bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of teliospores and promycelium and basidiospore formation in the two-spored form of Gymnoconia nitens, one of the causes of orange rust of Rubus
Authors: Mims Charles W. , Richardson Elizabeth A.
Published: November 2007

Gymnoconia nitens (Schwein.) Kern & H. W. Thurston consists of two forms that cause orange rust of Rubus . The teliospores of both of these forms are morphologically identical to aeciospores, but upon germination form promycelia that give rise to either two or four basidiospores. In this study, we examined the teliospores and the sequence of events leading to basidiospore development in the two-spored form of G. nitens. The teliospores of this species are formed in chains from uninucleate sporogenous cells that line the base of each sorus on infected Rubus argutus Link. (blackberry) leaves. Fluorescence microscopy revealed that approximately 90% of the mature teliospores were uninucleate. During germination, the teliospore nucleus migrated into the developing promycelium and underwent a single mitotic division. A transverse septum formed between the two daughter nuclei creating two uninucleate cells. A tapered sterigma arose from each cell and gave rise to a basidiospore. These findings indicate that the basidiospores of the two-spored form of G. nitens were formed in an asexual fashion.
Freezing and heat tolerance ofOpuntiacacti native to the Canadian prairie provinces
Authors: Ishikawa Masaya , Gusta Lawrence V.
Published: November 2007

Seasonal changes in the freezing tolerance in situ were determined for Opuntia fragilis and Opuntia polyacantha native to southern Saskatchewan, Canada. Wintering terminal cladodes of O. fragilis and O. polyacantha survived −50 and −40 °C, respectively, without any apparent tissue injury. Approximately 50% of the cladodes of O. fragilis collected on either 10 October or 10 December 1985 tolerated −70 °C and immersion in liquid nitrogen (−196 °C) following slow prefreezing to −40 °C. These are the lowest values reported for the freezing tolerance of cacti as determined by regrowth and tissue necrosis. Newly formed cladodes of the same species did not tolerate −3.5 °C in June, but freezing tolerance increased from −7 to −50 °C from 6 September to 10 October. This increase in freezing tolerance was accompanied by a decrease in water content from 5.4 to 2.6 g H2O/g dry wt. and the cladodes were shrunken and reduced by approximately 30% in diameter. Although Opuntia is a succulent plant that avoids drought by storing water in the cladodes, during cold acclimation O. fragilis appears to shift to a more drought-tolerating strategy. In midsummer, the current year cladodes of O. fragilis tolerated a 60-min exposure to 50 °C, while the previous year cladodes tolerated 55 °C without any visible symptoms of injury. Temperature extremes of −30 and 51 °C were recorded at the microhabitats of O. fragilis. This study demonstrates that this species can acclimate to tolerate both the high and low temperature extremes experienced in its native habitat. Keywords: cacti, cold acclimation, freezing tolerance, heat tolerance, Opuntia, water relations.
Nectar secretion pattern, removal effects, and breeding system ofLigaria cuneifolia(Loranthaceae)
Authors: Rivera Guillermo L. , Galetto Leonardo , Bernardello L.
Published: November 2007

Some aspects of the reproductive biology of Ligaria cuneifolia have been studied, addressing the following questions: (i) Are there temporal differences in the female and male functions? (ii) How do nectar composition, volume, concentration, and amount of sugar vary throughout the flower lifetime? (iii) How does the plant respond to nectar removal? (iv) What is the breeding system of this species? Flowers last 4 days. There is a predominance of the male function in the first days and of the female function in the last days. Chemical composition of nectar varies throughout the flower lifetime; there is a constant decrease in sucrose along with an increase in glucose. Nectar is secreted during nights, and every secretion period is followed by a cessation interval. After the final cessation, a period of active resorption follows. During the mostly male phase of the flower, nectar has more sucrose than hexose, its secretion is discontinuous, and nectar removal reduces the rate of nectar production. During the mostly female phase, nectar has more hexose than sucrose, its secretion ceases, nectar removal does not affect nectar production, and a resorption period is inferred. Tests for spontaneous autogamy and apomixis were negative. Low fruit set is obtained when autogamous, geitonogamous, and xenogamous hand pollinations are performed on flowers less than 2 days old compared with flowers at least 3 days old (0, 15, and 47% versus 19, 37.5, and 89%, respectively). These results indicate the the reproductive system of L. cuneifolia is primarily xenogamous, but reproductive success is related to flower age. Keywords: Loranthaceae, Ligaria, nectar chemistry, breeding system, flower phenology, reproductive biology.
An analysis of the causes of genetic isolation in two Pacific Coast iris hybrid zones
Authors: Young Nelson D.
Published: November 2007

In: two Pacific Coast Iris hybrid zones, the causes of genetic isolation appear to differ substantially. The Iris douglasiana – Iris innominata hybrid zone follows an ecotone a few kilometres inland from the ocean, implying different habitat associations for the two species, perhaps because of climate. Reciprocal transplant experiments showed that habitat association plays a major role in isolation. Each species survives best in its own habitat. Additional differences in perianth-tube length and flowering time between the two species have not developed into significant genetic isolating factors. The second hybrid zone occurs where species with different perianth-tube lengths co-occur (Iris chrysophylla – Iris tenax). Crosses between long- and short-tubed species suggest that differences in perianth-tube length can limit gene flow. Gene flow is also limited in the other direction, because the long-tubed species, I. chrysophylla, blooms earlier (though the flowering periods overlap). Coupled with the fact that these irises are all protandrous (anthers mature about 3 days before stigmas), relatively few days will be available when the long-tubed species can pollinate the short-tubed species. This combination of factors is probably a major form of genetic isolation in the I. chrysophylla – I. tenax zone. Keywords: speciation, reciprocal transplant, habitat association, phenology.
FLUCTUATIONS, CORRELATIONS AND FINITE VOLUME EFFECTS IN HEAVY ION COLLISION
Authors: TURKO LUDWIK
Published: November 2007

