bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymorphism for vernalization requirement in a population of Avena fatua
Authors: Darmency H. , Aujas C.
Published: January 2008

Polymorphism for vernalization requirement has been observed within a population of wild oats, Avena fatua L., grown under greenhouse conditions. One group of plants was early flowering ("spring type," [Formula: see text]), whereas another was late flowering ("winter type," [Formula: see text]). Vernalization of the winter type was obtained by germinating seeds for 2 weeks at 4 °C and resulted in shortening the time to heading by 50 days. However, this polymorphism was not observed in the field when plants germinated before mid-May. Hence, vernalization requirements did not appear to have any adverse or beneficial effects on time to heading and may be a neutral character in this population. Nevertheless, the frequency of the winter type in the population increased significantly over 6 years. Mechanisms are suggested to account for this phenomenon.
Comparison of ectomycorrhizal–basidiomycete communities in red spruce versus northern hardwood forests of West Virginia
Authors: Bills G. F. , Holtzman G. I. , Miller Jr. O. K.
Published: January 2008

Sporocarps of Basidiomycetes belonging to families containing some species known to form ectomycorrhizae were enumerated in 12 plots (16 × 16 m) subdivided into contiguous 2 × 2 m quadrats during the growing seasons of 1981 – 1983. Plots were distributed equally between homogeneous second-growth red spruce stands and heterogeneous northern hardwood stands in southeastern West Virginia. A few major species accounted for most of the abundance, while most species fruited rarely, but abundance and phenology varied broadly from year to year, apparently in response to rainfall and temperature. Fungal species composition, spatial frequency, and sporocarp density in the two forest types differed as would be expected in light of the symbiotic nature of the fungi and trees considered. Of 54 fungal species encountered over 3 years, 19 occurred exclusively in spruce plots, 27 occurred exclusively in hardwood plots, and 8 occurred in both forest types. In both forest types, approximately 40% of the species were Russulaceae. Species frequency and sporocarp abundance were greater in spruce plots than in hardwood plots. The Shannon–Wiener index, the dominance–diversity curve, the species–area curve, and ordination confirmed that fungal species richness, equitability, and diversity were greater in the mixed-hardwood plots, which hosted many rare fungal species, than in the single-species coniferous plots, which were dominated by a few ubiquitous fungal species.
Altérations de l'embryogenèse de Marsilea vestita provoquées par un faible abaissement de température et phénomènes de récupération après retour aux conditions initiales
Authors: Chenou Éliane , Kuligowski Janine , Ferrand Michèle
Published: January 2008

Under controlled conditions, all the fertilized eggs of Marsilea vestita give rise to well-organized embryos in a few hours. The first cleavage divisions of the zygote are fast and synchronous at 24 °C, whereas they are very modified, slowed down, and unstable at 16 °C. Cold treatment induces morphological and structural alterations, the number and the degree of which are correlated with the treatment duration. The most important alteration concerns the mitotic spindle orientation, which is often aberrant. The ensuing cell wall formation is disrupted, branched, and incomplete; consequently the daughter nuclei exhibit abnormal locations. Furthermore they no longer divide synchronously. The identification of the first segments then becomes impossible. In these cells, some chromatic elements having the appearance of mitotic chromosomes are often located near the spindle; these misplaced chromosomes, therefore, are not integrated to the spindle apparatus. A cold treatment applied at fertilization is effective in preventing the polyspermy block. The supernumerary spermatozoids remain in the cytoplasm of the zygote but never fuse with its nucleus. Despite their altered ontogeny, most treated specimens display, when returned to 24 °C, a surprising ability to recover a normal topographic organization.
An ultrastructural study of postmeiotic development in the megasporocarp of Azolla microphylla
Authors: Herd Y. R. , Cutter E. G. , Watanabe I.
Published: January 2008

The development of megasporocarps of Azolla microphylla, after the retention of a single functional megaspore within the megasporangium, was studied by light and transmission electron microscopy, using material grown under controlled conditions. The young megaspore contained a thin layer of cytoplasm with various organelles and was bounded by a thin exine. It was surrounded by a dense periplasmodial tapetum, which consisted of a peripheral vacuolate region, containing degenerated megaspores, a middle region containing nuclei and large organelles such as amyloplasts and mitochondria, and an inner zone, invaginated round the spore, comprising microtubules, ribosomes, and coated vesicles. At a later stage the exine increased in thickness, and greater vacuolation occurred at the periphery of the periplasmodium. The endoperine was formed by deposition of granular material between the exine and the periplasmodium, and further granular material deposited in small vacuoles gave rise to the exoperine. The floats were formed from three (tapetal) membrane-bounded chambers, in which granular material gradually became organised to form the pseudocells. Characteristic exoperinal filaments were formed in channels in the periplasmodium, which was eventually completely used up in the formation of floats, collar, and megaspore wall, in which sporopollenin was probably present. The megaspore itself became engorged with cytoplasm and storage products such as lipid and starch. Cells of Anabaena with relatively thick walls were present between the megasporangial wall and the indusium.
Cultural characters and anamorphs of Biscogniauxia (= Nummularia) marginata, B. dennisii, and B. repanda
Authors: Callan Brenda E. , Rogers Jack D.
Published: January 2008

Cultural data and anamorphs of Biscogniauxia marginata, B. dennisii, and B. repanda are presented. Each species produces a characteristic anamorph which can be accommodated in the hyphomycetous genus Nodulisporium. They are separable from one another on gross colony morphology and conidiophore morphology.
Inflorescence structure and development in the Zingiberales: Thalia geniculata (Marantaceae)
Authors: Kirchoff Bruce K.
Published: January 2008

