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Identifying and quantifying the processes governing nanoparticle transport in porous media using breakthrough curves with or without retention profiles from laboratory column experiments is frequently subject to uncertainty due to the limited information content of such datasets. An integrated system of automated, non-invasive magnetic susceptibility monitoring and numerical modelling (MSMM) has been developed to provide exceptionally detailed datasets for assessing the validity of transport models of magnetic nanoparticles within a column. MSMM produces the equivalent of a breakthrough curve for each monitored location along the column and uses the enhanced dataset to constrain numerical models more effectively. The results of 2 example column experiments using magnetite nanoparticles are presented to demonstrate the approach: (i) using quartz sand (with 46,002 susceptibility measurements over 37 h) and (ii) using crushed Triassic Sandstone (with 19,654 measurements over 20 h). The quartz sand experiment showed no nanoparticle retention: MSMM showed the system could be well described by an advection-dispersion model, which predicted a breakthrough curve consistent with that derived from magnetic monitoring and with the breakthrough curve acquired independently using a fluorescein tracer. In contrast, no breakthrough was observed in the sandstone experiment, but even in the absence of a breakthrough curve, MSMM indicated that the retention processes were spatially heterogeneous and consistent with a combination of parameterised models of physical straining and limited capacity irreversible attachment.

Pump-limited kW-class operation in a multimode fiber amplifier using adaptive mode control was achieved. A photonic lantern front end was used to inject an arbitrary superposition of modes on the input to a kW-class fiber amplifier to achieve a nearly diffraction-limited output. We report on the adaptive spatial mode control architecture which allows for compensating transverse-mode disturbances at high power. We also describe the advantages of adaptive spatial mode control for optical phased array systems. In particular, we show that the additional degrees of freedom allow for broader steering and improved atmospheric turbulence compensation relative to piston-only optical phased arrays.

Microbially induced calcite precipitation (MICP) offers an attractive alternative to traditional grouting technologies for creating barriers to groundwater flow and containing subsurface contamination, but has only thus far been successfully demonstrated at the laboratory scale and predominantly in porous media. We present results of the first field experiments applying MICP to reduce fractured rock permeability in the subsurface. Initially, the ureolytic bacterium, Sporosarcina pasteurii, was fixed in the fractured rock. Subsequent injection of cementing fluid comprising calcium chloride and urea resulted in precipitation of large quantities (approximately 750 g) of calcite; significant reduction in the transmissivity of a single fracture over an area of several m(2) was achieved in around 17 h of treatment. A novel numerical model is also presented which simulates the field data well by coupling flow and bacterial and solute reactive transport processes including feedback due to aperture reduction via calcite precipitation. The results show that MICP can be successfully manipulated under field conditions to reduce the permeability of fractured rock and suggest that an MICP-based technique, informed by numerical models, may form the basis of viable solutions to aid pollution mitigation.

Forced gradient tracer tests between two boreholes can be used to study contaminant transport processes at the small field scale or investigate the transport properties of an aquifer. Full depth tests, in which tracer samples are collected just from the discharge of the abstraction borehole, often give rise to breakthrough curves with multiple peaks that are usually attributed to different flow paths through the aquifer that can rarely be identified from the test results alone. Tests in selected levels of the aquifer, such as those between packer-isolated sections of the boreholes, are time consuming, expensive; and the identification of major transport pathways is not guaranteed. We present a method for simultaneously conducting multiple tracer tests covering the full depth of the boreholes, in which tracer sampling and monitoring is carried out by a novel multilevel sampling system allowing high frequency and cumulative sampling options. The method is applied to a tracer test using fluorescein conducted in the multilayered sandstone aquifer beneath the city of Birmingham, UK, producing six well-defined tracer breakthrough curves.

Despite the potential contribution of microbially induced carbonate precipitation (MICP) to a range of environmental technologies, little is known about the controls on the rate of ureolysis and precipitate size and morphology using attached bacterial communities. This paper presents results of experiments using Sporosarcina pasteurii biofilms, of varying density, grown on perspex and granite surfaces then immersed in fluids comprising calcium chloride and urea of varying concentrations. Denser biofilms resulting from higher nutrient conditions led to faster nucleation of calcite and higher rates of ammonium production found to be related to crystal size via a power law. The observed morphology of the precipitates was variable depending on precipitation rates and nucleation of calcite was independent of the substrate mineralogy. In some cases the calcite layer became non-porous, and the bridging of pores within the granite was also observed. We show how ureolysis is limited eventually by the encapsulation of the biofilm by calcite and present a novel model that enables the reaction to be optimised to yield maximum calcite precipitation over a desired timescale. Slower reaction rates may in some circumstances be desirable for maximum reaction efficiency. The results have important implications for the design of engineering solutions involving MICP.

