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The ability to identify, at potential managed aquifer recharge sites, the presence of connected pathways of hydraulically conductive sediments from the ground surface to the water table could help minimize costs and risks associated with recharge operations. A spatially dense dataset had previously been acquired in an almond [Prunus dulcis (Mill.) D.A. Webb] grove in Tulare, CA, using tTEM, a towed transient electromagnetic (tTEM) geophysical method. In order to interpret reliable information about sediment type from the tTEM data, a transform from the tTEM‐derived property, electrical resistivity, to sediment type is required. The uncertainty associated with derived models of sediment type can be significantly reduced if a site‐ and dataset‐specific transform is used. Cone penetrometer testing (CPT) was conducted at five locations, strategically selected based on a review of the tTEM data. Co‐located measurements of sediment type, derived from the CPT, and electrical resistivity, derived from the tTEM data, were used to create a resistivity‐to‐sediment‐type transform, with sediment type classified as either coarse‐grain‐dominated (sand and gravel) or fine‐grain‐dominated (silt and clay) material. The transform captured the uncertainty associated with variable water salinity and content, the resolution of the tTEM data, and other components of the tTEM measurement workflow. Using this transform, models of sediment type were generated for the unsaturated zone at the site. Within these models are features, which we interpret as potential recharge pathways, corresponding to high fractions of coarse‐grain‐dominated material amongst regions of fine‐grain‐dominated material. The workflow developed at this site can provide a framework for using tTEM and CPT for recharge site assessment.

IntroductionYoung people aged 16 to 24 have the highest prevalence of genital chlamydia and gonorrhoea compared with other age groups and re-infection rates following treatment are high. Long-term adverse health effects include subfertility and ectopic pregnancy, particularly among those with repeated infections. We developed the safetxt intervention delivered by text message to reduce sexually transmitted infection (STI) by increasing partner notification, condom use and (STI) testing among young people in the UK.Methods and analysisA single-blind randomised trial to reliably establish the effect of the safetxt intervention on chlamydia and gonorrhoea infection at 1 year. We will recruit 6250 people aged 16 to 24 years who have recently been diagnosed with chlamydia, gonorrhoea or non-specific urethritis from health services in the UK. Participants will be allocated to receive the safetxt intervention (text messages designed to promote safer sexual health behaviours) or to receive the control text messages (monthly messages asking participants about changes in contact details) by an automated remote online randomisation system. The primary outcome will be the cumulative incidence of chlamydia and gonorrhoea infection at 1 year assessed by nucleic acid amplification tests. Secondary outcomes include partner notification, correct treatment of infection, condom use and STI testing prior to sex with new partners.Ethics and disseminationEthics approval was obtained from NHS Health Research Authority - London – Riverside Research Ethics Committee (REC reference: 15/LO/1665) and the London School of Hygiene & Tropical Medicine. We will submit the results of the trial for publication in peer-reviewed journals.Trial registration numberInternational Standard Randomised Controlled Trials Number:ISRCTN64390461. Registered on 17thMarch 2016.WHO trial registration data setavailable at:http://apps.who.int/trialsearch/Trial2.aspx?TrialID=ISRCTN64390461.Trial protocol version12, 19thJuly 2018.

Background Irbesartan, a long acting selective angiotensin-1 receptor inhibitor, in Marfan syndrome might reduce aortic dilatation, which is associated with dissection and rupture. We aimed to determine the effects of irbesartan on the rate of aortic dilatation in children and adults with Marfan syndrome. Methods We did a placebo-controlled, double-blind randomised trial at 22 centres in the UK. Individuals aged 6–40 years with clinically confirmed Marfan syndrome were eligible for inclusion. Study participants were all given 75 mg open label irbesartan once daily, then randomly assigned to 150 mg of irbesartan (increased to 300 mg as tolerated) or matching placebo. Aortic diameter was measured by echocardiography at baseline and then annually. All images were analysed by a core laboratory blinded to treatment allocation. The primary endpoint was the rate of aortic root dilatation. This trial is registered with ISRCTN, number ISRCTN90011794. Findings Between March 14, 2012, and May 1, 2015, 192 participants were recruited and randomly assigned to irbesartan (n=104) or placebo (n=88), and all were followed for up to 5 years. Median age at recruitment was 18 years (IQR 12–28), 99 (52%) were female, mean blood pressure was 110/65 mm Hg (SDs 16 and 12), and 108 (56%) were taking β blockers. Mean baseline aortic root diameter was 34·4 mm in the irbesartan group (SD 5·8) and placebo group (5·5). The mean rate of aortic root dilatation was 0·53 mm per year (95% CI 0·39 to 0·67) in the irbesartan group compared with 0·74 mm per year (0·60 to 0·89) in the placebo group, with a difference in means of −0·22 mm per year (−0·41 to −0·02, p=0·030). The rate of change in aortic Z score was also reduced by irbesartan (difference in means −0·10 per year, 95% CI −0·19 to −0·01, p=0·035). Irbesartan was well tolerated with no observed differences in rates of serious adverse events. Interpretation Irbesartan is associated with a reduction in the rate of aortic dilatation in children and young adults with Marfan syndrome and could reduce the incidence of aortic complications. Funding British Heart Foundation, the UK Marfan Trust, the UK Marfan Association.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden. The ERIC-PPCI trial was funded by a British Heart Foundation clinical study grant (grant number CS/14/3/31002) and a University College London Hospitals/University College London Biomedical Research Centre clinical research grant. The CONDI-2 trial was funded by Danish Innovation Foundation grants (grant numbers 11-108354 and 11-115818), Novo Nordisk Foundation (grant number NNF13OC0007447), and TrygFonden (grant number 109624). DJH was supported by the British Heart Foundation (grant number FS/10/039/28270), the National Institute for Health Research (NIHR) Biomedical Research Centre at University College London Hospitals, the Duke-National University Singapore Medical School, the Singapore Ministry of Health’s National Medical Research Council under its Clinician Scientist-Senior Investigator scheme (grant number NMRC/CSA-SI/0011/2017) and its Collaborative Centre Grant scheme (grant number NMRC/CGAug16C006), and the Singapore Ministry of Education Academic Research Fund Tier 2 (grant number MOE2016-T2-2-021). HEB was supported by the Novo Nordisk Foundation (grant numbers NNF14OC0013337, NNF15OC0016674). RKK is supported by the Oxford NIHR Biomedical Centre. The research was also supported by the NIHR infrastructure at Leeds. The views expressed are those of the author(s) and not necessarily those of the National Health Service, the NIHR, or the Department of Health. This article is based on the work of COST Action EU-CARDIOPROTECTION (CA16225) and supported by COST (European Cooperation in Science and Technology). We thank all study personnel for their invaluable assistance. Sí

The rationale and study design for the multicentre, randomized, controlled CONDI2/ERIC-PPCI study are discussed.

