse of spent SF6 after purification can also reduce the power consumption. The calculated environmental impacts were unified with two types of environmental indexes using Eco‐Indicator 99 and LIME (Life‐cycle Impact assessment Method based on Endpoint modeling), and the scenarios were evaluated and compared. © 2006 American Institute of Chemical Engineers Environ Prog, 2006
Field observations, rheological testing and numerical modelling of a debris‐flow event
Authors: Sosio R. , Crosta G. B. , Frattini P. 
Published: August 2006

AbstractDebris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy.We investigate the dynamics and the rheological properties of a 90 000 m3 debris‐flow event triggered by a rapid regressive landslide with high water content. Field evidence revealed a maximum flow depth of 7–8 m, with an estimated peak discharge of 350–400 m3 s−1. Depositional evidence and grain‐size distribution of the debris pose the debris flow in an intermediate condition between the fluid‐mud and grain‐flow behaviour.The debris‐flow material has silt–clay content up to 15 per cent. The rheological behaviour of the finer matrix was directly assessed with the ball measuring system. The measurements, performed on two samples at 45–63 per cent in sediment concentration by volume, gave values of 3·5–577 Pa for the yield strength, and 0·6–27·9 Pa s for the viscosity. Based on field evidence, we have empirically estimated the yield strength and viscosity ranging between 4000 ± 200 Pa, and 108–134 Pa s, respectively.We used the Flo‐2D code to replicate the debris‐flow event. We applied the model with rheological properties estimated by means of direct measurements and back‐analyses. The results of these models show that the rheological behaviour of a debris‐flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts. For debris flows composed by a significant number of coarse clasts a back‐analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows. In these cases, the back‐estimated coefficients do not adequately describe the rheological properties of the debris flow. Copyright © 2006 John Wiley & Sons, Ltd.
The interaction between armouring and particle weathering for eroding landscapes
Authors: Sharmeen Saniya , Willgoose Garry R. 
Published: August 2006

AbstractThe interaction between particle weathering and surface armouring and its effect on erosion has been investigated. The effect of soil armouring is to decrease sediment transport with time by preferentially stripping away fine particles. On the other hand the effect of weathering, which breaks down the particles in the armour, is generally believed to increase erosion. By extending an existing armouring model, ARMOUR, and using a variety of published weathering mechanisms this interaction has been explored. The model predicts that while this is generally true, in some cases erosion can be decreased by weathering. When the particles generated by weathering were approximately of equal diameter, erosion increased while armouring decreased. When weathering produced very fine particles by spalling, erosion increased and armouring also increased. When weathering produced a range of particles from fine to coarse, the armour layer broke down and erosion decreased relative to the no‐weathering case. This latter decrease in erosion was due to the high entrainment of coarser transportable materials from the bed decreasing the sediment transport capacity of the flow. In these studies clear regimes could be identified where erosion was limited by either the energy of the flow alone (i.e. ‘transport‐limited’), or the rate of weathering (‘weathering‐limited’); however, for some mechanisms there was an interaction between the two, which we called ‘weathering/transport limited’. Copyright © 2006 John Wiley & Sons, Ltd.
The use of GIS‐based digital morphometric techniques in the study of cockpit karst
Authors: Lyew‐Ayee P. , Viles H. A. , Tucker G. E. 
Published: August 2006

AbstractCockpit karst landscapes are among the most distinctive landscapes in the world, and have been the focus of long‐standing scientific interest. Early researchers used largely descriptive techniques to categorize the terrain, and subsequent work has not attempted to critically re‐evaluate descriptions of landscapes using more sophisticated methods. The distinctive surface topography of cockpit karst areas can be characterized in order to compare them with other karst as well as non‐karst areas, and to determine geological and/or climatic conditions that are responsible for the observed terrain. Process models of the rate of karst denudation or evolution can only be accurate if the contemporary morphology of the landscape is quantitatively and unambiguously defined. A detailed analysis of cockpit karst terrain is carried out using the latest GIS‐based digital morphometric techniques in order to assess the nature of such terrain and provide further information for subsequent modelling, as well as other non‐geomorphological applications, such as environmental management and conservation issues. The paper presents the methodology used for the digital analysis of terrain and landforms in the distinctive Cockpit Country area of Jamaica and its environs. The results indicate that cockpit karst may be categorized based on its vertical, horizontal and shape characteristics, as well as by looking at the semivariogram, slope characteristics, and landscape relief scale, which combine measures of vertical and horizontal scales. Copyright © 2006 John Wiley & Sons, Ltd.
Effects of variable attribute weights on landform classiﬁcation
Authors: Deng Y. X. , Wilson J. P. , Sheng J. 
Published: August 2006

