UC Santa Cruz Tip Sheet February 10, 1995
Research news and feature ideas, issued periodically by the UCSC Public Information Office. For more information, contact Robert Irion at (408) 459-2495 or irion@ua.ucsc.edu.
Cosmology Lightweight neutrinos zip nicely into latest models of the universe
The discovery that the ghostly particles called neutrinos may have a small mass supports a special class of theoretical models of how the universe has evolved, according to a group led by cosmologist Joel Primack of UCSC.
Physicists at Los Alamos National Laboratory have found strong evidence that neutrinos have mass. If the claim holds up, it has deep implications for models of the universe that probe how its structure is influenced by dark matter. Because neutrinos are ubiquitous--a billion of them for each electron and proton in the universe--even a vanishingly small mass could make them a crucial element of dark matter.
Detailed computer simulations by Primack's team of the evolution of structure in the universe show that neutrinos should compose about 20 percent of its mass. That fraction is consistent with early results from Los Alamos. Neutrinos represent a special kind of dark matter--"hot" dark matter, which moves quickly, as opposed to sluggish "cold" dark matter. The Los Alamos findings and astronomical observations both strongly favor a dark-matter recipe with cold plus hot ingredients, Primack says. Further, his group proposes two types of neutrinos, each with a small but equal mass, as the best theoretical solution yet to the dark-matter puzzle.
"Neutrinos with mass will force us to zero in on a small class of models as acceptable," says Primack. Even the existence of one species of neutrino with a mass above a certain threshold, he notes, is "essentially fatal" to today's most popular class of models--those that rely upon a low density of cold dark matter in the universe plus a "cosmological constant." A paper by Primack's group will appear shortly in the journal Physical Review Letters.
Contact: Joel Primack--(408) 459-2580 or joel@lick.ucsc.edu
Environmental hazards Lead-poisoning therapy: More harm than good?
A drug commonly used to treat lead poisoning may increase the amount of lead absorbed from the gastrointestinal tract into other parts of the body, according to a pilot study. The study's authors call for research on a larger scale using people with moderate cases of lead poisoning. Meanwhile, they urge doctors to keep patients in lead-clean places while giving them the drug, called "succimer." Otherwise, the patients' bodies might absorb additional lead and store it in bones or critical organs, which can cause long-term harm.
"It's common sense that when you treat people for lead exposure, you shouldn't return them to the same environment during treatment," says toxicologist Donald Smith of UCSC. "This study provides preliminary evidence that we should justifiably be concerned when that happens--and the reality is that it may happen."
Succimer, considered the safest drug to treat lead poisoning, clamps onto lead and other toxic metals and allows patients to excrete them. However, it is not clear whether succimer also moves lead from the blood, stomach, or intestines to other parts of the body, such as the skeleton and brain. Such transfers would compromise the effectiveness of the drug--especially for children, who are most susceptible to lead's insidious behavioral and neurological effects.
In the study, twelve men ingested a tiny amount of a nonradioactive isotope of lead, followed by one dose of either the drug or a placebo. By examining the subjects' urine, feces, and blood, the research team found clues that succimer did cause the participants to absorb some lead through their gastrointestinal tracts. Smith and his coworkers published their results in the October 1994 issue of the journal Environmental Research.
Contact: Donald Smith--(408) 459-5041 or drs@earthsci.ucsc.edu
Marine toxicology Just a spoonful of blubber makes the pesticides come 'round
A new technique designed to extract contaminants from tiny samples of seal blood and blubber may prove to be the best means yet for measuring levels of pollutants in living animals. The method, perfected over the past year at UCSC, yields highly accurate estimates--well within guidelines set by the Environmental Protection Agency. It is so effective that scientists at the Centers for Disease Control now plan to use it to measure dioxins in human blood.
According to postdoctoral researcher Walter Jarman, part of a team that developed the method, its charm is its practicality: "It uses small samples, it's cheap, and it saves a lot of time."