Ureolysis-driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport. In this study urea hydrolysis and calcite precipitation rates for the model bacterium Sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite (up to 50 g L−1). We conducted microcosm experiments in oxic artificial and anoxic natural groundwaters (collected from the Permo-Triassic sandstone aquifer at Birmingham, UK) that were inoculated with aerobically grown S. pasteurii. The rate constants for urea hydrolysis, kurea, ranged between 0.06 and 3.29 d−1 and were only affected by inoculum density. Higher Ca2+ concentration (50–500 mM Ca2+) as well as differences in fO2 did not inhibit the ureolytic activity of S. pasteurii and did not significantly impact kurea. These results demonstrate that S. pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters, especially if indigenous communities lack ureolytic activity. Urea hydrolysis by indigenous groundwater communities was investigated in anoxic, natural groundwaters amended with urea and CaCl2. A notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients (with best results from blackstrap molasses). Furthermore, there was a considerable lag time (12–20 days) before ureolysis and calcite precipitation began. Calculated ureolysis rate constants, kurea, ranged between 0.03 and 0.05 d−1 and were similar to kurea values produced by S. pasteurii at low inoculum densities. Overall, this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface, and thus can be used to induce calcite precipitation in these environments. The time required for urea hydrolysis to begin is almost instantaneous if an inoculum of S. pasteurii is included, while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active.

Summary This paper evaluates the use of standard regional groundwater flow models in predicting regional patterns of water chemistry based on wellwater samples. The regional groundwater flow in a moderately sized sandstone aquifer has been represented using a time-variant, three layer numerical model typical of those developed for water resource management. Reverse particle tracking was used to determine the implied age distribution of the water in the aquifer and the age structure and recharge location of the wellwaters at the time of sampling. At the regional scale, the model age predictions are broadly consistent with a pre-existing interpretation of wellwater chemistry, though the model suggests a complexity far greater than could be mapped using the 150 wells from which analyses were available. The main features of the chemical distribution pattern are controlled to a significant degree by the pre-abstraction flows within the aquifer, even though heavy pumping has occurred over a period of more than 100 years. The model suggests that some modern recharge is expected almost everywhere across the aquifer, despite its cover of low permeability Quaternary deposits. At individual wells, wide ranges in water age are often predicted, suggesting that water quality prediction for individual wells is likely to be uncertain, providing an explanation for locations where apparently anomalous wellwater chemistry occurs. We conclude that particle tracking using the implied flow field of a standard regional groundwater flow model has proved very worthwhile in the case studied. It has highlighted uncertainties in both flow and regional qualitative water quality interpretations, has confirmed or revised various explanations associated with water quality distributions, indicates that joint chemical and head calibration is advantageous, and suggests that broad predictions of future water quality changes might be attempted using the same approach, though predictions of the chemistry of individual wells is highly uncertain. The aquifer studied is typical of many sandstone aquifers, and we suggest that particle tracking investigations using existing regional-scale multi-layer, transient models might also be undertaken with advantage elsewhere.

Summary A method for upscaling coupled hydro-mechanical properties in fractured rock from the small (metre) scale to the large (decametre to kilometre) scale has been developed and applied within a stochastic modelling framework. The method was implemented to assess the impact on estimates of advective travel times and transport pathways in the geosphere arising from uncertainties in the mechanical properties of a fractured host rock. A 2D hypothetical geological environment for a deep nuclear waste repository, characterized using rock and fracture property data from the site investigations at Sellafield, UK, was used for the assessment. Hydro-mechanical modelling was undertaken to obtain block scale equivalent hydraulic properties for discrete fracture networks described by power-law statistics for fracture length and density. Values of the mechanical properties for the host rock were employed to derive a basic statistical model of the uncertainty in the key fracture property values: joint compressive strength ( JCS ) and joint roughness coefficient ( JRC ). The block upscaling was carried out in two stages. First, mechanical modelling was undertaken to determine aperture distributions throughout each modelled fracture network using the distinct element code UDEC. The Barton–Bandis model for fracture closure was adopted in UDEC and each fracture network was modelled under a range of stress conditions with five ( JCS , JRC ) pairs that reflected the spread of mechanical properties observed in the actual field data. Second, mean block scale hydraulic conductivity tensors were determined for each stress and mechanical property combination by inverting the results from steady state hydraulic models for the mechanically controlled fracture networks. Finally, a Monte-Carlo simulation experiment was performed on a 2D profile model of the geosphere populated by sampling from the block upscaled hydraulic results. Particle tracking was applied to each realisation of the flow field in the geosphere to study the range of advective travel times from the repository to the seabed (biosphere). The simulated travel times were found to depend significantly on the rock and fracture mechanical properties with breakthrough times at the seabed ranging between 4000 years and 2,560,000 years. The spread of travel times in the simulation results demonstrate the significance of both hydro-mechanical rock properties and their spatial distribution. The very low joint compressive strength ( JCS ) of the uppermost formation and the assumed lateral uniformly distributed mechanical and hydraulic parameters of this formation are observed to provide the dominant control on the particle travel times. The present study suggests that observations of hydro-mechanical property data and their spatial distribution can offer useful additional information for developing models of the regional scale hydraulic behaviour of a fractured host rock mass.

