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BEIJING, July 26 (Xinhuanet) -- Hong Kong scientists announced that they had determined the idea of time travel is impossible by proving nothing can travel faster than the speed of light.The finding is contained in a study done by a research team from Hong Kong University of Science and Technology. The study was published Monday in a scientific journal "Physical Review Letters" in the United States."The study, which showed that single photons also obey the speed limit c, confirms Einstein's causality, that is, an effect cannot occur before its cause," the university said on its website."By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon." said Professor Du Shengwang, who led the study.The possibility of time travel was raised 10 years ago when scientists discovered the optical pulses in some specific medium might propagate information in a faster-than-light speed."Our findings will also likely have potential applications by giving scientists a better picture on the transmission of quantum information." Du said.

WASHINGTON, Aug. 31 (Xinhua) -- Astronomers using NASA's Chandra X-ray Observatory discovered the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way, NASA announced Wednesday.Approximately 160 million light years from Earth, the pair is the nearest known such phenomenon.The black holes are located near the center of the spiral galaxy NGC 3393. Separated by only 490 light years, the black holes are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.Both of the supermassive black holes are heavily obscured by dust and gas, which makes them difficult to observe in optical light. Because X-rays are more energetic, they can penetrate this obscuring material. Chandra's X-ray spectra show clear signatures of a pair of supermassive black holes."If this galaxy weren't so close, we'd have no chance of separating the two black holes the way we have," said Pepi Fabbiano of the Harvard-Smithsonian Center for Astrophysics, who led the study that appeared Wednesday in on-line issue of the journal Nature. "Since this galaxy was right under our noses by cosmic standards, it makes us wonder how many of these black hole pairs we've been missing."Previous observations in X-rays and at other wavelengths indicated that a single supermassive black hole existed in the center of NGC 3393. However, a long look by Chandra allowed the researchers to detect and separate the dual black holes. Both black holes are actively growing and emitting X-rays as gas falls towards them and becomes hotter.When two equal-sized spiral galaxies merge, astronomers think it should result in the formation of a black hole pair and a galaxy with a disrupted appearance and intense star formation. A well-known example is the pair of supermassive black holes in NGC 6240, which is located about 330 million light years from Earth.However, NGC 3393 is a well-organized spiral galaxy, and its central bulge is dominated by old stars. These are unusual properties for a galaxy containing a pair of black holes.

CHANGSHA, July 17 (Xinhua) -- Chinese State Councilor Liu Yandong has called for more communications in language and culture among the people in China and foreign countries.Liu made the remarks during a meeting with the contestants of the 10th "Chinese Bridge" competition, an international Chinese proficiency competition for foreign college students, which opened Saturday in Changsha, capital of central Hunan Province.The "Chinese Bridge" competition has attracted over 100,000 college students from more than 70 countries over the past ten years, and contestants have improved their Chinese language, experienced the Chinese culture and established deep friendship with others during the competition, Liu said.She said that language is a tool for cultural communications, and linguistic learning and exchanges can promote the mankind's civilization and progress in a broader reach."The Chinese government always encourages the public, especially the youths, to learn foreign languages, and through the learning, they are enlightened on the diversified cultures around the world," she said."This also helps promote the good-will exchanges and cooperation among the Chinese and foreign peoples," she added.Liu said the Chinese government is also making efforts to meet the needs of foreign people to learn the Chinese language. She called on foreign young students to improve their Chinese proficiency and to use the Chinese language as a bridge to fell a real China in a comprehensive way.She expressed her hope that the foreign students will spread the good will and sincerity of the Chinese people to other parts of the world, in order to promote the joint efforts for the peace and prosperity of the world.

