bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transesterification of an RNA model in buffer solutions in H2O and D2O
Authors: Virtanen Noora , Nevalainen Ville , Lehtinen Taru , Mikkola Satu 
Published: February 2007

AbstractTransesterification of a phosphodiester bond of RNA models has been studied in various buffer solutions, under neutral and slightly alkaline conditions in H2O and D2O. The results show that imidazole is the only buffer system where a clear buffer catalysis on the cleavage of a phosphodiester bond is observed. The rate enhancement in sulphonic acid buffers is smaller, and a sulphonate base, particularly, is inactive as a catalyst. The rate‐enhancing effect of imidazole is, however, catalytic, and the catalytic inactivity of sulphonate buffers can be attributed to their structure and/or charge. The catalysis by imidazole is a complex system which, in addition to first‐order reactions, involves a process that shows a second‐order dependence in imidazole concentration. The latter reaction becomes significant in acidic imidazole buffers (pH < pKa), as the buffer concentration increases. The kinetic solvent deuterium isotope effect kH/kD, referring to first‐order catalysis by imidazole base, is 2.3 ± 0.3. That referring to second‐order catalysis is most probably much larger, but an accurate value could not be obtained. Copyright © 2007 John Wiley & Sons, Ltd.
Effects of ortho‐substituents in SE1 protonolysis of phenylmercuric chloride
Authors: Wang Yulan , Zhang Jinli , Wu Yangjie 
Published: February 2007

AbstractThe kinetics of the reactions of o‐substituted phenylmercuric chlorides, o‐RC6H4HgCl (R = CH3, H, C2H5O, CH3O, C6H5, F, COOC2H5, Cl, Br, CF3, NO2), with hydrochloric acid in 80% aqueous dioxane in the presence of NaI were studied. The reactions are of the first order. The rate constant at 40°C decreases in the order of R: CH3 > H > C2H5O > CH3O > C6H5 > F > COOC2H5 > Cl > Br > CF3 > NO2. The analysis of effects of those o‐substitutes is carried out through multiple regression of log k/kH with the corresponding inductive substituent constants σI and the various resonance substituent constants σ, σR(BA), σ, σ and σx, and the corresponding Swain–Lupton field effect constant $\Im $ and resonance effect constant $\Re $. The results showed that o‐substituent intramolecular coordination with the neighbor mercury (field effect) is the main effect in effects of o‐substituents on rate of the SE1 protonolysis. Copyright © 2007 John Wiley & Sons, Ltd.
Cryoelectrochemical reduction of a phenyl sulfide in tetrahydrofuran: mediated reduction gives different products compared to direct reduction
Authors: Burasov Alexander V. , Paddon Christopher A. , Bhatti Farrah L. , Donohoe Timothy J. , Compton Richard G. 
Published: February 2007

AbstractAn electrocatalytic reduction of [(3‐{[trans‐4‐(methoxymethoxy)cyclohexyl]oxy}propyl)thio]benzene (RSPh) in the presence of naphthalene as a mediator is investigated, using steady‐state voltammetry at various sized platinum microelectrodes and at low temperature (201 K) in tetrahydrofuran (THF). This mediated process has been found to involve the transfer of one electron, in contrast to the direct electrochemical reduction which involves two electrons. In addition, the mediated reduction proceeds at a potential, some 500 mV less negative than the direct electrochemical reduction. The evidence for the proposed mechanism has been obtained from theoretical simulations, using DIGISIM which shows satisfactory fitting to experimental results and allowed the determination of the rate constant for the homogeneous step. In contrast to direct reduction of RSPh where only one product, trans‐1‐ (methoxymethoxy)‐4‐propoxycyclohexane (RH), has been obtained, the isolation of two products, RH and the dimer, diphenyl disulfide, PhSSPh, following mediated preparative electrolysis of RSPh, in presence of naphthalene shows that this one‐electron process may be carried out at the reduction potential of naphthalene at low temperature and has also validated deductions made from voltammetric results. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis, dynamic light scattering, and luminescence properties of copolymers containing iridium(III) bisterpyridine in the side chain
Authors: Aamer Khaled A. , Tew Gregory N. 
Published: February 2007

