Palaeomagnetism of granitic intrusives from the Precambrian basement under eastern Kansas: orienting drill cores using secondary magnetization components     

Kenneth P. Kodama 《Geophysical Journal International》1984,76(2):273-287

Summary. The Precambrian basement under east-central Kansas was drilled at two circular aeromagnetic positives, one at Osawattamie and one at Big Springs. The core retrieved from these sites is a coarse to medium grained granite which has been dated by U-Pb to be 1350 Ma old. The palaeomagnetism of these azimuthally unoriented cores was studied to see if a technique which uses low-coercivity, low-temperature magnetization components to orient the cores would allow an independent confirmation of the core's mid-Proterozoic age. Orthogonal projection plots of the alternating field (af) and thermal demagnetization data show that the magnetization of these cores is relatively simple, having only two components: a low-temperature, low-coercivity magnetization with steep positive inclinations and a shallow, negative inclination characteristic magnetization for the Osawattamie core or a positive, moderate inclination characteristic magnetization for the Big Springs core. If the declination of the low-temperature, low-coercivity component is aligned parallel to the present field declination, the characteristic directions may be azimuthally oriented. This allows the calculation of palaeomagnetic poles for the Big Springs core (lat. = 4.5°S, long. = 29.9°E) and the Osawattamie core (lat.= 20.2°N, long. = 39.3°E) which are consistent with Irving's apparent polar wander path for Laurentia at about 1300–1400 Ma. Comparison of anhysteretic remanent magnetization (ARM), viscous remanent magnetization (VRM), and isothermal remanent magnetization af demagnetization curves with a natural remanent magnetization (NRM) demagnetization curve suggests that the Osawattamie core probably acquired a piezoremanent magnetization (PRM) parallel to the core axis during drilling.  相似文献   

Results from the Eso Large Program on Transneptunian Objects and Centaurs     

Boehnhardt  Hermann  Barucci  Antonella  Delsanti  Audrey  De Bergh  Catherine  Doressoundiram  Alain  Romon  Jennifer  Dotto  Elisabetta  Tozzi  Gianpaolo  Lazzarin  Monica  Fornasier  Sonia  Peixinho  Nuno  Hainaut  Olivier  Davies  John  Rousselot  Philippe  Barrera  Luis  Birkle  Kurt  Meech  Karen  Ortiz  JoseLuis  Sekiguchi  Tomohiko  Watanabe  Jun-ichi  Thomas  Nick  West  Richard 《Earth, Moon, and Planets》2003,92(1-4):145-156

BVRI photometry of 107 TNOs and Centaurs establishes the range of spectral gradients to be between –5 to 55%/100 nm (with one exception). A cluster of very red Cubewanos is firmly identified in orbits of low inclination and eccentricity beyond 40 AU from the Sun. Further correlations between surface colours and dynamical parameters (inclination and perihelion distance) are suggested for Cubewanos and scattered disk objects, but lack complete confidence for their reality. Plutinos and Centaurs do not show any clear correlation between surface colours and orbital parameters. We present in this paper 12 spectra obtained in the visible region and nine of them for which we obtained also near infrared spectra up to 2.4 microns. A few other objects have been observed, but the data are still under reduction and analysis. The principal reported results obtained are: (i) a wide range of visible slopes; (ii) evidence for surface variations on 2001 PT₁₃; and (iii) possible detection of few percent of water ice (1999 TC_36}, 2000 EB₁₇₃, 1999 DE₉, 2001 PT₁₃, 2000 QC₂₄₃, 1998 SG₃₅).  相似文献   

Testing the hypothesis of the morphological transformation from field spiral to cluster S0     

Tadayuki Kodama  Ian Smail 《Monthly notices of the Royal Astronomical Society》2001,326(2):637-642

Hubble Space Telescope observations of distant clusters have suggested a steep increase in the proportion of S0 galaxies between clusters at high redshifts and similar systems at the present day. It has been proposed that this increase results from the transformation of the morphologies of accreted field galaxies from spirals to S0s. We have simulated the evolution of the morphological mix in clusters based on a simple phenomenological model where the clusters accrete a mix of galaxies from the surrounding field, the spiral galaxies are transformed to S0s (through an unspecified process) and are added to the existing cluster population. We find that in order to reproduce the apparently rapid increase in the ratio of S0 galaxies to ellipticals in the clusters, our model requires that: (1) the galaxy accretion rate has to be high (typically, more than half of the present-day cluster population must have been accreted since z ∼0.5) , and (2) most of the accreted spirals, with morphological types as late as Scdm, must have transformed to S0s. Although the latter requirement may be difficult to meet, it is possible that such bulge-weak spirals have already been 'pre-processed' into the bulge-strong galaxies prior to entering the cluster core and are eventually transformed into S0s in the cluster environment. On the basis of the evolution of the general morphological mix in clusters our model suggests that the process responsible for the morphological transformation takes a relatively long time (∼ 1–3 Gyr) after the galaxy has entered the cluster environment.  相似文献   

The Colour–Magnitude Relation and the Formation of Early-Type Galaxies     

T. Kodama 《Astrophysics and Space Science》2001,276(2-4):877-884

The colour-magnitude relation provides important information on the formation and evolution of cluster galaxies. By looking into the evolution of the relation as a function of redshift and using the small colour scatter around the relation in Coma, we put constraints on the star formation history and the galaxy merging history of cluster early-type galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Meteor Streams and Comets     

