Mechanisms and effects of dry and wet Sahel epochs

<p>The Sahel is Northern African region between the equator and the Sahara desert. It is home to a belt of semi-arid grassland that stretches from the Atlantic and across the continent westward towards the Red Sea. The monsoon type rainfall season that occurs in this region is influenced by the way that moisture transport along this belt region combines along the Inter Tropical Convergence Zone (ITCZ). The Sahel is one of the most productive crop areas of Africa, and if the rains fail – it has long lasting implications for its community. Due to its  planetary location dry conditions pervade the Sahel for most of the year, with food production and livelihoods reliant on the summer monsoon rainy season between July and September. In this study we use (where available) up to 100 years of re-analysis records (GPCC rainfall, NCAR wind and HadiSST ocean data) together with an accurate signal decomposition approach (dominant frequency state analysis, DFSA). With this we assess how the teleconnection influence of the Pacific ENSO and the Atlantic dipole mechanisms influence the dry and wet Sahel rain conditions. The severe Sahelian drought of the 1980’s is shown to be a compounded sequence of drying dynamic effects that combined to occur suddenly over the span of 5-10 years. Our work indicates that dry and wet conditions appear to be related to land-air evaporation and condensation in the vicinity of the Sahel river catchments, with the land locked Lake Chad catchment having a particularly sensitive arid climate. Our latest finding’s help explain how the Atlantic and Pacific physical mechanism influence the Sahel monsoon and its extremes. With an assessment of agricultural data we also show how agricultural growth in the region is impacted by these factors. We present and discuss Africa dry and wet rainfall epoch forecasts over the next 30 years for Sahel based on stable and altered climate hysteresis scenarios.</p>

A point absorber wave energy converter with nonlinear hardening spring power-take-off systems in regular waves

Point absorber wave energy converter is one of the most effective wave energy harness devices. Most of the wave energy converters generate energy by oscillating the floating body. Usually, the power-take-off system is simplified as a linear spring and a linear damper. However, the narrow frequency bandwidth around a particular resonant frequency is not suitable for real vibrations applications. Thus, a nonlinear hardening spring and a linear damper are applied in the power-take-off system. The bandwidth of hardening mechanism is discussed. The dynamic model of wave energy converter is built in regular waves with time domain method. The results show that the nonlinear wave energy converter has higher conversion efficiency than the linear wave energy converter more than the natural frequency state. The conversion efficiency of the nonlinear wave energy converter in the low frequency state is closed to the linear converter. The amplitude of the incident wave, the damping of the nonlinear wave energy converter and the nonlinear parameter [Formula: see text] affect the energy capture performance of the wave energy converter.

STUDI ANALISIS UFR (UNDER FREQUENCY RELAY) PADA GARDU INDUK PESANGGARAN

The disruption of the electric power system due to overcurrent causes a trip to the 3rd generator of pesanggaran power plant . This causes a decrease in frequency due to the system losing its supply. Frequency interference can be detected automatically with UFR (Under Frequency Relay). The working principle of UFR is to compare the value of the system frequency and the value of the frequency setting. The comparison will determine how much load is released to balance the generator supply. This study analyzes UFR performance at Pesanggaran Substation by simulating a case of the generator being released so as to produce a decreased system frequency state. The method used is by comparing the ETAP simulation results and calculation results. The results of the comparison obtained the system recovery time when the conditions (gen1 tripped), (gen1 and gen2 tripped), and (gen1, gen2, and gen3 tripped), each is 1.171s; 4,531s; and 4,514s.

Profiling Multiscale Frequency State of Normal Phonocardiogram: Feasibility Study

Phonocardiogram (PCG) signals contain very important information regarding the heart condition. Recently, several automatic detection algorithms have been explored to profile the characteristics of heart sounds to aid in disease diagnosis. However, many of these methods has been demonstrated only on clean signals with limited test data and variety of PCG signals that can accurately provide information of diagnostic importance with higher sensitivity and specificity. In this work, we propose to characterize the multiscale frequency state of the normal PCG signals that can aid in accurate profiling of PCG to discriminate from pathological conditions.