Summary A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1 md−1 or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.

Ziel der vorliegenden Arbeit ist die Entwicklung einer Methode zur Ermittlung der hydraulischen Durchlassigkeit und des reprasentativen Elementarvolumens (REV) in Kluftgrundwasserleitern, die zur hydraulischen Modellierung von grosraumigen Kluftsystemen verwendet werden kann. Fur die Ermittlung der Durchlassigkeit wurden zweidimensionale stochastische Kluftnetze simuliert. Aufgrund der Tatsache, dass die Kluftdichten im Untersuchungsgebiet stark variieren, wurde eine Sensitivitatsstudie durchgefuhrt, in der drei verschiedene Kluftdichten hinsichtlich ihrer hydraulischen Eigenschaften genauer untersucht wurden. Das Fliesverhalten in den Kluftnetzen wurde durch das kubische Gesetz (cubic law) beschrieben. Die hydraulische Modellierung im Kluftgestein zeigte, dass nicht fur alle Kluftnetze ein REV ermittelt werden konnte. Fur Kluftnetze mit einer mittleren (P21 = 13,1 m–1) und grosen Kluftdichte (P21 = 16,9 m–1) konnte bis auf eine einzige Ausnahme fur alle drei untersuchten Gesteinsformationen ein REV mit einer Grose von 10 m × 10 m ermittelt werden. Hingegen konnte fur Kluftnetze mit einer geringen Kluftdichte (P21 = 5,1 m–1) kein REV bestimmt werden.

A methodology for addressing the DECOVALEX III Bench Mark Test 2 is presented. Hydro-mechanical (HM) modelling has been conducted on fracture networks generated from fracture length and density statistics, which have been described by a power law. For each rock formation in the test, effective hydraulic conductivity tensors have been derived for a range of mechanical parameters and depths below ground level. The upscaled hydraulic conductivities have been used in a site scale continuum model of groundwater flow and transport to assess performance indicators, including time of travel from repository to ground surface. Preliminary results indicate that interpretation of the fracture length and density data can have a significant effect on upscaling calculations, including the determination of a suitable hydraulic representative elementary volume. HM modelling shows that there is a non-linear decrease in the change of fracture aperture with depth, and that although large aperture fractures remain at depth, the majority of fractures tighten to almost the residual aperture at about 750 m below ground level. Consequently, anisotropy of the effective hydraulic conductivity also changes with depth. Flow and transport modelling at the field scale indicates that, of the controls investigated, mechanical properties of the rock have the greatest influence on solute travel times.

A statistical, rule-based algorithm for generating fracture patterns similar to those observed in Limestone is presented. For each fracture set, initial seed points are randomly positioned within the modelled domain with the same density as the fractures observed in the field. An orientation is associated with each point by sampling from the distribution of orientations for the corresponding fracture set. Fractures are then allowed to grow from the seed points in both directions with this orientation until they meet other fractures whereupon they continue or terminate according to a fixed probability. A mathematical analysis of this method is presented for the case in which fractures within a set are assumed to be parallel. Approximations to the distribution of semi-trace lengths are derived which are shown to be in good agreement with simulation results. Fracture spacing distributions are also derived for this case.

