Researchers from the UCLA School of Dentistry investigating how stem cells can be used to regenerate dental tissue have discovered a way to produce cells with stem cell-like characteristics from the most common type of human skin cell in the epidermis.These skin cells, called keratinocytes, form the outermost layer of skin and can be cultured from discarded skin tissues or biopsy specimens.
The findings, published in the Nov. 4 edition of the peer-reviewed Journal of Biological Chemistry, may be beneficial for individuals with limited sources of endogenous stem cells.
The gene known as ∆Np63α is highly synthesized in regenerating cells of various tissues. The UCLA researchers found that introducing ∆Np63α into skin keratinocytes makes them lose their skin-cell characteristics and de-differentiate to resemble mesenchymal stem cells (MSCs), undifferentiated cells that can self-renew and differentiate to yield specialized cells of various tissue types.
MSCs may serve as an internal repair system by replenishing cells needed for tissue regeneration and homeostasis and are currently being investigated for a number of regenerative therapeutics.
The conversion of keratinocytes into mesenchymal-like cells involves a process known as epithelial-mesenchymal transition. This is the first study to show that the gene ∆Np63α triggers this process in human skin keratinocytes and that the transformed cells acquire multipotent stem cell characteristics.
Since the skin cells transformed by ∆Np63α are induced to acquire the mesenchymal and stem cell characteristics, the research team named them "induced mesenchymal stem cells," or iMSCs. Specifically, the researchers demonstrated that iMSCs can be triggered to form bone-like tissues or become fat tissues in a laboratory setting.
Dr. Mo K. Kang, the Jack A. Weichman Chair of Endodontics at the UCLA School of Dentistry and a member of the research team, said the finding had great significance for human health.
"Since iMSCs may be obtained by taking a small punch-biopsy of skin tissues from patients, these cells are an easily accessible, patient-specific source of stem cells, which can be used for regenerative purposes," Kang said.
Stem cell-based therapies are currently being developed to treat degenerative conditions such as heart disease, diabetes, neuronal disorders and liver diseases. Many of these diseases are strongly associated with aging. Endogeneous MSCs found in various tissues, such as bone marrow, fat tissues and, in certain cases, dental tissues such as dental pulp, lose their regenerative potential during the aging process.
"It is possible that iMSCs retain their stem-cell characteristics even when derived from aged patients," Kang said. "In such cases, this new approach may be useful, especially for geriatric patients or individuals with limited therapeutic value of their endogenous stem cells."
"The UCLA School of Dentistry is very proud to be at the forefront of this research inquiry, which may facilitate future advances in regenerative dentistry and medicine," said Dr. No-Hee Park, dean of the UCLA School of Dentistry and one of the study's co-authors. "While the focus of this study was on the use of adult stem cells to regenerate dental tissue, including dental pulp and periodontal ligament, these findings could lead to further development of a variety of cell-based therapies."
The dye, a compound called orcein, and a related substance, called O4, bind preferentially to small amyloid aggregates that are considered to be toxic and cause neuronal dysfunction and memory impairment in Alzheimer's disease.O4 binding to small aggregates promotes their conversion into large, mature plaques which researchers assume to be largely non-toxic for neuronal cells. Further research with animal models is needed to determine whether this new approach by Dr. Jan Bieschke (Max Delbrück Center for Molecular Medicine, MDC, Berlin-Buch), Dr. Martin Herbst (Charité – Universitätsmedizin Berlin) and Professor Erich Wanker (MDC) in Berlin, Germany, will be useful for therapy development (Nature Chemical Biology.
Protein misfolding is considered to be the cause of Alzheimer's, Parkinson's and also Huntington's disease. In a multistep process, proteins misfold and accumulate into large extra- or intracellular plaques. Researchers assume that small misfolded protein aggregates that are precursors of mature plaques are toxic for nerve cells and are the reason why they are eventually destroyed.
Dye from the Canary Islands
The dye orcein is isolated from lichens that grow on the Canary Islands, among other places. Lichens have been used for centuries to color fabrics and food. Eight years ago Professor Wanker screened hundreds of natural compounds to find potential candidate drug molecules for the treatment of neurodegenerative diseases. Among those substances he found orcein, a compound made up of about 14 small molecules. As these molecules might have different biological effects, the researchers in Berlin began to search for pure chemicals with similar properties. They identified the substance O4, a blue dye, which is structurally very similar to one of the 14 molecules. Moreover, they showed that O4 stimulates the formation of large, non-toxic protein plaques from small toxic protein assemblies.
