Sun-powered desalination for villages in India

Around the world, there is more salty groundwater than fresh, drinkable groundwater. For example, 60 percent of India is underlain by salty water -- and much of that area is not served by an electric grid that could run conventional reverse-osmosis desalination plants.

Now an analysis by MIT researchers shows that a different desalination technology called electrodialysis, powered by solar panels, could provide enough clean, palatable drinking water to supply the needs of a typical village. The study, by MIT graduate student Natasha Wright and Amos Winter, the Robert N. Noyce Career Development Assistant Professor of Mechanical Engineering, appears in the journal Desalination.

Winter explains that finding optimal solutions to problems such as saline groundwater involves "detective work to understand the full set of constraints imposed by the market." After weeks of field research in India, and reviews of various established technologies, he says, "when we put all these pieces of the puzzle together, it pointed very strongly to electrodialysis" -- which is not what is commonly used in developing nations.

The factors that point to the choice of electrodialysis in India include both relatively low levels of salinity -- ranging from 500 to 3,000 milligrams per liter, compared with seawater at about 35,000 mg/L -- as well as the region's lack of electrical power. (For on-grid locations, the team found, reverse-osmosis plants can be economically viable.)

Such moderately salty water is not directly toxic, but it can have long-term effects on health, and its unpleasant taste can cause people to turn to other, dirtier water sources. "It's a big issue in the water-supply community," Winter says.

Expanding access to safe water

By pairing village-scale electrodialysis systems -- a bit smaller than the industrial-scale units typically produced today -- with a simple set of solar panels and a battery system to store the produced energy, Wright and Winter concluded, an economically viable and culturally acceptable system could supply enough water to meet the needs of a village of 2,000 to 5,000 people. They estimate that deployment of such systems would double the area of India in which groundwater -- which is inherently safer, in terms of pathogen loads, than surface water -- could provide acceptable drinking water.

While many homes in India currently use individual, home-based filtration systems to treat their water, Wright says after consulting with nongovernmental organizations that work in the area, she and Winter concluded that village-scale systems would be more effective -- both because fewer people would be left out of access to clean water, and because home-based systems are much harder to monitor to ensure effective water treatment.

Most organizations working to improve clean-water access focus their attention on controlling known pathogens and toxins such as arsenic, Wright says. But her analysis showed the importance of "what the water tastes like, smells like, and looks like." Even if the water is technically safe to drink, that doesn't solve the problem if people refuse to drink it because of the unpleasant salty taste, she says.

At the salinity levels seen in India's groundwater, the researchers found, an electrodialysis system can provide fresh water for about half the energy required by a reverse-osmosis system. That means the solar panels and battery storage system can be half as big, more than offsetting the higher initial cost of the electrodialysis system itself.

How it works

Electrodialysis works by passing a stream of water between two electrodes with opposite charges. Because the salt dissolved in water consists of positive and negative ions, the electrodes pull the ions out of the water, Winter says, leaving fresher water at the center of the flow. A series of membranes separate the freshwater stream from increasingly salty ones.

Both electrodialysis and reverse osmosis require the use of membranes, but those in an electrodialysis system are exposed to lower pressures and can be cleared of salt buildup simply by reversing the electrical polarity. That means the expensive membranes should last much longer and require less maintenance, Winter says. In addition, electrodialysis systems recover a much higher percentage of the water -- more than 90 percent, compared with about 40 to 60 percent from reverse-osmosis systems, a big advantage in areas where water is scarce.

Having carried out this analysis, Wright and Winter plan to put together a working prototype for field evaluations in India in January. While this approach was initially conceived for village-scale, self-contained systems, Winter says the same technology could also be useful for applications such as disaster relief, and for military use in remote locations.

Susan Amrose, a lecturer in civil and environmental engineering at the University of California at Berkeley who was not involved in this work, says, "This paper raises the bar for the level and type of scientific rigor applied to the complex, nuanced, and extremely important problems of development engineering. … Solar-ED isn't a new technology, but it is novel to suggest developing it for systems in rural India, and even more novel to provide this level of detailed engineering and economic analysis to back up the suggestion."

Amrose adds, "The water scarcity challenges facing India in the near future cannot be overstated. India has a huge population living on top of brackish water sources in regions that are water-scarce or about to become water-scarce. A solution with the potential to double recoverable water in an environment where water is becoming more precious by the day could have a huge impact."

The research was funded by Jain Irrigation Systems, an Indian company that builds and installs solar-power systems, and sponsored by the Tata Center for Technology and Design at MIT.

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Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by David L. Chandler. Note: Materials may be edited for content and length.

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Journal Reference:

1.     Natasha C. Wright, Amos G. Winter. Justification for community-scale photovoltaic-powered electrodialysis desalination systems for inland rural villages in India. Desalination, 2014; 352: 82 DOI: 10.1016/j.desal.2014.07.035

Geomagnetic storm mystery solved: How magnetic energy turns into particle energy

             Date:  September 10, 2014

    Source:  DOE/Princeton Plasma Physics Laboratory

Summary:  Magnetic reconnection can trigger geomagnetic storms that disrupt cell phone service, damage satellites and black out power grids. But how reconnection, in which the magnetic field lines in plasma snap apart and violently reconnect, transforms magnetic energy into explosive particle energy remains a major unsolved problem in plasma astrophysics.