Finite volume corrections to higher moments are important observable quantities. They make possible to differentiate between different statistical ensembles even in the thermodynamic limit. It is shown that this property is a universal one. The classical grand canonical distribution is compared to the canonical distribution in the rigorous procedure of approaching the thermodynamic limit.
AMPLIFICATION OF QUANTUM MESON MODES IN THE LATE TIME OF THE CHIRAL PHASE TRANSITION
Authors: WATANABE K. , TSUE Y.
Published: November 2007

We investigate the time evolution of the quantum meson modes in the late time of chiral phase transition. In particular, it is shown that there exists a possible solution to the equation of motion for the quantum meson modes, which reveals a parametric resonance and/or resonance through forced oscillation induced by the small oscillation of the chiral condensate. After that, we demonstrate the unstable regions for the quantum meson modes in both the cases of a uniform and spatially expanding system.
HEND: A DATABASE FOR HIGH-ENERGY NUCLEAR DATA
Authors: BROWN DAVID , VOGT RAMONA
Published: November 2007

We propose to develop a high-energy heavy-ion experimental database and make it accessible to the scientific community through an on-line interface. The database will be searchable and cross-indexed with relevant publications, including published detector descriptions. It should eventually contain all published data from older heavy-ion programs such as the Bevalac, AGS, SPS and FNAL fixed-target programs, as well as published data from current programs at RHIC and new facilities at GSI (FAIR), KEK/Tsukuba and the LHC collider. This data includes all proton-proton, proton-nucleus to nucleus-nucleus collisions as well as other relevant systems and all measured observables. Such a database would have tremendous scientific payoff as it makes systematic studies easier and allows simpler benchmarking of theoretical models to a broad range of experiments. To enhance the utility of the database, we propose periodic data evaluations and topical reviews. These reviews would provide an alternative and impartial mechanism to resolve discrepancies between published data from rival experiments and between theory and experiment. Since this database will be a community resource, it requires the high-energy nuclear physics community's financial and manpower support.
PRODUCTION OF ANTICENTAURO EVENTS IN ULTRA-RELATIVISTIC HEAVY ION COLLISIONS
Authors: SOOD G.
Published: November 2007

We propose a novel method for studying the production of anticentauro events in high energy heavy ion collisions utilizing Chebyshev expansion coefficients. These coefficients have proved to be very efficient in investigating the pattern of fluctuations in neutral pion fraction. For the anticentauro like events, the magnitude of first few coefficients is strongly enhanced (≈ 3 times) as compared to those of normal HIJING events. Various characteristics of Chebyshev coefficients are studied in detail and the probability of formation of exotic events is calculated from the simulated events.
ELECTROMAGNETIC PROBES AT RHIC-II
Authors: DAVID GABOR
Published: November 2007

We will summarize how future measurements of electromagnetic probes at the upgraded Relativistic Heavy Ion Collider (RHIC-II), in connection with theoretical analysis, can advance our understanding of strongly interacting matter at high energy densities and temperatures. Electromagnetic probes have already played a very important role at SPS and RHIC to date. We will try to identify key physics objectives and observables that remain to be addressed. These include measuring the initial temperature and examining the transition properties via continuum radiation, studying the energy loss mechanism in the medium, the system size evolution via photon-photon correlations as well as medium modifications of vector mesons via low-mass dileptons. We will argue that detector upgrades, increased experimental precision, order of magnitude higher statistics than currently achievable, as well as a detailed scan of colliding species and energies are necessary to allow for sufficient discrimination power in theoretical interpretations.
VARIABLE-ANGLE OPTICAL REFLECTIVITY AND ANGLE-RESOLVED PHOTOLUMINESCENCE STUDIES OF 2D ACTIVE PHOTONIC CRYSTAL BASED ON QUANTUM DOTS
Authors: BLOKHIN S. A. , MAXIMOV M. V. , USOV O. A. , NASHCHEKIN A. V. , ARAKCHEEVA E. M. , TANKLEVSKAYA E. M. , GUREVICH S. A. , KONNIKOV S. G. , ZHUKOV A. E. , LEDENTSOV N. N. , USTINOV V. M.
Published: November 2007

A two-dimensional photonic crystal with hexagonal lattice of air-holes is patterned into an active planar waveguide containing InAs / InGaAs quantum dots. Variable-angle reflectivity spectroscopy is used to map out the photonic band structure. Fano-type resonances observed in the measured reflectivity spectra in TE (TM) polarizations along the Γ–K (Γ–M) lattice direction are attributed to resonance coupling of the optically active photonic bands to external light. Angle-resolved photoluminescence measurements are shown to trace the band structure of the leaky mode. The revealed three-fold emission intensity enhancement of photonic crystals is ascribed to both Purcell and Bragg scattering effects.
PRESSURE-INDUCED TRANSITION OF 2DEG IN δ-DOPED GaAs TO INSULATING STATE
Authors: DIZHUR E. M. , VORONOVSKY A. N. , FEDOROV A. V. , KOTEL'NIKOV I. N. , DIZHUR S. E.
Published: November 2007