AbstractSupramolecular block‐random copolymers containing [Ir(terpy)2]3+ in the side chain were synthesized via postfunctionalization of a P(S‐b‐ACterpy) block copolymer. Absorbance and emission spectra compared to a model compound show that the polymer backbone has a minor effect on the polymer absorbance but produces a larger shift for the phosphorescence signals to higher wavelength. Dynamic light scattering of the metal complex containing copolymer studied in various solvents showed monomodal aggregation with decreasing aggregate size as the solvent dielectric constant increased. The copolymer precursor P(S‐b‐ACterpy) shows multimodal aggregation in different solvents with the major population consisting of single chains. This difference in behavior between the two polymers is attributed to the electrolytic nature of the complex and the amphiphilicity induced by the charged metal complex. Supramolecular copolymers like these will continue to have interesting self‐organizational properties and may find applications in multicomponent systems for photoinduced charge separation processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1109–1121, 2007
Temperature‐induced spontaneous sol–gel transitions of poly(D,L‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L‐lactic acid‐co‐glycolic acid) triblock copolymers and their end‐capped derivatives in water
Authors: Yu Lin , Chang Guangtao , Zhang Huan , Ding Jiandong 
Published: February 2007

AbstractThe spontaneous hydrogel formation of a sort of biocompatible and biodegradable amphiphilic block copolymer in water was observed, and the underlying gelling mechanism was assumed. A series of ABA‐type triblock copolymers [poly(D,L‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(D,L‐lactic acid‐co‐glycolic acid)] and different derivatives end‐capped by small alkyl groups were synthesized, and the aqueous phase behaviors of these samples were studied. The virgin triblock copolymers and most of the derivatives exhibited a temperature‐dependent reversible sol–gel transition in water. Both the poly(D,L‐lactic acid‐co‐glycolic acid) length and end group were found to significantly tune the gel windows in the phase diagrams, but with different behaviors. The critical micelle concentrations were much lower than the associated critical gel concentrations, and an intact micellar structure remained after gelation. A combination of various measurement techniques confirmed that the sol–gel transition with an increase in the temperature was induced not simply via the self‐assembly of amphiphilic polymer chains but also via the further hydrophobic aggregation of micelles resulting in a micelle network due to a large‐scale self‐assembly. The coarsening of the micelle network was further suggested to account for the transition from a transparent gel to an opaque gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1122–1133, 2007
Mechanical weathering rates on Signy Island, maritime antarctic
Authors: Hall Kevin 
Published: February 2007

AbstractBy means of re‐evaluating a number of properties of rock tablets left in the field for varying time periods, an estimation of rock breakdown rates is attained. From data obtained during the last five years, it would appear that rates are very slow, only of the order of 2% mass loss per 100 years. These rates refer to omnidirectionally frozen, relatively wet samples and, on the basis of laboratory simulation results, are over 50 times greater than for unidirectionally frozen bedrock. It is suggested that mechanical weathering rates in the maritime Antarctic are very slow.
A note on biological weathering on nunataks of the juneau icefield, Alaska
Authors: Hall Kevin , Otte Wulf 
Published: February 2007

AbstractObservations on a number of nunataks of the Juneau Icefield indicate that chasmolithic algae play a major role in the breakdown of granitic rock. Expansion and contraction of the algal mucilage, caused by wetting and drying episodes, results in the surface flaking of the rock. Available data suggest that the average mass of material lost per year from 1 m2 of rock could be as high as 562 g. It is suggested that biological weathering may be a major destructive mechanism of the granitic lithologies.
Relict periglacial features east of waterton‐glacier parks, alberta and montana, and their palaeoclimatic significance
Authors: Karlstrom Eric T. 
Published: February 2007

AbstractStratigraphy and inferred genesis of relict periglacial features east of Waterton‐Glacier Parks provide information on the magnitude of Quaternary climate changes. Periglacial wedges, involutions, patterned ground and soil wedges are locally preserved in pre‐Wisconsinan outwash/ alluvium and till on a series of erosion surfaces east of the Lewis Range mountain front and in Wisconsinan outwash near Cutbank, Montana. Formation of periglacial wedges required development of perennially frozen ground and mean annual temperatures at least about 10°C below those of today. All the observed relict periglacial features occur within about 20 km of Wisconsinan glacier margins. Strongly weathered, 2+ m thick, pre‐Illinoian palaeosols, also preserved locally on the erosion surfaces, are truncated and/or completely stripped in the areas most affected by cryoturbation. Hence, most of the periglacial features postdate the palaeosols. Stratigraphic and geomorphic relations suggest that the periglacial features formed during at least three glacial/periglacial episodes, probably including the Wisconsinan, Illinoian and a pre‐Illinoian glaciation.
Sedimentology and genesis of slope deposits at sonskyn, Eastern Cape Drakensberg, South Africa
Authors: Hanvey Patricia M. , Lewis Colin A. 
Published: February 2007

