Hensen's node in chicken embryos governs movement of neural cells, study shows

For us living creatures with backbones, existence begins as a single fertilized cell that then subdivides and grows into a fetus with many, many cells. But the details of how those cells end up as discrete organs instead of undifferentiated heaps of cells is only now being understood in microscopic detail.

Why, for example, should some of the cells migrate to the region that will become the brain, while others travel netherward to make a spinal cord? Although some details are known about which cells contribute to particular regions of the nervous system and which signals help to establish the organization of the brain, much less is known about factors that guide the development of the spinal cord.

In a new study, researchers from the California Institute of Technology have gained unprecedented information about the molecular signals and cell movements that coordinate to form the spinal cord. The study takes advantage of recently developed bioimaging and cell labeling techniques to follow individual cell movements in a developing chick embryo through a clear "window" cut into a fertilized egg. The results, reported in the June issue of the journal Nature Cell Biology, suggest that a proliferative stem zone at the tail end of the growing embryo contributes descendants to the growing neuraxis.

"The basic idea is that descendants of cells from Hensen's node, the structure that lays down the trunk, are sequentially distributed along the elongating spinal cord" says Luc Mathis, a former researcher in the lab of Caltech biology professor Scott Fraser, and lead author of the paper. "In the past, we did not have the ability to follow individual cells in living vertebrate embryos and could not determine how neural precursor cells could remain within Hensen's node, while some descendants leave it to form the spinal cord. "

In the paper, the researchers explain that neural precursor cells get displaced into the neural axis by the proliferation in Hensen's node. The researchers labeled cells near Hensen's node in 40-hour old chick embryos by using an external electric field to deliver an expression vector encoding green fluorescent protein (GFP) into cells, a process called electroporation. Using state-of-the-art imaging techniques developed by postdoctoral researcher Paul Kulesa, the group recorded the motion of fluorescent cells in ovo using a confocal microscope set up for time-lapse imaging and surrounded by a heated chamber to maintain embryo development.

"As the cells proliferate, some progenitors are displaced from the stem zone to become part of the neural plate and spinal cord," Mathis says. "Our analyses show that the Hensen's node produces daughter cells that are eventually displaced out of the node zone on the basis of their position in relation to other proliferating cells, and not on the basis of asymmetric cell divisions."

The paper also addresses the molecular signaling involved in the spreading of the cells. Previous work has shown that fibroblast growth factor (FGF) is somehow involved in formation of the posterior nervous system. To test the possibility that FGF could act by maintaining the stem zone of cell proliferation, the researchers disrupted FGF signaling within Hensen's node. Indeed, the result was a seriously shortened spinal cord and premature exit of cells from the node, indicating that FGF is required for the proliferation of neural precursor cells in the stem zone that generates the spinal cord.

A structure similar to Hensen's node—called simply a "node"—is found in mammals, and analogous zones are found in other vertebrates as well. The cell behavior and genetic control discovered in the chick might also be responsible for the development of the spinal cord in mammals, including humans.

"This new understanding of the formation of the spinal cord is the result of a fusion between hypotheses that arose during previous studies that I had conducted in France, the great embryological background and imaging facilities provided by Scott Fraser, and the original experimental systems of cell tracking developed by Paul Kulesa" concludes Mathis."

Scott Fraser is the Anna L Rosen Professor of Biology and the director of the Biological Imaging Center of Caltech's Beckman Institute. Luc Mathis is a former researcher at the Biological Imaging Center who is currently at the Pasteur Institute in Paris. Paul Kulesa is a senior research fellow supported by the computational molecular biology progam and associated with the Biological Imaging Center.

Contact: Robert Tindol (626) 395-3631

Writer: 
RT

Caltech Uses Fluorescent Protein to Visualize the Work of Living Neurons

Neuroscientists have long suspected that dendrites—the fine fibers that extend from neurons—can synthesize proteins. Now, using a molecule they constructed that "lights up" when synthesis occurs, a biologist and her colleagues from the California Institute of Technology have proven just that.