The tunneling and the lateral conductance of 2DEG formed in the GaAs with the δ-doped layer were measured simultaneously at hydrostatic pressures at helium temperatures. The resistivity of the δ-doped layer sharply increases by > 3 orders of magnitude at about 2 GPa, and its temperature coefficient changes from ~ - 0.04 to ~ - 4 K -1. The tunneling resistance shows only slight change of exponential behavior at about 1.5 GPa, while a drastic change of the Zero Bias Anomaly (ZBA) takes place just at the metal–insulator transition. Such a behavior is interpreted in terms of pressure dependence of the GaAs band structure and the DX-level position.
MBE GROWTH OF GaAs NANOWHISKERS STIMULATED BY THE ADATOM DIFFUSION
Authors: DUBROVSKII V. G. , SOSHNIKOV I. P. , TONKIKH A. A. , USTINOV V. M. , CIRLIN G. E. , SAMSONENKO YU. B.
Published: November 2007

The growth mechanisms of GaAs nanowhiskers (NWs) during molecular beam epitaxy (MBE) are studied theoretically and experimentally. A kinetic model of the diffusion-induced NW growth is presented that allows one to predict the dependence of NW length on the drop radius and on the technologically controlled MBE growth conditions. The results of scanning electron microscopy studies of GaAs NWs grown at different conditions on the GaAs (111) B surface activated by Au are presented and analyzed. It is shown that the length of NWs increases with decreasing the drop radius and with decreasing the deposition rate of GaAs , while its temperature dependence has a certain maximum. The aspect ratio of MBE-grown GaAs NWs is higher than 100. The maximum length of NWs is several times larger than the effective thickness of the deposited GaAs . The obtained results demonstrate that the NW growth is controlled by the adatom diffusion toward their tip rather than by the adsorption-induced vapor–liquid–solid mechanism. The growth conditions' influence on the NW morphology may be used for the controlled fabrication of NWs by MBE for different applications.
TRANSIENT CHARACTERISTICS OF SiGe/Si QW STRUCTURES AT THz LASING
Authors: KAGAN M. S. , ALTUKHOV I. V. , PAPROTSKIY S. K. , SINIS V. P. , YASSIEVICH I. N. , KOLODZEY J.
Published: November 2007

Transient characteristics of SiGe -QW laser structures were studied. The excitation of stimulated THz emission is shown to be the result of carrier injection through contacts. The mechanism of intra-center population inversion caused by carrier injection is suggested.
OPTICAL AND STRUCTURAL ANALYSIS OF Ge/Si QUANTUM DOTS GROWN ON A Si(001) SURFACE COVERED WITH A SiO2 SUB-MONOLAYER
Authors: FONSECA A. , ALVES E. , LEITÃO J. P. , SOBOLEV N. A. , CARMO M. C. , NIKIFOROV A.
Published: November 2007

In this work we performed measurements of photoluminescence (PL), scanning tunneling microscopy (STM), and Rutherford backscattering (RBS) at grazing angles of incidence in a set of samples grown by molecular beam epitaxy, in which a Ge layer was deposited on a Si (001) substrate covered with a thin SiO 2 layer. Three different thicknesses for either layer were deposited: 0.5, 0.75 or 1 monolayer (ML) of SiO 2, and 0.3, 0.6 or 0.9 nm of Ge . The PL measurements for the samples with thicker layers show a broad band at ~ 0.85 eV superimposed on a dislocation related band at ~ 0.81 eV . The attribution of the high energy band to Ge islands in this sample is supported by STM and RBS measurements, as well as by PL measurements after hydrogen passivation of the sample surface. For the samples with thinner SiO 2 and Ge layers, no evidence for the formation of Ge islands was found.
Historical aerial photographs for landslide assessment: two case histories
Authors: Walstra J. , Dixon N. , Chandler J.H.
Published: November 2007

This paper demonstrates the value of historical aerial photographs for assessing long-term landslide evolution. The study focused on two case histories, the Mam Tor and East Pentwyn landslides. In both case histories we explored the variety of data that could be derived relatively easily using an ordinary PC desktop, commercially available software and commonly available photographic material. The techniques to unlock qualitative and quantitative data captured in the photographic archive were based on the principles of aerial photo-interpretation and photogrammetry. The products created comprised geomorphological maps, automatically derived digital elevation models (DEMs), displacement vectors and animations. The measured horizontal displacements of the Mam Tor landslide ranged from 0.09 to 0.74 m a
−1
between 1953 and 1999, which was verified by independent survey data. Moreover, the observed displacement patterns were consistent with photo-interpreted geomorphological information. The photogrammetric measurements from the East Pentwyn landslide (horizontal displacements up to 6 m a
−1
between 1971 and 1973) also showed a striking resemblance to independent data. In both case histories, the vertical accuracy was insufficient for detecting significant elevation changes. Nevertheless, DEMs proved to be a powerful tool for visualization. Overall, the results in this study validated the techniques used and strongly encourage the use of historical photographic material in landslide studies.
Identifying the significant factors that influence temporal and spatial trends in nitrate concentrations in the Dorset and Hampshire Basin Chalk aquifer of Southern England
Authors: Roy S. , Speed C. , Bennie J. , Swift R. , Wallace P.
Published: November 2007

