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Engineers are turning to innovative approach to hush aircraft noise and reduce environmental problems for communities near airports.For instance, Georgia Tech Research Institute (GTRI) are relying on honeycomb-like structures to reduce sound more effectively than conventional methods.

‘This approach dissipates acoustic waves by essentially wearing them out,’ said Jason Nadler, a GTRI research engineer. ‘It’s a phenomenological shift, fundamentally different from traditional techniques that absorb sound using a more frequency-dependent resonance.’

Most sound-deadening materials - such as foams or other cellular materials comprising many small cavities - exploit the fact that acoustic waves resonate through the air on various frequencies, Nadler explained. An automobile muffler, for example, uses a resonance-dependent technique to reduce exhaust noise.

The drawback with these traditional noise-reduction approaches is that they only work with some frequencies - those that can find cavities or other structures in which to resonate, according to a GTRI press release.

Nadler’s research involves broadband acoustic absorption, a method of reducing sound that doesn’t depend on frequencies or resonance.

In this approach, tiny parallel tubes in porous media such as metal or ceramics create a honeycomb-like structure that traps sound regardless of frequency. Instead of resonating, sound waves plunge into channels and dissipate through a process called viscous shear.

Viscous shear involves the interaction of a solid with a gas or other fluid. In this case, a gas - sound waves composed of compressed air - contacts a solid, the porous medium, and is weakened by the resulting friction.

‘It’s the equivalent of propelling a little metal sphere down a rubber hose when the sphere is just a hair bigger than the rubber hose,’ Nadler explained. ‘Eventually the friction and the compressive stresses of contact with the tube would stop the sphere.’

Creating such low-density structures presents an interesting challenge, Nadler said. It requires a material that’s light, strong enough to enable the walls between the tubes to be very thin, and yet robust enough to function reliably amid the high-temperature, aggressive environments inside aircraft engines.

National Public Radio, already strong online with free downloads from many of its shows, is boosting its digital ambitions with Monday’s introduction of social-networking features akin to Facebook.

NPR also plans to overhaul its Web site and expand the tools for sharing its programs elsewhere over the next few months. And it is working to increase the flexibility of its popular “podcasts,” audio downloads that have tripled in usage over the past two years.

These digital initiatives are aimed at capturing and retaining audiences — particularly younger people who aren’t habitual radio listeners but who represent the future for fundraising at NPR’s member stations.

Yet NPR faces a challenge in finding common ground with the stations, which rely on traditional, local radio offerings to draw contributions.

The national organization, acknowledging that its early Internet initiatives at times collided with its member stations, insists many of the new offerings have been developed with the stations’ needs and concerns in mind.

“We definitely see ourselves at a pivotal point,” said Dana Davis Rehm, NPR’s senior vice president for strategy and partnerships. “We know where we want to be, but navigating the waters can be challenging at times. Every now and then we get rough seas.”

Jeffrey Dvorkin, a former NPR ombudsman now with the Ryerson School of Journalism in Toronto, described the tensions as “growing pains as NPR uses its considerable editorial and creative muscle to use the Internet to maximum effect.”

The fears come down to whether enhancing the NPR.org Web site will encourage listeners to bypass the individual stations on the Web as well as on air. If listeners get everything they need from the central organization to which local stations pay dues, they might stop giving or give less to their local stations.

But both public radio audiences and contributions to public radio have been going up. NPR stations combined had 31.3 million weekly listeners in spring 2008, a 3 percent increase from the same period a year earlier. Although aggregate fundraising numbers were not available, NPR and several individual stations contacted by The Associated Press reported increases.

Online traffic is also up. According to comScore, NPR.org had 2.6 million unique visitors in August, a 78 percent increase from a year earlier.

Rehm, at NPR, said the national organization now sees stations as partners. Long gone, she said, are the days when NPR waited “until the 11th hour, if ever” to consult with stations on its digital plans.

Ken Stern left NPR as chief executive in March, reportedly ousted over his style and clashes with stations over their digital future. A permanent replacement isn’t expected until early next year, though NPR last week hired Kinsey Wilson from USA Today as its digital chief, effective Oct. 20.

Stations are warming up.

“Certainly years ago there was much more of an attitude of us-them,” said Bob Lyons, director of new media for WGBH in Boston. “That’s largely dissipated. There have been changes at NPR, changes at the stations and changes in the world all around.”

Lyons said the new social-networking tools, even though they initially will be available only at NPR.org, will help local listeners connect with one another and with local stations.

The new tools let listeners create personal profiles and declare other listeners or NPR staffers as friends. They also can add a photo of themselves and list their favorite books, movies and NPR programs and — soon — their local station.

NPR also plans to expand its library of Application Programming Interfaces, or APIs, which are software tools to let the general public and local stations incorporate NPR content into their own applications.

One use of the APIs plots the subjects of NPR stories on a world map. Another lets people listen to stories on Apple Inc.’s iPhone.

Upcoming ones promise to help stations blend local and national content online.

“That will help strengthen their own Web sites,” said Mitch Praver, NPR’s chief operating officer. “Rather than force the audience to come to NPR’s Web site, the journalism is being extended to sites all over the world.”

Many stations credit the Internet for exposing local programs to a broader audience, be it “The Leonard Lopate Show” on WNYC in New York, “The Kojo Nnamdi Show” from WAMU in Washington, D.C., or a 24-hour classical-music feed from KUHF in Houston.

“The burden is somewhat on stations to diversify and produce compelling content,” WAMU spokeswoman Kay Summers said.