Erin M. Schuman, an associate professor of biology at Caltech and an assistant investigator with the Howard Hughes Medical Institute, along with colleagues Girish Aakalu, Bryan Smith, Nhien Nguyen, and Changan Jiang, published their findings last month in the journal Neuron. Proving that protein synthesis does indeed occur in intact dendrites suggests the dendrites may also have the capacity to adjust the strength of connections between neurons. That in turn implies they may influence vital neural activities such as learning and memory.

Schuman and colleagues constructed a so-called "reporter" molecule that, when introduced into neurons, emits a telltale glow if protein synthesis is occurring. "There was early evidence that protein-synthesis machinery was present in dendrites," says Schuman. "Those findings were intriguing because they implied that dendrites had the capacity to make their own proteins."

The idea that dendrites should be able to synthesize proteins made sense to Schuman and others because it was more economical and efficient. "It's like the difference between centralized and distributed freight shipping," she says. "With central shipping, you need a huge number of trucks that drive all over town, moving freight from a central factory. But with distributed shipping, you have multiple distribution centers that serve local populations, with far less transport involved."

Previous studies had indicated that, in test tubes, tiny fragments of dendrites still had the capacity to synthesize proteins. Schuman and her colleagues believed that visualizing local protein synthesis in living neurons would provide a more compelling picture than was currently available.

The scientists began their efforts to create a reporter molecule by flanking a gene for a green fluorescent protein with two segments of another gene for a particular enzyme. Doing this ensured that the researchers would target the messenger RNA (mRNA) for their reporter molecule to dendrites.

Next, in a series of experiments, the group inserted the reporter molecule into rat neurons in culture, and then triggered protein synthesis using a growth factor called BDNF. By imaging the neurons over time, the investigators showed that the green fluorescent protein was expressed in the dendrites following BDNF treatment—proof that protein synthesis was taking place. Going a step further, the researchers showed they could cause the fluorescence to disappear by treating the neurons with a drug that blocked protein synthesis.

Schuman and her colleagues also addressed whether proteins synthesized in the main cell body, called the soma, could have diffused to the dendrites, rather than the dendrites themselves performing the protein synthesis. The researchers proved the proteins weren't coming from the soma by simply snipping the dendrites from the neurons, while maintaining their connection to their synaptic partners. Sure enough, the isolated dendrites still exhibited protein synthesis.

Intriguingly, says Schuman, hot spots of protein synthesis were observed within the dendrites. By tracking the location of the fluorescent signal over time, the researchers could see that these hotspots waxed and waned consistently in the same place. "The main attraction of local protein synthesis is that it could endow synapses with the capacity to make synapse-specific changes, which is a key property of information-storing systems," says Schuman. "The observation of such hot spots suggests there are localized areas of protein synthesis near synapses that may provide new proteins to synapses nearby."

Schuman and her colleagues are now applying their reporter molecule system to more complex brain slices and whole mice. "In the whole animals, we're exploring the role of dendritic protein synthesis in information processing and animal learning and behavior," says Schuman.

Writer: 
MW
Writer: 

Brightest Quasars Inhabit Galaxies withStar-Forming Gas Clouds, Scientists Discover

A team of scientists at the California Institute of Technology and the State University of New York at Stony Brook has found strong evidence that high-luminosity quasar activity in galaxy nuclei is linked to the presence of abundant interstellar gas and high rates of star formation.

In a presentation at the summer meeting of the American Astronomical Society, Caltech astronomy professor Nick Scoville and his colleagues reported today that the most luminous nearby optical quasar galaxies have massive reservoirs of interstellar gas much like the so-called ultraluminous infrared galaxies (or ULIRGs). The quasar nucleus is powered by accretion on to a massive black hole with mass typically about 100 million times that of the sun while the infrared galaxies are powered by extremely rapid star formation. The ULIRG "starbursts" are believed to result from the high concentration of interstellar gas and dust in the galactic centers.

"Until now, it has been unclear how the starburst and quasar activities are related," Scoville says, "since many optically bright quasars show only low levels of infrared emission which is generally assumed to measure star formation activity.

"The discovery that quasars inhabit gas-rich galaxies goes a long way toward explaining a longstanding problem," Scoville says. "The number of quasars has been observed to increase very strongly from the present back to Redshift 2, at which time the number of quasars was at a maximum.

