NASA Satellite Tracks Severity of African Drought

Surface relative humidity anomalies in percent, during July 2011 compared to the average surface relative humidity over the previous eight years, as measured by the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua spacecraft. The driest areas are shown in oranges and reds. 

Image credit: NASA/JPL-Caltech 

Northeast Africa continues to reel from the effects of the worst drought to strike the region in decades. The arid conditions are contributing to famines that the U.S. Department of State says are affecting more than 11.5 million people, particularly in Somalia, Ethiopia, Kenya and Djibouti. 

The drought is tied to strong La Nina conditions that prevailed in late 2010 and early 2011. La Nina shifts ocean temperatures and air pressure over the Pacific Ocean, causing effects that ripple through weather patterns around the world. In East Africa, La Nina typically brings drought.

The current dry conditions are illustrated in this new map, created using nine years of data on surface relative humidity from the Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua spacecraft. Surface relative humidity measures the percent of water vapor in the air nearest to Earth's surface, where people, animals and plants live.

Scientists at NASA's Jet Propulsion Laboratory, Pasadena, Calif., created a climatology for the region by averaging eight years of July AIRS surface relative humidity data from 2003 through 2010, and then subtracting the result from the AIRS relative humidity data for July 1-18, 2011. Areas shown in greens, yellows, oranges and reds represent regions that are drier in July 2011 than the average of all the previous Julys dating back to 2003. The driest conditions, shown in red, are found in northeast Africa, while large regions throughout the Middle East are moderately dry. Areas in blue were moister in 2011 than in the previously studied years. White areas represent data voids caused primarily by the effects of mountain and highland topography.

In regions that are traditionally dry, the additional drying of more than 15 percent relative humidity is very stressful to crops, causing them to dry out and die.

AIRS is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., under contract to NASA. JPL is a division of the California Institute of Technology in Pasadena.

More information about AIRS can be found at http://airs.jpl.nasa.gov.

Contacts and sources:
Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.

Sun-Free Photovoltaics: Materials Engineered To Give Off Precisely Tuned Wavelengths Of Light When Heated Are Key To New High-Efficiency Generating System.

A new photovoltaic energy-conversion system developed at MIT can be powered solely by heat, generating electricity with no sunlight at all. While the principle involved is not new, a novel way of engineering the surface of a material to convert heat into precisely tuned wavelengths of light — selected to match the wavelengths that photovoltaic cells can best convert to electricity — makes the new system much more efficient than previous versions. 

A variety of silicon chip micro-reactors developed by the MIT team. Each of these contains photonic crystals on both flat faces, with external tubes for injecting fuel and air and ejecting waste products. Inside the chip, the fuel and air react to heat up the photonic crystals. In use, these reactors would have a photovoltaic cell mounted against each face, with a tiny gap between, to convert the emitted wavelengths of light to electricity. 

Photo: Justin Knight

The key to this fine-tuned light emission, described in the journal Physical Review A, lies in a material with billions of nanoscale pits etched on its surface. When the material absorbs heat — whether from the sun, a hydrocarbon fuel, a decaying radioisotope or any other source — the pitted surface radiates energy primarily at these carefully chosen wavelengths.

Based on that technology, MIT researchers have made a button-sized power generator fueled by butane that can run three times longer than a lithium-ion battery of the same weight; the device can then be recharged instantly, just by snapping in a tiny cartridge of fresh fuel. Another device, powered by a radioisotope that steadily produces heat from radioactive decay, could generate electricity for 30 years without refueling or servicing — an ideal source of electricity for spacecraft headed on long missions away from the sun.

According to the U.S. Energy Information Administration, 92 percent of all the energy we use involves converting heat into mechanical energy, and then often into electricity — such as using fuel to boil water to turn a turbine, which is attached to a generator. But today's mechanical systems have relatively low efficiency, and can't be scaled down to the small sizes needed for devices such as sensors, smartphones or medical monitors.

