Radiochemical observations on manganese nodules from three sedimentary environments in the north Pacific     

Hun Chih-An  Ku Teh-Lung 《Geochimica et cosmochimica acta》1984,48(5):951-963

Decay-series isotopes were measured on manganese nodules from three sedimentary environments, characterized by substrates of red clay (R), siliceous ooze (S) and hemipelagic clay (H). Growth rates of nodules are shown to be site dependent: 1–2 mm/Myr at site R, 3–8 mm/Myr at sites S, and 20–50 mm/ Myr at site H. Correlation between growth rate and the parameter Mn/Fe² suggests that regional diagenetic variations control the compositions and growth rates of the nodules. The frequency of nodule turnover and the period of their growth are assessed from the “top” vs. “bottom” distributions of several nuclides. Based on the ²³⁰Th, ²³¹Pa and ²²⁶Ra data, turnover times of 10³ to 10⁵ years are estimated and they vary with relative size and shape of the specimens at a given site. The presence of unsupported ²¹⁰Pb and ²²⁸Th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years, despite their old ages. The data also indicate that turnover rates are not more frequent than once every several years or decades.The ²³⁰Th-²²⁶Ra, ²²⁶Ra-²¹⁰Pb and ²³²Th-²²⁸Th disequilibrium relationships in the nodules allow the migratory behavior of ²²⁶Ra, ²²²Rn and ²²⁸Ra and their fluxes to be deduced: thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites R and S. At site R there is a net loss of radium to the sea; the opposite is true at site S. Surface nodules at site H trap radium from both sides, probably due to more intense diagenetic input of radium from sediment pore water. The effective diffusivities of ²²⁶Ra in nodules vary from $\text{3 × 10}{}^{\mathrm{?12}}$ to $\text{8 × 10}{}^{\mathrm{?14}}$ cm²/s, dependent on the textural variation of the nodule material, which crudely reflects the growth rate and hence sedimentary environment. ²²²Rn diffuses out of nodules from all sides, with an effective diffusivity of ca. $\text{(2–6) × 10}{}^{\mathrm{?8}}\text{cm}{}^2\text{/s}$. At all sites nodules serve as a more effective source of ²²²Rn to sea water than their adjacent sediments. The outward flux of ²²²Rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments, an effect caused by the fact that Mn-rich nodules from more reduced environment act as a more efficient trap for ²²⁶Ra.  相似文献   

Summertime Characteristics of the Atmospheric Boundary Layer and Relationships to Ozone Levels over the Eastern United States   总被引：1，自引：0，他引：1  

S.T. Rao  J.Y. Ku  S. Berman  K. Zhang  H. Mao 《Pure and Applied Geophysics》2003,160(1-2):21-55

— This paper examines the spatial and temporal distributions of the mixing height, ventilation coefficient (defined as the product of mixing height and surface wind speed), and cloud cover over the eastern United States during the summer of 1995, using the high-resolution meteorological data generated by MM5 (Version 1), a mesoscale model widely used in air quality studies. The ability of MM5 to simulate the key temporal and spatial features embedded in the time series of observations of temperature, wind speed, and moisture is assessed using spectral decomposition methods. Also, mixing heights estimated from the MM5 outputs are compared with those derived from observations at a few locations where data with high temporal resolution are available in the Northeast. In addition, the uncertainties associated with the estimation of the evolution of the boundary layer during the morning time are examined. The results indicate that nighttime mixing heights averaged <200?m, rising to 1 km by 10 EST, and to about 2.5?km in the afternoon. Ventilation coefficients followed a similar diurnal pattern, increasing from 500?m²/s at night?to 15,000?m²/s in the afternoon; the increase due to the growing mixing height and increasing surface wind speeds. Spatial variability of these parameters was relatively small (coefficient of variation=0.25) at?night and in the afternoon when conditions were quasi-stationary, but increased (to 0.5) during morning?and evening hours when mixing heights and wind speeds were changing rapidly. Analyses of surface ozone observations from about 400 sites throughout the eastern United States indicate that days with numerous stations reporting surface ozone concentrations in excess of 80 ppb (i.e., “high ozone” days) generally had less daytime cloud cover, lower surface wind speeds, higher mixing heights, and lower ventilation coefficients than did comparable “low ozone” days. Such meteorological features are consistent with a synoptic anticyclone centered over the mid-south region (Kentucky, Tennessee). Low ozone days were characterized by more disturbed weather conditions (low pressure systems, fronts, greater cloud cover, and precipitation events). Ozone observations at two elevated platforms (～400?m agl) in Garner, NC, and Chicago, IL, indicated that ozone concentrations aloft were about 40% larger on “high ozone” days than on “low ozone” days. On average, high levels of ozone persist aloft for about 2 to 3 days. Strong vertical mixing in the daytime can bring this pool of upper-level ozone downward to augment surface ozone production. Since ozone can be transported downwind several hundred kilometers from its source region over this time scale, depending on upper-level winds, effective ozone control strategies must take into consideration spatial scales ranging from local to regional, and time scales of the order of several days.  相似文献   