"The higher number of quasars seen when the universe was younger can now be explained, since a larger fraction of the galaxies at that time had abundant interstellar gas reservoirs. At later times, much of this gas has been used up in forming stars.

"In addition, the rate of merging galaxies was probably much higher, since the universe was smaller and galaxies were closer together."

The new study shows that even optically bright quasar-type galaxies (QSOs) have massive reservoirs of interstellar gas, even without strong infrared emission from the dust clouds associated with star formation activity. Thus, the fueling of the central black hole in the quasars is strongly associated with the presence of an abundant interstellar gas supply.

The Scoville team used the millimeter-wave radio telescope array at Caltech's Owens Valley Radio Observatory near Bishop, California, for an extremely sensitive search for the emission of carbon monoxide (CO) molecules in a complete sample of the 12 nearest and brightest optical quasars previously catalogued at the Palomar 200-inch telescope in the 1970s. In particular, the researchers avoided selecting samples with bright infrared emissions, since that would bias the sample toward those with abundant interstellar dust clouds.

In this optically selected sample, eight out of the 12 quasars exhibited detectable CO emission-implying masses of interstellar molecular clouds in the range of two to 10 billion solar masses. (For reference, the Milky Way galaxy contains approximately two billion solar masses of molecular clouds.) Such large gas masses are found only in gas-rich spiral or colliding galaxies. The present study clearly shows that most quasars are also in gas-rich spiral or interacting galaxies, not gas-poor elliptical galaxies as previously thought.

The new study supports the hypothesis that there exists an evolutionary link between the two most luminous classes of galaxies: merging ultraluminous IR galaxies and ultraviolet/optically bright QSOs. Both the ULIRGs and QSOs show evidence of a recent galactic collision.

The infrared luminous galaxies are most often powered by prodigious starbursts in their galactic centers, forming young stars at 100 to 1,000 times the current rate in the entire Milky Way. The quasars are powered by the accretion of matter into a massive black hole at their nuclei at a rate of one to 10 solar masses per year.

The detection of abundant interstellar gas in the optically selected QSOs suggests a link between these two very different forms of galactic nuclear activity. The same abundant interstellar gases needed to form stars at a high rate might also feed the central black holes.

In normal spiral galaxies like the Milky Way, most of the interstellar molecular gas is in the galactic disk at distances typically 20,000 light-years from the center-well out of reach of a central black hole.

However, during galactic collisions, the interstellar gas can sink and accumulate within the central few hundred light-years, and massive concentrations of interstellar gas and dust are, in fact, seen in the nuclear regions of the ULIRGs. Once in the nucleus, this interstellar matter can both fuel the starburst and feed the central black hole at prodigious rates.

The discovery of molecular gas in the optically selected QSOs that do not have strong infrared emissions suggests that the QSO host galaxies might be similar systems observed at a later time after the starburst activity has subsided, yet with the black hole still being fed by interstellar gas.

For the remaining four quasars where CO was not detected, improved future instrumentation may well yield detections of molecular gas, Scoville says. Even in the detected galaxies the CO emission was extraordinarily faint due to their great distances-typically over a billion light-years. The remaining four galaxies could well have molecular gas masses only a factor of two below those that were detected.

Future instrumentation such as the CARMA and ALMA millimeter arrays will have vastly greater sensitivity, permitting similar studies out to much greater distances.

Other members of the team are David Frayer and Eva Schinnerer, both research scientists at Caltech, Caltech graduate students Micol Christopher and Naveen Reddy and Aaron Evans at SUNY (Stony Brook).

###

Contact:Robert Tindol (626) 395-3631

Writer: 
RT

Biochemical "On/Off" Switch Discovered

PASADENA, Ca.— Proteins are the cell's arbiters. In a complex and still largely mysterious cascade of events, proteins tell a cell when to divide and grow—and when to die. To properly control cell behavior, proteins need to be turned on when they are needed, and turned off when they are not. Now a California Institute of Technology biologist and his colleagues have shed important new light on how this takes place in animals and plants.

In a paper published in the May 18 issue of the journal Science, biologist Raymond Deshaies and his graduate students show that an assemblage of proteins known as CSN may serve as a kind of biochemical on/off switch for other proteins.

