Spoiler Alert: First 3-D Printed Records Sound Awful

The needle drops and a series of high, repetitive whines come from the album. Then a crackling sound, and a muffled guitar riff. Finally, Kurt Cobain’s voice — audible, but distant and hollow, like he is singing in a tunnel with a scarf over his mouth.

It’s about the worst version of “Smells Like Teen Spirit” you could find. But it is awesome all the same for its totally unique medium. This particular LP is part of the batch of the first records ever to be created on a 3-D printer.

“It’s surprising how much you can deform and down-sample an audio file and still recognize it,” says Amanda Ghassaei, assistant tech editor at Instructables, who printed the record, and several others, including music from the Pixies, Daft Punk, and Radiohead.

Ghassaei used a state-of-the-art Objet Connex 500 printer to generate the disc. The whole process is possible because printing resolution has finally become high enough to create the audio-laden grooves for the needle to track and amplify. For her printed records, Ghassaei sets the machine to its finest setting, 600 dpi, with 16 micron steps, about the highest quality available on the market. But it’s still far lower resolution than on a vinyl LP, by a factor of 10 or so; hence the muddled sound that results in part from the needle responding to the layering of the printed plastic. Ghassaei used an 11 Khz sampling rate — the highest the resolution would allow, around 1/4 what you get from an MP3. Even at that low of a rate, the printer’s deficiencies cut off the song’s high-range tones.

“It’s really stripped down, it’s down to the bare essentials,” she says. “It’s never going to be as good as vinyl. It’s not really set up for that. But it’s cool because you can really be creative with it.”

To create the 3-D model for the record, Ghassaei essentially reverses the process of ripping an MP3. As the groove of a record is a microscopic image of the analog audio, she starts with the digitized waveform, using Python to take it directly from the MP3 file, and renders the shape of it into an STL wireframe using Processing, an open source tool that automates the file generation. She then uses the software to wrap it in a spiral on a 3-D 12-inch disc, varying the depth of the groove to match the waveform. Compared to a normal record, hers have increased amplitude and groove depth to account for the coarse resolution.

While it’s a first for a printed proper LP, others have toyed with simpler forms of 3-D printable music. Earlier this year, Fred Murphy generated “Stairway to Heaven” and three other songs on discs for the classic Fisher Price record player. That toy turntable is different than the common vinyl record player, though; it uses a music-box system with tines that sound as they rotate over the record’s raised bumps. Murphy posted the how-to for his project on Instructables, and offers pre-made versions of his discs through Shapeways.

Ghassaei, like Murphy, has put her project up on Instructables, though it’s not particularly useful unless you have access to a high-end printer in the range of hundreds of thousands of dollars. She is also limited to the first 60 seconds or so, because of the data- and memory-intense 3-D file. A full song would take up a whole side of the album, and the file size would exceed a gigabyte. But that’s not really the point.

“It’s really cool to kind of push the technology and see what you can get out of it,” says Ghassaei. “I’ve got a bunch more that I want to do.”

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“Gangnam Style” in line for UK dictionary inclusion

LONDON (Reuters) – He has the most-watched video in Youtube history, become a pop sensation with a horse-riding dance craze that has swept the world and now Korean singer Psy may cement his place in popular culture with recognition from a British dictionary.

“Gangnam Style,” Psy’s signature song, has been chosen along with “fiscal cliff” and “Romneyshambles” as some of Collins Dictionary‘s words of the year.

“We were looking for words that told the story of the year,” said Ian Brookes, the dictionary‘s consultant editor.

“Some words are from events that have been and gone and so are not likely to stick around … but others are probably here to stay.”

Other headline entries centered on American politics.

“Fiscal cliff” has drawn a lot of attention as the deadline for Congress and President Obama to agree on government spending and tax plans draws nearer.

While the term “Romneyshambles” entered the British public’s consciousness after Mitt Romney‘s gaffe-ridden visit to London in July in which he questioned Britain’s readiness to host the Olympics.

