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郑州激光治疗近视有用吗
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发布时间: 2025-06-02 12:21:04北京青年报社官方账号
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  郑州激光治疗近视有用吗   

After almost two years circling an ancient asteroid hundreds of millions of miles away, a NASA spacecraft this week will attempt to descend to the treacherous, boulder-packed surface and snatch a handful of rubble.The drama unfolds Tuesday as the U.S. takes its first crack at collecting asteroid samples for return to Earth, a feat accomplished so far only by Japan.Brimming with names inspired by Egyptian mythology, the Osiris-Rex mission is looking to bring back at least 2 ounces (60 grams) worth of asteroid Bennu, the biggest otherworldly haul from beyond the moon.The van-sized spacecraft is aiming for the relatively flat middle of a tennis court-sized crater named Nightingale — a spot comparable to a few parking places here on Earth. Boulders as big as buildings loom over the targeted touchdown zone.“So for some perspective, the next time you park your car in front of your house or in front of a coffee shop and walk inside, think about the challenge of navigating Osiris-Rex into one of these spots from 200 million miles away,” said NASA’s deputy project manager Mike Moreau.Once it drops out of its half-mile-high (0.75 kilometer-high) orbit around Bennu, the spacecraft will take a deliberate four hours to make it all the way down, to just above the surface.Then the action cranks up when Osiris-Rex’s 11-foot (3.4-meter) arm reaches out and touches Bennu. Contact should last five to 10 seconds, just long enough to shoot out pressurized nitrogen gas and suck up the churned dirt and gravel. Programmed in advance, the spacecraft will operate autonomously during the unprecedented touch-and-go maneuver. With an 18-minute lag in radio communication each way, ground controllers for spacecraft builder Lockheed Martin near Denver can’t intervene.If the first attempt doesn’t work, Osiris-Rex can try again. Any collected samples won’t reach Earth until 2023.While NASA has brought back comet dust and solar wind particles, it’s never attempted to sample one of the nearly 1 million known asteroids lurking in our solar system until now. Japan, meanwhile, expects to get samples from asteroid Ryugu in December — in the milligrams at most — 10 years after bringing back specks from asteroid Itokawa.Bennu is an asteroid picker’s paradise.The big, black, roundish, carbon-rich space rock — taller than New York’s Empire State Building — was around when our solar system was forming 4.5 billion years ago. Scientists consider it a time capsule full of pristine building blocks that could help explain how life formed on Earth and possibly elsewhere.“This is all about understanding our origins,” said the mission’s principal scientist, Dante Lauretta of the University of Arizona.There also are selfish reasons for getting to know Bennu better.The solar-orbiting asteroid, which swings by Earth every six years, could take aim at us late in the next century. NASA puts the odds of an impact at 1-in-2,700. The more scientists know about potentially menacing asteroids like Bennu, the safer Earth will be.When Osiris-Rex blasted off in 2016 on the more than 0 million mission, scientists envisioned sandy stretches at Bennu. So the spacecraft was designed to ingest small pebbles less than an inch (2 centimeters) across.Scientists were stunned to find massive rocks and chunky gravel all over the place when the spacecraft arrived in 2018. And pebbles were occasionally seen shooting off the asteroid, falling back and sometimes ricocheting off again in a cosmic game of ping-pong.With so much rough terrain, engineers scrambled to aim for a tighter spot than originally anticipated. Nightingale Crater, the prime target, appears to have the biggest abundance of fine grains, but boulders still abound, including one dubbed Mount Doom.Then COVID-19 struck.The team fell behind and bumped the second and final touch-and-go dress rehearsal for the spacecraft to August. That pushed the sample grab to October.“Returning a sample is hard,” said NASA’s science mission chief, Thomas Zurbuchen. “The COVID made it even harder.”Osiris-Rex has three bottles of nitrogen gas, which means it can touch down three times — no more.The spacecraft automatically will back away if it encounters unexpected hazards like big rocks that could cause it to tip over. And there’s a chance it will touch down safely, but fail to collect enough rubble.In either case, the spacecraft would return to orbit around Bennu and try again in January at another location.With the first try finally here, Lauretta is worried, nervous, excited “and confident we have done everything possible to ensure a safe sampling.”___The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content. 4807