In plants, research done in the laboratory of Deshaies's collaborator, Xing-Wang Deng of Yale University, has shown that CSN prevents photomorphogenesis (roughly, the growth of plants controlled by light) when light is absent. CSN is widely distributed in animals as well, but until now no one knew what any of its functions were. Now Deshaies's research shows that CSN may be linked to a recently discovered protein modification known as "neddylation," the physical attachment of a small protein, called NEDD8, to another protein. Neddylation is thought to alter the functioning of whatever protein NEDD8 attaches to. For example, when it attaches to the enzyme SCF (previously discovered by the Deshaies's team), SCF activity increases dramatically. Although the enzymes that attach NEDD8 to proteins like SCF were already known, the enzymes that remove it were not.

Deshaies's team discovered that CSN removes the NEDD8 that is attached to SCF. Based on this finding, they conclude that CSN controls the on-and-off switching of proteins. For example, when NEDD8 is not removed from its partners in plant cells, the plant doesn't respond normally to hormones that control its development.

Many different physiological roles have been proposed for CSN, including roles in the synthesis of new proteins, control of cell division, and control of inflammation. The Deshaies team's finding that CSN acts by removing NEDD8 from other proteins suggests that NEDD8, in turn, is likely to serve as a linchpin in these processes.

Deshaies and his laboratory colleagues are interested in the regulation of cell division, and in identifying the specific functions of various proteins within a cell that participate in this process. The proper regulation of cell division is critical for the normal development of organisms. In animals, aberrations in cell division can have profound consequences; unchecked cell division, for example, can lead to cancer.

Writer: 
MW
Exclude from News Hub: 
No

Environmental Study of Local Area Conducted by Caltech Team

PASADENA, Calif.— California Institute of Technology researchers have received a $100,000 grant from the Alice C. Tyler Perpetual Trust to study the human impact on land and water in the San Gabriel Valley and San Gabriel River watershed. Ecosystems bordering major metropolitan areas are subject to intense pressures from pollutants produced by transportation, industrial activities, power generation, and recreational activities. This project will measure and document these environmental changes in order to predict future impacts.

The research project, "Environmental Quality Near Large Urban Areas," is being coordinated by Janet Hering, associate professor of environmental engineering science at Caltech. Other members of the group include Michael Hoffmann, the James Irvine Professor of Environmental Science; James Randerson, assistant professor of global environmental science; and Paul Wennberg, professor of atmospheric chemistry and environmental engineering science.

The project will also teach Caltech undergraduate students fundamental concepts in environmental chemistry, providing them with practical training and field experience in the collection, measurement, and analysis of human-induced changes on air quality, plants, soil, and water. The training program will allow undergraduates to gain a perspective on the impact of human activities on the atmosphere and biosphere.

The Alice C. Tyler Perpetual Trust was established to contribute to the improvement of the world's environment, including the preservation of all living things, the land, the waters, and the atmosphere.

Contact: Deborah Williams-Hedges (626) 395-3227 debwms@caltech.edu

Visit the Caltech Media Relations Web site at: http://pr.caltech.edu/media ###

Writer: 
DWH
Writer: 

New Analysis of BOOMERANG Data Uncovers Harmonics of Early Universe

Cosmologists from the California Institute of Technology and their international collaborators have discovered the presence of acoustic "notes" in the sound waves that rippled through the early universe.

The existence of these harmonic peaks, discovered in an analysis of images from the BOOMERANG experiment, further strengthens results last year showing that the universe is flat. Also, the new results bolster the theory of "inflation," which states that the universe grew from a tiny subatomic region during a period of violent expansion a split second after the Big Bang.

Finally, the results show promise that another Caltech-based detector, the Cosmic Background Imager (CBI), located in the mountains of Chile, will soon detect even finer detail in the cosmic microwave background. Analysis of this fine detail is thought to be the means of precisely determining how slight fluctuations billions of years ago eventually resulted in the galaxies and stars we see today.