The inclusion of “47 percent” on the list after a leaked video showed Romney telling donors that 47 percent of Americans would definitely vote for Obama because of their dependency on the government capped off a bad year for the losing presidential candidate.

Collins received over 7,000 submissions on its online database.

Twelve words of the year – one for each month – were then selected on the basis of the frequency with which they were spoken, how many places they appeared and their longevity in public discourse.

Appearing on the Collins words of the year list is no guarantee of insertion in the next dictionary.

But Gangnam Style stands a very good chance, Brookes said.

“It’s obviously a craze, so there’s the possibility it will go away. But it’s been heard by so many people that I think it’s probably earned the right to go into the dictionary.”

Other words of the year include “mummy porn” after the popularity of the “Fifty Shades of Grey” books, and “superstorm” after Superstorm Sandy wreaked havoc along the east coast of America in October.

(Reporting By Peter Schwartzstein, editing by Paul Casciato)

Music News Headlines – Yahoo! News

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Robert Bork, failed Supreme Court nominee, dies at age 85

Robert H. Bork, whose failed Supreme Court nomination in 1987 infuriated conservatives and politicized the confirmation process for the ensuing decades, died Wednesday at the age of 85. 

The former Yale law professor and judge on the U.S. Court of Appeals for the D.C. Circuit had a history of heart problems and had been in poor health for some time.

But Bork was a towering figure for an early generation of conservatives. In the 1960s and '70s, he argued that a liberal-dominated Supreme Court was abusing its power and remaking American life by ending prayers in public schools, by extending new rights to criminals, by ordering cross-town busing and by voiding the laws against abortion.

PHOTOS: Robert Bork | March 1, 1927 - Dec. 19, 2012

He was an influential legal advisor in the Nixon administration and served as a footnote to history in the Watergate scandal. When the embattled president ordered the firing of special counsel Archibald Cox, the attorney general and his deputy resigned in protest. Bork, who was in the No. 3 post as U.S. solicitor general, then carried out Nixon’s order.

But Bork’s biggest moment came during the Reagan administration in the 1980s. He left Yale and came to Washington when Reagan appointed him to the U.S. court of appeals in the District of Columbia. The job was seen as a steppingstone to the high court.

In 1986, Bork was passed over for a younger colleague when Reagan named Judge Antonin Scalia to the Supreme Court. A year later, Bork’s turn came when Justice Lewis Powell, the swing vote on the closely divided court, announced his retirement.

PHOTOS: Notable deaths of 2012

Democrats, led by Sen. Edward Kennedy, launched an all-out attack on Bork’s nomination, saying he would set back the cause of civil rights, women’s rights and civil liberties.

The summer of 1987 saw campaign-style attacks on Bork’s reputation.  In televised hearings, the bearded, heavy-set professor tried to explain his views, but he won few converts. The Senate defeated his nomination by a 58-42 vote.

In his place, Reagan eventually chose Judge Anthony Kennedy, who was confirmed unanimously. The switch proved to have lasting consequences. Kennedy cast decisive votes to uphold Roe vs. Wade and to preserve the ban on school-sponsored prayers.

Bork stepped down from the bench a year after his defeat, but wrote several books renewing his criticism of liberalism. In the past year, he served as a chairman of Mitt Romney’s advisory committee on the judiciary and the courts.

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Eagle Picks Up a Kid: Real or Fake?

Sometimes I feel like Peter Parker. (You know, Spider-Man.) I have real work to do, but then I hear these sirens on the internet and I must go to action.

Well, what about this kid being carried away by an eagle? What can be done with this video? Here is the evidence I will present. Let me just say that I sure hope it’s fake. I would hate to have all our babies snatched away by flying eagles. That would just suck. Although, maybe the eagle is just pumped up about the movie The Hobbit and thinks that kid is actually a hobbit.

Analysis of Camera Shake

This is my first go-to tool when looking at videos. One of the tricks fakers use is to record the video with a tripod. A steady video makes it much easier to add in special effects later. Of course, who records with a tripod? That seems unrealistic. To account for this, the fakers will add “fake shake” to the video.