We report the most comprehensive study of survival of peptide bonds and epitopes (antibody binding sites) in fossil shells from a semi-continuous New Zealand brachiopod sequence extending for 3 Ma. The study reveals for the first time long-term trends in proteins survival. The investigation focused on a sub-set of the total skeletal biomolecules, those protected from exposure to a strong oxidising agent (NaOCl); the so-called intra-crystalline component. The extent of peptide bond hydrolysis was compared with the declining immunological signal. The proportion of free amino acids increased very rapidly but between 5 and 10% of the amino acids remained peptide bound in all samples. The pattern of loss of immunological reactivity broadly mirrored the loss of peptide bonds, but overall loss of signal was much greater. Significant antibody response was observed in some but not all late Pliocene fossils (>3 Ma), but against a panel of antisera the pattern of reactivity was lost in samples >0.5 Ma. Alternative models of polypeptide chain scission were used in an to attempt to relate the rate of peptide bond hydrolysis to the loss of immunological determinants. The findings suggest that, despite early optimistic reports, the application of immunology to shell carbonates does not appear capable of extending into deep time.

Efficient combination of an array of lasers requires alignment of their polarization states. We demonstrate a simple architecture for polarization control by coherently combining eight passive non-PM fibers resulting in a PER of 19 dB.

As part of an investigation into the dual porosity behaviour of fractured limestone aquifers, a sequence of converging flow tracer tests was devised and conducted at an extensively investigated experimental site in a major aquifer in the UK. The tests were designed specifically to produce detailed, high-resolution information about the tails of the breakthrough curves typically observed in this kind of aquifer and test. A set of mutually compatible, low detection limit tracers was identified through laboratory investigations. Two tests were carried out over distances of 20 m and 40 m along each of the two radii towards an abstraction borehole where tracer concentration was monitored. Simple dual porosity models were calibrated using the data from one test on each radius. Blind validations of these models were undertaken by attempting to predict the outcome of the second test on each radius, producing one success and one significant failure.

Lagoons at Villa Farm near Coventry, UK were used for the disposal of industrial liquid waste after 1967. The lagoons were unlined and a leachate plume developed in the underlying thin sand aquifer. As part of a research programme into controls on the migration of landfill leachate, a two-dimensional areal model describing the regional scale movement of chloride and phenol in the aquifer has been developed. Parameter ranges for advection, dispersion, degradation and adsorption have been established through model calibration, constrained by the results from previous laboratory studies. Linear representations of the adsorption and degradation processes are found to yield satisfactory results on the time and space scales adopted for the simulations. The model development has highlighted some important issues that have to be confronted when analysing the evolution of a plume based on short-term, late-time data. The uncertainty in the geometry of the aquifer on the simulated flow system has been examined using geostatistical methods.

Forced gradient tracer tests between two boreholes can be used to study contaminant transport processes at the small field scale or investigate the transport properties of an aquifer. Full depth tests, in which tracer samples are collected just from the discharge of the abstraction borehole, often give rise to breakthrough curves with multiple peaks that are usually attributed to different flow paths through the aquifer that can rarely be identified from the test results alone. Tests in selected levels of the aquifer, such as those between packer-isolated sections of the boreholes, are time consuming, expensive; and the identification of major transport pathways is not guaranteed. We present a method for simultaneously conducting multiple tracer tests covering the full depth of the boreholes, in which tracer sampling and monitoring is carried out by a novel multilevel sampling system allowing high frequency and cumulative sampling options. The method is applied to a tracer test using fluorescein conducted in the multilayered sandstone aquifer beneath the city of Birmingham, UK, producing six well-defined tracer breakthrough curves.

A study site located in a quarry on the Lincolnshire Limestone has been selected to examine the validity of the ‘dual porosity’ hypothesis and its application in models for the prediction of solute migration. An integrated approach has been adopted for the experimental programme, combining data obtained from both field and laboratory-scale investigations with mathematical modelling. The results of the first to stages of the experimental developments at the site are reported and the results are discussed in relation to he development of a full tracer test programme. Fracture mapping has been conducted on the face and the floor of the quarry where the vertical fractures are seen to be discontinuous over depth. However, extensive horizontal bedding plane fissures are readily identifiable in the boreholes and represent the main paths for lateral flows. An extensive data collection programme has been conducted to characterize the hydraulic properties of these fissures, as well as the adjacent altered and unaltered matrix. Important results for future tracer testing were obtained from the hydraulic tests which suggest the strong possibility of non-Darcian flow in the fissures under pumping and tracer test conditions and the probability of strong spreading of solutes at injection wells under forced inflows. Preliminary tracer tests confirm the difficulty of employing laboratory defined diffusion coefficients as input data to ‘dual porosity’ models of local-scale transport.