New Mechanism
A few years ago Professor Wanker and his colleagues discovered that EGCG (Epigallocatechin-3-gallate), a natural chemical compound found in green tea, renders toxic protein assemblies non-toxic. With orcein and O4 the researchers have now found another mechanism to eliminate small toxic protein aggregates. However, instead of remodeling protein plaques, the dyes reduce the abundance of small, toxic precursor protein assemblies by accelerating the formation of large plaques, as the researchers could now show in their laboratory.
"This is a new mechanism," Professor Wanker explained. "Up to now it has been considered to be very difficult to stop the formation of small toxic protein assemblies. If our hypothesis is correct that the small aggregates, which are precursors of plaques, indeed cause neuronal death, with O4 we would have a new mechanism to attack the disease."
The synthetic dye methylene blue is currently being tested in clinical trials. This dye also seems to stimulate the formation of large plaques in a way similar to O4. Other therapeutic approaches tested in clinical trials which aim at eliminating small precursor aggregates have so far not led to a significant improvement of disease symptoms.
However, it still remains to be seen whether the blue dye O4 can also be effective against small amounts of misfolded proteins in the brains of Alzheimer's patients and whether the accelerated formation of larger plaques can indeed reduce the signs and symptoms of Alzheimer's disease in humans. Further studies will be necessary to address the question whether the accelerated formation of large plaques can be a therapeutic approach. "We hope that our findings will stimulate research activities in this direction, especially in drug discovery," Professor Wanker said.
Researchers working at the Clarendon Laboratory at the University of Oxford in England have managed to get one small diamond to communicate with another small diamond utilizing "quantum entanglement," one of the more mind-blowing features of quantum physics.
Entanglement has been proven before but what makes the Oxford experiment unique is that concept was demonstrated with substantial solid objects at room temperature.
Previous entanglements of matter involved submicroscopic particles, often at cold temperatures.
The vibrational states of two spatially separated, millimeter-sized diamonds are entangled at room temperature by scattering a pair of strong pump pulses (green). The generated motional entanglement is verified by observing nonclassical correlations in the inelastically scattered light. Credit: Dr. Lee and colleagues, Image Copyright Science|AAAS
This experiment employed millimeter-scale diamonds, "not individual atoms, not gaseous clouds," said Ian Walmsley, professor of experimental physics at Oxford's Clarendon Laboratory, one of the international team of researchers.
The experiment is reported
in this week's edition of Science.
When zapping one artificial diamond with ultrashort laser pulses they managed to change the vibrations of a second diamond sitting a half a foot away without touching it.
Entanglement originated in the mind of Albert Einstein, who ironically came up with the notion trying to disprove quantum mechanics, a branch of physics he mistrusted all his life.
Under the theory, if two particles, say electrons, are created together, some of their attributes will become "entangled." If the two are then separated, doing something to one instantly affects the other. This would happen whether they were next to each other or across the universe.
For instance, electrons act as if they have tiny bar magnets that point up or down, described by an attribute called "spin." If the two electrons are entangled through their spins -- up or down -- and a scientist measures the spin of one, the spin of the other will react even if one is on a lab table in Oxford and the other were on a planet near the star Antares, 1,000 light years away. Instantly.
This would mean that the information about the change traveled faster than the speed of light -- which Einstein said was impossible -- or that long distances are some kind of illusion.
Einstein disparaged it as "spooky action at a distance." The German physicist Erwin Schrodinger used the term "entanglement" in a letter to Einstein. He didn't believe in quantum mechanics either.
"I think I can safely say no one understands quantum mechanics," the late physicist Richard Feynman once famously explained.
Nonetheless, quantum mechanics is now the paradigm for nature at the atomic level. It serves as the foundation of much of modern technology, from lasers to transistors. And entanglement comes as part of the package. Physicists have been demonstrating it in laboratories since the 1980s, and it is being used in laboratories experimenting with the building blocks of quantum computers.
The diamonds Walmsley and his international team used were approximately 3 millimeters (a tenth of an inch) square and 1 millimeter thick.