BackgroundNovel cardioprotective strategies are required to improve clinical outcomes in higher-risk patients undergoing coronary artery bypass graft (CABG) with or without valve surgery. Remote ischaemic preconditioning (RIPC) in which brief episodes of non-lethal ischaemia and reperfusion are applied to the arm or leg has been demonstrated to reduce perioperative myocardial injury (PMI) following CABG with or without valve surgery.ObjectiveTo investigate whether or not RIPC can improve clinical outcomes in this setting in the Effect of Remote Ischaemic preconditioning on Clinical outcomes in patients undergoing Coronary Artery bypass graft surgery (ERICCA) study in patients undergoing CABG surgery.DesignMulticentre, double-blind, randomised sham controlled trial.SettingThe study was conducted across 30 cardiothoracic centres in the UK between March 2010 and March 2015.ParticipantsEligible patients were higher-risk adult patients (aged > 18 years of age; additive European System for Cardiac Operative Risk of ≥ 5) undergoing on-pump CABG with or without valve surgery with blood cardioplegia.InterventionsPatients were randomised to receive either RIPC (four 5-minute inflations/deflations of a standard blood pressure cuff placed on the upper arm) or the sham control procedure (simulated RIPC protocol) following anaesthetic induction and prior to surgical incision. Anaesthetic management and perioperative care were not standardised.Main outcome measuresThe combined primary end point was the rate of major adverse cardiac and cerebral events comprising cardiovascular death, myocardial infarction, coronary revascularisation and stroke within 12 months of randomisation. Secondary end points included perioperative myocardial and acute kidney injury (AKI), intensive care unit and hospital stay, inotrope score, left ventricular ejection fraction, changes in quality of life and exercise tolerance.ResultsIn total, 1612 patients (sham control group,n = 811; RIPC group,n = 801) were randomised in 30 cardiac surgery centres in the UK. There was no difference in the primary end point at 12 months between the RIPC group and the sham control group (26.5% vs. 27.7%; hazard ratio 0.95, 95% confidence interval 0.79 to 1.15;p = 0.58). Furthermore, there was no evidence for any differences in either adverse events or the secondary end points of PMI (72-hour area under the curve for serum high-sensitivity troponin T), inotrope score, AKI, intensive therapy unit and hospital stay, 6-minute walk test and quality of life.ConclusionsIn patients undergoing elective on-pump CABG with or without valve surgery, without standardisation of the anaesthetic regimen, RIPC using transient arm ischaemia–reperfusion did not improve clinical outcomes. It is important that studies continue to investigate the potential mechanisms underlying RIPC, as this may facilitate the translation of this simple, non-invasive, low-cost intervention into patient benefit. The limitations of the study include the lack of standardised pre-/perioperative anaesthesia and medication, the level of missing and incomplete data for some of the secondary end points and the incompleteness of the data for the echocardiography substudy.Trial registrationClinicalTrials.gov NCT01247545.FundingThis project was funded by the Efficacy and Mechanism Evaluation programme, a MRC and NIHR partnership, and the British Heart Foundation.

Introduction: Psychological theory suggests that participants may be more likely to volunteer to join a clinical trial if they perceive places in the trial are a scarce commodity. Material and methods: We conducted a single blind, randomized controlled trial to test recruitment strategies within the larger txt2stop smoking cessation trial. 1862 people who were eligible for the txt2stop trial but had not yet consented to join were randomized to receive either A) a reminder about the txt2stop trial plus a message that there were only 300 places left, or B) a reminder about the trial only. The outcome was the participant's consent to join the txt2stop trial 3 days after messages were sent. Results Of 895 participants randomized to the intervention group, 90 (10.1%) had consented to join the txt2stop trial. Of the 967 participants randomized to the control group, 67 (6.9%) had consented to join the txt2stop trial (OR = 1.50, 95% CI 1.07–2.12). Discussion Scarcity messages were an effective way to increase recruitment into the txt2stop trial and could be relevant to other trials. Conclusions Communicating scarcity is an effective way to increase trial recruitment.

BACKGROUND: Increased consumption of n-3 (omega-3) long-chain polyunsaturated fatty acids (LC PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may maintain cognitive function in later life. OBJECTIVE: We tested the hypothesis that n-3 LC PUFA supplementation would benefit cognitive function in cognitively healthy older people. DESIGN: At total of 867 cognitively healthy adults, aged 70-79 y, from 20 general practices in England and Wales were randomly assigned into a double-blind controlled trial of daily capsules providing 200 mg EPA plus 500 mg DHA or olive oil for 24 mo. Treatment-allocation codes were obtained from a central computerized randomization service. Trained research nurses administered a battery of cognitive tests, including the primary outcome, the California Verbal Learning Test (CVLT), at baseline and 24 mo. Intention-to-treat analysis of covariance, with adjustment for baseline cognitive scores, age, sex, and age at leaving full-time education, included 748 (86%) individuals who completed the study. RESULTS: The mean age of participants was 75 y; 55% of the participants were men. Withdrawals and deaths were similar in active (n = 49 and n = 9, respectively) and placebo (n = 53 and n = 8, respectively) arms. Mean (+/-SD) serum EPA and DHA concentrations were significantly higher in the active arm than in the placebo arm at 24 mo (49.9 +/- 2.7 mg EPA/L in the active arm compared with 39.1 +/- 3.1 mg EPA/L in the placebo arm; 95.6 +/- 3.1 mg DHA/L in the active arm compared with 70.7 +/- 2.9 mg DHA/L in the placebo arm). There was no change in cognitive function scores over 24 mo, and intention-to-treat analysis showed no significant differences between trial arms at 24 mo in the CVLT or any secondary cognitive outcome. CONCLUSIONS: Cognitive function did not decline in either study arm over 24 mo. The lack of decline in the control arm and the relatively short intervention period may have limited our ability to detect any potential beneficial effect of fish oil on cognitive function in this study. The Older People And n-3 Long-chain polyunsaturated fatty acids (OPAL) Study was registered at www.controlled-trials.com as ISRCTN 72331636.

With the goal of improving the understanding of the subsurface structure beneath the Harkins Slough recharge pond in Pajaro Valley, California, USA, we have undertaken a multimodal approach to develop a robust velocity model to yield an accurate seismic reflection section. Our shear-wave reflection section helps us identify and map an important and previously unknown flow barrier at depth; it also helps us map other relevant structure within the surficial aquifer. Development of an accurate velocity model is essential for depth conversion and interpretation of the reflection section. We incorporate information provided by shear-wave seismic methods along with cone penetrometer testing and seismic cone penetrometer testing measurements. One velocity model is based on reflected and refracted arrivals and provides reliable velocity estimates for the full depth range of interest when anchored on interface depths determined from cone data and borehole drillers’ logs. A second velocity model is based on seismic cone penetrometer testing data that provide higher-resolution 1D velocity columns with error estimates within the depth range of the cone penetrometer testing. Comparison of the reflection/refraction model with the seismic cone penetrometer testing model also suggests that the mass of the cone truck can influence velocity with the equivalent effect of approximately one metre of extra overburden stress. Together, these velocity models and the depth-converted reflection section result in a better constrained hydrologic model of the subsurface and illustrate the pivotal role that cone data can provide in the reflection processing workflow.

