A block chain or blockchain is a distributed database that maintains a continuously growing list of data records that are hardened against tampering and revision ...
A block chain is a transaction database shared by all nodes participating in a system based on the Bitcoin protocol. A full copy of a currency's block chain ...
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Blockchain technology is mundane and unsexy, but has the potential to transform how people and businesses co-operate
“I can take your immune system and transplant it into a mouse that I’ve genetically engineered to have no immune system of it’s own, so that I can model the genetics of your immune system and find immunoregulatory defects that will determine how you are going to respond to the cellular therapy needed to treat your disease.”
"The discoveries that I made went against conventional wisdom. I just believed in it, so I kept working on it": The multi award-winning scientist whose work may have helped 2 billion people worldwide.
World renowned scientist, Dr Robert Langer, on how 'engineering can…
BBC.IN
羅伯特·薩母耳·蘭格二世（英語：Robert Samuel Langer, Jr.，1948年8月29日－），生於美國紐約州奧爾巴尼，生物工程學者，是麻省理工學院（MIT）的戴維·H·科克學院教授（MIT一共有14位學院教授，學院教授是MIT教授所能獲得的最高榮譽）。蘭格教授發表了超過1175篇論文。他還擁有超過800個專利（包括正在審核和已經通過的）。這些專利授權給了超過250個製藥、化學、生物技術和醫學儀器公司。蘭格教授是迄今被引用次數最多的工程學家。..... 蘭格教授是生物工程學領域的著名學者，尤其以對靶向藥物輸送系統和組織工程學的研究而知名。蘭格在麻省理工的實驗室是世界最大的生物醫學工程實驗室，年度經費超過$1000萬，有超過100名研究人員。[2]
Langer is recognized as the most cited engineer in history.[3] Langer's research laboratory at MIT is the largest biomedical engineering lab in the world, maintaining over $10 million in annual grants and over 100 researchers.[5]Langer is also currently[when?] on the board of directors at Bind Therapeutics and Ocata Therapeutics.[6] In 2015, Langer was awarded the Queen Elizabeth Prize for Engineering, the most influential prize in the world for engineering.[7][8][9]
Finding could have implications for high-temperature superconductivity
A team of physicists led by Caltech's David Hsieh has discovered an unusual form of matter—not a conventional metal, insulator, or magnet, for example, but something entirely different. This phase, characterized by an unusual ordering of electrons, offers possibilities for new electronic device functionalities and could hold the solution to a long-standing mystery in condensed matter physics having to do with high-temperature superconductivity—the ability for some materials to conduct electricity without resistance, even at "high" temperatures approaching –100 degrees Celsius.
"The discovery of this phase was completely unexpected and not based on any prior theoretical prediction," says Hsieh, an assistant professor of physics, who previously was on a team that discovered another form of matter called a topological insulator. "The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties."
Hsieh and his colleagues describe their findings in the November issue of Nature Physics, and the paper is now available online. Liuyan Zhao, a postdoctoral scholar in Hsieh's group, is lead author on the paper.
The physicists made the discovery while testing a laser-based measurement technique that they recently developed to look for what is called multipolar order. To understand multipolar order, first consider a crystal with electrons moving around throughout its interior. Under certain conditions, it can be energetically favorable for these electrical charges to pile up in a regular, repeating fashion inside the crystal, forming what is called a charge-ordered phase. The building block of this type of order, namely charge, is simply a scalar quantity—that is, it can be described by just a numerical value, or magnitude.
In addition to charge, electrons also have a degree of freedom known as spin. When spins line up parallel to each other (in a crystal, for example), they form a ferromagnet—the type of magnet you might use on your refrigerator and that is used in the strip on your credit card. Because spin has both a magnitude and a direction, a spin-ordered phase is described by a vector.
