Geochemistry of DSDP Leg 65 basalts

Leg 65 of the Deep Sea Drilling Project successfully recovered basalts from four sites in the mouth of the Gulf of California, thus completing a transect begun during Leg 64 from the continental margin of Baja California to the east side of the East Pacific Rise (EPR). Sixty-three whole-rock samples from Sites 482, 483, and 485 have been analyzed by X-ray fluorescence techniques, and a further eleven samples by instrumental neutron-activation techniques, in order to assess magma variability within and between sites. Although the major element compositions and absolute hygromagmatophile (HYG) element abundances are quite variable, all of the basalts are subalkaline tholeiites exhibiting strong more-HYG element (e.g., Rb, La, Nb, Ta) depletion (LaN/YbN ~ 0.4; Nb/Zr ~ 0.02; Ba/Zr ~ 0.23; Th/Hf ~ 0.05). These ratios, together with La/Ta ratios of 20 and Th/Ta ratios of 1.25, demonstrate that the Leg 65 basalts resemble the depleted "N-type" ocean ridge basalts recovered from the Mid-Atlantic Ridge (MAR) at 22 °N and other sections of the EPR. Zr/Ti, Zr/Y, and La/Yb ratios increase with increasing fractionation. It is clear that the basalts recovered from Sites 482, 483, and 485 were all derived from a compositionally similar source and that the compositional differences observed between lithological units can be explained by varying degrees of open system fractional crystallization (magma mixing) in subridge magma chambers. The basaltic rocks recovered from Site 474 near the margin of Baja California, and Sites 477, 478, and 481 in the Guaymas Basin, all drilled during Leg 64, have consistently higher Th/Hf, La/Sm, Zr/Ti, and Zr/Y ratios and higher absolute Sr contents than the Leg 65 basalts. While some of these variations may be explained by different conditions of partial melting, it is considered more likely that the mantle source underlying the Guaymas Basin is chemically distinct from that feeding the EPR at the mouth of the Gulf. These source variations probably reflect the complex tectonic setting of the Gulf of California, the magmas formed at the inception of spreading and in the central part of the Gulf containing a minor but significant component of sub-continental (calc-alkaline) material.

A refined solution to Earth's hidden niobium: implications for evolution of continental crust and mode of core formation

New high-precision niobium (Nb) and tantalum (Ta) concentration data are presented for early Archaean metabasalts, metabasaltic komatiites and their erosion products (mafic metapelites) from SW Greenland and the Acasta gneiss complex, Canada. Individual datasets consistently show sub-chondritic Nb/Ta ratios averaging 15.1+/-11.6. This finding is discussed with regard to two competing models for the solution of the Nb-deficit that characterises the accessible Earth. Firstly, we test whether Nb could have sequestered into the core due to its slightly siderophile (or chalcophile) character under very reducing conditions, as recently proposed from experimental evidence. We demonstrate that troilite inclusions of the Canyon Diablo iron meteorite have Nb and V concentrations in excess of typical chondrites but that the metal phase of the Grant, Toluca and Canyon Diablo iron meteorites do not have significant concentrations of these lithophile elements. We find that if the entire accessible Earth Nb-deficit were explained by Nb in the core, only ca. 17% of the mantle could be depleted and that by 3.7 Ga, continental crust would have already achieved ca. 50% of its present mass. Nb/Ta systematics of late Archaean metabasalts compiled from the literature would further require that by 2.5 Ga, 90% of the present mass of continental crust was already in existence. As an alternative to this explanation, we propose that the average Nb/Ta ratio (15.1+/-11.6) of Earth's oldest mafic rocks is a valid approximation for bulk silicate Earth. This would require that ca. 13% of the terrestrial Nb resided in the Ta-free core. Since the partitioning of Nb between silicate and metal melts depends largely on oxygen fugacity and pressure, this finding could mean that metal/silicate segregation did not occur at the base of a deep magma ocean or that the early mantle was slightly less reducing than generally assumed. A bulk silicate Earth Nb/Ta ratio of 15.1 allows for depletion of up to 40% of the total mantle. This could indicate that in addition to the upper mantle, a portion of the lower mantle is depleted also, or if only the upper mantle were depleted, an additional hidden high Nb/Ta reservoir must exist. Comparison of Nb/Ta systematics between early and late Archaean metabasalts supports the latter idea and indicates deeply subducted high Nb/Ta eclogite slabs could reside in the mantle transition zone or the lower mantle. Accumulation of such slabs appears to have commenced between 2.5 and 2.0 Ga. Regardless of these complexities of terrestrial Nb/Ta systematics, it is shown that the depleted mantle Nb/Th ratio is a very robust proxy for the amount of extracted continental crust, because the temporal evolution of this ratio is dominated by Th-loss to the continents and not Nb-retention in the mantle. We present a new parameterisation of the continental crust volume versus age curve that specifically explores the possibility of lithophile element loss to the core and storage of eclogite slabs in the transition zone. (C) 2003 Elsevier Science B.V. All rights reserved.

