BOSTON (Reuters) - Eleven robots faced off in a Massachusetts field on Wednesday, showing off their ability to independently track down objects in a hunt for $1.5 million in prize money at a NASA-sponsored contest aimed at speeding technological development.

In the first day of a three-day event, robots designed by teams from the United States, Canada and Estonia set out from a platform in a 2-acre (0.8 hectare) park at Worcester Polytechnic Institute in Worcester, Massachusetts, to search among rolling hills, rocks, trees and a gazebo to find geologic samples.

They operated without human control, with the goal of encouraging advancements in autonomous navigation and robotics technologies, NASA officials said.

"Improving this technology will be a huge boon, not just to NASA and space exploration, but also for countless applications here on Earth," including industrial purposes, Sam Ortega, program manager of Centennial Challenges, said in a statement.

The Centennial Challenges program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama, is part of the agency's Space Technology Mission Directorate, which develops hardware for future missions.

Robots in the contest will be required to retrieve samples in a range of shapes and sizes, from shoe-box-like forms to objects resembling tennis balls. Prizes range from $100,000 to $1.5 million, depending on the complexity of the samples retrieved.

Organizers chose the park setting to provide real-world challenges to the robots.

At last year's event, also held at Worcester Polytechnic, no prize money was awarded because the one robot that qualified for the contest failed to collect the required samples in the allotted time.

Robots entered in the contest can weigh no more than 80 kilograms (176 pounds) and measure up to 1.5 meters (about 5 feet) square.

The program caters mostly to citizen inventors, but also small businesses and universities that have developed robots, Ortega said. Cash prizes can be awarded to U.S. citizens only, he said, but the non-monetary "guts and glory" reward remained a strong motivator for entrants, he added.

While NASA does not claim any right to the intellectual property of the winning robots it encourages winners to start businesses, for example the agency would like access to it as part of the competition, he said.

Technological innovations that emerge through the contest could help NASA designers overcome challenges in creating robots used in five to 10 years, Ortega said.

(Editing by Scott Malone and Carol Bishopric)

There is no sign that the North Korean regime is in danger or that U.S. President Barack Obama and Chinese President Xi Jinping will discuss that possibility when they meet this week in California. Any such talk would alarm North Korea if word got out.

But in China, talk of a North Korean collapse is no longer the taboo subject it once was. Academics are increasingly willing to discuss it and a former top U.S. admiral said he has detected, during informal meetings, a willingness of Chinese officials to consider such discussions.

That reflects internal debate in China and dismay about North Korean brinkmanship in the aftermath of rocket and nuclear tests this winter that defied China, which supplies the North with crucial food, energy and diplomatic support.

Young North Korean leader Kim Jong Un appears to have consolidated control since taking power a year-and-a-half ago, and the spike in tension that followed its February nuclear test has eased in recent weeks. But there's a perennial threat of fighting with South Korea on one of the world's most militarized frontiers. China would want to avoid any conflict that could draw in its forces from the North, and U.S. forces from South Korea, as during the 1950-53 Korean War. Both powers would be concerned about the fate of North Korea's arsenal of chemical weapons, missiles and nuclear weapons and facilities.

But China also has reason to fear a North Korean collapse. That could trigger an exodus of hungry refugees across its border and lead to a reunified Korea allied with the United States, hosting American troops on China's doorstep.

Analysts say that until Chinese leaders decide among themselves what kind of outcome they are prepared to accept on the Korean Peninsula, they won't discuss the subject with U.S. officials. Still, they see some changes in China's attitude.

William Fallon, a former chief of U.S. Pacific Command, said the U.S. and China would have a shared interest in working together on North Korea and discussing issues such as securing its nuclear weapons. He said that in unofficial meetings in China this year with former and current Chinese government and military officials, he raised that possibility in broad terms and detected a willingness to consider it.

"I certainly suggested, and I know others have officially and formally suggested that it's about time we sat down to talk because we have common interest here," Fallon said. "I think that idea is not being rejected. The heads are nodding and they are considering it. I would expect that this would move forward, carefully."

Such cooperation would require Beijing and Washington overcoming deep, mutual suspicions that characterize their relations as China's economic and military power grows and the U.S. looks to boost its profile and long-established presence in Asia.

