After decent rally, perhaps time for a pause

NEW YORK (Reuters) - Stocks could struggle to extend their seven-week winning streak as the quarterly earnings period draws to a close and the market bumps into strong technical resistance.

Many analysts say the market could spend the next few weeks consolidating gains that have lifted the benchmark Standard & Poor's 500 <.spx> by 6.6 percent since the start of the year.

The S&P 500 ended up 0.1 percent for the week, recovering from a late sell-off on Friday after a Bloomberg report about slow February sales at Wal-Mart triggered a slide in the retailer's shares. It was the index's seventh week of gains.

Odds of a pullback are increasing, with the market in slightly overbought territory, said Bruce Zaro, chief technical strategist at Delta Global Asset Management in Boston.

"I do suspect the closing of the earnings season will lead to at least a pause and possibly a pullback," Zaro said. The S&P 500 could shave 3 to 5 percent between now and early April, he said.

Fourth-quarter earnings have mostly beaten expectations. Year-over-year profit growth for S&P 500 companies is now estimated at 5.6 percent, up from a January 1 forecast for 2.9 percent growth, and 70 percent of companies are exceeding analyst profit expectations, above the 62 percent long-term average, according to Thomson Reuters data.

On Thursday, Wal-Mart, the world's largest retailer, is due to report results, unofficially closing out the earnings period. Investors will be keen to see its quarterly numbers, especially after the Friday's news report that rattled investors.

The S&P 500 has gained 4.3 percent since Alcoa kicked off the earnings season on January 8.

The approaching March 1 deadline for across-the-board federal budget cuts unless Congress reaches a compromise adds another reason for caution, especially with recent economic data indicating the recovery remains bumpy.

Manufacturing output fell 0.4 percent last month, the Federal Reserve said on Friday, but production in November and December was much stronger than previously thought.

TESTING RESISTANCE

The S&P 500 has been trading near five-year highs, and it notched its highest level since November 2007 this week. But the gains have pushed the benchmark index almost as far as it is likely to go in the near term, with strong resistance hovering around 1,525 and 1,540, one analyst said.

As a result, the index is set to move sideways, said Dave Chojnacki, market technician at Street One Financial in Huntington Valley, Pennsylvania. "We just don't have the volume or the catalyst right now" to go above those levels, he said.

At the same time, other analysts say, the market has not shown significant signs of slowing, including a break below 15- and 30-day moving averages.

Such moves would be needed to show that momentum is slowing or that the market is at risk of a correction, said Todd Salamone, director of research for Schaeffer's Investment Research in Cincinnati, Ohio. The S&P 500's 14-day moving average is at 1,511 while the 30-day is at 1,494. The index closed Friday at 1,519.

Recent M&A activity, including news this week of a merger between American Airlines and US Airways Group , helped provide some strength for the market this week and optimism that more deals may be on the way.

In the coming days, the market will focus on minutes from the latest Federal Reserve meeting, due to be released on Wednesday, which could provide support if they suggest the Fed will remain on its current course of aggressive monetary easing.

The Fed minutes released in January spooked markets a bit when they revealed that some Fed officials thought it would be appropriate to consider ending asset purchases later in 2013. U.S. Treasury yields rose on that news, though market worries about a near-term end to quantitative easing have since faded.

Among other companies expected to report earnings next week are Nordstrom , Hewlett-Packard and Marriott International

(Reporting By Caroline Valetkevitch; Editing by Leslie Adler)

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Loi Journal: In Vietnam, Some Chose to Be Single Mothers

Justin Mott for the International Herald Tribune

Nguyen Thi Nhan at home with her grandson, Thao, 2. Abandoned by her husband after the war, she asked another man to impregnate her.

LOI, Vietnam — They had no plan to break barriers or cause trouble. But 30 years ago in this bucolic village in northern Vietnam, the fierce determination of one group of women to become mothers upended centuries-old gender rules and may have helped open the door for a nation to redefine parenthood.

One recent morning in Loi, as farmers in conical straw hats waded quietly through rice paddies, a small group of women played with their grandchildren near a stream. Their husbands were nowhere to be found, not because they perished in the war, but because the women decided to have children without husbands.

