Researchers Build Artificial Immune System to Solve Computational Problems

This figure shows the optimal solutions found in a certain landscape by the new vaccine-enhanced algorithm, Vaccine-AIS. Image credit: Woldemariam and Yen. ©2009 IEEE.

By mimicking the way that a living body acquires immunity to disease through vaccination, researchers have designed an artificial immune system to solve optimization problems more effectively than before. The results show that the biologically motivated approach is better at exploring a greater amount of space and quickly locating the desired local and global optima than previous methods.

The researchers, Kumlachew M. Woldemariam and Gary G. Yen, both from Oklahoma State University, have published their study in a recent issue of IEEE Transactions on Systems, Man, and Cybernetics - Part B: Cybernetics.
As the researchers explain, the field of artificial immune systems (AIS) is an emerging branch of evolutionary computation in which computational systems are based on the structure and behavior of the immune system. By providing methods in pattern recognition, data analysis, and machine learning, AIS has applications in fields including computer science, robotics, and information technology.
Unlike previous artificial immune systems, the system in the new study specifically takes advantage of the way that vaccines can improve the performance of the immune system. The antibody cells in the immune system are constantly trying to recognize foreign or malfunctioning cells (antigens such as bacteria, viruses, and tumors) in the midst of the body’s own healthy cells (mainly other antibodies). The way that the immune system distinguishes between different kinds of cells can be formulated as an optimization problem, in which the antibodies are the points in the decision space and the antigens are the solutions that the immune system looks for.
Although the immune system usually works very well, sometimes it doesn’t identify an antigen quickly enough to prohibit it from causing illness. To accelerate the immune system’s functioning, vaccines can be administered to enable the immune system to detect a new (weakened) antigen and develop an immunological memory so that it can quickly recognize the same antigen in the future.
Drawing inspiration from how such vaccines work, the researchers’ artificial immune system can be enhanced to quickly identify optimum solutions by being injected with certain points in decision space that act as weak antigens, or vaccines. In their study, Woldemariam and Yen explain how to determine which points should be used as vaccines to be “injected” into the algorithm. Once in the algorithm, the vaccines activate the antibody population to incorporate more diverse antibodies and explore new landscapes in decision space, so that the antibodies continually come closer to locating a desired local optimum point.

“The main idea of introducing the notion of vaccines in the evolutionary algorithm is to help enhance the diversity of antibodies,” Yen told.

“The way the vaccines are extracted from the decision space is in such a way that the decision space is explored widely. The implementation of the algorithm in multimodal optimization problem shows how fast and efficiently the antibodies, triggered by the vaccines, learn and locate the local and global optimal solutions of the problem. Therefore the vaccines help antibodies to achieve a speedy learning and diversified exploration.”
When comparing the new algorithm, called Vaccine-AIS, to other artificial immune systems, the researchers found that Vaccine-AIS outperformed the others by locating the global and local optima in a plot in fewer evaluations. The key to the improved performance is that the algorithm can cover a larger portion of the search space, due to help from the vaccines. As Yen added, AIS has the potential for improving computational abilities in many other areas.
“AIS was originally designed for data mining, anomaly detection and the like,” Yen said. “Its use as an optimization tool is a very young research area but its performance is drawing interest from researchers. Recently there has been research on using artificial immune systems in fault estimation and to design a power system stabilizer. The application of AIS in medical image processing for MRI (magnetic resonance imaging) is being studied as well.”

More information: Kumlachew M. Woldemariam and Gary G. Yen. “Vaccine-Enhanced Artificial Immune System for Multimodal Function Optimization.” IEEE Transactions on Systems, Man, and Cybernetics - Part B: Cybernetics, Vol. 40, No. 1, February 2010.

Original Article at http://www.physorg.com/news179060729.html

Scientists make bendable, transparent LEDs—without organics

Organic LEDs, or OLEDs, promise to bring flexible, transparent displays to the market, but some researchers have found a way to get the same effect by printing microscopic inorganic LEDs onto plastic and glass.

