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LOS ANGELES, May 1 (Xinhua) -- Middle-aged adults who sleep too less or too much may be more likely to suffer cognitive decline, a new study suggests.According to the study, less than six hours of sleep each night is considered too little and more than eight hours as too much for middle-aged adults.The study, conducted by researchers at University College London Medical School, was published May 1 in the American medical journal Sleep.The researchers conducted the study in two periods -- the 1997- 1999 period and the 2003-2004 period. The participants were asked how many hours they slept on an average week night, and were asked the same question in 2003-2004 after an average 5.4 years of follow-up.The researchers compared those who reported changes in their sleep patterns with people whose sleep duration stayed the same over the course of the study.In the follow-up, each individual was given a battery of standard tests to assess his or her memory, reasoning, vocabulary, global cognitive status and verbal fluency.The study findings show that women who slept seven hours per night had the highest score for every cognitive measure, followed by those who had six hours of sleep. For men, cognitive function was similar for those who reported sleeping six, seven or eight hours.However, less than six hours of sleep -- or more than eight hours -- were associated with lower scores."Sleep provides the body with its daily need for physiological restitution and recovery," explained Jane Ferrie, a senior research fellow in the department of epidemiology and public health at the school. "While seven hours a night appears to be optimal for the majority of human beings, many people can function perfectly well on regular sleep of less or more hours."However, since most research has focused on the effects of sleep deprivation on biological systems, it is not yet fully understood why seven hours is optimal -- or why long sleeping appears to be detrimental, Ferrie said."Chronic short sleep produces hormones and chemicals in the body which increase the risk of developing heart disease and strokes, and other conditions like high blood pressure and cholesterol, diabetes and obesity," she added.

PARIS, May 20 (Xinhua) -- Heavy-load launcher Ariane 5, carrying two communication satellites GSAT-8 and ST-2, lifted off at around 22:38 p.m. Paris time (GMT 2038) on Friday from Europe' s Spaceport in French Guiana.Built by Japan's Mitsubishi Electric Company, ST-2 will offer Ku-and C-band relay services across the Middle East, Central Asia, India and Southeast Asia to the ST-2 Satellite Ventures joint company of Singapore Telecommunications Ltd (SingTel) and Taiwan' s Chunghwa Telecom Company Ltd..With a weight around 5.1 tons at launch, ST-2 was separated first around 27 minutes after the lift-off. It has a designed life of 15 years and will function at 88 degree East.The lighter passenger GSAT-8, built by the Indian Space Research Organization (ISRO), will serve to augment India's Ku- band relay capabilities and offer aircraft navigation assistance over Indian airspace and adjoining areas with its two-channel GAGAN system.GSAT-8 was expected to be ejected off around 31 minutes into the flight and will be orbited at 55 degree East. Weighed about 3. 1 tons, it has a designed life span of at least 12 years.Arianespace started its 2011 busy year for heavy-lift Ariane 5 with the milestone launch of Europe's second Automated Transfer Vehicle (ATV) on February 16.The next launch of Ariane 5 planned to lift off two TV broadcast and telecommunications relay satellites: BSAT-3c/JCSAT- 110R for Japan's Broadcasting Satellite System Corporation (B-SAT) and SKY Perfect JSAT Corporation, and ASTRA 1N for Luxemburg-based SES company.

LUQA, Malta, Feb. 28 (Xinhua) -- Four chartered planes of China Eastern Airlines left Malta Monday, taking home 1,115 Chinese nationals evacuated from Libya. The forth Airbus A340 plane with 275 evacuees on board took off from the Malta International Airport at about 08:40 p.m. local time (1940GMT), bringing the total number of Chinese nationals back home from Malta to 2,223.The flight CES 266 with 275 Chinese nationals on board flew to Beijing while the other three will land in Shanghai, according to Chinese Embassy in Malta.Three chartered flights are expected on Tuesday, the embassy said.In the past 48 hours, three chartered cruise ship with 4,800 Chinese evacuees have reached Valletta, capital of Malta.