The Sanaga discharge at the Edea Catchment outlet (Cameroon): An example of hydrologic responses of a tropical rain‐fed river system to changes in precipitation and groundwater inputs and to flow regulation

The Sanaga River is one of Sub‐Saharan Africa's largest and greatly regulated rivers. Available flow data for this hydrosystem largely cover the pre‐ and post‐regulation periods. From comparisons between unregulated (hypothetical) and observed scenarios, it has been possible to separate and to quantify hydro‐climatic (groundwater + rainfall) change effects from anthropogenic impacts (especially dam‐related alterations). To appreciate shifts in the river regime, discontinuity detection tests and the IHA model were applied to discharge data series reflecting average and extreme flow conditions, respectively. Results obtained principally from the Hubert segmentation method reveal that a major discontinuity occurred in 1970–1971 separating a surplus phase between 1945–1946 and 1969–1970, and a deficient and much contrasted one, from 1971/1972. This implies that the Sanaga catchment is dominantly affected by hydro‐climatic changes. However, wide land cover/land use changes experienced here since 1988 have resulted in an increase in surface runoff. Additional quickflows linked to these changes may have partly compensated for the substantial decline in the dry season rainfall and groundwater inputs observed from this date. Although at the monthly scale, dam‐related impacts on average flows increase with stage of regulation, the seasonal variability of the river regime remains generally unaffected. A comparison of the IHA statistics, calculated from unregulated and observed streamflow data, show that hydrologic shifts occurring in maximum and minimum discharges are mostly significant from 1971/1972 and are mainly due to the action of dams. Minimum flows appear, however, widely impacted, thus reflecting the prime objective assigned to the existing reservoirs, constructed to supplement flows for hydroelectricity production during the dry season. Copyright © 2010 John Wiley & Sons, Ltd.     

Determinants of Domestic Water Use by Rural Households Without Access to Private Improved Water Sources in Benin: A Seemingly Unrelated Tobit Approach

This paper analyzes the determinants of domestic water use in rural areas. The focus is on households without access to private improved water sources. These households use either only free sources, only purchased sources or a combination of free and purchased sources. We also analyze households’ water use behaviors as a function of water availability by explicitly estimating domestic water use for both rainy and dry seasons. Using a Seemingly Unrelated Tobit approach to simultaneously account for the censored nature of water demand and the correlation of error terms between free and purchased water use equations, we find that purchased water demand is perfectly price inelastic due to water scarcity. The important determinants of water use are household size and composition, access to water sources, wealth and time required for fetching water. Nevertheless, the effects of these determinants vary between household types and seasons, and the policy implications of the findings are discussed.     

Diagnosis of hepatocellular carcinoma by needle puncture--aspiration and cytological test. The experience in Cameroon

Acute appendicitis is believed to be one of the commonest causes of the acute abdomen in tropical Africa. Negative appendicectomy rates are usually above 20%, which is now considered unacceptably high because of increased risk to patients and the availability of diagnostic facilities to aid clinical decision-making. Our negative appendicectomy rate over a 4-year retrospective period was 29.7% in males, and 47% in females. These reduced to 11% and 10%, respectively, after the introduction of laparoscopy for doubtful cases of acute abdominal pain.     

Hybrid Wireless Sensors Deployment Scheme with Connectivity and Coverage Maintaining in Wireless Sensor Networks

With the rapid growth of the internet of things (IoT), an impressive number of IoT’s application based on wireless sensor networks (WSNs) has been deployed in various domain. Due to its wide ranged applications, WSNs that have the capability to monitor a given sensing field, became the most used platform of IoT. Therefore, coverage becomes one of the most important challenge of WSNs. The search for better positions to assign to the sensors in order to control each point of an area of interest and the collection of data from sensors are major concerns in WSNs. This work addresses these problems by providing a hybrid approach that ensures sensors deployment on a grid for targets coverage while taking into account connectivity. The proposed sequential hybrid approach is based on three algorithms. The first places the sensors so as to all targets are covered. The second removes redundancies from the placement algorithm to reduce the number of sensors deployed. The third one, based on the genetic algorithm, aims to generate a connected graph which provide a minimal path that links deployed sensors and sink. Simulations and a comparative study were carried out to prove the relevance of the proposed method.

     

Semiconducting Nanowire‐Based Optoelectronic Fibers

The recent ability to integrate semiconductor‐based optoelectronic functionalities within thin fibers is opening intriguing opportunities for flexible electronics and advanced textiles. The scalable integration of high‐quality semiconducting devices within functional fibers however remains a challenge. It is difficult with current strategies to combine high light absorption, good microstructure and efficient electrical contact. The growth of semiconducting nanowires is a great tool to control crystal orientation and ensure a combination of light absorption and charge extraction for efficient photodetection. Thus far, however, leveraging the attributes of nanowires has remained seemingly incompatible with fiber materials, geometry, and processing approaches. Here, the integration of semiconducting nanowire‐based devices at the tip and along the length of polymer fibers is demonstrated for the first time. The scalable thermal drawing process is combined with a simple sonochemical treatment to grow nanowires out of electrically addressed amorphous selenium domains. First principles density‐functional theory calculations show that this approach enables to tailor the surface energy of crystal facets and favors nanowire growth along a preferred orientation, resulting in fiber‐integrated devices of unprecedented performance. This novel platform is exploited to demonstrate an all‐fiber‐integrated fluorescence imaging system, highlighting novel opportunities in sensing, advanced optical probes, and smart textiles.     

硅酸水垢及防治方法研究进展

在水资源再生利用过程中水中硅酸会沉淀在设备管道内壁或膜表面形成硅垢,影响设备的正常运行。硅垢的主要成分为无机硅酸盐和无定形SiO_2,是最难处理的水垢。抑制硅垢的方法有设备内添加阻垢剂和设备外预处理降低硅酸浓度等。设备内添加阻垢剂的方法又包括提高硅酸溶解度法和投加分散剂法;设备外预处理降低硅酸浓度的方法包括超滤膜法、反渗透膜法、絮凝法、离子交换法等。     

Estimating rural households' willingness to pay for water supply improvements: a Benin case study using a semi-nonparametric bivariate probit approach

This paper estimates households' willingness to pay (WTP) to improve rural water supply in Benin. Particular attention is given to the distribution of WTP, which is traditionally addressed using parametric assumptions. To avoid distributional assumptions, a semi-nonparametric bivariate probit approach is introduced. Results provide the first evidence that, in rural Benin, households wanting to improve water supply are willing to pay more than the current price. WTP for water supply is determined by wealth, education, and characteristics of existing and new water systems. Results indicate that a demand-driven management approach can contribute to water supply improvements and sustainability.