AbstractThe morphology and sedimentology of slope deposits exposed in a road cutting at Sonskyn are examined. The deposits have a lobate morphology and extend outwards from the lower reaches of a basin hollow at an altitude of approximately 2000 m a.s.l. The general stratigraphy shows an upward sequence from shattered bedrock and isolated pockets of colluvium, through stratified angular sediments which in turn are truncated by a series of channelized bouldery deposits.The concentration of colluvium towards the base of the sequence, together with the subjacent shattered bedrock, suggest cold‐climatic conditions, a scarcity of vegetation cover and slopewash processes. The transition up‐sequence to more clastic stratified sediments is indicative of freeze‐thaw cycles accompanied by slopewash during the melting phases. This has been attributed to the seasonal ablation of a snow patch. The overlying channelized bouldery deposits are attributed to solifluction processes related to the final dissolution of the snow patch.Palaeolithic artefacts found within the stratified sediments were used in southern Africa between 140000 and 40000 years BP. This indicates that the slope deposits at Sonskyn were laid down within the last 140000 years.
Pentes, Granulométrie et Mobilité des Matériaux le long d'un Talus d'Eboulis en Milieu Alpin
Authors: Francou Bernard 
Published: February 2007

AbstractOn a sélectionné dans les Alpes deux talus d'éboulis présentant un matériel de faible cohésion sur le profil desquels on a fait des mesures de pente et de granulométrie selon un pas régulier. Sur l'un d'eux, on a relevé et localisé les apports reçus de la corniche pendant 10 ans et mesuré le déplacement des fragments pendant 2 ans. Le traitement statistique de ces données et les résultats obtenus convergent vers un modèle biphasé de ce type d'accumulation: le segment proximal fonctionne en accumulation‐transit, le segment distal en accumulation pure. Le passage d'une phase à l'autre se réalise par un point de rupture dynamique bien repérable sur le profil. Ce modèle remet en question les précédents, notamment ceux qui ont été conçus à partir de talus artificiels.
Localisation, Genèse et Fonte de Quelques Naleds du Nord du Yukon (Canada)
Authors: Lauriol B. , Clark J. Cinq Mars Et I. D. 
Published: February 2007

AbstractLes naleds sont fréquents dans le nord du Yukon, surtout dans le lit des rivières qui entaillent les monts British et Richardson. Presque tous se situent dans le voisinage de massifs calcaires et de failles. Leur épaisseur atteint plusieurs mètres et leur surface peut couvrir des kilomètres carrés. Le plus grand, celui de la rivière Firth, atteint 28 km2. Les eaux et les dépéts de calcite de quatre naleds, ceux de Timber Creek, Fish Hole Creek, Babbage River et Salmon Fork River ont fait l'objet d'analyses isotopiques é18O, é13C et é2H. Les résultats indiquent que l'origine des eaux est locale et que leur gel par la base est un processus assez lent, ce qui permet à la calcite de pr°Cipiter en équilibre á une température proche de 0 °C. Une comparaison entre la superficie du naled de la rivière Firth au cours de l'été et les valeurs de rayonnement solaire enregistrées à Inuvik, montre une bonne corrélation.
Changes in microstructure of fine‐grained soils due to freezing
Authors: Grechishchev S. E. , Pavlov A. V. , Ponomarev V. V. 
Published: February 2007

AbstractA microstructural model of thermorheological processes during the freezing of fine‐grained soils is described. Using electron microscopy and X‐ray diffractometry, the changes due to freezing in the microstructures of kaolin, bentonite and askangel were experimentally studied. Curves of aggregate distribution and pore size for different freezing periods are presented. It is shown that there is good agreement between experimental results and theoretical hypotheses.
Prospecting and mapping of mountain permafrost and associated phenomena
Authors: King Lorenz , Gorbunov Aldar P. , Evin Michèle 
Published: February 2007

