Webster removed the muscle from the pigs' chests and placed Taser barbs close to their hearts before shocking the animals.

"The previous research made a mistake," Webster said. "I was a little surprised. But I believe this research more accurately reflects the anatomy of humans."

While most Taser shots land too far from the heart to be lethal, barbs that penetrate the spaces between the ribs that surround the heart may have the potential to cause electrocution, he said.

Steve Tuttle, a spokesman for Taser International, which makes the weapons, said Webster's research was flawed and did not reflect the way that Tasers were used in humans. The current from a Taser shock is dispersed through the body rather than running directly into the heart, Tuttle said in an e-mail statement.

The earlier studies on pigs were financed by Taser International. The Justice Department paid for Webster's study, which is not yet completed. An abstract is posted on Webster's Web site.

Not a firearm

Tasers are pistol-shaped weapons that fire barbs up to 35 feet, delivering a 50,000-volt shock. Because they propel the barbs with compressed nitrogen instead of gunpowder, Tasers are not considered firearms and are not regulated by the Bureau of Alcohol, Tobacco and Firearms or any other federal agency.

Dr. Ted Chan, a professor of clinical medicine at the University of California at San Diego who has studied the effect of Taser shocks on human volunteers, said Webster's research did not prove that Tasers could cause lethal heart disturbances.

In his research, which is also financed by the Justice Department, Chan has shocked more than 100 people and not found any changes in heart rhythms. More sophisticated tests conducted on about a dozen people have also failed to find damage, Chan said.

"Animal studies can point in certain directions, but ultimately you have to look at humans," he said.

Chan did add that most of the volunteers he tested were not shocked directly over their hearts.

More than 150 people have died after being shocked by Tasers, according to data compiled by Amnesty International, which has called for a moratorium on use of the guns. The weapons are used by almost 10,000 police departments in the United States and internationally, as well as the military. Tasers have been used or tested on volunteers about 200,000 times, Tuttle said.

Coroners have attributed most of the deaths to causes other than the Taser shock, like cocaine overdoses. But in a handful of cases Tasers have been listed as the primary or contributing cause.

Doctors and scientists have questioned whether Tasers can cause ventricular fibrillation, a lethal heart rhythm disturbance, as well as acidosis, a dangerous change in blood chemistry. Taser International says that many of the deaths have resulted from drug overdoses and that its weapons are safer than most other ways that police officers can use to restrain people.

Limited use recommended

Since 2002, Tasers have become popular with police departments because they offer officers a way to incapacitate people without having to touch them and because most people do not appear to suffer long-term injury after being shocked. Concerns about safety hurt Taser sales last year, but they have picked up in 2006, with Taser International reporting $14 million in sales in the first quarter.

In October, the Police Executive Research Forum, a nonprofit group that is dedicated to improving police tactics and strategies, recommended that officers be allowed to use the weapons only on suspects who are actively resisting arrest. Some police departments have allowed officers to use Tasers on people who are simply refusing to follow their orders.

The forum's recommendations are not binding. But police departments that do not follow them could face greater legal liability.

Webster shocked 10 anesthetized pigs with a Taser after removing the skin and muscle over their hearts. On average, the pigs suffered ventricular fibrillation when a Taser barb was placed within 0.7 inch of their heart, according to the abstract of the clinical trial posted on Webster's Web site. In humans, the heart is situated 0.4 to 2 inches under the skin, Webster said.

Ventricular fibrillation is an electrical disturbance that causes the heart to beat irregularly and be unable to pump blood. It causes death within minutes unless the heart's normal rhythm is restored.

Hooper was placed on administrative leave pending the internal affairs investigation. Strickland said it was common procedure to review incidents involving the use of force by an officer.

Chandler and a male student involved in the fight, 17-year-old Stacey Rucker, both were arrested.

Chandler waived her right to a preliminary hearing that had been previously scheduled for Friday and the case has been sent to Superior Court, said Lee Darragh, district attorney for the Northeastern Judicial Circuit.

The district attorney's office is considering the case for possible indictment.

Chandler is charged with affray, or fighting, disrupting a public school, obstruction and making terroristic threats, authorities said.

Strickland said Hooper, who is trained to use a Taser, has nearly 20 years of experience without a reprimand or citation. Hooper's record remains without a blemish after he was cleared of any wrongdoing.

Chandler and Rucker's altercation allegedly began over an incident in which one of their vehicles was keyed.

Authorities said both began arguing and then fought in the hallway of the school about 10 a.m.

Chandler made "threatening comments toward (Rucker)," authorities said. Hooper attempted to dissolve the altercation by giving verbal commands, but those were ignored by Chandler, Strickland said.

Chandler had recently returned from a five-day suspension for a prior incident at the school, he said.

Both Chandler and Rucker were suspended five days for the May 4 fight, which took place about two weeks before the end of the school year.

Rucker also was arrested on charges of affray and disrupting a public school, authorities said.

He was released from the Hall County Detention Center the same day of the fight on $1,700 bond.

Chandler was released from jail the next day after posting a bond of $4,500.

All light or other electromagnetic waves would be steered around the object, making it invisible, said study author David Smith, a professor of electrical and computer engineering at Duke University in Durham, N.C.

