574 research outputs found
Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels
No full textMitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion
Diets of seabirds and consequences of changes in food supply
No full textResearch conducted by members of the Working Group on Seabird Ecology, on issues most likely to be raised within the ICES community concerning the foraging ecology of seabirds and waders, and the potential interactions between these groups of birds and fisheries.
A review of issues related to seabird consumption of fish and shellfish stocks, discards and mariculture as well as the trophic role and ecology of seabirds and waders: G. L. Hunt, W. A. Montevecchi, and M. F. Leopold.
Consumption of pre-recruit fish by seabirds and the possible use of this as an indicator of fish stock recruitment: S. P. R. Greenstreet, P. H. Becker, R. T. Barrett, P. Fossum, and M. F. Leopold.
Variation in prey taken by seabirds: M. L. Tasker, C. J. Camphuysen, and P.Fossum.
Evaluation of the role of discards in supporting bird populations and their effects on the species composition of seabirds in the North Sea: S. Garthe, U. Walter, M. L. Tasker, P. H. Becker, G. Chapdelaine, and R. W. Furness.
Exploration of the short-and medium-term consequences of a reduction in the amounts of fish discarded: M. L. Tasker, P. H. Becker, and G. Chapdelaine
Evidence for decadal scale variations in seabird population ecology and links with the North Atlantic oscillation: J. B. Reid, P. H. Becker, and R. W. Furness.
A review of the causes, and consequences at the population level, of mass mortalities of seabirds : C. J. Camphuysen, P. J. Wright, M. Leopold, O. Hüppop, and J. B. Reid.
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METAL NON-METAL AND OTHER INTERFACES - THE ROLE OF IMAGE INTERACTIONS
No full textThe authors argue that many phenomena associated with metal/nonmetal interfaces and similar situations with a large dielectric constant mismatch can be understood in terms of the image interactions due to charges in the nonmetal. The effects are additional to the traditional interactions, and are especially significant when no reactions between the phases occur. The image-charge concept allows one to rationalise much apparently unrelated information concerning: (a) the systematics of wetting and nonwetting of oxides by liquid metals; (b) the systematics of strong metal-support interaction in catalysis; (c) the spatial variation of stoichiometry in oxides grown on metals; (d) the dependence on thickness of the observed changes in the wetting by water of oxide grown on silicon; (e) some features of radiation-enhanced adhesion; and (f) a number of correlations of behaviour with nonmetal properties in which the precise choice of metal is not critical
Building MIII clusters with derivatised salicylaldoximes
No full textThis thesis describes the synthesis of a host of polynuclear iron complexes
synthesised with phenolic oxime ligands, fundamentally developing the coordination
chemistry of iron with these ligands. The metallic cores that occur within iron
phenolic oxime clusters were found to contain almost exclusively oxo-centred
triangles and oxo-centred tetrahedra. We found that we could alter the reaction
conditions or derivatise the ligands and develop these basic building blocks into
more elaborate arrays, exerting a degree of control over creating larger or smaller
clusters. Chapter one describes the syntheses, structures and magnetic properties of
new iron complexes alongside previously synthesised related complexes (4, 5, 8, 9
and 15) containing salicylaldoxime (saoH2) or derivatised salicylaldoximes (RsaoH2).
These are [Fe3O(OMe)(Ph-sao)2Cl2(py)3]·2MeOH (1·2MeOH),
[Fe3O(OMe)(Ph-sao)2Br2(py)3]·Et2O (2·Et2O), [Fe4(Ph-sao)4F4(py)4]·1.5MeOH
(3·1.5MeOH), [Fe6O2(OH)2(Et-sao)2(Et-saoH)2(O2CPh)6] (4),
[HNEt3]2[Fe6O2(OH)2(Et-sao)4(O2CPh(Me)2)6]·2MeCN (5·2MeCN),
[Fe6O2(O2CPh)10(3-tBut-5-NO2-sao)2(H2O)2]·2MeCN (6·2MeCN),
[Fe6O2(O2CCH2Ph)10(3-tBut-sao)2(H2O)2]·5MeCN (7·5MeCN),
{[Fe6Na3O(OH)4(Me-sao)6(OMe)3(H2O)3(MeOH)6]·MeOH}n (8·MeOH) and
[HNEt3]2[Fe12Na4O2(OH)8(sao)12(OMe)6(MeOH)10] (9). The predominant building
block appears to be the triangular [Fe3O(R-sao)3]+ species which can self-assemble
into more elaborate arrays depending on reaction conditions. The four hexanuclear
and two octanuclear complexes of formulae [Fe8O2(OMe)4(Mesao)
6Br4(py)4]·2Et2O·MeOH (10·2Et2O·MeOH), [Fe8O2(OMe)3.85(N3)4.15(Mesao)
6(py)2] (11), [Fe6O2(O2CPh-4-NO2)4(Me-sao)2(OMe)4Cl2(py)2] (12),
[Fe6O2(O2CPh-4-NO2)4(Et-sao)2(OMe)4Cl2(py)2]·2Et2O·MeOH (13·2Et2O·MeOH),
[HNEt3]2[Fe6O2(Me-sao)4(SO4)2(OMe)4(MeOH)2] (14) and [HNEt3]2[Fe6O2(Etsao)
4(SO4)2(OMe)4(MeOH)2] (15) all are built from series of edge-sharing [Fe4( μ4-
O)]10+ tetrahedra. Complexes 10 and 11 display a new μ4-coordination mode of the
oxime ligand and join a small group of Fe-phenolic oxime complexes with nuclearity
greater than six.