Over the last several decades, physicists have developed sophisticated techniques to look for both of these types of phases. But what if the electrons in a material are not ordered in one of those ways? In other words, what if the order were described not by a scalar or vector but by something with more dimensionality, like a matrix? This could happen, for example, if the building block of the ordered phase was a pair of oppositely pointing spins—one pointing north and one pointing south—described by what is known as a magnetic quadrupole. Such examples of multipolar-ordered phases of matter are difficult to detect using traditional experimental probes.
As it turns out, the new phase that the Hsieh group identified is precisely this type of multipolar order.
To detect multipolar order, Hsieh's group utilized an effect called optical harmonic generation, which is exhibited by all solids but is usually extremely weak. Typically, when you look at an object illuminated by a single frequency of light, all of the light that you see reflected from the object is at that frequency. When you shine a red laser pointer at a wall, for example, your eye detects red light. However, for all materials, there is a tiny amount of light bouncing off at integer multiples of the incoming frequency. So with the red laser pointer, there will also be some blue light bouncing off of the wall. You just do not see it because it is such a small percentage of the total light. These multiples are called optical harmonics.
The Hsieh group's experiment exploited the fact that changes in the symmetry of a crystal will affect the strength of each harmonic differently. Since the emergence of multipolar ordering changes the symmetry of the crystal in a very specific way—a way that can be largely invisible to conventional probes—their idea was that the optical harmonic response of a crystal could serve as a fingerprint of multipolar order.
"We found that light reflected at the second harmonic frequency revealed a set of symmetries completely different from those of the known crystal structure, whereas this effect was completely absent for light reflected at the fundamental frequency," says Hsieh. "This is a very clear fingerprint of a specific type of multipolar order."
The specific compound that the researchers studied was strontium-iridium oxide (Sr2IrO4), a member of the class of synthetic compounds broadly known as iridates. Over the past few years, there has been a lot of interest in Sr2IrO4 owing to certain features it shares with copper-oxide-based compounds, or cuprates. Cuprates are the only family of materials known to exhibit superconductivity at high temperatures—exceeding 100 Kelvin (–173 degrees Celsius). Structurally, iridates and cuprates are very similar. And like the cuprates, iridates are electrically insulating antiferromagnets that become increasingly metallic as electrons are added to or removed from them through a process called chemical doping. A high enough level of doping will transform cuprates into high-temperature superconductors, and as cuprates evolve from being insulators to superconductors, they first transition through a mysterious phase known as the pseudogap, where an additional amount of energy is required to strip electrons out of the material. For decades, scientists have debated the origin of the pseudogap and its relationship to superconductivity—whether it is a necessary precursor to superconductivity or a competing phase with a distinct set of symmetry properties. If that relationship were better understood, scientists believe, it might be possible to develop materials that superconduct at temperatures approaching room temperature.
Recently, a pseudogap phase also has been observed in Sr2IrO4—and Hsieh's group has found that the multipolar order they have identified exists over a doping and temperature window where the pseudogap is present. The researchers are still investigating whether the two overlap exactly, but Hsieh says the work suggests a connection between multipolar order and pseudogap phenomena.
"There is also very recent work by other groups showing signatures of superconductivity in Sr2IrO4 of the same variety as that found in cuprates," he says. "Given the highly similar phenomenology of the iridates and cuprates, perhaps iridates will help us resolve some of the longstanding debates about the relationship between the pseudogap and high-temperature superconductivity."
Hsieh says the finding emphasizes the importance of developing new tools to try to uncover new phenomena. "This was really enabled by a simultaneous technique advancement," he says.
Furthermore, he adds, these multipolar orders might exist in many more materials. "Sr2IrO4 is the first thing we looked at, so these orders could very well be lurking in other materials as well, and that's exactly what we are pursuing next."
Additional Caltech authors on the paper, "Evidence of an odd-parity hidden order in a spin–orbit coupled correlated iridate," are Darius H. Torchinsky, Hao Chu, and Vsevolod Ivanov. Ron Lifshitz of Tel Aviv University, Rebecca Flint of Iowa State University, and Tongfei Qi and Gang Cao of the University of Kentucky are also coauthors. The work was supported by funding from the Army Research Office, the National Science Foundation (NSF), and the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support from the Gordon and Betty Moore Foundation.