The women’s story began during the American War, as it is called here, when many put the revolution before their families. As peace settled more than a decade later, it became clear that they — like so many of their generation — had sacrificed their marriageable years to the war.

At that time Vietnamese women traditionally married around 16, and those still single at 20 would often be considered “qua lua,” or “past the marriageable age.” When single men who survived the war returned home, they often preferred younger brides, exacerbating the effects of a sex ratio already skewed by male mortality in the war. According to the Vietnam Population and Housing Census of 2009, after reunification in 1979 there were on average only about 88 men for every 100 women between 20 and 44.

Unlike previous generations of unwanted Vietnamese women who dutifully accepted the “so,” or “destiny,” of living a solitary life, a group of women in Loi decided to take motherhood into their own hands. They had endured the war, developed a new strength and were determined not to die alone.

One by one they asked men — whom they would never interact with afterward — to help them conceive a child. The practice became known as “xin con,” or “asking for a child,” and it meant breaking with tradition, facing discrimination and enduring the hardships of raising a child alone.

“It was unusual, and quite remarkable,” said Harriet Phinney, an assistant professor of anthropology at Seattle University who is writing a book on the practice of xin con in Vietnam. Purposely conceiving a child out of wedlock, she said, “was unheard-of” before the revolutionary era.

It was a product of the mothers’ bravery, said Ms. Phinney, but also of a postwar society that acknowledged the unique situation of women across Vietnam, including thousands of widows, who were raising children alone.

Some of the women in Loi were willing to share their stories, though they always kept the names of the fathers a tightly held secret. One of the first women in Loi to ask for a child was Nguyen Thi Nhan, now 58.

Ms. Nhan had led a platoon of women during the war, and though she never saw battle, was awarded a medal for her exemplary leadership. Her husband, with whom she had a daughter, abandoned her after the war. Ms. Nhan moved to the cheapest land she could find, a field near the stream on the outskirts of Loi, where a few refugees from bombing nearby still lived. She then asked for a second child, ending up with the son she wished for.

Her first several years were hard. Despite her best efforts, food and money were scarce. The villagers eventually set aside prejudices and accepted her choice, offering to share the little food they could spare. Eventually, Ms. Nhan was joined by more than a dozen other women. Among them was Nguyen Thi Luu, 63. She had fallen in love with a soldier who was killed in battle in 1972.

“I was 26 when the war ended,” Ms. Luu said. “That was considered too old for marriage, in those times. I did not want to marry a bad, older man, and no single men came to me.”

But Ms. Luu wanted to become a mother, not least so she would have support in her old age. In Vietnam, nursing homes are scarce, and care for the elderly is considered a filial duty.

“I was afraid to die alone,” Ms. Luu said. “I wanted someone to lean on in my old age. I wanted a child of my own.”

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How Ben Affleck & Jennifer Garner Are Making a Hollywood Marriage Work

By Michelle Tauber

02/14/2013 at 07:30 PM EST

Ben Affleck & Jennifer Garner

Ramey

He kept his arm tenderly around her back. She beamed as he told her "I love you" from the stage, and when the show was over, gently reminded him to take his jacket. For Ben Affleck and Jennifer Garner, the British Academy Film Awards in London on Feb. 10 was another successful date night – and a rare grown-ups' weekend getaway, with their three kids staying home with Garner's sister.

Well, almost: "He's just like a child!" Garner lovingly joked to a friend as she tugged her still-schmoozing husband–who won the night's two biggest honors for his film Argo – toward the exit. Could an Oscar for Best Picture be his next stop? "This is a second act for me," he said in his London acceptance speech. "I am so grateful and proud." As he told PEOPLE recently, "I am very lucky. I have to knock on wood about my life."

Especially about the woman who's a lock for Best Supporting Spouse. After seven years of marriage and three kids–Violet, 7, Seraphina, 4, and Samuel, who turns 1 on Feb. 27–Affleck and Garner, both 40, seem to have struck that rarest of things for a Hollywood couple: balance. It's an old-fashioned arrangement, with Garner handling most of the day-to-day responsibility for keeping the children's schedules humming while Affleck rides his Argo hot streak – including Screen Actors Guild and Golden Globe wins, despite a snub for the Oscar directing category.

"I've got a great family; I'm really inspired by where my career is," Affleck says. "I've seen a lot of different things rambling around in this business, and I'm just really, really happy to find myself where I am."

