Source wavelet estimation for waveform inversion of crosshole georadar data

AbstractFor a wide range of environmental, hydrological, and engineering applications there is a fast growing need for high-resolution imaging. In this context, waveform tomographic imaging of crosshole georadar data is a powerful method able to provide images of pertinent electrical properties in near-surface environments with unprecedented spatial resolution. In contrast, conventional ray-based tomographic methods, which consider only a very limited part of the recorded signal (first-arrival traveltimes and maximum first-cycle amplitudes), suffer from inherent limitations in resolution and may prove to be inadequate in complex environments. For a typical crosshole georadar survey the potential improvement in resolution when using waveform-based approaches instead of ray-based approaches is in the range of one order-of- magnitude. Moreover, the spatial resolution of waveform-based inversions is comparable to that of common logging methods. While in exploration seismology waveform tomographic imaging has become well established over the past two decades, it is comparably still underdeveloped in the georadar domain despite corresponding needs. Recently, different groups have presented finite-difference time-domain waveform inversion schemes for crosshole georadar data, which are adaptations and extensions of Tarantola's seminal nonlinear generalized least-squares approach developed for the seismic case. First applications of these new crosshole georadar waveform inversion schemes on synthetic and field data have shown promising results. However, there is little known about the limits and performance of such schemes in complex environments. To this end, the general motivation of my thesis is the evaluation of the robustness and limitations of waveform inversion algorithms for crosshole georadar data in order to apply such schemes to a wide range of real world problems.One crucial issue to making applicable and effective any waveform scheme to real-world crosshole georadar problems is the accurate estimation of the source wavelet, which is unknown in reality. Waveform inversion schemes for crosshole georadar data require forward simulations of the wavefield in order to iteratively solve the inverse problem. Therefore, accurate knowledge of the source wavelet is critically important for successful application of such schemes. Relatively small differences in the estimated source wavelet shape can lead to large differences in the resulting tomograms. In the first part of my thesis, I explore the viability and robustness of a relatively simple iterative deconvolution technique that incorporates the estimation of the source wavelet into the waveform inversion procedure rather than adding additional model parameters into the inversion problem. Extensive tests indicate that this source wavelet estimation technique is simple yet effective, and is able to provide remarkably accurate and robust estimates of the source wavelet in the presence of strong heterogeneity in both the dielectric permittivity and electrical conductivity as well as significant ambient noise in the recorded data. Furthermore, our tests also indicate that the approach is insensitive to the phase characteristics of the starting wavelet, which is not the case when directly incorporating the wavelet estimation into the inverse problem.Another critical issue with crosshole georadar waveform inversion schemes which clearly needs to be investigated is the consequence of the common assumption of frequency- independent electromagnetic constitutive parameters. This is crucial since in reality, these parameters are known to be frequency-dependent and complex and thus recorded georadar data may show significant dispersive behaviour. In particular, in the presence of water, there is a wide body of evidence showing that the dielectric permittivity can be significantly frequency dependent over the GPR frequency range, due to a variety of relaxation processes. The second part of my thesis is therefore dedicated to the evaluation of the reconstruction limits of a non-dispersive crosshole georadar waveform inversion scheme in the presence of varying degrees of dielectric dispersion. I show that the inversion algorithm, combined with the iterative deconvolution-based source wavelet estimation procedure that is partially able to account for the frequency-dependent effects through an "effective" wavelet, performs remarkably well in weakly to moderately dispersive environments and has the ability to provide adequate tomographic reconstructions.