To obtain the highest-resolution ray-based tomographic images from crosshole ground-penetrating radar (GPR) data, wide angular ray coverage of the region between the two boreholes is required. Unfortunately, at borehole spacings on the order of a few meters, high-angle traveltime data (i.e., traveltime data corresponding to transmitter-receiver angles greater than approximately 50° from the horizontal) are notoriously difficult to incorporate into crosshole GPR inversions. This is because (1) low signal-to-noise ratios make the accurate picking of first-arrival times at high angles extremely difficult, and (2) significant tomographic artifacts commonly appear when high- and low-angle ray data are inverted together. We address and overcome thesetwo issues for a crosshole GPR data example collected at the Boise Hydrogeophysical Research Site (BHRS). To estimate first-arrival times on noisy, high-angle gathers, we develop a robust and automatic picking strategy based on crosscorrelations, where reference waveforms are determined from the data through the stacking of common-ray-angle gathers. To overcome incompatibility issues between high- and low-angle data, we modify the standard tomographic inversion strategy to estimate, in addition to subsurface velocities, parameters that describe a traveltime ‘correction curve’ as a function of angle. Application of our modified inversion strategy, to both synthetic data and the BHRS data set, shows that it allows the successful incorporation of all available traveltime data to obtain significantly improved subsurface velocity images.

Whether remote ischemic preconditioning (transient ischemia and reperfusion of the arm) can improve clinical outcomes in patients undergoing coronary-artery bypass graft (CABG) surgery is not known. We investigated this question in a randomized trial.We conducted a multicenter, sham-controlled trial involving adults at increased surgical risk who were undergoing on-pump CABG (with or without valve surgery) with blood cardioplegia. After anesthesia induction and before surgical incision, patients were randomly assigned to remote ischemic preconditioning (four 5-minute inflations and deflations of a standard blood-pressure cuff on the upper arm) or sham conditioning (control group). Anesthetic management and perioperative care were not standardized. The combined primary end point was death from cardiovascular causes, nonfatal myocardial infarction, coronary revascularization, or stroke, assessed 12 months after randomization.We enrolled a total of 1612 patients (811 in the control group and 801 in the ischemic-preconditioning group) at 30 cardiac surgery centers in the United Kingdom. There was no significant difference in the cumulative incidence of the primary end point at 12 months between the patients in the remote ischemic preconditioning group and those in the control group (212 patients [26.5%] and 225 patients [27.7%], respectively; hazard ratio with ischemic preconditioning, 0.95; 95% confidence interval, 0.79 to 1.15; P=0.58). Furthermore, there were no significant between-group differences in either adverse events or the secondary end points of perioperative myocardial injury (assessed on the basis of the area under the curve for the high-sensitivity assay of serum troponin T at 72 hours), inotrope score (calculated from the maximum dose of the individual inotropic agents administered in the first 3 days after surgery), acute kidney injury, duration of stay in the intensive care unit and hospital, distance on the 6-minute walk test, and quality of life.Remote ischemic preconditioning did not improve clinical outcomes in patients undergoing elective on-pump CABG with or without valve surgery. (Funded by the Efficacy and Mechanism Evaluation Program [a Medical Research Council and National Institute of Health Research partnership] and the British Heart Foundation; ERICCA ClinicalTrials.gov number, NCT01247545.).

BackgroundLong-term kidney allograft survival has remained unchanged in recent years despite immunosuppressive and surgical advances. Ischaemia–reperfusion (IR) injury sustained at transplantation contributes to kidney damage that limits allograft lifespan. Interventions to reduce IR injury may prolong graft life, delaying the need for a return to dialysis. Remote ischaemic preconditioning (RIPC), in which brief episodes of non-lethal ischaemia applied to the limb activate a systemic protective reflex against subsequent damaging IR injury, has been reported to cause cardiac, renal and neurological protection in small-scale trials.ObjectivesThe REmote preconditioning for Protection Against Ischaemia–Reperfusion in renal transplantation (REPAIR) trial investigated whether RIPC improves kidney function and other outcomes following living-donor renal transplantation.DesignMulticentre, multinational, double-blind, 2 × 2 factorial designed randomised controlled trial.SettingThirteen tertiary care hospitals in the UK, the Netherlands, Belgium and France.ParticipantsThe REPAIR trial recruited 406 live donor–recipient pairs aged ≥ 18 years. Patients on adenosine triphosphate (ATP)-sensitive potassium channel opening or blocking drugs, on ciclosporin, with a known iodine sensitivity or with ABO incompatibility or those requiring human leucocyte antigen (HLA) antibody removal therapy were excluded.InterventionsEach pair was randomised using a factorial design to one of four groups: sham RIPC, early RIPC (immediately before surgery), late RIPC (24 hours before surgery) and dual RIPC (early and late RIPC). The donor and recipient received the same intervention (active RIPC or sham RIPC) at the two time points.Main outcome measuresThe primary outcome was glomerular filtration rate (GFR) 12 months after transplantation measured by iohexol clearance. Important secondary outcomes were estimated GFR (eGFR) (using routine clinical assessment), safety, inflammatory cytokine profile and biological mechanisms.ResultsIn total, 406 donor–recipient pairs were randomised: 99 to sham RIPC, 102 to early RIPC, 103 to late RIPC and 102 to dual RIPC. Early RIPC resulted in a small but clinically important increase in iohexol GFR (ml/minute/1.73 m2) at 12 months, although the evidence is weak [58.3 vs. 55.9; adjusted difference 3.08, 95% confidence interval (CI) –0.89 to 7.04;p = 0.13], likely because of the higher than expected variability in the iohexol measurements. There was stronger evidence for a treatment effect when eGFR was used and missing values imputed (adjusted difference 3.41, 95% CI –0.21 to 7.04;p = 0.065) and when eGFR was used to assess kidney function (adjusted difference 4.98, 95% CI 1.13 to 8.29;p = 0.011). Late RIPC had no effect on renal outcomes, there was no benefit of combining early and late RIPC and RIPC had no effect on the inflammatory response to surgery. RIPC was safe and well tolerated by recipients and donors.ConclusionsRIPC is a safe intervention in living-donor transplantation. The evidence for an effect of RIPC on GFR (primary outcome) was weak, but other measures of GFR (in our secondary analysis) provided persuasive evidence of a clinically meaningful improvement in kidney function after transplantation. Future work should investigate the role of RIPC in deceased-donor kidney transplantation.Trial registrationCurrent Controlled Trials ISRCTN30083294.FundingThis project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a Medical Research Council and National Institute for Health Research partnership.

