Until now, scientists have thought that the process of erasing information requires energy. But a new study shows that, theoretically, information can be erased without using any energy at all. Instead, the cost of erasure can be paid in terms of another conserved quantity, such as spin angular momentum.
In the study, physicists Joan Vaccaro from Griffith University in Queensland, Australia, and Stephen Barnett from the University of Strathclyde in Glasgow, UK, have quantitatively described how information can be erased without any energy, and they also explain why the result is not as contentious as it first appears. Their paper is published in a recent issue of the Proceedings of the Royal Society A.
Traditionally, the process of erasing information requires a cost that is calculated in terms of energy – more specifically, heat dissipation. In 1961, Rolf Landauer argued that there was a minimum amount of energy required to erase one bit of information, i.e. to put a bit in the logical zero state. The energy required is positively related to the temperature of the system’s thermal reservoir, and can be thought of as the system’s thermodynamic entropy. As such, this entropy is considered to be a fundamental cost of erasing a bit of information.
However, Vaccaro and Barnett have shown that an energy cost can be fully avoided by using a reservoir based on something other than energy, such as spin angular momentum. Subatomic particles have spin angular momentum, a quantity that, like energy, must be conserved. Basically, instead of heat being exchanged between a qubit and thermal reservoir, discrete quanta of angular momentum are exchanged between a qubit and spin reservoir. The scientists described how repeated logic operations between the qubit’s spin and a secondary spin in the zero state eventually result in both spins reaching the logical zero state. Most importantly, the scientists showed that the cost of erasing the qubit’s memory is given in terms of the quantity defining the logic states, which in this case is spin angular momentum and not energy.
The scientists explained that experimentally realizing this scheme would be very difficult. Nevertheless, their results show that physical laws do not forbid information erasure with a zero energy cost, which is contrary to previous studies. The researchers noted that, in practice, it will be especially difficult to ensure the system’s energy degeneracy (that different spin states of the qubit and reservoir have the exact same energy level). But even if imperfect conditions cause some energy loss, there is no fundamental reason to assume that the cost will be as large as that predicted by Landauer’s formula.
The possibility of erasing information without using energy has implications for a variety of areas. One example is the paradox of Maxwell’s demon, which appears to offer a way of violating the second law of thermodynamics. By opening and closing a door to separate hot and cold molecules, the demon supposedly extracts work from the reservoir, converting all heat into useful mechanical energy. Bennett’s resolution of the paradox in 1982 argues that the demon’s memory has to be erased to complete the cycle, and the cost of erasure is at least as much as the liberated energy. However, Vaccaro and Barnett’s results suggest that the demon’s memory can be erased at no energy cost by using a different kind of reservoir, where the cost would be in terms of spin angular momentum. In this scheme, the demon can extract all the energy from a heat reservoir as useful energy at a cost of another resource.
As the scientists explained, this result doesn't contradict historical statements of the second law of thermodynamics, which are exclusively within the context of heat and thermal reservoirs and do not allow for a broader class of reservoirs. Moreover, even though the example with Maxwell’s demon suggests that mechanical work can be extracted at zero energy cost, this extraction is associated with an increase in the information-theoretic entropy of the overall system.
“The maximization of entropy subject to a constraint need apply not only to heat reservoirs and the conservation of energy,” Vaccaro explained to PhysOrg.com.
The results could also apply to hypothetical Carnot heat engines, which operate at maximum efficiency. If these engines use angular momentum reservoirs instead of thermal reservoirs, they could generate angular momentum effort instead of mechanical work.
As for demonstrating the concept of erasing information at zero energy cost, the scientists said that it would take more research and time.
“We are currently looking at an idea to perform information erasure in atomic and optical systems, but it needs much more development to see if it would actually work in practice,” Vaccaro said.
She added that the result is of fundamental significance, and it’s not likely to have practical applications for memory devices.
“We don't see this as having a direct impact in terms of practical applications, because the current energy cost of information erasure is nowhere near Landauer's theoretical bound,” she said. “It's more a case of what it says about fundamental concepts. For example, Landauer said that information is physical because it takes energy to erase it. We are saying that the reason it is physical has a broader context than that.”
A recent study confirmed that low socioeconomic status (SES) is associated with higher risk of depressive symptoms in patients with rheumatoid arthritis (RA). Statistically significant differences in race, public versus tertiary-care hospital, disability and medications were found between depressed and non-depressed patients. Study findings are reported in the February issue of Arthritis Care & Research, a journal published by Wiley-Blackwell on behalf of the American College of Rheumatology (ACR).
