Dark Energy Found Stifling Growth in Universe

Dark Energy Found Stifling Growth in Universe

December 17, 2008

For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be.

This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity.

Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field.

To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time.

"This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down."

Vikhlinin and his colleagues used Chandra to observe the hot gas in dozens of galaxy clusters, which are the largest collapsed objects in the universe. Some of these clusters are relatively close and others are more than halfway across the universe.

The results show the increase in mass of the galaxy clusters over time aligns with a universe dominated by dark energy. It is more difficult for objects like galaxy clusters to grow when space is stretched, as caused by dark energy. Vikhlinin and his team see this effect clearly in their data. The results are remarkably consistent with those from the distance measurements, revealing general relativity applies, as expected, on large scales.

"For years, scientists have wanted to start testing how gravity works on large scales and now, we finally have," said William Forman, a co-author of the study from the Smithsonian Astrophysical Observatory. "This is a test that general relativity could have failed."

When combined with other clues -- supernovas, the study of the cosmic microwave background, and the distribution of galaxies -- this new X-ray result gives scientists the best insight to date on the properties of dark energy.

The study strengthens the evidence that dark energy is the cosmological constant. Although it is the leading candidate to explain dark energy, theoretical work suggests it should be about 10 raised to the power of 120 times larger than observed. Therefore, alternatives to general relativity, such as theories involving hidden dimensions, are being explored.

"Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever."

These results have consequences for predicting the ultimate fate of the universe. If dark energy is explained by the cosmological constant, the expansion of the universe will continue to accelerate, and the Milky Way and its neighbor galaxy, Andromeda, never will merge with the Virgo cluster. In that case, about a hundred billion years from now, all other galaxies ultimately would disappear from the Milky Way's view and, eventually, the local superclusters of galaxies also would disintegrate.

Astrophysicists recreate stars in the lab

Astrophysicists recreate stars in the lab
by European Science Foundation

Astronomers are recruiting the physics laboratory to unravel the high energy processes involved in formation of stars and other critical processes within the universe. Experiments with high energy radiation and plasmas in the laboratory involving temperatures and magnetic fields over a million times greater than normally encountered on earth are also producing spin off benefits for important applications, notably in the drive towards nuclear fusion as a source of clean carbon-neutral energy.

Although a great deal has been learnt through a combination of theoretical models and observation of the universe right across the electromagnetic spectrum including visible light with conventional optical telescopes, many questions on energetic processes taking place billions of miles away still remain unanswered.This is why astrophysicists are turning to a third ingredient, the high energy laboratory, fusing results obtained there with theoretical models and direct observation through instruments. The state of this highly promising field was discussed at a recent workshop organised by the European Science Foundation (ESF), which also set out a roadmap for future collaborative research in Europe over the next five years.

The workshop is setting up a European framework for conducting coordinated experiments in Extreme Laboratory Astrophysics (ELA), aiming to simulate the high temperatures and magnetic fields experienced in a variety of formative processes occurring throughout the universe's history. Full blown ELA builds on earlier more tentative initiatives, such as the JETSET network, which is a four-year Marie Curie Research Training Network (RTN) funded by the European Commission, designed to build a vibrant interdisciplinary European Research and Training community centred on rigorous and novel approaches to plasma jet studies, with a focus on flows produced during star formation. Plasma jets comprise high energy atomic nuclei stripped of their electrons, expelled from stars during their formation and early in their lives.

ELA experiments however, as discussed at the ESF workshop, go much further than the study of plasma jets, and therefore expand on the foundations created by JETSET. "The JETSET network was truly innovative in that it combined not only theoretical and observational astrophysics, but also for the first time experiments," said Andrea Ciardi, convenor of the ESF workshop and plasma physicist at the Ecole Normale Superieure in Paris. "However JETSET was limited in terms of astrophysical phenomena studied (jets from young stars) and in terms of groups involved. The workshop aims at the creation of an XLA framework combining numerical modelling, experiments and theory, to complement observations in the study of a broader range of astrophysical phenomena."

The workshop fulfilled its objectives of stimulating the required interdisciplinary research effort, and providing a broad outlook of future objectives. Furthermore it generated great excitement about prospects for the field, according to Ciardi. "The workshop covered a large spectrum of research both in astrophysics and in laboratory plasma physics: from cosmic rays acceleration, to the properties of fast winds in stars, and from high-power lasers aimed at achieving fusion to experiments producing magnetic bubbles expanding at hundreds of kilometres per second," said Ciardi. "Indeed the excitement comes from being able to re-create in the laboratory astrophysical phenomena taking place in some of the most extreme and exotic objects in the universe."

