2,148 research outputs found
Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging: Part I - Processing parameters, mechanical properties and microstructure
A study simulating thin slab continuous casting followed by direct charging into an equalisation furnace has been undertaken based on six low carbon (0.06wt-%) vanadium microalloyed steels. Mechanical and impact test data showed properties were similar or better than those obtained from similar microalloyed conventional thick cast as rolled slabs. The dispersion plus dislocation strengthening was estimated to be in the range 80-250MPa.A detailed TEM/EELS analysis of the dispersion sized sub-15nm particles showed that in all the steels, they were essentially nitrides with little crystalline carbon detected. In the Steels V-Nb, V-Ti and V-Nb-Ti, mixed transition metal nitrides were present. Modelling of equilibrium precipitates in these steels, based on a modified version of ChemSage, predicted that only vanadium rich nitrides would precipitate in austenite but that the C/N ratio would increase through the two phase field and in ferrite. The experimental analytical data clearly points to the thin slab direct charging process, which has substantially higher cooling rates than conventional casting, nucleating non-equilibrium particles in ferrite which are close to stoichiometric nitrides. These did not coarsen during the final stages of processing, but retained their highly stable average size of ~7nm resulting in substantial dispersion strengthening. The results are considered in conjunction with pertinent published literature
Psammomermis sericesthidis n. sp. (Nematoda : Mermithidae) : a parasitoid of pasture feeding scarab larvae (Coleoptera : Scarabaeidae) in southeastern Australia
#Psammomernis sericesthidis n. sp. est un parasitoïde des larves des scarabés, #Sericesthis geminata Boisduval, #S. nigrolineata (Boisduval) (#Melolonthinae), #Dasygnathus sp., #Anoplognathus sp. (#Rutelinae), #Heteronyx sp. and #Anomalomorpha sp. (#Dynastinae) dans la région des plateaux du sud-est australien. #P. sericesthidis n. sp. se distingue de toutes les espèces décrites dans le genre - sauf #P. aricephala Ipatjeva et Pimenova, 1985 - par la présence d'un seul ergot hypodermique céphalique. #P. sericesthidis n. sp. diffère de #P. aricephala par la forme de la tête, la taille et la position des amphides, et la taille beaucoup plus grande du corps. (Résumé d'auteur
ALMA lensing cluster survey: Hubble space telescope and spitzer photometry of 33 lensed fields built with CHArGE
We present a set of multiwavelength mosaics and photometric catalogs in the Atacama Large Millimeter/submillimeter Array (ALMA) lensing cluster survey fields. The catalogs were built by the reprocessing of archival data from the Complete Hubble Archive for Galaxy Evolution compilation, taken by the Hubble Space Telescope (HST) in the Reionization Lensing Cluster Survey, Cluster Lensing And Supernova survey with Hubble, and Hubble Frontier Fields. Additionally, we have reconstructed the Spitzer Infrared Array Camera 3.6 and 4.5 μm mosaics, by utilizing all the available archival IPAC Infrared Science Archive/Spitzer Heritage Archive exposures
The Quark Propagator from the Dyson-Schwinger Equations: I. the Chiral Solution
Within the framework of the Dyson-Schwinger equations in the axial gauge, we
study the effect that non-perturbative glue has on the quark propagator. We
show that Ward-Takahashi identities, combined with the requirement of matching
perturbative QCD at high momentum transfer, guarantee the multiplicative
renormalisability of the answer. Technically, the matching with perturbation
theory is accomplished by the introduction of a transverse part to the
quark-gluon vertex. We show that this transverse vertex is crucial for chiral
symmetry breaking, and that massless solutions exist below a critical value of
the strong coupling constant. Using the gluon propagator that we previously
calculated, we obtain small corrections to the quark propagator, which keeps a
pole at the origin in the chiral phase.Comment: 21 pages, 6 figures; McGill/94-24, SHEP 93/94-26 We generalise our
results by showing that they are not sensitive to the specific choice that we
make for the transverse vertex. We illustrate that fact in two new figure
Spread of metals through an invertebrate food chain as influenced by a plant that hyperaccumulates nickel
Hyperaccumulation of metals in the shoot
system of plants is uncommon, yet taxonomically and geographically
widespread. It may have a variety of functions,
including defense against herbivores. This study investigated
the effects of hyperaccumulation on metal concentrations
across trophic levels. We collected plant material,
soil, and invertebrates from Portuguese serpentine outcrops
whose vegetation is dominated by the nickel hyperaccumulator
Alyssum pintodasilvae. Samples were analyzed for
nickel, chromium, and cobalt. Grasshoppers, spiders, and
other invertebrates collected from sites where A. pintodasilvae
was common had significantly elevated concentrations
of nickel, compared to nearby sites where this hyperaccumulator
was not found. Chromium and cobalt, occurring in
high concentrations in the serpentine soil but not accumulated
by A. pintodasilvae, were not elevated in the invertebrates.
