884 resultados para Protection by p-cycles


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Supplemental to Building research at the National Bureau of Standards, by P.R. Achenbach.

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Historic Wales, by P. H. Ditchfield.--The church of north Wales, by G. H. Jones.--The cathedral churches of Bangor and St. Asaph; The religious houses of north Wales; The parish churches of north Wales, by H. H. Hughes.--The Eisteddvod, by L. J. Roberts.--The poetry of north Wales, by Sir Edward Anwyl.--The castles of north Wales, by H. H. Hughes.--Llewelyn the Great; Llewelyn the Last, by W. L. Williams.--The social and economic conditions of north Wales in the 14th-16th centuries, by Edward Owen.--The cromlechs of north Wales, by J. E. Lloyd.--Owen Glyndwr, by L. J. Roberts.--Archbishop Williams, by J. A. Price.--The origin of nonconformity in north Wales, by J. H. Davies.--Relics, civic plate, regalia, &c., by E. A. Jones.--Index.

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"The publication of Öfversigt af K. Vetenskaps-akademiens förhandlingar and Bihang til K. Svenska vetenskaps-akademiens handlingar ... will not be continued. A yearbook and four publications will be published instead. These four publications are named: Arkiv för matematik ... Arkiv för kemi ... Arkiv för botanik, Arkiv för zoologi."

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Included in the original collection of the Starling Medical College.

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Compiled by P. Zilcken.

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"Fifty copies. A separate impression from the Chess monthly, for private distribution."

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Sulfadoxine is predominantly used in combination with pyrimethamine, commonly known as Fansidar, for the treatment of Plasmodium falciparum. This combination is usually less effective against Plasmodium vivax, probably due to the innate refractoriness of parasites to the sulfadoxine component. To investigate this mechanism of resistance by P. vivax to sulfadoxine, we cloned and sequenced the P. vivax dhps (pvdhps) gene. The protein sequence was determined, and three-dimensional homology models of dihydropteroate synthase (DHPS) from P. vivax as well as P. falciparum were created. The docking of sulfadoxine to the two DHPS models allowed us to compare contact residues in the putative sulfadoxine-binding site in both species. The predicted sulfadoxine-binding sites between the species differ by one residue, V585 in P. vivax, equivalent to A613 in P. falciparum. V585 in P. vivax is predicted by energy minimization to cause a reduction in binding of sulfadoxine to DHPS in P. vivax compared to P. falciparum. Sequencing dhps genes from a limited set of geographically different P. vivax isolates revealed that V585 was present in all of the samples, suggesting that V585 may be responsible for innate resistance of P. vivax to sulfadoxine. Additionally, amino acid mutations were observed in some P. vivax isolates in positions known to cause resistance in P. falciparum, suggesting that, as in P. falciparum, these mutations are responsible for acquired increases in resistance of P. vivax to sulfadoxine.

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The basis for the neuroprotectant effect of D-mannitol in reducing the sensory neurological disturbances seen in ciguatera poisoning, is unclear. Pacific ciguatoxin-1 (P-CTX-1), at a concentration 10 nM, caused a statistically significant swelling of rat sensory dorsal root ganglia (DRG) neurons that was reversed by hyperosmolar 50 MM D-mannitol. However, using electron paramagnetic resonance (EPR) spectroscopy, it was found that P-CTX-1 failed to generate hydroxyl free radicals at concentrations of toxin that caused profound effects on neuronal excitability. Whole-cell patch-clamp recordings from DRG neurons revealed that both hyper- and iso-osmolar 50 MM D-mannitol prevented the membrane depolarisation and repetitive firing of action potentials induced by P-CTX-1. In addition, both hyper- and iso-osmolar 50 MM D-mannitol prevented the hyperpolarising shift in steady-state inactivation and the rise in leakage current through tetrodotoxin (TTX)-sensitive Na-v channels, as well as the increased rate of recovery from inactivation of TTX-resistant Nav channels induced by P-CTX-1. D-Mannitol also reduced, but did not prevent, the inhibition of peak TTX-sensitive and TTX-resistant I-Na amplitude by P-CTX-1. Additional experiments using hyper- and isoosmolar D-sorbitol, hyperosmolar sucrose and the free radical scavenging agents Trolox (R) and L-ascorbic acid showed that these agents, unlike D-mannitol, failed to prevent the effects of P-CTX-1 on spike electrogenesis and Na-v channel gating. These selective actions of D-mannitol indicate that it does not act purely as an osmotic agent to reduce swelling of nerves, but involves a more complex action dependent on the Nav channel subtype, possibly to alter or reduce toxin association. (c) 2005 Elsevier Ltd. All rights reserved.

