中山哪里看肛肠好(中山为什么会拉出血) (今日更新中)

WASHINGTON, June 15 (Xinhua) -- Using the deepest X-ray image ever taken, astronomers found the first direct evidence that massive black holes were common in the early universe, the U.S. National Aeronautics and Space Administration (NASA) said Wednesday in a statement.The discovery from NASA's Chandra X-ray Observatory shows that very young black holes grew more aggressively than previously thought, in tandem with the growth of their host galaxies.By pointing Chandra at a patch of sky for more than six weeks, astronomers obtained what is known as the Chandra Deep Field South (CDFS). When combined with very deep optical and infrared images from NASA's Hubble Space Telescope, the new Chandra data allowed astronomers to search for black holes in 200 distant galaxies, from when the universe was between about 800 million to 950 million years old."Until now, we had no idea what the black holes in these early galaxies were doing, or if they even existed," said Ezequiel Treister of the University of Hawaii, lead author of the study to appear Thursday in journal Nature. "Now we know they are there, and they are growing like gangbusters."The super-sized growth means that the black holes in the CDFS are less extreme versions of quasars -- very luminous, rare objects powered by material falling onto supermassive black holes. However, the sources in the CDFS are about a hundred times fainter and the black holes are about a thousand times less massive than the ones in quasars.The observations found that between 30 and 100 percent of the distant galaxies contain growing supermassive black holes. Extrapolating these results from the small observed field to the full sky, there are at least 30 million supermassive black holes in the early universe. This is a factor of 10,000 larger than the estimated number of quasars in the early universe."It appears we've found a whole new population of baby black holes," said co-author Kevin Schawinski of Yale University. "We think these babies will grow by a factor of about a hundred or a thousand, eventually becoming like the giant black holes we see today almost 13 billion years later."

BEIJING, July 11 (Xinhuanet) -- Gay and bisexual men account for around one in every three new cases of HIV in China, according to the latest official statistics released by the Ministry of Health.About 5 percent of the group - officially termed men who have sex with men, or MSM - are living with the virus, which is a rate that is 88 times higher than the national HIV prevalence rate of 0.057 percent.The problem is particularly acute in large urban centers, with the prevalence rate in some southwestern cities reaching almost 20 percent.However, the statistics also show that less than half of all gay and bisexual men have access to HIV screening, while about 15 percent of those who are infected are not receiving treatment."Cities are at the heart of China's development and progress and must remain at the forefront of its HIV response," said Michel Sidibe, executive director of the Joint United Nations Programme on HIV/AIDS (UNAIDS), during a workshop about the HIV impact on MSM on Saturday in Chengdu, capital of Southwest China's Sichuan province."Through bold action cities can lead the way to achieving the UNAIDS vision of zero new HIV infections, zero discrimination and zero AIDS-related deaths," he said, according to a UNAIDS news release. "We hope that over the next year, many more Chinese cities will implement MSM strategies."Almost 10 percent of gay and bisexual men in Chengdu are HIV-positive, according to Yang Xiaoguang, director of the city's health bureau. He agreed with Sidibe that cities have a crucial role to play in AIDS prevention and added: "By working to build a strong, multi-sector response in Chengdu, with meaningful community participation, we can scale-up coverage of prevention, treatment and care services among MSM and halt the spread of HIV."During the workshop, senior Chinese health officials, representatives from civil societies and other delegates discussed a new five-year strategy that increases coverage of HIV prevention and treatment for the MSM population and promotes the participation of community organizations.Government estimates put China's population of gay men at between 5 and 10 million, although Zhang Beichuan, a leading expert on HIV at Qingdao University, puts the number closer to 30 million.Tong Ge, coordinator of China's MSM Health Forum, noted the importance of ensuring strong cooperation between the government and society."By building on the experiences of cities like Chengdu, which already have well developed AIDS responses, we can help promote multi-sector collaboration on an equal, orderly basis and strengthen the response to HIV nationwide," he said. "The next step will be to implement similar strategies in other cities nationwide."Chengdu's new strategy underscores the critical role community organizations can play in reaching MSM and other populations at a higher risk of infection, experts at the workshop said.In 2009, China had an estimated 740,000 people living with HIV/AIDS, according to UNAIDS statistics.

BEIJING, June 28 (Xinhuanet) -- A truck-sized asteroid passed over the Atlantic Ocean within 7,500 miles of the Earth on Monday, according to NASA's Jet Propulsion Laboratory.The space rock, called asteroid 2011 MD, is the second space rock to zip extremely close to the Earth this year.The asteroid, with latest size estimates ranging from 16 to 66 feet (5 to 20 meters) wide, was discovered just last week on June 22, but there was never any risk of it impacting the Earth, NASA scientists said. That means asteroid 2011 MD would likely be too small to survive the fiery plunge through the Earth's atmosphere, let alone reach the surface, NASA scientists said. Asteroids this size can be expected to buzz Earth with close shaves about once every six years, they added.The space rock flew well below geosynchronous satellites, which orbit 22,236 miles (35,786 km) above the Earth, but well above the 220-mile (354-km) altitude of the International Space Station.There was little chance that the asteroid would hit a satellite because of the vastness of space and relatively small number of satellites, experts said.

WASHINGTON, Aug. 11 (Xinhua) -- The unique fossils of an adult plesiosaur and its unborn baby may provide the first evidence that these ancient animals gave live birth like mammals, according to a new study to be published Friday in the journal Science.The 78-million-year-old, 15.4-foot-long (4.7-meter-long) adult specimen is a Polycotylus latippinus, one of the giant, carnivorous, four-flippered reptiles that lived during the Mesozoic Era.Dr. Robin O'Keefe of Marshall University in West Virginia and Dr. Luis Chiappe, Dinosaur Institute director of the Natural History Museum in Los Angeles County, have determined that it is the fossil of an embryonic marine reptile contained within the fossil of its mother.The embryonic skeleton contained within shows much of the developing body, including ribs, 20 vertebrae, shoulders, hips, and paddle bones.O'Keefe and Chiappe have also determined that plesiosaurs were unique among aquatic reptiles in giving birth to a single, large offspring, and that they may have lived in social groups and engaged in parental care.Although live birth has been documented in several other groups of Mesozoic aquatic reptiles, no previous evidence of it has been found in the important order of plesiosaurs."Scientists have long known that the bodies of plesiosaurs were not well suited to climbing onto land and laying eggs in a nest," O'Keefe said."So the lack of evidence of live birth in plesiosaurs has been puzzling. This fossil documents live birth in plesiosaurs for the first time, and so finally resolves this mystery."

BEIJING, Sept. 6 (Xinhuanet) -- NASA will launch on Thursday twin lunar orbiters built to map the gravity of Earth's moon in unprecedented detail, media reported Tuesday.The twin lunar probes, Graili-A and Graili-B, will blast off from Florida's Cape Canaveral Air Force Station at 8:37 a.m. EDT and at 9:16 a.m. EDT respectively Thursday, according to NASA.The Grail twins will travel three to four months to get to the moon under a slower but more economical plan.Artist concept of GRAIL mission. Grail will fly twin spacecraft in tandem orbits around the moon for several months to measure its gravity field in unprecedented detail.The two spacecrafts will reach the moon around New Year's Day when they will begin to probe the moon's composition from the crust to the core, according to NASA.The data collected by the probes will be used to better understand the moon's evolution and formation, NASA scientists said.Researchers will also use the twin probes to pinpoint the best landing sites for future explorations.The mission, from start to finish, costs 496 million U.S. dollars. The two Grail probes will crash into the moon after its mission.

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