The ELA experiments should also have practical benefits. "ELA research has an inherent duality: experiments developed initially for laboratory astrophysics, including new diagnostics, theoretical and numerical models, can be useful for example to fusion research, which is pursuing a clean source of energy, which in some cases uses similar theoretical and experimental techniques," said Ciardi.

ELA research could also help improve weather forecasts by leading to better understanding of cosmic rays that strike the earth's atmosphere and have a significant effect on cloud formation and thunderstorm activity.

Breakthrough experiment on high-temperature superconductors

Breakthrough experiment on high-temperature superconductors

New information about the metallic state from which high temperature superconductivity emerges, has been revealed in an innovative experiment performed at the University of Bristol.

The international team of physicists, led by Professor Nigel Hussey from the University’s Physics Department, publish their results today in Science Express, a rapid online access service for important new publications in the journal Science.

Superconductivity is a process by which a pair of electrons travelling in opposite directions and with opposite spin direction suddenly become attracted to one another. By pairing up, the two electrons manage to lose all their electrical resistance. This superconducting state means that current can flow without the aid of a battery.

Historically, this remarkable state had always been considered a very low temperature phenomenon, thus the origin of the superconductivity peculiar to very unusual metallic materials termed ‘high temperature superconductors’, still remains a mystery.

Hussey and his team used ultra-high (pulsed) magnetic fields – some of the most powerful in the world – to destroy the superconductivity and follow the form of the electrical resistance down to temperatures close to absolute zero.

They found that it was as the superconductivity becomes stronger, so does the scattering that causes the resistance in the metallic host from which superconductivity emerges. At some point however, the interaction that promotes high temperature superconductivity gets so strong, that ultimately it destroys the very electronic states from which the superconducting pairs form. The next step will be to identify just what that interaction is and how might it be possible to get around its self-destructive tendencies.

In doing this experiment, the team was able to reveal information that will help theorists to develop a more complete theory to explain the properties of high temperature superconductors.

“Indeed”, said Hussey, “if researchers are able to identify what make these superconductors tick, and the electrons to pair up, then material scientists might be able to create a room temperature superconductor. This holy grail of superconductivity research holds the promise of loss-free energy transmission, cheap, fast, levitated transport and a whole host of other revolutionary technological innovations.”

Related Journal : Anomalous Criticality in the Electrical Resistivity of La_2-xSr_xCuO₄

Researchers explain mystery of gravity fingers

Researchers explain mystery of gravity finger
by: MIT Writer

Researchers at MIT recently found an elegant solution to a sticky scientific problem in basic fluid mechanics: why water doesn't soak into soil at an even rate, but instead forms what look like fingers of fluid flowing downward.

Scientists call these rivulets "gravity fingers," and the explanation for their formation has to do with the surface tension where the water—or any liquid—meets the soil (or other medium). Knowing how to account for this phenomenon mathematically will have wide-ranging impact on science problems and engineering applications, including the recovery of oil from reservoirs and the sequestration of carbon underground.

The solution reported in the Dec. 12 issue of Physical Review Letters involves borrowing a mathematical phrase, if you will, from the mathematical description of a similar problem, a solution both simple and elegant that had escaped the notice of many researchers in earlier attempts to describe the phenomenon.

Co-authors Luis Cueto-Felgueroso and Ruben Juanes of the MIT Department of Civil and Environmental Engineering discovered the solution while studying the larger question of how water displaces oil in underground reservoirs. (Petroleum engineers commonly flush oil reservoirs with water to enhance oil recovery.)

"Our paper addresses a long-standing issue in soil physics," said Cueto-Felgueroso. "Lab experiments of water infiltration into homogeneous, dry soil, repeatedly show the presence of preferential flow in the form of fingers. Yet, after several decades, the scientific community has been unable to capture this phenomenon using mathematical models."

"This was the type of problem that required someone from a different research discipline to take a look at it and come up with the solution," said Juanes, the ARCO Assistant Professor in Energy Studies. "Luis applied his expertise to a fluid mechanics problem in another medium—porous media flows—and quickly figured out the solution."