Written by Kimm Fesenmaier
- See more at: http://www.caltech.edu/news/caltech-physicists-uncover-novel-phase-matter-48573#sthash.DcK42pEh.dpuf
"The discovery of this phase was completely unexpected and not based on any prior theoretical prediction. The whole field of electronic materials is driven by the discovery of new phases, which provide the playgrounds in which to search for new macroscopic physical properties."—David Hsieh, assistant professor of physics
Artist's rendition of spatially segregated domains of multipolar order in the Sr2IrO4 crystal. The orientation of the multipolar order in each domain is depicted by the multi-lobed object. Credit: Liuyan Zhao - See more at: http://www.caltech.edu/news/caltech-physicists-uncover-novel-phase-matter-48573#sthash.DcK42pEh.dpuf
If you’ve heard of fusion energy, you’ve probably heard of tokamaks. These doughnut-shaped devices are meant to cage ionized gases called plasmas in magnetic fields while heating them to the outlandish temperatures needed for hydrogen nuclei to fuse. Tokamaks are the workhorses of fusion—solid, symmetrical, and relatively straightforward to engineer—but progress with them has been plodding.
Now, tokamaks’ rebellious cousin is stepping out of the shadows. In a gleaming research lab in Germany’s northeastern corner, researchers are preparing to switch on a fusion device called a stellarator, the largest ever built. The €1 billion machine, known as Wendelstein 7-X (W7-X), appears now as a 16-meter-wide ring of gleaming metal bristling with devices of all shapes and sizes, innumerable cables trailing off to unknown destinations, and technicians tinkering with it here and there. It looks a bit like Han Solo’s Millennium Falcon, towed in for repairs after a run-in with the Imperial fleet. Inside are 50 6-tonne magnet coils, strangely twisted as if trampled by an angry giant.
Although stellarators are similar in principle to tokamaks, they have long been dark horses in fusion energy research because tokamaks are better at keeping gas trapped and holding on to the heat needed to keep reactions ticking along. But the Dali-esque devices have many attributes that could make them much better prospects for a commercial fusion power plant: Once started, stellarators naturally purr along in a steady state, and they don’t spawn the potentially metal-bending magnetic disruptions that plague tokamaks. Unfortunately, they are devilishly hard to build, making them perhaps even more prone to cost overruns and delays than other fusion projects. “No one imagined what it means” to build one, says Thomas Klinger, leader of the German effort.
W7-X could mark a turning point. The machine, housed at a branch of the Max Planck Institute for Plasma Physics (IPP) that Klinger directs, is awaiting regulatory approval for a startup in November. It is the first large-scale example of a new breed of supercomputer-designed stellarators that have had most of their containment problems computed out. If W7-X matches or beats the performance of a similarly sized tokamak, fusion researchers may have to reassess the future course of their field. “Tokamak people are waiting to see what happens. There’s an excitement around the world about W7-X,” says engineer David Anderson of the University of Wisconsin (UW), Madison.
Adapted from IPP by C. Bickel and A. Cuadra/Science
Wendelstein 7-X, the first large-scale optimized stellarator, took 1.1 million working hours to assemble, using one of the most complex engineering models ever devised, and must withstand huge temperature ranges and enormous forces.
Stellarators face the same challenge as all fusion devices: They must heat and hold on to a gas at more than 100 million degrees Celsius—seven times the temperature of the sun’s core. Such heat strips electrons from atoms, leaving a plasma of electrons and ions, and it makes the ions travel fast enough to overcome their mutual repulsion and fuse. But it also makes the gas impossible to contain in a normal vessel.
Instead, it is held in a magnetic cage. A current-carrying wire wound around a tube creates a straight magnetic field down the center of the tube that draws the plasma away from the walls. To keep particles from escaping at the ends, many early fusion researchers bent the tube into a doughnut-shaped ring, or torus, creating an endless track.