AbstractThis paper focuses on the attribute weight issue and advocates use of modiﬁable attribute weights in terrain‐based environmental analysis and classiﬁcation. A question was asked: ‘How much will the result of a terrain‐based environmental analysis be affected if the weights of used terrain attributes are changed?’ The literature on landform classiﬁcation and the fuzzy k‐means method was reviewed in particular to help clarify the background and importance of this weight assignment issue. As an example, the effects of modifying attribute weights were evaluated for fuzzy k‐means landform classiﬁcation in a case study area. A total of 102 classiﬁcations were compared with each other and with a soil map, and comparison methods were speciﬁcally designed to evaluate the differences between these classiﬁcations. The results show that fuzzy k‐means landform classiﬁcation is sensitive to weight adjustments of adopted terrain attributes. The sensitivity is particularly high when the attribute weights started to be tuned away from the standard (i.e. uniform) weight of one. Better matching between landform classiﬁcation and a soil map may be produced when attribute weights are tuned. In all, we advocate the widespread adoption of an exploratory attitude in assigning attribute weights for environmental analysis and classiﬁcation. Copyright © 2006 John Wiley & Sons, Ltd.
Textural and compositional controls on modern beach and dune sands, New Zealand
Authors: Kasper‐Zubillaga J. J. , Ortiz‐Zamora G. , Dickinson W. W. , Urrutia‐Fucugauchi J. , Soler‐Arechalde A. M. 
Published: August 2006

AbstractTextural, compositional, physical and geophysical determinations were carried out on 111 beach and dune sand samples from two areas in New Zealand: the Kapiti–Foxton coast sourced by terranes of andesite and greywackes and the Farewell Spit–Wharariki coast sourced by a wide variety of Paleozoic terranes. Our aim is to understand how long‐shore drift, beach width and source rock control the sedimentological and petrographic characteristics of beach and dune sands. Furthermore, this study shows the usefulness of specific minerals (quartz, plagioclase with magnetite inclusions, monomineralic opaque grains) to interpret the physical processes (fluvial discharges, long‐shore currents, winds) that distribute beach and dune sands in narrow and wide coastal plains. This was done by means of direct (grain size and modal analyses) and indirect (specific gravity, magnetic/non‐magnetic separations M/NM, magnetic susceptibility measurements, hysteresis loops) methods. Results are compared with beach sands from Hawaii, Oregon, the Spanish Mediterranean, Elba Island and Southern California.Compositionally, the Kapiti–Foxton sands are similar to first‐order immature sands, which retain their fluvial signature. This results from the high discharge of rivers and the narrow beaches that control the composition of the Kapiti–Foxton sands. The abundance of feldspar with magnetite inclusions controls the specific gravity of the Kapiti–Foxton sands due to their low content of opaque minerals and coarse grain size. Magnetic susceptibility of the sands is related mainly to the abundance of feldspars with Fe oxides, volcanic lithics and free‐opaque minerals.The Farewell Spit–Wharariki sands are slightly more mature than the Kapiti–Foxton sands. The composition of the Farewell Spit–Wharariki sands does not reflect accurately their provenance due to the prevalence of long‐shore drift, waves, little river input and a wide beach. Low abundance of feldspar with magnetite inclusions and free opaque grains produces poor correlations between specific gravity (Sg) and Fe oxide bearing minerals. The small correlation between opaque grains and M/NM may be related to grain size. The magnetic susceptibility of Farewell Spit–Wharariki sands is low due to the low content of grains with magnetite inclusions. Hysteresis and isothermal remnant magnetization (IRM) agree with the magnetic susceptibility values. Copyright © 2006 John Wiley & Sons, Ltd.
Soil properties controlling seepage erosion contributions to streambank failure
Authors: Wilson G. V. , Periketi R. K. , Fox G. A. , Dabney S. M. , Shields F. D. , Cullum R. F. 
Published: August 2006