Cueto-Felgueroso, a post-doctoral associate who has previously worked primarily on airflow fluid mechanics problems, had a Eureka! moment when he realized that gravity fingers in soil (or clay or sand) look very similar to water flowing down a window pane, a fairly well-understood phenomenon. He and Juanes then pulled the mathematical explanation (think of it as a phrase of words or music) from the equation describing water on a window, and included that mathematical phrase in the equation describing liquid moving downward through soil.

After rigorous comparison of data produced by the new mathematical model with observed phenomena, the two realized they'd found the solution, a solution described by one scientist reviewing the paper in Physical Review Letters as "simple and elegant" and a "major breakthrough" in the field.

The Cueto-Felgueroso and Juanes solution also describes one aspect of the water-flowing-down-a-windowpane phenomenon that previously was not understood by scientists, who actually refer to this as "the flow of thin films": why water builds up at the tips of the fingers. Again, the answer has to with the surface tension. Before the water can flow down the film, it must build up enough energy to overcome the tension holding it in place.

So what was missing from earlier models of water moving downward through soil that made it appear to move as a steady, horizontal front, rather than in finger-like paths—even when the soil was homogenous in particle size and shape?

The missing mathematical phrase describes the surface tension of the entire finger of water, which may be several centimeters in width, as opposed to the tension existing at the micron-scale of pores between soil particles.

And that phrase will sound like music to the ears of physicists and engineers.

Renewable energy source

Renewable energy source inspired by fish

Edwin Cartlidge

November 28, 2008

An engineer in the US has built a machine that can harness energy from the slow-moving currents found in oceans and rivers around the world. By exploiting the vortices that fish use to propel themselves forward, the device could, he says, provide a new kind of reliable, affordable and environmentally-friendly energy source.

Turbines and water mills can generate electricity from flowing water, but can only do so in currents with speeds of around 8–10 km/h if they are to operate efficiently. Unfortunately, most of the currents found in nature move at less than 3 km/h. The new device is called VIVACE, which stands for vortex induced vibrations for aquatic clean energy, and its inventor claims it can operate in such slow-moving flows.

VIVACE has been developed by University of Michigan engineer Michael Bernitsas, and in its prototype form exists as an aluminium cylinder ( 91 cm long with a diameter of 12.5 cm) suspended by a pair of springs inside a tank. The tank, located in the university’s marine renewable energy laboratory, contains water that flows across the cylinder at around 2 km/h. The device does not convert the energy of the flow directly into electricity but instead exploits the vortices that form on opposite sides of any rounded object placed in a flow (J. Offshore Mech. Arct. Eng. 130 041101).

Vortex-driven fish
As such, it works like a moving fish. Fish cannot propel themselves forward using muscle power alone; instead they curve their bodies so that they form a vortex on one side of their body, straighten out, and then curve the other way to form a vortex on their other side, in order to glide between vortices. VIVACE remains in a fixed position in the water but is pushed and pulled by the vortices on either side, and these vibrations are then converted into electrical energy (the current cylinder is smooth, but future versions will have scale-like structures on the surface to enhance vortices). It dawned on me four years ago that I can enhance these vibrations to harness energy Michael Bernitsas, University of Michigan

Bernitsas explains that engineers usually do all they can to suppress such vibrations, which can occur in either water or air, as they can cause enormous damage. They were, for example, responsible for destroying the Tacoma Narrows bridge in the US in 1940. “But,” he says, “it dawned on me four years ago that I can enhance these vibrations to harness energy. My colleagues and I searched the scientific literature and patents and found out to our surprise that no one had done this before.”

The total amount of energy generated by the Earth’s slow-moving currents is vast, but the density of this energy is low. This means that the VIVACE technology, like any other ocean-based device, will only ever be part of the solution to the world’s energy needs. However, Bernitsas believes it has a number of advantages over alternative ocean-based sources, pointing out that, unlike wave devices, for example, it is unobtrusive, and should also pose no harm to marine life.

Tests in the Detroit River
The group is currently installing a 3 kW device in the Detroit River to provide energy that will light a new pier being built there. Bernitsas says that the technology could then be scaled up by constructing arrays of cylinders, either suspended from ladders or built upwards from the river or sea floor, in order to build power stations large enough to power tens of thousands of houses. The electricity from such a plant would be cheaper than many alternative renewable sources, he adds — some 5.5. cents per kilowatt hour, compared with 7 for wind and at least 16 for solar.

