permafrost). Of the remainder, the vast majority is groundwater, so that just 0.4 per cent of the world's total freshwater is available at the surface as lakes, soil moisture, air humidity, marshes, wetlands, rivers and biomass. And water is proving an increasingly critical component in agricultural activities. Earlier this month, the Chinese government declared an emergency for the first time ...

The efficient development of effective vaccines and therapeutics is perhaps the most challenging of the myriad promises of post-genomic biology. Fortunately, as the list of sequenced bacterial pathogens grows, so does the opportunity to use whole genome sequence as a potentially powerful tool in vaccine development. According to Rino Rappuoli, vice president of vaccine research at Chiron, genom...

could have worked. " The scientists hypothesise that interbreeding between our ancestral humans and early chimps created a third, infertile 'hybrid' species, the human equivalent of a mule, the infertile offspring of a horse and donkey. Though incapable of breeding among its own, the hybrid is believed to have survived by mating with its parent human or chimp species, before the two separated t...

Over-wintering monarch butterflies in the forests of central Mexico may be looking forward to more secure rest following an announcement by the Mexican government of a budget boost of $4.6 million per year to improve the conditions for the migrant butterflies and for the many often prominent human visitors, and to tackle illegal logging. Conservation officials said that the additional funds for...

previously inaccessible ocean as its territory. But Britain’s moves in the Antarctic are sure to anger many neighbouring countries in the region. The UK’s Antarctic submission reflects efforts to secure resources for the future as oil and gas reserves dwindle over the coming years. The substantial gas and oil reserves in the North Sea, on which the country has depended for more than 30 years, a...

In this paper, we derive the discrete-time model for the power-factor-correction (PFC) buck-boost converter in terms of a stroboscopic switching map. Fast-scale instability is analysed through a fold diagram, which exposes the periodicity of the operation as well as the locations of the critical phase angles of the line voltage at which instability begins to occur along a half-line cycle. The a...

This paper presents a small-scale prototype of a wind-photovoltaic hybrid system, having batteries as energy storage components. All devices are connected to a common dc-bus using appropriate power converters. The photovoltaic modules are connected through a dc-dc buck converter using Perturb and Observe Maximum Power Point Tracking control. The permanent magnet synchronous generator (wind gene...

A Double input DC to DC converter for low voltage energy sources applications is proposed in this paper. The proposed converter is buck-boost converter which can step up or step down the input voltage according to output voltage required at load end. The converter is able to boost up voltage of energy sources such as solar photovoltaic and wind energy system of relatively low voltage. The conve...

The paper focuses on a DC/DC converter that is used to adapt a varying output voltage from a solar panel to demands of an electrolyzer unit or battery charging purposes. The converter covers an input voltage span from 9 V to 24 V and has an output voltage of 12 V at a maximum current of 50 A. A modular topology of the converter is described along with a microcontroller control strategy. Finally...