Roughly 1.3 million Americans are affected by RA—a chronic autoimmune disease that can cause functional limitations and may lead to physical disability in many patients. Prior studies have shown that depression is common, occurring in 13% to 42% of RA patients and is associated with worse outcomes, including greater risk of heart attack, suicide, and death. In the U.S., socioeconomic position as measured by race, gender, age, income, education and health access has significant impact on overall health.
Mary Margaretten, M.D., from the Arthritis Research Group at the University of California, San Francisco (UCSF) and lead study author explained, "We assessed the extent to which low SES influences the relationship between disability and depression in order to better identify those patients at higher risk for depression." Researchers used data obtained from the UCSF RA cohort in which participants were enrolled from an urban county, public hospital that serves the poor and a referral, tertiary-care medical center. The data included 824 visits for 466 patients, 223 from the public hospital and 243 from the tertiary-care clinic.
Analysis showed that 37% of participants had moderate to severe depression, scoring 10 or higher on the Patient Health Questionnaire (PHQ-9). The mean Health Assessment Questionnaire (HAQ) score was 1.2 and the disease activity score (DAS28) was 4, indicating fairly high levels of functional impairment and disease activity, respectively. Researchers also found significant differences between depressed and non-depressed patients related to race, public versus university hospital, functional limitation and disease modifying anti-rheumatic drug (DMARD) treatment. Differences in depression severity were not impacted by gender, age, disease duration, steroid use and dose, or biologic therapy.
Furthermore, the team found that county hospital patients also had significantly higher depression scores (PHQ-9 of 7.3) than patients at the university medical center (PHQ-9 of 5.7). An interaction existed between socioeconomic status and disability such that the association of functional limitation with depression scores was stronger for patients at the public hospital clinic compared to those at the tertiary-care clinic.
Dr. Margaretten concluded, "For the same level of disability, patients with low SES may be more likely to experience depression. Detection and documentation of the differing effects of disability on depression between patients of different socioeconomic status can help rheumatologists improve health outcomes by initiating appropriate and timely treatment for depression."
A team of physicists has taken a big step toward the development of useful graphene spintronic devices. The physicists, from the City University of Hong Kong and the University of Science and Technology of China, present their findings in the American Institute of Physics' Applied Physics Letters.
Graphene, a two-dimensional crystalline form of carbon, is being touted as a sort of "Holy Grail" of materials. It boasts properties such as a breaking strength 200 times greater than steel and, of great interest to the semiconductor and data storage industries, electric currents that can blaze through it 100 times faster than in silicon.
Spintronic devices are being hotly pursued because they promise to be smaller, more versatile, and much faster than today's electronics. "Spin" is a quantum mechanical property that arises when a particle's intrinsic rotational momentum creates a tiny magnetic field. And spin has a direction, either "up" or "down." The direction can encode data in the 0s and 1s of the binarysystem, with the key here being that spin-based data storage doesn't disappear when the electric current stops.
"There is strong research interest in spintronic devices that process information using electron spins, because these novel devices offer better performance than traditional electronic devices and will likely replace them one day," says Kwok Sum Chan, professor of physics at the City University of Hong Kong "Graphene is an important material for spintronic devices because its electron spin can maintain its direction for a long time and, as a result, information stored isn't easily lost."
It is, however, difficult to generate a spin current in graphene, which would be a key part of carrying information in a graphene spintronic device. Chan and colleagues came up with a method to do just that. It involves using spin splitting in monolayer graphene generated by ferromagnetic proximity effect and adiabatic (a process that is slow compared to the speed of the electrons in the device) quantum pumping. They can control the degree of polarization of the spin current by varying the Fermi energy (the level in the distribution of electron energies in a solid at which a quantum state is equally likely to be occupied or empty), which they say is very important for meeting various application requirements.
UK-based Cella Energy has developed a synthetic fuel that could lead to US$1.50 per gallon gasoline. Apart from promising a future transportation fuel with a stable price regardless of oil prices, the fuel is hydrogen based and produces no carbon emissions when burned. The technology is based on complex hydrides, and has been developed over a four year top secret program at the prestigious Rutherford Appleton Laboratory near Oxford. Early indications are that the fuel can be used in existing internal combustion engined vehicles without engine modification.
According to Stephen Voller CEO at Cella Energy, the technology was developed using advanced materials science, taking high energy materials and encapsulating them using a nanostructuring technique called coaxial electrospraying.
