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Research Roundup: Bay area landslides, fruit fly taste receptors, and more...

26 August 2004

Bay Area landslides detailed with new imaging techniques

In what is perhaps the most detailed study yet of the active landslides in the East Bay hills, a UC Berkeley-led research team has found that the slides were moving downhill between 5 and 38 millimeters per year over a decade of study. Their findings demonstrate the power of a satellite-mapping technique that provides far more information than was previously possible through labor-intensive field studies.

Using high-resolution interferometric synthetic aperture radar, which processes data to create very detailed images of ground movement too subtle to detect by conventional means, the scientists analyzed data collected between 1992 and 2001 by two European Remote Sensing satellites. Not surprisingly, during the period of heavy rains brought on during the 1997-98 El Niño years, when seasonal precipitation increased by 200 percent, the researchers found that sliding rates increased by as much as 30 percent.

“We believe the seasonal acceleration of these landslides may be strongly controlled by elevated water pressures in the ground subsurface,” said George Hilley, a postdoctoral researcher at Berkeley’s Department of Earth and Planetary Science and lead author of the study. “Once you go about understanding the physics of these slides and how they respond to changing conditions due to precipitation and groundwater flow, then you can actually start to develop strategies for mediating these types of structures.”
Hilley worked with Roland Bürgmann, associate professor of earth and planetary science at the Berkeley Seismological Laboratory, to study the effect of precipitation on the landslides. The researchers charted the time lag from the onset of heavy rains to the acceleration of the landslides, noting that most slide movement occurs during the latter part of the rainy season, when subsurface water pressures may be high.

“The spatial and temporal resolution we’ve been able to obtain in this study is unprecedented,” said Hilley. “Unlike the slides in the East Bay hills, which have been recognized previously, the methods we demonstrated in this study may eventually be used to identify unrecognized landslides in other urban areas.”

Sarah Yang

Human thermal-comfort model developed

Berkeley researcher Zhang Hui has helped develop a sophisticated mathematical model to predict human thermal comfort. The model, based on measurements of skin and body core temperatures and their rates of change, can be used to design energy-efficient temperature systems that make people more comfortable in vehicles, buildings, and outdoor spaces.

In her research, the information from those measurements was correlated with the subjective sensation and comfort assessments of 27 people in changing, neutral, cold, and warm environments in an office setting. Additional experiments, conducted in an automobile inside a hot — then cold — wind tunnel, validate the model results from Hui’s workplace study.

Hui’s model provides “an important missing link between human physiological response to the thermal environment and our subjective experience,” said Charlie Huizenga, a research specialist in the Building Sciences Group in the College of Environmental Design and a supervisor of Hui’s doctoral dissertation study. The model can gauge temperatures of the head, face, neck, breathing zone, chest, back, pelvis, left and right upper arms, left and right hands, left and right thighs, left and right lower legs, and left and right feet. An onscreen human body can then indicate in various colors the different body-temperature changes brought on by varying thermal air conditions. The model also presents temperature charts for each part of the body for those conditions. Engineers, architects, and experts in heating, air conditioning, and ventilation can use the model to design thermally comfortable spaces.

Kathleen Maclay

Accounting for a fly’s taste experience

In the first detailed genetic study of fly taste receptors, Berkeley neuroscientist Kristin Scott and her colleagues showed that fruit flies, like humans, have receptors devoted to sweet and bitter tastes. While human taste receptors are limited to the tongue, the receptors in flies are mounted on bristles scattered all over the body, including the legs, the wings, the food-sucking proboscis, and the egg-laying ovipositor.

Tracing the taste receptor nerve cells into the brain, Scott and her team showed that fly brains contain a map both of the location of each receptor on the body and the type or quality of the taste it records. She says that a fly’s taste system is much simpler than the smell (olfactory) sensory system: The latter uses 50 different odor detectors to discriminate among thousands of smells, while the 68 taste receptors are reduced to only a few different taste categories in the fly brain. Taste is geared mainly to locating food and deciding whether or not to eat it, without any fine taste distinctions, she said.

This also is true of mammals, whose taste receptors send the brain only the basic taste notes of food. Odor receptors provide the fine discrimination of smells that allows us to distinguish foods and enjoy eating.

“The simplicity of the gustatory map of the fruit fly indicates that it will be a model system to examine how the brain translates chemical cues in the periphery into taste perception and behavior,” the authors concluded in their research paper.

Robert Sanders