形成中的大陆壳

大陆地壳总成分是安山质的，这样的成分不可能通过现代地壳生长的主导方式即会聚边缘和板内玄开岩浆作用而产生。由此表明，太古代存在另一种不同的大陆壳产生方式，而且下地壳的拆沉作用可能是一种重要的循环作用。     

在计算合成震波图中震源和接收器井孔效果的组合

由于震源移入不同的地层及由于井孔环境的变化，井孔震源的辐射图形有很大变化，同样，地震检波器也有能够影响记录波形的接收图形。我们用两种方式将这些振幅和相位以合成震波图中。首先，由３－Ｄ有限并分的直接解为相对较小的地球模型提供精确的全波形解。对于震源／接收器大间距的模拟，我们将震源辐射的静止相位解与射线追踪的接收图形相结合。有限差分震波图与从均匀试验介质中计算出射线追踪结果的比较表明：根据射线计算出的     

Comet Sugano-Saigusa-Fujikawa (1983V)--a small, puzzling comet

Spectroscopic and infrared observations of Comet Sugano-Saigusa-Fujikawa (1983V) were obtained during its close approach to the Earth on 11-14 June 1983. The [O I] production rates of 1.8 +/- 0.9 x 10(26) atoms/s observed on 12.3 June and 7 +/- 3.5 x 10(26) atoms/s on 13.4 June lead to derived water-production rates of 3 x 10(27) mol/s on 12 June and 1.1 x 10(28) mol/s on 13 June. The abundances of the minor species NH2, CN, C2, and C3 are unusually low relative to [O I]. The upper limit to the average nuclear radius from our infrared and visual photometry on 12-13 June (assuming that the entire signal came from the nucleus) is approximately 370 m. The dust/gas mass ratio was <0.01 on June 12 and <0.005 on June 13.     

Proposed in situ secondary ion mass spectrometry on Mars

Secondary ion mass spectrometry is a powerful analytical tool, which has the potentiality, through molecular ion emission, of detecting minor phases, as well as the unique capability of directly measuring isotope abundances in mineral or organic phases without any prior physical, chemical or thermal processing. Applied to the in situ analysis of the Martian regolith, it can provide evidence of the presence of carbonates and, by inference (if carbonates constitute significant deposits), of past liquid water--a necessary condition for the development of life. In addition, oxygen isotopic composition of carbonates preserves a record of the temperature at which this phase precipitated and may therefore help decipher the past climatology of Mars. Detection of a carbon isotopic composition shift between carbonates and organic matter (on Earth, the result of a kinetic fractionation effect during photosynthesis) would provide a definite clue regarding the existence of a past biochemical activity on Mars.     

Could organic matter have been preserved on Mars for 3.5 billion years?

3.5 billion years (byr) ago, when it is thought that Mars and Earth had similar climates, biological evolution on Earth had made considerable progress, such that life was abundant. It is therefore surmised that prior to this time period the advent of chemical evolution and subsequent origin of life occurred on Earth and may have occurred on Mars. Analysis for organic compounds in the soil buried beneath the Martian surface may yield useful information regarding the occurrence of chemical evolution and possibly biological evolution. Calculations based on the stability of amino acids lead to the conclusion that remnants of these compounds, if they existed on Mars 3.5 byr ago, might have been preserved buried beneath the surface oxidizing layer. For example, if phenylalanine, an amino acid of average stability, existed on Mars 3.5 byr ago, then 1.6% would remain buried today, or 25 pg-2.5 ng of C g-1 Martian soil may exist from remnants of meteoritic and cometary bombardment, assuming that 1% of the organics survived impact.     

Recovery in rubble fields: long-term impacts of blast fishing

This paper presents initial results from a study of factors that inhibit or enhance hard coral recovery in rubble fields created by blast fishing in Komodo National Park and Bunaken National Park, Indonesia. Within nine sites monitored since 1998, there was no significant natural recovery. Levels of potential source coral larvae were assessed with settlement tiles in the rubble fields and in nearby high coral cover sites. Rubble movement was measured and shown to be detrimental to small scleractinians, especially in high current areas. In shallow water (2-6 m deep), rubble is often overgrown by soft corals and corallimorpharians, which inhibit hard coral survival. There is increased scleractinian recruitment in quadrats cleared of soft coral, and Acropora nubbins transplanted into soft coral fields suffer greater mortality than those transplanted above the soft coral canopy. Gaining an understanding of the prognosis for coral recovery is essential not only in order to assess the long-term impacts of blast fishing, but also to improve management decisions about protection of intact reefs and potential restoration of damaged areas.     

Model parameters for simulating fate and transport of on-site wastewater nutrients

This paper presents a critical review of model-input parameters for transport of on-site wastewater treatment system (OWS) pollutants. Approximately 25% of the U.S. population relies on soil-based OWS for effective treatment and protection of public health and environmental quality. Mathematical models are useful tools for understanding and predicting the transport and fate of wastewater pollutants and for addressing water-budget issues related to wastewater reclamation from site to watershed scales. However, input parameters for models that simulate fate and transport of OWS pollutants are not readily obtained. The purpose of this analysis is to illustrate an objective, statistically supported method for choosing model-input parameters related to nitrogen (N) and phosphorus (P). Data were gathered from existing studies reported in the literature. Cumulative frequency distributions (CFDs) are provided for OWS effluent concentrations of N and P, nitrification and denitrification rates, and linear sorption isotherm constants for P. When CFDs are not presented, ranges and median values are provided. Median values for model-input parameters are as follows: total N concentration (44 mg/L), nitrate-N (0.2 mg/L), ammonium (60 mg/L), phosphate-P (9 mg/L), organic N (14 mg/L), zero-order nitrification rate (264 mg/L/d), first-order nitrification (2.9/d), first-order dentrification (0.025/d), maximum soil capacity for P uptake (237 mg/kg), linear sorption isotherm constant for P (15.1 L/kg), and OWS effluent flow rates (260 L/person/d).     

Temporal changes in water quality at a childhood leukemia cluster

Since 1997, 15 cases of acute lymphocytic leukemia and one case of acute myelocytic leukemia have been diagnosed in children and teenagers who live, or have lived, in an area centered on the town of Fallon, Nevada. The expected rate for the population is about one case every five years. In 2001, 99 domestic and municipal wells and one industrial well were sampled in the Fallon area. Twenty-nine of these wells had been sampled previously in 1989. Statistical comparison of concentrations of major ions and trace elements in those 29 wells between 1989 and 2001 using the nonparametric Wilcoxon signed-rank test indicate water quality did not substantially change over that period; however, short-term changes may have occurred that were not detected. Volatile organic compounds were seldom detected in ground water samples and those that are regulated were consistently found at concentrations less than the maximum contaminant level (MCL). The MCL for gross-alpha radioactivity and arsenic, radon, and uranium concentrations were commonly exceeded, and sometimes were greatly exceeded. Statistical comparisons using the nonparametric Wilcoxon rank-sum test indicate gross-alpha and -beta radioactivity, arsenic, uranium, and radon concentrations in wells used by families having a child with leukemia did not statistically differ from the remainder of the domestic wells sampled during this investigation. Isotopic measurements indicate the uranium was natural and not the result of a 1963 underground nuclear bomb test near Fallon. In arid and semiarid areas where trace-element concentrations can greatly exceed the MCL, household reverse-osmosis units may not reduce their concentrations to safe levels. In parts of the world where radon concentrations are high, water consumed first thing in the morning may be appreciably more radioactive than water consumed a few minutes later after the pressure tank has been emptied because secular equilibrium between radon and its immediate daughter progeny is attained in pressure tanks overnight.