But China is taking a tougher stance on North Korea, as the U.S. hoped it would. It has supported tighter U.N. sanctions in response to the February nuclear test and stepped up border inspections. Most notably, a leading Chinese state bank shut accounts of North Korea's Foreign Trade Bank, its main foreign exchange institution.

Two weeks ago, China hosted a top North Korean envoy, a visit that Brookings Institution scholar Cheng Li says was expedited in advance of the U.S.-China summit that starts Friday. The North has since adopted a less confrontational stance and declared a willingness to return to the negotiating table.

But the U.S. sees that as little progress by North Korea, noting that the day after Vice Marshal Choe Ryong returned home, Pyongyang repudiated the goal of denuclearization a U.S. prerequisite for restarting long-stalled aid-for-disarmament negotiations.

While China is speaking out more against the North's nuclear ambitions, it is not taking steps that could hasten the end of the Kim regime, such as cutting supplies.

"Any chaos or armed conflict on the Korean Peninsula would have a major impact on China's national security interests. We have to keep that in mind all the time," China's ambassador to the U.S., Cui Tiankai, told Foreign Policy magazine.

While the more critical recent tone of Chinese scholars and their willingness to discuss once-forbidden issues like reunification is probably not the position of China's leaders, it reflects the government's frustrations with North Korea and could be intended to send a message for it not to push China too far, said former senior State Department official Evans Revere.

China's own strategic interests have been affected by Pyongyang's recent threats of pre-emptive nuclear strikes against the U.S. and its allies. The U.S. scaled up military exercises with South Korea staging flights of nuclear-capable B-52 and B-2 bombers and boosting its missile defenses in China's backyard.

"The new Chinese leadership has been alarmed by how quickly North Korea destabilized the entire region with its threats," said John Park, a Northeast Asia expert at the Massachusetts Institute of Technology. "It's presented them with a strategic dilemma."

At unofficial talks on Northeast Asian security held in Germany last week, government-linked Chinese academics signaled that Beijing's long-held interest in maintaining stability at all costs in North Korea is shifting, and it is putting increasing emphasis on denuclearization, said Frank Jannuzi of Amnesty International USA, who attended the conference.

Yet the prospects for diplomacy remain bleak, if Pyongyang demands to be treated as a nuclear power, and Washington insists on concrete signs of the North's willingness to disarm before international negotiations can restart.

"China feels they've done their part by convincing North Korea to return to dialogue and now it's up to the U.S. and South Korea to do their part and welcome them back," said Jannuzi, a former Asia policy adviser to then Sen. John Kerry, now Washington's top diplomat. "They feel like the ball is in our court."

____

Associated Press writer Charles Hutzler in Beijing contributed to this report

SEATTLE (Reuters) - A former Microsoft executive plans to create the first U.S. national marijuana brand, with cannabis he hopes to eventually import legally from Mexico, and said he was kicking off his business by acquiring medical pot dispensaries in three U.S. states.

Jamen Shively, a former Microsoft corporate strategy manager, said he envisions his Seattle-based enterprise becoming the leader in both recreational and medical cannabis - much like Starbucks is the dominant name in coffee, he said.

Shively, 45, whose six years at Microsoft ended in 2009, said he was soliciting investors for $10 million in start-up money.

The use, sale and possession of marijuana remains illegal in the United States under federal law. Two U.S. states have, however, legalized recreational marijuana use and are among 18 states that allow it for medical use.

"It's a giant market in search of a brand," Shively said of the marijuana industry. "We would be happy if we get 40 percent of it worldwide."

A 2005 United Nations report estimated the global marijuana trade to be valued at $142 billion. http://www.unodc.org/pdf/WDR_2005/volume_1_web.pdf

Washington state and Colorado became the first two U.S. states to legalize recreational marijuana when voters approved legalization in November.

Shively laid out his plans, along with his vision for a future in which marijuana will be imported from Mexico, at a Thursday news conference in downtown Seattle.

Joining him was former Mexican President Vicente Fox, a longtime Shively acquaintance who has been an advocate of decriminalizing marijuana. Fox said he was there to show his support for Shively's company but has no financial stake in it.

"What a difference it makes to have Jamen here sitting at my side instead of Chapo Guzman," said Fox, referring to the fact he would rather see Shively selling marijuana legally than the Mexican drug kingpin selling it illegally. "This is the story that has begun to be written here."

