Velocity model determination by the SMART method, Part 2: Application SP3.8

International audienceThe SMART (Sequential Migration Aided Reflection Tomography) method, as explained in the first part of this paper, starts after a first set of traveltimes in the unmigrated prestack data has been picked and the inventarization of useful a priori knowledge related to these traveltimes has been made. Thereto a preparative phase is needed. First a global estimate of the subsurface structure is made. Hereto we use the standard stacking and poststack interpretation procedures which 'allow for getting insight in the degree of complexity of the subsurface. Next the traveltimes can be picked. When interpreting prestack data important qualitative structural information in difficult target zones (e-g. fault zones or salt structure flanks) can be obtained. Such an analysis guides the interpreter in selecting and picking the best traveltimes of primary events. Once the preparation is finished the SMART method can be applied for a detailed determination of a structural and velocity model in a very consistent way. It is emphasized that velocity variations in complex structures can be determined accurately by prestack traveltime inversion techniques. This phase has an iterative character. In order to update the velocity model after the first iteration additional traveltimes are needed. Next additional traveltimes are obtained by interpretation of the cube of migrated data which can be easier than in the time domain due to the focussing and positioning effect of the migration process. By tracing rays in the same velocity model as was used for mi.gration on the newly interpreted events, we will obtain additional traveltimes which will make the set of input data for the next iteration of tomography more complete. A new velocity model is calculated and the data are remigrated. In this paper we will demonstrate the feasibility of this approach using a 2D real data set. We executed a number of iterations of the SMART method and ended up with of the complex structure. a very satisfactory depth image THE DATA We used for this application a 2D dataset covering a salt structure. It consists of 300 shotrecords at a regular interval of 40m. The acquisition was done in a split spread. The half spread length is 1920 meters with 48 geophones. The data were delivered with a standard preprocessing (filtering, zero-phase deconvolution and muting). Because of some clearly visible groundroll, we applied a second filter in order to remove most of this in Figure 1. low frequency noise. A partial stack of the data is shown THE PREPARATIVE PHASE Analysis of complexity In order to get an idea of the degree of complexity of a subsurface, it is useful to construct several partial stacks with the same stacking velocity model. Because the stacking process is based on flattening of the hyperbola's in CMP's, through some NMO and DMO based correction, differences in between the partial stacks demonstrate the failure of the process. In areas with complex subsurface structures these hyperbola's aren't necessarily flat due to different raypaths left and right of the midpoint. In this dataset this phenomenon can be observed in a series of CMP's covering the saltdome (See Figure 2). Another way to get an idea of the complexity is to do a post stack depth migration by a layer stripping approach using the best partial stack. For these data the results are satisfactory for the sedimentary zones left and right of the dome, but are incorrect for the deep interfaces and the base of the salt. This is partially due to events that are lost during the stacking procedure. Other causes for this failure are: the uncertainty in picking the right interface that serves as the next velocity boundary and the difficult choice of the velocities which becomes more and more hazardous as the depth increases. The final result is unreliable and the resulting depth for the base of the salt depends largely on the choices made by the interpreter Clearly these data cannot be handled by standard processing techniques. Left and right of the salt dome and below it the nature of the trace gathers is too complex. A prestack imaging method using a velocity model computed by tomography seems adequate for solving the aforementioned problems. Data preparation for the SMART method The next step after the analysis of the complexity is the data preparation for the SMART method. Its goal is to prepare an initial set of traveltimes to be used in the first iteration. We split this phase in a number of consecutive sub-phases: • Creating a initial set of guides for the prestack interpretation. • Picking traveltimes. • Quality control of the traveltimes. • Selection of representative traveltimes and calculation of the associated weights. Creating a set of guides. Guides are indicators for the interpreter suggesting where to look in the prestack unmigrated data for a certain event. They are also warnings for complicated situations as multiples, triplications and situations were no reliable indications for the nature of an event is available. The geologic guides are qualitative (e.g. presence of a fault) or quantitative (e.g. the depth of horizon A is 2500m). The geophysical guides are for example the presence of multiples or diffractions. They are derived from the unstacked or stacked data. For this dataset the following data were used: a set of (partial) stacks, time-and depth-migrated stacks and the cube of preprocessed prestack data. It allowed us to determine the zones where picking traveltimes directly in the unmigrated data could lead to incorrect traveltime information for the tomography. These zones are indicated in Figure 1 (Za and Zb, a zone with triplications and a series of unexplained events. Picking the first set of traveltimes Using the guides the picking of the traveltimes can start. This is done in the cube of unmigrated data. There is no preference for picking in a specific trace gather. This depends of the available guide. When it is a geological one the common offset gathers are most suited. Using a geophysical one the interpretation is done in the shotgathers or the common midpoint gathers. Whatever direction is chosen, one has to end 142

Garden footprint area and water use of gated communities in South Africa

Gated community homes in South Africa are popular amongst property buyers in urban environments such as cities and metropoles due to the  increased security and lifestyle improvements offered. Garden design and layout requirements are prescribed in architectural guidelines compiled by the homeowners associations of these communities. Garden footprint area in gated community homes is of importance to researchers and planners, because of the influence on water use. This study used a quantitative approach to evaluate the spatial data of garden footprint area as a percentage of total plot area for 1 813 gated community homes in different regions of South Africa. The research reviewed how garden footprint area is prescribed and how it is applied in gated community homes. The impact of garden footprint area on water use was also analysed. The results were compared to relevant information lifted from specific architectural design guidelines developed for each gated community. Data from 11 gated communities were analysed and the average garden footprint area was found to be 36% of the total plot area. Gated community homes with a garden area smaller than 100 m2 were found to have limited influence on monthly water consumption, while the water use of gated community homes with a larger garden footprint area increased proportionally with garden footprint area. The seasonal fluctuation of water use is illustrative of garden irrigation and other outdoor water use. The results provided useful input for incorporation in outdoor water use modelling of gated  community homes Keywords: garden irrigation household water consumption plot are

