Science & Technology

New Approach to Invisibility Cloaking Gets Much Closer to the Science-Fiction Version

David L. Chandler
PhysOrg
Tue, 25 Jan 2011 00:00 UTC

The idea of being able to become invisible, especially by simply covering up a person or an object with a special cloak, has a perennial appeal in science-fiction and fantasy literature. In recent years, researchers have found ways to make very exotic "metamaterials" that can perform a very crude version of this trick, keeping an object from being detected by a certain specific frequency of radiation, such as microwaves, and only working at microscopic scales. But a system that works in ordinary visible light and for objects big enough to be seen with the naked eye has remained elusive.

Now, a team of researchers in the Singapore-MIT Alliance for Research and Technology (SMART) Centre has found a relatively simple, inexpensive system that can hide an object as big as a peppercorn from view in ordinary visible light. The team's discovery has been published online in Physical Review Letters and will appear soon in the print version of the journal.

Unlike the other attempts to produce invisibility by constructing synthetic layered materials, the new method uses an ordinary, common mineral called calcite - a crystalline form of calcium carbonate, the main ingredient in seashells. "Very often, the obvious solution is just sitting there," says MIT mechanical-engineering professor George Barbastathis, one of the new report's co-authors.

Next Generation Cloaking Device Demonstrated

PhysOrg
Thu, 15 Jan 2009 00:00 UTC

A device that can bestow invisibility to an object by "cloaking" it from visual light is closer to reality. After being the first to demonstrate the feasibility of such a device by constructing a prototype in 2006, a team of Duke University engineers has produced a new type of cloaking device, which is significantly more sophisticated at cloaking in a broad range of frequencies.

The latest advance was made possible by the development of a new series of complex mathematical commands, known as algorithms, to guide the design and fabrication of exotic composite materials known as metamaterials. These materials can be engineered to have properties not easily found in natural materials, and can be used to form a variety of "cloaking" structures. These structures can guide electromagnetic waves around an object, only to have them emerge on the other side as if they had passed through an empty volume of space.

The results of the latest Duke experiments were published Jan. 16 in the journal Science. First authors of the paper were Duke's Ruopeng Liu, who developed the algorithm, and Chunlin Li. David R. Smith, William Bevan Professor of electrical and computer engineering at Duke, is the senior member of the research team.

Broadband Invisibility in the Microwave Range

Miranda Marquit
PhysOrg
Fri, 11 Sep 2009 00:00 UTC

In the series Star Trek, Klingons and Romulans have spaceships outfitted with cloaking devices that hide their presence from sight, as well as from the sensors of their rivals' spaceships. Unlike current invisibility cloaks, which are mostly effective only over a narrow range, these fictional devices provide a broadband type of invisibility that so far has eluded modern scientists.

Now, though, a team at the Helsinki University of Technology in Finland has demonstrated broadband cloaking of cylindrical objects in the microwave regime. "This really is a helpful development," Sergei Tretyakov tells PhysOrg.com. "Most other invisibility devices are very narrow in the range they affect." Additionally, many invisibility cloaks are produced with the use of materials with extreme electromagnetic properties. "These are exotic materials that often have a great deal of loss and are dispersive," Tretyakov continues.

Along with Pekka Alitalo, Olli Luukkonen and Constantin Simovski, Tretyakov believes that invisibility can be obtained over a broader range of frequencies without the need for electromagnetic mumbo-jumbo. Instead, the Helsinki team makes use of a simple metallic structure made from layers. The results of their experiment can be seen in Physical Review Letters: "Broadband electromagnetic cloaking of long cylindrical objects."

Scientists Closer to Making Invisibility Cloak a Reality

PhysOrg
Thu, 05 Mar 2009 00:00 UTC

J.K. Rowling may not have realized just how close Harry Potter's invisibility cloak was to becoming a reality when she introduced it in the first book of her best-selling fictional series in 1998. Scientists, however, have made huge strides in the past few years in the rapidly developing field of cloaking. Ranked the number five breakthrough of the year by Science magazine in 2006, cloaking involves making an object invisible or undetectable to electromagnetic waves.

A paper published in the March 2009 issue of SIAM Review, "Cloaking Devices, Electromagnetic Wormholes, and Transformation Optics," presents an overview of the theoretical developments in cloaking from a mathematical perspective.