We present MATLAB codes for finite-difference time-domain (FDTD) modeling of ground-penetrating radar (GPR) in two dimensions. Surface-based reflection GPR is modeled using a transverse magnetic (TM-) mode formulation. Crosshole and vertical radar profiling (VRP) geometries are modeled using a transverse electric (TE-) mode formulation. Matrix notation is used in the codes wherever possible to optimize them for speed in the MATLAB environment. To absorb waves at the edges of the modeling grid, we implement perfectly matched layer (PML) absorbing boundaries. Although our codes are two-dimensional and do not incorporate features such as dispersion in electrical properties, they capture many of the important elements of GPR surveying and run at a fraction of the computational cost of more elaborate algorithms. In addition, the codes are well commented, relatively easy to understand, and can be easily modified for the user's specific purpose.

Image texture is one of the key features used for the interpretation of radar facies in ground-penetrating radar (GPR) data. Establishing quantitative measures of texture is therefore a critical step in the effective development of advanced techniques for the interpretation of GPR images. This study presents the first effort to evaluate whether different measures of a GPR image capture the features of the data that, when coupled with a neural network classifier, are able to reproduce a human interpretation. The measures compared in this study are instantaneous amplitude and frequency, as well as the variance, covariance, Fourier-Mellin transform, R-transform, and principle components (PCs) determined for a window of radar data. A [Formula: see text] GPR section collected over the William River delta in Saskatchewan, Canada, is used for the analysis. We found that measures describing the local spatial structure of the GPR image (i.e., covariance, Fourier-Mellin, R-transform, and PCs) were able to reproduce human interpretations with greater than 93% accuracy. In contrast, classifications based on image variance and the instantaneous attributes agreed with the human interpretation less than 68% of the time. Among the textural measures that preserve spatial structure, we found that the best ones are insensitive to within facies variability while emphasizing differences between facies. For the specific case of the William River delta, the Fourier-Mellin transform, which retains information about the spatial correlation of reflections while remaining insensitive to their orientation, outperformed the other measures. Our work in describing radar texture provides an important first step in defining quantitative criteria that can be used to aid in the classification of radar data.

Numerical models that account for realistic transmitter and receiver antenna behavior are necessary to develop waveform-based inversion methods for crosshole ground-penetrating radar (GPR) data. A challenge in developing such models is simulating the antennae in a computationally efficient manner so that inversions can be performed in a reasonable amount of time. We present an approach to efficiently simulate crosshole GPR transmission and reception in heterogeneous media. The core of our approach is a finite-difference time-domain (FDTD) solution of Maxwell's equations in 2D cylindrical coordinates. First, we determine the behavior of the current on a realistic GPR antenna in a borehole through detailed FDTD modeling of the antenna and its immediate surroundings. To model transmission and reception, we then replicate this antenna current behavior on a much-coarser grid using a superposition of point-electric-dipole source and receiver responses. Results obtained with our technique agree with analytical results, with numerical modeling results where the transmitter antenna and borehole are explicitly accounted for using a fine discretization, and with crosshole GPR field data.

To obtain tomographic images with the highest possible resolution from crosshole ground-penetrating radar (GPR) data, raypaths covering a wide range of angles between the boreholes are required. In practice, however, the inclusion of high-angle ray data in crosshole GPR inversions often leads to tomograms so dominated by inversion artifacts that they contain little reliable subsurface information. Here, we investigate the problems that arise from the standard assumption that all first-arriving energy travels directly between the centers of the antennas. Through numerical modeling, we show that this assumption is often incorrect at high transmitter-receiver angles and can lead to significant errors in tomographic velocity estimates when the antenna length is a significant fraction of the borehole spacing.

Summary Background The long-term outcome of an interventional strategy in patients with non-ST-elevation acute coronary syndrome is unknown. We tested whether an interventional strategy (routine angiography followed by revascularisation) was better than a conservative strategy (ischaemia-driven or symptom-driven angiography) over 5 years' follow-up. Methods In a multicentre randomised trial, 1810 patients (from 45 hospitals in England and Scotland, UK) with non-ST-elevation acute coronary syndrome were randomly assigned to receive an early intervention (n=895) or a conservative strategy (n=915) within 48 h of the index episode of cardiac pain. In each group, the aim was to provide the best medical treatment, and also to undertake coronary arteriography within 72 h in the interventional strategy with subsequent management guided by the angiographic findings. Analysis was by intention to treat and the primary outcome (composite of death or non-fatal myocardial infarction) had masked independent adjudication. RITA 3 has been assigned the International Standard Randomised Control Trial Number ISRCTN07752711. Findings At 1-year follow-up, rates of death or non-fatal myocardial infarction were similar. However, at a median of 5 years' follow-up (IQR 4·6–5·0), 142 (16·6%) patients with intervention treatment and 178 (20·0%) with conservative treatment died or had non-fatal myocardial infarction (odds ratio 0·78, 95% CI 0·61–0·99, p=0·044), with a similar benefit for cardiovascular death or myocardial infarction (0·74, 0·56–0·97, p=0·030). 234 (102 [12%] intervention, 132 [15%] conservative) patients died during follow-up (0·76, 0·58–1·00, p=0·054). The benefits of an intervention strategy were mainly seen in patients at high risk of death or myocardial infarction (p=0·004), and for the highest risk group, the odds ratio of death or non-fatal myocardial infarction was 0·44 (0·25–0·76). Interpretation In patients with non-ST-elevation acute coronary syndrome, a routine invasive strategy leads to long-term reduction in risk of death or non-fatal myocardial infarction, and this benefit is mainly in high-risk patients. The findings provide support for national and international guidelines in the need for more robust risk stratification in acute coronary syndrome.

Aims The RITA 3 trial randomized patients with non-ST-elevation myocardial infarction or unstable angina to strategies of early intervention (angiography followed by revascularization) or conservative care (ischaemia or symptom driven angiography). The aim of this analysis was to investigate the impact of gender on the effect of these two strategies. Methods and results In total, 1810 patients (682 women and 1128 men) were randomized. The risk factor profile of women at presentation was markedly different to men. There was evidence that men benefited more from an early intervention strategy for death or non-fatal myocardial infarction at 1 year (adjusted odds ratios 0.63, 95% confidence interval 0.41–0.98 for men and 1.79, 95% confidence interval 0.95–3.35 for women; interaction p -value=0.007). Men who underwent the assigned angiogram were more likely to be put forward for coronary artery bypass surgery, even after allowing for differences in disease severity. Conclusion An early intervention strategy resulted in a beneficial effect in men which was not seen in women although caution is needed in interpretation. Further research is needed to evaluate why women do not appear to benefit from early intervention and to identify treatments that improve the prognosis of women.

Explicitly defining large-scale heterogeneity is a necessary step of groundwater model calibration if accurate estimates of flow and transport are to be made. In this work, neural networks are used to estimate radar facies probabilities from ground penetrating radar (GPR) images, yielding stochastic facies-based models that honour the large-scale architecture of the subsurface. For synthetic GPR images, a neural network was able to correctly identify radar facies with an accuracy of approximately 90%. Manual interpretation of a set of 450 MHz GPR field data from the Borden aquifer resulted in the identification of four radar facies. Of these, a neural network was able to identify two facies with an accuracy of near 80% and one with an accuracy of 44%. The neural network was not able to identify the fourth facies, likely due to the choice of defining facies characteristics. Sequential indicator simulation was used to generate facies realizations conditioned to the radar facies probabilities. Numerical simulations indicate that significant improvements in the prediction of solute transport are possible when GPR is used to constrain the facies model compared to using well data alone, especially when data are sparse.

