Orders Of Magnitude Variation Research Articles

Quality Criteria for Re-Use of Organotin-Containing Sediments on Land (7 pp)

Background, Aim and Scope The use of organotin compounds as antifouling agents on ships is prohibited at EU level since 1 July 2003. Because of its persistence, the presence of organotin compounds in harbour sediment will however remain a problem for years. Dumping of dredged sediment in sea is subject to very strict quality criteria, stimulating the exploration of re-use alternatives, such as re-use on land. Within the TBT Clean project (EU LIFE Project 02/ENV/B/341) an assessment framework for re-use of organotin containing treated sediment on land as secondary granular building material was developed. Three scenarios were considered: free re-use on land, re-use above groundwater level with cover layer, and re-use under groundwater level (the latter two scenarios are referred to as restricted re-use). Receptors considered were humans, ecosystem and groundwater. Generic upper concentration limits and sediment leaching limits were calculated. Materials and Methods: Upper concentration limits were calculated with the Vlier-Humaan model. This model allows to calculate soil remediation values according to the Flemish legal framework. The focus of the methodology is the protection of human health, although a check for ecotoxicity was included in the project. The soil remediation value for residential land-use was selected within the scenario for free re-use; for restricted re-use (no direct contact possible), the soil remediation value for industrial land-use was selected. Leaching values were calculated with an analytical soil and groundwater transport model. The reference scenario behind the leaching criteria of the European Landfill Directive was modified to fit the project objectives. Default values for application height and length were used. The point-of-compliance was situated at 20 m distance in the groundwater. Physicochemical properties were taken from literature; sorption characteristics were taken from literature and were measured on 6 treated sediment samples during the project. Plant-uptake values were taken from the literature. Toxicological criteria were taken from EFSA. Results: The assessment framework provided an upper limit (SedUL) and an leaching value (SedLV) for each scenario, expressed as mg/kg dm in the sediment. Criteria were calculated for tributyltin (TBT) and dibutyltin (DBT); too few data were available for monobutyltin (MBT). The SedUL equalled 0.51 mg TBT/kg dm and 0.07 mg DBT/kg dm for free re-use and 195 mg TBT/kg dm and 205 mg DBT/kg dm for restricted re-use (two scenarios). For free re-use the SedLV was only limiting for TBT at Kd of < 2000 l/kg in the sediment. Under re-use above groundwater level with coverage SedLV values ranged from 6.9 – 29 mg TBT/kg dm and from 12 – 33.3 mg DBT/kg dm (Kd ranging from 100 – 10000 l/kg); under re-use below groundwater level SedLV values ranged from 0.007 – 0.77 mg TBT or DBT/kg dm (Kd ranging from 100 – 10000 l/kg). Discussion: Results are subject to large uncertainties because of variation in input data; the model output is sensitive to variation in plant uptake (SedUL for free re-use), Koc or Kd (SedUL for restricted re-use, SedLV for re-use with coverage), Henry's law coefficient (SedUL for restricted re-use); all these parameters show orders of magnitude variation. Conclusions: A feasible and consistent framework for evaluation of the re-use of treated organotin containing sediment was developed. However, the resulting quality criteria are still subject to large uncertainties, due to uncertainties in input data. Recommendations and Perspectives: High-quality data on plant uptake and soil sorption of organotin compounds, the influence of soil properties on these processes, and long-term terrestrial toxicity data are needed to refine the calculations. The quality criteria should be reviewed when these data become available.

Long-term flow rates and biomat zone hydrology in soil columns receiving septic tank effluent