Several sources who know the couple well say that both stars are at ease in their "quite traditional roles," as a Garner friend puts it. Garner dialed back on her own career to commit herself to making the ballet-karate-playdate rounds.

"She blows my mind," says Affleck's Argo costar Clea Duvall. "She's such an amazing mom and such an amazing wife and so supportive of him. It's just . . . they're kind of the ideal." Although Affleck has made his share of school runs during a busy awards season, in many ways he's an old-fashioned dad.

Says a source who knows the couple: "Have you ever seen Mad Men? That's how he approaches [marriage and kids] – providing for your family is your priority, and raising the kids day-to-day is the wife's priority." But when he's not working, he's plenty hands-on, reading to the girls at bookstores and taking them to the farmers' market. "His wife and family are the best things that ever happened to him," says an Affleck pal. "They have always come first and always will."

 

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Study: Fish in drug-tainted water suffer reaction

BOSTON (AP) — What happens to fish that swim in waters tainted by traces of drugs that people take? When it's an anti-anxiety drug, they become hyper, anti-social and aggressive, a study found. They even get the munchies.

It may sound funny, but it could threaten the fish population and upset the delicate dynamics of the marine environment, scientists say.

The findings, published online Thursday in the journal Science, add to the mounting evidence that minuscule amounts of medicines in rivers and streams can alter the biology and behavior of fish and other marine animals.

"I think people are starting to understand that pharmaceuticals are environmental contaminants," said Dana Kolpin, a researcher for the U.S. Geological Survey who is familiar with the study.

Calling their results alarming, the Swedish researchers who did the study suspect the little drugged fish could become easier targets for bigger fish because they are more likely to venture alone into unfamiliar places.

"We know that in a predator-prey relation, increased boldness and activity combined with decreased sociality ... means you're going to be somebody's lunch quite soon," said Gregory Moller, a toxicologist at the University of Idaho and Washington State University. "It removes the natural balance."

Researchers around the world have been taking a close look at the effects of pharmaceuticals in extremely low concentrations, measured in parts per billion. Such drugs have turned up in waterways in Europe, the U.S. and elsewhere over the past decade.

They come mostly from humans and farm animals; the drugs pass through their bodies in unmetabolized form. These drug traces are then piped to water treatment plants, which are not designed to remove them from the cleaned water that flows back into streams and rivers.

The Associated Press first reported in 2008 that the drinking water of at least 51 million Americans carries low concentrations of many common drugs. The findings were based on questionnaires sent to water utilities, which reported the presence of antibiotics, sedatives, sex hormones and other drugs.

The news reports led to congressional hearings and legislation, more water testing and more public disclosure. To this day, though, there are no mandatory U.S. limits on pharmaceuticals in waterways.

The research team at Sweden's Umea University used minute concentrations of 2 parts per billion of the anti-anxiety drug oxazepam, similar to concentrations found in real waters. The drug belongs to a widely used class of medicines known as benzodiazepines that includes Valium and Librium.

The team put young wild European perch into an aquarium, exposed them to these highly diluted drugs and then carefully measured feeding, schooling, movement and hiding behavior. They found that drug-exposed fish moved more, fed more aggressively, hid less and tended to school less than unexposed fish. On average, the drugged fish were more than twice as active as the others, researcher Micael Jonsson said. The effects were more pronounced at higher drug concentrations.

"Our first thought is, this is like a person diagnosed with ADHD," said Jonsson, referring to attention deficit-hyperactivity disorder. "They become asocial and more active than they should be."

Tomas Brodin, another member of the research team, called the drug's environmental impact a global problem. "We find these concentrations or close to them all over the world, and it's quite possible or even probable that these behavioral effects are taking place as we speak," he said Thursday in Boston at the annual meeting of the American Association for the Advancement of Science.

Most previous research on trace drugs and marine life has focused on biological changes, such as male fish that take on female characteristics. However, a 2009 study found that tiny concentrations of antidepressants made fathead minnows more vulnerable to predators.

It is not clear exactly how long-term drug exposure, beyond the seven days in this study, would affect real fish in real rivers and streams. The Swedish researchers argue that the drug-induced changes could jeopardize populations of this sport and commercial fish, which lives in both fresh and brackish water.

