Acoustic waves attenuation and velocity dispersion in fluid-filled porous media: theoretical and experimental investigations

New model of acoustic wave propagation in saturated porous media is developed. Like the Biot/Squirt flow (BISQ) theory it combines both the Biot and Squirt flow mechanisms. The novelty in this model is that the expression of average pore fluid pressure is independent of the characteristic squirt flow length introduced in the BISQ theory. Taking advantage of t he analytical relation between velocity (attenuation) and measurable rock physical parameters such as permeability, porosity, Pore fluid viscosity and compressibility, velocity and attenuation dispersion versus frequency is modelled for different permeability values: 1.25 md, 5 md, 10 md and 20 md. The results using the proposed model and the earlier BISQ theory show the same order of magnitude in attenuation and velocity dispersion versus frequency but reverse behaviour with respect to permeability change. An attempt to determine permeability using both theories on experimental data from highly permeable beach sands (unlithified) material shows good agreement with laboratory measured values. Ultrasonic data acquired on two different sets of sandstone samples are compared to velocity and attenuation prediction from the Biot/Squirt flow (BISQ) model and our newly proposed model. Our model better resolves measured velocity from the first set of sandstone samples. The attenuation however is highly underestimated by both models. In the second set of samples, the Gassmann's velocity is calculated from measured dry P- and S-wave velocities at different confining pressures and is compared to the result of low-frequency velocity prediction from the previous models. It was expected that velocity predicted by both models converges to the Gassmann's velocity at confining pressure high enough to suppress the squirt flow effect. Despite evidence (from the velocity vs. confining pressure curves) of the closure of microcracks that enhance the squirt flow effect the Gassmann's velocity was still much larger than other models prediction. We argue that evidence of clay inclusion in the sandstone matrix might be responsible for the poor resolution of attenuation in the former set of samples, and the misfit between velocities in the second set. Qualitative agreement was observed between velocity dispersion estimated from field experimental data and theoretical prediction using the reformulated BISQ model

Dynamics of germs responsible for acute bacterial meningitis in Burkina Faso in the last ten years (2005-2014)

The aim of this study was to analyze ten (10) years of epidemiological surveillance data of meningitis in Burkina Faso for high risk germs patterns identification in order to contribute to the strengthening of prevention strategies.A retrospective study of the past decade (2005- 2014) of cases of acute bacterial meningitis occurred in the thirteen health regions, collected through epidemiological surveillance data meningitis in Burkina Faso. From a total of 88 057 suspected cases of acute bacterial meningitis, we recorded 9134 deaths. From the laboratory confirmed cases, the identified germs were as follows: 56.79% of Neisseria meningitidis, 41.09% of Streptococcus pneumoniae and 2.13% of Haemophilus influenzae. Among the meningococcus isolated, we observed the following distribution: 23.11% of NmA, 58.84% of NmW and 18% of NmX.Mortality associated with acute bacterial meningitis remains still high in Burkina Faso despite the complete disappearance of NmA since 2012, after the conjugate vaccine A (MenAfriVac) has been introduced in this country. However the emergence of NmX, the reemergence of NmW and the persistence of high prevalence of Streptococcus pneumoniae are a major concern in the fight against meningitis in Burkina Faso. So, it is necessary, in addition to the strengthening of surveillance, diagnosis and case management to develop and make available and accessible a conjugate trivalent vaccine against NmA the NmX and NmW serogroups.Keywords: meningococcal meningitis, W and X serogroups, Streptococcus pneumoniae, MenAfriVa

Cause-specific childhood mortality in Africa and Asia : evidence from INDEPTH health and demographic surveillance system sites

Childhood mortality, particularly in the first 5 years of life, is a major global concern and the target of Millennium Development Goal 4. Although the majority of childhood deaths occur in Africa and Asia, these are also the regions where such deaths are least likely to be registered. The INDEPTH Network works to alleviate this problem by collating detailed individual data from defined Health and Demographic Surveillance sites. By registering deaths and carrying out verbal autopsies to determine cause of death across many such sites, using standardised methods, the Network seeks to generate population-based mortality statistics that are not otherwise available.; To present a description of cause-specific mortality rates and fractions over the first 15 years of life as documented by INDEPTH Network sites in sub-Saharan Africa and south-east Asia.; All childhood deaths at INDEPTH sites are routinely registered and followed up with verbal autopsy (VA) interviews. For this study, VA archives were transformed into the WHO 2012 VA standard format and processed using the InterVA-4 model to assign cause of death. Routine surveillance data also provided person-time denominators for mortality rates. Cause-specific mortality rates and cause-specific mortality fractions are presented according to WHO 2012 VA cause groups for neonatal, infant, 1-4 year and 5-14 year age groups.; A total of 28,751 childhood deaths were documented during 4,387,824 person-years over 18 sites. Infant mortality ranged from 11 to 78 per 1,000 live births, with under-5 mortality from 15 to 152 per 1,000 live births. Sites in Vietnam and Kenya accounted for the lowest and highest mortality rates reported.; Many children continue to die from relatively preventable causes, particularly in areas with high rates of malaria and HIV/AIDS. Neonatal mortality persists at relatively high, and perhaps sometimes under-documented, rates. External causes of death are a significant childhood problem in some settings