Magnetic reconnection can trigger geomagnetic storms that disrupt cell phone service, damage satellites and black out power grids. But how reconnection, in which the magnetic field lines in plasma snap apart and violently reconnect, transforms magnetic energy into explosive particle energy remains a major unsolved problem in plasma astrophysics. Magnetic field lines represent the direction, and indicate the shape, of magnetic fields.

Now scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) have taken a key step toward a solution, as described in a paper published this week in the journal Nature Communications. In research conducted on the Magnetic Reconnection Experiment (MRX) at PPPL, the scientists not only identified how the mysterious transformation takes place, but measured experimentally the amount of magnetic energy that turns into particle energy.

The investigation showed that reconnection converts about 50 percent of the magnetic energy, with one-third of the conversion heating the electrons and two-thirds accelerating the ions -- or atomic nuclei -- in the plasma. In large bodies like the sun, such converted energy can equal the power of millions of tons of TNT.

"This is a major milestone for our research," said Masaaki Yamada, the principal investigator for the MRX and first author of the Nature Communications paper. "We can now see the entire picture of how much of the energy goes to the electrons and how much to the ions in a prototypical reconnection layer."

The findings also suggested the process by which the energy conversion occurs. Reconnection first propels and energizes the electrons, according to the researchers, and this creates an electrically charged field that "becomes the primary energy source for the ions," said Jongsoo Yoo, a postdoctoral fellow at PPPL and coauthor of the paper. Also contributing to the paper were physicists Hantao Ji and Russell Kulsrud, and doctoral candidates Jonathan Jara-Almonte and Clayton Myers.

If confirmed by data from space explorations, the PPPL results could help resolve decades-long questions and create practical benefits. These could include a better understanding of geomagnetic storms that could lead to advanced warning of the disturbances and an improved ability to cope with them. Researchers could shut down sensitive instruments on communications satellites, for example, to protect the instruments from harm.

The PPPL team will eagerly watch a four-satellite mission that NASA plans to launch next year to study reconnection in the magnetosphere -- the magnetic field that surrounds Earth. The team plans to collaborate with the venture, called the Magnetospheric Multiscale (MMS) Mission, by providing MRX data to it. The MMS probes could help to confirm the Laboratory's findings.

This work was supported by the DOE Office of Science.

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Story Source:

The above story is based on materials provided by DOE/Princeton Plasma Physics Laboratory. Note: Materials may be edited for content and length.

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Journal Reference:

1.     Masaaki Yamada, Jongsoo Yoo, Jonathan Jara-Almonte, Hantao Ji, Russell M. Kulsrud, Clayton E. Myers. Conversion of magnetic energy in the magnetic reconnection layer of a laboratory plasma. Nature Communications, 2014; 5: 4774 DOI: 10.1038/ncomms5774

Nerve impulses can collide, continue unaffected

               Date:  September 10, 2014

        Source:  University of Copenhagen - Niels Bohr Institute

  Summary: According to the traditional theory of nerves, two nerve impulses sent from opposite ends of a nerve annihilate when they collide. New research now shows that two colliding nerve impulses simply pass through each other and continue unaffected. This supports the theory that nerves function as sound pulses.

According to the traditional theory of nerves, two nerve impulses sent from opposite ends of a nerve annihilate when they collide. New research from the Niels Bohr Institute now shows that two colliding nerve impulses simply pass through each other and continue unaffected. This supports the theory that nerves function as sound pulses.

The results are published in the scientific journal Physical Review X.

Nerve signals control the communication between the billions of cells in an organism and enable them to work together in neural networks. But how do nerve signals work?

Old model

In 1952, Hodgkin and Huxley introduced a model in which nerve signals were described as an electric current along the nerve produced by the flow of ions. The mechanism is produced by layers of electrically charged particles (ions of sodium and potassium) on either side of the nerve membrane that change places when stimulated. This change in charge creates an electric current.

This model has enjoyed general acceptance. For more than 60 years, all medical and biology textbooks have said that nerves function is due to an electric current along the nerve pathway. However, this model cannot explain a number of phenomena that are known about nerve function.

New model

Researchers at the Niels Bohr Institute at the University of Copenhagen have now conducted experiments that raise doubts about this well-established model of electrical impulses along the nerve pathway.

"According to the theory of this ion mechanism, the electrical signal leaves an inactive region in its wake, and the nerve can only support new signals after a short recovery period of inactivity. Therefore, two electrical impulses sent from opposite ends of the nerve should be stopped after colliding and running into these inactive regions," explains Thomas Heimburg, Professor and head of the Membrane Biophysics Group at the Niels Bohr Institute at the University of Copenhagen.

Thomas Heimburg and his research group conducted experiment in the laboratory using nerves from earthworms and lobsters. The nerves were removed and used in an experiment in which allowed the researchers to stimulate the nerve fibres with electrodes on both ends. Then they measured the signals en route.