How do you detect a fake shake? The first step is to use a video-analysis tool like the awesome and free Tracker Video Analysis. With this, I can track the motion of the background in the video to see how the camera moves. Here are four samples of background motion.

Which, if any, of these background motions do you think correspond to a real person with a real camera? Here are the answers:

• A: This is the background motion from the Human Birdwings video. In case you missed it, a guy posted a video of his homemade wings that let him fly like a bird. It was fake.


• B: This is from the eagle-kid video. Real or fake?


• C: This is fake shake from this fake spinning water video. You can see how the camera takes similar pixel size jumps. It’s faker than Sweet ‘N Low.


• D: This is a real video recorded from a real person (me). What does this background look like? To me, it looks like a random walk. Maybe that’s just me.

For this eagle video, which case does it look like? It doesn’t look as bad as the other two known fake videos. However, it doesn’t look like my video either. One of the things I haven’t looked at (yet) is the stabilizing video features that YouTube offers for videos.

I would say that this shake analysis is mostly inconclusive.

Acceleration of a Falling Object

Next, let’s look at the part of the video where the eagle drops the kid. The drop distance is small enough that air resistance should be negligible. This means that the vertical acceleration should have a value of -9.8 m/s² if this eagle and kid are on the surface of the Earth. Here is a plot of vertical motion of the kid after he (or she) is dropped.

I put the arrow to indicate the part of the data where the kid was dropped. Now, I don’t know the scale — but it might not matter. Does this look like constant acceleration? No, it looks like constant velocity. I’m not even going to use the quadratic fit in this case to find the scale.

Instead, let’s look at the time of the fall. From the video, the child was falling for 0.367 seconds. If the child was dropped from rest (or close to it), how high would the kid have to be to fall for this time? Normally, I break down the kinematic equations and show where this comes from, but let me just skip right to it.

Putting in my value for the time, I get a dropped height of 0.66 meters. OK, that’s not as bad as I thought it would be. However, the position function should still be a parabola and not a straight line.

Center of Mass

Here is a shot of the kid while being carried by the eagle.

Look at the angle that the kid is “swinging” back. It could be as high as 30° – but that is just an “eyeball” guess. So what? This actually shows a common misconception. It shows the idea that if something is moving at a constant velocity, there must be a constant force on it. However, at low speeds with no air resistance there wouldn’t need to be a force pulling the kid forward.

If the bird were accelerating, then the kid would swing back. From the swingback angle, you can figure out the acceleration. You can find all the details on how this works in my Iron Man 3 post. Here also is a diagram of a person hanging from something that is accelerating.

The kid hanging back at an angle couldn’t be moving at a constant speed since the horizontal forces don’t add up to zero. If I use an angle of 30°, then the bird would have to accelerate at 5.6 m/s². That’s pretty high for a bird carrying a kid.

How Much Can an Eagle Lift?

Bigger-mass birds need bigger wings, right? Also, a larger wingspan bird could lift more “cargo”. So how much could an eagle lift? Here is my favorite graph showing the relationship between a bird’s wingspan and mass.

Bigger-mass birds need bigger wings. Seems obvious. So, what about a Golden Eagle? Wikipedia lists these as having a mass of about 6.5 kg and a wingspan of about 2.3 meters. What about the kid? Let’s say the kid is 2 years old with a mass of about 13 kg. That is about double the mass of the eagle! Sure, eagles can pick stuff up — but not something this big.

OK — I think we can all agree this video is fake.

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A Minute With: Jessica Chastain on “Zero Dark Thirty”

NEW YORK (Reuters) – Jessica Chastain carries the weight of starring in one of the year’s most anticipated films, “Zero Dark Thirty,” about the decade-long hunt and eventual killing of Osama bin Laden.

Critics say Chastain pulls it off seamlessly as “Maya,” based on a real-life CIA agent who played a major role in tracking down bin Laden at his hideout in Pakistan.