Soil absorption systems (SAS) are used commonly to treat and disperse septic tank effluent (STE). SAS can hydraulically fail as a result of the low permeable biomat zone that develops on the infiltrative surface. The objectives of this experiment were to compare the hydraulic properties of biomats grown in soils of different textures, to investigate the long-term acceptance rates (LTAR) from prolonged application of STE, and to assess if soils were of major importance in determining LTAR. The STE was applied to repacked sand, Oxisol and Vertisol soil columns over a period of 16 months, at equivalent hydraulic loading rates of 50, 35 and 8 L/m 2/d, respectively. Infiltration rates, soil matric potentials, and biomat hydraulic properties were measured either directly from the soil columns or calculated using established soil physics theory. Biomats 1 to 2 cm thick developed in all soils columns with hydraulic resistances of 27 to 39 d. These biomats reduced a 4 order of magnitude variation in saturated hydraulic conductivity ( K s) between the soils to a one order of magnitude variation in LTAR. A relationship between biomat resistance and organic loading rate was observed in all soils. Saturated hydraulic conductivity influenced the rate and extent of biomat development. However, once the biomat was established, the LTAR was governed by the resistance of the biomat and the sub-biomat soil unsaturated flow regime induced by the biomat. Results show that whilst initial soil K s is likely to be important in the establishment of the biomat zone in a trench, LTAR is determined by the biomat resistance and the unsaturated soil hydraulic conductivity, not the K s of a soil. The results call into question the commonly used approach of basing the LTAR, and ultimately trench length in SAS, on the initial K s of soils.

Anisotropy of nonlinear coupling of two counter-propagating waves in photorefractiveFe:KNbO3

The dependence of self-pumped photorefractive two-beam coupling in $\mathrm{Fe}:{\mathrm{KNbO}}_{3}$ with crystal angle has been measured at $532\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ for the $a$-$c$ and $b$-$c$ crystal planes using a combination of oil immersion and relay imaging. A significant deviation between existing theory and experiment is found for large crystal angles. We propose this is due to a highly anisotropic effective charge trap density in $\mathrm{Fe}:{\mathrm{KNbO}}_{3}$ of almost two orders of magnitude variation with crystal angle in the $a$-$c$ plane.

Aging of oil-in-water emulsions: The role of the oil

Controlling stability and aging of emulsions is important from commercial and scientific perspectives. Achieving such control comes through gaining an understanding of the relationship between emulsion constituents and microstructure and how these influence the kinetics and mechanism of destabilisation. We present here an investigation determining the rate of destabilisation as a function of time for a series of water/ n-alkane/Triton X-100 oil-in-water emulsions. The time dependence of the emulsions was investigated using static light scattering, PFG-NMR and measurement of gross phase separation. By changing the chain length of the oil from hexane to tetradecane, an almost five orders of magnitude variation in emulsion lifetime could be achieved, while maintaining most of the other chemical and physical characteristics of the emulsions. Further, we show that while Ostwald ripening is the dominant destabilisation mechanism, two distinct regimes are evident. Initially, we observed an enhanced Ostwald ripening regime due to the presence of oil-swollen micelles in the aqueous continuum, that is a depletion flocculation mechanism is followed. The presence of oil-swollen micelles was confirmed using PFG-NMR. The micelles aid the gross oil transport between the discrete oil domains. Upon phase separation the oil-swollen micelles are predominantly removed from the emulsion along with the excess water resulting in a concomitant reduction in the ripening rate, producing the more general Ostwald ripening cubic dependence of droplet radius as a function of time for the lower molecular weight oils. The oils with higher molecular weight (decane and above), however, were observed to switch over to destabilisation via creaming. PFG-NMR was shown to be a powerful technique to fully probe emulsion microstructure as a function of time with droplet size and spacing being directly obtained from the data.

Size‐Dependent Variation in Shoot Light‐Harvesting Efficiency in Shade‐Intolerant Conifers

