American Scientist

This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters.

Content to Get Older

They say that youth is wasted on the young, and a new study adds evidence to this maxim. Data from the General Social Survey, a yearly interview done with more than 50,000 Americans since 1972, shows that older adults report being happier than younger people. Older adults were not always so cheerful; they report that becoming older conferred contentment. Although they are likely to endure physical ailments and the loss of family members, those of more advanced age have fewer financial, interpersonal or crime problems. Youth, in contrast, enjoy good health but generally experience predicaments in their finances, emotional relationships and professional lives.

Yang, Y. Social inequalities in happiness in the United States, 1972 to 2004: An age-period-cohort analysis. American Sociological Review 73:204-226 (April)

Pesticides Don't Smell Fishy to Trout

Although concentrated pollution has been eliminated from most waterways, low levels of pesticides and other chemicals still end up in streams. A new study replicated typical trace concentrations of 10 contaminants in water containing captive rainbow trout. After four days of exposure, although the trout could still smell, they could not detect changes in the level of an odor produced by predators, meaning they could not sense the distance to, say, a wading bear. Since salmon are close relatives of trout, failure to evade predators may be one reason for plummeting salmon stocks in North America.

Tierney, K. B., et al. Salmon olfaction is impaired by an environmentally realistic pesticide mixture. Environmental Science and Technology 42:4996-5001 (published online June 4)

Look Out Above!

Avalanches can happen quickly and with very little provocation. A new study finds that a major factor determining when the snow will go is a brittle, collapsible layer of icy grains that sits between a dense slab on top and a rigid base below. Scientists had thought that the critical crack size to start an avalanche would increase as the slope angle decreases, but this study found that the length was pretty much constant. Instead the investigators found that when the brittle middle layer collapses and leaves large cavities, these can form large networks of instabilities, meaning there is no minimum angle to start a slide. This result could explain why some cross-country skiers, when moving over flat snow cover, can still trigger a remote avalanche on a hill above them.

Heierli, J., P. Gumbsch and M. Zaiser. Anticrack nucleation as a triggering mechanism for snow slab avalanches. Science 321:240-243 (July 11)

The Ocean Eats Ozone

Halogens, such as iodine and bromine, are released by seawater in the form of spray, and destroy ozone. A new study has found that open ocean produces more halogens than predicted, suggesting that 50 percent more ozone is scrubbed above the tropical Atlantic Ocean than previously thought. The same process produces hydroxyls that may also pull methane out of the lower atmosphere at rates slightly higher than expected. Such data could be important additions to climate models. However, this natural mechanism for keeping these greenhouse gases in check may be overwhelmed by rising emissions.

Read, K. A., et al. Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean. Nature 453:1232-1235 (June 26)

Like Your Own Arm

In an advance that could lead to brain-controlled prosthetics, a new study has shown that monkeys can be taught to use only neural signals to make a robot arm grasp snacks and feed themselves. The rhesus macaques were fitted with a small grid of electrodes, about the size of a freckle, over a patch of cells known to signal arm and hand movement. The electrodes collected the signals from neurons, which were analyzed by a computer that then fed the electronic command to the arm. After several days, the monkeys were able to adjust the grip of the arm depending on the softness of the food, use the arm to push morsels into their mouths, and generally adopted it as if it were their own.

Velliste, M., et al. Cortical control of a prosthetic arm for self-feeding. Nature 453:1098-1101 (June 19)

Shunning the Dirt

Some materials are naturally attracted to water. These hydrophilic substances also tend to repel impurities in water, leaving a film of pure water along their surfaces. Researchers decided to exploit this phenomenon to build a water filtration system that requires no moving parts or disposable filters, making it simple and potentially inexpensive. The filter consists of a needle-sized tube made of a hydrophilic polymer, connected to two concentric steel tubes at one end. Water contaminated with tiny latex spheres, soil and bacteria flows through the tube and separates into two streams—one of pure water near the walls, another with contaminants at the center. The inner steel tube collects the dirty water, separating it from the purified stream.

Klyuzhin, I., et al. New method of water purification based on the particle-exclusion phenomenon. Environmental Science and Technology ASAP (published online July 11)

Rooted to Family

Plants may seem to be passive, defenseless organisms, but at least one species can sense if it's surrounded by relatives or strangers and respond accordingly. A study finds that the annual plant Cakile edentula, or Great Lakes sea rocket, when placed in pots with plants that are unrelated to it, will divert resources into root growth in order to escalate its competition with the invaders. However, if the plant is put in containers with siblings, it refrains from this behavior. This finding argues that the plant is able to recognize kin, something that not even all animals are capable of doing.

Dudley, S. A., and A. L. File. Yes, kin recognition in plants! Biology Letters 4: 69-70 (February 23)