BEIJING, June 3 (Xinhua) -- Google lacked evidence to support its accusations that Chinese hackers are behind the alleged cyber attacks on hundreds of its email accounts and the timing to make such accusations is evil-intentioned, Chinese experts said on Friday."Google's accusation is neither serious nor credible as it has not published any evidence that shows the hackers are from China," said Dai Yiqi, a cyber security expert with Tsinghua University.Eric Grosse, engineering director of Google's Security Team wrote on the company blog Wednesday that unidentified hacker attacks likely originated from the eastern Chinese city of Jinan, tried to collect user passwords of the Gmail accounts of hundreds of users, including senior U.S. government officials, Chinese "human rights activists" and journalists.A report released in 2009 by the United States-China Economic and Security Review Commission, an organization created by the U.S. Congress, claimed that Jinan is the home of a Chinese military reconnaissance office.An anonymous cyber security expert believes, despite Google not referring to the Chinese government in the latest attack claim, the company is targeting the Chinese government by listing the victims of the attacks as those whom only the Chinese government are interested in."Both their intentions and the timing of the accusation are dubious," Dai said.Google's accusation followed on the heel of the reported Pentagon's first formal cyber strategy. The Wall Street Journal reported Tuesday that the Pentagon concluded that computer sabotage coming from another country can count as an act of war and the United States may respond by using traditional military force.Li Shuisheng, a research fellow with a top military science academy of the People's Liberation Army, believes there are political motives behind Google's accusation.Google may well have attempted to instigate a new round of the cyber row between China and the United States, Li said.Wednesday's accusation by Google came more than a year after the company allegedly uncovered a cyber attack on its systems that it said it traced to China.In January, 2010, Google said it had been attacked by hackers supported by the Chinese government, and later announced to withdraw from Chinese mainland. The row ended up with Google redirecting Chinese mainland users to a site in Hong Kong.In such cyber attacks, it is easy to locate the IP address of hackers but hard to tell where the hackers actually are, said Dai."Hackers usually launch attacks by camouflaging their own IP addresses or controlling computers of others. Therefore, we can hardly tell the location of the hacker unless we have sufficient evidence," he said.China is one of the leading targets of cyber attacks. It has the world's largest number of computers infected with bot, a type of malware which allows a cyber attacker to gain control over the affected computer.About 13 percent of the world's computers infected with bot are in China."Without cooperation between governments, absolute security cannot be guaranteed in cyber community," said Li , adding only cooperation can ensure safe information exchange.

WASHINGTON, June 6 (Xinhua) -- The tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures within the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase, according to a new climate study by Stanford University scientists. The results will be published later this month in the journal Climatic Change.In the study, the Stanford team concluded that many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades. Middle latitudes of Europe, China and North America -- including the United States -- are likely to undergo extreme summer temperature shifts within 60 years, the researchers found."According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," said the study's lead author, Noah Diffenbaugh, an assistant professor of environmental Earth system science and fellow at the Woods Institute for the Environment at Stanford. The study is co-authored by Stanford research assistant Martin Scherer."When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" Diffenbaugh said. " That got us thinking -- at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?"To determine the seasonal impact of global warming in coming decades, Diffenbaugh and Scherer analyzed more than 50 climate model experiments -- including computer simulations of the 21st century when global greenhouse gas concentrations are expected to increase, and simulations of the 20th century that accurately " predicted" the Earth's climate during the last 50 years. The analysis revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years."We also analyzed historical data from weather stations around the world to see if the projected emergence of unprecedented heat had already begun," Diffenbaugh said. "It turns out that when we look back in time using temperature records, we find that this extreme heat emergence is occurring now, and that climate models represent the historical patterns remarkably well."According to both the climate model analysis and the historical weather data, the tropics are heating up the fastest. "We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the authors wrote.Tropical regions may see the most dramatic changes first, but wide swaths of North America, China and Mediterranean Europe are also likely to enter into a new heat regime by 2070, according to the study.This dramatic shift in seasonal temperatures could have severe consequences for human health, agricultural production and ecosystem productivity, Diffenbaugh said. As an example, he pointed to record heat waves in Europe in 2003 that killed 40,000 people. He also cited studies showing that projected increases in summer temperatures in the Midwestern United States could reduce the harvest of staples, such as corn and soybeans, by more than 30 percent.

来源：资阳报