Shoots and foliage elements of shade‐intolerant conifers strongly vary in size, but the effects of size on shoot light‐harvesting efficiency have not been quantified. We investigated shoot adaptation to seasonal average integrated quantum flux density in gymnosperms Pinus palustris Mill., P. patula Schlect. & Cham., and P. radiata D. Don. and angiosperm Casuarina glauca Sieb. ex Spreng. In addition, P. sylvestris L., sampled from infertile and fertile sites, and P. taeda L. were included to test for general correlations among shoot architecture and size. All studied species possess needle‐like photosynthetic elements. A shoot model was fitted to the data to separate the determinants of shoot light‐harvesting efficiency. The model estimated shoot light harvesting on the basis of angular distribution of foliage surface areas, degree of spatial clumping, foliage area density in shoot volume, and beam path length in shoot volume. Increases in irradiance primarily led to greater foliage aggregation, greater foliage area density in shoot volume, and to a minor degree, to changes in foliage area angular distribution. Greater foliage aggregation resulted in lower efficiency of light harvesting but greater investment of foliar biomass in high light where the photosynthetic returns are greater. The species behave similarly except that the light‐harvesting characteristics of P. patula, which has long, strongly bending needles, were independent of light. In all species, the shoots were larger in higher irradiance, and the fraction of biomass in shoot axis increased with increasing irradiance, indicating greater costs for light harvesting in high light. There were further significant species differences in light‐harvesting efficiency that were linked to differences in foliage and shoot size. Foliage element length varied between 1.1 and 31.4 cm and shoot axis length between 1.2 and 36.5 cm among the species, leading to 4 orders of magnitude variation in shoot cylinder volume and three orders of magnitude variation in foliage area density (ρ); ρ decreased with increasing foliage element length and shoot volume. The degree of foliage clumping scaled positively with ρ and negatively with foliage element length. Foliage clumping was positively associated with foliage dry mass to shoot silhouette area ratio, signifying a trade‐off between efficient light harvesting and large photosynthetic biomass accumulation. These data demonstrate a general increase of light‐harvesting efficiency with increasing length of foliage elements, but they also demonstrate that this increase is limited by enhanced bending of longer foliage elements and by augmented support costs.

Effluent flux prediction in variably saturated soil zones within a septic tank—soil absorption trench

The treatment and hydraulic mechanisms in a septic tank–soil absorption system (SAS) are highly influenced by the clogging layer or biomat zone which develops on bottom and lower sidewall surfaces within the trench. Flow rates through the biomat and sub-biomat zones are governed largely by the biomat hydraulic properties (resistance and hydraulic conductivity) and the unsaturated hydraulic conductivity of the underlying soil. One- and 2-dimensional models were used to investigate the relative importance of sidewall and vertical flow rates and pathways in SAS. Results of 1-dimensional modelling show that several orders of magnitude variation in saturated hydraulic conductivity (Ks) reduce to a 1 order of magnitude variation in long-term flow rates. To increase the reliability of prediction of septic trench hydrology, HYDRUS-2D was used to model 2-dimensional flow. In the permeable soils, under high trench loading, effluent preferentially flowed in the upper region of the trench where no resistant biomat was present (the exfiltration zone). By comparison, flow was more evenly partitioned between the biomat zones and the exfiltration zones of the low permeability soil. An increase in effluent infiltration corresponded with a greater availability of exfiltration zone, rather than a lower resistance of biomat. Results of modelling simulations demonstrated the important role that a permeable A horizon may play in limiting surface surcharge of effluent under high trench hydraulic loading.

The MET receptor tyrosine kinase contributes to invasive tumour growth in rhabdomyosarcomas

The receptor tyrosine kinase MET and its ligand hepatocyte growth factor (HGF), have been implicated in the genesis of the paediatric tumour rhabdomyosarcoma (RMS). Addition of exogenous HGF to RH30 RMS cells enhanced non-chemotactic migration. Stable transfection of dominant negative MET into RH30 cells attenuated Matrigel invasion and in vivo tumour growth. To assess the role of a putative HGF–MET pathway in human RMS, we measured their expression in a panel of 68 human primary tumours. All tumours expressed MET but with a three orders of magnitude variation of expression and 62% of tumours co-expressed HGF. In contrast with other tumour types, neither high-MET expression nor HGF/MET coexpression correlated with metastatic disease. In a microarray screen, we identified CCN1 as being 7.8-fold up regulated following addition of HGF to RH30 cells and in RMS tumours, CCN1 expression correlated with HGF expression. Surprisingly, we identified MET as a consistent feature of embryonal and not alveolar RMS.