"Being able to convert heat from various sources into electricity without moving parts would bring huge benefits," says Ivan Celanovic ScD '06, research engineer in MIT's Institute for Soldier Nanotechnologies (ISN), "especially if we could do it efficiently, relatively inexpensively and on a small scale."

It has long been known that photovoltaic (PV) cells needn't always run on sunlight. Half a century ago, researchers developed thermophotovoltaics (TPV), which couple a PV cell with any source of heat: A burning hydrocarbon, for example, heats up a material called the thermal emitter, which radiates heat and light onto the PV diode, generating electricity. The thermal emitter's radiation includes far more infrared wavelengths than occur in the solar spectrum, and "low band-gap" PV materials invented less than a decade ago can absorb more of that infrared radiation than standard silicon PVs can. But much of the heat is still wasted, so efficiencies remain relatively low.

An ideal match

The solution, Celanovic says, is to design a thermal emitter that radiates only the wavelengths that the PV diode can absorb and convert into electricity, while suppressing other wavelengths. "But how do we find a material that has this magical property of emitting only at the wavelengths that we want?" asks Marin Soljačić, professor of physics and ISN researcher. The answer: Make a photonic crystal by taking a sample of material and create some nanoscale features on its surface — say, a regularly repeating pattern of holes or ridges — so light propagates through the sample in a dramatically different way.

"By choosing how we design the nanostructure, we can create materials that have novel optical properties," Soljačić says. "This gives us the ability to control and manipulate the behavior of light."

The team — which also includes Peter Bermel, research scientist in the Research Laboratory for Electronics (RLE); Peter Fisher, professor of physics; and Michael Ghebrebrhan, a postdoc in RLE — used a slab of tungsten, engineering billions of tiny pits on its surface. When the slab heats up, it generates bright light with an altered emission spectrum because each pit acts as a resonator, capable of giving off radiation at only certain wavelengths.

This powerful approach — co-developed by John D. Joannopoulos, the Francis Wright Davis Professor of Physics and ISN director, and others — has been widely used to improve lasers, light-emitting diodes and even optical fibers. The MIT team, supported in part by a seed grant from the MIT Energy Initiative, is now working with collaborators at MIT and elsewhere to use it to create several novel electricity-generating devices.

Mike Waits, an electronics engineer at the Army Research Laboratory in Adelphi, Md., who was not involved in this work, says this approach to producing miniature power supplies could lead to lighter portable electronics, which is "critical for the soldier to lighten his load. It not only reduces his burden, but also reduces the logistics chain" to deliver those devices to the field. "There are a lot of lives at stake," he says, "so if you can make the power sources more efficient, it could be a great benefit."

The button-like device that uses hydrocarbon fuels such as butane or propane as its heat source — known as a micro-TPV power generator — has at its heart a "micro-reactor" designed by Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, and fabricated in the Microsystems Technology Laboratories. While the device achieves a fuel-to-electricity conversion efficiency three times greater than that of a lithium-ion battery of the same size and weight, Celanovic is confident that with further work his team can triple the current energy density. "At that point, our TPV generator could power your smartphone for a whole week without being recharged," he says.

Celanovic and Soljačić stress that building practical systems requires integrating many technologies and fields of expertise. "It's a really multidisciplinary effort," Celanovic says. "And it's a neat example of how fundamental research in materials can result in new performance that enables a whole spectrum of applications for efficient energy conversion."

Contacts and sources:

Nancy W. Stauffer, MITEI
MIT
David L. Chandler contributed to this story.

Real Star Trek Tricorder! Cell Phones Now A Global Health Tool, UCLA Bio-Photonic Lab-in-a-Phone

Holy tricorder! Batman.  UCLA researchers have transformed a cell phone into a bio-photonic laboratory able to perform on the spot analysis much like the fictional tricorder of Star Trek fame.

Flow cytometry, a technique for counting and examining cells, bacteria and other microscopic particles, is used routinely in diagnosing disorders, infections and cancers and evaluating the progression of HIV and AIDS. But flow cytometers are big, bulky contraptions that cost tens of thousands of dollars, making them less than ideal for health care in the field or other settings where resources are limited.