"We used short pulse lasers with pulse durations of around 100 femtoseconds (a quadrillionth of a second). A femtosecond is to a second as a nickel is to the debt of the federal government generally speaking," he said.
They chose diamonds because they are crystals, so it was easier to measure molecular vibrations, and because they are transparent in visible wavelengths. Light from the lasers altered a kind of mass vibration in the diamond crystal called phonons, and the measurements showed they were entangled: The vibrations of the second diamond reacted to what happened to the vibrations of the first.
Performing the experiment with ultrafast laser pulses enabled the researchers to catch entanglement, which is usually very short-lived in large objects at room temperature.
"It remains a counterintuitive way of thinking about objects," Walmsley admitted.
"It's a very nice and clever piece of work with potentially big implications," said Sidney Perkowitz, a physicist at Emory University in Atlanta, and author of "Slow Light: Invisibility, Teleportation and Other Mysteries of Light," a book partially about entanglement. The macroscopic size, and the fact that this was done at room temperature, would be important steps toward a practical quantum technology for telecommunications and computing, and toward deeper understanding of how the quantum world and the human-scale world are related."
Previously, the maximum resolution of optical instruments, including cameras and microscopes, was fundamentally limited to a precision that corresponded to approximately half of the wavelength of incoming light.
The new scheme, developed by researchers from the RIKEN SPring-8 Center in Harima and Nagoya University, has a resolution up to 380 times better than the UV light used in the experiments. For microscopes using visible light, which means wavelengths of a few hundred nanometers, the best achievable resolution is around 100 nanometers, which fails to resolve the smallest structures on a computer chip. Imaging smaller nanostructures, or even atoms, requires light of much shorter wavelengths, such as x-rays that are difficult to handle, and which provide different types of images to those captured using visible light.
Led by Kenji Tamasaku of RIKEN, the researchers used a non-linear optical effect to achieve atomic resolution in diamond. Their process is based on the intrinsic interaction between the electrons of the material’s crystal atoms and UV light that splits an incoming x-ray beam into a UV beam and a lower energy x-ray beam. The combined energy of these scattered beams is the same as that of the incoming beam. This process depends strongly on the activation of the UV beam, which occurs only in the vicinity of the electrons in the atoms, and only if the optical response of the electrons is a match to the incoming x-ray beam, Tamasaku explains.
Analyzing the scattered beams allowed a precise reconstruction of the motion of the electrons under UV illumination. Using a diamond crystal as an imaging object, the researchers demonstrated a resolution of 0.054 nanometers (Fig. 1). Because Tamasaku and colleagues used a non-linear optical effect, they obtained new information not only about how electrons move but also about atomic position.
There are many possibilities for using this new method, says Tamasaku. “This technique is very useful for the study of the physical properties of materials that couple to light.” An example is the study of electronic materials, in which the sensitivity of the technique to the electron’s electronic states can be used to probe electrical charges in materials such as high-temperature superconductors. Using the team's new approach, this will now be possible with atomic resolution.
For the first time, the team showed that light can be used to obtain information about the spin of electrons flowing over the material’s surface, and has even found a way to control these electron movements by varying the polarization of a light source.
The materials could open up possibilities for a new kind of devices based on spintronics, which makes use of a characteristic of electrons called spin, instead of using their electrical charge the way electronic devices do. It could also allow for much faster control of existing technologies such as magnetic data storage.
Topological insulators are materials that possess paradoxical properties. The three-dimensional bulk of the material behaves just like a conventional insulator (such as quartz or glass), which blocks the movement of electric currents. Yet the material’s outer surface behaves as an extremely good conductor, allowing electricity to flow freely.
This diagram illustrates how lasers can be used to control an electric current on these new materials. Electrons (blue spheres) travel, as if on a highway, in different directions, with their axis of spin (arrows) aligned differently according to the direction of travel. A circularly polarized laser beam (left) affects only electrons going in one direction, removing them from the flow, leaving a net flow — an electric current — going the other way. Photo: Gedik Group
The key to understanding the properties of any solid material is to analyze the behavior of electrons within the material — in particular determining what combinations of energy, momentum and spin are possible for these electrons, explains MIT assistant professor of physics Nuh Gedik, senior author of two recent papers describing the new findings. This set of combinations is what determines a material’s key properties — such as whether it is a metal or not, or whether it is transparent or opaque. “It’s very important, but it’s very challenging to measure,” Gedik says.