But the torus shape creates another problem: Because the windings of the wire are closer together inside the hole of the doughnut, the magnetic field is stronger there and weaker toward the doughnut’s outer rim. The imbalance causes particles to drift off course and hit the wall. The solution is to add a twist that forces particles through regions of high and low magnetic fields, so the effects of the two cancel each other out.
Stellarators impose the twist from outside. The first stellarator, invented by astro-physicist Lyman Spitzer at Princeton University in 1951, did it by bending the tube into a figure-eight shape. But the lab he set up—the Princeton Plasma Physics Laboratory (PPPL) in New Jersey—switched to a simpler method for later stellarators: winding more coils of wire around a conventional torus tube like stripes on a candy cane to create a twisting magnetic field inside.
In a tokamak, a design invented in the Soviet Union in the 1950s, the twist comes from within. Tokamaks use a setup like an electrical transformer to induce the electrons and ions to flow around the tube as an electric current. This current produces a vertical looping magnetic field that, when added to the field already running the length of the tube, creates the required spiraling field lines.
Both methods work, but the tokamak is better at holding on to a plasma. In part that’s because a tokamak’s symmetry gives particles smoother paths to follow. In stellarators, Anderson says, “particles see lots of ripples and wiggles” that cause many of them to be lost. As a result, most fusion research since the 1970s has focused on tokamaks—culminating in the huge ITER reactor project in France, a €16 billion international effort to build a tokamak that produces more energy than it consumes, paving the way for commercial power reactors.
But tokamaks have serious drawbacks. A transformer can drive a current in the plasma only in short pulses that would not suit a commercial fusion reactor. Current in the plasma can also falter unexpectedly, resulting in “disruptions”: sudden losses of plasma confinement that can unleash magnetic forces powerful enough to damage the reactor. Such problems plague even up-and-coming designs such as the spherical tokamak (Science, 22 May, p. 854).
Stellarators, however, are immune. Their fields come entirely from external coils, which don’t need to be pulsed, and there is no plasma current to suffer disruptions. Those two factors have kept some teams pursuing the concept.
The largest working stellarator is the Large Helical Device (LHD) in Toki, Japan, which began operating in 1998. Lyman Spitzer would recognize the design, a variation on the classic stellarator with two helical coils to twist the plasma and other coils to add further control. The LHD holds all major records for stellarator performance, shows good steady-state operation, and is approaching the performance of a similarly sized tokamak.
Two researchers—IPP’s Jürgen Nührenberg and Allen Boozer of PPPL (now at Columbia University)—calculated that they could do better with a different design that would confine plasma with a magnetic field of constant strength but changing direction. Such a “quasi-symmetric” field wouldn’t be a perfect particle trap, says IPP theorist Per Helander, “but you can get arbitrarily close and get losses to a satisfactory level.” In principle, it could make a stellarator perform as well as a tokamak.
The design strategy, known as optimization, involves defining the shape of magnetic field that best confines the plasma, then designing a set of magnets to produce the field. That takes considerable computing power, and supercomputers weren’t up to the job until the 1980s.
The first attempt at a partially optimized stellarator, dubbed Wendelstein 7-AS, was built at the IPP branch in Garching near Munich and operated between 1988 and 2002. It broke all stellarator records for machines of its size. Researchers at UW Madison set out to build the first fully optimized device in 1993. The result, a small machine called the Helically Symmetric Experiment (HSX), began operating in 1999. “W7-AS and HSX showed the idea works,” says David Gates, head of stellarator physics at PPPL.
That success gave U.S. researchers confidence to try something bigger. PPPL began building the National Compact Stellarator Experiment (NCSX) in 2004 using an optimization strategy different from IPP’s. But the difficulty of assembling the intricately shaped parts with millimeter accuracy led to cost hikes and schedule slips. In 2008, with 80% of the major components either built or purchased, the Department of Energy pulled the plug on the project (Science, 30 May 2008, p. 1142). “We flat out underestimated the cost and the schedule,” says PPPL’s George “Hutch” Neilson, manager of NCSX.