Asymptotic Giant Branch Stars as Tracers of Star Formation Histories: the GAIA Context     

Arūnas Kučinskas  Vladas Vansevičius  Toshihiko Tanabé 《Astrophysics and Space Science》2002,280(1-2):151-157

We discuss a possible use of the asymptotic giant branch (AGB) stars for tracing star formation histories on the Galactic and extragalactic distance scales with the ESA's astrometric space mission GAIA. Extensive numerical simulations demonstrate that metallicities (Δ [M/H] ≲ 0.3) can be obtained for the AGB stars with GAIA up to the distances of ∼ 200 kpc, if no interstellar extinction is present. Reliable population ages can be also obtained from the AGB stars if their T _eff are constrained precisely. We show that precise effective temperatures can be obtained by fitting observed spectral energy distributions of the AGB stars with theoretical fluxes calculated from the synthetic spectra. A combination of the derived effective temperatures with the bolometric luminosities allows to derive precise population ages for a wide range of ages and metallicities over the large distance scales. This demonstrates that AGB stars can be employed very effectively for tracing star formation histories with GAIA, allowing to refine the global evolutionary scenarios of stellar populations in the Milky Way and the galaxies beyond. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Directional properties of small strain shear stiffness in soils     

Taeseo Ku  Paul W. Mayne 《Geomechanics and Geoengineering》2015,10(1):68-81

A compiled database of shear wave velocity measurements in a variety of clays, silts and sands shows directional hierarchies between downhole (V_sVH), standard crosshole (V_sHV), and rotary crosshole (V_sHH) tests. The special in situ database has been collected from 33 well-documented geotechnical test sites. Expressions relating the small-strain shear modulus in terms of effective confining stress level, stress history and void ratio are explored for each of these three modes of directional shear wave velocity. The relationships are separated initially into soil groups (intact clays, fissured clays, sands and silts), and then generalised to consider all soil types together.  相似文献   

A Comparative Study of Ozonation,Homogeneous Catalytic Ozonation,and Photocatalytic Ozonation for C.I. Reactive Red 194 Azo Dye Degradation     

A. Özlem Yıldırım  Şermin Gül  Orkide Eren  Erdal Kuşvuran 《洁净——土壤、空气、水》2011,39(8):795-805

In this study, the decolorization, dearomatization, and mineralization efficiencies of different advanced oxidation processes (AOPs; namely O₃, O₃/Fe(II), O₃/Fe(II)/UVA, and O₃/TiO₂/UVA) were investigated for the azo dye C.I. Reactive Red 194 (RR194). The effects of pH (3–11), amount of TiO₂ (0.05–1 g/L), and concentration of Fe(II) (0.1–1.6 mM) were investigated for the applied methods. The decolorization and mineralization efficiencies of the photocatalytic ozonation system (O₃/TiO₂/UVA) were increased by decreasing the pH of the dye solution in contrast to the ozonation system (O₃). Decolorization of RR194 was increased in the photocatalytic ozonation system with an increasing amount of catalyst however, a decreasing was occurred for the homogeneous catalytic system (O₃/Fe(II)) when increasing the concentration of catalyst. The decolorization efficiency of the homogeneous catalytic system (O₃/Fe(II)) was enhanced when combined with UVA light. In our study, the most efficient method for dearomatization and mineralization was the O₃/TiO₂/UVA among the applied AOPs.  相似文献   

3-D Structure of the Galactic Interstellar Matter: A Contribution from GAIA     

Jokūbas Sūdžius  Saulius Raudeliūnas  Arūnas Kučinskas  Audrius Bridžius  Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):109-114