The diagenesis of ancient bone collagen appears bewildering in its variety. We have simulated collagen diagenesis using a simple conceptual model in which the degradation is controlled by two key processes: (i) depolymerization of collagen by chemical hydrolysis of peptide bonds; and (ii) dissolution (i.e. melting free) of those polypeptide fragments retained by fewer than a critical number of hydrogen bonds, biodeterioration being ignored. The model predicts that the curve describing weight loss is approximately sigmoidal in form, a pattern in accord with the sparse experimental data for non-mineralized collagen. The conclusion from studies of mineralized collagen is that the weight loss curve is exponential (i.e. a first-order reaction), but we argue that the experimental design of those studies was flawed. Other predictions of the model relating to the changing size distribution of residual fragments, N-termini, physical properties and significance of cross-linking are reported. Cross-linking appears to be a particularly significant phenomenon, which causes a marked tailing of the weight loss curve and thus the enhanced preservation of cross-linked, low collagen bone. The validity of applying this simple conceptual model to archaeological collagen is discussed.

[1] A mathematical model describing the steady state flows in a forced gradient tracer test between an injection and pumping borehole in a multilayered sandstone aquifer has been developed that includes the effect of vertically variable background heads. A second model describing the recovery of tracer from a layer in which there are discharges due to vertical flow in the injection borehole is also presented. Application of the models to field tracer test data indicates that the observed recoveries, which are not proportional to the abstraction rate in each layer, are consistent with the hydraulic behavior of the aquifer when natural vertical head gradients are taken into account. Investigation with the models illustrates that the vertical distribution of tracer recovery depends strongly upon the background heads and that tracer tests conducted in the same aquifer, but at different times, may interrogate different aquifer layers. It is also shown generally that for a given abstraction rate the vertical distribution of tracer recovery in small-scale tracer tests is controlled largely by the transmissivity distribution but that as the spatial scale of the test increases, the distribution of recovery becomes proportional to the discharges from the injection borehole because of vertical flows within it, which may be natural or induced by pumping in the monitoring borehole. Uncertainties inherent in the design of forced gradient tracer tests in multilayered aquifers and the problems of applying the results of such tests to natural gradient contaminant migration are discussed.

[1] The growth and stability of the free-gas zone (FGZ) beneath gas-hydrate related bottom-simulating seismic reflectors (BSRs) is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas. For a model based on the continental slope west of Svalbard (a continental margin of north Atlantic type), we find that the FGZ is inherently unstable under a wide range of conditions because upward flow of under-saturated liquid depletes free gas faster than it is produced by hydrate recycling. In these scenarios, the 150-m-thick FGZ that presently exists there would deplete within 105–106 years. We suggest the FGZ is in a stable state, however, that is formed by a diffusion-dominated mechanism that produces low concentrations of gas in a FGZ of steady state thickness. Gas forms across a thick zone because the upward fluid flux is relatively low and because the gas–water solubility decreases to a minimum several hundred meters below the seabed. This newly understood solubility-curvature effect is complementary to hydrate recycling, but becomes the most important factor controlling the presence and properties of the BSR in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low (i.e., rifted continental margins). If the present-day FGZ is in steady state, we estimate that the upward fluid flux in the west Svalbard site must be less than 0.15 mm a−1.

The potential hydraulic behaviour of the fracture network in a major Triassic sandstone aquifer in the UK has been evaluated. The properties of the fracture network were determined using results from detailed scan line surveys at 10 sites, television and geophysical borehole logging, and packer testing. Six sets of discontinuities common to all sites were identified and statistically characterised (dip, strike, orientation, density, size, and estimated transmissivity). A discrete fracture network model was then used stochastically to investigate the properties of the network. In general, the network is poorly connected: it is estimated that 9% of the discontinuities intersecting boreholes are transmissive. The hydraulic behaviour of the network is generally dominated by one sub-horizontal bedding plane fracture set, although when present, a relatively infrequent north-south striking, sub-vertical set modifies the bulk flow properties significantly. Ignoring this latter set, the network's minimum representative volume is about 35 x 35 x 35 m. The upscaled permeability is anisotropic, being typically 23 times greater in the horizontal than in the vertical. Tortuosity in the north-south direction is around 1.6.

