Strain field measurements of rubber by image analysis and design criteria for laminated rubber bearings (LRB)

Although seismic isolation rubber bearings in bridges and buildings have proven to be a very effective passive method for reducing earthquake‐induced forces, a detailed mechanical modeling of the rubber that is used in bearings under large strains has not been established. Therefore, a 3D model of failure behavior and the design criteria for the safety evaluation of seismic isolation bearings have not yet been developed. This paper presents: (1) correlation‐based template‐matching algorithms to measure large strain fields of continua; (2) a failure criterion for rubber; and (3) the design criteria for the safety evaluation of laminated algorithms, data‐validation algorithms were developed and implemented to eliminate possible unrealistic displacement vectors present in the measured displacement field. The algorithms were successfully employed in the strain field measurement of LRB and rubber materials that are subjected to failure. The measured local strains for rubber material at failure were used to develop a failure criterion for rubber. The validity of the proposed criterion was evaluated by applying it to the LRB; the criterion was introduced into a 3D finite element model of LRB, compared with the experimental results of bearings failure, and verified. Finally, design criteria are proposed for LRB for the safety evaluation. Copyright © 2003 John Wiley & Sons, Ltd.     

Estimation of net accumulation rate at a Patagonian glacier by ice core analyses using snow algae

Snow algae in a 45.97-m-long ice core from the Tyndall Glacier (50°59′05″S, 73°31′12″W, 1756 m a.s.l.) in the Southern Patagonian Icefield were examined for potential use in ice core dating and estimation of the net accumulation rate. The core was subjected to visual stratigraphic observation and bulk density measurements in the field, and later to analyses of snow algal biomass, water isotopes (¹⁸O, D), and major dissolved ions. The ice core contained many algal cells that belonged to two species of snow algae growing in the snow near the surface: Chloromonas sp. and an unknown green algal species. Algal biomass and major dissolved ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻) exhibited rapid decreases in the upper 3 m, probably owing to melt water elution and/or decomposition of algal cells. However, seasonal cycles were still found for the snow algal biomass, ¹⁸O, D-excess, and major ions, although the amplitudes of the cycles decreased with depth. Supposing that the layers with almost no snow algae were the winter layers without the melt water essential to algal growth, we estimated that the net accumulation rate at this location was 12.9 m a^− 1 from winter 1998 to winter 1999, and 5.1 m from the beginning of winter to December 1999. These estimates are similar to the values estimated from the peaks of ¹⁸O (17.8 m a^− 1 from summer 1998 to summer 1999 and 11.0 m from summer to December 1999) and those of D-excess (14.7 m a^− 1 from fall 1998 to fall 1999 and 8.6 m a^− 1 from fall to December 1999). These values are much higher than those obtained by past ice core studies in Patagonia, but are of the same order of magnitude as those predicted from various observations at ablation areas of Patagonian glaciers.     

http://www.sciencedirect.com/science/article/pii/S167498711300162X

Seismic observations have shown structural variation near the base of the mantle transition zone(MTZ)where subducted cold slabs,as visualized with high seismic speed anomalies(HSSAs),flatten to form stagnant slabs or sink further into the lower mantle.The different slab behaviors were also accompanied by variation of the "660 km" discontinuity depths and low viscosity layers(LVLs) beneath the MTZ that are suggested by geoid inversion studies.We address that deep water transport by subducted slabs and dehydration from hydrous slabs could affect the physical properties of mantle minerals and govern slab dynamics.A systematic series of three-dimensional numerical simulation has been conducted to examine the effects of viscosity reduction or contrast between slab materials on slab behaviors near the base of the MTZ.We found that the viscosity reduction of subducted crustal material leads to a separation of crustal material from the slab main body and its transient stagnation in the MTZ.The once trapped crustal materials in the MTZ eventually sink into the lower mantle within 20-30 My from the start of the plate subduction.The results suggest crustal material recycle in the whole mantle that is consistent with evidence from mantle geochemistry as opposed to a two-layer mantle convection model.Because of the smaller capacity of water content in lower mantle minerals than in MTZ minerals,dehydration should occur at the phase transformation depth,~660 km.The variation of the discontinuity depths and highly localized low seismic speed anomaly(LSSA) zones observed from seismic P waveforms in a relatively high frequency band(~1 Hz) support the hypothesis of dehydration from hydrous slabs at the phase boundary.The LSSAs which correspond to dehydration induced fluids are likely to be very local,given very small hydrogen(H~+) diffusivity associated with subducted slabs.The image of such local LSSA zones embedded in HSSAs may not be necessarily captured in tomography studies.The high electrical conductivity in the MTZ beneath the northwestern Pacific subduction zone does not necessarily require a broad range of high water content homogeneously.     

The inner solar system cratering record and the evolution of impactor populations

We review previously published and newly obtained crater size-frequency distributions in the inner solar system. These data indicate that the Moon and the terrestrial planets have been bombarded by two populations of objects. Population 1,dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. Population 2, dominating since about 3.8–3.7 Gyr,had the same size distribution as near-Earth objects(NEOs) and a much lower impact flux, and produced a crater size distribution characterized by a differential –3single-slope power law in the crater diameter range 0.02 km to 100 km. Taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. The NEO population is the source of Population 2 and it has been in near-steady state over the past ～ 3.7–3.8 Gyr; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. However, Population 1 was composed of main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during orbit migration of giant planets;this caused the so-called Late Heavy Bombardment(LHB). The LHB began some time before ～3.9 Gyr, peaked and declined rapidly over the next ～ 100 to 300 Myr,and possibly more slowly from about 3.8–3.7 Gyr to ～2 Gyr. A third crater population(Population S) consisted of secondary impact craters that can dominate the cratering record at small diameters.     

Detection of large color variation in the potentially hazardousasteroid （297274） 1996 SK

Low-inclination near-earth asteroid(NEA)(297274) 1996 SK,which is also classified as a potentially hazardous asteroid,has a highly eccentric orbit.It was studied by multi-wavelength photometry within the framework of an NEA color survey at Lulin Observatory.Here,we report the finding of large color variation across the surface of(297274) 1996 SK within one asteroidal rotation period of4.656 ± 0.122 hours and classify it as an S-type asteroid according to its average colors of B- V = 0.767 ± 0.033,V- R = 0.482 ± 0.021,V- I = 0.801 ± 0.025and the corresponding relative reflectance spectrum.These results might be indicative of differential space weathering or compositional inhomogeneity in the surface materials.     

Radiocarbon anomaly found in aquicultural scallops suspended in coastal sea

The radiocarbon content of scallops aquiculturally suspended and grown in coastal sea, Funka Bay, were determined. While the ¹⁴C values of carbonate shells coincided with that of ambient seawater, those of soft tissues were smaller than the seawater value and varied rather widely. To clarify the cause of this variation, we further divided the soft tissues of composite scallops into each organ and determined their radiocarbon content. The results show that only the ¹⁴C of adductor (Kaibashira in Japanese) of scallops was significantly smaller than the others, those of gill and mantle coincided to that of seawater. This strange finding cannot be explained by the present knowledge on the dietary sources of scallops and the present theory of isotopic fractionation, unless any unknown physiological or oceanographical process determines the radiocarbon content of the organisms.