"We were waiting for the other shoe to drop, and this is it," says Andrew Lange, U.S. team leader and a professor of physics at Caltech. Lange was one of a group of cosmologists revealing new results on the cosmic microwave background at the American Physical Society's spring meeting April 29. Other presenters included teams from the DASI and MAXIMA projects.

The new results are from a detailed analysis of high-resolution images obtained by BOOMERANG, which is an acronym for Balloon Observations of Millimetric Extragalactic Radiation and Geophysics. BOOMERANG is an extremely sensitive microwave telescope suspended from a balloon that circumnavigated the Antarctic in late 1998. The balloon carried the telescope at an altitude of almost 37 kilometers (120,000 feet) for 10 and one-half days.

"The key to BOOMERANG's ability to obtain these new images is the marriage of a powerful new detector technology developed at Caltech and the Jet Propulsion Lab with the superb microwave telescope and cryogenic systems developed in Italy at ENEA, IROE/CNR, and La Sapienza," Lange says.

The images were published just one year ago, and the Lange team at the time reported that the results showed the most precise measurements to date of the geometry of space-time. The initial analysis revealed that the single detectable peak represented about a 1-degree expanse, which is precisely the size of large detail predicted by theorists if space-time is indeed flat. Larger peaks would have indicated that the universe is "closed" like a ball, doomed to eventually collapse in on itself, while smaller peaks would have indicated that the universe is "open," or shaped like a saddle, and would expand forever.

Cosmologists believe that the universe was created approximately 12 to 15 billion years ago in an enormous explosion called the Big Bang. The intense heat that filled the embryonic universe is still detectable today as a faint glow of microwave radiation that is visible in all directions. This radiation is known as the cosmic microwave background (CMB). Whatever structures were present in the very early universe would leave their mark imprinted as a very faint pattern of variations in brightness in the CMB.

The CMB was first discovered by a ground-based radio telescope in 1965. Within a few years, Russian and American theorists had independently predicted that the size and amplitude of structures that formed in the early universe would form what mathematicians call a "harmonic series" of structure imprinted on the CMB. Just as the difference in harmonic content allows us to distinguish between a piano and a trumpet playing the same note, so the details of the harmonic content imprinted in the CMB allow us to understand the detailed nature of the universe.

Detection of the predicted features was well beyond the technology available at the time. It was not until 1991 that NASA's COBE (Cosmic Background Explorer) satellite discovered the first evidence for structures of any sort in the CMB.

The BOOMERANG images are the first to bring the CMB into sharp focus. The images reveal hundreds of complex regions that are visible as tiny variations—typically only 100 millionths of a degree (0.0001 C)—in the temperature of the CMB. The new results, released today, show the first evidence for a harmonic series of angular scales on which structure is most pronounced.

The images obtained cover about 3 percent of the sky, generating so much data that new methods had to be invented before it could be thoroughly analyzed. The new analysis provides the most precise measurement to date of several of the parameters which cosmologists use to describe the universe.

The BOOMERANG team plans another campaign to the Antarctic in the near future, this time to map even fainter images encoded in the polarization of the CMB. Though extremely difficult, the scientific payoff of such measurements "promises to be enormous," maintains the U.S team leader of the new effort, John Ruhl, of the University of California at Santa Barbara. "By imaging the polarization, we may be able to look right back to the inflationary epoch itself—right back to the very beginning of time."

Data from the MAXIMA project is also being presented at the American Physical Society meeting, along with data from the CBI, which is also a National Science Foundation-supported mission. The CBI investigators, led by Caltech astronomy professor Tony Readhead, reported early results in the March 1 issue of the Astrophysical Journal. These results were in agreement with the finding of the other projects.

The 36 BOOMERANG team members come from 16 universities and organizations in Canada, Italy, the United Kingdom, and the United States. Primary support for BOOMERANG comes from the Italian Space Agency, Italian Antarctic Research Programme, and the University of Rome "La Sapienza" in Italy; from the Particle Physics and Astronomy Research Council in the United Kingdom; and from the National Science Foundation and NASA in the United States.

