Rainfall monitoring based on commercial terrestrial microwave links is tested for the first time in Burkina Faso, in Sahelian West Africa. In collaboration with one national cellular phone operator, Telecel Faso, the attenuation on a 29 km long microwave link operating at 7 GHz was monitored at 1 s time rate for the monsoon season 2012. The time series of attenuation is transformed into rain rates and compared with rain gauge data. The method is successful in quantifying rainfall: 95% of the rainy days are detected. The correlation with the daily rain gauge series is 0.8, and the season bias is 6%. The correlation at the 5 min time step within each event is also high. These results demonstrate the potential interest of exploiting national and regional wireless telecommunication networks for monitoring rainfall in Africa, where operational rain gauge networks are degrading and the hydrometeorological risk increasing.

WHAT: Eighty-seven participants from 18 countries met to discuss the prospect for rainfall measurement and high-resolution mapping based on commercial microwave links in Africa. Experts from Europe and Israel provided training to African students, scientists, and meteorologists on this innovative method.

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We used a one-dimensional simulation program Solar Cell Capacitance Simulator in 1 Dimension (SCAPS-1D) to investigate Copper-Indium-Gallium-Diselenide-(CIGS-) based solar cells properties. Starting with a conventional ZnO-B/i-ZnO/CdS/CIGS structure, we simulated the parameters of current-voltage characteristics and showed how the absorber layer thickness, hole density, and band gap influence the short-circuit current density ( sc ), open-circuit voltage ( oc ), fill factor (FF), and efficiency of solar cell. Our simulation results showed that all electrical parameters are greatly affected by the absorber thickness (w) below 1000 nm, due to the increase of back-contact recombination and very poor absorption. Increasing hole density (p) or absorber band gap ( g ) improves oc and leads to high efficiency, which equals value of 16.1% when p = 10 16 cm −3 and = 1.2 eV. In order to reduce backcontact recombination, the effect of a very thin layer with high band gap inserted near the back contact and acting as electrons reflector, the so-called back-electron reflector (EBR), has been investigated. The performances of the solar cells are significantly improved, when ultrathin absorbers (w < 500 nm) are used; the corresponding gain of sc due to the EBR is 3 mA/cm 2 . Our results are in good agreement with those reported in the literature from experiments.

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This paper reports numerical investigation, using SCAPS-1D program, of the influence of Cu2ZnSnS4(the so-called CZTS) material features such as thickness, holes, and defects densities on the performances of ZnO:Al/i-ZnO/CdS/CZTS/Mo solar cells structure. We found that the electrical parameters are seriously affected, when the absorber thickness is lower than 600 nm, mainly due to recombination at CZTS/Molybdenum interface that causes the short-circuit current density loss of 3.6 mA/cm2. An additional source of recombination, inside the absorber layer, affects the short-circuit current density and produces a loss of about 2.1 mA/cm2above this range of absorber thickness. TheJ-Vcharacteristic shows that the performance of the device is also limited by a double diode behavior. This effect is reduced when the absorber layer is skinny. Our investigations showed that, for solar cells having a CZTS absorber layer of thin thickness and high-quality materials (defects density ~1015 cm−3), doping less than 1016 cm−3is especially beneficial. Such CZTS based solar cell devices could lead to conversion efficiencies higher than 15% and to improvement of about 100 mV on the open-circuit voltage value. Our results are in conformity with experimental reports existing in the literature.

Measurements of the specific heat of quasi one-dimensional conductors, (TaSe 4 ) 2 I and (NbSe 4 ) 3 I, between 0.1 and 8 K, are reported. Whereas no deviation from the P law occurs at low temperature for (NbSe 4 ) 3 I, we have measured two anomalies in (TaSe^I: an excess heat capacity with a peak at J= 1.75 K and a specific heat which follows a P 2 law below 0.4 K. We ascribe this excess heat capacity to the charge-density-wave phase excitations above their pinning frequency in the insulating Peierls state (rp = 263 K).PACS numbers: 65.40.Em, 63.20.Dj, 63.50, + x, 72.15.Nj It is now well known that many few-dimensional compounds are unstable and undergo a Peierls transition at a critical temperature, T ? } This instability is characterized by the opening of an electronic gap at the Fermi level, by a softening in the phonon spectrum at 0==2/c F with A: F the Fermi wave vector, and by a modulation of the electron charge density with the same periodicity called a charge-density wave (CDW). Below T ? the soft-phonon branch splits into two different modes 2 " 4 : an opticlike amplitude mode and an acousticlike phase mode. For ideal one-dimensional conductors, when Q is incommensurate with the lattice, the phase mode or phason exists at zero frequency and corresponds to the current provided by the sliding motion of the CDW as proposed by Frohlich. 5 In real systems, as shown by Lee, Rice, and Anderson, 3 the gapless character of the phase mode is destroyed through various mechanisms, especially impurity pinning.Recently, the interest has focused on several families of one-dimensional inorganic compounds undergoing Peierls transitions, namely, transition-metal trichalcogenides (NbSe 3 , TaS 3 ), blue bronze, and halogenated transition-metal tetrachalcogenide (TaSe^L 6 In these compounds an extra dc current appears when the applied electric field is higher than a threshold value (typically 0.1-1 V/cm). This extra conductivity has been ascribed to Frohlich-type conduction when the CDW becomes unpinned and moves through the crystal. 6 By complex-impednace measurements in the millimeter-wave range the pinned sliding model for NbSe 3 and TaS 3 is found to be overdamped with a spectral response in the megahertz-gigahertz range, 7 whereas for (TaSe^I this mode is underdamped, indicating a pinning frequency 8 of 35 GHz or 1.7 K. The frequency of this pinned mode is just in the right frequency range to allow for the detection of CDW excitations by thermodynamical measurements.Hereafter we report on heat-capacity measurements on (TaSe^I and, for comparison, on (NbSe 4 ) 3 I. These compounds consist of parallel MSe 4 chains well separated from one another by halogen atoms. In each MSe 4 chain the metal atom is located at the center of a rectangular antiprism of eight Se atoms. The d z2 band filling of the transition metal M can be varied according to the composition. This change in band filling leads to quite different structural and electrical properties: (TaSe 4 ) 2 I and (NbSe 4 )ioI 3 undergo a Peierls transition at T P ...

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