Chapter three then introduces co-ligands to the reaction scheme to compete
with the salicylaldoxime ligands for metal coordination sites. Five tetranuclear and
two nononuclear complexes are stabilised with salicylaldoxime (saoH2) or
derivatised salicylaldoximes (R-saoH2) in conjunction with either 1,4,7-
triazocyclononane (tacn), 2-hydroxymethyl pyridine (hmpH) or 2,6-pyridine
dimethanol (pdmH2), [Fe4O2(sao)4(tacn)2]·2MeOH (16·MeOH), [Fe4O2(Mesao)
4(tacn)2]·2MeCN (17·2MeCN), [Fe4O2(Et-sao)4(tacn)2]·MeOH (18·MeOH),
[Fe9NaO4(Et-sao)6(hmp)8]·3MeCN·Et2O (19·3MeCN·Et2O), [Fe4 (Etsao)
4(hmp)4]·Et-saoH2 (20·Et-saoH2), [Fe4(Ph-sao)4(hmp)4]·2MeCN (21·2MeCN)
[Fe9O3(sao)(pdm)6(N3)7(H2O)] (22).
Chapter four straps two salicylaldoxime units together in the 3-position, using
ligands with aliphatic a,W-aminomethyl links, allowing the assembly of the
polynuclear complexes [Fe7O2(OH)6(H2L1)3(py)6](BF4)5·6H2O·14MeOH
(23·6H2O·14MeOH), [Fe6O(OH)7(H2L2)3][(BF4)3]·4H2O·9MeOH
(24·4H2O·9MeOH) and
[Mn6O2(OH)2(H2L1)3(py)4(MeCN)2](BF4)5(NO3)·3MeCN·H2O·5py
(25·3MeCN·H2O·5py). In each case the metallic skeleton of the cluster is based on a
trigonal prism in which two [MIII
3O] triangles are tethered together via three helically
twisted double-headed oximes. The latter are present as H2L2- in which the oximic
and phenolic O-atoms are deprotonated and the amino N-atoms protonated, with the
oxime moieties bridging across the edges of the metal triangles. Both the identity of
the metal ion and the length of the straps connecting the salicylaldoxime units have a
major impact on the nuclearity and topology of the resultant cage, with, perhaps
counter-intuitively, the longer straps producing the “smallest” clusters
Ode to the warlike genius of Great Britain. By the Rev. W. Tasker, A.B. Dedicated to the Right Honourable Lord Amherst [electronic resource].