"The device is highly scalable", said Bernitsas. "It could be used to build small devices of 5 kW, medium of 50 kW, larger of 500 kW and put them together to build large stations of 10 MW", he said. "The next step up is 100 MW and finally huge offshore underwater stations of the size of 1 GW, the size of a nuclear power plant".

Stephen Salter of Edinburgh University, who has carried out research on tidal and wave energy, believes that low-velocity flows are an important potential source of renewable energy. He points out that there are several kinds of structure that could be used to harness this energy, including, for example, hydrofoils. But he believes that cylinders could turn out to be cheaper and more efficient than the alternatives, if they can be made to move with sufficiently high velocities.

Bernitsas has founded a company called Vortex Hydro Energy to commercialize the technology.

Space experts offer anti-asteroid plan

Space experts offer anti-asteroid plan

By DANICA KIRKA , Associated Press Writer

(AP) -- It is disaster planning on a galactic scale: Space experts want to come up with a contingency plan on what to do in case a killer asteroid collides with Earth.

The experts, including former American astronaut Rusty Schweickart, told U.N. officials Tuesday that the international community needs a plan to counter so-called Near Earth Objects in advance of the potential catastrophe. Deflecting asteroids - or at least evacuating people in areas where they might strike - could save millions of lives.

"This is a natural disaster, which is larger, potentially, than any other natural disaster we know of," Schweickart said. "However, it is preventable ... that's a very important thing to keep in mind. But it is our responsibility to take action to do that."

Asteroids are small planetary bodies that revolve around the sun, according to the NASA Web site, which states that many scientists believe an asteroid collided with Earth about 65 million years ago, helping cause environmental changes that led to the extinction of the dinosaurs.

Schweickart, a former Apollo 9 crew member, spoke at a news conference after briefing U.N. officials on a recent report called "Asteroid Threats: A Call for Global Response." The report was compiled by the International Panel on Asteroid Threat Mitigation that is made up of members of the Association of Space Explorers, among others.

The report, among other things, calls for an international decision-making program within the framework of the United Nations to decide on actions to counter asteroids. It also urges the creation of an information, analysis and warning system that would operate telescopes worldwide to detect and track possibly harmful objects.

Schweickart acknowledged that devastating collisions happen "very infrequently" but warned the risk could not be ignored. Next year alone, six asteroids have a "very small" probability of hitting the Earth, he said.

He added that over the coming years, researchers will increasingly be able to predict possible collisions, enabling early warnings and deflection operations.

While rare, Near Earth Objects have caused considerable damage in the not-too-distant past. One known as the Tunguska object slammed into remote central Siberia in 1908, unleashing energy equivalent to a nuclear bomb explosion. It wiped out 60 million trees over a 2,150-square-kilometer (830-square-mile) area. Had it hit a populated area, the loss of life would have been staggering.

For Walther Lichem, an Austrian member of the panel who was also at the news conference, investing in preventive measures is key to making sure such incidents don't happen again with more devastating effects.

"The damage potential is so incredible that we have to take the responsibility," he said.

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On the Net:

• Asteroid Threats: A Call for Global Response
• NASA on asteroids

Scientists Engineer Superconducting Thin Films

Scientists Engineer Superconducting Thin Films

One step closer to fabrication of useful devices such as superconductive transistors

October 8, 2008

UPTON, NY - One major goal on the path toward making useful superconducting devices has been engineering materials that act as superconductors at the nanoscale — the realm of billionths of a meter. Such nanoscale superconductors would be useful in devices such as superconductive transistors and eventually in ultrafast, power-saving electronics.

In the October 9, 2008, issue of Nature, scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory report that they have successfully produced two-layer thin films where neither layer is superconducting on its own, but which exhibit a nanometer-thick region of superconductivity at their interface. Furthermore, they demonstrate the ability to elevate the temperature of superconductivity at this interface to temperatures exceeding 50 kelvin (-370°F), a relatively high temperature deemed more practical for real-world devices. 

“This work provides definitive proof of our ability to produce robust superconductivity at the interface of two layers confined within an extremely thin, 1-2-nanometer-thick layer near the physical boundary between the two materials,” said physicist Ivan Bozovic, who leads the Brookhaven thin film research team. “It opens vistas for further progress, including using these techniques to significantly enhance superconducting properties in other known or new superconductors.”