The inflorescence of Thalia geniculata is among the most complex in a family characterized by complex inflorescences. The main axis of the inflorescence bears primary bracts which subtend either enriching branches, in the enriching zone, or pairs of flowers, in the florescence. The enriching branches repeat the structure of the inflorescence as a whole, with the addition of two specialized bracts: a prophyll and an interphyll. The paired flowers of the Marantaceae are mirror images of each other. The first bract of the inflorescence is formed in the plane of distichy of the leaves. Subsequent bracts are formed slightly to one side of the apex, giving a one-sided distichous arrangement. On an enriching branch the sterile prophyll is formed adaxially, followed by a fertile, abaxial interphyll. The first bract following the interphyll lies in a plane approximately perpendicular to the plane of the prophyll and interphyll. With the second bract the alternating divergence angles of approximately 115 and 145° begin to be established. The paired flowers of the florescence are subtended by a single, adaxial prophyll. Unlike many other Marantaceae no interphyll or bracteoles are formed below the flowers.
The effects of deicing salts on vegetation in Pinhook Bog, Indiana
Authors: Wilcox Douglas A.
Published: January 2008

A 4-year study identified the effects of road salt contamination on the vegetation of Pinhook Bog after operation of an uncovered salt storage pile adjacent to the bog for 10 years. Nearly all of the endemic plant species (excluding moat species) were absent from the portion of the bog where mean salt concentrations as high as 468 mg/L sodium and 1215 mg/L chloride were measured in the interstitial waters of the peat mat. Skeletons of dead tamaracks remained. The impacted area was invaded by nonbog species and dominated by Typha angustifolia. As salt concentrations decreased by over 50% in 4 years, many of the endemic bog plants, including Sphagnum, returned to the impacted area. Declines were noted in the abundance of some of the invading species, while others continued expansion. Many of the invading and reestablished bog plants are known to be both salt tolerant and pioneers in secondary succession of disturbed bogs.
Survival and growth of pines with specific ectomycorrhizae after 3 years on a highly eroded site
Authors: Valdés Maria
Published: January 2008

Container-grown pine seedlings inoculated with vegetative mycelium of Pisolithus tinctorius, Laccaria laccata, or P. tinctorius plus the saprophytic Lepiota lutea were outplanted on a highly eroded reforestation site in Mexico. After 3 years, seedlings initially colonized by P. tinctorius plus L. lutea had the highest survival. Seedlings with P. tinctorius mycorrhizae (either alone or with L. lutea) had greater height, stem diameter, and seedling volume than both seedlings with L. laccata mycorrhizae and noninoculated seedlings. The average volume of seedlings with P. tinctorius or with P. tinctorius plus L. lutea was 538 and 423%, respectively, of that of noninoculated seedlings. The potential benefit of utilizing P. tinctorius inoculum in reforestation programs in Mexico is discussed.
Heteromeles and Photinia (Rosaceae, subfam. Maloideae) of Mexico and Central America
Authors: Phipps J. B.
Published: January 2008

This paper revises the Mexican and Central American species of Heteromeles M. Roemer and Photinia Lindley (Rosaceae, subfamily Maloideae). One genus, Heteromeles, is monotypic, whereas in Photinia five species are recognised. Of the Photinia species, one, P. mexicana, is highly distinct and the remainder are closely related to, or part of, the P. microcarpa complex. A numerical taxonomic study has been conducted to assist in differentiating the last-named group of taxa. One new species, Photinia guerreris, and two new subspecies of Photinia microcarpa, sspp. elliptica and hintonii, are described. In Photinia microcarpa ssp. hintonii a new variety, var. brevis, is created. Key words: Heteromeles, Photinia, Rosaceae, taxonomy, Mexico, Central America.
Ascospore development in Ophiostoma piceae
Authors: Wyk P. W. J. van , Wingfield M. J.
Published: January 2008

The development of ascoma, ascus, and ascospore in Ophiostoma piceae was studied ultrastructurally and compared with that of other Ascomycetes. Ascospore delimitation commenced with the formation of double delimiting membranes in the ascus. The ascospore wall, consisting of the primary and secondary walls, was deposited between these membranes. The elongate ascospores of O. piceae differed from other species having similarly shaped ascospores, with respect to the shape and arrangement of asci in the ascoma, the number of wall layers of the ascospore, and formation of the secondary wall. Asci in O. piceae are spindle shaped, arranged along the periphery of the ascomatal wall. The ascospores have three layered walls, whereas some other species in Ceratocystis s.l. also with elongated ascospores probably have only two wall layers. Key words: Ophiostoma, elongated ascospores, sheaths, centrum.
Effect of temperature on decomposition and development of microfungal communities in leaf litter microcosms
Authors: Carreiro Margaret M. , Koske R. E.
Published: January 2008