No full textThe titlepage is a cancel.Price from imprint: price One Shilling.Electronic reproduction.English Short Title Catalog,Reproduction of original from Huntington Library
Endothelin-1-induced ischemic damage and functional impairment is mediated primarily by NR2B-containing NMDA receptors
No full textIschemic stroke accounts for 70–80% of stroke cases worldwide and survivors are frequently left with compromising sensorimotor deficits localized to one or more body regions. Most animal models of stroke involve transient or permanent occlusion of one or more major vessels such as the middle cerebral artery and are characterized by widespread damage to cortical and subcortical structures that result in deficits that can confound studies of neuroprotection and neurorehabilitation. Localized microinjections of the vasoconstricting peptide endothelin-1 (ET-1) into specific brain regions are becoming increasingly popular for such studies, but the pharmacology of endothelin-induced ischemic damage is poorly understood. To test the hypothesis that NMDA receptors, and particularly those containing the NR2B subunit, are involved in ET-1-mediated excitotoxicity and functional impairment, male CD1 rats (N = 32) were pre-treated with either the non-competitive NMDA antagonist MK-801 or the NR2B-selective antagonist Ro25-6981 (or vehicle) prior to unilateral microinjections of endothelin-1 into the somatosensory cortex and striatum. Rats were then tested using 4 established tests of sensory and/or motor function over 14 days. Lesion volumes were quantified post-mortem using standard histology and image analysis. Results confirmed reproducible lesions and significant deficits in all tests in vehicle-treated rats that were significantly reduced in both drug groups but were not different between drugs, providing evidence that endothelin-induced ischemic damage is mediated almost exclusively by NR2B-containing NMDA receptors
Development of foam-based support material for coaxial bioprinting of ionically crosslinking bioinks
No full textIn this study, a foam-based method is developed for three-dimensional coaxial bioprinting of ionically crosslinking bioinks. This method introduces the crosslinker to the bioink in calcium chloride-albumin foam which eliminates the need for multiple crosslinking steps and offers an excellent control over the crosslinking rate and the diameter of the hollow fibers. The effects of the foam and alginate flow rates were investigated on the outer diameter and the wall thickness of the hollow fibers. Various structures were 3D printed and characterized by printability number and the method showed an excellent layer adhesion among printed layers. The effects of foam composition and the alginate concentration on the mechanical properties were assessed through breaking strain and filament collapse tests to determine the optimum composition for hollow fiber fabrication. The hollow fiber composed of 2% (w/v) sodium alginate that is crosslinked with a foam made of 1.07% (w/v) albumin and 1.07% (w/v) calcium chloride showed superior mechanical properties. Furthermore, the viability of co-incubation with Neuro-2a cells over seven days was investigated and no significant negative effect of the used concentrations of albumin and calcium chloride was observed on the viability of the cells.National Sciences and Research Council of CanadaCanada Foundation for Innovatio
Endothelin-1-induced ischemic damage and functional impairment Is mediated primarily by NR2B-vontaining NMDA receptors [Epub ahead of print]
No full textComparative Evaluation of Optimum Power and Efficiency Terminations Predicted by Alternative Methods for GaN Ka-band Power Amplifier Design
No full textA comparative evaluation is provided in this paper regarding two design approaches for Ka-band Gallium Nitride Power Amplifiers. The first approach uses the standard electrical models provided by the foundry, while the alternative approach uses a custom model derived from in-house load-pull characterization. Both Power Amplifiers are designed to provide 30 dBm output power and 30% efficiency in the 31 - 35 GHz bandwidth. It is shown that the PA based on the custom model has a better PAE performance by about 4% and higher output power by 0.3 dB. </p
Oxidation of Aluminium-Magnesium alloys at elevated temperature in the solid, semi-liquid and liquid states
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Sensitive thermogravimetric equipment was used to monitor the oxidation rates of A1-1 to 9% Mg alloys in 0.21 oxygen/0.79 helium mixtures with and without 0.03 atm water vapour pressure, in the temperature range 500-725°C which include their respective solid, semi-liquid and liquid states. These measurements were supported by structural and topographical studies of oxide films using SEM, X-ray diffraction, and TEM with electron diffraction and EDX techniques. The objective was to provide information in the context of dross formation during melting operations. The only oxidation product observed was MgO. The oxidation rates do not follow simple rate laws. The rate normally increases as the temperature is raised except for a curious inverse relationship for liquid alloys just above the liquidus temperatures due to the formation of undulating surfaces. An amorphous MgO film formed on liquid alloys restricted the initial oxidation but, following an incubation period, crystallisation of the film induced breakaway oxidation. The crystallisation was promoted by high magnesium contents, high temperatures and moist atmospheres. The oxidation rates for alloys in the semi-liquid state were as follows: (i) for 50% liquid, the rates were initially faster than those for wholly liquid alloys due to the presence of solid phase particles which acted both as disruptive stress-raisers and as sources of nuclei for crystallisation of the amorphous oxide film over the liquid phase. For the moist atmosphere: (i) wholly solid alloys and semi-liquid alloys with 50% liquid oxidised faster than in the dry atmosphere because of the injection of OH- ions into the oxide with consequent disruptive effects caused by hydrogen absorption by the alloy. The addition of 0.003% Be to Al-8% Mg alloy decreased the oxidation rate markedly by toughening the MgO films preventing cracking and hence the nucleation of tertiary MgO. Small additions of Mn or Zr offset the effect of Be and probably enhanced the Mg 2+ ion conductivity in the oxide by the 4+ injection of Mn 2+ , Mn 4+ or Zr ions. For alloys with Be, although breakaway eventually occurred it was not initiated by crystallisation of the amorphous film and moisture in the atmosphere increased the oxidation throughout the temperature range, 500-725°C.Financial support was provided by the
Science and Engineering Research Council (SERC), Swindon, U.K
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