"The theory has only now become relevant because we can make metamaterials with the properties we are looking for," Smith said in a release.

No such cloak exists yet, but the first versions for masking radiation such as microwaves could be made in about 18 months, said study co-author John Pendry, a physicist at Imperial College London.

The cloak could also have applications for wireless communications, the team said.

"This is very interesting science and a very interesting idea and it is supported on a great mathematical and physical basis," Nader Engheta, a professor of electrical and systems engineering at the University of Pennsylvania, told the Associated Press.

Engheta was not involved in the study, but he is also working on metamaterials.

"Noctilucent" clouds, which glow at night, form in the upper atmosphere, at an altitude of about 80 kilometres, and their glow can be seen just after sunset or just before sunrise.

"Even though the Sun's gone down and you're in darkness, the clouds are so high up, the Sun is still illuminating them," explains AIM principal investigator James Russell at Hampton University in Virginia, US. Russell described the mission on Thursday at a meeting of the American Geophysical Union in Baltimore, Maryland, US.

Bigger and brighter

The clouds were first observed above polar regions in 1885 - suggesting they may have been caused by the eruption of Krakatoa two years before. But they have spread to latitudes as low as 40° in recent years. "They're also getting brighter, and each year there are more of them than in the previous year," Russell told New Scientist.

Many researchers believe this proliferation is down to human activities. "You need three things for clouds to form: particles that water can condense onto; water; and cold temperatures," says Russell. He says pollution and global warming are thought to be responsible for two of those factors.

Atmospheric water may be boosted by livestock farming and the burning of fossil fuels, which spew methane into the atmosphere: sunlight breaks down the methane, releasing hydrogen that can bond with oxygen to form water.

And greenhouse gases such as carbon dioxide actually help to cool the upper atmosphere, where the clouds form. That is because the atmospheric density is so low at that altitude that the gases cannot trap heat as they do closer to the Earth's surface, and the heat is simply radiated into space.

Alien ice

As yet, it is not clear what the source of the particles that "seed" the clouds is. The clouds form during the local summer months, when the pole is bathed in perpetual sunlight. So one possibility is that warm air rising above the pole could carry dust upwards from lower atmospheric altitudes, onto which water can condense.

But the dust could also have a cosmic source, dropping into the atmosphere from space. "It may be there's a constant supply of particles but a changing temperature and water environment makes the conditions right to grow ice particles," says Russell.

AIM will use three instruments to study the clouds. One is a suite of four cameras that will provide panoramic views of the poles and clouds. Another, called the Solar Occultation for Ice Experiment (SOFIE), will study the chemistry of the ice particles and clouds - measuring molecules such as methane. It will also observe the Sun through the atmosphere to measure how much sunlight is dimmed by dust in the atmosphere.

The third instrument, called the Cosmic Dust Experiment, is a plastic film that sits on top of the spacecraft. It will record every "hit" from a dust particle that rains down on it from space.

Cloud umbrella

"We want to know why the clouds form and why they vary," says Russell. "If there is a human connection, it'll tell us that we're doing something to the atmosphere and that we need to determine what the long-term consequences are."

Some scientists speculate that the clouds might actually help mitigate global warming, says Russell. "If these clouds were to continue to grow and cover broad areas of Earth, they would form something like a thin, semi-transparent umbrella," he told New Scientist. "They would reduce the amount of solar rays making it to the ground, so they could actually reduce the effects of global warming."

The AIM satellite will launch into a polar orbit from California's Vandenburg Air Force Base. Russell says it may lift off in December, but its exact launch date has not been set because mission planners are still working to minimise vibration forces on the spacecraft due to its Pegasus XL launch rocket.

In an editorial for The Wall Street Journal and two nationally televised interviews, the mayor reiterated his long-standing belief that the 12 million undocumented immigrants in the United States should be given the opportunity for citizenship, saying that deporting them is impossible and would devastate the economy.

Aides said Bloomberg believes his views are relevant because he has a rare perspective as a former businessman who ran a company for two decades before he became mayor, in charge of enforcing the laws in a city with an estimated half-million illegal immigrants. They said that the editorial was his idea and that CNN and Fox News approached him to discuss his views on the air.

In the article and on air, Bloomberg slammed lawmakers who want to deport all illegal immigrants, saying on Fox News that "they are living in a fantasy world."

Asked in that interview whether his opinions put him at odds with his political party, the mayor, a former Democrat, shot back: "With which party?

"I'm not a partisan guy," Bloomberg said. "I am a mayor who has to deal with 500,000 people who are integral to our economy but are undocumented."

Bloomberg compared his proposed federal identification database to the Social Security card, insisting that such a system would not violate citizens' privacy and was not a civil liberties issue.

"You don't have to work _ but if you want to work for a company you have to have a Social Security card," he said. "The difference is, in the day and age when everybody's got a PC on their desk with Photoshop that can replicate anything, it's become a joke."

The mayor said DNA and fingerprint technology could be used to create a worker ID database that will "uniquely identify the person" applying for a job, ensuring that cards are not illegally transferred or forged.

