Patterns and controls of surface sediment distribution: west-central Florida inner shelf

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems.     

青藏高原中部湖泊沉积物中Zr/Rb值及其环境意义

由于青藏高原及其周边地区构造复杂,湖泊沉积物中的粒级差别很大,单一的测量方法往往难以奏效。Rb、Zr是表生地球化学过程中的稳定元素,但它们之间也存在显著差别,Rb一般富集在细颗粒中,Zr则在粗颗粒中含量较高。研究发现,湖泊沉积物中Zr/Rb比值与粘土(<2μm)含量存在显著相关,Zr/Rb值反映了湖泊沉积物的粒度大小。Zr/Rb比值所揭示的青藏高原中部280万年来经历的3次大的环境演化过程与岩性变化、孢粉指标反映的环境特征是一致的。     

Composition and distribution of phytoplankton with size fraction results at southwestern east/japan sea

Abundance and distribution of phytoplankton in seawater at southwestern East/Japan Sea near Gampo were investigated by HPLC analysis of photosynthetic pigments during summer of 1999. Detected photosynthetic pigments were chlorophyll a, b, c₁₊₂ (Chl a, Chl b, Chl c₁₊₂), fucoxanthin (Fuco), prasinoxanthin (Pras), zeaxanthin (Zea), 19’-butanoyloxyfucoxanthin (But-fuco) and beta-carotene (β-Car). Major carotenoid was fucoxanthin (bacillariophyte) and minor carotenoids were Pras (prasinophyte), Zea (cyanophyte) and But-fuco (chrysophyte). Chl a concentrations were in the range of 0.16-8.3/land subsurface chlorophyll maxima were observed at 0-10m at inshore and 30–50 m at offshore. Thermocline and nutricline tilted to the offshore direction showed a mild upwelling condition. Results from size-fraction showed that contribution from nano+picoplankton at Chl a maximum layer was increased from 18% at inshore to 69% at offshore on average. The maximum contribution from nano+picoplankton was found as 87% at St. E4. It was noteworthy that contribution from nano+picoplanktonic crysophytes and green algae to total biomass of phytoplankton was significant at offshore. Satellite images of sea surface temperature indicated that an extensive area of the East/Japan Sea showed lower temperature (<18 °C) but the enhanced Chl a patch was confined to a narrow coastal region in summer, 1999. Exceptionally high flux of low saline water from the Korea/Tsushima Strait seemed to make upwelling weak in summer of 1999 in the study area. Results of comparisons among Chl a from SeaWIFs, HPLC and fluorometric analysis showed that presence of Chl b cause underestimation of Chl a about 30% by fluorometric analysis but overestimation by satellite data about 30-75% compared to HPLC data.     

关于OH/IR星的质量损失率计算公式的讨论

利用几种不同的半经验公式计算一批OH／IR星的质量损失率,并通过比较计算结果来讨论所用的公式．在一些情况下,计算质量损失率必须先给定气尘比．通过计算出样品星的气尘比,并讨论气尘比的变化情况,以修正由尘埃质量损失率到总质量损失率的关系式．     

Evidence for Chemical Heterogeneity in the Nucleus of C/1995 O1 (Hale–Bopp)

We present an analysis of OH, CN, and C₂ jets observed in thecoma of Comet Hale–Bopp on UT April 22, 23, and 25, 1997. Monte Carlomodels designed to simulate the gas jets were employed to analyze thenuclear active areas responsible for the observed coma gas jets. Ourresults indicate that four active areas are necessary to reproduce theCN and C₂ jets while five active areas are required to simulatethe OH jets. The additional OH active area must produce significantlevels of OH, but cannot emit measurable quantities of either carbonradical. This difference suggests that the nucleus of Comet Hale–Boppis chemically heterogeneous.     

Challenging a Paradigm: Do We Need Active and Inactive Areas to Account for Near-Nuclear Jet Activity?

We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei. The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley, for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images of the coma.     

Optical Spectroscopy of Comet C/2000 WM1 (LINEAR) at the Guillermo Harro Astrophysical Observatory in Mexico

We present a preliminary analysis of medium resolution optical spectra of comet C/2000 WM1 (LINEAR) obtained on 22 November 2001. Theemission lines of the molecules C₂, C₃, CN, NH₂,H₂O⁺ and presumably CO (Asundi and triplet bands) and C₂ ^-were identified in these spectra. By analysing the brightnessdistributions of the C₂, C₃, CN emission lines along theslit of the spectrograph we determined some physical parameters of theseneutrals, such as their lifetimes and expansion velocities inthe coma. The Franck–Condon factors for the CO Asundi bands and C₂ ^- bands were calculated using a Morse potential model.     

Spin Axis Direction of Comet 19p/Borrelly Based on Observations from 2000 and 2001

We calculate the direction of the rotational angular momentum vector,M, of comet 19P/Borrelly based on rotational lightcurve data from 2000, groundbased imaging of the coma during the Deep Space 1encounter, and the basic near-nucleus coma morphology as revealed by the Deep Space 1 spacecraft. For the most likely direction, we derivea family of solutions (with center at RA = 221°, Dec = -7°) if the direction of M is towards the sunward hemisphere during the Deep Space 1 encounter, whereas if the rotation is of opposite sense, the diametrically opposite family of solutions (with center at RA = 41°, Dec = 7°) would result. We argue that the coma morphology in September 2001 is consistent with the nucleus being a principal axis rotator or one observationally indistinguishable from it. Therefore, for all practical purposes, the direction of the rotational angular momentum vector coincides with the spin axis. We also discuss why the determination of the spin axis direction based on observations from the last apparition is in disagreement with the current result.     

HD 104237,εCha和HD 100546的演化状态

根据Ｈｉｐｐａｒｃｏｓ的资料和ＴＤ－１对εＣｈａ和ＨＤ１００５４６的紫外观测资料讨论了εＣｈａ、ＨＤ１０４２３７和ＨＤ１００５４６在赫罗图上的位置以及它们的演化状态．     

数字滤波技术在射电天文测量中的应用

随着数字技术的发展，数字信号处理芯片的速度越来越快，这为高速数字滤波的实时实现提供了可能。简要阐述了数字滤波的原理，并对两种数字滤波的实现方法进行了分析；给出了数字滤波较模拟滤波的优势；介绍了数字滤波在射电天文测量中的各种应用。