Nitrate data collected by the Environment Agency over a 30 year period from groundwater monitoring points in the Dorset and Hampshire Chalk aquifer are used to investigate the temporal and spatial evolution of nitrate concentration in the saturated zone. Time series of nitrate data are compared with effective precipitation and groundwater level data aggregated over groundwater bodies to identify long-term trends. Seasonal variability in nitrate concentrations is more pronounced in the east of the aquifer, with winter peaks taking the nitrate concentration over the 11.3 mg N l
−1
Drinking Water Standard. Phase lags between effective precipitation, groundwater level and nitrate peaks of 2–3 months suggest that piston flow is the main transport mechanism for nitrate to the saturated zone. Multiple linear regression of the groundwater body data indicates that seasonal cycles are superimposed on a longer-term trend of rising nitrate concentrations. The relationship of groundwater level with nitrate concentrations is more direct, and has less of a time lag than that with effective precipitation. Groundwater level is therefore a better predictor of seasonal changes in nitrate concentrations in the model than effective precipitation. Contours of equal nitrate concentration produced for the aquifer using 5 year means between 1976 and 2006 show that nitrate concentrations have increased by a mean value of 30% and up to 115% at one site, over the 30 year record. Statistical modelling of over 8000 nitrate measurements indicates that nitrate varies significantly with time, borehole depth and groundwater level, and between Chalk formation, land-use and groundwater body. Arable and Urban land-uses are significantly more likely to be associated with higher groundwater nitrate concentrations than Managed Grassland.
Assessing the effectiveness of Scotland's groundwater nitrate monitoring network
Authors: Ó Dochartaigh B.É. , MacDonald A.M. , Griffiths K.J. , Lilly A. , DeGroote J. , Chilton P.J. , Hughes A.G.
Published: November 2007

Many countries expend considerable resources collecting and reporting data from national groundwater quality monitoring networks to assess diffuse nitrate contamination, but the reliability of these data depends on the effectiveness of the network. Without a representative monitoring network of reliable monitoring points, there is a risk that groundwater management policies could be developed and implemented based on poor evidence. To help increase confidence in nitrate data, a robust, practical and repeatable method was developed to assess the effectiveness of groundwater nitrate monitoring networks, and applied to a network in Scotland. The method combines a rapid site assessment of monitoring points and local pollution pressures in order to judge the reliability of monitoring points, with a wider characterization of the network to identify which land uses and hydrogeological environments are being monitored. The analysis indicates that, with minor exceptions, Scotland's groundwater nitrate monitoring network broadly represents the diversity of conditions expected in Scotland.
Nitrate occurrence and attenuation in the major aquifers of England and Wales
Authors: Rivett M.O. , Smith J.W.N. , Buss S.R. , Morgan P.
Published: November 2007

The current occurrence of nitrate in the major aquifers of England and Wales is presented and the evidence for denitrification is critically reviewed. Denitrification is the principal nitrate attenuation process in the subsurface and its potential for mitigating the widespread nitrate inputs is considered. The study focuses on the three most important major aquifers: the Cretaceous Chalk, Permo-Triassic Sandstone and Jurassic Limestone. Elevated ground-water nitrate concentrations are shown to be widespread and continue to rise, with leaching from soils predicted to remain significant. Some 60% of groundwater bodies in England may fail to meet the Water Framework Directive requirement of ‘good status’ by 2015. Acquiring reliable evidence of denitrification is non-trivial and typically comprises integrated assessment of electron donor conditions, nitrogen oxide products, stable isotope ratios, nitrogen/argon ratios, microbiology and comparative velocity estimates. The available field studies confirm that denitrification in unconfined aquifers is relatively limited. Detailed unsaturated zone studies of both the Chalk and Sherwood Sandstone have demonstrated only minor decreases in nitrate concentrations, estimated at just 1–2% of the nitrate load within infiltrating water. Such decreases are unlikely to significantly influence regional groundwater quality. Within the saturated zones of the Chalk, Sherwood Sandstone and Jurassic Limestone aquifers, denitrification was significant only once these aquifers became confined and dissolved oxygen depleted. However, evidence for denitrification is typically weak at the regional aquifer scale and low nitrate concentrations may sometimes be simply ascribed to dilution or non-arrival of plumes. Denitrification within the Chalk or Jurassic Limestone matrix, although geochemically possible, may not occur, as bacteria are potentially excluded by the narrow pore throats. Although it is concluded that denitrification is unlikely to lead to very significant mitigation of the nitrate problems manifest in these aquifers, further research is still warranted to better understand its role. Relatively little denitrification research has been conducted in the major aquifers over the last decade. Organic carbon controls, in-fracture v. in-matrix denitrification and recent trends in nitrate and denitrification at historically monitored sites should all be further investigated.
Modelling land-use scenarios to reduce groundwater nitrate pollution: the European
Water4All
project
Authors: Hiscock K. , Lovett A. , Saich A. , Dockerty T. , Johnson P. , Sandhu C. , Sünnenberg G. , Appleton K. , Harris B. , Greaves J.
Published: November 2007