OBJECTIVES This study was designed to compare the long-term consequences of percutaneous transluminal coronary angioplasty (PTCA) and continued medical treatment. BACKGROUND The long-term effects of percutaneous coronary intervention need evaluating, especially in comparison with an alternative policy of continued medical treatment. METHODS The Second Randomized Intervention Treatment of Angina (RITA-2) is a randomized trial of PTCA versus conservative (medical) care in 1,018 patients considered suitable for either treatment option. Information on clinical events, interventions, and symptoms is available for a median seven years follow-up. RESULTS Death or myocardial infarction (MI) occurred in 73 (14.5%) PTCA patients and 63 (12.3%) medical patients (difference +2.2%, 95% confidence interval -2.0% to +6.4%, p = 0.21). There were 43 deaths in both groups, of which 41% were cardiac-related. Among patients assigned PTCA 12.7% subsequently had coronary artery bypass grafts, and 14.5% required additional non-randomized PTCA. Most of these re-interventions occurred within a year of randomization, and after two years the re-intervention rate was 2.3% per annum. In the medical group, 35.4% required myocardial revascularization: 15.0% in the first year and an annual rate of 3.6% after two years. An initial policy of PTCA was associated with improved anginal symptoms and exercise times. These treatment differences narrowed over time, mainly because of coronary interventions in medical patients with severe symptoms. CONCLUSIONS In RITA-2 an initial strategy of PTCA did not influence the risk of death or MI, but it improved angina and exercise tolerance. Patients considered suitable for PTCA or medical therapy can be safely managed with continued medical therapy, but percutaneous intervention is appropriate if symptoms are not controlled.

Wavelet dispersion caused by frequency‐dependent attenuation is a common occurrence in ground‐penetrating radar (GPR) data, and is displayed in the radar image as a characteristic “blurriness” that increases with depth. Correcting for wavelet dispersion is an important step that should be performed before GPR data are used for either qualitative interpretation or the quantitative determination of subsurface electrical properties. Over the bandwidth of a GPR wavelet, the attenuation of electromagnetic waves in many geological materials is approximately linear with frequency. As a result, the change in shape of a radar pulse as it propagates through these materials can be well described using one parameter, Q*, related to the slope of the linear region. Assuming that all subsurface materials can be characterized by some Q* value, the problem of estimating and correcting for wavelet dispersion becomes one of determining Q* in the subsurface and deconvolving its effects using an inverse‐Q filter. We present a method for the estimation of subsurface Q* from reflection GPR data based on a technique developed for seismic attenuation tomography. Essentially, Q* is computed from the downshift in the dominant frequency of the GPR signal with time. Once Q* has been obtained, we propose a damped‐least‐squares inverse‐Q filtering scheme based on a causal, linear model for constant‐Q wave propagation as a means of removing wavelet dispersion. Tests on synthetic and field data indicate that these steps can be very effective at enhancing the resolution of the GPR image.

We collected SH‐wave seismic reflection data over a shallow aquifer in southwestern British Columbia to investigate the use of such data in hydrogeologic applications. We used this data set in developing a methodology that uses cone penetrometer data as an integral part of the inversion and interpretation of the seismic data. A Bayesian inversion technique converts the seismic amplitude variations to velocity variations, honoring the probabilities of the priors and adhering to a geologically reasonable sparseness criterion. Velocity measurements acquired with the cone penetrometer provide velocity profiles and vertical seismic profiling (VSP) data, all of which are valuable in properly constraining the Bayesian inversion. The differentiation of lithologies (in this data set, sand and clay) is accomplished by first using a normalization procedure to remove the impact of effective stress, which dominates the velocity variation in the upper 10 to 20 m. The final transformation of seismic velocities to void ratio for the sand‐dominated regions is made using laboratory‐derived measurements; it provides an image of the heterogeneity of the near‐surface aquifer.

▪ Abstract Ground penetrating radar (GPR) is a near-surface geophysical technique that can provide high resolution images of the dielectric properties of the top few tens of meters of the earth. In applications in contaminant hydrology, radar data can be used to detect the presence of liquid organic contaminants, many of which have dielectric properties distinctly different from those of the other solid and fluid components in the subsurface. The resolution (approximately meter-scale) of the radar imaging method is such that it can also be used in the development of hydrogeologic models of the subsurface, required to predict the fate and transport of contaminants. GPR images are interpreted to obtain models of the large-scale architecture of the subsurface and to assist in estimating hydrogeologic properties such as water content, porosity, and permeability. Its noninvasive capabilities make GPR an attractive alternative to the traditional methods used for subsurface characterization.

We have used geostatistical analysis of radar reflections to quantify the correlation structures found in 2-D ground‐penetrating radar (GPR) images. We find that the experimental semivariogram, the product of the geostatistical analysis of the GPR data, is well‐defined and can be modeled using standard geostatistical models to obtain an estimate of the range or correlation length, and the maximum correlation direction, in the 2-D GPR image. When we compare the results from geostatistical analysis of GPR data from selected deltaic and barrier‐spit depositional environments we find different correlation structures in GPR images from different depositional environments. GPR images from braid deltas have near‐horizontal correlation directions and correlation lengths on the order of a few meters. In contrast, the GPR image of a fan‐foreset delta has a very long (>24 m) correlation length and a maximum correlation direction plunging 20°. In the GPR images from barrier spits, we find maximum correlation directions that are horizontal or plunging a few degrees. The correlation lengths range from 7 to 43 m, depending on the orientation of the GPR image relative to spit end growth, and on the specific radar facies that is analyzed.

We have found that high‐quality vertical seismic profile (VSP) data can be collected for near‐surface applications using the seismic cone penetrometer. Cone‐mounted accelerometers are used as the VSP receivers, and a sledgehammer against the cone truck baseplate is used as a source. This technique eliminates the need to drill a borehole, thereby reducing the cost of the survey, and results in a less invasive means of obtaining VSP data. Two SH-wave VSP surveys were acquired over a deltaic sand/silt sequence and compared to an SH-wave common‐depth‐point (CDP) reflection profile. The VSP data were processed using a combination of singular‐value‐decomposition filtering, deconvolution, and f-k filtering to produce the final VSP extracted traces. The VSP traces correlate well with cone geotechnical logs and the CDP surface‐seismic data. The first breaks from the VSP can be used to generate shear‐wave velocity profiles that are important for time‐to‐depth conversion and the velocity correction of the CDP surface data.

