"We really have explored every area of efficiency, " said Mr Carter.

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Solar charge times are determined by the total area and efficiency of the solar cells -- the Spark uses high-efficiency monocristalline cells which will charge an iPad from about 10 hours of sunshine.

ENGADGET: Voltaic Spark Tablet Case powers your pad with the Sun's rays

The Olympics are not the only area in which efficiency is a concern.

ECONOMIST: A new democracy | The

In agriculture, creating a global productivity target would help countries focus on a key but neglected area: the efficiency and output of hundreds of millions of small farmers who live in poverty.

WSJ: Bill Gates on the Importance of Measurement

But he left government work because he always wanted to start a company and he saw energy--particularly energy efficiency--as an area likely to grow.

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The Pacers lead the league in defensive efficiency and align themselves in a way that limits shots from the painted area and the 3-point line.

WSJ: Knicks Should Consider Plan B

The book is a tour de force, showing, for example, how the potential contribution of biofuels can be approximated from just three numbers: the intensity of sunlight, the efficiency with which plants turn that sunlight into stored energy and the available land area in Britain.

ECONOMIST: What to do?

Any technique that improves our understanding of spinal tissue and improves the efficiency of determining whether potential treatments work will go a long way to improving research in this area.

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The Springboks outplayed England in all facets, dominating the contact area, rarely giving England's backs the opportunity to attack, while their line-out functioned with ruthless efficiency.

BBC: England 11-21 South Africa

Battery efficiency, lifespan and even safety could be vastly improved, the researchers believe, by increasing the surface area of the active materials that make up the battery electrodes.

FORBES: Magazine Article