The influence of temperature on litter decomposition rates and on the composition and structure of microfungal communities was determined by incubating milled, deciduous leaf litter in microcosms at 0, 10, and 20 °C. Changes in species composition were assessed after 10 and 90 weeks using the dilution-plating method. Dry weight loss from litter after 90 weeks was 13.5, 19.0, and 30.7% at 0, 10, and 20 °C, respectively. Temperature caused major differences in the species composition and structure of the microfungal communities isolated. As temperature decreased, Zygomycete species richness increased, whereas Deuteromycete species richness decreased. Although species richness was similar at all three temperatures, diversity was highest at 20 °C and lower at 0 and 10 °C where the communities were dominated by single species. At 0 and 10 °C, communities were dominated by the Deuteromycetes Geomyces pannorus and Geomyces asperulatus, respectively, and by several species in the Zygomycete genera Mortierella and Mucor. At 20 °C the community consisted almost entirely of Deuteromycetes, with the genera Trichoderma, Humicola, and Sporothrix being most abundant. This study demonstrates that a distinct, low-temperature community of microfungi exists and can be active in litter at 0 °C. Key words: fungal community structure, litter decomposition, temperate forest, low-temperature microfungi, psychrophilic.
Paraliomyces lentiferus: an ultrastructural study of a little-known marine ascomycete
Authors: Read S. J. , Hsieh S.-Y. , Jones E. B. G. , Moss S. T. , Chang H. S.
Published: January 2008

A collection of Paraliomyces lentiferus from Taiwan, Republic of China, is compared with that of the type description and examined at both scanning and transmission electron microscope levels as part of our review of the taxonomy of the marine Ascomycotina. Particular attention was devoted to the structure of the ascospore appendage. The ascospore wall comprises a mesosporium, an episporium, and a mucilaginous sheath (exosporium?) In addition, there is a single, gelatinous, lateral appendage adjacent to the central septum. The appendage comprises electron-opaque fibrils that in immature ascospores are connected to the ascospore wall via fine electron-opaque strands and larger electron-opaque aggregates of material. The origin of the appendage is discussed. Key words: ascospore, attachment, marine ascomycete, scanning electron microscopy, spore appendage, transmission electron microscopy.
Pollen marqueur de transports à longue distance dans l'atmosphère du sud de l'Ontario (Canada)
Authors: Cambon G. , Ritchie J. C. , Guinet P.
Published: January 2008

An analysis of weekly air samples at four sites in southern Ontario (London, Toronto, Peterborough, Sudbury) provides conclusive evidence for the long-distance transport of pollen of the exotic taxa Entada (Mimosaceae), Dodonaea (Sapindaceae), and Ephedra (Ephedraceae), originating far to the south (at least 1000 km) of the recording stations. The nearest source area for the first two taxa is in the West Indies and Mexico, while Ephedra, previously noted in Late Quaternary sediments from the Great Lakes region, grows commonly in the southwestern region of the United States. Long-distance transport is corroborated by air-mass trajectory analysis and surface-wind patterns at time of exotic occurrences. Key words: aeropalynology, Ontario, airstreams, pollen transport.
Analyse écologique des peuplements de frêne noir (Fraxinus nigra) des rives du lac Duparquet, nord-ouest du Québec
Authors: Tardif Jacques , Bergeron Yves
Published: January 2008

Spring and early summer flood is one of the main factors affecting the dynamics of black ash (Fraxinus nigra Marsh.) stands growing on lake floodplains in the boreal forest. The effect of flooding on the vegetation was studied in five stands on the shore of Lake Duparquet in Abitibi, northwestern Quebec. Divisive hierarchical classification analysis (Twinspan) revealed the existence of four different vegetation types: (i) black ash – speckled alder (Alnus rugosa) – bog willow (Salix pedicellaris), (ii) black ash – balsam poplar (Populus balsamifera) – ostrich fern (Matteuccia struthiopteris), (iii) black ash – pussy willow (Salix discolor) – sensitive fern (Onoclea sensibilis), and (iv) black ash – speckled alder – sensitive fern. Detrended correspondance analysis (Decorana) shows that elevation and drainage are the main factors affecting plant distribution and dynamics. Geomorphology also plays a major role in the way each stand responds to flooding. For each of the vegetation types studied, black ash shows a particular regeneration pattern and sexual regeneration tends to become less frequent with increasing exposure to flooding. Finally, the strong sexual regeneration and the youth of the populations found in the most elevated sites could be related to a possible alteration of the flood regime. Key words: Fraxinus nigra Marsh., flooding, boreal forest, floodplain, ecological gradiant, regeneration.
Effect of ovule position on seed maturation and seed weight in Ulex europaeus and Ulex gallii (Fabaceae)
Authors: Gutiérrez David , Menéndez Rosa , Obeso José R.
Published: January 2008

We examined the effect of ovule position within the pod on the probability of seed maturation and on seed weight in two woody legumes, Ulex europaeus and Ulex gallii. Results showed that ovule position had a significant effect on the probability of seed maturation in both species. Ovules in a central position were found to have a higher probability of maturation in U. europaeus, whereas those in a stylar position were favored in U. gallii. Ulex europaeus showed no effect of position on seed weight. The smallest seed within the pod was more frequently at stylar positions in U. gallii. These results might be explained by several non-exclusive hypotheses: time of fertilization, constraints on seed development (e.g., fruit shape and access to maternal resources), and genetic quality. The effects of seed weight on progeny performance estimated as probability of germination and seedling weight were tested in a laboratory experiment. Neither U. europaeus nor U. gallii exhibited any effect of seed weight on the probability of germination. However, seedling weight was dependent on seed weight in both species. Keywords: woody legumes, probability of maturation, seed position, seed weight.
Bromus tectorum seed germination: between-population and between-year variation
Authors: Beckstead Julie , Meyer Susan E. , Allen Phil S.
Published: January 2008

