Risk-Based Engineering Design for a Landfill Leachate Collection and Liner System

A methodology is used to identify the tradeoffs between costs and exposure risk associated with landfill leachate collection and low permeable systems. The results are useful in demonstrating the point at which additional levels of sophistication in design of a leachate/liner system do not produce significant reductions of exposure risk. The case study application to the Durham Regional landfill demonstrates that clay liner hydraulic conductivity is the parameter with the largest influence on the risk of exceedance at the point of compliance. When the underlying clay is more permeable, there is a significant merit associated with use of a QA/QC program.     

On the expected performance of a solar oscillation network

We have estimated the performance of several hypothetical ground-based networks intended to provide continuous observations of solar oscillations for one year. These networks were composed of from 2 to 6 stations distributed both in longitude and between the northern and southern hemispheres. Weather patterns at each site were simulated using a 4 parameter climate model and the results analyzed to yield the duty cycle of the representative networks.The results indicate that a 2 station network might achieve a 60% annual mean duty cycle, 3 stations might provide 75%, 4 stations might yield 82%, and 6 stations might give a 93% annual mean duty cycle. Comparison of an existing 6 station network with our model of the same network suggests that the modelling procedure is realistic provided that the estimates of the climate parameters are accurate.To illustrate the influence of such networks on observations of solar oscillations, we have created a synthetic time-line of solar velocities from published data and analyzed the power spectrum of the signal as observed by various networks.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.NCAR is sponsored by the National Science Foundation.     

The structure of high-temperature flare plasma

In Paper I (Emslie, 1985) we derived scaling laws which relate peak loop temperature to injected non-thermal electron flux in electron-heated models of the flare corona. In this paper, we compare these predicted relationships with recent coordinated observations in hard X-rays and soft X-rays. Satisfactory agreement is found for large events, while for smaller events the plasma electron temperature determined by soft X-ray spectral fitting is too high. We discuss a possible resolution of this apparent discrepancy through careful examination of the method used to determine the temperature of the soft X-ray emitting plasma. It is concluded that temperatures determined by spectral fitting over a series of lines are not necessarily representative of the true temperature of the plasma, since the fitting technique is plagued by the same difficulties as a more straightforward technique involving a single spectral line or portion of continuum (Craig and Brown, 1976). The differences between actual and derived temperatures are sufficiently large to remove the above discrepancy between observations and modeling of electron-heated coronae.Presidential Young Investigator.     

Energetic electrons as an energy transport mechanism in solar flares

We review the observations and theory relating to the role of energetic electrons in the solar flare, with particular emphasis on discriminating between thermal and nonthermal origins of these electrons. We discuss diagnostics in hard X-rays, especially those relating to the recent observations of the SMM and HINOTORI satellites. We also briefly address the response of the atmosphere to energy input in the form of high energy electrons, in particular through the diagnostics of both the Fe K feature and optically thin transition region lines such as 0V. Finally, we discuss the relative roles of electron and proton heating in -ray flare events.     

Magnetic fields and the structure of the solar corona

Several different mathematical methods are described which use the observed line-of-sight component of the photospheric magnetic field to determine the magnetic field of the solar corona in the current-free (or potential-field) approximation. Discussed are (1) a monopole method, (2) a Legendre polynomial expansion assuming knowledge of the radial photospheric magnetic field, (3) a Legendre polynomial expansion obtained from the line-of-sight photospheric field by a least-meansquare technique, (4) solar wind simulation by zero-potential surfaces in the corona, (5) corrections for the missing flux due to magnetograph saturation. We conclude (1) that the field obtained from the monopole method is not consistent with the given magnetic data because of non-local effects produced by monopoles on a curved surface, (2) that the field given by a Legendre polynomial (which is fitted to the measured line-of-sight magnetic field) is a rigorous and self-consistent solution with respect to the available data, (3) that it is necessary to correct for the saturation of the magnetograph (at about 80 G) because fields exceeding 80 G provide significant flux to the coronal field, and (4) that a zero-potential surface at 2.5 solar radii can simulate the effect of the solar wind on the coronal magnetic field.     

Radar detection of Vesta

Asteroid 4 Vesta was detected on 1979 November 6 with the Arecibo Observatory's S-band (12.6-cm-wavelength) radar. The echo power spectrum, received in the circular polarization opposite to that transmmited,, yields a radar cross section of (0.2 ± 0.1)πa², for a = 272 km. The data are too noisy to permit derivation of Vesta's rotation period.     

Estimates using fluorescence spectroscopy of the present state of petroleum hydrocarbon contamination in the water column of the northwest Atlantic Ocean

Concentrations of petroleum hydrocarbons in seawater from the general region between Nova Scotia and Bermuda were estimated using fluorescence spectroscopy. Concentrations in surface water (0–3 mm) averaged 20.4 μg/l, and in water from 1 and 5 m they averaged 0.8 and 0.4 μg/l respectively. No significant concentrations could be detected in deeper water. There was considerable variability in the concentrations suggesting that the distribution of oil in seawater is quite patchy, especially in surface waters. Seawater samples for hydrocarbon analysis cannot be collected with conventional sampling equipment. Due to adsorption problems, the inner surface of samplers must come into contact only with the water being sampled and must be rinsed with organic solvent after samples are removed. Because these precautions were not taken in previous investigations, much of the published data of hydrocarbons in seawater is unreliable.     

The biogeochemistry of sediments in two Gulf of Maine basins

Pore water, sediment and microbiological samples were collected from two areas in the Gulf of Maine. The Jeffreys Basin sediments had low organic carbon and low reduced sulfur values; the quality of their pore water indicated that nitrification and subsequent denitrification were major biogeochemical processes occurring in the upper 115 cm. Sediments from the Wilkinson Basin had higher values of organic carbon and higher reduced sulfur and total plate-count bacteria. These data indicate that the major biogeochemical processes occurring in these sediments are denitrification followed by sulfate reduction. The differences in the rates of these microbially mediated processes can be related to differences in sedimentation rates at the two sites.     

A new dry combustion method for the simultaneous determination of total organic carbon and nitrogen in seawater

A new dry combustion method for the simultaneous determination of total organic carbon and nitrogen in seawater is presented. Concentrations of total organic carbon obtained using this method average about 2.0 mg/l in surface water and 1.5 mg/l in deep water in the Northwest Atlantic. These concentrations are significantly greater than those reported using wet oxidation and wet combustion methods, but are comparable to concentrations reported by Russian workers using a similar dry combustion method. Organic nitrogen concentrations average 0.44 mg/l in surface water and 0.12 mg/l in deep water, yielding CN ratios for total organic matter of 5 and 12 respectively.