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The incorporation of organic matter ( OM) in soils that are able to rapidly sorb applied phosphorus ( P) fertiliser reportedly increases P availability to plants. This effect has commonly been ascribed to competition between the decomposition products of OM and P for soil sorption sites resulting in increased soil solution P concentrations. The evidence for competitive inhibition of P sorption by dissolved organic carbon compounds, derived from the breakdown of OM, includes studies on the competition between P and (i) low molecular weight organic acids (LOAs), (ii) humic and fulvic acids, and (iii) OM leachates in soils with a high P sorption capacity. These studies, however, have often used LOAs at 1 - 100 mM, concentrations much higher than those in soils ( generally < 0.05 mM). The transience of LOAs in biologically active soils further suggests that neither their concentration nor their persistence would have a practical benefit in increasing P phytoavailability. Higher molecular weight compounds such as humic and fulvic acids also competitively inhibit P sorption; however, little consideration has been given to the potential of these compounds to increase the amount of P sorbed through metal - chelate linkages. We suggest that the magnitude of the inhibition of P sorption by the decomposition products of OM leachate is negligible at rates equivalent to those of OM applied in the field. Incubation of OM in soil has also commonly been reported as reducing P sorption in soil. However, we consider that the reported decreases in P sorption ( as measured by P in the soil solution) are not related to competition from the decomposition products of OM breakdown, but are the result of P release from the OM that was not accounted for when calculating the reduction in P sorption.

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Bacterial chaperonin, GroEL, together with its co-chaperonin, GroES, facilitates the folding of a variety of polypeptides. Experiments suggest that GroEL stimulates protein folding by multiple cycles of binding and release. Misfolded proteins first bind to an exposed hydrophobic surface on GroEL. GroES then encapsulates the substrate and triggers its release into the central cavity of the GroEL/ES complex for folding. In this work, we investigate the possibility to facilitate protein folding in molecular dynamics simulations by mimicking the effects of GroEL/ES namely, repeated binding and release, together with spatial confinement. During the binding stage, the (metastable) partially folded proteins are allowed to attach spontaneously to a hydrophobic surface within the simulation box. This destabilizes the structures, which are then transferred into a spatially confined cavity for folding. The approach has been tested by attempting to refine protein structural models generated using the ROSETTA procedure for ab initio structure prediction. Dramatic improvements in regard to the deviation of protein models from the corresponding experimental structures were observed. The results suggest that the primary effects of the GroEL/ES system can be mimicked in a simple coarse-grained manner and be used to facilitate protein folding in molecular dynamics simulations. Furthermore, the results Sur port the assumption that the spatial confinement in GroEL/ES assists the folding of encapsulated proteins.

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Root respiration uses a significant proportion of photosynthetically fixed carbon (C) and is a globally important source of C liberated from soils. Mangroves, which are an important and productive forest resource in many tropical and subtropical countries, sustain a high ratio of root to shoot biomass which may indicate that root respiration is a particularly important component in mangrove forest carbon budgets. Mangroves are often exposed to nutrient pollution from coastal waters. Here we assessed the magnitude of fine root respiration in mangrove forests in Belize and investigated how root respiration is influenced by nutrient additions. Respiration rates of excised fine roots of the mangrove, Rhizophora mangle L., were low (4.01 +/- 0.16 nmol CO2 g(-1) s(-1)) compared to those measured in temperate tree species at similar temperatures. In an experiment where trees where fertilized with nitrogen (N) or phosphorus (P) in low productivity dwarf forests (1-2 m height) and more productive, taller (47 m height) seaward fringing forests, respiration of fine roots did not vary consistently with fertilization treatments or with forest stature. Fine roots of taller fringe trees had higher concentrations of both N and P compared to dwarf trees. Fertilization with P enhanced fine root P concentrations in both dwarf and fringe trees, but reduced root N concentrations compared to controls. Fertilization with N had no effect on root N or P concentrations. Unlike photosynthetic C gain and growth, which is strongly limited by P availability in dwarf forests at this site, fine root respiration (expressed on a mass basis) was variable, but showed no significant enhancements with nutrient additions. Variation in fine root production and standing biomass are, therefore, likely to be more important factors determining C efflux from mangrove sediments than variations in fine root respiration per unit mass.