One application is in marine mammalogy, Jarman says. Seals, whales, and sea otters are particularly vulnerable to pollution because their tissues can accumulate toxic substances. During lifetimes spent munching tainted seafood, they become unwitting storehouses for a wide range of unsavory ingredients. As such, they may be the best guide to local pollution levels, or even serve as an early warning system for new contaminants.
But effective surveys require many individuals. For this reason, the new analysis--which can use samples from live animals --is ideal. Now researchers can test a beach-load of breeding elephant seals or a pen of oil-slicked sea otters, rather than depending on the occasional windfall of a long-dead beached whale. In the first test run, Jarman and three coworkers sampled 20 elephant seals at the Ano Nuevo rookery and the Marine Mammal Center in Sausalito. Using less than one gram of blubber and two milliliters of blood from each seal, the researchers determined both pesticide and PCB levels. Their work appeared last year in the journal Chemosphere.
Contact: Walter Jarman--(408) 459-3769 or wmjarma@ucsco.ucsc.edu (Writer: Pamela Donegan)
Astrophysics Dwarf galaxies passing near Milky Way should create streams of stars
Galaxies often collide, spectacular events we can see across the vast reaches of space. Now it appears such a collision is happening in our own backyard. Astronomers last year found a new dwarf galaxy hidden behind the dusty core of our Milky Way. Its stretched shape suggests the Milky Way is ripping it asunder.
Astrophysicist Lars Hernquist of UCSC and his colleagues recognized that the dwarf--now the closest known galaxy to our own--offers a rare chance for scientists to study a tidal interaction between galaxies. The team explored the possible history and fate of the dwarf with a powerful tool: supercomputer simulations. The study reveals that dwarf galaxies spiraling into the gravitational maw of the Milky Way should leave visible trails of debris that persist for a billion years or more.
Astronomers could learn much about the evolution of the Milky Way by finding these faint remains. For instance, many such trails would bolster a theory that the Milky Way formed and continues to grow by capturing smaller galaxies and subsuming their stars and gas. On the other hand, an absence of trails might mean that our galaxy's appetite for stellar hors d'oeuvres is lower than many astronomers believe.
"When the Milky Way disrupts a dwarf galaxy, it takes some time for its stars to disperse," says Kathryn Johnston, a graduate student under Hernquist. "We think that observations of these moving groups of stars are feasible. If they exist, they will offer an exciting window on the history of the galaxy." Johnston discussed the research in January at a meeting of the American Astronomical Society.
Contact: Kathryn Johnston--(408) 459-2774 or kvj@lick.ucsc.edu
Seismology Cape Mendocino earthquakes: Aftershocks illuminate a triple threat
Aftershocks of a large earthquake near Eureka, California, in 1992 have shed new light on the interplay among three tectonic plates at the Mendocino Triple Junction, one of the country's most complex seismic settings.
The Mendocino Triple Junction marks the southern limit of the Cascadia Subduction Zone, which threatens the Pacific Northwest with potential quakes of magnitude 8 or larger. The subduction zone and two other faults largely vanish near the junction, leaving seismologists in the past to scratch their heads about how the tectonic plates interact there. That all changed on April 25, 1992, when a magnitude 7.1 earthquake struck at the triple junction. Within a day, UCSC seismologist Susan Schwartz and others deployed portable seismometers to measure aftershocks in great detail.
Schwartz's study suggests that the Gorda plate, a wedge of Pacific Ocean seafloor, is plunging in fits and starts under both the North American and Pacific plates. In addition, the study indicates that the fault between the Gorda and North American plates is weak: It broke even though the stress in the direction of the earthquake rupture was low before the main quake.
Schwartz compares the fault to the section of the San Andreas Fault that caused the Loma Prieta quake of 1989. "In both cases, the regional stress field was not favorably oriented to make the faults slip," she says. "Only a little shear stress was enough to make them move. However, even with a weak fault, you can still have large earthquakes." She discussed her work in December at a meeting of the American Geophysical Union.
Contact: Susan Schwartz--(408) 459-3133 or susan@earthsci.ucsc.edu
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