Shively told Reuters he hoped Fox would serve an advisory role in his enterprise, dubbed Diego Pellicer after Shively's hemp-producing great grandfather.

The sale of cannabis or marijuana remains illegal in much of the world although countries mainly in Europe and the Americas have decriminalized the possession of small quantities of it. A larger number of countries have decriminalized or legalized cannabis for medical use.

SKEPTICISM

Shively acknowledges that his business plans conflict with U.S. federal law and are complicated by regulations in both Washington state and Colorado. He said he is interested in buying dispensaries that comply with local and state rules and are less likely to attract the scrutiny of authorities.

"If they want to come talk to me, I'll be delighted to meet with them," he said of federal officials. "I'll tell them everything that we're doing and show them all our books."

Washington state's marijuana consultant, Mark Kleiman, said he was skeptical of Shively's plans, and feared that the businessman is seeking to profit off others' addiction.

"It's very hard for me to understand why anybody seriously interested in being in the marijuana business, which after all is against the federal law, would so publicly announce his conspiracy to break that law," said Kleiman, a professor of public policy at the University of California, Los Angeles.

Emily Langlie, spokeswoman for the U.S. Attorney's Office in Seattle, referred questions to the Department of Justice headquarters. Department officials did not immediately return calls seeking comment.

Washington state Representative Reuven Carlyle, a Seattle Democrat, sees promise in Shively's initiative. Any industry emerging from the shadows will inevitably undergo consolidation - and thereby simplify the task of regulators, he said.

"The fact that an entrepreneur is publicly pushing the envelope around a branding and value-based pricing opportunity, I would say that's in the water in Seattle," said Carlyle, chairman of the House Finance Committee. "That's in our DNA ... We could have predicted that as much as the rain."

Shively said he has already acquired the rights to the Northwest Patient Resource Center, a medical marijuana operation that includes two Seattle store fronts. He added that he was close to acquiring another dispensary in Colorado, as well as two more each in Washington state and California, with the owners given the option to retain a stake in their businesses.

"We've created the first risk-mitigated vehicles for investing directly in this business opportunity," he said.

Shively said he ultimately plans to create separate medical and recreational-use marijuana brands. Shively said he also plans to launch a study of the effectiveness of concentrated cannabis oil in the treatment of cancer and other illnesses.

(Editing by Cynthia Johnston and Andrew Hay)

BRUSSELS/PARIS (Reuters) - Growing concern in European capitals about aggressive tax avoidance by high-profile corporations such as Amazon, Google and Apple looks set to steal the agenda of a European Union summit in Brussels on Wednesday.

The summit was originally called to discuss energy policy and tax coordination, but press reports in Britain, France and the United States exposing how little tax major international companies have been paying by carefully structuring their European operations has forced the issue up the agenda.

France and Britain in particular have grown concerned by the sheer scale of the legal tax schemes, with a U.S. investigation revealing on Monday that Apple Inchad paid just 2 percent tax on $74 billion in overseas income, largely by exploiting a loophole in Ireland's tax code.

That followed reports that the British unit of Amazonpaid just $3.7 million tax on 2012 sales of $6.5 billion, and similar revelations concerning Google'sand Starbucks'sUK operations.

In all, officials have said that tax avoidance and evasion costs the EU around 1 trillion euros a year.

"A lot of these revenues (from the digital economy) are not getting taxed," said a French diplomat briefing reporters in Paris ahead of the EU summit. "We need to find a way of bringing home the tax on these activities."

Officials said French President Francois Hollande could raise the issue with the EU's 27 leaders, although it was unclear what agreement could be reached with little advanced preparation and just four hours of talks scheduled.

A draft of the summit's declaration, which is agreed in advance but can be changed, set out nine specific proposals for strengthening tax policy and coordination, including fighting tax avoidance schemes and the process of routing profits abroad.

"Work will be carried forward as regards the Commission's recommendations on aggressive tax planning and profit shifting," a draft seen by Reuters read.

"The Commission intends to present a proposal before the end of the year for the revision of the 'parent/subsidiary' directive, and is reviewing the anti-abuse provisions in relevant EU legislation."

NAME NO NAMES

But officials played down the possibility of immediate steps to close tax loopholes or any 'naming and shaming' of companies in the final summit declaration, saying it was primarily up to EU member states to craft the necessary legislation.

