Effectiveness of superelastic bars for seismic rehabilitation of clay‐unit masonry walls     

Kshitij C. Shrestha  Yoshikazu Araki  Takuya Nagae  Toshihiro Omori  Yuji Sutou  Ryosuke Kainuma  Kiyohito Ishida 《地震工程与结构动力学》2013,42(5):725-741

This paper presents the results on shaking table tests of half‐scale brick walls performed to investigate the effectiveness of newly developed Cu–Al–Mn superelastic alloy (SEA) bars in retrofitting of historical masonry constructions. Problems associated with conventional steel reinforcing bars lie in degradation of stiffness and strength, or pinching phenomena, under cyclic loading, and presence of large residual cracks in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu–Al–Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Sets of unreinforced, steel reinforced, and SEA‐reinforced specimens are subjected to scaled earthquake excitations in out‐of‐plane direction. Whereas steel‐reinforced specimens showed large residual inclinations, SEA‐reinforced specimens resulted in stable rocking response with slight residual inclinations. Corresponding nonlinear finite element (FE) models are developed to simulate the experimental observations. The FE models are further used to examine the sensitivity of the response with respect to the variations in experimental conditions. Both the experimental and numerical results demonstrate the superiority of Cu–Al–Mn SEA bars to conventional steel reinforcing bars in avoiding pinching phenomena. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry     

Takuya Sagawa  Kazuhiro Toyoda  Tadamichi Oba 《第四纪科学杂志》2006,21(1):63-73

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Radio and infrared recombination studies of the southern massive star forming region G333.6−0.2     

Takuya Fujiyoshi  Craig H. Smith  James L. Caswell  Toby J. T. Moore  Stuart L. Lumsden  David K. Aitken  Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》2006,368(4):1843-1855

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Noble gases in Muong Nong‐type tektites and their implications     

Sayaka MIZOTE  Takuya MATSUMOTO  Jun‐ichi MATSUDA  Christian KOEBERL 《Meteoritics & planetary science》2003,38(5):747-758

Abstract— We have the elemental abundances and isotopic compositions of noble gases in Muong Nong‐type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong‐type tektites compared to those in normal splash‐form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong‐type tektites, but the Ne/Ar ratios were lower than those in splash‐form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong‐type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong‐type tektites are mostly identical to those in air, except for the presence of radiogenic ⁴⁰Ar. The obtained K‐Ar ages for Muong Nong‐type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong‐type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong‐type tektites. Likely, Muong Nong‐type tektites solidified at the altitude (between the surface and a maximum height of 8–30 km) lower than that for splash‐form tektites.  相似文献   

Near-infrared imaging observations of the southern massive star-forming region G333.6−0.2     

Takuya Fujiyoshi  Craig H. Smith  Toby J. T. Moore  Stuart L. Lumsden  David K. Aitken  Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》2005,356(3):801-809

We present near-infrared broad-band JHK ' images of the southern massive star-forming region G333.6−0.2. The slope of the K -luminosity function towards the region  (0.24 ± 0.01)  is considered to be equivalent to that expected for main-sequence stars in the solar neighbourhood. Point sources with their ( H − K ) colour greater than 1 are more likely to be located in extended emission and it is suggested that these objects are physically associated with the H  ii region.  相似文献   

Distribution of noble gases in Chinese tektites: Implication for neon solubility in natural glasses     

Daniele L. PINTI  Takuya MATSUMOTO  Jun‐Ichi MATSUDA  Zhong FANG 《Meteoritics & planetary science》2004,39(1):87-96

Abstract— Five indochinites from Hainan Island and the Leizhou Peninsula, China were analyzed for noble gas abundances and isotopic ratios. These splash‐form tektites show vesiculation ranging from 0.4 vol% to 8 vol%, as determined by digital image analysis (software SXM®) on thin section photographs. To study the distribution of noble gases in vesicles and in glass, the gases were extracted by heating and by crushing, respectively, on 2 aliquots of the same sample. The results show that 5 to 53% of the total measured ²⁰Ne resides in vesicles. The calculated concentration of neon dissolved in the glass is higher (0.7‐1 times 10^?7 cm³STP/g) than that expected from solubility equilibrium (1 times 10^?8 cm³STP/g), assuming solubility data from MORB glasses. The neon concentration of splash‐form tektites, those analyzed in this work and those from other strewn‐fields worldwide, is correlated with the SiO₂ content of glass and with the nonbridging oxygen per tetrahedral cation in the melt (hereafter NBO/T ratio), the latter being an index of the free‐volume in the silica network where neon could be dissolved. These correlations suggest that the glass structure of tektite has a larger free‐volume available for dissolving noble gases than MORB glasses.  相似文献   