As the film opens in limited U.S. release on Wednesday, Chastain, who is tipped as a likely best actress Oscar nominee for the role, talked to Reuters about playing a character she could not meet and why the film is an important look at America’s role in a dark war.

Q. What did you think when you saw this film finished?

A. “It is a tough one for me to watch, because there is so much responsibility with playing this woman. I find her to be incredible. And I didn’t want to change her story or make her a Hollywood version, with a lot of makeup. I didn’t want to trivialize what she did … I want her to like it, but I don’t know if she will ever see it.”

Q. How did you play someone you had never met?

A. “There was three months of working with (screenplay writer) Mark Boal, doing research, reading lists and talking to people. And then anything I could not solve through research, like what is her favorite candy – ’cause when we are all overseas we have something we do when we are homesick – I had to answer that question myself.”

Q. Boal hasn’t gone into too much detail about her?

A. “We have to protect her because she is an undercover CIA operative, still working.”

Q. What else did you know about her?

A. “When we finished the movie, when the Navy Seal book ‘No Easy Day’ came out. I raced to go read it, because I was like, ‘I need to know if my character is in the book!’ And they talk about Jen, the young CIA girl. Well, everything matched up. She was the only one that said 100 percent ‘he is there.’… They talked about how she had been on it close to a decade and they were only on it for 40 minutes. They said she was crying on the airplane afterwards.”

Q. During filming, were you ever worried about your safety, that the film might be misconstrued?

A. “As an actor you always worry about that. Because you think, maybe someone will see a film and they won’t understand the difference between acting and reality. The good thing is, what (director Kathryn Bigelow) and Mark have done, is that they have not made a propaganda film. They tried to make it as authentic as possible and respectful of the actual historical event as they could. That includes showing the intense interrogation techniques that were used. The end of the film – it’s not a lot of fist pumping and saying, ‘Here is our journey over 10 years and it was so difficult and we finally did it.’ It ends actually on a very different note.”

Q. Can you elaborate on that?

A. “Well, for me the whole thing is about the arc of this woman. She shows up in the beginning and she is wearing her best suit. She thinks she knows what she is in for, and she is completely out of her element. But over the 10 years, this woman, who has been trained to be unemotional and analytically precise … we see her struggling to keep it contained for 10 years and as she descends down the rabbit hole of the world she is in.

“So finally at the end when she is asked, ‘Where do you want to go?’ there is no way to answer that question. … She has no idea where she belongs, now that this is done. But not only does it speak in terms of that, but the movie ends with that question – where do you want to go? Where do we go now as a country? Where do we go as a society? It is not a movie that ends with an answer, and I find that powerful.”

Q. How did you cope with filming the torture scenes?

A. “We filmed in a real Jordanian prison, in the middle of nowhere. The environment wasn’t great, especially as a woman.

“They had a lot of trust between the actors, nothing was dangerous or unsafe. There was a lot of discussion to make sure that we weren’t doing something that was going to be salacious. They just wanted it to be accurate.

“I know I am playing a character who has trained to be unemotional. But I have spent my entire life allowing myself to be emotional, and allowing myself to feel everything. … There was actually one day that we were doing a scene, and I said, ‘I am sorry’ and I just had to walk away, and I just started crying … it was a very intense experience.”

Q. You are a top chance for Oscar nomination. Would that be more or less rewarding for this role?

A. “Because she is still an active member of the CIA and undercover, she can’t take credit for what she’s done. … And by making this film, it is my idea as a way of thanking her. It would be very emotional because of that.”

Q. You compare your character to getting lost down a CIA rabbit hole. What about your own dizzying rise as an actress?

A. “That’s a good question. I do think that next year I need to go somewhere for a month and be in a room by myself and be like, ‘Ok, what now Jessica?’ But I am nowhere near where she was at the end of this mission.”