One method involves light waves bending around a region or object and emerging on the other side as if the waves had passed through empty space, creating an "invisible" region which is cloaked. For this to happen, however, the object or region has to be concealed using a cloaking device, which must be undetectable to electromagnetic waves. Manmade devices called metamaterials use structures having cellular architectures designed to create combinations of material parameters not available in nature.

Silicon Photonic Crystals Key to Optical Cloaking

PhysOrg
Wed, 25 Jun 2008 00:00 UTC

In computer simulations, the researchers have demonstrated an approximate cloaking effect created by concentric rings of silicon photonic crystals. The mathematical proof brings scientists a step closer to a practical solution for optical cloaking.

"This is much more than a theoretical exercise," said Harley Johnson, a Cannon Faculty Scholar and professor of mechanical science and engineering at Illinois. "An optical cloaking device is almost within reach."

In October 2006, an invisibility cloak operating in the microwave region of the electromagnetic spectrum was reported by researchers at Duke University, Imperial College in London, and Sensor Metrix in San Diego. In their experimental demonstration, microwave cloaking was achieved through a thin coating containing an array of tiny metallic structures called ring resonators.

Scientists One More Step Closer to Realizing Invisible Technology

PhysOrg
Wed, 09 May 2007 00:00 UTC

A unique computer model designed by a mathematician at the University of Liverpool has shown that it is possible to make objects, such as aeroplanes and submarines, appear invisible at close range.

Scientists have already created an 'invisibility cloak' made out of 'metamaterial' which can bend electromagnetic radiation - such as visible light, radar or microwaves - around a spherical space, making an object within this region appear invisible.

Until now, scientists could only make objects appear invisible from far away. Liverpool mathematician Dr Sébastien Guenneau, together with Dr Frédéric Zolla and Professor André Nicolet from the University of Marseille, have proven - using a specially designed computer model called GETDP - that objects can also be made to appear invisible from close range when light travels in waves rather than beams.

Scientists predict that metamaterials could be of use in military technology, such as in the construction of fighter jets and submarines, but it will be some years before invisibility cloaks can be developed for human beings.

Twin Births Doubled in Three Decades in U.S.

Agence France-Presse
Thu, 05 Jan 2012 06:07 UTC

© Corbis
Women in their 30s tend to have higher rates of "spontaneous twinning," or becoming pregnant with twins without the use of fertility therapy, than younger women.

Advances in fertility treatment and a trend toward later-life childbirth are fueling a boom in twins in the United States, where one in 30 babies is a twin, according to data.

The number of twins doubled in 2009 compared to 1980, rising from 68,339 to over 137,000 births, said the National Center for Health Statistics' data brief on three decades of twin births in the United States.

The overall birth rate of twins surged 76 percent over the last 30 years, going from 1.9 percent of all births to 3.3 percent.

That means one in every 30 US babies is a twin, compared to one in 53 in 1980.

Over the last three decades, twin birth rates rose in every state, by nearly 100 percent among women aged 35-39 and more than 200 percent among women aged 40 and over, it said.

Women in their 30s tend to have higher rates of "spontaneous twinning," or becoming pregnant with twins without the use of fertility therapy, than younger women.

Physicists Propose Test for Loop Quantum Gravity

Lisa Zyga
PhysOrg
Tue, 03 Jan 2012 16:02 UTC

As a quantum theory of gravity, loop quantum gravity could potentially solve one of the biggest problems in physics: reconciling general relativity and quantum mechanics. But like all tentative theories of quantum gravity, loop quantum gravity has never been experimentally tested. Now in a new study, scientists have found that, when black holes evaporate, the radiation they emit could potentially reveal "footprints" of loop quantum gravity, distinct from the usual Hawking radiation that black holes are expected to emit.

In this way, evaporating black holes could enable the first ever experimental test for any theory of quantum gravity. However, the proposed test would not be easy, since scientists have not yet been able to detect any kind of radiation from an evaporating black hole.

The scientists, from institutions in France and the US, have published their study called "Probing Loop Quantum Gravity with Evaporating Black Holes" in a recent issue of Physical Review Letters.