Single-crystal X-ray diffraction and spectroscopic studies on humboldtine and lindbergite: weak Jahn–Teller effect of Fe<Superscript>2+</Superscript> ion     

Takuya Echigo  Mitsuyoshi Kimata 《Physics and Chemistry of Minerals》2008,35(8):467-475

The single-crystal of humboldtine [Fe²⁺(C₂O₄) · 2H₂O] was first synthesized and the crystal structure has been refined. Single-crystal X-ray diffraction data were collected using an imaging-plate diffractometer system and graphite-monochromatized MoKα radiation. The crystal structure of humboldtine was refined to an agreement index (R1) of 3.22% calculated for 595 unique observed reflections. The mineral crystallizes in the monoclinic system, space group C2/c, with unit cell dimensions of a = 12.011 (11), b = 5.557 (5), c = 9.920 (9) Å, β = 128.53 (3)?, V = 518.0 (8) Å³, and Z = 4. In this crystal structure, the alternation of oxalate anions [(C₂O₄)^2?] and Fe²⁺ ions forms one-dimensional chain structure parallel to [010]; water molecules (H₂O)⁰ create hydrogen bonds to link the chains, where (H₂O)⁰ is essentially part of the crystal structure. The water molecules with the two lone electron pairs (LEPs) on their oxygen atom are tied obliquely to the chains, because the one lone electron pair is considered to participate in the chemical bonds with Fe²⁺ ions. Humboldtine including hydrogen bonds is isotypic with lindbergite [Mn²⁺(C₂O₄) · 2H₂O]. The donor–acceptor separations of the hydrogen bonds in humboldtine are slightly shorter than those in lindbergite, which suggests that the hydrogen bonds in the former are stronger than those in the latter. The infrared and Raman spectra of single-crystals of humboldtine and lindbergite confirmed the differences in hydrogen-bond geometry. In addition, Fe²⁺–O stretching band of humboldtine was split and broadened in the observed Raman spectrum, owing to the Jahn–Teller effect of Fe²⁺ ion. These interpretations were also discussed in terms of bond-valence theory.  相似文献   

Degassing, crystallization and eruption dynamics at Stromboli: trace element and lithium isotopic evidence from 2003 ashes     

Federica Schiavi  Katsura Kobayashi  Takuya Moriguti  Eizo Nakamura  Massimo Pompilio  Massimo Tiepolo  Riccardo Vannucci 《Contributions to Mineralogy and Petrology》2010,159(4):541-561

During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions and lava effusions, while the LP one is related to more energetic paroxysms. During the March–April 2003 explosive activity, Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards. Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses, along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to ~20 ppm) and lower δ⁷Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ⁷Li ranging between +4.6 and +0.9‰). Fractional crystallization models based on major and trace element compositions, combined with a degassing model based on open-system Rayleigh distillation and on the assumption that ^melt/fluidD_Li > 1, show that abundant (~30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre- and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system.  相似文献   

Infrared polarimetry of the southern massive star-forming region G333.6−0.2     

Takuya Fujiyoshi  Craig H. Smith  Christopher M. Wright  Toby J. T. Moore  David K. Aitken  Patrick F. Roche 《Monthly notices of the Royal Astronomical Society》2001,327(1):233-243

We present     spectropolarimetry, and 12- and 2-μm imaging polarimetry of the southern massive star-forming region G333.6−0.2. Spectro-polarimetry measurements show that the polarization observed towards the nebula contains a mixture of both absorptive and emissive polarizations. Model fitting to the spectra indicates that the temperature of the mid-infrared emitting dust grains is generally ∼200 K and the optical depth of the absorbing dust at 9.7 μm is ∼1.5. Fits are also made to the polarimetry spectra, which show a reasonably constant peak absorptive polarization (∼3.4 per cent at 43°) across the face of the H  ii region. This absorptive polarization position angle is consistent with that found by the 2-μm imaging polarimetry     and is most likely due to the Galactic magnetic field local to G333.6−0.2. When the absorptive polarization is subtracted from the 12-μm polarization image, the emissive polarization pattern that is intrinsic to the star-forming region is revealed. A probable magnetic field configuration implied by the intrinsic polarization suggests star formation initially influenced by the Galactic magnetic field which is eventually perturbed by the star formation process.  相似文献   

Lateral structural variation across a collision zone in central Hokkaido, Japan, as revealed by wide-angle seismic experiments     

Takaya Iwasaki  Oguz Ozel  Takeo Moriya  Shin'ichi Sakai  Sadaomi Suzuki  Gen Aoki  Takuya Maeda†  & Takashi Iidaka 《Geophysical Journal International》1998,132(2):435-457

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