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This paper is the initial part of a comprehensive bipartite monograph of palynomorphs (viz., acritarchs, prasinophyte phycomata, and chitinozoans) that are represented profusely in marine lower Palaeozoic strata of the Canning Basin, Western Australia. The prime aim is to establish a palynologically based zonal scheme for the Ordovician sequence as represented in five cored boreholes drilled through the Lower to Middle Ordovician strata of the central-northeastern Canning Basin. These strata embrace the Oepikodus communis through Phragmodus-Plectodina conodont zonal interval and comprise (in ascending order) the Willara, Goldwyer, and Nita formations, of inferred early Arenig to Llanvirn age. All three formations contain moderately diverse and variably preserved palynomorphs. The palynomorph taxa, detailed systematically in the current Part One of this monograph, comprise 66 species of acritarchs and six of prasinophytes. Of these, two species of prasinophytes and 11 of acritarchs are newly established: Cymatiosphaera meandrica and Pterospermella franciniae; Aremoricanium hyalinum, A. solaris, Baltisphaeridium tenuicomatum, Gorgonisphaeridium crebrum, Lophosphaeridium aequalium, L. aspersum, Micrhystridium infrequens, Pylantios hadrus, Sertulidium amplexum, Striatotheca indistincta, and Tribulidium globosum. Pylantios (typified by P. hadrus), Sertulidium (typified by S. amplexum), and Tribulidium (typified by T globosum); are defined as new acritarch genera. Three new combinations are instituted: Baltisphaeridium pugiatum (PLAYFORD & MARTIN 1984), Polygonium canningianum (COMRAZ & PENIGUEL 1972), and Sacculidium furtivum (PLAYFORD & MARTIN 1984); and Ammonidium macilentum PLAYFORD & MARTIN 1984 and Sacculidium furtivum (PLAYFORD & MARTIN 1984) are emended. An appreciable number of palynomorph species are not formally named owing to lack of sufficient or adequately preserved specimens; others are compared but not positively identified with previously instituted species. The ensuing Part Two of this study will complete the systematic-descriptive documentation, i.e., chitinozoans, and evaluate the Canning Basin palynoflora in terms of its chronological and stratigraphic-correlative significance.

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Competition between three foliose, saxicolous lichens common on slate rock in South Gwynedd, Wales, U.K. was studied experimentally using the de Wit design. Fragments of the three species were cut from the edges of large thalli, glued to 5 x 5 cm plots marked out on pieces of slate which were then placed on boards in the field. For each combination of pairs of species, the two species were grown either in monoculture at a density of 24 fragments per plot or together in three mixtures in differing proportions, i.e. species A:B with 16:8, 12:12 and 8:16 fragments per plot; the density remaining constant throughout. Area of the species in the plots after 3 years was used as an estimate of growth. Physcia orbicularis and Parmelia glabratula ssp. fuliginosa grew similarly in monoculture. In mixtures of the two, growth of each species was linearly related to its proportion in a mixture, suggesting little competition had occurred during three years. By contrast, the growth of Parmelia conspersa in monoculture was significantly greater than that of P. orbicularis or P. glabratula. In addition, the growth of both species was substantially reduced in mixtures with P. conspersa; P. glabratula being eliminated in the mixture in which it was the minority species. These results suggest that P. conspersa should predominate in communities with either of the other two species and, in the absence of P. conspersa, communities dominated by P.orbicularis and P. glabratula should be more stable.