The traditional way of measuring this is to shine a light on a chunk of the solid material: The light knocks electrons out of the solid, and their energy, momentum and spin can be measured once they are ejected. The challenge, Gedik says, is that such measurements just give you data for one particular point. In order to fill in additional points on this landscape, the traditional approach is to rotate the material slightly, take another reading, then rotate it again, and so on — a very slow process.
Gedik and his team, including graduate students Yihua Wang and James McIver, and MIT postdoc David Hsieh, instead devised a method that can provide a detailed three-dimensional mapping of the electron energy, momentum and spin states all at once. They did this by using short, intense pulses of circularly polarized laser light whose time of travel can be precisely measured.
By using this new technique, the MIT researchers were able to image how the spin and motion are related, for electrons travelling in all different directions and with different momenta, all in a fraction of the time it would take using alternative methods, Wang says. This method was described in a paper by Gedik and his team that appeared Nov. 11 in the journal Physical Review Letters.
In addition to demonstrating this novel method and showing its effectiveness, Gedik says, “we learned something that was not expected.” They found that instead of the spin being precisely aligned perpendicular to the direction of the electrons’ motion, when the electrons moved with higher energies there was an unexpected tilt, a sort of warping of the expected alignment. Understanding that distortion “will be important when these materials are used in new technologies,” Gedik says.
The team’s high-speed method of measuring electron motion and spin is not limited to studying topological insulators, but could also have applications for studying materials such as magnets and superconductors, the researchers say.
One unusual characteristic of the way electrons flow across the surface of these materials is that unlike in ordinary metal conductors, impurities in the material have very little effect on the overall electrical conductivity. In most metals, impurities quickly degrade the conductivity and thus hinder the flow of electricity. This relative imperviousness to impurities could make topological insulators an important new material for some electronic applications, though the materials are so new that the most important applications may not yet be foreseen. One possibility is that they could be used for transmission of electrical current in situations where ordinary metals would heat up too much (because of the blocking effect of impurities), damaging the materials.
In a second paper, appearing today in the journal Nature Nanotechnology, Gedik and his team show that a method similar to the one they used to map the electron states can also be used to control the flow of electrons across the surface of these materials. That works because the electrons always spin in a direction nearly perpendicular to their direction of travel, but only electrons spinning in a particular direction are affected by a given circularly polarized laser beam. Thus, that beam can be used to push aside all of the electrons flowing in one direction, leaving a usable electric current flowing the other way.
“This has very immediate device possibilities,” Gedik says, because it allows the flow of current to be controlled completely by a laser beam, with no direct electronic interaction. One possible application would be in a new kind of electromagnetic storage, such as that used in computer hard drives, which now use an electric current to “flip” each storage bit from a 0 to a 1 or vice versa. Being able to control the bits with light could offer a much quicker response time, the team says.
This harnessing of electron behavior could also be a key enabling technology that could lead to the creation of spintronic circuits, using the spin of the electrons to carry information instead of their electric charge. Among other things, such devices could be an important part of creating new quantum computing systems, which many researchers think could have significant advantages over ordinary computers for solving certain kinds of highly complex problems.
Professor of physics Zhi-Xun Shen of Stanford University, who was not involved in this work, says the MIT team has confirmed the theorized structure of the topological surface by using their novel experimental method. In addition to this confirmation, he says, their second paper “is to date one of the most direct experimental evidences for optical coupling” between the laser and the surface currents, and thus “has interesting potential for opto-spintronics.”
But it seems the Golden orb web spider has developed a way to keep its home clear of the little buggers. The secret uncovered by researchers from the National University of Singapore (NUS) and the University of Melbourne relates to a chemical compound the spider adds to its web that appears to repel ants. So not only are spider webs providing inspiration for better adhesives and stronger materials, they may also provide the basis for new, environmentally friendly, ant-repelling pesticides.
Golden orb web spiders are already in high demand amongst researchers due to the strength of their webs. The silk of this particular spider is almost as strong as Kevlar, and only a fraction of the weight. But NUS Associate Professor Daiqin Li was more interested in the possible ant-repelling nature of the spider's web after noting that, although ants were ever abundant near the webs of the orb web spiders, they don't typically end up trapped in the webs.