The
Water4All
project funded by the EU InterregIIIB programme aimed to demonstrate groundwater protection in the context of spatial planning and the implementation of the EU Water Framework Directive. Through a series of workshops, the four partner countries (Denmark, Germany, the Netherlands and the UK) developed a handbook containing an approach for risk-based land and water management to reduce diffuse pollution of groundwater from agricultural sources. Best practice guidelines were catalogued as a matrix of compensated and non-compensated ‘soft’ to ‘hard’ measures and were supported by illustrative case studies. The
Water4All
project also showed that spatially targeted measures can have wider benefits as part of a ‘whole landscape’ approach to planning and management. As an example, this paper explores a set of theoretical land-use scenarios, developed in consultation with stakeholders, which could potentially decrease nitrate concentrations in the regionally important Lincolnshire Limestone aquifer in eastern England. The results of a combined export coefficient and numerical groundwater modelling approach showed that a decrease in groundwater nitrate concentrations can be achieved over several decades with the implementation of a groundwater protection zone in which there is a significant element of land conversion from arable to woodland and grass. Hence, a long-term commitment to land management is required if the alternative and expensive end-of-pipe water treatment is to be avoided.
Insights into the faulting process from numerical simulations of rock-layer bending
Authors: Couples G. D. , Lewis H. , Olden P. , Workman G. H. , Higgs N. G.
Published: November 2007

An elastic–plastic material model, with strain-hardening or -softening, and volumetric strains, implemented within a general-purpose finite-element system (SAVFEM
TM
), is shown to reproduce the stress–strain relationships and localized to de-localized (brittle to ductile) changes in strain response that have long been observed in typical laboratory experiments on common porous rocks. Based on that validation of the implementation, SAVFEM
TM
is then used to create numerical simulations that reproduce the patterns of localized shear zones, and their growth history, that occur in experimental (physical) models of fold–fault systems in layered rocks. These simulations involve a progressive evolution of the mechanical state, illustrating a geometrically dominated type of localization behaviour. Part of the deformation simulated here represents a crestal graben system. Analysis of the evolving mechanical state in the system of simulated faults poses challenges to some longstanding ideas concerning the way that faults operate, suggesting the need for a new fault-process paradigm.
Improved seismic identification of inter-fault damage via a linked geomechanics-seismic approach
Authors: Hall S. A. , Lewis H. , Macle X.
Published: November 2007

Predicting deformation-driven permeability changes in the subsurface requires knowledge of the character and distribution of dilatant and compactant rock damage. Seismic reflection data can be used to gain insight into aspects of the deformation such as the geometry of seismically resolvable faults and bulk material property distributions. However, interpretations of material properties from seismic data are non-unique. This paper addresses the use of established seismic techniques to identify the signatures of fault-associated open fractures, modified and improved by a new linked geomechanics–seismic approach. The paper also addresses how each of stress state and open fractures affect seismic anisotropy. The geomechanics–seismic approach is demonstrated using a model of a North Sea hydrocarbon field in which a series of potential fracture arrays are assumed and the fracture apertures are modified to reflect the geomechanically generated stress states. Seismic anisotropy predictions based on these modified fracture distributions are then compared with a pre-existing seismic anisotropy interpretation to determine the best match. Using geomechanical simulation to support a seismic anisotropy-based method produces a higher-confidence result and can lead to better prediction of altered permeabilities in faulted regions. Because of the geomechanical focus of this Special Publication, the background for seismic identification of faults and inter-fault damage is also outlined, including a review of current seismic practice.
Localization processes in a coupled hydrogeomechanically sensitive fractured system
Authors: Reynolds M. A. , Couples G. D. , Lewis H. , Pickup G. E.
Published: November 2007

Simulation of coupled dynamic fluid flow and geomechanical loading of fractured systems shows that complex behaviours can result, even for geometrically simple fracture systems and simple loading. Using a bi-directionally coupled simulation tool, HYDRO–DDA, we examine how fluids and discontinuum processes interact in a fractured, porous rock layer that is being flexed. The changes in fracture aperture, and hence the equivalent permeabilities of this system, exhibit marked localization or delocalization responses in spite of the geometrical and mechanical simplicity of this model. Typically the linked flow-deformation behaviour develops markedly non-linear responses. In some cases the permeability varies by more than three orders of magnitude for minor changes in input variables. Upscaling methods that are suitable representations of this permeability variation are developed. These non-linear behaviours develop in a porous material, which would be expected to suppress non-linear effects. If the range of behaviours seen in this geometrically simple coupled system is typical of other, potentially more complex, fully coupled systems, then the results obtained here can be used to explain the spatially and temporally high variability of the permeability characteristics of fractured systems.
The progression from damage to localization of displacement observed in laboratory testing of porous rocks
Authors: Logan J. M.
Published: November 2007

Laboratory experiments suggest that fault zones form in porous rocks through the extension and coalescence of fractures of predictable geometries. These fractures form in an array of Riedel fractures in R
1
, R
2
, P and Y orientations. Displacement along closely spaced fractures leads to the formation of comminuted fault gouge. Localization of displacement within the fault gouge progresses from distributed shearing to comminution and compaction of the fault rock material culminating in fractures in the Riedel orientations. Colour boundaries within the simulated gouge zones show the change in accommodation of displacement to fractures in the Y orientation as shear strain progresses. Clay–quartz mixtures demonstrate that the clay inhibits localization and the achievement of steady-state sliding as well as stick-slip. A reduction in the coefficient of friction does not occur until about 30% of the clay is present and continues to decrease until about 70% is reached. Localization of slip appears as a necessary condition for steady-state sliding as well as unstable behaviour. Field studies show the implication of grain-size reduction in the localization process by porosity decrease inhibiting fluid flow normal to the fault zone. The pervasive Y fractures, however, facilitate fluid migration parallel to some faults.
Microscale damage evolution in compacting sandstone
Authors: DiGiovanni A. A. , Fredrich J. T. , Holcomb D. J. , Olsson W. A.
Published: November 2007