OzcanCellCytometer

Credit: UCLA

Now imagine you could achieve the same results using a device that weighs about half an ounce and costs less than five dollars.

Credit: UCLA

Researchers at the BioPhotonics Laboratory at the UCLA Henry Samueli School of Engineering and Applied Science have developed a compact, lightweight and cost-effective optofluidic platform that integrates imaging cytometry and florescent microscopy and can be attached to a cell phone. The resulting device can be used to rapidly image bodily fluids for cell counts or cell analysis.

The research, which was led by Aydogan Ozcan, a professor of electrical engineering and bioengineering and a member of the California NanoSystems Institute at UCLA, is currently available online in the journal Analytical Chemistry.

"In this work, we developed a cell phone–based imaging cytometry device with a very simple optical design, which is very cost-effective and easy to operate," said Hongying Zhu, a UCLA Engineering postdoctoral scholar at the BioPhotonics Lab and co-author of the research. "It has great potential to be used in resource-limited regions to help people there improve the quality of their health care."

The device is the latest advance by Ozcan's research team, which has developed a number of innovative, scaled-down, cell phone–based technologies that have the potential to transform global health care.

"We have more than 5 billion cell phone subscribers around the world today, and because of this, cell phones can now play a central role in telemedicine applications," Ozcan said. "Our research group has already created a very nice set of tools, including cell phone microscopes, that can potentially replace most of the advanced instruments used currently in laboratories."

How it works

Ozcan's group integrated compact optical attachments to create the optofluidic fluorescent cytometry platform. The platform, which weighs only 18 grams, includes:

• 1 simple lens (less than $3)

• 1 plastic color filter (less than $1)

• 2 LEDs (less than 30 cents each)

• Simple batteries

The microfluidic assembly is placed just above a separate, inexpensive lens that is put in contact with the cell phone's existing camera unit. This way, the entire cross-section of the microfluidic device can be mapped onto the phone's CMOS sensor-chip. The sample fluid is delivered continuously through a disposable microfluidic channel via a syringe pump.

The device is illuminated from the side by the LEDs using a simple butt-coupling technique. The excitation light is then guided within the cross-section of the device, uniformly exciting the specimens in the imaging fluid. The optofluidic pumping scheme also allows for the use of an inexpensive plastic absorption filter to create the dark-field background needed for fluorescent imaging.

In addition, video post-processing and contour-detection and tracking algorithms are used to count and label the cells or particles passing through the microfluidic chip.

In order to demonstrate proof-of-concept for the new platform, the team used the device to measure the density of white blood cells in human whole-blood samples, as white blood cell density is routinely tested to diagnosis various diseases and infections, including leukemia, HIV and bone marrow deficiencies.

"For the next step, we'd like to explore other potential applications of this device," Zhu said. "For example, we also want to utilize this device to count potential waterborne parasites for water-quality monitoring."

"We'd like to translate our devices for testing in the field and start using them in places they're supposed to be used," Ozcan said. "So I think the next stage for several of our technologies, including this one, is to deploy and test them in extremely poor-resource countries."

Contacts and sources: 

Story by Wileen Wong Kromhout

UCLA

This study was funded by the National Institutes of Health, the National Science Foundation, the Office of Naval Research, the Gates Foundation and the Vodafone Americas Foundation.

The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional degree programs and has an enrollment of almost 5,000 students. The school's distinguished faculty are leading research to address many of the critical challenges of the 21st century, including renewable energy, clean water, health care, wireless sensing and networking, and cybersecurity. Ranked among the top 10 engineering schools at public universities nationwide, the school is home to seven multimillion-dollar interdisciplinary research centers in wireless sensor systems, nanoelectronics, nanomedicine, renewable energy, customized computing, and the smart grid, all funded by federal and private agencies. (www.engineer.ucla.edu | www.twitter.com/uclaengineering)