Bozovic foresees future research investigating different combinations of non-superconducting materials. “Further study of the temperature-enhancement mechanism might even tell us something about the big puzzle — the mechanism underlying high-temperature superconductivity, which remains one of the most important open problems in condensed matter physics,” he said.

Bozovic’s team had reported in 2002 the bizarre observation that the critical temperature — the temperature below which the sample superconducts — could be enhanced by as much as 25 percent in bilayers of two dissimilar copper-based materials. However, at that time, the scientists had no understanding of what caused this enhancement and in which part of the sample the superconductivity was located.

To investigate this further, they synthesized more than 200 single-phase, bilayer and trilayer films with insulating, metallic, and superconducting blocks in all possible combinations and of varying layer thickness. The films were grown in a unique atomic-layer-by-layer molecular beam epitaxy system designed and built by Bozovic and coworkers to enable the synthesis of atomically smooth films as well as multilayers with perfect interfaces. “The greatest technical challenge was to prove convincingly that the superconducting effect does not come from simple mixing of the two materials and formation of a third, chemically and physically distinct layer between the two constituent layers,” Bozovic said. Collaborators at Cornell University ruled out this possibility using atomic-resolution transmission electron microscopy to identify the samples’ constituent chemical elements, proving that the layers indeed remained distinct.

“It is too early to tell what applications this research might yield,” Bozovic said, “but already at this stage we can speculate that this brings us one big step closer to fabrication of useful three-terminal superconducting devices, such as a superconductive field-effect transistor.” In such a device, one would be able to switch the transistor from the superconducting to the resistive state by means of an external electric field, controlled by applying a voltage and using the third (gate) electrode. Circuits built from such devices would be much faster and use less power than the current ones based on semiconductors.

“No matter what the applications, this work is a nice demonstration of our ability to engineer and control materials at sub-nanometer scale, with designed and enhanced functionality,” Bozovic said.

The Brookhaven scientists have filed a U.S. provisional patent application for this work. For information about licensing, please contact Kimberley Elcess, 631-344-4151, elcess@bnl.gov.

In addition to Bozovic, the research team includes Adrian Gozar, Gennady Logvenov, and Anthony Bollinger of Brookhaven Lab, Lenna Fitting Kourkoutis and David A. Muller of Cornell University, and Lucille A. Giannuzzi of the FEI Company, Hillsboro, Oregon. The research at Brookhaven Lab was funded by the Office of Basic Energy Sciences within the DOE’s Office of Science; the Cornell work was funded by the Office of Naval Research.

New 'nano-positioners' may have atomic-scale precision

August 20, 2008 
New 'nano-positioners' may have atomic-scale precision

WEST LAFAYETTE, Ind. -  Engineers have created a tiny motorized positioning device that has twice the dexterity of similar devices being developed for applications that include biological sensors and more compact, powerful computer hard drives.

The device, called a monolithic comb drive, might be used as a "nanoscale manipulator" that precisely moves or senses movement and forces. The devices also can be used in watery environments for probing biological molecules, said Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering, who created the design.

The monolithic comb drives could make it possible to improve a class of probe-based sensors that detect viruses and biological molecules. The sensors detect objects using two different components: A probe is moved while at the same time the platform holding the specimen is positioned. The new technology would replace both components with a single one - the monolithic comb drive.

The innovation could allow sensors to work faster and at higher resolution and would be small enough to fit on a microchip. The higher resolution might be used to design future computer hard drives capable of high-density data storage and retrieval. Another possible use might be to fabricate or assemble miniature micro and nanoscale machines.

Research findings were detailed in a technical paper presented in July during the University Government Industry Micro/Nano Symposium in Louisville. The work is based at the Birck Nanotechnology Center at Purdue's Discovery Park.

Conventional comb drives have a pair of comblike sections with "interdigitated fingers," meaning they mesh together. These meshing fingers are drawn toward each other when a voltage is applied. The applied voltage causes the fingers on one comb to become positively charged and the fingers on the other comb to become negatively charged, inducing an attraction between the oppositely charged fingers. If the voltage is removed, the spring-loaded comb sections return to their original position. 

By comparison, the new monolithic device has a single structure with two perpendicular comb drives. 