Recent field, laboratory, and theoretical studies suggest that under certain stress conditions, compaction of porous rock may be accommodated by narrow zones of localized compressive deformation oriented perpendicular to the maximum compressive stress. Triaxial compression experiments were performed on Castlegate sandstone, an analogue reservoir sandstone, that included acoustic emission detection and location. Initially, acoustic emissions were concentrated in horizontal bands that initiated at the sample ends (perpendicular to the maximum compressive stress) but, with continued loading, progressed axially towards the sample centre. High-resolution field-emission SEM was performed to elucidate the micromechanics of compaction. The microscopy revealed that compaction of this weakly cemented sandstone proceeded in two phases: an initial stage of porosity decrease accomplished by breakage of grain contacts and grain rotation, and a second stage of further porosity reduction accommodated by intense grain breakage and rotation. Quantitative stereological measurements corroborated the decrease in the intergrain spacing and the increase in grain boundary contacts that the microstructural observations suggest occurred during the first stage of compaction. The microstructural data show that a five-fold increase in the surface area per unit volume resulted from the extensive microfracturing that occurred during the second stage of compaction.
Influence of grain size and geothermal gradient on the ductile-to-brittle transition in arenaceous sedimentary rocks: implications for fault structure and fluid flow
Authors: Fisher Q. J. , Harris S. D. , Casey M. , Knipe R. J.
Published: November 2007

To investigate the interaction between the rheology of arenaceous sedimentary rocks (sand and sandstone) and stress conditions during burial we have coupled published results from deformation experiments with a simple quartz cementation model. The model provides valuable insights into controls on sandstone deformation consistent with observations from nature. A transitional zone exists in subsiding sedimentary basins, here referred to as the ductile-to-brittle transition (DBT), above which faults in normally pressured arenites will tend to form fluid flow barriers, and below which they will tend to form conduits. The DBT depth in sandstone is dependent upon geothermal gradient, burial rate and grain size. Low geothermal gradients, rapid sedimentation rates and coarse grain sizes favour a deep DBT and vice versa. Fine-grained arenites may only deform in a brittle manner for most natural burial rates and geothermal gradients, explaining why they do not usually contain thick deformation band zones. Coarser-grained arenites may deform in a brittle–ductile or ductile manner, which is why they often contain thick deformation band zones and occasionally experience pervasive porosity collapse. Sandstones within high geothermal gradient areas may deform to produce fluid flow conduits at shallow depths when porosities in the sequence as a whole are high; this possibly favours fault-related mineralization.
Fracture aperture, length and pattern geometry development under biaxial loading: a numerical study with applications to natural, cross-jointed systems
Authors: Olson J. E.
Published: November 2007

Fracture mechanics modelling of fracture pattern development was used to analyse pattern geometry and population statistics for natural opening-mode fractures. Orthogonal fracture network geometries were generated under biaxial extension loading conditions from a slightly anisotropic initial strain state. Fracture statistics were analysed by grouping all fracture orientations into one population for these unique orthogonal pattern geometries. Fracture aperture distributions resembled negative exponential curve shapes, consistent with published observations for stratabound fractures in sedimentary rock. Fracture length distributions had a strongly power-law shape, and showed that longer fractures grew first and reached their fullest extent before shorter fractures began propagating. The power-law shape of the length distribution was first established by the growth of the longest fractures in the population, followed by the later growth of shorter fractures that extended the power-law shape to smaller sizes. The shortest fracture length at which the power-law distribution was truncated varied with the magnitude of the applied strain. Other variations in fracture pattern results were tied to mechanical layer thickness and subcritical crack growth propagation properties of the fractured media.
Permeability of fault rocks from the Median Tectonic Line in Ohshika-mura, Nagano, Japan as studied by pressure-cycling tests
Authors: Uehara S. , Shimamoto T.
Published: November 2007

We describe laboratory measurements of the permeability of fault rocks and their host protoliths obtained from the Median Tectonic Line (MTL), the largest strike-slip fault in Japan. The measurements are made using a gas-medium apparatus that simulates
in situ
conditions. Samples of fault gouge, cataclastic mylonite, and protoliths were collected from the Kitagawa and Ankoh outcrops of the MTL and adjacent areas in Ohshika-mura, Nagano Prefecture, central Japan. Permeabilities of these samples were measured at room temperature under dry conditions, with nitrogen as the pore fluid. Most samples from the incohesive fault zone have a permeability ranging between 10
−13
and 10
−17
m
2
(100–0.01 mD). These permeabilities are greater than those of cemented cataclasites and mylonites by more than two orders of magnitude at all effective pressures (
P
e
) up to 180 MPa. Clayey fault gouge material has a permeability as low as 10
−19
m
2
(0.1 µD) at high effective pressures, but such impermeable fault gouge does not constitute a continuous zone on the two outcrops we studied. Permeability of the incohesive fault rocks exhibits large hysteresis upon
P
e
cycling, compared with cataclasite and mylonite, because those cemented, cohesive fault rocks undergo much less inelastic deformation during the pressure cycling.
Follow-up of GK rats during prediabetes highlights increased insulin action and fat deposition despite low insulin secretion
Authors: Movassat Jamileh , Bailbé Danièle , Lubrano-Berthelier Cécile , Picarel-Blanchot Françoise , Bertin Eric , Mourot Jacques , Portha Bernard
Published: November 2007

