Observations of HCN in comet P/Halley

We present observations of the HCN J = 1-0 rotational transition at 3.4 mm wavelength in comet P/Halley. The data were obtained during a total of 56 individual observing sessions between November 1985 and May 1986 and represent the first time that a cometary parent molecule has been so extensively monitored. The HCN production rate is well correlated with the total visual magnitude of the comet, and comparison of the HCN production to the total gas production of the comet indicates that it is a relatively minor constituent with 0.1% the abundance of H2O. Comparison of HCN and CN production suggests that HCN is a major parent molecule of CN, but probably not the sole parent. HCN spectra obtained by binning the data with heliocentric distance show that the line width, and thus the parent outflow velocity, increases with decreasing heliocentric distance, and that there is a tendency for the lines to be blue shifted due to anisotropic outgassing from the nucleus. Finally, there is evidence of day-to-day time variability in the total HCN emission and in the hyperfine ratios. The time variation of the total emission is consistent with the known time variable behavior of the comet, and detailed comparisons to optical data, where possible, confirm this interpretation. However, non-LTE values of the hyperfine ratios are not consistent with theoretical modeling of the excitation of these transitions.     

Towards sustainable groundwater use: setting long-term goals, backcasting, and managing adaptively

The sustainability of crucial earth resources, such as groundwater, is a critical issue. We consider groundwater sustainability a value-driven process of intra- and intergenerational equity that balances the environment, society, and economy. Synthesizing hydrogeological science and current sustainability concepts, we emphasize three sustainability approaches: setting multigenerational sustainability goals, backcasting, and managing adaptively. As most aquifer problems are long-term problems, we propose that multigenerational goals (50 to 100 years) for water quantity and quality that acknowledge the connections between groundwater, surface water, and ecosystems be set for many aquifers. The goals should be set by a watershed- or aquifer-based community in an inclusive and participatory manner. Policies for shorter time horizons should be developed by backcasting, and measures implemented through adaptive management to achieve the long-term goals. Two case histories illustrate the importance and complexity of a multigenerational perspective and adaptive management. These approaches could transform aquifer depletion and contamination to more sustainable groundwater use, providing groundwater for current and future generations while protecting ecological integrity and resilience.     

Agricultural pollutant penetration and steady state in thick aquifers

The leakage of pollutants from agricultural lands to aquifers has increased greatly, driven by increasing fertilizer and pesticide use. Because this increase is recent, ground water pollutant concentrations, loads, and exports may also be increasing as pollutants penetrate more deeply into aquifers. We established in an aquifer profile a ground water recharge and pollutant leakage chronology in an agricultural landscape where 30 m of till blankets a 57-m thick sandstone aquifer. Pollutant concentrations increased from older ground water (1963) at the aquifer base to younger ground water (1985) at its top, a signal of increasing pollutant leakage. Nitrate-N increased from 0.9 to 13.2 mg/L, implying that leakage increased from 1.9 to 16.5 kg/ha/year. Nitrate load and export could increase from 130% to 230% before reaching a steady state in 20 to 40 years. Chloride increases were similar. Pesticide residues alachlor ethane sulfonic acid (ESA), metolachlor ESA, and atrazine residues partially penetrated the aquifer profile. Their concentration-age-date patterns exhibited an initial increase and then a leveling corresponding to the timing of product adoption and leveling of demand. Unlike NO(3), projecting pesticide residue steady states is complicated by the phasing in and out of pesticide products over time; for example, neither alachlor nor atrazine is currently used in the area, and newer products, which have not had time to transit to the aquifer, have been adopted. The circumstances that resulted in the lack of a pollutant steady state are not rare; thus, the lack of steady states in agricultural region aquifers may not be uncommon.     