Comparison of three acellular tests for assessing the oxidation potential of nanomaterials

Great effort is put into developing reliable, predictive, high-throughput, and low-cost screening approaches for the toxicity evaluation of ambient and manufactured nanoparticles (NP). These tests often consider oxidative reactivity, as oxidative stress is a well-documented pathway in particle toxicology. Based on a panel of six carbonaceous and five metal/metal oxide (Me/MeOx) nanoparticles, we: (i) compared the specifications (linearity, detection limits, repeatability) of three acellular reactivity tests using either dithiothreitol (DTT assay), dichlorofluorescein (DCFH assay), or ascorbic acid (AA-assay) as the reducing agent; and (ii) evaluated which physicochemical properties were important for explaining the observed reactivity. The selected AA assay was found to be neither sensitive nor robust enough to be retained. For the other tests, the surface properties of carbonaceous NP were of utmost importance for explaining their reactivity. In particular, the presence of "strongly reducing" surface functions explained most of its DCFH reactivity and a large part of its DTT reactivity. For the selected Me/MeOx, a different picture emerged. Whereas all particles were able to oxidize DCFH, dissolution and complexation processes could additionally influence the measured reactivity, as observed using the DTT assay. This study suggests that a combination of the DTT and DCFH assays provides complementary information relative to the quantification of the oxidative capacity of NP.

Comparative resilience of clinical perimetric tests to induced levels of intraocular straylight.

PURPOSE: To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT).¦METHODS: Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument.¦RESULTS: SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss.¦CONCLUSIONS: The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Les paramètres du cycle vital de Physa acuta (Gastropoda, Mollusca) en milieu expérimental.

The values of the life history parameters expressed in the Lotka's equation were measured in the experimental conditions (20ºC, food ad libitum) for the aquatic pumonate Physa acuta. The estimated fitness value allows the population to double in about 4 weeks. The life cycle is very short (about 3 times shorter than for Lymnaea peregra in similar conditions) because of the important relative size of the eggs, a very high growth rate and an early maturity. This kind of strategy seems adaptive in eutrophic and temporary pools, where the adult mortality is important and density-independant. While the longevity shows very poor correlations with all other parameters, adult size, age at maturity and fecundity are strongly correlated. Structural and functionnal interpetations of these correlations are proposed. A mixed strategy seems a good hypothesis for this usually bivoltine species: the little-size, early-maturity and high-fecondity strategy may be selected during the summer, and the big-size, delayed-maturity and poor fecundity strategy during the winter

Allergy to betalactam antibiotics in children: a prospective follow-up study in retreated children after negative responses in skin and challenge tests.

BACKGROUND: Up to 10% of the patients in whom suspected betalactam hypersensitivity (HS) has been excluded by skin and challenge tests report suspected allergic reactions during subsequent treatments with the same or very similar betalactams. It has been suggested that the reactions may result from a resensitization induced by the challenge performed at the time of the allergological work-up. However, most patients did not undergo a second allergological work-up, to determine if the reactions resulted from betalactam HS or not. OBJECTIVES: We aimed to determine if children diagnosed nonallergic to betalactams have tolerated subsequent treatments with the initially suspected and/or other betalactams, and, in case of a reaction, if the reaction resulted from betalactam HS. Methods: We sent a questionnaire concerning the clinical history of their children to the parents of 256 children previously diagnosed nonallergic to betalactams. A second allergological work-up was performed in the children reporting suspected allergic reactions during subsequent treatments with the same and/or other betalactams. Skin tests were performed with the soluble form of the suspected (or very similar) betalactams and other betalactams from the same and other classes. Skin test responses were assessed at 15-20 min (immediate), 6-8 h (semi-late) and 48-72 h (late). Oral challenge (OC) was performed in children with negative skin tests, either at the hospital (immediate and accelerated reactions), or at home (delayed reactions). RESULTS: A response was obtained from 141 children (55.3%). Forty-eight (34%) of those children had not been treated with the betalactams for whom a diagnosis of allergy had been ruled out previously. Seven (7.5%) of the 93 children who had been treated again reported suspected allergic reactions. Skin tests and OC were performed in six of those children, and gave negative results in five children. In one child previously diagnosed nonallergic to amoxicillin associated with clavulanic acid, we diagnosed a delayed HS to clavulanic acid and a serum sickness-like disease to cefaclor. Thus, the frequency of reactions resulting from betalactam HS in children with negative skin and challenge tests is very low, and does not exceed 2.1% (2/93) if we consider that the child which refused a second allergological work-up is really allergic to betalactams. CONCLUSION: Our results in a very large number of children show that reactions presumed to result from betalactam HS are rare in children in whom the diagnosis of betalactam allergy has been ruled out previously. Moreover, they suggest that, as shown for the initial reactions, most of the reactions during subsequent treatments are rather a consequence of the infectious diseases for whom betalactams have been prescribed than a result of betalactam HS. Finally, they suggest that the risk of resensitization by OC is very low, and do not support the notion that skin testing should be repeated in children diagnosed nonallergic to betalactams.