Cheatgrass (Bromus tectorum L., Poaceae), an introduced winter annual, has invaded a variety of habitats in western North America. This study examines variation in cheatgrass germination response and after-ripening patterns that are related to differences in habitat and to yearly differences in weather conditions during seed maturation. Seeds collected from five contrasting populations in 1992 and 1993 were subjected to controlled dry storage and then incubated across a range of temperatures. Recently harvested seeds were dormant and germinated slowly, while fully after-ripened seeds were nondormant and germinated rapidly. The optimal incubation temperature for mean germination time shifted from 5:15 to 20:30 °C as a result of after-ripening. Between-population differences in germination response appear to be related to the potential risk of precocious summer germination. The results from this 2-year study suggest that the more extreme yet predictable environments select for seed germination and after-ripening patterns that are genetically fixed, while populations from more favorable environments tended to show more between-year variations, suggesting more phenotypic plasticity. Germination percentage showed greater between-year variation than mean germination time. Between-year differences could not be explained simply by differences in maximum temperature or total precipitation during maturation. Adaptive germination responses in cheatgrass populations from contrasting habitats may have both genetic and environmental components, thus explaining why this species can become established in such a variety of habitats. Keywords: after-ripening, invading species, dormancy, mean germination time, cheatgrass, downy brome.
Changes in levels of foliar carbohydrates and myo-inositol before premature leaf senescence of Populus nigra induced by a mixture of O3 and SO2
Authors: Fialho R. C. , Bücker J.
Published: January 2008

Specimens of Populus nigra L. cv. Loenen exhibit premature leaf senescence when exposed for a few weeks to realistic air pollution. In this study, the changes in levels of foliar carbohydrates and myo-inositol (MI) due to 30 ± 1 nL/L O3 + 12 ± 1 nL/L SO2 from the onset of exposure to the occurrence of premature abscission is presented. Petioles and laminae of the 12 oldest leaves were separately analysed on days 0, 4, 8, 12, 16, 20, 22, and 32 of continuous exposure, which was performed in open-top chambers (OTC). On days 8 to 12, clearly prior to yellowing (starting on day 22), total nonstructural carbohydrates (TNC; starch + raffinose + sucrose + glucose + fructose + MI) in the fumigated laminae exceeded that in controls by about 30%. This increase was due to higher amounts of different soluble forms, while starch remained unaltered. From day 20 onwards, the level of TNC in the fumigated laminae progressively fell below that in controls. This decrease was due to a progressive decline in starch, which had started on day 16 and was dominating, although glucose and raffinose increased significantly. In the petioles, starch, sucrose, and glucose decreased because of fumigation with the occurrence of leaf yellowing, while raffinose increased. In contrast, MI in the petioles progressively accumulated directly on exposure until leaf yellowing occurred. The results are discussed in terms of the "general adaption syndrome" of H. Selye (1936. Nature (London), 138: 32). The marked MI response in petioles is concluded to be an early indication of phytorelevant O3 + SO2 pollution. Keywords: air pollution, carbohydrates, myo-inositol, pigments, Populus nigra L., senescence, stress.
Differentiation of Sclerotinia minor depends on thiol redox state and oxidative stress
Authors: Patsoukis Nikolaos , Georgiou Christos D.
Published: January 2008

Sclerotial differentiation in Sclerotinia minor is associated with oxidative stress and thiol redox state. The significance of oxidative stress to sclerotial differentiation was revealed by the higher oxidative stress of S. minor compared with a nonsclerotiogenic counterpart. The effect of thiol redox state on sclerotial differentiation was shown by the antioxidant action of the thiol (-SH) group of N-acetylcysteine and cysteine and by an unknown (not antioxidant) role of glutathione (GSH) on S. minor. The nonantioxidant role of GSH was indicated by the differentiation-inhibiting and differentiation-noninhibiting actions of the GSH biosynthesis inhibitor l-buthionine-S,R-sulfoximine and the GSH biosynthesis inducer l-2-oxo-thiazolidine-4-carboxylate, respectively, and by the increase of oxidative stress they caused during the transition from the undifferentiated to differentiated state of S. minor. Moreover, N-acetylcysteine can be used as a potent nontoxic fungicide against this phytopathogenic fungus by acting as a growth-inhibiting cytotoxic oxidant and by sustaining the fungus in the undifferentiated hyphal stage, which is vulnerable to degradation by soil microorganisms.
PIXE ANALYSIS ON PREDOMINANT ELEMENTAL ACCUMULATION ON THE MANDIBLE OF VARIOUS TERMITES
Authors: OHMURA W. , SUZUKI Y. , IMASEKI H. , ISHIKAWA T. , ISO H. , YOSHIMURA T. , TAKEMETSU Y.
Published: January 2008

Information concerning the metallic component of termite mandibles may provide a significant clue for solving the evolutionary theory of termite species. Micro-beam scanning PIXE analysis was used, which is a power tool for detecting elemental components, along with two-dimensional information about the elemental distribution in the analyzed area. The distribution of three specific elements ( Mn , Zn and Cl ) is the focus of this paper. Especially, Mn and Zn are known to be distinctive factors in taxonomic studies of termite mandibles. In this study, mandibles of 12 species from 5 families were analyzed. Mn was detected in all the termites, except for Mastotermes darwiniensis. On the other hand, only kalotermitid termites had Zn as a predominant metal in the cutting edges. The elemental analysis of these mandibles showed significant information to solve the uncertainty of the phylogenetic relation of termites.
APPLICATION OF A DROPLET-PIXE SYSTEM TO STUDY RADIATION EFFECTS ON ECOSYSTEM FUNCTIONING
Authors: ISHII N. , HOMMA-TAKEDA S. , TAGAMI K. , FUMA S. , TAKEDA H.
Published: January 2008