典型韵律互层式灰岩与泥灰岩的地球化学特征对比

通过对德国南部地区上侏罗统麻姆组典型韵律互层式灰岩与泥灰岩进行逐层采样,并进行不溶残余物分析和地球化学测定对比,发现两者所含非碳酸盐物质没有区别。SiO₂、Al₂O₃、Fe₂O₃、K₂O和TiO₂等来源于陆源碎屑物,在灰岩与泥灰岩中的比例完全相同,其含量的不同完全由碳酸盐物质的稀释所引起。元素Sr、Zn、Mn和Mg归为成岩作用控制元素,最先存在形式与碳酸盐有关,但成岩阶段变化极大,Mg的含量主要受白云岩化作用程度控制。另一组元素如S、Ba、Rb和P等介于以上两组元素之间,表现为部分受陆源碎屑物含量控制,部分受成岩作用影响。研究表明,灰岩与泥灰岩韵律互层形成的原因主要是由于碳酸盐物质的沉积速率变化所致,成岩阶段的压溶作用加大了两者的差异,但这种差异只表现在于碳酸盐物质与酸不溶残余物的比例上,而地球化学组成没有本质区别。     

Total dissolved and particulate lead in the Western Harbor of Alexandria,a Mediterranean basin under stress

The Western Harbor of Alexandria, the largest harbor of Egypt on the Mediterranean Sea, receives different internal and external untreated pollutants affecting dramatically its water, sediments and biota. Surface and bottom water samples were collected bimonthly from this harbor for studying vertical, regional and monthly distributions of total suspended matter (TSM), total dissolved lead (TDPb) and total particulate lead (TPPb). The high surface TSM values coincided with air-borne dust, organic aggregates, plankton productivity and discharged wastes. The high TSM averages in winter resulted mainly from turbulence of the water column by wind action. The highest averages of TDPb in the petroleum and coal basins in the Western Harbor reflect their effects on the water column, while the lowest averages of TDPb and TPPb were found at a location far away from pollution sources. For the water column, the maximum and minimum monthly averages of TPPb and TDPb respectively in June reflect the increase in the rate of lead uptake by phytoplankton abundant in summer, favored by temperature elevation. The annual mean concentration of TPPb was nearly double that of TDPb, indicating that lead was transported to the Western Harbor mainly in particulate form. This reflects the high TSM content in the harbor water onto which a considerable part of lead was adsorbed.     

浙江沿岸贝类生物体中Hg、Cd、Pb、As含量的分析

运用冷原子荧光法、无火焰原子吸收分光光度法及分光光度法对 1 998年 5～ 6月所采集的浙江沿岸 1 4个测站 2 3个贝类生物样品中的重金属 Hg、 Cd、 Pb、 As含量进行了分析。结果表明 :贝类生物样品中重金属平均含量 :Hg为 0 .0 2 0× 1 0 - 6、Cd为 1 .5 4× 1 0 - 6、Pb为 0 .49× 1 0 - 6 、 As为 1 .73× 1 0 - 6 。贝类不同科间重金属含量存在明显差异 ,蚶科含 Cd量最高 ,帘蛤科含 As量最高。同时对不同海区的贝类生物体中重金属含量进行了比较     

The hydrocarbon ring C3H2 is ubiquitous in the Galaxy

We report the discovery of a strong microwave (lambda 1.6 cm) spectral line, the carrier of which is common and widespread throughout the Galaxy. A survey of a large number of sources shows that the line appears in emission in cold dust clouds, in absorption in the direction of the Galactic center, and exhibits complex profiles toward H II regions. Toward Cas A and distant H II regions, intervening "spiral arm" clouds produce absorption. For almost all cases, the absorption features show a striking 1 : 1 radial velocity correspondence with those seen, e.g., in H2CO spectra of the same objects. The data indicate that the line arises between low-lying energy states of rather polar molecule. Recent work by Thaddeus, Vrtilek, and Gottlieb, reported in 1985 incorporating the present data, shows that the line in question is the 1(10)-1(01) transition of the small hydrocarbon ring C3H2.     

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors

Analysis of the data from Giotto's Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (>10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.     

Interpretation of the surface brightness of Phobos

Analysis of disk resolved images of Phobos obtained by the Phobos 2 spacecraft allows us to study the surface scattering law and albedo variations. From low phase angle images we find variations in local geometric albedo approximately 10%, with a correlation length approximately 1km. The scattering law is reasonably well matched by the recent proposed LPI (Lumme et al. 1990a) model, which allows us to deduce a small scale (approximately 1 mm) surface roughness (approximately 0.5), defined here as the rms. tangent of the local surface normal relative to the mean surface normal in the Duxbury (1991) model of Phobos. This value is very close to what has been found for Mercury and the Moon.