In vitro prevention of the emergence of daptomycin resistance in Staphylococcus aureus and enterococci following combination with amoxicillin/clavulanic acid or ampicillin.

Daptomycin is bactericidal against meticillin-resistant Staphylococcus aureus (MRSA), glycopeptide-intermediate-resistant S. aureus (GISA) and vancomycin-susceptible and -resistant enterococci. However, selection for daptomycin-resistant derivatives has occasionally been reported during therapy in humans. Here we evaluate whether selection for daptomycin-resistant S. aureus or enterococci could be prevented in vitro by combining daptomycin with amoxicillin/clavulanic acid, ampicillin, gentamicin or rifampicin. Six strains of S. aureus (four MRSA and two GISA) and four strains of enterococci (two Enterococcus faecalis and two Enterococcus faecium) were serially exposed in broth to two-fold stepwise increasing concentrations of daptomycin alone or in combination with a fixed concentration [0.25x minimum inhibitory concentration (MIC)] of either of the second agents. The daptomycin MIC was examined after each cycle. Exposure to daptomycin alone gradually selected for S. aureus and enterococci with an increased MIC. Gentamicin did not prevent the emergence of daptomycin-resistant bacteria. Rifampicin was also unable to prevent daptomycin resistance, although resistance was slightly delayed. In contrast, amoxicillin/clavulanic acid or ampicillin prevented or greatly delayed the selection of daptomycin-resistant mutants in S. aureus and enterococci, respectively. Addition of amoxicillin/clavulanic acid or ampicillin to daptomycin prevents, or greatly delays, daptomycin resistance in vitro. Future studies in animal models are needed to predict the utility of these combinations in humans.

Responsiveness of astrocytes in serum-free aggregate cultures to epidermal growth factor: dependence on the cell cycle and the epidermal growth factor concentration.

Serum-free aggregating cell cultures of fetal rat telencephalon treated with low doses (0.5 nM) of epidermal growth factor (EGF) showed a small, transient increase in DNA synthesis but no significant changes in total DNA and protein content. By contrast, treatment with high doses (13 nM) of EGF caused a marked stimulation of DNA synthesis as well as a net increase in DNA and protein content. The expression of the astrocyte-specific enzyme, glutamine synthetase, was greatly enhanced both at low and at high EGF concentrations. These results suggest that at low concentration EGF stimulates exclusively the differentiation of astrocytes, whereas at high concentration, EGF has also a mitogenic effect. Nonproliferating astrocytes in cultures treated with 0.4 microM 1-beta-D-arabinofuranosyl-cytosine were refractory to EGF treatment, indicating that their responsiveness to EGF is cell cycle-dependent. Binding studies using a crude membrane fraction of 5-day cultures showed a homogeneous population of EGF binding sites (Kd approximately equal to 2.6 nM). Specific EGF binding sites were found also in non-proliferating (and nonresponsive) cultures, although they showed slightly reduced affinity and binding capacity. This finding suggests that the cell cycle-dependent control of astroglial responsiveness to EGF does not occur at the receptor level. However, it was found that the specific EGF binding sites disappear with progressive cellular differentiation.

Le cycle de la conjoncture chez Schumpeter : éternel retour du même ?