After observing spun webs and analyzing the compounds in the silk, the scientists soon discovered the mystery substance, which was later determined to be an alkaloid compound. Once discovered, scientists observed ants in the presence of the compound and discovered that they displayed evasive behavior whenever they came near the alkaloid.
"We found that large Golden orb web spiders add a defensive alkaloid chemical onto the silk, which stops the ants from walking onto the web when they come into contact with it," said Diaqin Li of Biological Sciences, NUS.
"The type of chemical deterrent found in the spider silk is known as a pyrrolidine alkaloid, which acts as a predator deterrent in many species of ants, moths and caterpillars," added Professor Mark Elgar from the University of Melbourne's Department of Zoology. "The orb spider is potentially vulnerable to attack from groups of ants while sitting in its web waiting for prey, so the chemical defense in web silk may have evolved to not only protect the spider, but to reduce the time and energy that would otherwise be required to chase away invading ants."
The discovery offers the prospect of the development of a pesticide for keeping ants away from where they aren't wanted.
2012 has only just begun and it is already shaping up to be one of the most exciting and active years for marijuana law reform in some time. More than a dozen state legislatures are currently considering reform measures in some respect and 8 states are attempting to put legalization initiatives before voters this November.
Many of these efforts are still in the signature gathering stage. Check out the list below to see if you might be able to vote ‘Yes’ on marijuana legalization in your state this year and how you can get involved to make that a reality. In addition to the legalization initiatives below several states, such as Ohio and Massachusetts, are working to also put medical marijuana initiatives before voters this year. To stay up to date on all the efforts to reform marijuana laws you can follow our “Legalize It 2012″ hub on Facebook and Twitter.
California
Regulate Marijuana Like Wine
Details: “The “Regulate Marijuana Like Wine” initiative intends to repeal prohibition of marijuana for adults, strictly regulate marijuana, just like the wine industry, allow for hemp agriculture and products while not changing laws regarding medical marijuana, impairment, work place drug laws, or laws regarding vehicle operation. This initiative would also provide specific personal possession exemptions, require dismissal of pending court cases for marijuana possession, and ban the advertising of non-medical marijuana.”
Details: “Aims to repeal current state criminal laws prohibiting the personal possession, use, transportation, and cultivation of cannabis by adults 19 years of age and older. During the first 180-days following the passage of the Act, the Legislature is authorized to create the California Cannabis Commission. This Commission will develop appropriate regulations for the commercial production and sales of cannabis, including licensing and taxation. Individuals are allowed to possess up to three pounds and grow a 100 sq. ft. canopy without being subject to regulations. It maintains penalties for possession by persons under 19, distribution to persons under 19, and driving while impaired.”
Details: “The Regulate Marijuana Like Alcohol Act of 2012 makes the adult use of marijuana legal, establishes a system in which marijuana is regulated and taxed similarly to alcohol, and allows for the cultivation of industrial hemp.”
The 2012 Michigan Ballot Initiative to End Marijuana Prohibition
Details: “Proposes a state constitutional amend that states: “For persons who are at least 21 years of age who are not incarcerated, marihuana acquisition, cultivation, manufacture, sale, delivery, transfer, transportation, possession, ingestion, presence in or on the body, religious, medical, industrial, agricultural, commercial or personal use, or possession or use of paraphernalia shall not be prohibited, abridged or penalized in any manner, nor subject to civil forfeiture; provided that no person shall be permitted to operate an aircraft, motor vehicle, motorboat, ORV, snowmobile, train, or other heavy or dangerous equipment or machinery while impaired by marihuana.”
Details: “A constitutional measure which would regulate cannabis like alcohol, provide access to medicine for cannabis patients, and open a market for farming industrial hemp in Missouri.”
Montana First: Ending Criminal Penalties for Marijuana
Details: “The new petition is for a proposed amendment to the state constitution. It would add just two sentences to a portion of the constitution concerning adult rights, which already contains a reference to the legal age for the consumption of alcohol. [Stating] Adults have the right to responsibly purchase, consume, produce, and possess marijuana, subject to reasonable limitations, regulations, and taxation. Except for actions that endanger minors, children, or public safety, no criminal offense or penalty of this state shall apply to such activities.”