“We have developed new micro-beads that can be used in an existing gasoline or petrol vehicle to replace oil-based fuels,” said Voller. “Early indications are that the micro-beads can be used in existing vehicles without engine modification.”
“The materials are hydrogen-based, and so when used produce no carbon emissions at the point of use, in a similar way to electric vehicles”, said Voller.
The technology has been developed over a four-year top secret programme at the prestigious Rutherford Appleton Laboratory near Oxford, UK.
The development team is led by Professor Stephen Bennington in collaboration with scientists from University College London and Oxford University.
Professor Bennington, Chief Scientific Officer at Cella Energy said, “our technology is based on materials called complex hydrides that contain hydrogen. When encapsulated using our unique patented process, they are safer to handle than regular gasoline.”
Questions such as how much fresh water we have left on Earth, where it is located, and how we can access it are all nearly impossible to answer. However, scientists working on understanding and revealing the planet's surface structure are helping to hone in on an answer. University of British Columbia researchers have created a world's-first with their new map that outlines how fluid flows through Earth's various porous surfaces. Information gleaned from the map can help us discover more about water supplies worldwide.
According to Science Daily, the maps, published earlier this week in Geophysical Research Letters, could help with both water resource management and climate modeling, since a better understanding of how fluid permeates rock and sediments can reveal how and where rainwater travels as it flows into the water table. While most maps so far have dealt with permeability down to one or two meters of soil, and across smaller areas, this new map tracks permeability to depths of about 100 meters across the globe.
"This is the first global-scale picture of near-surface permeability, and is based on rock type data at greater depths than previous mapping," says Tom Gleeson, a postdoctoral researcher with the Department of Earth and Ocean Sciences.
Mapping groundwater supplies in such detail is important for managing use of water, especially in where and how much is extracted. Such water source mapping has helped recently in uncovering to what extent groundwater supplies in southern Asia are contaminated with arsenic. Researchers were able to create a 3D map to show that the deeper a well went for water, the more likely it was to be contaminated.
We still don't know exactly how much fresh water we have left, but we know it is shrinking and we are hitting (or have already hit) peak water, since we're draining aquifers, over-exploiting rivers, and dropping the groundwater table ever deeper.
Zeitgeist: Moving Forward, by director Peter Joseph, is a feature length documentary work which will present a case for a needed transition out of the current socioeconomic monetary paradigm which governs the entire world society.
This subject matter will transcend the issues of cultural relativism and traditional ideology and move to relate the core, empirical "life ground" attributes of human and social survival, extrapolating those immutable natural laws into a new sustainable social paradigm called a "Resource-Based Economy".
One voice can make a difference........a million voices can change the world!
Space launches have evoked the same image for decades: bright orange flames exploding beneath a rocket as it lifts, hovers and takes off into the sky. But an alternative propulsion system proposed by some researchers could change that vision.
Instead of explosive chemical reactions on-board a rocket, the new concept, called beamed thermal propulsion, involves propelling a rocket by shining laser light or microwaves at it from the ground. The technology would make possible a reusable single-stage rocket that has two to five times more payload space than conventional rockets, which would cut the cost of sending payloads into low-Earth orbit.
NASA is now conducting a study to examine the possibility of using beamed energy propulsion for space launches. The study is expected to conclude by March 2011.
In a traditional chemical rocket propulsion system, fuel and oxidizer are pumped into the combustion chamber under high pressure and burnt, which creates exhaust gases that are ejected down from a nozzle at high velocity, thrusting the rocket upwards.
A beamed thermal propulsion system would involve focusing microwave or laser beams on a heat exchanger aboard the rocket. The heat exchanger would transfer the radiation's energy to the liquid propellant, most likely hydrogen, converting it into a hot gas that is pushed out of the nozzle.
“The basic idea is to build rockets that leave their energy source on the ground,” says Jordin Kare, president of Kare Technical Consulting, who developed the laser thermal launch system concept in 1991. “You transmit the energy from the ground to the vehicle.”
With the beam shining on the vehicle continually, it would take 8 to 10 minutes for a laser to put a craft into orbit, while microwaves would do the trick in 3 to 4 minutes. The vehicle would have to be designed without shiny surfaces that could reflect dangerous beams, and aircraft and satellites would have to be kept out of the beam’s path. Any launch system would be built in high-altitude desert areas, so danger to wildlife shouldn’t be a concern, Kare says.
Thermal propulsion vehicles would be safer than chemical rockets since they can’t explode and don’t drop off pieces as they fly. They are also smaller and lighter because most of the complexity is on the ground, which makes them easier and cheaper to launch.