Droplet PIXE analysis was applied to the study of radiation effects on soil ecosystem functioning. A paddy soil sample was flooded with well water to prepare soil ecosystem specimens (microcosms), and then the microcosms were chronically exposed to gamma rays at a dose rate of 1 Gy day−1 for 5 days. After the final irradiation, a brownish discoloration was observed in the liquid phases of the irradiated microcosms.To clarify the factors causing the discoloration, minerals in the solutions of the microcosms were analyzed by the droplet PIXE system.Elemental profiles from the XRF spectrum showed marked iron peaks. Exposure of microcosms to gamma rays resulted in a decrease in the iron levels. Since iron is released in the form of Fe(II) from the solid soil to the liquid phase, further determination of the Fe (II) levels was performed. The percentages of Fe (II) to the total iron in the liquid phase of the irradiated microcosms were lower than those of the controls. This result may be caused by the change of Fe species from soluble Fe (II) to insoluble Fe (III) during gamma irradiation, and the Fe (III) species with a brownish color may be associated with the discoloration of the irradiated samples. The conversion from soluble to insoluble forms may also contribute the small amount of dissolved iron in the irradiated microcosms. Iron is an essential trace nutrient for plants, and thus the amount of dissolved iron is one aspect of ecosystem functioning. Effects of gamma radiation on the dissolved iron could involve a change in the soil ecosystem through the depression of iron flux in the long term.
OPTIMAL DOPANT PROFILING BASED ON ENERGY-TRANSPORT SEMICONDUCTOR MODELS
Authors: DRAGO CONCETTA R. , PINNAU RENÉ
Published: January 2008

We consider optimal design problems for semiconductor devices which are simulated using the energy transport model. We develop a descent algorithm based on the adjoint calculus and present numerical results for a ballistic diode. Furthermore, we compare the optimal doping profile with results computed based on the drift diffusion model. Finally, we exploit the model hierarchy and test the space mapping approach, especially the aggressive space mapping algorithm, for the design problem. This yields a significant reduction of numerical costs and programming effort.
HOPF SOLUTIONS TO A FLUID-ELASTIC INTERACTION MODEL
Authors: GUIDORZI M. , PADULA M. , PLOTNIKOV P. I.
Published: January 2008

In this paper, we give a global existence theorem of weak solutions to model equations governing interaction fluid structure in a two-dimensional layer, cf. Refs. 8 and 14. To our knowledge this is the first existence theorem of global in time solutions for such model. The interest of our result is double because, first, we change the original initial value problem by deleting one initial condition, second, we construct a solution through the classical Galerkin method for which several computing codes have been constructed.
EFFECTIVE DATA DISSEMINATION FOR INFORMATION SHARING BASED ON INTER-VEHICLE COMMUNICATION
Authors: SAGO HIROYUKI , SHINOHARA MASAKO , HARA TAKAHIRO , NISHIO SHOJIRO
Published: January 2008

In an Intelligent Transport System (ITS), information sharing based on inter-vehicle communication is effective for improving data availability. In this paper, we propose a data dissemination method for sharing data items among vehicles, which increases the opportunity for vehicles to acquire more fresh data items that users request. In our proposed method, vehicles are grouped according to their locations, and movement directions that are estimated from their route information. Then, data items that are more likely to be accessed in the near future are disseminated between two groups. We also present simulation results to evaluate the performance of our proposed method.
STOCHASTIC MODELING AND ANALYSIS OF AN ACTIVE CONGESTION CONTROL PROTOCOL UNDER DIFFERENTIATED BURSTY TRAFFIC
Authors: WANG LAN , MIN GEYONG , AWAN IRFAN
Published: January 2008

Traffic congestion degrades not only the user-perceived Quality-of-Service (QoS), such as leading to high packet loss rates, low throughput, and increased delays, but also causes excessive energy consumption in energy-sensitive systems (e.g., wireless sensor networks). A simple way to detect congestion is to monitor and measure queue length in network nodes or routers. This paper develops an analytical performance model for a finite capacity queueing system with an enhanced Random Early Detection (RED) congestion control scheme based on the instantaneous queue length in the presence of differentiated classes of bursty traffic. The aggregate traffic is captured by the superposition of 2-state Markov Modulated Poisson Processes (MMPP). The individual threshold is assigned to each traffic class in order to differentially control traffic injection rate. The accuracy of this model is verified by comparing the analytical results against those obtained from simulation experiments. The model is adopted to investigate the effects of traffic burstiness and system capacity on the performance of the congestion control scheme.
ENHANCED ROUTING METRIC FOR LOAD-BALANCING IN WIRELESS MESH NETWORKS
Authors: MA LIANG , DENKO MIESO K.
Published: January 2008

Wireless mesh networks (WMNs) have been drawing significant attention in recent years due to their flexibility in providing extensive wireless backbone. WMNs typically consist of mesh routers and mesh clients with each node operating not only as a host but also as a router. Due to the traffic patterns in WMNs, load-balancing becomes an important issue and may degrade the performance of the entire network. This paper proposes a routing metric known as Weighted Cumulative Expected Transmission Time with Load-Balancing (WCETT-LB) for wireless mesh networks. WCETTT-LB enhances the basic Weighted Cumulative Expected Transmission Time (WCETT) by incorporating load-balancing into the routing metric. Unlike existing schemes, WCETT-LB implements load-balancing at mesh routers. WCETT-LB provides a congestion-aware routing and traffic splitting mechanism to achieve global load-balancing in the network. By conducting an extensive simulation experiments, the result shows that WCETT-LB outperforms the existing routing metrics in load-balancing in terms of achieving high packet delivery ratio, low average end-to-end delay and low average congestion level in wireless mesh networks. The qualitative and quantitative analysis also show the significance of the proposed scheme.
ONLINE DYNAMICALLY BALANCED ASCENDING AND DESCENDING GAIT GENERATIONS OF A BIPED ROBOT USING SOFT COMPUTING
Authors: VUNDAVILLI PANDU RANGA , SAHU SAMBIT KUMAR , PRATIHAR DILIP KUMAR
Published: January 2008