Details: “Add Proposition 19 to the Nebraska Constitution whose object is to regulate and tax all commercial uses of cannabis, also known as marijuana, and to remove all laws regulating the private, noncommercial use of cannabis.”
Details: “The Oregon Cannabis Tax Act 2012 is a citizen’s initiative campaign to regulate marijuana and restore hemp. Just as ending alcohol prohibition and regulating that market has protected society, regulating marijuana will help wipe out crime. Restoring hemp, made from the seeds and stems of the marijuana plant for fuel, fiber and food, will put Oregon on the cutting edge of exciting new sustainable green industries and create untold multitudes of new jobs.”
Citizens for Sensible Law Enforcement: Initiative IP-24
Details: “Currently known as IP-24, the measure would allow adults over 21 to use marijuana for personal use without fear of criminal sanctions. The bill has substantial safeguards to protect children and public safety. With hundreds of signature gatherers on the streets every day, CSLE is confident the measure will appear on the November 2012 ballot.”
Details: “Washington State Initiative Measure No. 502 (I-502) would license and regulate marijuana production, distribution, and possession for persons over twenty-one; remove state-law criminal and civil penalties for activities that it authorizes; tax marijuana sales; and earmark marijuana-related revenues.”
These synthetic cricket hairs can now also be tuned very precisely for a certain range of frequencies: the hairs are 10 times more sensitive in this range. The researchers of the MESA+ Institute for Nanotechnology are presenting these new results in the scientific journal Applied Physics Letters.
Just as you always hear your own name if it is spoken at a busy gathering, these synthetic cricket hairs also suddenly become more sensitive to a specific frequency of air flow. The hair itself does not have to be modified for this, the enhanced sensitivity is achieved by adjusting its spring stiffness electronically.
The synthetic cricket hair is an example of biomimicry, the hairs on a cricket’s abdomen – on the projections known as ‘cerci’ - form the source of inspiration. These hairs enable the cricket to feel/hear the approach of its enemies and estimate their distance and direction unerringly. These characteristics can be simulated by making a hair that is suspended in a flexible microsystem. The hair is made of polymer SU8, is 0.9 millimetre in length and is thicker at the base than at the top. The smallest movements are registered by the flexibly-suspended plate to which the hair is attached; the electrical capacity changes as a result and gives a measure for the movement.
You could enhance sensitivity by using another type of hair that is not as stiff, but Harmen Droogendijk discovered that it is also possible to adjust the spring stiffness of the hair in question electronically. He investigated the alternating voltage needed to get the hair, or spring, ‘limp’ at the required moment, thus making it extra sensitive to the related frequencies. The effect is substantial: a hair is 10 times more sensitive at the adjusted frequency.
This makes the sensor more easily applicable without having to alter the design. Potential applications include direction sensors used by robots and the study of very specific air flows. In the longer term, the synthetic hairs could also be used in hearing aids. The hairs can be made extra sensitive to certain frequencies in all these applications.
Greece's largest police union has threatened to issue arrest warrants for officials from the country's European Union and International Monetary Fund lenders for demanding deeply unpopular austerity measures.
In a letter obtained by Reuters Friday, the Federation of Greek Police accused the officials of "...blackmail, covertly abolishing or eroding democracy and national sovereignty" and said one target of its warrants would be the IMF's top official for Greece, Poul Thomsen.
The threat is largely symbolic since legal experts say a judge must first authorize such warrants, but it shows the depth of anger against foreign lenders who have demanded drastic wage and pension cuts in exchange for funds to keep Greece afloat.
"Since you are continuing this destructive policy, we warn you that you cannot make us fight against our brothers. We refuse to stand against our parents, our brothers, our children or any citizen who protests and demands a change of policy," said the union, which represents more than two-thirds of Greek policemen.
"We warn you that as legal representatives of Greek policemen, we will issue arrest warrants for a series of legal violations ... such as blackmail, covertly abolishing or eroding democracy and national sovereignty."
The letter was also addressed to the European Central Bank's mission chief in Greece, Klaus Masuch, and the former European Commission chief inspector for Greece, Servaas Deroose.
Policemen have borne the brunt of the anger of massed protesters who frequently march to parliament and clash with police in riot gear. Chants of "Cops, pigs, murderers!" are regularly hurled at policemen or scribbled on walls.