“People can launch small satellites for education, science experiments, engineering tests, etc. whenever they want, instead of having to wait for a chance to share a ride with a large satellite,” Kare says.
Another cost advantage comes from larger payload space. While conventional propulsion systems are limited by the amount of chemical energy in the propellant that's released by combustion, in beamed systems you can add more energy externally. That means a spacecraft can gain a certain momentum using less than half the amount of propellant of a conventional system, allowing more room for the payload.
“Usually in a conventional rocket you have to have three stages with a payload fraction of three percent overall,” says Kevin Parkin, leader of the Microwave Thermal Rocket project at the NASA Ames Research Center. “This propulsion system will be single stage with a payload fraction of five to fifteen percent.”
Having a higher payload space along with a reusable rocket could make beamed thermal propulsion a low-cost way to get material into low Earth orbit, Parkin says.
Parkin developed the idea of microwave thermal propulsion in 2001 and described a laboratory prototype in his 2006 PhD thesis. A practical real-world system should be possible to build now because microwave sources called gyrotrons have transformed in the last five decades, he says. One megawatt devices are now on the market for about a million US dollars.
"They're going up in power and down in cost by orders of magnitude over the last few decades,” he says. “We've reached a point where you can combine about a hundred and make a launch system."
Meanwhile, the biggest obstacle to using lasers to beam energy has been the misconception that it would require a very large, expensive laser, Kare says. But you could buy commercially available lasers that fit on a shipping container and build an array of a few hundred. "Each would have its own telescope and pointing system," he says. "The array would cover an area about the size of a golf course."
The smallest real laser launch system would have 25 to 100 megawatts of power while a microwave system would have 100 to 200 megawatts. Building such an array would be expensive, says Kare, although similar to or even less expensive than developing and testing a chemical rocket. The system would make most economic sense if it was used for at least a few hundred launches a year.
In addition, says Parkin, “the main components of the beam facility should last for well over ten thousand hours of operation, typical of this class of hardware, so the savings can more than repay the initial cost.”
In the near term, beamed energy propulsion would be useful for putting microsatellites into low Earth orbit, for altitude changes or for slowing down spacecraft as they descend to Earth. But the technology could in the future be used to send missions to the Moon or to other planets and for space tourism.
Kare has looked into the possibility of using lasers to propel interstellar probes for NASA’s Institute of Advanced Concepts. A deep space launch would require higher power lasers with larger telescope systems as well as laser relay stations in space. Powering missions over interplanetary distance would require even bigger lasers and telescopes, as well as different propulsion techniques using propellants easier to store than liquid hydrogen.
Sending a spacecraft to a moon of Jupiter, for instance, would require a laser that gives billions of watts of power. "You'd have to have another couple generations of space-based telescopes to do something like that,” Kare says. “You can in fact launch an interstellar probe that way but now you’re talking about lasers that might be hundreds of billions of Watts of power." Laser technology could reach those levels in another 50 years, he says.
Israeli researchers have created a recyclable membrane based on supramolecular linkages that can be used to filter nanoparticles. The membrane, which unusually comprises non-covalent bonds, performs just as well as conventional sieves, offering a green and versatile alternative for size-separation and purification of nanoparticles.
Standard filtration membranes are usually held together by strong covalent bonds, which give membranes suitable strength to withstand the pressures involved in filtration processes. The problem is that when membranes become clogged up they have to be discarded and replaced.
One idea is to make membranes based on supramolecular (non-covalent) interactions which can undergo reversible self-assembly. Since the bonds can be undone easily, they offer a recyclable and adaptable option. But making such membranes with a level of robustness to rival conventional options has remained a challenge.
Now, Boris Rybtchinski and colleagues at the Weizmann Institute of Science in Rehovot, Israel, have managed to make a robust and recyclable untrafiltration membrane with non-covalent hydrophobic linkages. 'This results in easy fabrication, recyclability, and versatility that cannot be achieved with regular covalent materials,' says Rybtchinski.
The team created a compound that self-assembles in water. It has a specially designed large and flat hydrophobic surface. 'In water, these surfaces experience very large attractive forces that hold them together, eventually forming porous nanostructured 3D networks possessing high robustness,' Rybtchinski explains. By filtering these structures onto a cheap commercial support with 400nm pores, they form a nanostructured membrane that works as a nanoparticle sieve.