The mineral dissolution rate conundrum: Insights from reactive transport modeling of U isotopes and pore fluid chemistry in marine sediments

Pore water chemistry and 234U/ 238U activity ratios from fine-grained sediment cored by the Ocean Drilling Project at Site 984 in the North Atlantic were used as constraints in modeling in situ rates of plagioclase dissolution with the multicomponent reactive transport code Crunch. The reactive transport model includes a solid-solution formulation to enable the use of the 234U/ 238U activity ratios in the solid and fluid as a tracer of mineral dissolution. The isotopic profiles are combined with profiles of the major element chemistry (especially alkalinity and calcium) to determine whether the apparent discrepancy between laboratory and field dissolution rates still exists when a mechanistic reactive transport model is used to interpret rates in a natural system. A suite of reactions, including sulfate reduction and methane production, anaerobic methane oxidation, CaCO 3 precipitation, dissolution of plagioclase, and precipitation of secondary clay minerals, along with diffusive transport and fluid and solid burial, control the pore fluid chemistry in Site 984 sediments. The surface area of plagioclase in intimate contact with the pore fluid is estimated to be 6.9 m 2/g based on both grain geometry and on the depletion of 234U/ 238U in the sediment via α-recoil loss. Various rate laws for plagioclase dissolution are considered in the modeling, including those based on (1) a linear transition state theory (TST) model, (2) a nonlinear dependence on the undersaturation of the pore water with respect to plagioclase, and (3) the effect of inhibition by dissolved aluminum. The major element and isotopic methods predict similar dissolution rate constants if additional lowering of the pore water 234U/ 238U activity ratio is attributed to isotopic exchange via recrystallization of marine calcite, which makes up about 10–20% of the Site 984 sediment. The calculated dissolution rate for plagioclase corresponds to a rate constant that is about 10 2 to 10 5 times smaller than the laboratory-measured value, with the value depending primarily on the deviation from equilibrium. The reactive transport simulations demonstrate that the degree of undersaturation of the pore fluid with respect to plagioclase depends strongly on the rate of authigenic clay precipitation and the solubility of the clay minerals. The observed discrepancy is greatest for the linear TST model (10 5), less substantial with the Al-inhibition formulation (10 3), and decreases further if the clay minerals precipitate more slowly or as highly soluble precursor minerals (10 2). However, even several orders of magnitude variation in either the clay solubility or clay precipitation rates cannot completely account for the entire discrepancy while still matching pore water aluminum and silica data, indicating that the mineral dissolution rate conundrum must be attributed in large part to the gradual loss of reactive sites on silicate surfaces with time. The results imply that methods of mineral surface characterization that provide direct measurements of the bulk surface reactivity are necessary to accurately predict natural dissolution rates.

The scaling and temperature dependence of vertebrate metabolism

Body size and temperature are primary determinants of metabolic rate, and the standard metabolic rate (SMR) of animals ranging in size from unicells to mammals has been thought to be proportional to body mass (M) raised to the power of three-quarters for over 40 years. However, recent evidence from rigorously selected datasets suggests that this is not the case for birds and mammals. To determine whether the influence of body mass on the metabolic rate of vertebrates is indeed universal, we compiled SMR measurements for 938 species spanning six orders of magnitude variation in mass. When normalized to a common temperature of 38 degrees C, the SMR scaling exponents of fish, amphibians, reptiles, birds and mammals are significantly heterogeneous. This suggests both that there is no universal metabolic allometry and that models that attempt to explain only quarter-power scaling of metabolic rate are unlikely to succeed.

Sample size and mass range effects on the allometric exponent of basal metabolic rate

The controversial relationship between body mass and basal metabolic rate in animals revolves around two questions: what is the allometric scaling exponent and what is the functional basis for it? For mammals, the first question could be resolved if measurements from all 4600 extant species were available, but this study shows that data for only 150 species, spanning three to four orders of magnitude variation in body mass, are sufficient to accurately determine the exponent. Because the currently available data set includes about 600 species that vary over five orders of magnitude in body size, further increases in sample size are unlikely to change the estimate of the scaling exponent.

Phantom materials for single point imaging pulse sequences

The popularity of pure phase encode MRI techniques, including single point imaging (SPI), is steadily increasing, particularly in instances where the samples of interest are solid-like, or for other reasons possess short effective transverse relaxation times, T 2 * . As the interest in these techniques grows, so too does the need for a phantom material which is representative of this class of samples. The characteristics of such a phantom should include chemical and physical stability, straightforward preparation, high signal to noise ratio and relaxation times which are both easily manipulated and representative. To this end, we have developed a gelatin/sucrose-based gel which addresses the above criteria and behaves as a very flexible short T 2 * phantom. An order of magnitude variation in T 1 and T 2 can be achieved over a reasonable range of sucrose concentration. Even larger changes can be achieved with the addition of further doping agents.