AbstractGeomorphologists as well as engineering geologists are increasingly interested in the prediction and mapping of mountain permafrost and associated phenomena. Using several indirect geophysical and geomorphological methods, it is possible to detect and map permafrost that is usually invisible at the surface. This paper summarizes the merits of the most frequently used methods, their difficulties and limitations, and gives recommendations on how to use them. Brief recommendations for future research are also given.
Present‐day periglacial processes and landforms in mountain areas
Authors: Lautridou J. P. , Francou B. , Hall K. 
Published: February 2007

AbstractThis paper outlines recent advances in our understanding of periglacial processes and landforms in mountain areas, as reported in the literature over the last 8 years. Landforms investigated include rockwalls, screes, avalanche paths, bedded slope deposits and patterned ground phenomena. Processes subject to quantification include cliff recession, rock displacements on slopes, rock thermal and moisture regimes, frost creep, mass wasting and solution. Laboratory experimentation and modelling studies have also been undertaken.
Construction, environmental problems and natural hazards in periglacial mountain belts
Authors: Haeberli Wilfried 
Published: February 2007

AbstractExperience with man‐induced permafrost problems in periglacial mountains has increased during recent years. Such problems can be local, as in the case of building foundations on ice‐bearing ground, or can affect larger areas, as in the case of ski‐run preparation on perennially and seasonally frozen ground. The most severe natural hazard concerns the destabilization, erosion and displacement by debris flows of loose, non‐frozen material or weak bedrock on steep slopes. Such flows often take place as a consequence of glacier retreat or permafrost degradation and relate to atmospheric warming, which may continue or even accelerate in the future.The greatest drawback in man's behaviour with respect to these problems remains the ignorance of mountain permafrost. This probably originates from the fact that permafrost is not directly visible and, hence, is often not considered in the planning stage. The most important progress with respect to construction technology, environment protection and hazard mitigation in periglacial mountain belts can be achieved by improving communication and sharing of experience among scientists and technicians.
Borehole logging in alpine permafrost, upper Engadin, Swiss Alps
Authors: Mühll Daniel S. Vonder , Holub Petr 
Published: February 2007

AbstractIn two boreholes through Alpine permafrost, borehole geophysical measurements were performed. At the borehole through rock glacier Murtèl‐Corvatsch, where cores were taken, the main difficulty was to fill up the hole with water. Consequently, only some of the logging methods could be applied. Nevertheless, gamma‐gamma log (and qualitatively also gamma‐ray) made it possible to obtain density and to calculate ice content. At the Pontresina‐Schafberg drill site, a complete set of logs was run in a water‐filled hole. The bedrock was reached at a depth of approximately 16 m. No cores were obtained by the air‐lift percussion technique. Logging measurements were done to determine thickness of the perennially frozen debris layer above the bedrock and to investigate P‐wave velocity, resistivity and ice content of the whole permafrost body. The boreholes at both drill sites show a high ice content layer (80–95 % by volume), although temperature characteristics are quite different.
Automated mapping of mountain permafrost using the program PERMAKART within the geographical information system ARC/INFO
Authors: Keller Felix 
Published: February 2007

AbstractThe application PERMAKART of the glaciological information system KRYO on ARC/INFO plots supposed mountain permafrost distribution on any topographical map. Results of fieldwork since 1970 and surface analyses based on a digital terrain model (DTM) are used. In Switzerland PERMAKART could become a planning tool for decisions about possible occurrence of mountain permafrost because the DTM RIMINI is available for the entire country.
A model of potential direct solar radiation for investigating occurrences of mountain permafrost
Authors: Funk Martin , Hoelzle Martin 
Published: February 2007

AbstractA model is described to compute the daily potential direct solar radiation on the basis of digital terrain models. This model is a useful tool for investigating distribution patterns of permafrost in mountain areas. An example of its application to a low‐altitude permafrost site in the Northern Prealps of Switzerland is presented.
Permafrost occurrence from BTS measurements and climatic parameters in the eastern Swiss Alps
Authors: Hoelzle Martin 
Published: February 2007

