Laser Light Can Lift Tiny Objects

Light has been put to work generating the same force that makes airplanes fly, a study appearing online December 5 in Nature Photonics shows. With the right design, a uniform stream of light has pushed tiny objects in much the same way that an airplane wing hoists a 747 off the ground.

Researchers have known for a long time that blasting an object with light can push the object away. That’s the idea behind solar sails, which harness radiation for propulsion in space, for instance. “The ability of light to push on something is known,” says study coauthor Grover Swartzlander of the Rochester Institute of Technology in New York.

Light’s new trick is fancier than a boring push: It created the more complicated force called lift, evident when a flow in one direction moves an object perpendicularly. Airfoils generate lift; as an engine propels a plane forward, its cambered wings cause it to rise.

Lightfoils aren’t about to keep an Airbus aloft for the time it takes to fly from JFK to LAX. But arrays of the tiny devices might be used to power micromachines, transport tiny particles or even enable better steering methods on solar sails.

Optical lift is “a really neat idea,” says physicist Miles Padgett of the University of Glasgow in Scotland, but it’s too early to say how the effect might be harnessed. “Maybe it’s useful, maybe it’s not. Time will tell.”

That light can have this unexpected lift effect started with a very simple question, Swartzlander says: “If we have something in the shape of a wing and we shine light through it, what happens?” Modeling experiments told the researchers that an asymmetrical deflection of light would create a surprisingly stable lift force. “So we thought we’d better do an experiment,” Swartzlander says. “Because this just looks too pretty.”

The researchers created tiny rods shaped kind of like airplane wings — flat on one side and rounded on the other. When these micron-sized lightfoils were immersed in water and hit with 130 milliwatts of light from the bottom of the chamber, they started to move up, as expected. But the rods also began moving to the side, a direction perpendicular to the incoming light. Tiny symmetrical spheres didn’t exhibit this lift effect, the team found.

Optical lift is different from the aerodynamic lift created by an airfoil. A plane flies because air flowing faster under its wing exerts more pressure than air flowing above. But in a lightfoil, the lift is created inside the object as the beam shines through. The shape of the transparent lightfoil causes light to be refracted differently depending on where it goes through, which causes a corresponding bending of the beam’s momentum that creates lift.

These lightfoils’ lift angles were about 60 degrees, the team found. “Most aerodynamic things take off at very gradual angles, but this has a very striking, very powerful lift angle,” Swartzlander says. “You can imagine what would happen if your airplane took off at 60 degrees — your stomach would be in your feet.”

As the rods lift, they shouldn’t stall out, the paper predicts. “The subtlety is that it actually self-stabilizes,” Padgett says. “It twists a little bit one way, and you think, ‘Oh dear, it’ll stop working,’ then the light rotates it back again.”

Swartzlander says he hopes to ultimately test the lightfoils in air, too, and try different shapes and materials with various refractive properties. In the study, the researchers used ultraviolet light to generate the lift, but other kinds of light would work just as well, Swartzlander says. “The beautiful thing about this is that it would work as long as you have light.”

Video: Riding a beam of light, a tiny particle thousandths of millimeters in size is pushed sideways by the same force that keeps airplanes aloft. Credit: Swartzlander et al.

See Also:

View the original article here

WikiLeaked Cable Sheds Light on Brazil Blackout

SAO PAULO — Despite widespread speculation at the time, a massive power outage that left 18 out of the 26 Brazilian states in the dark for up to six hours last year was not the result of a cyberattack, according to a classified diplomatic cable published by WikiLeaks last week.

The Nov. 10, 2009, blackout came just two days after the CBS News magazine 60 Minutes reported that an earlier outage in the Brazilian state of Espirito Santo in 2007 was the work of hackers. And it came just one day after Threat Level reported that, no, it wasn’t.

The suspicious timing of the outage triggered widespread speculation that hackers — even if they weren’t responsible for the 2007 blackout — may have caused the newer one. With Rio set to host the 2016 summer Olympics, the incident prompted U.S. diplomats to meet with top officials at ONS, Brazil’s power authority, to find out what had happened.

The leaked cable, dated Dec. 1, 2009 and classified Secret, describes the “strikingly open” conversations that followed.

[ONS president Plinio de] Oliveira and [ONS statistical director Wilkens] Geraldes further ruled out the possibility of hackers because, following some acknowledged interferences in past years, GOB has closed the system to only a small group of authorized operators, separated the transmission control system from other systems, and installed filters. [Energy ministry chief of staff José] Coimbra confirmed that the ONS system is a CLAN network using its own wires carried above the electricity wires. Oliveira pointed out that even if someone had managed to gain access to the system, a voice command is required to disrupt transmission.

Coimbra said that while sabotage could have caused the outages, this type of disruption would have been deadly, and investigators would have found physical evidence, including the body of the perpetrator. He also noted that any internal attempts by system employees to disrupt the system would have been easily traceable, a fact known to anyone with access to the system.

The blackout was caused by short circuits on high-voltage lines leading from the Itaburi substation near Sao Paulo, and was exacerbated by a number of factors, according to the cable, which appears to confirm the public reports of the blackout.

But what of the “acknowledged interferences in past years”?

Raphael Mandarino Jr., Brazil’s director of Homeland Security Information and Communication, says it refers to a cyber-extortion attack launched by Eastern European hackers around 2005 or 2006. The attackers penetrated an administrative machine at ONS after the system administrator left the computer with a default password.

The intruders, Mandarino says, downloaded and deleted files on the machine, and then left a message demanding ransom money for the data’s return. The person responsible for the system’s maintenance arrived to work at 8:00 a.m., and initially thought the ransom note was a joke. It took one hour to take the threat seriously.

No money was paid, says Mandarino, and most of the destroyed files were recovered from a backup.

“That was the first serious attack, which resulted in the issue being discussed in all the public administration”, he said.

Among the measures suggested to avoid a repeat occurrence was the creation of stronger passwords — the one they created right after the incident was cracked in a penetration test after just one week — and the recommendation that no outsourced workers have access to the passwords. Those measures were distributed to all the government’s branches and affiliates, including energy suppliers.

ONS’ Wilkens Geraldes, mentioned in the cable, referred inquiries to the agency’s PR team, which responded by saying that ONS has always had two different networks: The corporate network has suffered attacks, they say. But the utility operation network is isolated, and has yet to be breached from the outside.

In a broadcast Nov. 8, 2009, 60 Minutes cited unnamed sources in making the claim that a massive 2007 blackout that affected 3 million people was triggered by hackers targeting a utility company’s control systems.

In truth, a utility company’s negligent maintenance of high-voltage insulators on two transmission lines is what caused the outage, according to government regulators and others who investigated the incident for more than a year.

“I looked at the case as the top systems officer within the government, and I found nothing”, Mandarino reiterated this week, adding that he gave a taped interview to 60 Minutes rebutting the anonymous cyberwar claims, but CBS didn’t air it.

“There are indeed attacks against the energy websites. There was a defacement attack in 2008. There have been attempts at denial of service. Nothing that affected public utilities,” he says. “It’s still very difficult, because the system is not online. We have some [facilities] like thermoelectric plants that are remotely controlled, but they’ve suffered no attacks.”

Top image: Sao Paolo endures a power outage in 1999.
Dario Lopez-Mills/AP

View the original article here