We have investigated the use of ground-penetrating radar (GFR) as a means of characterizing the heterogeneity of the subsurface. Radar data were collected at several sites in southwestern British Columbia underlain by glaciodeltaic sediments. A cliff face study was conducted in which geostatistical analysis of a digitized photograph of the face and the radar image of the face showed excellent agreement in the maximum correlation direction and the correlation length determined from these two data sets. Other two-dimensional (2-D) sections of radar data were divided into sedimentary architectural elements on the basis of the distinct radar appearance of these sedimentary units. Examples of four sedimentary units were used to obtain semivariograms from the radar data and resulted in maximum correlation lengths between 0.5 and 4.8 m. A 3-D radar survey, collected over a package of gravel and sand foresets, was analyzed to determine the paleoflow direction; a correlation length of 4 m was found in that direction.

NMR experiments are ideally carried out in well-controlled magnetic fields. When samples of natural porous materials are studied, the situation can be complicated if the sample itself contains magnetic components, giving rise to internal magnetic fields in the pore space that modulate the externally applied fields. If not properly accounted for, the internal fields can lead to misinterpretation of relaxation, diffusion, or imaging data. To predict the potential effect of internal fields, and develop effective mitigation strategies, it is important to develop a quantitative understanding of the magnitude and distribution of internal fields occurring in natural porous media. To develop such understanding, we employ scanning SQUID microscopy, a technique that can detect magnetic field variations very accurately at high spatial resolution (∼3 μm). We prepared samples from natural unconsolidated aquifer material, and scanned areas of about 200 × 200 μm in a very low background magnetic field of ∼2 μT. We found large amplitude variations with a magnitude of about 2 mT, across a relatively long spatial scale of about 200 μm, that are associated with a large magnetic grain (>50 μm radius) with a strong magnetic remanence. We also detected substantial variations exceeding 60 μT on small spatial scales of about ∼10 μm. We attribute these small-scale variations to very fine-grained magnetic material. Because we made our measurements at very low background field, the observed variations are not induced by the background field but due to magnetic remanence. Consequently, the observed internal fields will affect even low-field NMR experiments.

Background Loss to follow-up of trial participants represents a threat to research validity. To date, interventions designed to increase participants’ awareness of benefits to society of completing follow-up, and the impact of a telephone call from a senior female clinician and researcher requesting follow-up have not been evaluated robustly. Purpose Trial 1 aimed to evaluate the effect on trial follow-up of written information regarding the benefits of participation to society. Trial 2 aimed to evaluate the effect on trial follow-up of a telephone call from a senior female clinician and researcher. Methods Two single-blind randomized controlled trials were nested within a larger trial, Txt2stop. In Trial 1, participants were allocated using minimization to receive a refrigerator magnet and a text message emphasizing the benefits to society of completing follow-up, or to a control group receiving a simple reminder regarding follow-up. In Trial 2, participants were randomly allocated to receive a telephone call from a senior female clinician and researcher, or to a control group receiving standard Txt2stop follow-up procedures. Results Trial 1: 33.5% (327 of 976) of the intervention group and 33.8% (329 of 974) of the control group returned the questionnaire within 26 weeks of randomization, risk ratio (RR) 0.99; 95% confidence interval (CI) 0.88–1.12. In all, 83.3% (813 of 976) of the intervention group and 82.2% (801 of/974) of the control group sent back the questionnaire within 30 weeks of randomization, RR 1.01; 95% CI 0.97, 1.05. Trial 2: 31% (20 of 65) of the intervention group and 32% (20 of 62) of the control group completed trial follow-up, RR 0.93; 95%CI 0.44, 1.98. Conclusions In presence of other methods to increase follow-up neither experimental method (refrigerator magnet and text message emphasizing participation's benefits to society nor a telephone call from study's principal investigator) increased participant follow-up in the Txt2stop trial.

Background Recruitment is a major challenge for trials but there is little evidence regarding interventions to increase trial recruitment. We report three controlled trials of interventions to increase recruitment to the Txt2stop trial. Purpose To evaluate: Trial 1. The impact on registrations of a text message regarding an online registration facility; Trial 2. The impact on randomizations of sending £5 with a covering letter to those eligible to join the trial; Trial 3. The impact on randomizations of text messages containing quotes from existing participants. Methods Single blind controlled trials with allocation concealment. Interventions: Trial 1: A text message regarding our new online registration facility; Trial 2: A letter with £5 enclosed; Trial 3: A series of four text messages containing quotes from participants. The control group in each trial received standard Txt2stop procedures. Results Trial 1: 3.6% (17/470) of the intervention group and 1.1% (5/467) of the control group registered for the trial, risk difference 2.5% (95% CI 0.6—4.5). 0% (0/ 470) of the intervention group and 0.2% (1/467) of the control group registered successfully online, risk difference —0.2 (95% CI —0.6—0.2); Trial 2: 4.5% (11/246) of the intervention group and 0.4% (1/245) of the control group were randomized into the Txt2stop trial, risk difference 4.0% (95% CI 1.4—6.7); Trial 3: 3.5% (14/405) of the intervention group and 0% (0/406) of the control group were randomized into the Txt2stop trial, risk difference 3.5 (95% CI 1.7—5.2). Limitations There were no baseline data available for trial 1. Allocation of participant IDs in trials 2 and 3 were systematic. Conclusion Sending a text message about an online registration facility increased registrations to Txt2stop, but did not increase online registrations. Sending a £5 reimbursement for participants’ time and sending text messages containing quotes from existing participants increased randomizations into the Txt2stop trial. Clinical Trials 2010; 7: 265—273. http://ctj.sagepub.com

[1] Over the past decade, significant interest has been expressed in relating the spatial statistics of surface-based reflection ground-penetrating radar (GPR) data to those of the imaged subsurface volume. A primary motivation for this work is that changes in the radar wave velocity, which largely control the character of the observed data, are expected to be related to corresponding changes in subsurface water content. Although previous work has indeed indicated that the spatial statistics of GPR images are linked to those of the water content distribution of the probed region, a viable method for quantitatively analyzing the GPR data and solving the corresponding inverse problem has not yet been presented. Here we address this issue by first deriving a relationship between the 2-D autocorrelation of a water content distribution and that of the corresponding GPR reflection image. We then show how a Bayesian inversion strategy based on Markov chain Monte Carlo sampling can be used to estimate the posterior distribution of subsurface correlation model parameters that are consistent with the GPR data. Our results indicate that if the underlying assumptions are valid and we possess adequate prior knowledge regarding the water content distribution, in particular its vertical variability, this methodology allows not only for the reliable recovery of lateral correlation model parameters but also for estimates of parameter uncertainties. In the case where prior knowledge regarding the vertical variability of water content is not available, the results show that the methodology still reliably recovers the aspect ratio of the heterogeneity.

