Evidence of micro-continent entrainment during crustal accretion

Peer reviewedPublisher PD

Crustal structure of southeast Australia from teleseismic receiver functions

Abstract. In an effort to improve our understanding of the seismic character of the crust beneath southeast Australia and how it relates to the tectonic evolution of the region, we analyse teleseismic earthquakes recorded by 24 temporary and 8 permanent broadband stations using the receiver function method. Due to the proximity of the temporary stations to Bass Strait, only 13 of these stations yielded usable receiver functions, whereas seven permanent stations produced receiver functions for subsequent analysis. Crustal thickness, bulk seismic velocity properties, and internal crustal structure of the southern Tasmanides – an assemblage of Palaeozoic accretionary orogens that occupy eastern Australia – are constrained by H–κ stacking and receiver function inversion, which point to the following: a ∼ 39.0 km thick crust; an intermediate–high Vp/Vs ratio (∼ 1.70–1.76), relative to ak135; and a broad (> 10 km) crust–mantle transition beneath the Lachlan Fold Belt. These results are interpreted to represent magmatic underplating of mafic materials at the base of the crust. a complex crustal structure beneath VanDieland, a putative Precambrian continental fragment embedded in the southernmost Tasmanides, that features strong variability in the crustal thickness (23–37 km) and Vp/Vs ratio (1.65–193), the latter of which likely represents compositional variability and the presence of melt. The complex origins of VanDieland, which comprises multiple continental ribbons, coupled with recent failed rifting and intraplate volcanism, likely contributes to these observations. stations located in the East Tasmania Terrane and eastern Bass Strait (ETT + EB) collectively indicate a crust of uniform thickness (31–32 km), which clearly distinguishes it from VanDieland to the west. Moho depths are also compared with the continent-wide AusMoho model in southeast Australia and are shown to be largely consistent, except in regions where AusMoho has few constraints (e.g. Flinders Island). A joint interpretation of the new results with ambient noise, teleseismic tomography, and teleseismic shear wave splitting anisotropy helps provide new insight into the way that the crust has been shaped by recent events, including failed rifting during the break-up of Australia and Antarctica and recent intraplate volcanism.PhD study of lead author has been jointly funded by Abubakar TafawaBalewa University (ATBU

Properties of Thirteen Viruses and Virus Variants Obtained from Eight Isolates of the Wheat Take-All Fungus, Gaeumannomyces graminis var. tritici.

The properties of polyhedral double-stranded ( s)RNA virus particles obtained from eight isolates of the wheat take-all fungus, Gaeumannomyces graminis var. tritici, have been investigated. Thirteen viruses and virus variants were distinguished and these were classified into three groups on the basis of serological and physical properties of the virus particles; viruses in a group were related serologicaUy to other members of the same group, but unrelated serologically to members of other groups. Group I viruses had particles of diam. 35 nm sedimenting at 109 to 126S; the virus capsid contained one polypeptide species, mol. wt. 54 × l03 to 60 × 103 and virus dsRNA consisted of two to four components, mol. wt. 1.0 x 10 6 tO I-3 X 106. Group II viruses had particles of diam. 35 nm sedimenting at 133 to 140S; the virus capsid contained one polypeptide species, tool. wt. 68 × 103 to 73 x 103 and virus dsRNA consisted of two to four components with mol. wt. 1.39 × 106 to 1.60 × l06. Group III viruses had particles of diam. 40 nm sedimenting at 159 to 163S; the viru

Novel explant model to study mechanotransduction and cell–cell communication

To understand in situ behavior of osteocytes, we characterized a model of osteocytes in their native bone matrix and demonstrated real-time biologic activity of osteocytes while bending the bone matrix. Using 43 male Sprague-Dawley rats, dumbbell-shaped explants were harvested from stainless steel femoral implants after 6–12 weeks and incubated in culture medium or fixed. Sixteen specimens were used to determine bone volume density (BV/TV), volumetric bone mineral density (BMD) and histology for different implantation periods. Osteocyte viability was evaluated by L-lactate dehydrogenase (LDH) activity in 12 cultured explants. Confocal microscopy was used to assess tracer diffusion in three explants and changes in osteocyte pH of a mechanically loaded explant. From 6 to 12 weeks, explant BV/TV and volumetric BMD trended up 92.5% and 101%, respectively. They were significantly and highly correlated. Tissues were uniformly intramembranous and all bone cell types were present. Explants maintained LDH activity through culture day 8. Diffusion at 200 µM was limited to 1,209 Da. Explants appeared capable of reproducing complex bone biology. This model may be useful in understanding osteocyte mechanotransduction in the context of a physiologically relevant bone matrix. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1687–1698, 2006Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55788/1/20207_ftp.pd