In the present paper, two algorithms based on soft computing have been developed for dynamically balanced gait generations of a biped robot ascending and descending a staircase. The utility of the soft computing tools is best justified, when the data available for the problem to be solved are imprecise in nature, difficult to model and exhibit large-scale solution spaces. The problem of online gait generation of a biped robot exhibits such a complex phenomenon, and ultimately soft computing has become a natural choice for solving it. The gait generation problems of a biped robot have been solved using two different approaches, namely genetic-neural (GA-NN) and genetic-fuzzy (GA-FLC) systems. In GA-NN, the gait generation problem of a two-legged robot has been modeled using two modules of Neural Network (NN), whose weights are optimized offline using a Genetic Algorithm (GA), whereas in GA-FLC, the above problem is modeled utilizing two modules of Fuzzy Logic Controller (FLC) and their rule bases are optimized offline using a GA. Once optimized, the GA-NN and GA-FLC systems will be able to generate dynamically balanced gaits of the biped robot online. The performances of the two approaches are compared with respect to the Dynamic Balance Margin (DBM).
Metasomatism of the upper mantle beneath the Hyblean Plateau (Sicily): evidence from pyroxenes and glass in peridotite xenoliths
Authors: Perinelli C. , Sapienza G. T. , Armienti P. , Morten L.
Published: January 2008

Coarse-grained, protogranular spinel peridotite xenoliths in the Upper Miocene Valle Guffari diatreme display a complex history for the shallow mantle underneath the Hyblean Plateau (SE Sicily). The mineral assemblage and composition (olivine Fo
89–91
, orthopyroxene En
88–91
, Cr-diopside En
48–49
Fs
4–6
Wo
45–48
, Cr-rich spinel with cr-number=25–39) record at least one depletion event caused by melt extraction, followed by metasomatic enrichment. One of these samples (HYB40) hosts a fresh glass vein. Rare earth elements (REE) in clinopyroxenes from these peridotites show three patterns: (1) light REE-enriched (La
n
/Yb
n
=7–17); (2) spoon-shaped (La
n
/Yb
n
=18–20; La
n
/Sm
n
=21–34; Sm
n
/Yb
n
<1); (3) nearly flat (La
n
/Yb
n
∼3). Whole-rock and clinopyroxene trace elements indicate that these patterns are associated with more or less complete equilibration with at least two distinct metasomatic melts: an alkaline silicate melt resembling the host basalt and a hawaiitic melt (for peridotite HYB40).
P
–
T
estimates yield 0.9–1.2 GPa and 870–1050 °C, suggesting that refertilization by metasomatizing melts occurred at the Crust–Mantle boundary or just below. In addition, the
P
–
T
data coincide with the palaeogeotherm reported by an earlier worker that is consistent with a high geothermal gradient. However, this thermal regime does not fit with the occurrence of an active mantle plume beneath the Hyblean area because of the deduced mantle potential temperatures, which are almost 200°C lower than those typical for a mantle plume.
f
O
2
calculation gives a redox state above the fayalite–magnetite–quartz buffer FMQ (up to +1.7 Δlog units) related to melt-driven metasomatism.
Metasomatism induced by alkaline magma in the upper mantle of northern Victoria Land (Antarctica): an experimental approach
Authors: Perinelli C. , Orlando A. , Conte A. M. , Armienti P. , Borrini D. , Faccini B. , Misiti V.
Published: January 2008

Magma generation in the Ross Sea system is related to partial melting of strongly metasomatized mantle sources where amphibole most probably plays a crucial role. In this context, metasomatism induced by a mela-nephelinite melt in lithospheric mantle of the Mt. Melbourne Volcanic Province (northern Victoria Land (NVL), Antarctica) was investigated experimentally studying the effects of melt interaction with lherzolite at 1.5–2.0 GPa and
T
=975–1300 °C, and wehrlite at 1.0 GPa and
T
=1050–1250 °C. The experiments were designed to induce melt infiltration into the ultramafic rocks. The observed modifications in minerals are compared with those found in mantle xenoliths from NVL. The effects of metasomatic modifications are evaluated on the basis of run temperature, distance from the infiltrating melt and the diffusion rates of chemical components. Both in lherzolite and wehrlite, clinopyroxene exhibits large compositional variations ranging from primary diopside to high-Mg–Cr–(Na) augitic and omphacitic clinopyroxenes in lherzolite, and to low-Mg and high-Ti–Al–Fe–Na augites in wehrlite. Olivine (in wehrlite) and spinel (in lherzolite) are also compositionally modified: the former shows enrichment in Fe and the latter displays a higher Cr/(Cr+Al) ratio. The systematic variations in mineral compositions imply modifications of the chemistry of the infiltrating melt as recorded by the glass veinlets and patches observed in some charges. In experiments involving wehrlite paragenesis, the glass composition approaches that of melt patches associated with both amphibole-free and amphibole-bearing natural samples, and is related to olivine + clinopyroxene crystallization coupled with primary clinopyroxene dissolution at the contact between the metasomatizing melt and the solid matrix. Even if amphibole crystallization was not attained in the experiments, we were able to explain the occurrence of amphibole in the natural system considering that in this case a hot metasomatizing melt infiltrates a cooler matrix.
Reconstruction of mantle sections beneath Yakutian kimberlite pipes using monomineral thermobarometry
Authors: Ashchepkov I. V. , Pokhilenko N. P. , Vladykin N. V. , Rotman A. Y. , Afanasiev V. P. , Logvinova A. M. , Kostrovitsky S. I. , Pokhilenko L. N. , Karpenko M. A. , Kuligin S. S. , Malygina E. V. , Stegnitsky Y. B. , Alymova N. A. , Khmelnikova O. S.
Published: January 2008