The hydrophobic interactions are strong enough to hold together the membrane and withstand the flow of particles, says Rybtchinski. Experiments with solutions containing gold nanoparticles of various sizes revealed that only particles smaller than 5nm could pass through a 12µm thick membrane. By increasing the thickness to 45µm, the team discovered that the membrane could separate smaller particles (CdTe quantum dots of 2-4nm in size) because of a time delay between different sized particles passing through the membrane, resulting in size-selective chromatography.
The membrane is easily disassembled by adding solvents such as ethanol which weakens the hydrophobic interactions. 'This way the material can be retrieved, cleaned, and reused for fabrication of another membrane,' says Rybtchinski. Furthermore, particles that are stuck in the filter can be recycled too, which is not always possible with conventional membranes.
Jonathan Nitschke, who researches self-assembling polymers at the University of Cambridge, UK says that Rybtchinski's use of non-covalent interactions to knit together a filtration membrane is innovative. 'Supramolecular linkages can be undone under certain conditions, allowing the membranes to be dissolved and recreated so it's an excellent way of cleaning and recycling them.'
Scientists recently discovered that DNA can be used as a molecular scaffold to make metal contacts to organic semiconductors. A key step in this process involves being able to tether the DNA to various surfaces and stretch the molecule to varying lengths.
Zhenan Bao and colleagues' new strategy involves synthesizing hybrid DNA-organic molecule-DNA (DOD) structures, then stretching and tethering the DOD assemblies between two microscopic metal electrodes. The researchers then make metal electrode-organic molecule-metal electrode (MOM) structures by further metallizing the DNA segments within the DOD structures.
The team then exploited so-called biotin-Streptavidin linkage chemistry to tether the DNA assemblies to device surfaces (quartz in this case). The basic steps are as follows: functionalizing the surface with amine (-NH2) terminated silanes; reacting the amines with N-hydroxysuccinimide (NHS) functionaliszed polyethylene glycol (PEG) chains terminated with biotin; and using Streptavidin to create a link to biotin-terminated DNA molecules.
A crucial step
"We have made progress in synthesizing these DOD hybrid structures and have now developed a reproducible surface chemistry technique to tether DNA molecules of different lengths to substrate surfaces," team member Guihua Yu told nanotechweb.org. "We have also developed a shear flow processing method to control DNA stretching and alignment. This represents a crucial step in making large-scale nanoelectronic devices based on DOD array structures."
Aside these practical applications, the technique could also be used to study single DNA molecules and how they rotate. DNA tethering and stretching may also help in manipulating nucleotides in single DNA molecules for genetic applications and to study how DNA reacts with proteins at the single-molecule level, said Yu. Other single-molecule technologies, such as DNA sequencing could also benefit.
Spurred on by these first results, the team is now working on a controllable, double-tethering process while developing in situDNA metallization for ultimately making larger-scale nanoelectronic devices based on single organic molecules. "We will then perform electrical transport measurements on these device arrays to probe how charge travels through single molecules with different chemical functionalities and length," added Yu.
Scientists said Monday they were moving closer to coming up with a non-physical definition of the kilo after discovering the metal artefact used as the international standard had shed a little weight.
Researchers caution there is still some way to go before their mission is complete, but if successful it would lead to the end of the useful life of the last manufactured object on which fundamental units of measure depend.
At the moment, the international standard for the kilo -- the equivalent of around 2.2 pounds -- is a chunk of metal, under triple lock-and-key in France since 1889.
But Scientists became concerned about the cylinder of platinum and iridium housed at the International Bureau of Weights and Measures (BIPM) in Sevres, near Paris, after discovering it had mysteriously lost a tiny amount of weight.
Experts at the institute revealed in 2007 that the metal chunk is 50 micrograms -- 0.0000017 ounces -- lighter than the average of several dozen copies, meaning it had lost the equivalent of a small grain of sand.
They are now searching for a non-physical way of defining the kilo, which would bring it in line with the six other base units that make up the International System of Units (SI).
The other units are the metre, the second, the ampere, the kelvin, the mole and the candela, and none of them are now based on a physical reference object.
Experiments are focused on establishing a link between mass and the Planck constant, the fundamental unit of measurement in quantum physics, to provide a new definition of the kilo.
Michael Stock, a BIPM scientist who will on Monday discuss the proposed change in London, said the metal chunk, known as the "international prototype", was coming to the end of its useful life.
"Measurements get more and more precise, and precise measurements require well-defined measurement units to express their results," he said.
He added that "our experiments are moving forward, however, it is too early to implement the new definition of the kilogram just yet."
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