Contact: Robert Tindol (626) 395-3631

Writer: 
RT

Scientists achieve breakthrough in fuel-cell technology

Embargoed for Release at 11 a.m. PST, Wednesday, April 18, 2001

PASADENA, Calif.—Gasoline averaging $3 per gallon? Oil drilling in an Alaskan wildlife reserve? A need to relax air quality standards? It seems the long-term future of fossil fuels is bleak. One promising solution scientists have been studying is fuel cells, but they've had limitations too. Now, in the April 19 issue of the science journal Nature, the California Institute of Technology's Sossina M. Haile reports on a new type of fuel cell that may resolve these problems.

Unlike the engines in our cars, where a fuel is burned and expanding gases do the work, a fuel cell converts chemical energy directly into electrical energy. Fuel cells are pollution free, and silent. The most common type now being developed for portable power—the type used in today's fuel-cell-powered prototype cars—is a polymer electrolyte fuel cell. An electrolyte is a chemical that can conduct electricity, and is at the heart of the fuel cell. Polymer electrolytes must be humidified in order for the fuel cell to function, can only operate over a limited temperature range, and are permeable. As a consequence, polymer electrolyte fuel cell systems require many auxiliary components and are less efficient than other types of fuel cells.

Haile, an assistant professor of materials science, has taken a completely different tack, developing an alternative type of fuel cell that is not a hydrated polymer, but is instead based on a so-called "solid acid." Solid acids are chemical compounds, such as KHSO4 (potassium hydrogen sulfate). Their properties are intermediate between those of a normal acid, such as H2SO4 (sulfuric acid), and a normal salt, such as K2SO4 (potassium sulfate). Solid acids can conduct electricity at similar values to polymers, they don't need to be hydrated, and they can function at high temperatures, up to 250 degrees Centigrade. Solid acids are also typically inexpensive compounds that are easy to manufacture.

But until now such solid acids have not been examined as fuel-cell electrolytes because they dissolve in water and can lose their shape at even slightly elevated temperatures. To solve these problems, Haile and her graduate students Dane Boysen, Calum Chisholm and Ryan Merle, operated the fuel cell at a temperature above the boiling point of water, and used a solid acid, CsHSO4, that is not very prone to shape changes.

The next challenge, says Haile, is to reduce the electrolyte thickness, improve the catalyst performance, and, most importantly, prevent the reactions that can occur upon prolonged exposure to hydrogen. Still, she says, solid acid fuel cells are a promising development.

"The system simplifications that come about (in comparison to polymer electrolyte fuel cells) by operating under essentially dry and mildly heated conditions are tremendous. While there is a great deal of development work that needs to be done before solid acid based fuel cells can be commercially viable, the potential payoff is enormous."

The Department of Energy, as part of its promotion of energy-efficient science research, recently awarded Haile an estimated $400,000 to continue her research in fuel cells. She also recently received the J.B. Wagner Award of the Electrochemical Society (High Temperature Materials Division). She is the recipient of the 2001 Coble Award from the American Ceramics Society, and was awarded the 1997 TMS Robert Lansing Hardy Award. Haile has received the National Science Foundation's National Young Investigator Award (1994–99), Humboldt Fellowship (1992–93), Fulbright Fellowship (1991–92), and AT&T Cooperative Research Fellowship (1986–92).

 

Writer: 
MW
Exclude from News Hub: 
No

Scientists Watch Dark Side of the Moon to Monitor Earth's Climate

Scientists have revived and modernized a nearly forgotten technique for monitoring Earth's climate by carefully observing "earthshine," the ghostly glow of the dark side of the moon.

Earthshine measurements are a useful complement to satellite observations for determining Earth's reflectance of sunlight (its albedo), an important climate parameter. Long-term observations of earthshine thus monitor variations in cloud cover and atmospheric aerosols that play a role in climate change.

Earthshine is readily visible to the naked eye, most easily during a crescent moon. Leonardo da Vinci first explained the phenomenon, in which the moon acts like a giant mirror showing the sunlight reflected from Earth. The brightness of the earthshine thus measures the reflectance of Earth.

In the current issue of the refereed journal Geophysical Research Letters, a team of scientists from the New Jersey Institute of Technology and the California Institute of Technology report on earthshine observations showing that Earth's albedo is currently 0.297, give or take 0.005.