Four original monomineral methods for mantle peridotite associations are used to reconstruct
P
–
T
conditions beneath the kimberlite pipes of Yakutia. The clinopyroxene Jd–Di method gives the closest coincidence with Opx barometry in accord with all physico-chemical boundaries. Garnet thermometers calibrated using Opx, Gar–Cpx and Ni-garnet thermometers and two variants of barometers were developed separately for pyroxenites and peridotites. A Cr–Sp thermobarometer uses the monomineralic version of the Ol–Sp thermometer and a newly calibrated Cr–Sp barometer. A picroilmenite method uses the Ol–Sp thermometer and a pressure-calibration of the geikielite component. Each mantle column is divided into two (upper and lower) sections by a pyroxenite layer located near 40 kbar. Below the pyroxenite layer, the lower section comprises 3–4 lithologically distinct horizons, with a thermally perturbed layer at the base. Above the pyroxenite layer are 3–5 lithologically distinct horizons, which are more fertile than the lower sections. Splitting of the geotherms characterizes most
P
–
T
diagrams and is ascribed to multistage melt percolation processes typical for the mantle beneath kimberlite pipes. The largest pipes are diamond-bearing and have a highly depleted peridotite lens above the asthenospheric layer.
Calcic amphiboles in peridotite xenoliths from Avacha volcano, Kamchatka, and their implications for metasomatic conditions in the mantle wedge
Authors: Ishimaru S. , Arai S.
Published: January 2008

Highly metasomatized parts of peridotite xenoliths from Avacha volcano, Kamchatka, Russia, characteristically contain calcic amphiboles, especially tremolites. They are rich in metasomatic pyroxenes with high Mg-number (= Mg/(Mg+Fe) atomic ratio), up to 0.94–0.98, and contain Cr-poor aluminous spinels. They have the spinel lherzolite mineral assemblage and equilibrium temperatures of 900–1000 °C or higher, beyond the stability field of tremolite. The tremolite was therefore retrogressively formed after the peak of high-temperature metasomatism. The high-Mg-number, low-alkali environment facilitates the formation of tremolite instead of Al-rich calcic amphiboles. A sulphur-bearing silicic melt derived from a slab is a probable agent involved in the metasomatism. High
f
O
2
recorded in the highly metasomatized peridotites is consistent with this process. This type of metasomatism can produce high-Mg-number peridotites and pyroxenites with low-Cr-number spinel within the mantle wedge where the Mg-number of silicates is positively correlated with the Cr-number of spinel in ambient peridotites.
Asthenospheric signature in fertile spinel lherzolites from the Viliga Volcanic Field in NE Russia
Authors: Ntaflos T. , Tschegg C. , Coltorti M. , Akinin V. V. , Kosler J.
Published: January 2008

Mantle xenolith bearing olivine melanephelinites from the Okhotsk sector of the Okhotsk–Chukotka Volcanic Belt (OCVB), northeastern Russia, occur as small isolated volcanoes emplaced within massive late Early to Late Cretaceous subduction-related calc-alkaline rocks. The xenoliths are typical medium- to fine‐grained anhydrous mainly spinel lherzolites that are strongly to weakly foliated with intensive to minor recrystallization to equigranular texture. The primitive mantle normalized whole-rock REE have flat patterns or patterns with slightly elevated light REE (LREE) ((La/Yb)
N
=0.48–1.38). The REE in clinopyroxenes have systematically decreasing normalized abundances from Sm to La, implying that the LREE enrichments in the whole‐rock REE patterns are attributed to circulation of minor intergranular fluids or melts. Equilibration temperatures and pressures calculated for the Viliga samples are in the range of 1050–1160 °C and 15–21 kbar, respectively. Ca diffusion rates in olivine reveal a rapid transport to the surface (2–6 days) of these peridotites. Model calculations have shown that the fertile lherzolites can be produced by 2–9% batch melting, whereas the depleted peridotites require 15% batch melting of a primitive source. The cessation of the interaction between the palaeo-Pacific plate and the NE Russian margin at
c
. 87 Ma apparently caused a ‘piecemeal’ collapse of the former followed by intrusion and ascent of olivine melanephelinitic magma, which entrained xenoliths from the asthenospheric mantle of the subducted plate during the Pliocene through the generated window(s). Moreover, clinopyroxenes that have low
87
Sr/
86
Sr and high
143
Nd/
144
Nd and plot in and above the mid-ocean ridge basalt (MORB) field are consistent with an upwelling asthenospheric mantle through the window(s) created by the ‘piecemeal’ collapse of the palaeo-Pacific plate.
Heterogeneous metasomatism in cumulate xenoliths from the Spanish Central System: implications for percolative fractional crystallization of lamprophyric melts
Authors: Orejana D. , Villaseca C.
Published: January 2008