Role of hormone cofactors in the human papillomavirus-induced carcinogenesis of the uterine cervix

peer reviewedIf human papillomavirus (HPV) is necessary for the development of (pre)neoplastic lesions of the uterine cervix, it is not sufficient. Among the cofactors involved in the malignant transformation of cells infected by HPV, sex hormones may facilitate the cervical carcinogenesis by different mechanisms, including the induction of squamous metaplasia in the transformation zone of the cervix, interactions between steroid hormones and HPV gene expression and alterations of the local immune microenvironment

External quality assessment of malaria microscopy in the Democratic Republic of the Congo

<p>Abstract</p> <p>Background</p> <p>External quality assessments (EQA) are an alternative to cross-checking of blood slides in the quality control of malaria microscopy. This study reports the findings of an EQA of malaria microscopy in the Democratic Republic of the Congo (DRC).</p> <p>Methods</p> <p>After validation, an EQA slide panel and a questionnaire were delivered to diagnostic laboratories in four provinces of DRC. The panel included three samples for diagnosis (sample 1: <it>Plasmodium falciparum</it>, 177,000/μl, sample 2: <it>P. falciparum</it>, 2,500/μl, sample 3: no parasites seen), one didactic sample (Howell-Jolly bodies) and one sample for assessing the quality of staining. Participating laboratories were addressed and selected through the network of the National Tuberculosis Control Programme. Participants were asked to return the responses together with a stained thin and thick blood film for evaluation of Giemsa stain quality.</p> <p>Results</p> <p>Among 174 participants (response rate 95.1%), 26.2% scored samples 1, 2 and 3 correctly and 34.3%, 21.5% and 5.8% of participants reported major errors in one, two or three samples respectively. Major errors included reporting "no malaria" or "non-<it>falciparum </it>malaria" for <it>Plasmodium falciparum</it>-positive samples 1 and 2 (16.1% and 34.9% of participants respectively) and "<it>P. falciparum</it>" for <it>Plasmodium </it>negative sample 3 (24.0%). Howell-Jolly bodies (didactic sample) were not recognized by any of the participants but reported as "<it>P. falciparum</it>" by 16.7% of participants. With parasite density expressed according to the "plus system", 16.1% and 21.5% of participants scored one "+" different from the reference score for samples 1 and 2 respectively and 9.7% and 2.9% participants scored more than two "+" different. When expressed as counts of asexual parasites/μl, more than two-thirds of results were outside the mean ± 2SD reference values. The quality of the Giemsa stain was poor, with less than 20% slides complying with all criteria assessed. Only one quarter of participants purchase Giemsa stain from suppliers of documented reliability and half of participants use a buffered staining solution. One third of participants had participated in a formal training about malaria diagnosis, half of them earlier than 2007.</p> <p>Conclusion</p> <p>The present EQA revealed a poor quality of malaria microscopy in DRC.</p

O(d,d)-invariance in inhomogeneous string cosmologies with perfect fluid

In the first part of the present paper, we show that O(d,d)-invariance usually known in a homogeneous cosmological background written in terms of proper time can be extended to backgrounds depending on one or several coordinates (which may be any space-like or time-like coordinate(s)). In all cases, the presence of a perfect fluid is taken into account and the equivalent duality transformation in Einstein frame is explicitly given. In the second part, we present several concrete applications to some four-dimensional metrics, including inhomogeneous ones, which illustrate the different duality transformations discussed in the first part. Note that most of the dual solutions given here do not seem to be known in the literature.Comment: 25 pages, no figures, Latex. Accepted for publication in General Relativity and Gravitatio

Downregulation of CD94/NKG2A inhibitory receptors on CD8+ T cells in HIV infection is more pronounced in subjects with detected viral load than in their aviraemic counterparts

The CD94/NKG2A heterodimer is a natural killer receptor (NKR), which inhibits cell-mediated cytotoxicity upon interaction with MHC class I gene products. It is expressed by NK cells and by a small fraction of activated CD8+ T lymphocytes. Abnormal upregulation of the CD94/NKG2A inhibitory NKR on cytotoxic T cells (CTLs) could be responsible for a failure of immunosurveillance in cancer or HIV infection. In this study, CD94/NKG2A receptor expression on CD8+ T lymphocytes and NK cells was assessed in 46 HIV-1-infected patients (24 viraemic, 22 aviraemic) and 10 healthy volunteers. The percentage of CD8+ T lymphocytes expressing the CD94/NKG2A inhibitory heterodimer was very significantly decreased in HIV-1-infected patients in comparison with non-infected controls. Within the HIV infected patients, the proportion of CD8+ T lymphocytes and NK cells expressing CD94/NKG2A was higher in subjects with undetectable viral loads in comparison with their viraemic counterparts. No significant difference was detected in the proportion of CD8+ T lymphocytes expressing the activatory CD94/NKG2C heterodimer between the HIV-1 infected patients and the healthy donors, nor between the vireamic and avireamic HIV-1 infected patients. In conclusion, chronic stimulation with HIV antigens in viraemic patients leads to a decreased rather than increased CD94/NKG2A expression on CD8+ T lymphocytes and NK cells