Donna Lieberman, director of the New York Civil Liberties Union, said a DNA or fingerprint database "doesn't sound like the free society we think we're living in."

"It will inevitably be used not just by employers but by law enforcement, government agencies, schools and all over the private sector," she said.

"This project will keep our economy growing by creating jobs and ensuring that businesses can expand. And it will make America less dependent on foreign sources of energy, eventually by up to a million barrels of crude oil a day -- a nearly 20 percent increase over our current domestic production," he said, calling on the US Senate to pass a similar bill.

The Senate has blocked previous attempts to permit oil drilling in the area, and environmental groups say scores of rare and endangered wildlife species would be put at risk by the proposal.

The House bill, which passed by a vote of 225 to 201, directs the US Secretary of the Interior to begin leasing a portion of the refuge along Alaskas northern coast for oil exploration.

Republicans have lobbied for years to allow exploration of Alaska's environmentally-sensitive wildlife refuge.

The Belarusian Foreign Ministry announced the ban on Thursday, after it was proposed this week by President Alexander Lukashenko.

"Belarus strictly observes symmetry in adopting any sort of retaliatory measures," a foreign ministry spokesman, Andrei Popov, told a news conference.

"These restrictions will apply only to two countries: the United States and Canada."

Popov said it hasn't been decided whether to ban all Canadian and American flights or only flights carrying official delegations.

It's not clear how many flights would be affected by the move. Canada and the United States pay roughly $200,000 to Belarus each year for the use of its airspace, west of Russia and north of Ukraine.

Foreign Affairs has not commented on the decision.

Stopover refused because of crackdowns

Ottawa refused to let the plane land on April 20 because of concerns about "the current regime's commitment to democratization and human rights," a foreign affairs spokeswoman, Pamela Greenwell, said at the time.

Lukashenko has come under increased international criticism following his controversial election win in March and subsequent crackdown on protests against the vote, which critics claim was rigged.

Hundreds of demonstrators have been arrested since Lukashenko's victory. The European Union has called on governments around the world to refuse to recognize the vote.

In early April, a Canadian journalist spent 15 days in prison while covering an anti-Lukashenko demonstration.

"In light of these concerns, we were not prepared to facilitate the entry of senior-level representatives of the Belarusian regime onto Canadian soil," Greenwell told CBC News Online.

Greenwell said she didn't know what alternate arrangements the plane made in order to land safely. The Cuban newspaper Granma said the plane had been carrying Sidorsky and a number of other government officials.

The European Union has given conflicting signals in recent days on its willingness to make further concessions on the WTO's "Doha" round, said Jason Hafemeister, the US Trade Representative's chief WTO negotiator.

But for Chirac to argue that the EU has done everything it can on agricultural trade "would be a problem, as that's not going to be adequate" to unblock the Doha round, he told reporters.

The EU has been cast as the villain in the WTO talks due to its refusal to go further in cutting the generous subsidies it gives to its farmers.

Big developing countries such as Brazil and India, however, are also under pressure from the EU and United States to bring down their commercial barriers in return for farming reform in the rich blocs.

The French leader, the EU's most ardent defender of the farming lobby, said after talks with Brazilian President Luiz Inacio Lula da Silva that the 25-nation bloc could go no further without concessions from others.

Europe "is not in a position to take a single step further" on agricultural reform when others "haven't made a single step towards Europe on industry and services", Chirac told a joint news conference in Brasilia with Lula.

Chirac also called on Brazil to join with Europe "to levy friendly pressure on the Americans to make them more reasonable" over the "excessive" export support given to US farmers.

"In reality it is the United States that holds the key to the problem. The key is neither in Europe, nor in Brazil, nor in emerging countries," he said.

The United States, however, says it has made a "bold" proposal on agriculture that exceeded its Doha requirements and is willing to go still further.

The offer contrasts with what Hafemeister called the "take-it-or-leave-it stance" of the EU on agriculture, and the "puny" cuts to industrial tariffs offered by some developing countries.

At talks in Paris this week, EU Trade Commissioner Peter Mandelson signalled that the bloc would be prepared to improve its offer on farm products if others are willing to cede ground.

Hafemeister argued that no formal or informal proposals had been presented in Paris.

"Just a minor move at the last minute is not going to make it," he added. "Until we see real serious proposals from other countries, there's a big void in the negotiations here."

US officials say that Crawford Falconer, New Zealand's WTO ambassador who is chairing the agricultural talks in Geneva, is preparing to submit new outlines of a deal around mid-June.

But that will leave precious little time to sign, seal and deliver a global package to dismantle world trade barriers by the end of the year.

The US government would then have just months to get a WTO deal through Congress before it loses its 'fast-track' trading authority at the start of July 2007.

Once the administration's 'Trade Promotion Authority' expires, Congress will regain the right to amend any trade agreement. At present, US lawmakers can only give a straight 'yes' or 'no' vote to an agreement.

Without a serious effort this summer, "you just start running out of time", Hafemeister said.

"It's true that Europe really is going to have to set the standard. We can't expect developing countries to cut their tariffs deeper than the European Union. That's why everybody is focussed on Europe," he said.