Updating of an instrumented building model considering amplitude dependence of dynamic resonant properties extracted from seismic response records

The authors would like to express their gratitude to their supporters. Drs Jim Cousins, S.R. Uma and Ken Gledhill facilitated this research by providing access to GeoNet seismic data and structural building information. Piotr Omenzetter’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.

Updating of an instrumented building model considering amplitude dependence of dynamic resonant properties extracted from seismic response records

The authors would like to express their gratitude to their supporters. Drs Jim Cousins, S.R. Uma and Ken Gledhill facilitated this research by providing access to GeoNet seismic data and structural building information. Piotr Omenzetter’s work within the Lloyd’s Register Foundation Centre for Safety and Reliability Engineering at the University of Aberdeen is supported by Lloyd’s Register Foundation. The Foundation helps to protect life and property by supporting engineering-related education, public engagement and the application of research.

Analysis of multiple cracking in metal/ceramic composites with lamellar microstructure

Financial support of this research by The Royal Society, UK (IE121116), The Carnegie Trust for the Universities of Scotland, UK (Trust Reference 31747) and DFG (PI 785/3-2, PI 785/1-2), Germany, is gratefully acknowledged. We thank Dr. S. Roy (KIT) for providing the microstructure images and Professor I. Tsukrov (University of New Hampshire, USA) for helpful discussions.

Modelling of Stress-Corrosion Cracking by Using Peridynamics

Acknowledgement The authors are grateful to Prof. Siegfried Schmauder and Prof. Erdogan Madenci for the useful discussions that occurred throughout the realization of this study and acknowledge the Defence Science and Technology Laboratory (DSTL) for the financial support. A special thanks go to the anonymous reviewers, whose time and contribution have been highly appreciated. Results were obtained using the EPSRC funded ARCHIE-WeSt High Performance Computer (www.archie-west.ac.uk). EPSRC grant no. EP/K000586/1.

Production of ethanol, organic acids and hydrogen : an opportunity for mixed culture biotechnology?

Peer reviewed

Modelling of stiffness degradation due to cracking in laminates subjected to multi-axial loading

Funding Financial support of this research by the Engineering and Physical Sciences Research Council (EPSRC/GR/L51348) and the British Ministry of Defence is gratefully acknowledged.

Simulations of charged droplet collisions in shear flow

Acknowledgments This research has been enabled by the use of computing resources provided by WestGrid, the Shared Hierarchical Academic Research Computing Network (SHARCNET: www.sharcnet.ca), and Compute/Calcul Canada. O.S. thanks NSERC for an Alexander Graham Bell Canada Graduate Scholarship.

Generation of a train of ultrashort pulses using periodic waves in tapered photonic crystal fibres

Funding This work was supported by the Ministry of Education , Nigeria for financial support through the TETFUND scholarship 55 scheme; CSIR [grant number 03(1264)/12/EMR-II].