Jun-ichi Watanabe 《Earth, Moon, and Planets》2004,95(1-4):49-61

Recent progress on the interrelation between meteor streams and comets is reviewed both on dynamical and physical aspects. The topics include the recent concept of the structure of meteor streams, resulted success of the prediction of the meteor storms, and the recent observational situation on the cometary dust grains and meteoroids. Two possible explanations for the origin of the meteoroids together with the implication for the relation between the birthplace of the parent comets and the meteoroids are discussed.  相似文献   

Protoclusters with evolved populations around radio galaxies at z∼ 2.5     

Masaru Kajisawa  Tadayuki Kodama  Ichi Tanaka  Toru Yamada  Richard Bower 《Monthly notices of the Royal Astronomical Society》2006,371(2):577-582

  相似文献   

Meteor Showers Originated from 73P/Schwassmann–Wachmann     

Shun Horii  Jun-ichi Watanabe  Mikiya Sato 《Earth, Moon, and Planets》2008,102(1-4):85-89

The nucleus of the Comet 73P/Schwassmann–Wachmann had been split into many fragments at least past two returns. Since the related dense dust trail has been detected in the space infrared observation, the strong activity of the meteor shower is highly expected in the future. We applied the so-called dust-trail theory to this interesting object, and obtained several results on the future encounter with the dust trail. In this paper we introduce our results on the forecasts.  相似文献   

The assessment of weathering stages in granites using an EC/pH meter     

Anestoria Shalkowski  Yoshinori Kodama  Shigenori Nakano 《Geomorphology》2009,105(3-4):253-260

The sidewall effects of a wind tunnel on aeolian sand transport were investigated experimentally. A wind tunnel was used to conduct the experiments with a given channel height of 120 cm and varying widths (B) of 40, 60, 80, 100 and 120 cm. Both vertical profiles of wind velocity and sand mass flux were measured at different locations across the test section. The results show that the wind velocity with saltation first increases and then decreases to a minimum, from the sidewall to the central line of the wind tunnel. The discrepancy among wind velocities at different locations of the transverse section decreases with decreasing tunnel width. The wind friction velocity across the wind tunnel floor, with the exception of the region closest to the sidewalls, does not deviate strongly in wide wind tunnels from that along the central line, whereas it does vary in narrow tunnels. The sand mass fluxes, with the exception of some near-bed regions, are larger along the central line of the wind tunnel than they are at the quarter width location from the sidewall. Unlikely previously reported results, the dimensionless sand transport rate, Qg / (ρu³) (where Q is the total sand transport rate, g is the gravitational acceleration constant, ρ is the air density, and u is the wind friction velocity), first decreases and then increases with the dimensionless friction velocity, u / u_t (where u_t is the threshold friction velocity). The above differences may be attributed to the sidewall effects of the wind tunnel. A dimensionless parameter, F_B = u / (gB)^1/2, is defined to reflect the sidewall effects on aeolian sand transport. The flows with F_B of 0.33 or less may be free from the sidewall effects of the wind tunnel and can ensure accurate saltation tunnel simulation.  相似文献   

Nitrogen stable isotope ratio in the manila clam, Ruditapes philippinarum, reflects eutrophication levels in tidal flats     

Satoshi Watanabe  Masashi Kodama 《Marine pollution bulletin》2009,58(10):1447-680

Understanding the effects of anthropogenic eutrophication on coastal fisheries may help in the enhancement of fishery production by effective utilization of sewage effluents, as well as in the consequent reduction of eutrophication. In this study, it was revealed that the nitrogen stable isotope ratio (δ¹⁵N) in the soft tissues of the manila clam, Ruditapes philippinarum, can be used as an indicator of anthropogenic eutrophication levels in tidal flat environments by investigation of δ¹⁵N in dissolved inorganic nitrogen (DIN), particulate organic matter (POM), sedimentary organic matter (SOM) and soft tissues of the clam in five tidal flats in Japan with different levels of DIN concentration. In addition, it was found that the acid insoluble fraction of the shell organic matrix, conchiolin, can be used as a proxy for the soft tissues in δ¹⁵N analyses. This will contribute in easier storage handling and the expansion of chances for sample acquisition.  相似文献   

Presence of high nitrate to phosphate ratio subsurface water in the Tsushima Strait during summer     

Taketoshi Kodama  Akihiko Morimoto  Tetsutaro Takikawa  Masashi Ito  Yosuke Igeta  Shoko Abe  Ken-Ichi Fukudome  Naoto Honda  Osamu Katoh 《Journal of Oceanography》2017,73(6):759-769

To identify water with an excess nitrate concentration to phosphate ratio and its potential source, the nutrient concentrations in the Tsushima Strait (TSS) were investigated over ten cruises in August and September 2007–2014, excluding 2010. On the basis of the Redfield ratio, water with an excess nitrate concentration of >1 μM (positive ExNOx water) was identified below the surface mixed layer during four cruises in 2011–2013. Positive ExNOx water was present mainly in less-saline (<34) waters with a density of 22–25 σ _θ , and 25–75 m depth. However, in August 2012, positive ExNOx was detected in dense (25–25.5 σ _θ ) and deep (50–110 m depth) waters near the salinity maximum, although the salinity during this period was significantly lower than that in other years. The horizontal length of positive ExNOx water was >100 km across the TSS during two cruises in August 2012 and September 2013, respectively. According to multi-regression analysis conducted on the silicate concentration, temperature, and salinity, the silicate concentration was increased in the less-saline subsurface water. The required amount of original freshwater was 10^8–9 m³ day^?1 based on the excess nitrate concentration. This evidence indicates that the positive ExNOx water originated from large river waters such as the Changjiang. Thus, discharged water from the rivers of the East Asia is contributing to the increased N:P ratio in the Tsushima Warm Current, southern Japan Sea.  相似文献