Cet article s'inscrit dans la lignée de précédents travaux visant à rapprocher l'entrepreneur schumpétérien et le surhumain nietzschéen. Les deux partagent une créativité pouvant s'interpréter comme l'extériorisation d'un surcroît de force qui, dans l'optique nietzschéenne, s'assimile à la source extra-morale de l'accrois- sement de la vie. Reste à savoir si le cadre dans lequel ils évoluent est le même. Au-delà d'une approche historique du cycle de la conjoncture, notre hypothèse est que l'approche philosophique d'un cycle du devenir s'avère être féconde pour une interprétation enrichie du cycle de la conjoncture, complétant et prolongeant ainsi notre interprétation du surhumain et de l'entrepreneur. Abstract: This article is in line with previous works aiming to analyse together Schumpeter's entrepreneur and Nietzsche's superhuman. Both share a creativity that can be interpreted as the externalization of an extra force. The latter, through Nietzsche's perspective, is very close to the extra-moral source of the increase of life. But what we have not analysed yet, is the context in which each of

Tests pharmacogénétiques: bientôt avant chaque prescription [Pharmacogenetic testing: soon before every prescription?]

Genetic polymorphisms have currently been described in more than 200 systems affecting pharmacological responses (cytochromes P450, conjugation enzymes, transporters, receptors, effectors of response, protection mechanisms, determinants of immunity). Pharmacogenetic testing, i.e. the profiling of individual patients for such variations, is about to become largely available. Recent progress in the pharmacogenetics of tamoxifen, oral anticoagulants and anti-HIV agents is reviewed to discuss critically their potential impact on prescription and contribution/limits for improving rational and safe use of pharmaceuticals. Prospective controlled trials are required to evaluate large-scale pharmacogenetic testing in therapeutics. Ethical, social and psychological issues deserve particular attention.

Use of a combined ex vivo/in vivo population approach for screening of human genes involved in the human immunodeficiency virus type 1 life cycle for variants influencing disease progression.

Humans differ substantially with respect to susceptibility to human immunodeficiency virus type 1 (HIV-1). We evaluated variants of nine host genes participating in the viral life cycle for their role in modulating HIV-1 infection. Alleles were assessed ex vivo for their impact on viral replication in purified CD4 T cells from healthy blood donors (n = 128). Thereafter, candidate alleles were assessed in vivo in a cohort of HIV-1-infected individuals (n = 851) not receiving potent antiretroviral therapy. As a benchmark test, we tested 12 previously reported host genetic variants influencing HIV-1 infection as well as single nucleotide polymorphisms in the nine candidate genes. This led to the proposition of three alleles of PML, TSG101, and PPIA as potentially associated with differences in progression of HIV-1 disease. In a model considering the combined effects of new and previously reported gene variants, we estimated that their effect might be responsible for lengthening or shortening by up to 2.8 years the period from 500 CD4 T cells/mul to <200 CD4 T cells/mul.

Prevalence of positive tuberculosis skin tests during 5 years of screening in a Swiss remand prison

BACKGROUND: Tuberculosis (TB) screening in prisons is recommended, but the appropriate methods remain controversial. Studies evaluating screening in remand prisons arc scarce. METHOD: Between 1997 and 2001, voluntary screening based on the tuberculin skin test (TST) was offered to all prisoners on entry into the largest remand prison in Switzerland. Prisoners with positive results underwent chest X-rays. We analysed this information collected in an anonymous database. RESULTS: A total of 4890 prisoners entered the prison and were eligible for screening; 3779 (77.3%) had TST performed on average 9 days after arrival: 46.9% were positive (induration >= 10 mm). Positive TST rates were similar over the 5 years. Women were more likely to have a negative TST (60.4%) than men (47.7%; P < 0.001, Pearson's chi(2) 16.5). Positive TSTs varied according to the prisoner's country of origin (64% for sub-Saharan Africa, 57% for Eastern Europe, 56% for North Africa, 51% for Asia and 34% for North and West Europe). CONCLUSION: The percentage of TST-positive subjects was high, and most did not receive preventive treatment for latent TB. The usefulness of systematic TST for all prisoners on entry is limited, as diagnosis of TB disease usually remains the priority in prisons. Keywords