  郑州激光治疗近视有用吗   

A white Arkansas man faces up to 20 years in prison after being found guilty in the beating of an African-American man during racially charged protests last summer in Charlottesville, Virginia.Jacob Scott Goodwin, 23, was among a group of attackers captured on widely shared cell phone video in the August 12 beating of DeAndre Harris in a parking garage during the Unite the Right rally.Goodwin was found guilty of malicious wounding by a Charlottesville Circuit Court jury Tuesday evening. He remains in the Albemarle-Charlottesville Regional Jail and will face sentencing on August 23.The charge carries a maximum sentence of 20 years in prison. The jury recommended a sentence of 10 years and a ,000 fine, according to prosecutor Nina-Alice Antony.Phone calls to Goodwin's attorney were not immediately returned.Goodwin was the first of four alleged attackers to face a trial in the beating of Harris. Jury selection is set to begin Wednesday in the trial of Alex Michael Ramos, 34, who also faces a malicious wounding charge for his involvement in the attack.Two other men, Daniel Borden, 18, and Tyler Watkins Davis, 49, have trial dates set for the summer.Vonzz Long, a friend of Harris', told CNN the two of them were part of a group of people staging counterprotests that day against neo-Nazis and white supremacists. He said they got into an argument with people from hate groups who threw things and shouted racial slurs at them, and he and Harris got separated during the ensuing chaos.When Long eventually found him, Harris was surrounded by neo-Nazis in the garage and being beaten bloody, he said.Harris had faced an misdemeanor assault charge after a white protester claimed he had struck him in the head with a flashlight moments before the parking garage beating. But a judge acquitted him of the charges in March.  1849

  郑州激光治疗近视有用吗   

A: Santa's lead flying reindeerB: wife trying to get rid of me before Christmas pic.twitter.com/Cvmha58rVM— Tim McGraw (@TheTimMcGraw) December 8, 2020 169

  

AMC Theaters is looking for ways to get moviegoers back into theaters. One way they are doing that is by offering private screening rooms for .Last week, AMC said they could be depleted of cash by the end of the year due to the coronavirus affecting attendance, so this is their effort to find creative solutions to its unprecedented financial problems.On its website, AMC said you could invite up to 20 friends to join you. Popcorn is extra, and the price to rent out a theatre can go up to 9 depending on what movie you select to watch.The rental option is available in most states except New York, Alaska, and Hawaii. 634

  

A woman accused of mailing poison to President Donald Trump sent six similar letters to prison officials in Texas, according to court documents obtained by Scripps station WKBW in Buffalo, New York.Pascale Ferrier was arrested Sunday on the Peace Bridge — the bridge over Lake Erie that connects the U.S. and Canada at Buffalo, New York. Pascale, who was reportedly in possession of a gun and a knife, was charged with threatening the President of the United States.Ferrier's arrest came a day after the FBI announced it was investigating a suspicious letter addressed to Trump that contained ricin, a poison found naturally in castor seeds.According to an arrest warrant obtained Tuesday, Ferrier's referred to Trump in her letter as "The Ugly Tyrant Clown," and called for him to resign."You ruin USA and lead them to disaster. I have US cousins, then I don't want the next 4 years with you as president. Give up and remove your application for this election," she allegedly wrote.Ferrier's letter also referred to a "special gift" included in the envelope."This gift is in this letter," she allegedly wrote. " If it doesn't work, I'll find better recipe for another poison, or I might use my gun when I'll be able to come. Enjoy! FREE REBEL SPIRIT."According to an affidavit, the letters found in Texas also included a powdery substance, references to trying "another recipe" and also included the signature "FREE REBEL SPIRIT." Fingerprints taken from the letters match Ferrier's prints on file, according to court paperwork.The Royal Canadian Mounted Police are also investigating the incident. Monday, CTV News in Canada reported that they conducted an operation in St-Hubert, which is south of Montreal, Quebec.Ferrier is due in Federal Court in downtown Buffalo on Tuesday afternoon. 1799

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