[1] Statistical distributions of fracture trace length and density determined from two-dimensional fracture mapping generally provide biased estimates of the underlying distributions due in part to edge effects of the finite window of observation (censoring) and the protocol adopted for recording short traces (lower truncation limit). Although methods for estimating the parameters of an assumed underlying distribution exist, validation of the inferred models by forward prediction of the observed length distribution is rarely undertaken since mathematical formulations of the required distributions are not reported in the literature. This paper presents formulae that can be used simply to obtain these distributions, with results for rectangular windows given as a specific example. Formulae relating the observed and underlying fracture density are also given. The formulae are presented for underlying trace lengths that can be characterized by exponential, lognormal, or finite range power law distributions. Results for the semi-infinite range power law can also be obtained simply. The formulae are based upon the assumption that fracture locations can be adequately described by a uniform Poisson process, although the methodology is described more generally. The distributions of uncensored, singly censored and doubly censored trace lengths are also derived. The effects of the window of observation and the lower truncation limit for the frequently assumed semi-infinite range power law are outlined.

A methodology for understanding the importance of modelling hydro-mechanical (HM) processes in performance assessment of a radioactive waste site in fractured rock has been established. Results of HM-modelling performed with UDEC-BB, the universal distinct element code incorporating the empirical Barton-Bandis model, revealed large variations in hydraulic aperture distribution depending on the applied mechnical properties and the stress conditions. Continuum modelling was undertaken using mean upscaled hydraulic conductivity and porosity values for two cases - a hydraulic only analysis and a hydro-mechanical analysis for a hypothetical repository setting. The modelling of these cases showed that the most significant HM factors for performance assessment at the regional scale are the aperture distributions that depend on the variations and the spatial distribution of the mechanical properties. Uncertainties in the fracture density and the spatial distribution of different fracture densities appear to be less important than knowledge of the mechanical properties.

A methodology for quantifying the contributions of hydro-mechanical processes to fractured rock hydraulic property distributions has been developed and tested. Simulations have been carried out on discrete fracture networks to study the sensitivity of hydraulic properties to mechanical properties, stress changes with depth, mechanical boundary conditions, initial mechanical apertures and fracture network geometry. The results indicate that the most important (and uncertain) parameters for modelling HM processes in fractured rock are fracture density and rock/fracture mechanical properties. Aperture variation with depth below ground surface is found to be of second order importance.

Recent success in the amplification of ancient DNA (aDNA) from fossil humans has led to calls for further tests to be carried out on similar material. However, there has been little systematic research on the survival of DNA in the fossil record, even though the environment of the fossil is known to be of paramount importance for the survival of biomolecules over archaeological and geological timescales. A better understanding of aDNA survival would enable research to focus on material with greater chances of successful amplification, thus preventing the unnecessary loss of material and valuable researcher time. We argue that the thermal history of a fossil is a key parameter for the survival of biomolecules. The thermal history of a number of northwest European Neanderthal cave sites is reconstructed here and they are ranked in terms of the relative likelihood of aDNA survival at the sites, under the assumption that DNA depurination is the principal mechanism of degradation. The claims of aDNA amplification from material found at Lake Mungo, Australia, are also considered in the light of the thermal history of this site.

The successful retrieval of ancient DNA from two geographically dispersed Neanderthal skeletons1,2 has fuelled a demand for more Neanderthal DNA sequences for analysis. However, these exceptionally well-preserved specimens were geologically young and the mean annual temperature of their cave sites low, so the survival of this ancient DNA could have been due to unusually favourable conditions. Here we calculate the thermal history of a range of Holocene and Pleistocene bones whose DNA quality has been tested and find that in only very few sites with Neanderthal remains is the preservation of DNA likely to match the quality of that from the skeleton found at Mezmaiskaya Cave2. We recommend that any additional Neanderthal destined for destructive analysis should be carefully selected, taking into account its integrated thermal history.

A clinical association between insulin therapy and hypophosphatemia has frequently been made but a dose-response relationship has not been reported. Furthermore, the rapidity by which hypophosphatemia may be induced following an increment in plasma-free insulin concentration is not well defined. Therefore this study compared the effects of different rates of insulin infusion on the changes in plasma phosphate concentration in ketotic, hyperglycemic diabetic man. Sixteen prospective studies were performed in four insulin-dependent ketotic diabetic subjects. Insulin was infused according to one of four different protocols: high dose (1.0 U/kg/hr), low dose (0.1 U/kg/hr), very low dose (0.01 U/kg/hr) and control (saline only). Plasma phosphate, glucose, and free insulin concentrations were measured sequentially during the 60 min infusion periods. We observed that plasma phosphate concentrations declined significantly only with low-dose and high-dose insulin infusions. The magnitude and rapidity of fall of the mean phosphate concentration were greatest with high-dose insulin infusion. Significant hypophosphatemia can be observed within 30 min following the onset of insulin therapy.