AbstractThe majority of sediment leaving catchments may be from streambank failure. Seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks. The objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure. Seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern Mississippi. Using field observations as a guide, the soil profile conditions of a shallow (45 cm) streambank, consisting of 30 cm of topsoil, a 10 cm conductive layer, and a 5 cm restrictive layer, were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head. The time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer. Seepage erosion began within minutes of flow initiation and resulted in substantial (3 to 34 cm) undercutting of the bank. Sediment concentrations of seeps were as high as 660 g l−1 in situ and 4500 g l−1 in the lysimeters. Sediment concentrations were related to the layer slope, thereby indicating the importance of detailed site characterization. The USDA‐ARS Streambank Stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion, but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks. Published in 2006 by John Wiley & Sons, Ltd.
The Mechanism of Forming H2O from H2 and O2 over a Pt Catalyst via Direct Oxygen Reduction
Authors: Jacob T. 
Published: August 2006

AbstractDensity functional theory (DFT) was used with the B3LYP gradient‐corrected exchange–correlation functional to study the mechanism for the reaction of H2 + ${1 \over 2}$ O2 → H2O over a Pt catalyst via direct oxygen reduction.Within these studies we first examined the binding characteristics and energetics for each likely intermediate chemisorbed on the Pt(111) surface, modeled by a 35 atom cluster: O, H, O2, H2, OH, OOH, H2O.Then, the pathways for the dissociation processes of the various intermediates on the Pt35 cluster were calculated. For convenience in comparing different reaction steps, these energetics were used to calculate heats of formation (ΔHf), which were combined with the dissociation barriers. Two main reaction pathways were found for the formation of H2O from H2 and O2:•(OO‐Dissociation: Here O2 adsorbs on the surface, dissociates, and finally reacts with H sequentially to firstly form OH and then water. The rate‐determining step (RDS) for this mechanism is the Oad + Had → OHad with a barrier of 31.66 kcal mol–1 and not the dissociation of O2ad (barrier of 15.02 kcal mol–1).•OOH‐Formation: Here O2 reacts firstly with Had to form OOHad, which then dissociates to form OHad and Oad (the RDS, with a barrier of 17.13 kcal mol–1), which finally reacts with another Had to form water.Thus, under gas‐phase conditions, the OOH‐Formation mechanism is found to be the most favorable.
Covalent‐Ionically Cross‐linked Poly(Etheretherketone)‐Basic Polysulfone Blend Ionomer Membranes
Authors: Kerres J. 
Published: August 2006

AbstractSulfinated‐sulfonated PEEK was synthesized via partial reduction of sulfochlorinated PEEK with aqueous Na2SO3. From these polymers, covalent‐ionically cross‐linked ionomer blend membranes were prepared by mixing the sulfinated‐sulfonated PEEK with different base‐modified polysulfones (PSU‐base), followed by cross‐linking with 1,4‐diiodobutane. These membranes have been compared with covalently cross‐linked membranes which were obtained by the cross‐linking of sulfinated‐sulfonated PEEK and with ionically cross‐linked membranes obtained by mixing sulfonated PEEK with different PSU bases. The membranes have been characterized in terms of thermal stability by means of thermogravimetry (TGA) and coupled TGA‐FTIR, in terms of cross‐linking extent by extraction experiments, in terms of proton conductivity by impedance spectroscopy, and finally, in terms of water uptake by gravimetric analysis.
Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane
Authors: Scharfenberger G. , Meyer W. H. , Wegner G. , Schuster M. , Kreuer K.‐D. , Maier J. 
Published: August 2006

AbstractIntrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self‐dissociation of the imidazole moieties and “structure diffusion” of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities.To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized.The materials are thermally stable up to 200 °C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around σ = 1.5.10–3 S cm–1 at T = 160 °C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers.Proton self‐diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers.
Development of Hybrid Polymer Electrolyte Membranes Based on the Semi‐Interpenetrating Network Concept
Authors: Colicchio I. , Keul H. , Sanders D. , Simon U. , Weirich T. E. , Moeller M. 
Published: August 2006

AbstractHybrid inorganic/organic polymer electrolyte membranes for potential fuel cell applications are prepared by centrifugal casting from solutions of sulfonated polyetheretherketone (SPEEK) (DS 64%) and polyethoxysiloxane (PEOS) in dimethylacetamide, following the concept of a semi‐interpenetrating network. The in situ transformation of PEOS into SiO2 occurs in a “water free” process. The morphology of the films obtained is controlled by the phase segregation process, determined by the rate of evaporation of the solvent and by the transformation of PEOS into SiO2‐particles. The latter process is influenced by the presence of a catalyst. Moreover, N‐(3‐triethoxysilylpropyl)‐4,5‐dihydroimidazole is added to the mixture to enhance the interaction between SPEEK and PEOS and to influence the membrane morphology. The size and size‐distribution of the SiO2 particles formed in the organic matrix are examined by means of transmission electron microscopy. The TEM investigations show a strongly reduced particle size when N‐(3‐triethoxysilylpropyl)‐4,5‐dihydroimidazole is added to the mixture. Proton conductivity measurements are performed on the membranes by impedance spectroscopy in an open set‐up that allows measurements along the longitudinal direction of the sample. All the samples show a plateau in impedance at medium frequencies that represents the proton conducting process. Nafion® 115 is measured in the same set‐up for comparison.
On the Role of Reactant Transport and (Surface) Alloy Formation for the CO Tolerance of Carbon Supported PtRu Polymer Electrolyte Fuel Cell Catalysts
Authors: Kaiser J. , Colmenares L. , Jusys Z. , Mörtel R. , Bönnemann H. , Köhl G. , Modrow H. , Hormes J. , Behm R. J. 
Published: August 2006

AbstractThe role of atomic scale intermixing for the electrocatalytic activity of bimetallic PtRu anode catalysts in reformate operated polymer electrolyte fuel cells (PEFC) was investigated, exploiting the specific properties of colloid based catalyst synthesis for the selective preparation of alloyed and non‐alloyed bimetallic catalysts. Three different carbon supported PtRu catalysts with different degrees of Pt and Ru intermixing, consisting of (i) carbon supported PtRu alloy particles (PtRu/C), (ii) Pt and Ru particles co‐deposited on the same carbon support (Pt+Ru/C), and (iii) a mixture of carbon supported Pt and carbon supported Ru (Pt/C+Ru/C) as well as the respective monometallic Pt/C and Ru/C catalysts were prepared and characterized by electron microscopy (TEM), X‐ray absorption spectroscopy, and CO stripping. Their performance as PEFC anode catalysts was evaluated by oxidation of a H2/2%CO gas mixture (simulated reformate) under fuel cell relevant conditions (elevated temperature, continuous reaction and controlled reactant transport) in a rotating disk electrode (RDE) set‐up. The CO tolerance and H2 oxidation activity of the three catalysts is comparable and distinctly different from that of the monometallic catalysts. The results indicate significant transport of the reactants, COad and/or OHad, between Pt and Ru surface areas and particles for all three catalysts, with only subtle differences from the alloy catalyst to the physical mixture. The high activity and CO tolerance of the bimetallic catalysts, through the formation of bimetallic surfaces, is explained, e.g., by contact formation in nanoparticle agglomerates or by material transport and subsequent surface decoration/surface alloy formation during catalyst preparation, conditioning, and operation. The instability and mobility of the catalysts under these conditions closely resembles concepts in gas phase catalysis.