The alkaline lamprophyres and diabases from the Spanish Central System carry a heterogeneous suite of xenoliths including a group of highly altered ultramafic pyroxenites that contain Cr–Mg-rich high-
T
hydrous minerals (Ti-phlogopite and pargasitic to kaersutitic amphibole), indicative of modal metasomatism. The trace element mineral compositions of these xenoliths show three patterns: type A xenoliths, with light rare earth element enriched clinopyroxenes with high field strength element (HFSE) negative anomalies; type B xenoliths, with clinopyroxenes and amphiboles with high incompatible trace element contents (large ion lithophile elements (LILE), HFSE and REE); type C xenoliths, with relatively REE- and HFSE-poor clinopyroxenes and amphiboles. These metasomatic signatures suggest the involvement of three different metasomatic agents: carbonate, silicate and hydrous fluids or melts, respectively. These agents could have been derived from the progressive differentiation of a CO
2
–H
2
O-rich highly alkaline magma, genetically related to the Late Permian alkaline magmatism. Because of the original sub-alkaline nature of the pyroxenite xenoliths, they might have been formed originally as pyroxene-rich cumulates associated with underplated Hercynian calc-alkaline basic magmas. Metasomatism as a result of the infiltration of alkaline magmas within these cumulates might explain the relatively high radiogenic Nd composition of the altered ultramafic xenoliths.
Tyrosine phosphatase PTPα regulates focal adhesion remodeling through Rac1 activation
Authors: Herrera Abreu Maria Teresa , Castellanos Penton Patricia , Kwok Vivian , Vachon Eric , Shalloway David , Vidali Luis , Lee Wilson , McCulloch Christopher A. , Downey Gregory P.
Published: January 2008

We characterized the role of protein tyrosine phosphatase (PTP)-α in focal adhesion (FA) formation and remodeling using wild-type and PTPα-deficient (PTPα−/−) cells. Compared with wild-type cells, spreading PTPα−/− fibroblasts displayed fewer leading edges and formed elongated α-actinin-enriched FA at the cell periphery. These features suggest the presence of slowly remodeling cell adhesions and were phenocopied in human fibroblasts in which PTPα was knocked down using short interfering RNA (siRNA) or in NIH-3T3 fibroblasts expressing catalytically inactive (C433S/C723S) PTPα. Fluorescence recovery after photobleaching showed slower green fluorescence protein-α-actinin recovery in the FA of PTPα−/− than wild-type cells. These alterations correlated with reduced cell spreading, adhesion, and polarization and retarded contraction of extracellular matrices in PTPα−/− fibroblasts. Activation of Rac1 and its recruitment to FA during spreading were diminished in cells expressing C433S/C723S PTPα. Rac1−/− cells also displayed abnormally elongated and peripherally distributed FA that failed to remodel. Conversely, expression of constitutively active Rac1 restored normal FA remodeling in PTPα−/− cells. We conclude that PTPα is required for remodeling of FA during cell spreading via a pathway involving Rac1.
Adaptive responses to creatine loading and exercise in fast-twitch rat skeletal muscle
Authors: Gallo Maria , MacLean Ian , Tyreman Neil , Martins Karen J. B. , Syrotuik Daniel , Gordon Tessa , Putman Charles T.
Published: January 2008

We investigated the effects of chronic creatine loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular Ca2+, and the metabolic profile in rat plantaris muscle to ascertain the bases for our previous observations that creatine loading results in a higher proportion of myosin heavy chain (MHC) IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: creatine-fed sedentary, creatine-fed run-trained, control-fed sedentary, and control-fed run-trained animals. Proportion and cross-sectional area increased 10% and 15% in type IIb fibers and the proportion of type IIa fibers decreased 11% in the creatine-fed run-trained compared with the control-fed run-trained group ( P < 0.03). No differences were observed in fast Ca2+-ATPase isoform SERCA1 content ( P > 0.49). Creatine feeding alone induced a 41% increase ( P < 0.03) in slow Ca2+-ATPase (SERCA2) content, which was further elevated by 33% with running ( P < 0.02). Run training alone reduced parvalbumin content by 50% ( P < 0.05). By comparison, parvalbumin content was dramatically decreased by 75% ( P < 0.01) by creatine feeding alone but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through creatine loading, alleviates the need for intracellular Ca2+buffering by parvalbumin and increases the efficiency of Ca2+uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated by run training ( P < 0.003) but not by run training + creatine feeding. This indicates that creatine loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.
Setting the stage: possible mechanisms by which acute contraction restores insulin sensitivity in muscle
Authors: Thyfault John P.
Published: January 2008

It has long been known that acute exercise can dramatically improve insulin sensitivity in previously insulin-resistant muscle; however, the precise mechanisms underlying this clinically significant interaction remain unknown. Using hindlimb perfusions in obese Zucker rats, our group found that acute muscle contraction synergistically improved insulin-stimulated glucose transport in skeletal muscle, but contrary to our hypothesis, these findings were not associated with either improved insulin signaling or decreased intramuscular lipid metabolites. A further analysis revealed that the improved insulin sensitivity was associated with a robust increase in mitochondrial energy flux. These findings and reports from other labs suggest that mitochondrial energy flux and mitochondrial oxidative capacity may govern insulin sensitivity and override insulin signaling defects associated with obesity. This review will discuss the effects of acute exercise to enhance insulin sensitivity in previously insulin-resistant muscle and present possible novel mechanisms by which alterations in mitochondrial energy metabolism may play a regulatory role.