"Our study showed that the signals passed through each other completely unhindered and unaltered. That's how sound waves work. A sound wave doesn't stop when it meets another sound wave. Both waves continue on unimpeded. The nerve impulse can therefore be explained by the fact that the pulse is a mechanical wave in the form of a sound pulse, a soliton, that moves along the nerve membrane," explains Thomas Heimburg.

The theory is confirmed

When the sound pulse moves through the nerve pathway, the membrane changes locally from a liquid to a more solid form. The membrane is compressed slightly, and this change leads to an electrical pulse as a consequence of the piezoelectric effect. "The electrical signal is thus not based on an electric current but is caused by a mechanical force," points out Thomas Heimburg.

Thomas Heimburg, along with Professor Andrew Jackson, first proposed the theory that nerves function by sound pulses in 2005. Their research has since provided support for this theory, and the new experiments offer additional confirmation for the theory that nerve signals are sound pulses.

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Story Source:

The above story is based on materials provided by University of Copenhagen - Niels Bohr Institute. Note: Materials may be edited for content and length.

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Journal Reference:

1.     Alfredo Gonzalez-Perez, Rima Budvytyte, Lars D. Mosgaard, Søren Nissen, Thomas Heimburg. Penetration of Action Potentials During Collision in the Median and Lateral Giant Axons of Invertebrates. Physical Review X, 2014; 4 (3) DOI: 10.1103/PhysRevX.4.031047

Electronics that need very little energy? Nanotechnology used to help cool electrons with no external sources

     

               Date:  September 10, 2014

         Source:  University of Texas at Arlington

 Summary: A team of researchers has discovered a way to cool electrons to minus 228 degrees Celsius without external means and at room temperature, an advancement that could enable electronic devices to function with very little energy.

A team of researchers has discovered a way to cool electrons to -228 °C without external means and at room temperature, an advancement that could enable electronic devices to function with very little energy.

A chip, which contains nanoscale structures that enable electron cooling at room temperature, is pictured. The process involves passing electrons through a quantum well to cool them and keep them from heating. The team details its research in "Energy-filtered cold electron transport at room temperature," which is published in Nature Communications on Wednesday, Sept. 10.

"We are the first to effectively cool electrons at room temperature. Researchers have done electron cooling before, but only when the entire device is immersed into an extremely cold cooling bath," said Seong Jin Koh, an associate professor at UT Arlington in the Materials Science & Engineering Department, who has led the research. "Obtaining cold electrons at room temperature has enormous technical benefits. For example, the requirement of using liquid helium or liquid nitrogen for cooling electrons in various electron systems can be lifted."

Electrons are thermally excited even at room temperature, which is a natural phenomenon. If that electron excitation could be suppressed, then the temperature of those electrons could be effectively lowered without external cooling, Koh said. The team used a nanoscale structure -- which consists of a sequential array of a source electrode, a quantum well, a tunneling barrier, a quantum dot, another tunneling barrier, and a drain electrode -- to suppress electron excitation and to make electrons cold.

Cold electrons promise a new type of transistor that can operate at extremely low-energy consumption. "Implementing our findings to fabricating energy-efficient transistors is currently under way," Koh added.

Khosrow Behbehani, dean of the UT Arlington College of Engineering, said this research is representative of the University's role in fostering innovations that benefit the society, such as creating energy-efficient green technologies for current and future generations.

"Dr. Koh and his research team are developing real-world solutions to a critical global challenge of utilizing the energy efficiently and developing energy-efficient electronic technology that will benefit us all every day," Behbehani said. "We applaud Dr. Koh for the results of this research and look forward to future innovations he will lead." Usha Varshney, program director in the National Science Foundation's Directorate for Engineering, which funded the research, said the research findings could be vast. "When implemented in transistors, these research findings could potentially reduce energy consumption of electronic devices by more than 10 times compared to the present technology," Varshney said. "Personal electronic devices such as smart phones, iPads, etc., can last much longer before recharging."

In addition to potential commercial applications, there are many military uses for the technology. Batteries weigh a lot, and less power consumption means reducing the battery weight of electronic equipment that soldiers are carrying, which will enhance their combat capability. Other potential military applications include electronics for remote sensors, unmanned aerial vehicles and high-capacity computing in remote operations.

Future research could include identifying key elements that will allow electrons to be cooled even further. The most important challenge of this future research is to keep the electron from gaining energy as it travels across device components. This would require research into how energy-gaining pathways could be effectively blocked.

Co-authors of the paper are Pradeep Bhadrachalam, Ramkumar Subramanian, Vishva Ray and Liang-Chieh Ma from UT Arlington, and Weichao Wang, Prof. Jiyoung Kim and Prof. Kyeongjae Cho from UT Dallas who also were part of the research team.

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Story Source:

The above story is based on materials provided by University of Texas at Arlington. Note: Materials may be edited for content and length.

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Journal Reference:

1.     Pradeep Bhadrachalam, Ramkumar Subramanian, Vishva Ray, Liang-Chieh Ma, Weichao Wang, Jiyoung Kim, Kyeongjae Cho, Seong Jin Koh. Energy-filtered cold electron transport at room temperature. Nature Communications, 2014; 5: 4745 DOI: 10.1038/ncomms5745