Therefore, it appears likely that a flux of nickel to
herbivore and carnivore trophic levels is specifically facilitated
by the presence of plants that hyperaccumulate this
metal. The results may be relevant to the development of
phytoremediation and phytomining technologies, which use
plants to extract metals from the soil
Life cycle analysis of steel railway bridges
This paper focuses on the growth of cracks that arise from natural corrosion in steel bridges. It is shown that these two effects of corrosion and stress, need to be simultaneously analysed. A methodology used to compute the growth of such cracks in bridge steels is presented. A better understanding of the remaining life of steel bridges would help establish an assessment procedure and guide engineers when deciding between reinforcement and replacement
The impact of deep-sea fisheries and implementation of the UNGA Resolutions 61/105 and 64/72. Report of an international scientific workshop
The scientific workshop to review fisheries management, held in Lisbon in May 2011, brought together 22 scientists and fisheries experts from around the world to consider the United Nations General Assembly (UNGA) resolutions on high seas bottom fisheries: what progress has been made and what the outstanding issues are. This report summarises the workshop conclusions, identifying examples of good practice and making recommendations in areas where it was agreed that the current management measures fall short of their target
Topological Andr\'e-Quillen homology for cellular commutative -algebras
Topological Andr\'e-Quillen homology for commutative -algebras was
introduced by Basterra following work of Kriz, and has been intensively studied
by several authors. In this paper we discuss it as a homology theory on CW
-algebras and apply it to obtain results on minimal atomic -local
-algebras which generalise those of Baker and May for -local spectra and
simply connected spaces. We exhibit some new examples of minimal atomic
-algebras.Comment: Final revision, a version will appear in Abhandlungen aus dem
Mathematischen Seminar der Universitaet Hambur
Evolution of precipitates, in particular cruciform and cuboid particles, during simulated direct charging of thin slab cast vanadium microalloyed steels
A study has been undertaken of four vanadium based steels which have been processed by a simulated direct charging route using processing parameters typical of thin slab casting, where the cast product has a thickness of 50 to 80mm ( in this study 50 mm) and is fed directly to a furnace to equalise the microstructure prior to rolling. In the direct charging process, cooling rates are faster, equalisation times shorter and the amount of deformation introduced during rolling less than in conventional practice. Samples in this study were quenched after casting, after equalisation, after 4th rolling pass and after coiling, to follow the evolution of microstructure. The mechanical and toughness properties and the microstructural features might be expected to differ from equivalent steels, which have undergone conventional processing. The four low carbon steels (~0.06wt%) which were studied contained 0.1wt%V (V-N), 0.1wt%V and 0.010wt%Ti (V-Ti), 0.1wt%V and 0.03wt%Nb (V-Nb), and 0.1wt%V, 0.03wt%Nb and 0.007wt%Ti (V-Nb-Ti). Steels V-N and V-Ti contained around 0.02wt% N, while the other two contained about 0.01wt%N. The as-cast steels were heated at three equalising temperatures of 1050C, 1100C or 1200C and held for 30-60 minutes prior to rolling. Optical microscopy and analytical electron microscopy, including parallel electron energy loss spectroscopy (PEELS), were used to characterise the precipitates. In the as-cast condition, dendrites and plates were found. Cuboid particles were seen at this stage in Steel V-Ti, but they appeared only in the other steels after equalization. In addition, in the final product of all the steels, fine particles were seen, but it was only in the two titanium steels that cruciform precipitates were present. PEELS analysis showed that the dendrites, plates, cuboids, cruciforms and fine precipitates were essentially nitrides. The two Ti steels had better toughness than the other steels but inferior lower yield stress values. This was thought to be, in part, due to the formation of cruciform precipitates in austenite, thereby removing nitrogen and the microalloying elements which would have been expected to precipitate in ferrite as dispersion hardening particles
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