IPP/Wolfgang Filser
Wendelstein 7-X’s bizarrely shaped components must be put together with millimeter precision. All welding was computer controlled and monitored with laser scanners.
BACK IN GERMANY, the project to build W7-X was well underway. The government of the recently reunified country had given the green light in 1993 and 1994 and decided to establish a new branch institute at Greifswald, in former East Germany, to build the machine. Fifty staff members from IPP moved from Garching to Greifswald, 800 kilometers away, and others made frequent trips between the sites, says Klinger, director of the Greifswald branch. New hires brought staff numbers up to today’s 400. W7-X was scheduled to start up in 2006 at a cost of €550 million.
But just like the ill-fated American NCSX, W7-X soon ran into problems. The machine has 425 tonnes of superconducting magnets and support structure that must be chilled close to absolute zero. Cooling the magnets with liquid helium is “hell on Earth,” Klinger says. “All cold components must work, leaks are not possible, and access is poor” because of the twisted magnets. Among the weirdly shaped magnets, engineers must squeeze more than 250 ports to supply and remove fuel, heat the plasma, and give access for diagnostic instruments. Everything needs extremely complex 3D modeling. “It can only be done on computer,” Klinger says. “You can’t adapt anything on site.”
By 2003, W7-X was in trouble. About a third of the magnets produced by industry failed in tests and had to be sent back. The forces acting on the reactor structure turned out to be greater than the team had calculated. “It would have broken apart,” Klinger says. So construction of some major components had to be halted for redesigning. One magnet supplier went bankrupt. The years 2003 to 2007 were a “crisis time,” Klinger says, and the project was “close to cancellation.” But civil servants in the research ministry fought hard for the project; finally, the minister allowed it to go ahead with a cost ceiling of €1.06 billion and first plasma scheduled for 2015.
After 1.1 million construction hours, the Greifswald institute finished the machine in May 2014 and spent the past year carrying out commissioning checks, which W7-X passed without a hitch. Tests with electron beams show that the magnetic field in the still-empty reactor is the right shape. “Everything looks, to an extremely high accuracy, exactly as it should,” IPP’s Thomas Sunn Pedersen says.
Approval to go ahead is expected from Germany’s nuclear regulators by the end of this month. The real test will come once W7-X is full of plasma and researchers finally see how it holds on to heat. The key measure is energy confinement time, the rate at which the plasma loses energy to the environment. “The world’s waiting to see if we get the confinement time and then hold it for a long pulse,” PPPL’s Gates says.
Success could mean a course change for fusion. The next step after ITER is a yet-to-be-designed prototype power plant called DEMO. Most experts have assumed it would be some sort of tokamak, but now some are starting to speculate about a stellarator. “People are already talking about it,” Gates says. “It depends how good the results are. If the results are positive, there’ll be a lot of excitement.”
Einstein was troubled by how two particles can communicate with each other even if they are on opposite sides of the galaxy. Could it be true? Yes, scientists have now shown
A study in the Netherlands supports a long-held claim of quantum theory, one that Einstein refused to accept, that objects separated by great distance could affect each other’s behavior.
2015年10月６日、在日本東北的岩手縣立大學，聚集了近百位的大學員工和媒体工作者，等待收看網路傳來的諾貝爾物理獎消息。午後６時４５分, 瑞典皇家科學院的祕書長揭曉說: 「今年獲獎的，是有關於某一宇宙中人數最眾多的族群，其身份特徵可能轉變的發現。」 "This year's prize is about changes of identity among some of the most abundant inhabitants of the universe." 此一敘述的精確物理含義，對大多數人而言，是難以掌握的。接著，人們清楚聽到了，物理獎授予加拿大的亞瑟·麥克唐納(Arthur Bruce McDonald)和日本東京大學的梶田隆章，表彰他們發現了微中子振盪(neutrino oscillation)現象，從而證實了微中子的質量不為零。岩手縣立大學現場的人群，在啊的一聲之後，是嘆息，是一片靜默。