100th Anniversary Special Paper: Metal Concentrations in Crustal Fluids and Their Relationship to Ore Formation

A database of saline fluid compositions, including deep shield ground waters, sedimentary formation waters, geothermal brines, and fluids from metamorphic and igneous rocks and veins, is used to explore the controls on metal concentrations in crustal fluids. There are no systematic differences between analyses of fluids sampled by drilling and analyses of fluid inclusions. Over the wide range studied, temperature emerges as a dominant control on the concentrations of Fe, Mn, Zn, and Pb in solution, although the more limited data for Cu are equivocal. Chloride concentration is also important, with the mole ratio metal/chloride (Me/Cl) remaining reasonably constant at constant temperature over a wide range of chlorinities for all four metals considered in detail. There is no evidence for significant differences in transition-metal speciation with increasing chloride nor between low- and high-temperature fluids, although in the case of Zn, complexes with additional Cl may be important at low temperature. Plots of log Me/Cl versus 1/T for the transition metals considered each yield a linear correlation, with about five orders of magnitude variation in Me/Cl between diagenetic and magmatic temperatures. There is approximately two orders of magnitude variability at each temperature, which probably arises in large part from variations in pH. Limited data for low-salinity, CO2-rich fluids indicate that they lie on the same trends, with transition-metal concentrations controlled by fluid salinity and temperature. Order of magnitude concentrations of Fe, Mn, Zn, and Pb in any chloride-dominated crustal fluid can be predicted with the following equations (T in K, concentration ratios are molar): log (Fe/Cl) = 1.4 – (1,943/T) ± 1; log (Mn/Cl) = 0.55 – (1,871/T) ± 1; log (Zn/Cl) =– (1,781/T) ± 1; log (Pb/Cl) = –1.2 – (1,533/T) ± 1. The results demonstrate that crustal fluids are strongly buffered through interactions with the rocks (or melts) that host them. Thus, of the major variables influencing metal concentrations in solution, only temperature and chloride concentration can be considered as truly independent. The plots show that metal-rich fluids may arise through equilibration of chloride-rich waters with normal silicate rocks. Saline magmatic fluids, which may attain extremely high concentrations of transition metals, have clear ore-forming potential, as do formation brines from deep, hot basins; cooler basins do not permit such high concentrations of base metals to be attained. The results of this study emphasize the importance of the distribution and cycling of chloride in the crust for the distribution of base metal deposits; it is often the salinity of ore fluids that is the primary anomaly.

IC Outlier Identification Using Multiple Test Metrics

With increasing variation in parametric data, it is necessary to adopt statistical means and correlations that consider other process parameters. Determining an appropriate threshold is difficult because of the several orders of magnitude variation in fault-free I/sub DDQ/. Therefore, it is necessary to use secondary information to identify outliers. This article proposed a combination of two I/sub DDQ/ test metrics for screening outlier chips by exploiting wafer-level spatial correlation. No single metric alone suffices to screen all outliers. The addition of a secondary metric also comes at the risk of additional yield loss. Maintaining stringent process control proves to be challenging for deer-submicron technologies. Therefore, understanding underlying process variables and their impact on test parameters are crucial for yield requirements. As I/sub DDQ/ test loses its effectiveness, it becomes necessary to correlate multiple test metrics, and a combination of multiple outlier screening methods might be necessary. A combination of CR and NCR with other test parameters can be useful for screening low-reliability chips, and an analysis of wafer patterns can be useful in reducing the number of required vector pairs.

