Cadmium sulfide in a Mesoproterozoic terrestrial environment

Peer reviewedPostprin

Compression properties of polymeric syntactic foam composites under cyclic loading

Syntactic foams are composite materials frequently used in applications requiring the properties of low density and high damage tolerance. In the present work, polymer-based syntactic foams were studied under cyclic compression in order to investigate their compressibility, recoverability, energy dissipation and damage tolerance. These syntactic foams were manufactured by adding hollow polymer microspheres of various sizes and wall thicknesses into a polyurethane matrix. The associated loading and unloading curves during cyclic testing were recorded, revealing the viscoelastic nature of the materials. SEM images of the samples were obtained in order to study potential damage mechanisms during compression. It was observed that these syntactic foams exhibit high elastic recovery and energy dissipation over a wide range of compressional strains and the addition of polymer microspheres mitigate the damage under compressional loading.Comment: 25 pages, 13 figure

The combustion characteristics and stable carbon isotopic compositions of irradiated organic matter: implications for terrestrial and extraterrestrial sample analysis

Exposure to ionizing radiation causes the mean combustion temperature of naturally occurring, solid, terrestrial organic matter, derived from the radiation-induced polymerization of methane, to increase

A measurement of the cosmic ray elements C to Fe in the two energy intervals 0.5-2.0 GeV/n and 20-60 GeV/n

The study of the cosmic ray abundances beyond 20 GeV/n provides additional information on the propagation and containment of the cosmic rays in the galaxy. Since the average amount of interstellar material traversed by cosmic rays decreases as its energy increases, the source composition undergoes less distortion in this higher energy region. However, data over a wide energy range is necessary to study propagation parameters. Some measurements of some of the primary cosmic ray abundance ratios at both low (near 2 GeV/n) and high (above 20 GeV/n) energy are given and compared to the predictions of the leaky box mode. In particular, the integrated values (above 23.7 GeV/n) for the more abundant cosmic ray elements in the interval C through Fe and the differential flux for carbon, oxygen, and the Ne, Mg, Si group are presented. Limited statistics prevented the inclusion of the odd Z elements

Employing pre-stress to generate finite cloaks for antiplane elastic waves

It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic materials can be used as a mechanism to generate finite cloaks and thus render objects near-invisible to incoming antiplane elastic waves. This approach appears to negate the requirement for special cloaking metamaterials with inhomogeneous and anisotropic material properties in this case. These properties are induced naturally by virtue of the pre-stress. This appears to provide a mechanism for broadband cloaking since dispersive effects due to metamaterial microstructure will not arise.Comment: 4 pages, 2 figure

Hopane biomarkers traced from bedrock to recent sediments and ice at the Haughton Impact Structure, Devon Island: Implications for the search for biomarkers on Mars

Hopanoid biomarkers have been traced from bedrock to ice in the Haughton Impact Structure, suggesting that they represent a promising strategy in the search for life in ice deposits on Mars and other icy bodies

Nonlinear wave propagation and reconnection at magnetic X-points in the Hall MHD regime

The highly dynamical, complex nature of the solar atmosphere naturally implies the presence of waves in a topologically varied magnetic environment. Here, the interaction of waves with topological features such as null points is inevitable and potentially important for energetics. The low resistivity of the solar coronal plasma implies that non-MHD effects should be considered in studies of magnetic energy release in this environment. This paper investigates the role of the Hall term in the propagation and dissipation of waves, their interaction with 2D magnetic X-points and the nature of the resulting reconnection. A Lagrangian remap shock-capturing code (Lare2d) is used to study the evolution of an initial fast magnetoacoustic wave annulus for a range of values of the ion skin depth in resistive Hall MHD. A magnetic null-point finding algorithm is also used to locate and track the evolution of the multiple null-points that are formed in the system. Depending on the ratio of ion skin depth to system size, our model demonstrates that Hall effects can play a key role in the wave-null interaction. In particular, the initial fast-wave pulse now consists of whistler and ion-cyclotron components; the dispersive nature of the whistler wave leads to (i) earlier interaction with the null, (ii) the creation of multiple additional, transient nulls and, hence, an increased number of energy release sites. In the Hall regime, the relevant timescales (such as the onset of reconnection and the period of the oscillatory relaxation) of the system are reduced significantly, and the reconnection rate is enhanced.Comment: 13 pages, 10 figure

Reduction spheroids from the Upper Carboniferous Hopewell Group, Dorchester Cape, New Brunswick: notes on geochemistry, mineralogy and genesis