Water toxins specialist Anne McElroy of Stony Brook University in New York agreed: "These lower chronic exposures that may alter things like animals' mating behavior or its ability to catch food or its ability to avoid being eaten — over time, that could really affect a population."

Another possibility, the researchers said, is that more aggressive feeding by the perch on zooplankton could reduce the numbers of these tiny creatures. Since zooplankton feed on algae, a drop in their numbers could allow algae to grow unchecked. That, in turn, could choke other marine life.

The Swedish team said it is highly unlikely people would be harmed by eating such drug-exposed fish. Jonsson said a person would have to eat 4 tons of perch to consume the equivalent of a single pill.

Researchers said more work is needed to develop better ways of removing drugs from water at treatment plants. They also said unused drugs should be brought to take-back programs where they exist, instead of being flushed down the toilet. And they called on pharmaceutical companies to work on "greener" drugs that degrade more easily.

Sandoz, one of three companies approved to sell oxazepam in the U.S., "shares society's desire to protect the environment and takes steps to minimize the environmental impact of its products over their life cycle," spokeswoman Julie Masow said in an emailed statement. She provided no details.

___

Online:

Overview of the drug: http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682050.html

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Wall Street ends slightly higher, helped by acquisitions

NEW YORK (Reuters) - The S&P 500 eked out a small gain for a third straight session on Thursday, helped by a flurry of merger activity, though investors see no catalysts to lift the market further with major averages near multi-year highs.

The market's slowed advance took the S&P 500 to its highest intraday level since November 2007 on Wednesday. While the index notched its third straight day of gains, none was more than 0.2 percent.

Shares of H.J. Heinz Co jumped 20 percent to $72.50 after it said Warren Buffett's Berkshire Hathaway and 3G Capital will buy the food company for $72.50 a share, or $28 billion including debt. Berkshire's class B shares rose 1.3 percent to $99.21.

Also supporting the market was data showing the number of Americans filing new claims for unemployment benefits fell more than expected in the latest week. The CBOE Volatility index <.vix> fell 2.4 percent, dropping to 12.67.

"While I'm not bearish, I don't see many upside motivations at these levels," said Donald Selkin, chief market strategist at National Securities in New York, who cited the low level of the VIX as a sign the market was overbought.

Equities have struggled to break above current levels where they have been hovering for almost two weeks. The S&P 500 is up more than 6 percent so far this year.

"We need to digest some of our gains to go higher, but people are so eager to buy on the dips that we're not even seeing dips anymore. People are just chasing the market higher," said Selkin, who helps oversee about $3 billion in assets.

Stocks fell earlier after a report the euro zone's gross domestic product contracted by the steepest amount since the first quarter of 2009. In addition, Japan's GDP shrank 0.1 percent in the fourth quarter, crushing expectations of a modest return to growth.

The Dow Jones industrial average <.dji> was down 9.52 points, or 0.07 percent, at 13,973.39. The Standard & Poor's 500 Index <.spx> was up 1.05 points, or 0.07 percent, at 1,521.38. The Nasdaq Composite Index <.ixic> was up 1.78 points, or 0.06 percent, at 3,198.66.

Constellation Brands soared 37 percent to $43.75 after AB InBev's deal to take over Mexican brewer Grupo Modelo was revised to grant Constellation perpetual rights to distribute Corona and other Modelo brands in the United States. U.S. shares of AB InBev gained 5.1 percent to $92.77.

American Airlines and US Airways Group said they plan to merge in a deal that will form the world's biggest air carrier, with an equity valuation of about $11 billion. US Airways shares fell 4.6 percent to $13.99.

Weakness in Europe contributed to a 5 percent drop in revenue from the region for Cisco Systems , which nonetheless beat estimates as it reported its results late Wednesday. The company's shares dipped 0.7 percent to $20.99.

General Motors Co reported a weaker-than-expected fourth-quarter profit, also citing bigger losses in Europe alongside lower prices in its core North American market. The stock was off 3.3 percent to $27.73.

Only five more stocks rose than fell on the New York Stock Exchange, while 51 percent of Nasdaq-listed shares closed higher.

Volume was light, with about 6.36 billion shares changing hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, below the daily average so far this year of about 6.48 billion shares.