Clark calls the device monolithic because it contains comb drive components that are not mechanically and electrically separate. Conventional comb drives are structurally "decoupled" to keep opposite charges separated. 

"Comb drives represent an advantage over other technologies," Clark said. "In contrast to piezoelectric actuators that typically deflect, or move, a fraction of a micrometer, comb drives can deflect tens to hundreds of micrometers. And unlike conventional comb drives, which only move in one direction, our new device can move in two directions - left to right, forward and backward - an advance that could really open up the door for many applications."

Clark also has invented a way to determine the precise deflection and force of such microdevices while reducing heat-induced vibrations that could interfere with measurements.

Current probe-based biological sensors have a resolution of about 20 nanometers. 

"Twenty nanometers is about the size of 200 atoms, so if you are scanning for a particular molecule, it may be hard to find," Clark said. "With our design, the higher atomic-scale resolution should make it easier to find."

Properly using such devices requires engineers to know precisely how much force is being applied to comb drive sensors and how far they are moving. The new design is based on a technology created by Clark called electro micro metrology, which enables engineers to determine the precise displacement and force that's being applied to, or by, a comb drive. The Purdue researcher is able to measure this force by comparing changes in electrical properties such as capacitance or voltage.

Clark used computational methods called nodal analysis and finite element analysis to design, model and simulate the monolithic comb drives. 

The research paper describes how the monolithic comb drive works when voltage is applied. The results show independent left-right and forward-backward movement as functions of applied voltage in color-coded graphics. 

The findings are an extension of research to create an ultra-precise measuring system for devices having features on the size scale of nanometers, or billionths of a meter. Clark has led research to create devices that "self-calibrate," meaning they are able to precisely measure themselves. Such measuring methods and standards are needed to better understand and exploit nanometer-scale devices. 

The size of the entire device is less than one millimeter, or a thousandth of a meter. The smallest feature size is about three micrometers, roughly one-thirtieth as wide as a human hair. 

"You can make them smaller, though," Clark said. "This is a proof of concept. The technology I'm developing should allow researchers to practically and efficiently extract dozens of geometric and material properties of their microdevices just by electronically probing changes in capacitance or voltage."

In addition to finite element analysis, Clark used a simulation tool that he developed called Sugar.

"Sugar is fast and allows me to easily try out many design ideas," he said. "After I narrow down to a particular design, I then use finite element analysis for fine-tuning. Finite element analysis is slow, but it is able to model subtle physical phenomena that Sugar doesn't do as well."

Clark's research team is installing Sugar on the nanoHub this summer, making the tool available to other researchers. The nanoHub is operated by the Network for Computational Nanotechnology, funded by the National Science Foundation and housed at Purdue's Birck Nanotechnology Center.  

The researchers also are in the process of fabricating the devices at the Birck Nanotechnology Center.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu 
Sources: Jason Vaughn Clark, (765) 494-3437, jvclark@purdue.edu 
Purdue News Service: (765) 494-2096; purduenews@purdue.edu 

PHOTO CAPTION:

This illustration depicts a tiny device called a monolithic comb drive, which might be used as a high-precision "nanopositioner" for such uses as biological sensors, computer hard drives and other possible applications. The device was created by Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering at Purdue University. (Birck Nanotechnology Center, Purdue University)

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ABSTRACT 

Modeling a Monolithic Comb Drive for Large-Deflection Multi-DOF Microtransduction

J. V. Clark School of Electrical and Computer Engineering School of Mechanical Engineering Purdue University 

To help extend the investigation and exploitation of nanoscale phenomena, there is a need for high precision, large deflection microtransducers with multiple degrees of freedom (DOF). In this paper, we investigate the predicted performance of such a large deflection microtransducer using finite element analysis. To sense and actuate in three dimensions, we use three types of comb drives: a vertical comb drive, a planar comb drive, and a novel planar monolithic comb drive, which operates as an in-situ RC circuit. The two planar comb drives are used to translate a proof mass with independent in-plane x- and y-directions, and the vertical comb drive translates the proof mass in the out-of-plane z-direction. The device resists rotation about the z axis. We address precise sensing and actuation by using high-precision capacitance and voltage to detect position and to apply force, respectively. We explore design issues such as geometry and material properties, and we characterize the monolithic comb drive. We limit the geometry of the transducer to one structural layer, which is amenable to a simple one-mask fabrication process such as silicon-on-insulator (SOI).