AbstractRelations between climatic parameters such as temperature and potential direct solar radiation (PR) and measured bottom temperatures of the snow cover (BTS) as indicator of permafrost occurrence were investigated. No significant correlation exists between mean annual air temperature (MAAT) and BTS. The high correlation found between PR and BTS may help to develop a model for predicting permafrost distribution in mountain areas. This correlation and the low one between MAAT and BTS help to explain the existence of the low‐altitude permafrost in alpine regions.
Evidence of intrapermafrost groundwater flow beneath an active rock glacier in the Swiss Alps
Authors: Mühll Daniel S. Vonder 
Published: February 2007

AbstractTemperature measurements in borehole 2/1987 through rock glacier Murtèl Corvatsch revealed a very high mean heat flow of 150 mW/m2. Between 52 m and 56 m depth, seasonal variations are observed; above and underneath this zone temperatures have remained negative during the last 4 years. In addition, a zero curtain effect at the same depth hints at the existence of a water aquifer which is active mainly in summer. This phenomenon is interpreted as a talik at about 55 m depth. The permafrost may have a total thickness of approximately 100 m. The high heat flow is a result of the boundary conditions at the surface (mean annual temperature: −3 °C) and at the aquifer (at a depth of about 50 m), where the temperature is close to 0 °C.
Ground temperature measurements in mountain permafrost, Jotunheimen, southern Norway
Authors: Ødegård R. S. , Sollid J. L. , Liestøl O. 
Published: February 2007

AbstractGround temperatures have been measured over a 5 year period of between −1.8 °C and −2.3 °C at 10m depth on a mountain plateau, 1851 m a.s.l. in Jotunheimen, southern Norway (61°40′N, 8°20′E). On the basis of additional shallow ground temperature measurements at different altitudes, the change in ground temperature with altitude is estimated to be 0.57 °C/100 m. This estimate, combined with the measured mean annual ground temperature, indicates the lower limit of discontinuous permafrost in the area to be at 1450–1500 m a.s.l. The mean annual ground temperature above 2200 m a.s.l. is below −4 °C. These values are representative for flat or slightly convex areas. Owing to strong winds, there is little snow until late April at the ground temperature measurement site. Maximum snow depth in May is 0.5 m.
Cavity development in ice‐rich permafrost, Pangnirtung, Baffin Island, northwest territories
Authors: Hyatt James A. 
Published: February 2007

AbstractCavity development in ice‐rich permafrost at Pangnirtung followed a large rainstorm and runoff event in 1984. The cavities evolved along permeable zones in sediments containing segregated ice lenses. Cavities promoted subsurface flow and incremental collapse of the ground surface. Once formed, cavities remained relatively stable where they were free to drain, and where the enclosing ground remained frozen and rigid support was provided. Some cavities closed by infilling with sediment or freezing water, or by deformation of the surrounding frozen ground. Other cavities were enlarged by thermo‐erosional piping, a process involving both thermal and mechanical erosion of frozen ground together with sufficiently rapid throughflow to prevent refreezing.A classification of cavities in permafrost permits qualitative appraisal of their stability with respect to the depth of zero annual temperature change and the degree of natural arching support. Assessment based on elastic plate theory indicates that seasonal temperature changes are important factors in destabilizing near‐surface cavities.
Weichselian upper pleniglacial aeolian and ice‐cored morphology in the southern Netherlands (Noord‐Brabant, groote peel)
Authors: Kasse K. , Bohncke S. 
Published: February 2007

AbstractThe morphology of the Weichselian Late Pleniglacial land surface in the Groote Peel nature reserve (southern Netherlands) is characterized by numerous circular to oval depressions. The depressions are up to 90 m wide and 3 m deep. Some are surrounded by low (50–100 cm) ridges. Two depressions were selected for detailed study. One, of aeolian origin, is shallow (less than 1 m), the underlying sedimentary units are undisturbed and the ridge surrounding it consists of horizontally bedded aeolian sand. The second, formed by the melting of an ice core, is deeper (3 m) and dissects older units. The ice lens probably formed during the Weichselian Late Pleniglacial. Ice segregation was favoured by a low topographic gradient, impermeable beds in the subsoil and poor drainage. After partial decay of the ice core, a remnant survived during the cold, arid conditions of the Beuningen deflation phase. Final melting of the ice core occurred after deposition of Late Pleniglacial aeolian coversand, at the onset of the Late Glacial climatic amelioration. Palynological analysis indicates that infilling of the ice‐core depression started in the Late Glacial Older Dryas and possibly even during Oldest Dryas.