Optimisation of a ground anchor head for NDT monitoring

Peer reviewed

Modelling of Cutting Fibrous Composite Materials : Current Practice

Peer reviewed

O comportamento dos ajustes posturais antecipatórios na tibio-társica na sequência de levantar em indivíduos com doença de Parkinson

Introdução: A sequência de movimento de sentado para de pé (SPP) exige um elevado controlo postural (CP). Em indivíduos com doença de Parkinson (DP), os circuitos que envolvem os ajustes posturais antecipatórios (APA’s) parecem estar afetados, refletindo-se numa diminuição do CP com repercussões nesta sequência de movimento. Objetivo: Avaliar o comportamento dos APA’s na tibio-társica na sequência de movimento SPP em indivíduos com DP. Métodos: Recorreu-se ao estudo de 4 casos com DP, com tempo de evolução entre os 3 e 17 anos, objeto de uma intervenção de fisioterapia baseada nos princípios do Conceito de Bobath durante 12 semanas. Antes (M0) e após (M1) a intervenção procedeu-se ao registo eletromiográfico dos músculos tibial anterior (TA) e solear (SOL) bilateralmente e durante a sequência de SPP. Adicionalmente foram também utilizadas a Escala de Equilíbrio de Berg, a Modified Falls Efficacy Scale (MFES) e a Classificação Internacional de Funcionalidade (CIF), para, indiretamente, averiguar o impacto funcional da reorganização dos APA’s. Resultados: Em M0 os resultados sugerem uma diminuição APA’s, uma vez que se observou: 1) diferentes tempos de ativação do TA e do SOL entre membros e 2) uma ativação prévia do SOL ao TA para os participantes A, C e D. Em M1, observou-se uma aproximação ao comtemplado para os APA’s para a maioria dos indivíduos. Os resultados na escala de Berg e MFES, de M0 para M1, sugerem um aumento do equilíbrio e da capacidade de confiança na maioria dos participantes (A, 21/42 pontos, B manteve a pontuação final 31 pontos, C, 50/54 pontos e D 45/53 pontos na escala de Berg; A, 30/43 pontos, B, 21/18 pontos, C, 70/68 pontos e D, 40/64 pontos na MFES;). Também se observaram melhorias nas atividades e participação da CIF. Conclusão: nos indivíduos em estudo verificou-se, de uma forma geral, uma modificação no sentido da aproximação do período comtemplado para os APA’s, em M1. Nos sujeitos A, C, e D verificou-se uma modificação do tempo de activação do SOL em função da actividade do TA em M1. No individuo B, à esquerda não se verificou o mesmo comportamento, verificou-se a activação inversa do SOL ao TA.

Avaliação dos ajustes posturais em indivíduos com instabilidade funcional do tornozelo

Introdução:O Controlo Postural é um processo neural complexo envolvido na organização da estabilidade e orientação da posição do corpo no espaço. A Instabilidade Funcional (IF) do tornozelo é descrita como uma perceção subjetiva de instabilidade articular, que afeta o controlo postural. Apesar de vários estudos terem investigado os fatores inerentes à IF ainda existe inconsistência nos resultados da literatura sobre os mecanismos envolvidos nesta. Objetivo (s):avaliar os ajustes posturais envolvidos na resposta a uma perturbação externa realizada de forma previsível e imprevisível em indivíduos com IF. Métodos:Estudo observacional analítico transversal, teve uma amostra de 20 indivíduos, que foram divididos em grupo com IF e grupo de controlo. Foi recolhida atividade eletromiográfica bilateral dos músculos longo e curto peroneal (PL e PC), tibial anterior (TA) e solear (SOL) associado a uma perturbação externa aplicada de forma previsível e imprevisível. Os ajustes posturais foram avaliados através da análise do início da atividade muscular, da magnitude global dos ajustes posturais compensatórios e antecipatórios e magnitude das respostas de curta e média latência Resultados: Na perturbação imprevisível não se verificaram diferenças significativas no início da atividade muscular (p>0,05). Enquanto na magnitude das respostas de curta e média latência verificou-se diferenças nos músculos TA (Ia,p=0,000; II, p=0,011), CP (Ia,p=0,029; II, p=0,001) e LP (Ia, p=0,030) entre o membro com IF e o controlo e no LP (II, p=0,011) entre o membro sem IF do grupo com IF e o controlo. Na perturbação previsível observaram-se diferenças nos ajustes posturais antecipatórios (APA) dos músculos TA (p=0,006) e LP (p=0,020) entre o membro sem IF do grupo com IF e o controlo. Conclusão: Os indivíduos com IF apresentam défices na magnitude das respostas de média e curta latência numa perturbação imprevisível e nos APA na perturbação previsível.