(Editing by Nick Zieminski and Kenneth Barry)

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Russian Ethics Official Steps Aside Over Property Disclosures

MOSCOW — The chairman of the ethics committee in Russia’s lower house of Parliament temporarily relinquished his authority on Wednesday after bloggers posted a raft of documents on the Internet showing him as the owner of expensive real estate, including a luxury oceanfront apartment in South Beach, part of Miami Beach, as well as valuable property in Russia that he did not list on required disclosure forms.

The chairman, Vladimir A. Pekhtin, insisted in a televised statement that he had done nothing wrong, and that his voluntary surrender of authority over the ethics panel would last only for the duration of an investigation that he said would clear him.

But the documents, some of them easily available public property records, showed Mr. Pekhtin’s name on the deeds of at least three properties in Florida, including the South Beach apartment bought last year for nearly $1.3 million in a building where Mark Cuban, the billionaire owner of the Dallas Mavericks basketball team, also owns a unit.

Mr. Pekhtin’s official income and property declaration form, posted on Parliament’s Web site, lists no property outside of Russia.

The disclosure of his real estate holdings and the allegations that he failed to properly disclose his assets came just a day after President Vladimir V. Putin proposed legislation that would bar senior Russian officials from holding bank accounts or owning stocks outside the country.

While neither Mr. Putin’s proposal nor any existing law prohibits officials from owning real estate overseas, the disclosure of Mr. Pekhtin’s holdings provided powerful ammunition for critics of Mr. Putin and of United Russia, the party that controls Parliament.

The anticorruption blogger and political opposition leader Aleksei Navalny posted copies of property records and photographs, along with a narrative dripping with sarcasm.

United Russia could entrust Parliament’s ethics committee “only to the most honest, decent and ethical member of the State Duma,” he wrote. “Otherwise, if it turns out this person is not tactful and ethical, it would be embarrassing.”

He noted that another lawmaker, Sergei Zheleznyak, had voiced strong nationalist views and demanded an end to foreign influences in Russia, only to have pictures emerge recently of his children who live and study abroad. Russian bloggers and news organizations were apparently tipped off about the property by someone calling himself Doctor Z, whom the business newspaper Vedmosti described as a researcher living in Spain.

In appearances on Russian television, Mr. Pekhtin said that the property abroad belonged to his son, Aleksei, who lived and worked in the United States.

“I do not have any property abroad,” he said. “There is property belonging to my son.”

In October, Vedmosti reported that Mr. Pekhtin and his wife owned a huge mansion outside St. Petersburg and several other properties near the Bay of Finland, but had disclosed owning only the land and not any buildings on it.

Other records showed that the Pekhtins had bought a number of properties in an area where the government planned to build a new roadway, essentially guaranteeing them cash compensation.

In his statement on television, Mr. Pekhtin said he reserved the right to defend himself in court if necessary.  

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Kate Upton and the Models of Sports Illustrated Party in Las Vegas

02/13/2013 at 10:10 PM EST

Who wouldn't want to party with the models of Sports Illustrated's Swimsuit Issue?

The last few days have led up to what is considered the biggest event in the history of the celebrated franchise.

Following the reveal of the 2013 cover girl, Kate Upton (again!), the sexy bikini-clad ladies are heading to Las Vegas to party ... in a big way.

And you're invited!

Watch live from Sin City, starting at 10:15 p.m. ET, as Caesar's Palace is lit up in honor of the Swimsuit Issue. The models – including Upton, Chrissy Teigen, Anne V and countless others – will be there, walking the red carpet and attending a VIP party.

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Clues to why most survived China melamine scandal

WASHINGTON (AP) — Scientists wondering why some children and not others survived one of China's worst food safety scandals have uncovered a suspect: germs that live in the gut.

In 2008, at least six babies died and 300,000 became sick after being fed infant formula that had been deliberately and illegally tainted with the industrial chemical melamine. There were some lingering puzzles: How did it cause kidney failure, and why wasn't everyone equally at risk?

A team of researchers from the U.S. and China re-examined those questions in a series of studies in rats. In findings released Wednesday, they reported that certain intestinal bacteria play a crucial role in how the body handles melamine.