The bajada-playa sequence of terrestrial Upper Carboniferous redbeds of the Hopewell Group at Dorchester Cape, New Brunswick, hosts innumerable reduction spheroids in fine- to coarse-grained clastic sedimentary rocks, paleosols and caliche beds. The spheroids are grey-green, typically 2 to 3 cm in diameter, and may contain a dark, mineralized central core and less commonly one or more mineralized rings, concentric about the core. They decrease progressively in average diameter from 2.75 cm at the base to 0.85 cm at the top of an overall upward-fining 250 m thick measured stratigraphic section. Conditions controlling the genesis of the spheroids were established shortly after sedimentation. Development was subtly controlled by groundwater flow patterns and by various sedimentary structures. The enclosing redbeds provide an adequate source for the metals contained in the mineralized spheroids. Low-temperature chloride complexes originating from evaporative fluids concentrated during redbed formation are believed to have been responsible for transport of the metals to reduction sites. Precipitation probably occurred as a result of a change in redox potential governed by electrical self-potentials of various detrital and early diagenetic grains, particularly pyritc and/or Fe-Ti oxides. Electron microprobc analyses reveal Cu, Ag, Fe, Ti, U, V and REE enrichments in reduction spheroid cores. Mineralized rings arc less enriched in these elements but contain slightly greater concentrations of Ti-oxide minerals. Minerals observed other than bulk redbed constituents include: chatcocite, covellitc, cuprite, pyritc, il-menite, rutile, mottramite, roscoelite, xenotime, monazite, native copper, azurite and native silver with trace amounts of alloyed Hg. RÉSUMÉ La séquence de bajadas-playas des formations rouges terrestres du Carbonifere supérieur du groupe de Hopewell à Dorchester Cape, Nouveau-Brunswick, abrite d'innombrables sphéroides de réduction dans des couches de caliche, dc paléosol et de sédiments clastiques à grain fin à gros. Les sphéroides sont de couleur gris-vert, its ont généralement 2 à 3 cm de diamètre et ils peuvent renfermer un noyau central minéralisé de teinte foncée de même que, moins couramment, un ou plusieurs anneaux minéralisés concentriques au noyau. Leur diamètre moyen diminuc graduellement, passant de 2,75 cm à la base a 0,85 cm au sommet d'une section stratigraphique à affinement généralement ascendant d'une épaisseur mesurée de 250 m. Les conditions ay ant régi l'origine des sphéroldes ont été établies peu après la sédimentation. Leur développement a été subtilement gouverné par les configurations d'écoulement des eaux souterraines ct par diverses structures sédimentaires. Les formations rouges encaissantes constituent une source adéquate des métaux que ren ferment les sphéroldes minéraliseés. On croit que les complexes chlorurés de basse température provenant des fluides volatils concentrés pendant la constitution des formations rouges ont causé le transport des métaux à des points de réduction. Des précipitations sont probablement survenucs par suite d'un changement du potentiel d'oxydor&Juction gouverné par les polarisations spontanées éiectriques de divers grains diagénétiques détritiques ct anciens, en particulier de la pyrite ou des oxydes de fer-titane. Les analyses par microsonde éiectronique révèlent des enrichissements de Cu, d'Ag, de Fe, de Ti, d'U, de V et d'éléments des terres rares dans les noyaux des sphéroldes de réduction. Les anneaux minéralisés renferment des proportions moindres de certains de ces éléments, mais des concentrations légèrement plus fortes d'oxyde dc titane. Outre les composants bruts des couches rouges, les minéraux observes comprennent de la chalcocyte, de la covellite, de la cuprite, de la pyritc, de l'ilménite, du rutile, de la mottramite, de la roscoélite, du xénotime, du monazite, du cuivrc natif, de l’azurite et de l’argent natif avec des quantités infimes de mcrcure allie. [Traduit par la rédaction

Consequences of spontaneous reconnection at a two-dimensional non-force-free current layer

Magnetic neutral points, where the magnitude of the magnetic field vanishes locally, are potential locations for energy conversion in the solar corona. The fact that the magnetic field is identically zero at these points suggests that for the study of current sheet formation and of any subsequent resistive dissipation phase, a finite beta plasma should be considered, rather than neglecting the plasma pressure as has often been the case in the past. The rapid dissipation of a finite current layer in non-force-free equilibrium is investigated numerically, after the sudden onset of an anomalous resistivity. The aim of this study is to determine how the energy is redistributed during the initial diffusion phase, and what is the nature of the outward transmission of information and energy. The resistivity rapidly diffuses the current at the null point. The presence of a plasma pressure allows the vast majority of the free energy to be transferred into internal energy. Most of the converted energy is used in direct heating of the surrounding plasma, and only about 3% is converted into kinetic energy, causing a perturbation in the magnetic field and the plasma which propagates away from the null at the local fast magnetoacoustic speed. The propagating pulses show a complex structure due to the highly non-uniform initial state. It is shown that this perturbation carries no net current as it propagates away from the null. The fact that, under the assumptions taken in this paper, most of the magnetic energy released in the reconnection converts internal energy of the plasma, may be highly important for the chromospheric and coronal heating problem