"We agree that companies shouldn't be able to avoid tax by pursuing aggressive tax avoidance schemes," said an EU official involved in handling preparations for the summit.

"But while companies may be using loopholes to pay as little tax as possible, the truth is it's a national issue. It's up to the relevant member states to change their tax codes and tighten the net."

The official said the most likely outcome from the talks was tougher language on strengthening bilateral tax treaties and bolstering so-called "anti-abuse" rules in national legislation.

"I can see the issue hijacking this summit, but the fact is there are recommendations out there already and it's up to countries to explore them," he said, referring to recommendations the Commission made last December on tackling aggressive tax planning and the erosion of the tax base.

France has already shown its willingness to take on major U.S. companies. In 2011, French authorities raided Google in an investigation of whether its Paris office does sales work. The company was asked to pay 1.7 billion euros in back taxes.

A similar issue has arisen with how Google operates in Britain, with questions raised about whether its sales staff are based abroad or actually in the country.

Google has said it follows tax rules everywhere it operates and that references to selling in job ads reflect the fact Google likes to hire people with a sales background.

In a briefing ahead of the Wednesday's gathering, a senior EU diplomat sidestepped suggestions that EU leaders were looking to take on specific companies, but said the issue was serious.

(Writing by Luke Baker; additional reporting by Adrian Croft in Brussels and Mark John in Paris)

His visit to the ship on Sunday comes amid nagging questions about the cost and viability of the roughly $34 billion program and whether the Pentagon's plan to buy as many as 52 of the vessels should be chopped by as much as half because of budget constraints.

Docked at Changi Naval Base, the Freedom has been participating in naval exercises with countries in the region, and going through regular maintenance and logistical checks as part of an effort to work through any problems in its maiden mission.

Hagel is the first Pentagon chief to step aboard a littoral combat ship that has deployed, and this was his first visit to any ship as secretary. Former Defense Secretary Robert Gates toured one of the vessels when it was in development at Naval Station Mayport in Florida.

On board the warship, Hagel met with crew members, starting on the deck, where a Black Hawk helicopter stood ready to go, and moving to the bridge and then the compact operations center, with its array of computer stations and displays. He also watched as sailors in a rigid hull inflatable boat demonstrated a launch and landing, easily sliding up into the docking area then returning out in to the Singapore Strait.

The USS Freedom, with its crew of about 90 sailors, arrived in Singapore on April 18, for the first ever overseas deployment of an LCS.

Swift and agile, the smaller ships are designed to operate in littoral waters, which are more shallow and close to shore. Dwarfed by the Navy's larger aircraft carriers and destroyers, the LCS ships give the U.S. the ability to work better with navies from Asian nations such as Singapore, Malaysia, Brunei and Thailand that use smaller vessels to patrol the seas or battle piracy. The U.S. Navy's larger ships are often too big to pull into some ports in the region.

With a maximum speed of more than 40 knots compared to the Navy's larger destroyers and cruisers which travel at about 30 knots the littoral combat ships are about the size of a Coast Guard cutter. The USS Freedom is a bit longer that a football field.

The ship development program, however, has been fraught with cost hikes, design and construction problems and worries that plans to make two versions of the ship are pricey and may not be necessary.

But Lt. Cmdr. Clay Doss told reporters traveling with Hagel that recent maintenance issues are part of the process any vessel goes through when programs are beginning. It's not unusual, he said, for a ship to experience growing pains that have to be worked out during its first deployment.

Doss said the Freedom is scheduled to leave Singapore in December and the second LCS will arrive in August 2014. In mid-2015 the navy expects to have two of the ships in Singapore and the region at the same time.

Hagel is in Singapore to attend the Shangri-La Dialogue security conference as part of a weeklong trip that will also take him to Brussels for a meeting of NATO defense ministers.

According to a Congressional Research Service report issued about a week ago on the program, the Navy plans to buy 52 ships. So far, the U.S. has bought 12, but plans to buy four this year have been complicated by the automatic budget cuts, known at the sequester. The proposed 2014 budget requests about $1.8 billion for four more.

CRS said there are "concerns over the ships' ability to withstand battle damage, and concerns over whether the ships are sufficiently armed and will be able to perform their stated missions effectively."

The report concluded, however, that the LCS is still the most economical way to meet the mission needs of the Navy. And it said that some of the design and construction issues have been resolved during the normal course of development.