(Reporting By Christine Kearney, editing by Jill Serjeant and Doina Chiacu)

Movies News Headlines – Yahoo! News

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Global Update: African Children Still at Risk of Pneumonia Despite Ceramic Stoves

Small ceramic indoor stoves, such as those sold by women in AIDS self-help groups in Africa, do save fuel and cut down on eye-irritating smoke, a new study has found — but they do not save children from pneumonia.

The study, published in The American Journal of Tropical Medicine and Hygiene, compared 168 households in rural Kenya that used either “upesi jiko” stoves or traditional three-stone indoor fires. The former — the name means “quick stove” in Swahili — has a locally made ceramic firebox that sells for $3. Clay and mud must be built up around it to insulate it and support the pot.

Since it uses less wood, it saves local forests. But it has no chimney, so the smoke stays indoors.

Biweekly visits by researchers found that children in both the stove and open-fire homes got pneumonia equally often. Pneumonia is a leading cause of death for infants in poor countries, and a 2008 study showed that the fine particles and toxic gases in cooking smoke inflame their lungs, doubling the pneumonia risk.

Two years ago, Secretary of State Hillary Rodham Clinton committed $50 million in American aid to help the Global Alliance for Clean Cookstoves get 100 million efficient stoves into households by 2020. But experts are still divided over which stove to pursue; chimneys do not solve all the problems, and stoves with fans burn more cleanly but are expensive and fragile.

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A search for normality as Newtown schools reopen after massacre

The Newtown tragedy was in the minds of many as schools opened as usual across the country. Lee Woodruff met with a group of teachers in Westchester County, N.Y., about getting back to work after a difficult weekend.

By Tina Susman and Michael Muskal

December 18, 2012, 9:31 a.m.

NEWTOWN, Conn. -- Amid increased security, schools reopened here on Tuesday as this town searched for a road back to normality after last week’s massacre at a local elementary school.

Funerals for the 20 first-graders and six adults killed Friday morning at Sandy Hook Elementary School will continue throughout the week. Two children were buried on Monday amid the cold and rain and two more funerals are scheduled for Tuesday.

Sandy Hook remained closed, however, and will likely be shuttered for months as authorities continue their investigation into the shooting spree by Adam Lanza, 20, who killed himself after invading the school, opening fire on students and staff and then turning a gun on himself.

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Photos: Massacre at elementary school in Newtown, Conn.

Who they were: Connecticut school shooting victims

Full coverage: Connecticut school shooting

Transcript and video: Obama's speech

Timeline: Deadliest U.S. mass shootings

The weapons Lanza used were legally owned by his mother, Nancy, who was the first of the 28 people who died from bullets that morning.

Yellow school buses rumbled along roads Tuesday morning, some still dotted with makeshift memorials to those who were slain. Children laden with book bags waited outside their homes for the buses.

 PHOTOS: Shooting at Connecticut school

But it was clear this would not be a normal day for them despite teachers' efforts and the stepped-up presence oflawenforcement. Staffers met on Monday with psychologists and other specialists to hear how to handle their own grief and children's questions.

“It's important to try to make things feel normal for her,” a mother who would give only her first name -- Barbara -- said, explaining why she decided to have her 8-year-old daughter head back to classes.

 FULL COVERAGE: Shooting at Connecticut school

Barbara, who was driving her daughter to school, said she knew not all parents would be comfortable letting their kids go into the schools, even with extra security. “I'll be a lot more anxious than usual,” she admitted.

Newtown police Lt. George Sinko said sending children back to school is a personal choice and parents would have to make their own decisions.

“I can't imagine what it must be like being a parent with a child that young, putting them on a school bus,” Sinko said.

In addition to trying to reassure parents, the increased police presence helped keep the media from the schools. Police have also said they will severely prosecute anyone perpetrating hoaxes, such as two telephone calls saying there were bombs on the grounds of a local church, St. Rose of Lima Roman Catholic Church.

Police have been told to act aggressively, as they did in nearby Ridgefield on Monday where they shut down schools amid reports of a suspicious man at the train station. After investigating, police told reporters there was no threat.

