FLUXES: A NEW PARADIGM FOR GEOLOGIC EDUCATION?     

Warren W. Wood 《Ground water》1997,35(1):1-1

  相似文献   

A Semianalytical Model to Predict Recovery of Light, Nonaqueous Phase Liquids from Unconfined Aquifers     

Dan W. Waddill  Jack C. Parker 《Ground water》1997,35(2):280-290

  相似文献   

Effect of Rigid PVC Bailer Contact on Detection of Pesticides in Water Samples     

W.M. Schuh  R.L. Cline  M.J. Kosse  D.W. Sletton 《Ground Water Monitoring & Remediation》1997,17(1):81-90

A field experiment was conducted to examine the effect of short-term (one minute) contact of pesticide-laden water with a polyvinyl chloride (PVC) bailer on quantitative laboratory measurements of seven pesticide concentrations in distilled water samples subsequently decanted from the bailer. Pesticides were tested at two initial concentrations (low. based on current FPA maximum contaminant levels, or MCL: and high, based on a multiple of approximately lour times the MCL). Pesticide species included bromoxynil, diclofop-m, dimethoate. MCPA, methyl parathion, propiconazole, and trifluralin. Dimethoate recoveries were poor for all treatments. For all other pesticides there was no systematic difference between pesticide concentrations measured before and after bailer contact. Effectiveness of bailer decontamination treatments consisting of distilled water rinse alone was related to water solubility (S) for each species. Distilled water samples decanted from a rigid PVC bailer following initial bailer contact with pesticide-spiked water, and after the bailer had been cleaned with a single distilled water rinse, had measured pesticide concentrations of less than 2 percent of the pesticide concentration in the initial pesticide-spiked water, regardless of S. A single distilled water rinse effectively removed all trace of contaminants having S> 500 mg/L. Multiple distilled water rinses, and multiple distilled water rinses followed by 15 bailings of a well, effectively removed all trace of contaminants having S> 50 mg/L. Below threshold S, cleaning effectiveness decreased as a power function of S.  相似文献   

Relationship of Avalonian and Cadomian terranes to Grenville and Pan-African events     

Laura D. Mallard  John J. W. Rogers 《Journal of Geodynamics》1997,23(3-4)

Suturing of the supercontinent Rodinia in the Grenville event (˜ 1000 Ma) was followed by rifting in the late Proterozoic (˜ 800-700 Ma), reorganization to Gondwana in the Pan-African (˜ 700-500 Ma) and further accretion to develop Pangea at the end of the Paleozoic. One of the Rodinian rifts followed part of the Grenville suture, it produced the margin of eastern North America and southern Baltica and the contrasting margin of west Gondwana in present South America. The Paleozoic accretionary wedge against the Grenville-age margin of North America and Baltica contains Avalonian/Cadomian terranes that exhibit Pan-African erogenic events ± sediments apparently developed while the terranes were in or near Gondwana. These terranes carry lower-Paleozoic fauna (Acado-Baltic) that are not indigenous to North America and Baltica.U---Pb zircon ages range from 1500-1000 Ma in Grenville terranes and from 800–500 Ma with minor inheritance in Avalonian terranes; they are generally much older in Cadomian terranes, implying very little resetting during Pan-African events. T_DM ages are generally 2000–1200 Ma in Grenville terranes, 1300–600 Ma in Avalonian terranes and 2000–1200 in Cadomian terranes. These summary data show that: (1) the Grenville orogenic event produced almost no juvenile crust; (2) the Avalonian terranes of North America contain crust that evolved primarily in the late Proterozoic, possibly as a mixture of juvenile Pan-African material and Grenville or slightly older material; (3) the Cadomian terranes of Europe consist of old (middle-Proterozoic to Archean) crust with minor juvenile Pan-African material. The Avalonian terranes apparently evolved near, and partly on, the Grenville-age crust now in South America during the intense orogeny associated with rotation of Gondwana away from North America. The Cadomian terranes of Europe, however, appear to be fragments of other parts of Gondwana, probably West Africa.  相似文献   

Simulation studies of processes associated with stimulated electromagnetic emission (SEE) in the ionosphere     

W.A Scales  K.T Cheng  S Srivastava 《Journal of Atmospheric and Solar》1997,59(18):2373-2381

Results of numerical simulation studies of processes associated with Stimulated Electromagnetic Emission (SEE) produced during ionospheric heating experiments are presented. A one-dimensional magnetized electrostatic Particle-In-Cell (PIC) simulation model with uniform plasma density is used to investigate electrostatic wave generation in the region where the pump frequency ω₀ approximately equals the upper hybrid frequency ω_uh. In particular, the simulation plasma is driven with a uniform oscillating electric field to represent the long wavelength pump wave and power spectra of the electrostatic waves produced are taken. The pump wave frequency and amplitude are varied to consider the effects on the simulation power spectrum. The upper hybrid frequency in the model is varied through harmonics of the electron cyclotron frequency Ω_ce to consider the effects of stepping the pump frequency through cyclotron harmonics. The power spectrum from the simulation plasma is richly structured. The resulting power spectra show sidebands upshifted and downshifted from the pump frequency by multiples of the lower hybrid frequency ω_lh. The structure of the spectrum is highly sensitive to the proximity of the upper hybrid frequency to the cyclotron harmonic frequencies.  相似文献   

Effect of scallop shells and sediment grain size on phytoplankton flux to the bed     

C.A. Pilditch  C.W. Emerson  J. Grant 《Continental Shelf Research》1997,17(15):1869-1885