Laura Walker, chief executive for WNYC, said 60 percent of its contributions now come over the Internet, and the expanded audience for local shows has resulted in pledges from as far as Japan and China. But she said the station can’t be too aggressive, lest it divert contributions from fellow stations.

Rehm said fundraising is a key source of anxiety, but if done right, a strong Internet presence could bring “more giving from more people.”

“Consumers’ expectations are changing, and our audience wants more flexibility,” said Darren Mauro, a digital media director at NPR. “To be realistic, the Internet is a fast-moving place. That makes everybody nervous on one level, and everyone sees new opportunities on another.”

TiVo Inc. and Nero AG of Germany were set to announce Monday that they will be launching a package that turns a Windows PC into a TV recorder, just like a TiVo set-top box.

The kit will cost $199 when it goes on sale Oct. 15, and includes a remote and a TV tuner that plugs into the PC. The interface on the computer screen looks just like the one on a TV equipped with a TiVo box.

It’s not the first software that allows TV recording on the PC. That’s been possible for years on computers equipped with TV tuners, and some versions of Microsoft Corp.’s Windows Vista operating system include the necessary software. But it will be the first time that both the TiVo interface and functions have been replicated on a PC.

The Nero LiquidTV/TiVo PC will go on sale initially in the U.S., Mexico and Canada, but it could open up some markets where TiVo does not yet sell its set-top boxes. Joshua Danovitz, vice president and general manager of international business at TiVo, said the plan is to launch it in Europe next year, including in Nero’s home country, Germany. Britain is the only European country where TiVo currently has subscribers.

“It’s really part of a global TiVo strategy,” Danovitz said.

For people who already have a tuner-equipped PC, Nero — a private company mainly known for CD- and DVD-burning software — will sell the TV recording software separately, for $99. Either way, buyers will get a one-year subscription to TiVo’s program guide updates. Renewal will cost $99 per year.

The renewal cost sets the product apart from the digital video recording features of Windows Vista, which has a free program guide. However, Nero and TiVo are counting on the popularity of the TiVo interface and brand to overcome that hurdle.

Like TiVo’s existing TiVo Desktop software, LiquidTV will allow users to transfer shows recorded on other TiVo devices in the home to the PC’s hard drive, and bring shows out of the home, either on a laptop’s drive or on an iPod or PlayStation Portable. LiquidTV also allows users to burn shows onto DVDs if the computer has a DVD burner.

Waving and saluting, three Chinese astronauts emerged from their capsule Sunday in a jubilant return from their mission to carry out the country’s first spacewalk. The successful flight burnished China’s image for technological know-how and was seen as a sign of rising confidence as Beijing cements its status as a space power. A senior space official said the mission China’s most ambitious in space yet takes the country one step closer in its plan to land a man on the moon. State broadcaster CCTV showed the astronauts’ return after their Shenzhou 7 ship’s re-entry vehicle burst through the Earth’s atmosphere to make a landing under clear skies in the grasslands of China’s northern Inner Mongolia region.

The vessel touched ground at 5:37 p.m.

(0937 GMT) after floating gently down while attached to a giant, red-and-white striped parachute, marking the end of the 68-hour endeavor. “It was a glorious mission, full of challenges with a successful end,” said mission commander Zhai Zhigang, a 41-year-old fighter pilot.

“We feel proud of the motherland.” Zhai, Liu Boming and Jing Haipeng stayed inside the capsule after landing for about 45 minutes to adapt to Earth’s gravity before slowly crawling out of the narrow entrance.

Outside, the trio waved to cameras and reporters from Chinese state media before sitting down in blue fold-out chairs. They saluted as they were presented with bouquets of flowers.

Premier Wen Jiabao applauded at mission control in Beijing and shook hands with staff. “This mission’s success is a milestone, a stride forward,” Wen said.

“I would like to extend my congratulations to the heroic astronauts who successfully completed this mission.” The premier also reiterated Beijing’s longtime stance that it was the Chinese people “persistent aspiration” to develop space technologies for peaceful exploration.

China’s space program is backed by the country’s secretive military. While Beijing insists it is committed to a peaceful space program, analysts point to numerous potential applications for its technology.

In January last year, alarm rippled through the international community after China blasted apart an old satellite in space, using a land-based missile. Saturday’s spacewalk is a key step in mastering techniques for docking two orbiters to create China’s first orbiting space station.

Tethered to handles attached to the Shenzhou 7 ship’s orbital module, Zhai remained outside for about 13 minutes before climbing back inside. Wang Zhaoyao, deputy director of manned space flight, said China’s preliminary manned space plans included the launch of a target flight vehicle and the setup of a simple space lab by 2011.

There were also hopes of sending unmanned and manned space vehicles to perform docking activities with the target vehicle. By 2020, China will launch a manned mission to experiment with technologies that will enable the astronauts to take care of the spacecraft for longer periods of time, Wang told reporters at a briefing in Beijing after the astronauts returned.

“After we have successfully completed these three steps, we will go to even more remote areas,” he said. “We believe that as long as we can make further progress on the road of science and technology, China will achieve the target of putting a manned spacecraft on the moon in the near future.

” The United States was the first country to send a man to the moon in 1969, nearly 40 years ago. Riding a wave of pride and patriotism after hosting the Olympics, China’s communist leaders face few of the public doubts or budgetary pressures constraining such programs elsewhere.

All along, China has relied heavily on homegrown technology, partly out of necessity. China has trouble obtaining such technology abroad due to U.S. and European bans and is not a participant in the International Space Station.

China launched its first manned mission, Shenzhou 5, in 2003, becoming only the third country after Russia and the United States to launch a man into space. That was followed by a two-man mission in 2005.