The Navy is buying two versions of the ship, the Freedom and the Independence, and they are designed to be able to be able to switch out various packages of equipment in order to carry out particular missions, such as surface and anti-submarine warfare and mine countermeasures.

The Freedom version is being built by Lockheed Martin with Marinette Marine in Marinette, Wis., and the larger Independence version is being built by General Dynamics Austal USA in Mobile, Ala.

"Black Bodies in Propaganda: The Art of the War Poster," opens Sunday and continues until March 2 at the University of Pennsylvania Museum of Archaeology and Anthropology. Lectures, film screenings and other programming will be rolled out over the course of the exhibit's run.

The exhibit's 33 posters, dating from the Civil War to both World Wars and the African independence movements, are part of the personal collection of Tukufu Zuberi, a Penn professor of sociology and African studies and a host of the PBS series "History Detectives."

Zuberi began his collection in 2005 and owns 48 posters in all. There are five he's seeking to complete his collection, but he's not divulging any specifics.

"Oh, I don't want to go there," he said with a laugh. "If I say anything, then there's going to be someone out there with more money and I won't be able to buy anything again."

The collection includes posters with affirming messages and images of courageous black soldiers to stir in its intended audience a sense of national belonging and patriotic pride. Also implied was a promise that blacks who served their country in war would return home to America or Europe with the rights and freedoms that their white counterparts enjoyed.

That promise, as history shows, was not kept.

"They go and they fight and they're victorious, and when all is said and done, they return home," Zuberi said. "And it's 'Go back to your second-class citizen status, democracy is not here for you, you are not civilized and you are not ready for it.'"

Conversely, the collection also includes negative posters that used hateful stereotypes to portray Africans and African-Americans as threats to white society. Zuberi's favorite piece, perhaps surprisingly, is one of the most offensive in his collection.

Made in 1942 by Italian illustrator Gino Boccasile, "The Two-Dollar Venus" features a caricature of a black U.S. soldier as a brutish character with a buffoonish grin, his arm around the statue of Venus de Milo with "$2" scrawled across the torso.

"It's beautiful in itself. It has a very ugly, derogatory tone, but it's done very well," Zuberi said. "This is saying to the Italian people: 'If the U.S. comes here, they're going to bring these people; they're going to take a priceless cultural icon and put a price on it.'"

The exhibit also includes highly stylized posters made in China during the U.S. civil rights era and in Russia during the African independence movements expressing support of oppressed blacks against American and European aggressors.

A group of archival videos demonstrate how the same kinds of messages were communicated on film, including a 1945 Ronald Reagan-narrated recruitment short using the Tuskegee Airmen to claim American racial harmony and a 1944 Frank Capra-produced short that extols black war heroes without making mention of the entrenched segregation in the U.S. and its military.

A 1939 film shows Africans under European colonial rule as wholly benevolent relationships that brought the indigenous peoples "a fuller life, free from fear."

"It's a contradictory message given the reality that existed," Zuberi said, "but it's a very powerful message."

___

Online:

Exhibit details: http://bit.ly/19uYHuM

First baseman Teixeira (wrist) and third baseman Youkilis (back) hope to liven up the Yankees attack in this weekend's American League East showdown against the visiting Boston Red Sox, who have leapfrogged New York into the division lead.

The Yankees' skid was made even more painful since the last four defeats came against the New York Mets, who swept their Subway Series this week with a dominant run of pitching.

The sting would smart less, however, with a rebound against Boston (33-22).

"I'm sure there will be a buzz in the air and there will be excitement again tomorrow," Yankees manager Joe Girardi told reporters after Thursday's loss to the Mets. "Tomorrow is as good a day to get back to our winning ways as any."

The Yankees (30-23) could reclaim the AL East lead with a sweep of the three-game series.

More help is on the way for the New Yorkers, who have fielded a patch-work team to handle a spate of injuries.

Veteran starting pitcher Andy Pettitte (shoulder) is expected to return to action on Monday as the team slowly returns to health.