Surface-based ground-penetrating radar data were collected at the Hanford Site in Washington, U.S.A. to assess the use of radar reflection images as a means of quantifying the spatial variability of subsurface water content. Available at the selected test site were two sets of water content data derived from neutron probe measurements that had been made to a depth of ~18 m in 32 wells. The comparison of probe-derived water content data, synthetic radar data, and the acquired radar data indicated a good correspondence between the changes in probe-derived water content and the location of reflections in the radar data. Geostatistical analysis was conducted on the two sets of probe-derived water content values and the amplitudes of the reflections in the radar reflection image to determine the horizontal correlation length of water content. The experimental semivariograms for the water content data were fit with a single exponential model with a correlation length of 10 m. The semivariogram for the radar data was fit with a nested structure containing a dominant long-range structure with a correlation length of 14 m, and a smaller-scale structure with a correlation length of 0.3 m. Quantifying the scale triplet – the spacing, extent, and support –more » for the two forms of measurement provided a framework for comparing and assessing the derived correlation structures.« less

Background Securing and managing finances for multicentre randomised controlled trials is a highly complex activity which is rarely considered in the research literature. This paper describes the process of financial negotiation and the impact of financial considerations in four UK multicentre trials. These trials had met, or were on schedule to meet, recruitment targets agreed with their public-sector funders. The trials were considered within a larger study examining factors which might be associated with trial recruitment (STEPS). Methods In-depth semi-structured telephone interviews were conducted in 2003–04 with 45 individuals with various responsibilities to one of the four trials. Interviewees were recruited through purposive and then snowball sampling. Interview transcripts were analysed with the assistance of the qualitative package Atlas-ti. Results The data suggest that the UK system of dividing funds into research, treatment and NHS support costs brought the trial teams into complicated negotiations with multiple funders. The divisions were somewhat malleable and the funding system was used differently in each trial. The fact that all funders had the potential to influence and shape the trials considered here was an important issue as the perspectives of applicants and funders could diverge. The extent and range of industry involvement in non-industry-led trials was striking. Three broad periods of financial work (foundation, maintenance, and resourcing completion) were identified. From development to completion of a trial, the trialists had to be resourceful and flexible, adapting to changing internal and external circumstances. In each period, trialists and collaborators could face changing costs and challenges. Each trial extended the recruitment period; three required funding extensions from MRC or HTA. Conclusion This study highlights complex financial aspects of planning and conducting trials, especially where multiple funders are involved. Recognition of the importance of financial stability and of the need for appropriate training in this area should be paralleled by further similar research with a broader range of trials, aimed at understanding and facilitating the conduct of clinical research.

[1] Rock physics attempts to relate the geophysical response of a rock to geologic properties of interest, such as porosity, lithology, and fluid content. The geophysical properties estimated by field-scale surveys, however, are impacted by additional factors, such as complex averaging of heterogeneity at the scale of the survey and artifacts introduced through data inversion, that are not addressed by traditional approaches to rock physics. We account for these field-scale factors by creating numerical analogs to geophysical surveys via Monte Carlo simulation. The analogs are used to develop field-scale rock physics relationships that are appropriate for transforming the geophysical properties estimated from a survey into geologic properties. We demonstrate the technique using a synthetic example where radar tomography is used to estimate water content.

In order to obtain tomograms with the highest possible resolution from crosshole ground-penetrating radar (GPR) data, raypaths covering a wide range of angles between the boreholes are required. In practice, however, the inclusion of high-angle ray data in crosshole GPR inversions often results in tomograms dominated by inversion artifacts. We show that problems associated with high-angle rays in crosshole GPR tomography can arise from the standard assumption that all first-arriving energy travels directly between the centers of the antennas. As shown with a synthetic data set, an inversion scheme that accounts for radiation and reception from both the antenna feed and end points can lead to a more accurate reconstruction of the subsurface velocity model.

[1] Geostatistical analysis of a ground penetrating radar reflection image can be used to quantify the maximum correlation direction and the range of horizontal and sub-horizontal radar reflections. A review of previous work, and an analysis of a photograph of layered sediments, suggest that the vertical resolution of a radar image strongly affects its lateral correlation structure. Numerical modeling was used to generate synthetic radar sections and investigate the effect of the vertical resolution of the radar measurement on the link between the correlation structure of the radar reflections and the true correlation structure of subsurface water content. The horizontal range of the radar reflections decreased as the vertical resolution improved, closely matching that of the water content when the vertical resolution was approximately equal to the vertical range of the water content.

Moisture content is a critical parameter affecting both liquid-phase and vapor-phase contaminant transport in the vadose zone. The objective of our three-year research project is to determine the optimal way to use radar methods as a non-invasive means of determining in situ moisture content.

Wavelet dispersion caused by frequency-dependent attenuation is a common and significant problem in ground-penetrating radar (GPR) data. In the radar image, it is displayed as a characteristic 'blurriness' that increases with depth. Correcting for wavelet dispersion in GPR data is an important step that should be performed before either qualitative interpretation or quantitative determination of subsurface electrical properties are attempted. Over the bandwidth of a GPR wavelet, the attenuation of electromagnetic waves in many geologic materials is approximately linear with frequency. For this reason, the change in shape of a radar pulse as it propagates through these materials can be described using one parameter, Q*, which is related to the slope of the linear region. Assuming that all subsurface materials can be characterized by some Q* value, the problem of estimating and correcting for wavelet dispersion in GPR data becomes one of determining Q* in the subsurface and deconvolving its effects through the use of an inverse Q filter. A method for the estimation of Q* from GPR data based on a technique developed for seismic attenuation tomography is presented. Essentially, Q* is determined from the downshift in the dominant frequency of the GPR wavelet with time down a trace. Once Q* has been obtained, we propose an inverse Q filtering technique based on a causal, linear model for constant Q as a means of removing wavelet dispersion. Initial tests on field data indicate that this technique is very effective at enhancing the resolution of the GPR image.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a number of new ways to use the seismic cone penetrometer (SCPTU). These applications include the prediction of stratigraphic boundaries in advance of the cone as well as the refinement of the first break shear wave velocities. These applications depend upon the acquisition of vertical seismic profile (VSP) data using the cone. The VSP acquisition is achieved using standard SCPTU accelerometers and is an extension of SCPTU shear wave velocity surveys. The data consist of both an upgoing and downgoing seismic wavefield. These wavefields are easily identifiable and can be separated with a series of simple processing techniques. VSP data are most commonly associated with common depth point (CDP) reflection seismic surveys. We have demonstrated how the data can also be used effectively to obtain geotechnical information.

We have found that vertical seismic profile (VSP) data can be collected for near-surface applications by using existing cone penetration equipment. The cone-mounted accelerometers were used as the VSP receivers and a sledgehammer against the cone truck baseplate was used as a source. This technique eliminates the need to drill a borehole, which reduces the cost of the survey and results in a less invasive means of obtaining VSP data. In addition, the use of the cone optimized the receiver coupling and eliminated problems with borehole tube waves. An SH-wave VSP was obtained over 46 m of a shallow sand/silt sequence and coincides with an SH-wave CDP reflection profile. The VSP data are of excellent quality and provide both near-surface velocity control and important constraints on the interpretation of the CDP data.

Twelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to characterize the distribution and connectivity of hydraulic units. We have used GPR to locate the aquifer/aquitard boundary at several locations in the study area. The electrical contrast between these two materials makes the aquifer/aquitard boundary an excellent target for GPR surveys. GPR was also used to reconstruct the paleo-environment of one area of the Brookswood aquifer. This was accomplished by using a modification of the concept of architectural element analysis. Radar elements were identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area. These elements were used to develop an interpretation of the paleo-environment that provides information about the spatial distribution of hydraulic units. INTRODUCTION Hydrogeologists require quantitative data to produce a realistic model of the spatial variabilities in hydraulic properties of an aquifer. Such data can be difficult and expensive to obtain. A possible solution is to develop geophysical techniques as a means of aquifer characterization. Ground penetrating radar (GPR), a shallow geophysical technique, is well suited for this purpose as it can be used to image to a depth of up to 30m in sand and gravel environments. However, the image produced by a GPR survey does not supply hydrogeologic parameters directly. The focus of this paper is to investigate how GPR can be used for aquifer characterization. At an aquifer scale of lo’s to 100’s of meters, the most fundamental aspect of aquifer characterization is the determination of the aquifer’s hydraulic connectivity through mapping of aquifer/aquitard interfaces. GPR can be used for this purpose due to the large contrast in electrical conductivity between the sand and gravel material of an aquifer, and the clay rich material of an aquitard. The electrical conductivity of a material affects the penetration depth of radar waves, such that radar waves penetrate well through resistive material, but poorly through conductive material. Aquifers, composed of sands and gravels, are resistive, while aquitards, composed of clay rich materials, are electrically conductive. Therefore a radar survey will show good penetration in aquifer materials and very poor penetration in aquitards. By exploiting this difference in radar response, the aquifer boundaries can be mapped. At a smaller scale of centimeters to meters, the determination of the internal structure of an aquifer is also important for aquifer characterization. For example, anisotropy within the aquifer can cause significant differences in hydraulic properties and so must be identified where present. In addition, identification of sedimentary features aids in the determination of the paleo-environment that can provide important insight into the probable arcal extent and orientation of geological units. GPR can be used to image these features because of changes in their electrical properties. GPR and Sedimentology GPR has received considerable attention as a means of imaging sedimentary stratigraphy (Jo1 and Smith, 1992; Smith and Jol, 1992; Pratt and Miall, 1993; Greenhouse et al, 1987; Rea et al, 1991; Huggenberger et al, 1994). The key question that needs addressing is exactly which sedimentary aspects of the subsurface are imaged with GPR. A GPR survey, conducted by transmitting radar waves into the subsurface and recording the reflected energy, will image changes in the subsurface dielectric constant and conductivity. If these electrical properties correspond to changes in sedimentary parameters, then a GPR survey can be said to image sedimentary features. The dielectric constant and conductivity of earth materials are dependent upon composition and geometry of the solid and liquid components. Sedimentological classification is based upon five fundamental properties from which all others can be derived: grain composition, size, shapes, orientation and packing (Blatt et al, 1980). These five properties clearly are related to the composition and geometry of the solid component of a system. It is therefore reasonable to assume that a change in sedimentological properties at some boundary will cause a change in electrical properties. If the resulting change in electrical properties is large enough, then the sedimentary boundary will be imaged in a radar survey. The complicating issue is the liquid, usually water, component which does not play a role in sedimentary

Ground penetrating radar (GPR) images provide information about the location, scale and geometry of subsurface heterogeneities. With well control or geologic intuition, this information can be used by hydrogeologists to fix the location of boundaries in fluid flow and contaminant transport models. While the location of boundaries is important, the hydrogeologist also requires estimates of the physical properties within the boundaries, for instance the hydraulic conductivity and porosity of different stratigraphic units. In essence, what the hydrogeologist really wants are the input parameters to his or her model. If the model is deterministic, these inputs are a discretized map of hydrogeologic properties. If the model is stochastic, these inputs are geostatistical parameters such as the correlation length, distribution, mean, variance and trend of hydrogeologic properties. With our goal being to help the hydrogeologist, we are investigating the capabilities of GPR to map hydrogeologic properties and characterize the heterogeneity of shallow aquifers. This paper presents results of a detailed 3-D GPR survey conducted at the U.S.G.S. Toxic Waste Hydrology Research Site on Cape Cod. The survey was completed in an area encompassing two well arrays where the spatial heterogeneity of aquifer properties is being investigated. Survey parameters were selected to cover the relevant scales of hydraulic conductivity variability thought to control contaminant migration in the sand and gravel aquifer. Trace density is one trace per square foot in an area measuring 370 feet by 100 feet, making this one of the most detailed 3-D GPR data sets every collected. The data were processed to remove the effects of topography and acquisition geometry. Common midpoint soundings conducted at 16 locations and water table depths measured in 20 wells were used to construct a model of subsurface electromagnetic propagation velocities. This velocity model was used for depth conversion and to estimate the average dielectric properties of the saturated and unsaturated zones. An empirical relationship between permittivity and porosity was then used to estimate the average porosity of the aquifer material. Small-scale features in the GPR data were examined using a sophisticated visualization program. With this program, 3-D images may be sliced, rotated and magnified, allowing us to construct profiles coincident with the well arrays. Individual amplitude ranges may be specified to construct isosurfaces and highlight events of interest; this is useful for reducing the opacity of 3-D images and for examining the topology of different events such as the water table and apparent stratigraphic reflections. Using these techniques, a map of the water table was produced that was accurate to within several tens of centimeters. In addition, correlations were observed between apparent radar stratigraphy and hydraulic conductivity variations determined from borehole flowmeter measurements and a large-scale tracer test conducted previously at the site. Seven continuous cores were acquired to confirm radar interpretations and provide material for laboratory measurement of dielectric and hydrogeologic properties. By comparing GPR images with other field and laboratory measurements of material properties, a better understanding is gained of the capabilities and limitations of this shallow remote sensing tool.

The number of individuals with age-related cognitive impairment is rising dramatically in the UK and globally. There is considerable interest in the general hypothesis that improving the diet of older people may slow the progression of cognitive decline. To date, there has been little attention given to the possible protective role of n-3 long-chain polyunsaturated fatty acids (n-3 LCPs) most commonly found in oily fish, in age-related loss of cognitive function. The main research hypothesis of this study is that an increased dietary intake of n-3 LCPs will have a positive effect on cognitive performance in older people in the UK. To test this hypothesis, a double-blind randomised placebo-controlled trial will be carried out among adults aged 70–79 years in which the intervention arm will receive daily capsules containing n-3 LCP (0.5 g/day docosahexaenoic acid and 0.2 g/day eicosapentaenoic acid) while the placebo arm will receive daily capsules containing olive oil. The main outcome variable assessed at 24 months will be cognitive performance and a second major outcome variable will be retinal function. Retinal function tests are included as the retina is a specifically differentiated neural tissue and therefore represents an accessible window into the functioning of the brain. The overall purpose of this public-health research is to help define a simple and effective dietary intervention aimed at maintaining cognitive and retinal function in later life. This will be the first trial of its kind aiming to slow the decline of cognitive and retinal function in older people by increasing daily dietary intake of n-3 LCPs. The link between cognitive ability, visual function and quality of life among older people suggests that this novel line of research may have considerable public health importance.