Pt surface kinetics for a PrOx reactor for fuel cell feedstream processing

Rate expressions for the oxidation of carbon monoxide and hydrogen over a Pt catalyst are achieved using a combination of surface modeling and experimental measurements. The conditions studied are those expected within a preferential oxidation (PrOx) reactor in a fuel processor for a fuel cell stack. Convenient rate expressions for subsequent reactor modeling in a companion paper are derived from a set of elementary rate expressions using the approximation of near saturation of the catalyst surface by carbon monoxide and near partial equilibrium of adsorption/desorption of carbon monoxide and hydrogen. These rate expressions require only two Arrhenius kinetic parameters and satisfactorily represent our measured rates over the nearly three orders of magnitude variation in carbon monoxide and oxygen concentrations between 80 and 200 ∘ C.

Glacial isostatic adjustment on 3-D Earth models: a finite-volume formulation

SUMMARY We describe and present results from a finite-volume (FV) parallel computer code for forward modelling the Maxwell viscoelastic response of a 3-D, self-gravitating, elastically compressible Earth to an arbitrary surface load. We implement a conservative, control volume discretization of the governing equations using a tetrahedral grid in Cartesian geometry and a low-order, linear interpolation. The basic starting grid honours all major radial discontinuities in the Preliminary Reference Earth Model (PREM), and the models are permitted arbitrary spatial variations in viscosity and elastic parameters. These variations may be either continuous or discontinuous at a set of grid nodes forming a 3-D surface within the (regional or global) modelling domain. In the second part of the paper, we adopt the FV methodology and a spherically symmetric Earth model to generate a suite of predictions sampling a broad class of glacial isostatic adjustment (GIA) data types (3-D crustal motions, long-wavelength gravity anomalies). These calculations, based on either a simple disc load history or a global Late Pleistocene ice load reconstruction (ICE-3G), are benchmarked against predictions generated using the traditional normal-mode approach to GIA. The detailed comparison provides a guide for future analyses (e.g. what grid resolution is required to obtain a specific accuracy?) and it indicates that discrepancies in predictions of 3-D crustal velocities less than 0.1 mm yr−1 are generally obtainable for global grids with ∼3 × 106 nodes; however, grids of higher resolution are required to predict large-amplitude (>1 cm yr−1) radial velocities in zones of peak post-glacial uplift (e.g. James bay) to the same level of absolute accuracy. We conclude the paper with a first application of the new formulation to a 3-D problem. Specifically, we consider the impact of mantle viscosity heterogeneity on predictions of present-day 3-D crustal motions in North America. In these tests, the lateral viscosity variation is constructed, with suitable scaling, from tomographic images of seismic S-wave heterogeneity, and it is characterized by approximately 2 orders of magnitude (peak-to-peak) lateral variations within the lower mantle and 1 order of magnitude variations in the bulk of the upper mantle (below the asthenosphere). We find that the introduction of 3-D viscosity structure has a profound impact on horizontal velocities; indeed, the magnitude of the perturbation (of order 1 mm yr−1) is as large as the prediction generated from the underlying (1-D) radial reference model and it far exceeds observational uncertainties currently being obtained from space-geodetic surveying. The relative impact of lateral viscosity variations on predicted radial motions is significantly smaller.

The allometry of burrow geometry

The allometric relationship between body mass and burrow cross-sectional area for burrowing animals holds across greater than six orders of magnitude variation in body mass, and includes species separated by >500 million years of evolution from two phyla (Arthropoda and Chordata), seven classes (Arachnida, Insecta, Malacostraca, Osteichthyes, Amphibia, Reptilia, and Mammalia) and both terrestrial and marine habitats. Only birds, which construct relatively large burrows, and vermiform animals, which construct relatively narrow burrows, are separated from the remaining burrowing species. No difference is found between fossorial (burrowing animals that forage beneath the soil surface) and semi-fossorial (burrowing animals that forage terrestrially) mammals, suggesting that subterranean foragers do not modify burrow cross-sectional area to increase energy yields. However, solitary fossorial mammals do construct significantly larger nest chambers than semi-fossorial and colonial fossorial mammals. These large nest chambers probably assist in maintaining body temperature by providing a better thermally insulated microenvironment. This offsets the thermoregulatory problems faced by these animals, which are characterized by low, labile body temperatures and poor thermoregulatory ability. Colonial fossorial mammals, on the other hand, construct nest chambers that are the same relative size as those constructed by semi-fossorial mammals and probably maintain homeothermy by huddling with endothermic nest-mates.