Still in the wings are two of New York's biggest names, Derek Jeter (ankle) and Alex Rodriguez (hip), who are not expected back until after the All-Star break in July, while Curtis Granderson returned to the disabled list after breaking a knuckle when he was hit by a pitch last week. (Reporting by Larry Fine; Editing by Frank Pingue)

I'm scared other kids will make fun of me for being different. I have already gotten laughed at. What should I do? -- EMBARRASSED TEEN

DEAR EMBARRASSED TEEN: When people laugh at a person who has a disability, it is usually out of ignorance. Because this happened at school or another place where there is adult supervision, you and your parents should talk to the principal or person in authority so that person can speak privately with the guilty parties and explain why your hearing aids and the microphone are necessary. Your parents should also have a meeting with the principal of your high school before you go so the problem can be avoided.

When I was in grammar school, a classmate of mine had severe hearing loss. Because the students understood what her problem was, she was never ridiculed.

P.S. Making fun of a child who has a disability is a form of bullying, and should be treated as such.

DEAR ABBY: I'm 25 and have been with my husband for nine years, married for four. I cheated on him twice. He caught me both times.

Even though I strayed, he decided to stay. But now he treats me like I'm a child and a prisoner. He took away my phone, my Internet and I can't go anywhere. He says this is my punishment for what I did. Do I really deserve that? I know we're both wrong, but is he more wrong? -- BROKEN WIFE

DEAR BROKEN WIFE: From where I sit, you are equally wrong. How long ago did the cheating incidents occur? If they are recent, you two should be in marriage counseling. If they were long ago, then you must decide if you want to live the rest of your life being treated as a child and a prisoner.

Your husband doesn't trust you because you haven't been trustworthy. But taking away your phone and Internet and keeping you under lock and key will not help you to rebuild it.

You two need more help than anyone can give you in a letter, and I hope you will seek it. If he won't go for counseling, you should go without him because I don't think the status quo can last.

DEAR ABBY: My sister and brother-in-law passed away two years ago. I am the only living relative of their 28-year-old son, "Louis." He is a loner, spoiled and a poor houseguest. I invite Louis over only because I don't want him to be alone at holiday times. My husband, teenage daughter and I have nothing in common with him, and frankly, he spoils our holidays.

How can I stop inviting my nephew without feeling guilty? Or is there another solution? I hate to make waves. -- HOLIDAY HATER IN CANADA

DEAR HOLIDAY HATER: If you invite your nephew for fewer holidays you will be able to ease your conscience, enjoy more holidays and allow the young man a chance to become more proactive in planning entertainment for himself.

DEAR ABBY: I may be wrong, but isn't it presumptuous for someone to open the message card on a flower delivery before you get home when the flowers are for you? -- KIMBERLY IN MARYLAND

DEAR KIMBERLY: You're not wrong. The person opening the cards isn't being helpful, but nosy. And it wouldn't be out-of-line to tell the person not to do it again.

Dear Abby is written by Abigail Van Buren, also known as Jeanne Phillips, and was founded by her mother, Pauline Phillips. Write Dear Abby ator P.O. Box 69440, Los Angeles, CA 90069.

Abby shares more than 100 of her favorite recipes in two booklets: "Abby's Favorite Recipes" and "More Favorite Recipes by Dear Abby." Send your name and mailing address, plus check or money order for $14 (U.S. funds) to: Dear Abby, Cookbooklet Set, P.O. Box 447, Mount Morris, IL 61054-0447. (Shipping and handling are included in the price.)

ASPEN, Colo. (AP) -- The image was chilling: Snowmobile rider Caleb Moore, launched over his handlebars on a backflip gone wrong, rolled down the landing hill with his 450-pound machine somersaulting behind him.

Run over by his sled, Moore lay on the snow for several minutes before being helped off the course. As of Wednesday, he was hospitalized in critical condition because of bleeding around his heart and a complication involving his brain.

Moore's was the worst accident at the Winter X Games, which wrapped up Sunday night after four days of competition, but it wasn't the only harrowing moment. The wipeouts included a runaway snowmobile that sent spectators scrambling.

Even the highlights were hardly tame. Snowboarding star Shaun White soared a competition record 24 feet into the air during the superpipe competition, and fellow boarder Elena Hight showed off a difficult trick called a"double alley-oop backside rodeo" that involved a couple of backflips and a 180-degree rotation. It had never been seen in a competition.

All that, plus Moore's crash, has some wondering whether dialing up the difficulty each year improves action sports or has simply made them too dangerous.

"Should we be asking these questions? We absolutely should be," said Dan Lebowitz, the executive director of Sport in Society at Northeastern University, which examines the role of sports to promote healthy development and social responsibility.