The intestines of all mammals teem with different species of bacteria that perform different jobs. To see if one of those activities involves processing melamine, researchers from the University of North Carolina at Greensboro and Shanghai Jiao Tong University gave lab rats antibiotics to kill off some of the germs — and then fed them melamine.

The antibiotic-treated rats excreted twice as much of the melamine as rats that didn't get antibiotics, and they experienced fewer kidney stones and other damage.

A closer look identified why: A particular intestinal germ — named Klebsiella terrigena — was metabolizing melamine to create a more toxic byproduct, the team reported in the journal Science Translational Medicine.

Previous studies have estimated that fewer than 1 percent of healthy people harbor that bacteria species. A similar fraction of melamine-exposed children in China got sick, the researchers wrote. But proving that link would require studying stool samples preserved from affected children, they cautioned.

Still, the research is pretty strong, said microbiologist Jack Gilbert of the University of Chicago and Argonne National Laboratory, who wasn't involved in the new study.

More importantly, "this paper adds to a growing body of evidence which suggests that microbes in the body play a significant role in our response to toxicity and in our health in general," Gilbert said.

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Wall Street pauses after rally to five-year high

NEW YORK (Reuters) - Stocks drifted in light volume on Wednesday, ending little changed, as investors remained cautious after the S&P 500 index briefly hit its highest intraday level since November 2007.

The S&P 500 was buoyed by General Electric after cable company Comcast Corp said it will buy from GE the the part of NBCUniversal it didn't already own for $16.7 billion.

Comcast's stock hit the highest since 1999 before closing up 3 percent at $40.13 and GE gained 3.6 percent to $23.39.

The S&P 500 is up 6.6 percent so far this year, partly due to stronger-than-expected corporate earnings and a better economic outlook. The Dow industrials is about 1 percent away from an all-time intraday high, reached in October 2007.

Volume has been weak in recent days with the S&P moving sideways around 1,520. The index is about 3 percent away from closing at a record high.

A scarcity of sellers after a consistent string of gains is a positive sign and shows the uptrend is intact, King Lip, chief investment officer at Baker Avenue Asset Management in San Francisco, said.

"Last year we had double-digit returns in the first quarter. It's fairly possible we can move higher from here," he said.

The Dow Jones industrial average <.dji> fell 35.79 points or 0.26 percent, to 13,982.91, the S&P 500 <.spx> gained 0.9 point or 0.06 percent, to 1,520.33 and the Nasdaq Composite <.ixic> added 10.38 points or 0.33 percent, to 3,196.88.

The S&P gained 12 percent in the first three months of 2012.

Deere & Co , the world's largest farm equipment maker, forecast a modest increase in sales this year despite the prospect of the biggest corn crop in U.S. history. The forecast fell short of analysts' expectations, sending shares of Deere down 3.5 percent to $90.68.

In extended trading, shares of technology bellwether Cisco Systems fell 2 percent after it posted results.

Dr Pepper Snapple fell 5.8 percent to $42.69 after it forecast profit for the current year below analysts' estimates.

Cliffs Natural Resources lost a fifth of its market value a day after the miner reported a quarterly loss and slashed its dividend by 76 percent. Its shares fell 20 percent to 429.29.

According to the latest Thomson Reuters data, of the 364 companies in the S&P 500 that have reported results, 70.3 percent have exceeded analysts' expectations, above a 62 percent average since 1994 and 65 percent over the past four quarters.

About 5.9 billion shares changed hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, below the daily average in February last year of 6.94 billion.

On the NYSE, roughly seven issues rose for every five that fell and on Nasdaq more than six rose for every five decliners.

(Editing by Kenneth Barry and Bernadette Baum)

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Despite Claims of Third Blast, North Korean Nuclear Program Remains a Mystery

As scientists and world leaders scrambled Tuesday to judge the importance of North Korea’s claim that it had detonated a third nuclear bomb, the main thing that quickly became evident is how little is known about the country’s increasingly advanced atomic and missile programs.

Even the best news about the test — that it was small by world standards — could have a dangerous downside if the North’s statement that it is learning to miniaturize bombs is true. That technology, which is extremely difficult to master, is crucial to being able to load a weapon atop a long-range missile that might one day reach as far as the United States mainland.