"For decades, Planck-scale physics has been thought to be untestable," coauthor Aurélien Barrau of the French National Institute of Nuclear and Particle Physics (IN2P3) told PhysOrg.com. "Nowadays, it seems that it might enter the realm of experimental physics! This is very exciting, especially in the appealing framework of loop quantum gravity."

Remembrance of things future: Long-term memory sets the stage for visual perception

Stuart Mason Dambrot
MedicalXpress
Wed, 28 Dec 2011 15:49 UTC

Rather than being a passive state, perception is an active process fueled by predictions and expectations about our environment. In the latter case, memory must be a fundamental component in the way our brain generates these precursors to the perceptual experience - but how the brain integrates long-term memory with perception has not been determined. Recently, however, researchers in the Department of Experimental Psychology at the University of Oxford, by devising a method for integrating memory and attention, showed how LTM optimizes perception by varying brain states associated with anticipation of spatial localization in the visual field. The scientists also used fMRI to articulate a neural network involving a number of cortical areas likely to be active in the predictive use of memory in the visual cortex.

© PNAS
Experimental protocol for memory-guided attention. (A) In both EEG and fMRI experiments, participants first completed a learning task in which they searched for a target stimulus that was embedded within naturalistic scenes. Targets were presented on the right (Right Memory), left (Left Memory) or not at all (Neutral Memory). (B) Over repeated sessions, participants found, and learned, the location of target stimuli. The learning profile from the EEG experiment is plotted for search accuracy (left y axis, red) and search time (right y axis, blue) as a function of training session number (x axis). (C) On the following day, participants performed an attention task in which scenes from the initial learning task were used to cue the location of a subsequent target. The first scene was always presented without the target stimulus, whereas the second scene contained a target on 50% of trials. On target-present trials, previously learned locations were 100% predictive of the subsequent target location. Consequently, valid memory cue scenes could be used to predict the precise location of the subsequent target, whereas memories for neutral cues contained no task-relevant spatial information. (D) Behavioral data are shown for the EEG experiment, with sensitivity (left y axis, bars) and RT (right y axis, triangles) plotted as a function memory condition (memory vs. neutral). Detection sensitivity was higher for spatially predictive memories, and RTs were shorter. Error bars represent ±1 SEM. Copyright © PNAS, doi: 10.1073/pnas.1108555108

Baby Monkeys With 6 Genomes Are Scientific First

Live Science
Thu, 05 Jan 2012 15:14 UTC

They look like ordinary baby rhesus macaques, but Hex, Roku and Chimero are the world's first chimeric monkeys, each with cells from the genomes of as many as six rhesus monkeys.

Until now research on so-called chimeric animals, or those that have cells with different genomes, has been limited to mice; a recent procedure produced mice using cells from two dads.

The researchers turned to monkeys for more insight into the capabilities of embryonic stem cells. Most experiments on stem cell therapies are based on mice, and the researchers wanted to understand whether primate embryonic stem cells respond the same way as those of mice do.

To create the chimeric monkeys, researchers essentially glued together cells from individual rhesus monkey embryos and then implanting these mixed embryos into mama monkeys.

The key was mixing cells from very early-stage embryos, or blastocysts, that consisted of just two to four cells - each one of the cells still totipotent, capable of transforming into a whole animal as well as the placenta and other life-sustaining tissues. (This is in contrast to pluripotent stem cells, which can differentiate into any tissue type in the body, but not certain embryonic tissues or entire organisms.)

"The cells never fuse, but they stay together and work together to form tissues and organs," said Shoukhrat Mitalipov of the Oregon National Primate Research Center at Oregon Health & Science University. "The possibilities for science are enormous."

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Science & Technology

New Approach to Invisibility Cloaking Gets Much Closer to the Science-Fiction Version

Next Generation Cloaking Device Demonstrated

Broadband Invisibility in the Microwave Range

Scientists Closer to Making Invisibility Cloak a Reality

Silicon Photonic Crystals Key to Optical Cloaking

Scientists One More Step Closer to Realizing Invisible Technology

Twin Births Doubled in Three Decades in U.S.

Physicists Propose Test for Loop Quantum Gravity

Remembrance of things future: Long-term memory sets the stage for visual perception

Baby Monkeys With 6 Genomes Are Scientific First

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