In addition to the investigation at Ridgefield, about 20 miles from Newtown, there have been reports across the country of closures by anxious officials. Two schools were locked down in South Burlington, Vt., and a high school in Windham, N.H., was briefly locked down. Neither case involved any threat.

Two more children will be buried on Tuesday and both funerals will be held at St. Rose, which has been a center of grief counseling and community support. Services will be held for 6-year-olds Jessica Rekos and James Mattioli.

Jessica was avid about horses and had asked Santa for new cowgirl boots and a cowgirl hat this year, according to her family. “Jessica loved everything about horses,” her parents, Rich and Krista Rekos, said in a statement. “She devoted her free time to watching horse movies, reading horse books, drawing horses and writing stories about horses.”

James was described by his relatives as a “numbers guy” who loved math.

On Monday, two funeral homes were filled with mourners for Noah Pozner and Jack Pinto, both 6. Pozner had a Jewish service and Pinto a Christian one.

Noah Pozner’s twin, Arielle, survived the rampage because she was assigned a different classroom.

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Autodesk Developing CAD Software to Design, 3-D Print Living Tissue

Autodesk, the industry leader in CAD software, has announced it is partnering with biological printer manufacturer Organovo to create 3-D design software for designing and printing living tissue.

It’s an area of interest to Autodesk, whose software runs the industrial design and architecture worlds, allowing them to expand further into new fields by helping researchers interface with new tools.

Organovo’s bioplotter, one of the only machines that can shape living tissue, works like a standard desktop 3-D printers but uses living cells instead of ABS plastic. It creates tissue by printing a gel base material as a scaffold and then deposits cells which mature into living material that can be used in the process of developing new pharmaceuticals.

Specific details about the system, including pricing and availability, are not yet available. Even with scant details, executives at both companies are excited about the potential of such a system.

“Autodesk is an excellent fit for developing new software for 3D bioprinters,” Organovo CEO Keith Murphy says in a press release. “This partnership will lead to advances in bioprinting, including both greater flexibility and throughput internally, and the potential long-term ability for customers to design their own 3D tissues for production by Organovo.”

Jeff Kowalski, senior VP/CTO at Autodesk, echoes Murphy’s sentiment. “Bioprinting has the potential to change the world,” he says. “It’s a blend of engineering, biology and 3D printing, which makes it a natural for Autodesk. I think working with Organovo to explore and evolve this emerging field will yield some fascinating and radical advances in medical research.”

While this announcement is certainly big news, we’re multiple revisions away from 3-D printing replacement body parts. Even after the technical difficulties of printing organs or even tissue for live human use are worked through, any resulting process will need to be validated through complex clinical trials and a long review by the FDA and international authorities. Still, it will be exciting to see what medical researchers and DIY biohackers will do with these tools.

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HBO making “Game of Thrones”-themed beer

LOS ANGELES (TheWrap.com) – Winter is coming – and so is a new line of beers based on HBO‘s fantasy drama “Game of Thrones.” Presumably, all will boast a full, robust head, perhaps resting on top of a spike.

HBO is teaming with Cooperstown, N.Y. brewery Ommegang for a line of brews centered around the series, the New York Times reports. The first beer, Iron Throne Blonde Ale, is slated to go on sale in March, in time for the March 31 premiere of the show’s third season.

It sounds like the perfect libation for watching the premiere from the comfort of your $ 30,000 Iron Throne replica.

A second “GoT”-themed beer will go on sale in fall 2013, with two more varieties expected to go on sale in conjunction with new seasons of the series.

TV News Headlines – Yahoo! News

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Mind: A Misguided Focus on Mental Illness in Gun Control Debate

The gunman, Adam Lanza, 20, has been described as a loner who was intelligent and socially awkward. And while no official diagnosis has been made public, armchair diagnosticians have been quick to assert that keeping guns from getting into the hands of people with mental illness would help solve the problem of gun homicides.