“We don’t know enough to nail it, but we can’t rule out that they’ve done something dangerous” Ray E. Kidder, a scientist who pioneered early nuclear warhead designs at the Livermore weapons lab in California, said of the underground test.

As is usual with tests by the secretive North, it was not even clear if the underground test was nuclear, rather than conventional bomb blasts meant to mimic an underground nuclear test. Experts assume it was nuclear partly from the shape of its seismic signal and because the blast was at the same mountainous site as two earlier nuclear tests.

It also remains unclear whether the North used plutonium or enriched uranium to fuel the bomb. American officials believed that the country’s last two nuclear tests, in 2006 and 2009, used plutonium, and they fear a switch to uranium will allow the country a faster and harder-to-detect path to a bigger arsenal. While scientists are actively hunting for the airborne markers of a uranium test, it is not certain that gases needed to make that judgment escaped the test site.

Scientists said the relatively small size of Tuesday’s blast calmed, at least temporarily, their worst fears: that the North’s recent references to more powerful hydrogen bombs indicated the possibility that it might have at least enough technology to try to test one. Those bombs, nicknamed city-busters, are roughly 1,000 times stronger than atom bombs, and if the North were to get them it would represent an enormous leap in its known abilities. The first American hydrogen bomb to be tested caused the Pacific island of Elugelab to vanish.

What emerged most clearly Tuesday from sensitive global networks that measure faint rumbles in the earth was that the underground blast was most likely larger than North Korea’s past explosions. In Vienna, the preparatory commission for the Comprehensive Nuclear Test Ban Treaty Organization, which runs a global seismic network, said the blast measured 5.0 in seismic magnitude. The United States Geological Survey put its own estimate at 5.1 in magnitude.

Nuclear experts said the magnitude of the blast equaled an atomic blast of about 6,000 tons of high explosive, or six kilotons. The first test by Pyongyang is thought to have packed less than a kiloton of power and was considered a partial failure by the West. The state’s 2009 blast was judged by American intelligence officials to have a power of two kilotons, though some experts outside the government say it might have been as large as this week’s test.

In any case, said Paul Richards, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., it was “a serious explosion.”

Still, even the largest estimates are small by world standards. The first three nuclear tests of China, for instance, were measured at 22 kilotons, 35 kilotons and 250 kilotons.

North Korea’s tests “are limited in explosive power compared with most previous ones,” said Robert S. Norris, a senior fellow at the Federation of American Scientists in Washington, and the author of “Racing for the Bomb,” a biography of Gen. Leslie R. Groves, the Manhattan Project’s military leader. Determining whether the test was fueled by plutonium or uranium is critical because North Korea in 2007 shut down its reactor that made plutonium, prompting analysts to conclude that its supplies of the rare element are now running low. Intelligence officials estimated it had enough fuel for 6 to 10 bombs.

But in 2010, the state revealed what appears to be a fairly advanced program to enrich uranium, which in theory could fuel many bombs since experts believe that North Korea has rich uranium deposits.

Siegfried S. Hecker, a former director of the Los Alamos weapons lab in New Mexico who has repeatedly visited North Korea and learned details of Pyongyang’s nuclear program, has suggested that North Korea may be ready to switch to a pure uranium approach, in part because it might have a blueprint for a miniaturized uranium warhead.

He said the North’s leadership might have obtained the blueprint from A. Q. Khan, the rogue Pakistani nuclear expert, a blueprint of the type he gave Libya for a uranium bomb. It is well known that North Korea obtained its centrifuge design for uranium enrichment from Dr. Khan, and many experts say the Pakistani expert may have thrown in the warhead blueprint as a sweetener.

Analysts say the uranium approach may also offer North Korea the allure of a new secrecy. Centrifuge plants are much easier to hide than reactors.

Finding out whether the bomb was fueled by plutonium, uranium or a mix of the two materials could take some time or might never happen, analysts say.

Not all underground tests leak their explosive residues into the atmosphere or surrounding waters, and some say tests of the size of Tuesday’s blast are probably strong enough to seal any cracks in the rocks.

“If we get samples, I’m sure we’ll learn a lot about it,” Jay C. Davis, a nuclear scientist who helped found a federal effort to improve such analyses, said in an interview.

But if no bomb residue leaks, he added, the nature of the fuel that North Korean used for its third blast may remain a mystery.

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