A phylogenomic perspective on diversity, hybridization and evolutionary affinities in the stickleback genus Pungitius

Hybridization and convergent evolution are phenomena of broad interest in evolutionary biology, but their occurrence poses challenges for reconstructing evolutionary affinities among affected taxa. Sticklebacks in the genus Pungitius are a case in point: evolutionary relationships and taxonomic validity of different species and populations in this circumpolarly distributed species complex remain contentious due to convergent evolution of traits regarded as diagnostic in their taxonomy, and possibly also due to frequent hybridization among taxa. To clarify the evolutionary relationships among different Pungitius species and populations globally, as well as to study the prevalence and extent of introgression among recognized species, genomic data sets of both reference genome-anchored single nucleotide polymorphisms and de novo assembled RAD-tag loci were constructed with RAD-seq data. Both data sets yielded topologically identical and well-supported species trees. Incongruence between nuclear and mitochondrial DNA-based trees was found and suggested possibly frequent hybridization and mitogenome capture during the evolution of Pungitius sticklebacks. Further analyses revealed evidence for frequent nuclear genetic introgression among Pungitius species, although the estimated proportions of autosomal introgression were low. Apart from providing evidence for frequent hybridization, the results challenge earlier mitochondrial and morphology-based hypotheses regarding the number of species and their affinities in this genus: at least seven extant species can be recognized on the basis of genetic data. The results also shed new light on the biogeographical history of the Pungitius-complex, including suggestion of several trans-Arctic invasions of Europe from the Northern Pacific. The well-resolved phylogeny should facilitate the utility of this genus as a model system for future comparative evolutionary studies.Peer reviewe

Heat Pipe Solar Receiver Development Activities at Sandia National Laboratories

Over the past decade, Sandia National Laboratories has been involved in the development of receivers to transfer energy from the focus of a parabolic dish concentrator to the heater tubes of a Stirling engine. Through the isothermal evaporation and condensation of sodium. a heat-pipe receiver can efficiently transfer energy to an engine's working fluid and compensate for irregularities in the flux distribution that is delivered by the concentrator. The operation of the heat pipe is completely passive because the liquid sodium is distributed over the solar-heated surface by capillary pumping provided by a wick structure. Tests have shown that using a heat pipe can boost the system performance by twenty percent when compared to directly illuminating the engine heater tubes. Designing heat pipe solar receivers has presented several challenges. The relatively large area ({approximately}0.2 m{sup 2}) of the receiver surface makes it difficult to design a wick that can continuously provide liquid sodium to all regions of the heated surface. Selecting a wick structure with smaller pores will improve capillary pumping capabilities of the wick, but the small pores will restrict the flow of liquid and generate high pressure drops. Selecting a wick that is comprised of very tine filaments can increase the permeability of the wick and thereby reduce flow losses, however, the fine wick structure is more susceptible to corrosion and mechanical damage. This paper provides a comprehensive review of the issues encountered in the design of heat pipe solar receivers and solutions to problems that have arisen. Topics include: flow characterization in the receiver, the design of wick systems. the minimization of corrosion and dissolution of metals in sodium systems. and the prevention of mechanical failure in high porosity wick structures

The future of passive seismic acquisition

It is an exciting time to be a seismologist. In November 2018, the InSight lander touched down on Mars and the first seismometer was deployed on another planet. This incredible feat means planetary seismologists are currently searching for marsquakes and will hopefully soon be providing images of its interior and helping us to understand how rocky planets form. However, we have been doing this for a long time in more familiar territory back home on Earth, where the field of terrestrial seismology has reached a turning point with significant developments in instrumentation and the manner of their deployment in recent years. However, equipment available to the UK community has not kept pace and needs urgent regeneration if the UK is to lead in the field of passive seismology in the future. To begin the process of redesigning the UK’s equipment for the next few decades, the British Geophysical Association sponsored a meeting in Edinburgh in late 2018 to discuss the future of passive seismic acquisition. What follows is a historical account of how and why we arrived at the present day UK seismological research and resource base, a summary of the Edinburgh meeting, and a vision for the passive seismic facilities required to support the next 20 years of seismological research