Arguing against stricter gun-control measures, Representative Mike Rogers, Republican of Michigan and a former F.B.I. agent, said, “What the more realistic discussion is, ‘How do we target people with mental illness who use firearms?’ ”

Robert A. Levy, chairman of the Cato Institute, told The New York Times: “To reduce the risk of multivictim violence, we would be better advised to focus on early detection and treatment of mental illness.”

But there is overwhelming epidemiological evidence that the vast majority of people with psychiatric disorders do not commit violent acts. Only about 4 percent of violence in the United States can be attributed to people with mental illness.

This does not mean that mental illness is not a risk factor for violence. It is, but the risk is actually small. Only certain serious psychiatric illnesses are linked to an increased risk of violence.

One of the largest studies, the National Institute of Mental Health’s Epidemiologic Catchment Area study, which followed nearly 18,000 subjects, found that the lifetime prevalence of violence among people with serious mental illness — like schizophrenia and bipolar disorder — was 16 percent, compared with 7 percent among people without any mental disorder. Anxiety disorders, in contrast, do not seem to increase the risk at all.

Alcohol and drug abuse are far more likely to result in violent behavior than mental illness by itself. In the National Institute of Mental Health’s E.C.A. study, for example, people with no mental disorder who abused alcohol or drugs were nearly seven times as likely as those without substance abuse to commit violent acts.

It’s possible that preventing people with schizophrenia, bipolar disorder and other serious mental illnesses from getting guns might decrease the risk of mass killings. Even the Supreme Court, which in 2008 strongly affirmed a broad right to bear arms, at the same time endorsed prohibitions on gun ownership “by felons and the mentally ill.”

But mass killings are very rare events, and because people with mental illness contribute so little to overall violence, these measures would have little impact on everyday firearm-related killings. Consider that between 2001 and 2010, there were nearly 120,000 gun-related homicides, according to the National Center for Health Statistics. Few were perpetrated by people with mental illness.

Perhaps more significant, we are not very good at predicting who is likely to be dangerous in the future. According to Dr. Michael Stone, professor of clinical psychiatry at Columbia and an expert on mass murderers, “Most of these killers are young men who are not floridly psychotic. They tend to be paranoid loners who hold a grudge and are full of rage.”

Even though we know from large-scale epidemiologic studies like the E.C.A. study that a young psychotic male who is intoxicated with alcohol and has a history of involuntary commitment is at a high risk of violence, most individuals who fit this profile are harmless.

Jeffery Swanson, a professor of psychiatry at Duke University and a leading expert in the epidemiology of violence, said in an e-mail, “Can we reliably predict violence?  ‘No’ is the short answer. Psychiatrists, using clinical judgment, are not much better than chance at predicting which individual patients will do something violent and which will not.”

It would be even harder to predict a mass shooting, Dr. Swanson said, “You can profile the perpetrators after the fact and you’ll get a description of troubled young men, which also matches the description of thousands of other troubled young men who would never do something like this.”

Even if clinicians could predict violence perfectly, keeping guns from people with mental illness is easier said than done. Nearly five years after Congress enacted the National Instant Criminal Background Check System, only about half of the states have submitted more than a tiny proportion of their mental health records.

How effective are laws that prohibit people with mental illness from obtaining guns? According to Dr. Swanson’s recent research, these measures may prevent some violent crime. But, he added, “there are a lot of people who are undeterred by these laws.”

Adam Lanza was prohibited from purchasing a gun, because he was too young. Yet he managed to get his hands on guns — his mother’s — anyway. If we really want to stop young men like him from becoming mass murderers, and prevent the small amount of violence attributable to mental illness, we should invest our resources in better screening for, and treatment of, psychiatric illness in young people.

All the focus on the small number of people with mental illness who are violent serves to make us feel safer by displacing and limiting the threat of violence to a small, well-defined group. But the sad and frightening truth is that the vast majority of homicides are carried out by outwardly normal people in the grip of all too ordinary human aggression to whom we provide nearly unfettered access to deadly force.

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