A flume study was made of bed skin friction and phytoplankton (Thalassiosira weissf ogii) deposition about a sea scallop (Placopecten magellanicus) mimic on a coarse (mean grain dia. =1200 μm), medium (615 μm) and fine (170 μm) quarry sand. Bed skin friction immediately upstream, and at one shell diameter downstream of the mimic was 1.2–2.4 times higher than ambient values (8.1 × 10⁻² Pa). Directly downstream of the mimic there was a region of near-zero skin friction. Bed diatom density was correlated with changes in skin friction; after 21 h, cell densities were 36–87% greater in the regions of high skin friction upstream and downstream of scallop than in control experiments. The pattern of bed diatom density about the scallop was similar in the coarse and medium sands, but deposition to the fine bed was not affected by the mimic. Diatom density was significantly correlated with grain diameter; deposition in the coarse bed was 2.3 times higher than in the medium sand, and 7.4 times higher than in the fine sand. A field experiment confirmed that the coarse sand was a greater sink of phytoplankton pigment than the fine sand. Previous studies and scaling arguments suggest that the differences in bed diatom density were controlled by the magnitude of interfacial solute fluxes. Regions of high skin friction about the mimic increased the porewater exchange, resulting in greater concentrations of diatoms retained within the bed. Similarly, the more permeable coarse sand would have a greater rate of porewater exchange than the fine sand, explaining the higher bed diatom density. Differences in the predicted volume of interstitial void space as a function of grain size closely matched the observed differences in bed diatom density. Results suggest that alteration of boundary layer flows by centimetre scale topography such as scallops, increases the flux of particulate organic matter toward the bed, but whether it is retained within the bed, and thus made available to the benthos is dependent on the sediment granularity.  相似文献   

Response of the wadden sea to a rising sea level: a Predictive empirical model     

Burghard W. Flemming  Alexander BartholomÄ 《Ocean Dynamics》1997,49(2-3):343-353

  相似文献   

Qualitätsanforderungen an Oberflächengewässer: Zielvorgaben,Qualitätsziele und chemische Gewässergüteklassifizierung     

U. Irmer  W. Rocker  K. Blondzik 《洁净——土壤、空气、水》1997,25(2):62-70

Quality Requirements for Fresh Waters: Water Quality Targets, Water Quality Objectives, and Chemical Water Quality Classification In the Federal Republic of Germany, water quality requirements for the protection of inland surface waters against hazardous substances are formulated on the basis of a quality targets derivation concept developed jointly by the Federal Government and the Federal States. The quality requirements were termed “water quality targets” in order to make it clear that the values derived are orientational values rather than legally binding limit values. The international comparison of quality requirements for surface waters shows that, on the whole, the national quality targets ensure a high level of protection. According to present scientific knowledge, impairments of uses, such as supply of drinking water, or risks to aquatic communities need not to be expected if the quality targets are complied with. A comparison of water quality data with the water quality targets makes it possible, on the one hand, to identify those substances whose inputs must be further reduced; on the other hand, it also shows that, for a number of substances, there is no need at present for concern over their adversely water quality. A further differentiation of the aquatic hazard potential of pollutants allows a water quality classification system to be developed on the basis of the quality targets derivation concept. The basic elements of this water quality classification system are presented, and its application is explained by way of examples.  相似文献   

Abbau von Monochlornitrobenzolen durch Pseudomonas acidovorans CA50     

A. Kuhlmann  W. Hegemann 《洁净——土壤、空气、水》1997,25(6):298-305

Degradation of Monochloronitrobenzenes by Pseudomonas acidovorans CA50 Pseudomonas acidovorans strain CA50 was used for degradation experiments with monochloronitrobenzenes in aerobic batch culture. The monochloronitrobenzenes were reduced to the corresponding monochloroanilines. The reduction only occurred with an additional carbon and nitrogen source. Chlorocatechols were found to be present. 3-Chlorocatechol accumulated in the presence of 2-chloroaniline, whereas 4-chlorocatechol was an intermediate metabolite of 3- and 4-chloroaniline. Contrary to the degradation of monochloronitrobenzenes, Pseudomonas acidovorans strain CA50 used the monochloroanilines as a sole source of carbon, energy, and nitrogen for growth. The oxidation of monochloroanilines was not repressed by the additional substrates. 2-Chloronitrobenzene was degraded with the lowest rate because of the low turnover of the intermediate metabolite 2-chloroaniline. 3-Chloronitrobenzene was completely degraded also in a mixture. A complete degradation of 4-chloronitrobenzene was achieved only when it was the sole chloronitrobenzene. The results suggest that a dechlorination and mineralization of monochlornitrobenzenes is possible, but for a final proof, further investigations will be necessary.  相似文献   

The nonlinear association between ENSO and the Euro-Atlantic winter sea level pressure   总被引：1，自引：0，他引：1  

Aiming Wu  William W. Hsieh 《Climate Dynamics》2004,23(7-8):859-868

A nonlinear projection of the tropical Pacific sea surface temperature anomalies (SSTA) onto the Northern Hemisphere winter sea level pressure (SLP) anomalies by neural networks (NN) was performed to investigate the nonlinear association between El Niño-Southern Oscillation (ENSO) and the Euro-Atlantic winter climate. While the linear impact of ENSO on the Euro-Atlantic winter SLP is weak, the NN projection reveals statistically significant SLP anomalies over the Euro-Atlantic sector during both extreme cold and warm ENSO episodes, suggesting that the Euro-Atlantic climate mainly responds to ENSO nonlinearly. The nonlinear response, mainly a quadratic response to the SSTA, reveals that regardless of the sign of the SSTA, positive SLP anomalies are found over the North Atlantic, stretching from eastern Canada to Europe (with anomaly center located just northwestward of Portugal), and negative anomalies centered over Scandinavia and Norwegian Sea, consistent with the excitation of the positive North Atlantic Oscillation pattern.  相似文献