We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, E <sub>B-V</sub> = 0.06) will be easily traced with GAIA up to the distances of ∼ 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, E _B-V = 0.13) will be located up to the distances of ∼ 2.5 kpc. This holds for the reddening tracers of spectral types O – K2 brighter than V = 17. Inmost cases, due to their low spatial density, the early type stars (O– A2) cannot provide reliable information about the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification of the individual interstellar clouds beyond the distances of ∼ 3 kpc. Therefore, we conclude that the information available from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information, including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA itself (parallaxes, E _B-V etc.). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Current Structure and Volume Transport in the Jeju Strait Observed for a Year with Multiple ADCP Moorings     

Shin  Chang-Woong  Min  Hong Sik  Lee  Seok  Kang  Hyoun-Woo  Ku  Bonhwa  Kim  Dong Guk  Park  Joonseong  Kwon  Soonyeol  Choi  Byoung-Ju 《Ocean Science Journal》2022,57(3):365-380

Ocean Science Journal - The seasonal and spatial variation of the current structure and volume transport across the Jeju Strait (JS) is described based on an analysis of the data from five bottom...  相似文献   

台风暴雨的研究进展   总被引：45，自引：20，他引：45  

李江南  王安宇  杨兆礼  李国丽  何夏江  彭涛涌  古志明 《热带气象学报》2003,19(Z1):152-159

台风灾害的主要部分往往是由台风暴雨引起的,对台风暴雨的研究有利于提高对台风天气的预报水平.过去十几年中,在远距离台风暴雨、螺旋雨带的形成理论、台风系统对中纬度地区降水的影响、暴雨分布、下垫面特征对暴雨的影响和暴雨的突然增幅等方面都取得了新的进展.我们对上述进展作了综述,并对现阶段存在的问题进行讨论.  相似文献   

Binary asteroid population. 2. Anisotropic distribution of orbit poles of small,inner main-belt binaries     

P. Pravec  P. Scheirich  D. Vokrouhlický  A.W. Harris  P. Kušnirák  K. Hornoch  D.P. Pray  D. Higgins  A. Galád  J. Világi  Š. Gajdoš  L. Kornoš  J. Oey  M. Husárik  W.R. Cooney  J. Gross  D. Terrell  R. Durkee  F. Marchis 《Icarus》2012,218(1):125-143

Our photometric observations of 18 main-belt binary systems in more than one apparition revealed a strikingly high number of 15 having positively re-observed mutual events in the return apparitions. Our simulations of the survey showed that it cannot be due to an observational selection effect and that the data strongly suggest that poles of mutual orbits between components of binary asteroids in the primary size range 3–8 km are not distributed randomly: The null hypothesis of an isotropic distribution of the orbit poles is rejected at a confidence level greater than 99.99%. Binary orbit poles concentrate at high ecliptic latitudes, within 30° of the poles of the ecliptic. We propose that the binary orbit poles oriented preferentially up/down-right are due to either of the two processes: (i) the YORP tilt of spin axes of their parent bodies toward the asymptotic states near obliquities 0° and 180° (pre-formation mechanism) or (ii) the YORP tilt of spin axes of the primary components of already formed binary systems toward the asymptotic states near obliquities 0° and 180° (post-formation mechanism). The alternative process of elimination of binaries with poles closer to the ecliptic by dynamical instability, such as the Kozai effect due to gravitational perturbations from the Sun, does not explain the observed orbit pole concentration. This is because for close binary asteroid systems, the gravitational effects of primary’s irregular shape dominate the solar-tide effect.  相似文献   

Observation of Turbulence in Solar Surface Convection: I. Line Parameter Correlations     

A. Hanslmeier  A. Kučera  J. Rybák  H. Wöhl 《Solar physics》2008,249(2):293-306

By using slit observations of solar photospheric lines shifted by 0.4 arcsec, a 2D field on the Sun was scanned to obtain a 16-minute time series of 2D line-parameter variations. The aim was to investigate in detail the occurrence of turbulence that can be measured by line-width variations extracted from the line profiles. The continuum-intensity variation served as a proxy for granular (bright) and intergranular (dark) areas. The results show that turbulence is not limited to the intergranular space but is also produced by horizontal motions that may become supersonic, leading to turbulence. These motions lead to brightenings, as predicted by theoretical models. Thus, enhanced line-width variations are found to occur in both bright and dark areas. A Sobel filter served to detect the areas where strong gradients in the line parameters occur. By applying this filter to the different line-parameter variations over the 2D field observed, we can determine whether there exists a similarity of these strong-gradient patterns with other parameters that characterize granular motions such as intensity variations or velocity fluctuations.  相似文献