Organic light emitting diodes, or OLEDs, promise to bring a great deal of flexibility to where we can put a display—literally. Because of their organic components, it should be possible to create flexible and transparent displays, opening up a large number of potential uses. But now, just as OLEDs may finally be ready for the consumer market, some engineers have figured out a way to get many of the same properties using inorganic LEDs (ILEDs), using a method that's so simple, even a biologist could understand it. It's a few years away—at least—from commercialization, but it's a significant advance.
The paper that describes the process will be published today in Science. The basic idea is that, since LEDs are so efficient at converting electrical charges to light, the human eye can detect the light of very small LEDs. As a result, it's possible to make a display out of a surface where only a small fraction is occupied by the actual LEDs, which can be small enough to be invisible to the naked eye. Under these conditions, the display will take on the properties of whatever material the LEDs are embedded in: bendable, transparent, etc.
Unfortunately, although we've gotten rather good at depositing the layered structure needed for making a normal ILED, the manufacturing processes we use don't scale down to the size of individual pixels in a typical display, which need to be on the order of 100µm or less. So the researchers came up with a simple solution: make a big one, and then chop it into little pieces.
The researchers started with a permanent substrate topped with aluminum arsenide, and layered on all the typical materials (gallium, indium, phosphorous, etc.) needed to create an LED that would glow red. When that was completed, they used a technique called plasma ion etching to cut a rectangular grid into the slab, leaving behind small squares, approximately 50µm across, held in place by the AlAs substrate. The squares were then anchored in place by a small bit of material in two corners, and the AlAs substrate was etched away with hydrofluoric acid. What was left was a grid of small LEDs held in place by two small posts that could be broken away easily.
This array, however, is packed so tightly that it would completely obscure any surface it was transferred to. So the authors crafted printing devices from a flexible material that only contains slots for a subset of the total LED square (say, every third one). The elastic material can pick up the LEDs, "print" them onto a separate surface, and then return to the original source and pick up the next set over. By adjusting how far apart the LED slots are—every second LED in the grid, or every fifth—it's possible to print out devices with different spacing.
The authors prepared a flexible plastic surface by laying down a grid of wiring, printed the LEDs on it, and then locked them in place with epoxy; a second mesh of wiring completed the circuit. Given an adhesive, the plastic could be applied to just about anything. For demonstration purposes, the authors stuck it to a glass cylinder. They also created a wiring grid that acted as a passive matrix, allowing them to activate individual LEDs in the grid. For these applications, the LEDs only took up about one percent of the total surface, enough to leave it transparent (provided they weren't lit, obviously).
The authors also demonstrated how to create a bendable display. By pre-stretching the flexible plastic substrate before laying down the wiring, the wiring would buckle within the material when tension was relaxed. This provided enough slack to accommodate a fair degree of flexibility in the final material.
If, at this point, you think you're missing something, you're not—it really is that simple.
That said, it's still a long way from being ready for the market. The authors say that none of the LEDs failed during testing, but some of the wiring leading into the device wasn't up to the strains of their test procedures. As a result, most of the individual devices they made had rows of dead pixels. All the devices only worked in red, as well. Still, the process uses well-understood materials and techniques, so there's no reason it can't be rapidly improved on, and the transition to a production environment doesn't seem to face any major stumbling blocks.

Original post is here.

Flexible, self-healing antennae made from liquid metal

Researchers have embedded a self-healing liquid metal in a flexible substrate to create antennae that are flexible, self-healing, and can actually measure the stresses they're subjected to.

As engineers attempt to integrate electronics into things like clothing and medical devices, they're increasingly running up against the material properties of the substances we use to make the hardware. A lot of the materials that go into a typical electronic device are brittle, inflexible, and prone to damage, and materials scientists are looking at a variety of options for replacing them. A recent paper in Advanced Functional Materials describes a technique for forming an antenna from liquid metal. The resulting (not-so-) hardware is flexible, self-healing, and can change the frequency that it's sensitive to based on the stress it's subjected to.

The idea behind the new work is pretty simple, as liquid metal is obviously going to be pretty flexible. It's just as obvious, however, that containing it is also going to be challenging. There are also a limited number of choices when it comes to metals that are liquid anywhere near room temperatures, and not all of those are viable options—nobody's going to be enthused about bringing anything containing substantial amounts of liquid mercury to the market these days, for example.

The authors focused on an alloy of gallium (which is a liquid at room temperature) and indium, mixed in proportions that minimize the melting temperature. The alloy has a very useful property that came into play during some of the tests performed by the authors: when exposed to the air, it forms a thin oxidized coat that helps keep it from flowing freely.

That oxidized coat isn't very mechanically robust, so the research team started with a common, flexible polymer called polydimethylsiloxane (PDMS), which is used in a lot of materials science work. For most experiments, the PDMS was molded with an internal channel that was then filled with the gallium-indium mixture and then sealed.

The resulting device was pretty much as flexible as the starting material. It could be flexed, twisted, folded in half, and stretched an additional 40 percent beyond its normal length. When the stress was released, the PDMS snapped back into place; the antenna formed by the liquid metal within remained functional throughout.

The authors could even cut through the antenna with a razor blade and, in many cases, the two ends would spontaneously re-form a single, conducting wire once the blade was removed. In the other cases, the authors simply had to press the severed ends together to get it to re-establish a connection. That's where the thin oxide layer was critical, as it helped contain the liquid metal within the PDMS when it was cut, but wasn't robust enough to keep the ends from rejoining.

One of the interesting side-effects of this flexibility is that the physical configuration of the antenna can be changed simply by stretching it, and this will alter the frequencies that it's sensitive to. Simply by stretching the device 8mm, the peak response could be shifted by over 200MHz.

Obviously, a gallium-indium alloy is going to be a bit more expensive than many of the metals that are currently used in antennae. But the fact that the device is resistant to strain and can self-heal to a degree may make it substantially more durable, which can pay off in the long run. It can also eliminate the need for soldering, as simply jabbing a wire into the liquid should be enough to establish an electrical contact. The authors also suggest that the stress-induced changes in its properties could be put to good use for things like enabling remote monitoring of the integrity of machinery and structures like bridges.

Refer to the original post here.
Also see : 
 http://www.popsci.com/technology/article/2009-12/bendable-stretchable-shape-shifting-antenna?page=
and  http://www.physorg.com/news178897908.html

International Workshop on Electronic Structure Calculaitons at my place

International workshop on Frontiers in Electronic structure calculations : Techniques and Applications