In the early 20th century, the French astronomer André-Louis Danjon undertook the first quantitative observations of earthshine. But the method lay dormant for nearly 50 years, until Caltech team leader and professor of theoretical physics Steven E. Koonin coauthored a paper in 1991 describing its modern potential. The present data are the first that are precise and systematic enough to infer the relative health of Earth's climate.

"Earth's climate is driven by the net sunlight that it absorbs," says Philip R. Goode, leader of the New Jersey Institute of Technology team, Director of the Big Bear Solar Observatory, and a Distinguished Professor of Physics at NJIT. "We have found surprisingly large—up to 20 percent—seasonal variations in Earth's reflectance. Further, we have found a hint of a 2.5-percent decrease in Earth's albedo over the past five years."

A 2.5-percent change in reflectance may not seem like much, but if Earth reflected even 1 percent less light, the effect would be significant enough to be a concern when studying global warming.

Koonin notes that "studies of climate change require well-calibrated, long-term measurements of large regions of the globe. Earthshine observations are ideally suited to this, because, in contrast to satellite determinations of the albedo, they are self-calibrating, easily and inexpensively performed from the ground, and instantaneously cover a significant fraction of the globe."

The new albedo measurements are based on about 200 nights of observations of the dark side of the moon at regular intervals over a two-year period, and another 70 nights during 1994-95. Using a 6-inch refractor telescope and precise CCD at the Big Bear Solar Observatory, the researchers measure the intensity of the earthshine.

By simultaneously observing the bright "moonshine" from the crescent, they compensate for the effects of atmospheric scattering. The data are best collected one week before and one week after the new moon, when less than half of the lunar disk is illuminated by the sun. When local cloud cover is also taken into account, Earth's reflectance can be determined on about one-quarter of the nights.

The study relies on averages over long periods because the albedo changes substantially from night to night with changing weather, and even more dramatically from season to season with changing snow and ice cover. The locations of the land masses also affect the albedo as Earth rotates on its axis. For example, the observations from California easily detect a brightening of the earthshine during the night as the sun rises over Asia, because the huge continental land mass reflects more light than the Pacific Ocean.

"Thus, the averaging of lots of data is necessary for an accurate indication of a changing albedo," Goode says.

It is significant that the earthshine data suggest that the albedo has decreased slightly during the past five years since the sun's magnetic activity has climbed from minimum to maximum during that time. This supports the hypothesis that the sun's magnetic field plays an indirect role in Earth's climate. If supported by further observations, it would explain why there seem to be so many signatures of the sun's 11-year activity cycle in Earth's climate record, but the associated variations in the Sun's brightness are too weak to have an effect.

The researchers plan continuing observations from Big Bear. "These, supplemented with additional observations from a planned worldwide network, will allow even more precise, round-the-clock monitoring of the earth's reflectance," Goode says. "That precision will also make it possible to test connections between solar activity and Earth's climate."

"It's really amazing, if you think about it," Koonin says, "that you can look at this ghostly reflection on the moon and measure what Earth's climate is doing."

The study was funded by both NASA, beginning in 1998, and the Western Center for Global Environmental Change, during 1994-95. Beyond Goode, other members of the NJIT team are Jiong Qiu, Vasyl Yurchyshyn, and Jeff Hickey. Beyond Koonin, other members of the Caltech team are C. Titus Brown, Edwin Kolbe (now at the University of Basel), and Ming Chu (now at the Chinese University of Hong Kong).

Writer: 
Robert Tindol
Writer: 

Owls perform a type of multiplicationin locating ground prey in dark, study shows

Owls have long been known for their stunning ability to swoop down in total darkness and grab unsuspecting prey for a midnight snack.

In the April 13 issue of the journal Science, neuroscientists from the California Institute of Technology report that an owl locates prey in the dark by processing two auditory signal cues to "compute" the position of the prey. This computation takes place in the midbrain and involves about a thousand specialized neurons.

"An owl can catch stuff in the dark because its brain determines the location of sound sources by using differences in arrival time and intensity between its two ears," says Mark Konishi, who is Bing Professor of Behavioral Biology at Caltech and coauthor of the Science paper.