Efficient numerical simulation of ac conduction in heterogeneous materials at low temperatures

The problem of computing the effective frequency-dependent conductivity of heterogeneous materials at low temperatures is studied. In this problem the activation energies and, therefore, the local conductivities (or the transition rates in a master equation formulation) are broadly distributed, varying over many orders of magnitude. Such broad variations make the computations with large lattices that represent the materials very difficult. We use an efficient method, based on computing the wavelet scale and detail coefficients of the local conductivities, in order to compute the effective ac conductivity of such materials. The method identifies the high-conductance paths in a large lattice and reduces it to one that requires far less computation. Using the method, we compute the effective ac conductivity of a two-dimensional lattice in which the activation energies are distributed according to a probability distribution function (PDF). Five distinct PDFs are used, and the effective ac conductivity is computed over many orders of magnitude variations in the frequency. Depending on the size of the initial system, the speedup in the computations for two-dimensional systems varies anywhere from a factor of 35--40 to over 200.

Effects of pH and Cationic and Nonionic Surfactants on the Adsorption of Pharmaceuticals to a Natural Aquifer Material

A wide range of pharmaceutical compounds have been identified in the environment, and their presence is a topic of growing concern, both for human and ecological health. Adsorption to aquifer materials and sediments is an important factor influencing the fate and transport of pharmaceutical compounds in the environment. Surfactants and other amphiphiles are known to influence the adsorption of many compounds and may be present in the environment from wastewaters or other sources. The work described here examines the adsorption of four pharmaceutical compounds, acetaminophen, carbamazepine, nalidixic acid, and norfloxacin, in the presence of a natural aquifer material. Adsorption was studied as a function of pH and in the presence and absence of two surfactants, cetylpyridinium chloride (CPC), a cationic surfactant, and Tergitol NP9, an ethoxylated nonionic surfactant. In the absence of surfactants, results indicate a 1-2 orders of magnitude variation in adsorption affinity with changing pH for each of the two quinolone pharmaceuticals (nalidixic acid and norfloxacin) but no measurable adsorption for carbamazepine or acetaminophen. In the presence of surfactants, adsorption of acetaminophen and carbamazepine was enhanced to extents consistent with compound hydrophobicity, while adsorption of nalidixic acid and norfloxacin was not. At high pH values, the anionic species of nalidixic acid exhibited enhanced adsorption in the presence of the cationic surfactant, CPC.

How Do Disturbance Generated Patterns Influence the Spatial Dynamics of Ecosystem Processes?

Our studies following the 1988 Yellowstone fires demonstrated that succession was surprisingly more variable in space and time than even current theory would have suggested, and that initial spatial patterns of disturbance may persist to produce long­lasting changes in vegetation. Our focus now is on explaining the spatial and temporal patterns of succession and understanding how these patterns influence ecosystem function. The most interesting new questions revolve around the degree to which the spatial variation in postfire vegetation -- in particular, the six orders of magnitude variation in pine sapling density, ranging from 0 to greater than 500,000 saplings/ha --controls the spatial variability in ecosystem processes across the landscape.

Does Basal Metabolic Rate Contain a Useful Signal? Mammalian BMR Allometry and Correlations with a Selection of Physiological, Ecological, and Life‐History Variables

Basal metabolic rate (BMR, mL O2 h(-1)) is a useful measurement only if standard conditions are realised. We present an analysis of the relationship between mammalian body mass (M, g) and BMR that accounts for variation associated with body temperature, digestive state, and phylogeny. In contrast to the established paradigm that BMR proportional to M3/4, data from 619 species, representing 19 mammalian orders and encompassing five orders of magnitude variation in M, show that BMR proportional to M2/3. If variation associated with body temperature and digestive state are removed, the BMRs of eutherians, marsupials, and birds do not differ, and no significant allometric exponent heterogeneity remains between orders. The usefulness of BMR as a general measurement is supported by the observation that after the removal of body mass effects, the residuals of BMR are significantly correlated with the residuals for a variety of physiological and ecological variables, including maximum metabolic rate, field metabolic rate, resting heart rate, life span, litter size, and population density.