Thousands turned out Friday for the latest protest in Athens, this time against new austerity measures that include a 22 percent cut in the minimum wage.
A police union official said the threat to 'refuse to stand against' fellow Greeks was a symbolic expression of solidarity and did not mean police would halt their efforts to stop protests getting out of hand.
Source: Reuters - Reporting by Lila Chotzoglou, Writing by Deepa Babington, editing by Tim Pearce.
There have been some successes with simple 3-D shapes such as cubes, but the list of possible starting points that could yield the ideal self-assembly for more complex geometric configurations gets long fast. For example, while there are 11 2-D arrangements for a cube, there are 43,380 for a dodecahedron (12 equal pentagonal faces). Creating a truncated octahedron (14 total faces – six squares and eight hexagons) has 2.3 million possibilities.
"The issue is that one runs into a combinatorial explosion," said Govind Menon, associate professor of applied mathematics at Brown University. "How do we search efficiently for the best solution within such a large dataset? This is where math can contribute to the problem."
In a paper published in the Proceedings of National Academy of Sciences, researchers from Brown and Johns Hopkins University determined the best 2-D arrangements, called planar nets, to create self-folding polyhedra with dimensions of a few hundred microns, the size of a small dust particle. The strength of the analysis lies in the combination of theory and experiment. The team at Brown devised algorithms to cut through the myriad possibilities and identify the best planar nets to yield the self-folding 3-D structures. Researchers at Johns Hopkins then confirmed the nets' design principles with experiments.
This showas a few of the 2.3 million possible 2-D designs -- planar nets -- for a truncated octahedron (right column). The question is: Which net is best to make a self-assembling shape at the nanoscale? Credit: Credit: Shivendra Pandey/Gracias Lab, Johns Hopkins University.
"Using a combination of theory and experiments, we uncovered design principles for optimum nets which self-assemble with high yields," said David Gracias, associate professor in of chemical and biomolecular engineering at Johns Hopkins and a co-corresponding author on the paper. "In doing so, we uncovered striking geometric analogies between natural assembly of proteins and viruses and these polyhedra, which could provide insight into naturally occurring self-assembling processes and is a step toward the development of self-assembly as a viable manufacturing paradigm."
"This is about creating basic tools in nanotechnology," said Menon, co-corresponding author on the paper. "It's important to explore what shapes you can build. The bigger your toolbox, the better off you are."
While the approach has been used elsewhere to create smaller particles at the nanoscale, the researchers at Brown and Johns Hopkins used larger sizes to better understand the principles that govern self-folding polyhedra.
The researchers sought to figure out how to self-assemble structures that resemble the protein shells viruses use to protect their genetic material. As it turns out, the shells used by many viruses are shaped like dodecahedra (a simplified version of a geodesic dome like the Epcot Center at Disney World). But even a dodecahedron can be cut into 43,380 planar nets. The trick is to find the nets that yield the best self-assembly. Menon, with the help of Brown undergraduate students Margaret Ewing and Andrew "Drew" Kunas, sought to winnow the possibilities. The group built models and developed a computer code to seek out the optimal nets, finding just six that seemed to fit the algorithmic bill.
The students got acquainted with their assignment by playing with a set of children's toys in various geometric shapes. They progressed quickly into more serious analysis. "We started randomly generating nets, trying to get all of them. It was like going fishing in a lake and trying to count all the species of fish," said Kunas, whose concentration is in applied mathematics. After tabulating the nets and establishing metrics for the most successful folding maneuvers, "we got lists of nets with the best radius of gyration and vertex connections, discovering which nets would be the best for production for the icosahedron, dodecahedron, and truncated octahedron for the first time."
Gracias and colleagues at Johns Hopkins, who have been working with self-assembling structures for years, tested the configurations from the Brown researchers. The nets are nickel plates with hinges that have been soldered together in various 2-D arrangements. Using the options presented by the Brown researchers, the Johns Hopkins's group heated the nets to around 360 degrees Fahrenheit, the point at which surface tension between the solder and the nickel plate causes the hinges to fold upward, rotate and eventually form a polyhedron. "Quite remarkably, just on heating, these planar nets fold up and seal themselves into these complex 3-D geometries with specific fold angles," Gracias said.
"What's amazing is we have no control over the sequence of folds, but it still works," Menon added.
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