For example, if a mouse on the ground is slightly to the right of a flying owl, the owl first hears the sound the mouse makes in its right ear, and a fraction of a second later, in its left ear. This information is transmitted to the specialized neurons in the midbrain.

Simultaneously, the owl's ears also pick up slight differences in the intensity of the sound. This information is transmitted to the same neurons of the midbrain, where the two cues are multiplied to provide a precise two-dimensional location of the prey.

"What we did not know was how the neural signals for time and intensity differences were combined in single neurons in the map of auditory space in the midbrain," Konishi says. "These neurons respond to specific combination of time and intensity differences. The question our paper answers is how this combination sensitivity is established."

"The answer is that these neurons multiply the time and intensity signals," he says.

Thus, the neurons act like switches. The neurons do not respond to time or intensity alone, but to particular combinations of them.

The reason the neural signals are multiplied rather than added is that, in an addition, a big input from the time pathway alone might drive the neuron to the firing level. In a multiplication, however, this possibility is less likely because a multiplication reduces the effects of a big input on one side.

It's not clear how the owl perceives the location of the mouse in the third dimension, Konishi says, but it could be that the owl simply remembers how far it is to the ground or how much noise a mouse generally makes, and somehow adds this information into the computation.

The lead author of the Science paper is José Luis Peña, a senior research fellow in biology at Caltech.

Contact: Robert Tindol (626) 395-3631

Writer: 
RT

Seventy Percent of Americans Think Bush'sTax Plans Mainly Benefit Wealthy, Study Shows

Seven in 10 Americans think the Bush administration's proposed tax cuts would mainly benefit the wealthiest taxpayers, according to a national poll conducted by the University of Southern California and the California Institute of Technology's joint Center for the Study of Law and Politics (CSLP).

The study, which also revealed deep divisions along political and gender lines about how much of a tax cut should be enacted, shows that 29 percent of the public believe Bush's proposals would be of most benefit to the wealthiest 1 percent of Americans. An additional 41 percent believe the wealthiest 10 percent would be the beneficiaries.

Yet, in polling conducted while the Senate was considering President Bush's $1.6 trillion tax-cut proposal, 44 percent agreed with the president that the size of the cut was "just right"; 41 percent agreed with the majority of the Senate, who sliced the proposal by some $400 billion, that the President's cuts were "too big." Fifteen percent saw President Bush's tax cut as "too small."

"To see so much ambivalence in the American public about tax cuts shows how much work President Bush still has to do," noted Professor R. Michael Alvarez, a political scientist from Caltech associated with the CSLP, and one of the principal investigators of this study.

"It's clear that even though this was the centerpiece issue of his presidential campaign, President Bush has not closed the deal yet on his $1.6 trillion tax cut," Alvarez said.

Professor Edward McCaffery of the USC Law School and Caltech, director of CSLP, and another investigator on the study, noted that tax-cut fever is catching. "Everyone wants something from Uncle Sam, even if they know that others will get more."

Most respondents said they favored income tax cuts across the board (29 percent), followed by elimination of the marriage penalty (17 percent), Social Security or cuts in Medicare taxes (13 percent), elimination of the estate or death tax (11 percent), or new tax credits for retirement accounts (10 percent). Eight percent said they favored no tax cut at all or had no opinion on the matter.

But on this specific breakdown, as on other issues that CSLP is examining, McCaffery noted a pronounced gender gap: "When it comes to tax cuts, men are far more likely to have an opinion, and a positive one; women are less certain about the whole deal."

As an indication of the political fights facing President Bush, Alvarez pointed to the partisan conflict underlying public opinion about the tax cut: "62 percent of Republicans saw the Bush tax cut as `just right,' while 60 percent of Democrats said it is `too large.'" Importantly, survey respondents who said they were independent were divided, with 42 percent saying the Bush tax cuts were `too large' and 42 percent saying they were 'just right,' Alvarez added.

The national probability telephone survey was conducted between March 26 and April 6. Interviews were conducted by Interview Services of America, Inc. Fifteen hundred American adults were interviewed, with a margin of error for the sample of +/- 2.5 percent.

 

Writer: 
Robert Tindol
Writer: 

Pages

Subscribe to RSS - research_news