The adult Goto-Kakizaki (GK) rat is characterized by impaired glucose-induced insulin secretion in vivo and in vitro, decreased β-cell mass, decreased insulin sensitivity in the liver, and moderate insulin resistance in muscles and adipose tissue. GK rats do not exhibit basal hyperglycemia during the first 3 wk after birth and therefore could be considered prediabetic during this period. Our aim was to identify the initial pathophysiological changes occurring during the prediabetes period in this model of type 2 diabetes (T2DM). To address this, we investigated β-cell function, insulin sensitivity, and body composition in normoglycemic prediabetic GK rats. Our results revealed that the in vivo secretory response of GK β-cells to glucose is markedly reduced and the whole body insulin sensitivity is increased in the prediabetic GK rats in vivo. Moreover, the body composition of suckling GK rats is altered compared with age-matched Wistar rats, with an increase of the number of adipocytes before weaning despite a decreased body weight and lean mass in the GK rats. None of these changes appeared to be due to the postnatal nutritional environment of GK pups as demonstrated by cross-fostering GK pups with nondiabetic Wistar dams. In conclusion, in the GK model of T2DM, β-cell dysfunction associated with increased insulin sensitivity and the alteration of body composition are proximal events that might contribute to the establishment of overt diabetes in adult GK rats.
Pharmacological analysis of components of the change in transmural potential difference evoked by distension of rat proximal small intestine in vivo
Authors: Larsson Marie H. , Sapnara Maria , Thomas Evan A. , Bornstein Joel C. , Lindström Erik , Svensson David J. , Sjövall Henrik
Published: November 2007

The reflex response to distension of the small intestine in vivo is complex and not well understood. The aim of this study was to characterize the neural mechanisms contributing to the complex time course of the intestinal secretory response to distension. Transmucosal potential difference (PD) was used as a marker for mucosal chloride secretion, which reflects the activity of the secretomotor neurons. Graded distensions (5, 10, and 20 mmHg) of distal rat duodenum with saline for 5 min induced a biphasic PD response with an initial peak (rapid response) followed by a plateau (sustained response). The rapid response was significantly reduced by the neural blockers tetrodotoxin and lidocaine (given serosally) and by intravenous (iv) administration of the ganglionic blocker hexamethonium and the NK1 receptor antagonist SR-140333. Serosal TTX and iv SR-140333 significantly reduced the sustained response, which was also reduced by the NK3 receptor antagonist talnetant and by the vasoactive intestinal polypeptide (VPAC) receptor antagonist [4Cl-d-Phe6, Leu17]-VIP. Serosal lidocaine and iv hexamethonium had no significant effect on this component. Inhibition of nitric oxide synthase had no effect on any of the components of the PD response to distension. The PD response to distension thus seems to consist of two components, a rapidly activating and adapting component operating via nicotinic transmission and NK1 receptors, and a slow component operating via VIP-ergic transmission and involving both NK1 and NK3 receptors.
Temporal and spatial dynamics underlying capacitative calcium entry in human colonic smooth muscle
Authors: Kovac Jason R. , Chrones Tom , Sims Stephen M.
Published: November 2007

Following smooth muscle excitation and contraction, depletion of intracellular Ca2+stores activates capacitative Ca2+entry (CCE) to replenish stores and sustain cytoplasmic Ca2+(Ca2+i) elevations. The objectives of the present study were to characterize CCE and the Ca2+idynamics underlying human colonic smooth muscle contraction by using tension recordings, fluorescent Ca2+-indicator dyes, and patch-clamp electrophysiology. The neurotransmitter acetylcholine (ACh) contracted tissue strips and, in freshly isolated colonic smooth muscle cells (SMCs), caused elevation of Ca2+ias well as activation of nonselective cation currents. To deplete Ca2+istores, the sarcoplasmic reticulum Ca2+-ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid were added to a Ca2+-free bathing solution. Under these conditions, addition of extracellular Ca2+(3 mM) elicited increased tension that was inhibited by the cation channel blockers SKF-96365 (10 μM) and lanthanum (100 μM), suggestive of CCE. In a separate series of experiments on isolated SMCs, SERCA inhibition generated a gradual and sustained inward current. When combined with high-speed Ca2+-imaging techniques, the CCE-evoked rise of Ca2+iwas associated with inward currents carrying Ca2+that were inhibited by SKF-96365. Regional specializations in Ca2+influx and handling during CCE were observed. Distinct “hotspot” regions of Ca2+rise and plateau were evident in 70% of cells, a feature not previously recognized in smooth muscle. We propose that store-operated Ca2+entry occurs in hotspots contributing to localized Ca2+elevations in human colonic smooth muscle.
Oxygen or carbogen breathing before simulated submarine escape
Authors: Gennser M. , Blogg S. L.
Published: November 2007