The people performing these superhuman feats "really are just human," he said. "How do we maintain safety in that progression when that progression sometimes pushes every envelope to some amazingly extreme point?"

Moore's injuries underscore the dangers at Winter X, which was filled with numerous cover-your-eyes crashes.

Halldor Helgason of Iceland over-rotated on a flip in the snowboard big air competition and had to be taken off on a sled with a concussion. Rose Battersby of New Zealand sustained a lumbar spine fracture in a wipeout during practice before the skiing slopestyle competition, which will be an Olympic sport next winter at the Sochi Games.

Then there was this: Summer X Games motocross champion turned snowmobile newcomer Jackson Strong tumbled off his machine during the best trick competition, the throttle sticking and the sled swerving toward fans as they scurried away. The machine came to a rest when it got tangled in some netting and no one was seriously hurt.

Such a scenario had already crossed the mind of Levi LaVallee, a snowmobiler who captured two gold medals only to be sidelined for the final two competitions after tearing a muscle in his back.

"I've always thought about, 'What happens if the thing tips over and the throttle sticks?'" LaVallee said. "It was good, though, because it showed that X Games has a good setup with the fencing."

Whether action sports are too dangerous is an issue that's been raised before.

When freestyle skier Sarah Burke died in a training accident a little more than a year ago in Park City, Utah, there were questions about the halfpipe. Before that, the sport was examined when snowboarder Kevin Pearce suffered a severe brain injury in a fall in the same pipe as Burke two years earlier. Pearce has recovered and served as an analyst at Winter X.

But in general, the athletes accept the risks and defend their disciplines.

"To lose Sarah was such a blow to this entire industry," said snowboarder Gretchen Bleiler, who didn't compete this year as she recovers from a serious eye injury she suffered in training. "This sport brings so much joy, happiness and balance to my life and that far outweighs what could happen. You can't ever live your life with what could happen."

In a statement, X Games officials said they've paid close attention to safety issues over the event's 18-year history: "We've worked closely with athletes, risk management specialists, sport organizers and event managers to present the best possible experience for athletes and spectators. Further measures are constantly being evaluated."

Athletes say they prepare as best they can by trying out new tricks into foam pits and air bags set up at the bottom of courses. But even all the caution in the world can't prevent the fact that sometimes well-practiced maneuvers can go wrong in the air.

"You don't want to live your life in fear because of a situation," LaVallee said. "Look, I'm driving down the road right now and the worst-case scenario is a car could swerve over into my lane and run over me there it is, end of the road.

"That's kind of the same thing we think when we're competing. Hopefully, the preparation and countless hours of training and practicing will prevent the worst-case scenario from happening."

Tucker Hibbert the Shaun White of snowmobiling after winning his sixth straight SnoCross title just hopes casual fans understand that what they see on television is not true snowmobiling.

"You're seeing the most extreme side of what we do," Hibbert said. "That's a lot different than what the average person does on a snowmobile."

Hibbert doesn't participate in events such as best trick because, "I just wasn't born with those skills. I sit back and watch those guys, enjoy what they do."

He paused.

"You just hate to see anyone crash, anyone get hurt," Hibbert said.

Moore was in the middle of an impressive run in the freestyle event when he caught the top of the hill that was serving as a landing area. He initially walked away with help and went to a hospital with a concussion.

Moore later developed bleeding around his heart and had surgery. His family said that Moore, of Krum, Texas, also had a complication involving his brain.

Colten Moore, Caleb's younger brother and defending champion in the event, separated his pelvis in a crash later that same night.

LaVallee is no stranger to horrific wipeouts.

While training for the "Red Bull: New Year. No Limits" daredevil series two years ago in Southern California, LaVallee lost control of his snowmobile high in the air and landed violently on his side, bouncing down the landing ramp. He broke ribs, cracked his pelvis, collapsed one lung and punctured the other.

But he returned the next year and jumped a record 412 feet, 6 inches.

"We're passionate about the sport that we're in," LaVallee said.

"Anyone who competes has that drive to succeed, to go bigger than the next person or be the first one to do it."

The mentality is similar throughout action sports, even if the bar keeps getting raised.

"There are going to be benchmarks set and people trying to exceed that benchmark," Lebowitz said. "That's just the essence of our society and our social culture."