Raised internal pressure in a distressed submarine increases the risk of bubble formation and decompression illness after submarine escape. The hypothesis that short periods of oxygen breathing before submarine escape would reduce decompression stress was tested, using Doppler-detectable venous gas emboli as a measure. Twelve goats breathed oxygen for 15 min at 0.1 MPa before exposure to a simulated submarine escape profile to and from 2.5 MPa (240 m/seawater), whereas 28 control animals underwent the same dive without oxygen prebreathe. No decompression sickness (DCS) occurred in either of these two groups. Time with high bubble scores (Kisman-Masurel ≥3) was significantly ( P < 0.001) shorter in the prebreathe group. In a second series, 30 goats breathed air at 0.2 MPa for 6 h. Fifteen minutes before escape from 2.5 MPa, animals were provided with either air ( n = 10), oxygen ( n = 12), or carbogen (97.5% O2and 2.5% CO2) gas ( n = 8) as breathing gas. Animals breathed a hyperoxic gas (60% O2-40% N2) during the escape. Two animals (carbogen group) suffered oxygen convulsions during the escape but recovered on surfacing. Only one case of DCS occurred (carbogen group). The initial bubble score was reduced in the oxygen group ( P < 0.001). The period with bubble score of Kisman-Masurel ≥3 was also significantly reduced in the oxygen group ( P < 0.001). Oxygen breathing before submarine escape reduces initial bubble scores, although its significance in reducing central nervous system DCS needs to be investigated further.
Mechanisms of exertional dyspnea in patients with cancer
Authors: Travers J. , Dudgeon D. J. , Amjadi K. , McBride I. , Dillon K. , Laveneziana P. , Ofir D. , Webb K. A. , O'Donnell D. E.
Published: November 2007

Exertional dyspnea is an important symptom in cancer patients, and, in many cases, its cause remains unexplained after careful clinical assessment. To determine mechanisms of exertional dyspnea in a variety of cancer types, we evaluated cancer outpatients with clinically important unexplained dyspnea (CD) at rest and during exercise and compared the results with age-, sex-, and cancer stage-matched control cancer (CC) patients and age- and sex-matched healthy control participants (HC). Participants ( n = 20/group) were screened to exclude clinical cardiopulmonary disease and then completed dyspnea questionnaires, anthropometric measurements, muscle strength testing, pulmonary function testing, and incremental cardiopulmonary treadmill exercise testing. Dyspnea intensity was greater in the CD group at peak exercise and for a given ventilation and oxygen uptake ( P < 0.05). Peak oxygen uptake was reduced in CD compared with HC ( P < 0.05), and breathing pattern was more rapid and shallow in CD than in the other groups ( P < 0.05). Reduced tidal volume expansion during exercise correlated with reduced inspiratory capacity, which, in turn, correlated with reduced inspiratory muscle strength. Patients with cancer had a relatively reduced diffusing capacity of the lung for carbon monoxide, reduced skeletal muscle strength, and lower ventilatory thresholds during exercise compared with HC ( P < 0.05). There were no significant between-group differences in measurements of airway function, pulmonary gas exchange, or cardiovascular function during exercise. In the absence of evidence of airway obstruction or restrictive interstitial lung disease, the shallow breathing pattern suggests ventilatory muscle weakness as one possible explanation for increased dyspnea intensity at a given ventilation in CD patients.
Effects of chronic nitric oxide synthase inhibition on responses to acute exercise in swine
Authors: McAllister Richard M. , Newcomer Sean C. , Pope Eric R. , Turk James R. , Laughlin M. Harold
Published: November 2007

Nitric oxide (NO) is potentially involved in several responses to acute exercise. We tested the hypotheses that inhibition of NO formation reduces maximal O2delivery to muscle, but does not affect O2utilization by muscle, therefore lowering maximal O2consumption. To test these hypotheses, swine (∼30 kg) drank either tap water (Con, n = 25) or water with NG-nitro-l-arginine methyl ester (8.0 ± 0.4 mg·kg−1·day−1for ≥4 wk; LN, n = 24). Treatment efficacy was reflected by higher mean arterial pressure and lower plasma NO metabolite concentration in LN than Con (both P < 0.05). Swine completed two graded treadmill running tests to maximum. In the first test, O2consumption was determined at rest through maximal exercise intensity. O2consumption did not differ between groups at rest or at most exercise intensities, including maximum (Con, 40.8 ± 1.8 ml·min−1·kg−1; LN, 40.4 ± 2.9; not significant). In the second test, tissue-specific blood flows were determined using the radiolabeled-microsphere technique. At rest, blood flows were lower ( P < 0.05) in LN compared with Con for a number of tissues, including kidney, adrenal, lung, and several skeletal muscles. During both submaximal and maximal exercise, however, blood flows were similar between Con and LN for all 16 muscles examined; only blood flows to kidney (Con, 99 ± 16 ml·min−1·100 g; LN, 55 ± 15; P < 0.05) and pancreas (Con, 25 ± 7; LN, 6 ± 2; P < 0.05) were lower in LN at maximum. Endothelium-dependent, but not -independent, relaxation of renal arterial segments was reduced ( P < 0.05) in vitro. These data indicate that exercise-induced increases in muscle blood flows are maintained with chronic inhibition of NO formation and that maximal O2consumption is therefore preserved. Redundant vasodilatory pathways and/or upregulation of these pathways may underlie these findings.