To fully understand how nanomaterials behave, one must also understand the atomic-scale deformation mechanisms that determine their structure
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The early 2000s were a time of exceptional drought in the American Southwest. The year 2002 in particular was perhaps the driest in the last 500 years, according to tree-ring historical reconstructions.
This was bad news for the aspen trees of the Southwest, which died by the millions. But it also raised a scientific question: just how exactly does drought kill trees? A child easily grasps that lack of water will kill about any plant. But the specific biological mechanism by which trees die from drought has not been well-established. It's the difference between knowing that shooting someone in the chest will kill them, and understanding why a bullet puncturing the heart will end a life.
A team of scientists, led by Dr. William Anderegg of Princeton, have been working on the aspen question, and their results were published today in Nature Geoscience. The answer is something called "xylem cavitation." And unless we do something big about climate change soon, it will kill most of the aspens in the Southwest.
Here's what that means. Trees transport water through their xylem tissue (one example of which is regular old wood), basically composed of millions of tiny tubes, or "conduits." Xylem doesn't work like a mechanical pump — instead, water flows up the tree trunk through capillary action. That flow is maintained through evaporation at the leaf surface, removing water at the top so more can replace it, and supplied by the roots drawing water from the soil.
In hot, dry conditions, like the early 2000s drought, water evaporates more quickly from the leaf surface — and there is less water in the soil to maintain supply. Anderegg and his team quantified both of these with a factor they called "climatic water deficit." When the deficit is high, the water pressure inside the xylem decreases due to tension between the top and bottom of the tree.
If the pressure gets low enough, gas bubbles will spontaneously form in the water column — which is called cavitation. A bubble instantly blocks that particular xylem conduit and prevents the water from flowing. Block enough conduits, and the tree desiccates and dies.
It's "like a tree heart attack," says Anderegg. He and his team constructed a model of this cavitation mechanism, calculated a threshold at which aspens should die, and compared it with historical data on the early 2000s drought. They found pretty clear agreement, explaining about 75 percent of the tree mortality during that time (a good result, given how complex forests are). In this image, red and yellow represent when the model correctly predicted whether a tree would live or die, while green and blue are the corresponding wrong predictions:
Xylem cavitation has been understood for years, but this is strong evidence for this being the murder culprit, so to speak. (Note that this model only applies to deciduous tree species. Conifer species like lodgepole pine have also been killed en masse by climate change-fueled drought, but abnormal beetle swarms are what strike the killing blow.) Others had suggested different mechanisms, like starvation. What's more, this threshold model has some disturbing implications. All that is required to kill an aspen forest is a sufficiently hot and dry spell.
According to the big climate models, under a high-emission pathway (that is, assuming world society does little to combat climate change), large sections of current aspen forests will be consistently above the mortality threshold by the 2050s. But since all that is needed to kill an aspen tree is a couple of exceptional years, then the bulk of current aspen forests will likely be dead some time before that decade.
This matters not just for the aesthetic value of forests in themselves, but also for many human interests as well. Besides being a major tourist attraction — they're just about the only fall color in much of the Colorado mountains — aspen is a major commercially harvested species in the Southwest. Aspens also support a large variety of local wildlife, much of it important to local economies, and a variety of other ecosystem services (like water filtration).
Obliterating the aspens would not only be a great ecological crime, but also a terrific blow to local communities across the Southwest.
Therefore, the drought of the early 2000s was a "canary in the coal mine," says Anderegg. If we do nothing about climate change, then by 2050 the average year will be about like 2002 in terms of temperature and precipitation. The aspens, and everything that relies on them, will be dead.
You may have heard of Koko the gorilla or Alex the parrot, but what about Pia, Splinter, Oprah, and Persimmon the rats? Or Nixon the octopus? Or breeder pairs of mice named Tom and Katie or Brad and Angelina? It's not only the animals with good communication skills and long-term relationships with human researchers that get names. As Michael Erard explains in Science, "for many researchers naming is a practice whose time has come."
It hasn't always been that way. In the past, naming was frowned upon because it had the potential to introduce bias. A name might make a researcher ascribe personality traits to an animal on the basis of connotations carried by the name. It also introduced a personal connection to the animal that researchers strove to avoid. In a 1980s study of lab practices, researchers said that "they didn't name because they dealt with so many animals and were interested in them as sources of enzymes or data points, not as individuals."
But it turns out that naming can lead to better science. One lab that used names for monkeys was led to start looking at individual differences between them which "led to the discovery of the genetics and epigenetics of personality in monkeys." On a more general level,
Naming improves animals' lives, argues Brenda McCowan, a scientist at the California National Primate Research Center at the University of California, Davis, who manages the behavioral enrichment program for 5000 rhesus and titi monkeys. "Naming helps create positive human-animal interaction, which is better for the welfare of those animals," she says. Buckmaster adds that naming has become more accepted because "people realized the scientific value of the stress-free animal. … We have to make sure these are really happy animals, or none of the information that we get from them will be valid."
Read more about the history of research animal naming and its effect on science at Science Magazine.
Public arguments about fracking (at least among those who have heard of the natural gas production technique) have become contentious—a situation not helped by the technical and complicated topic. Lots of information and claims fly around, but there's little in the way of an established framework to help make sense of them.
Claims that fracking has contaminated water can be difficult to resolve, and some turn out to be unrelated to fracking. Geology differs from place to place in important ways that have to be taken into consideration when analyzing water. Regulations governing fracking vary from state to state, too. And the practice has been scrutinized at a level we haven’t subjected conventional oil and gas production to, meaning we might be discovering problems that are common to other techniques.
Still, we occasionally get a relatively simple case, even if its broader implications are minimal. In the summer of 2010, three nearby homes in northeast Pennsylvania started having disturbing problems with their water wells. Methane was seeping up—in one case accumulating to levels that necessitated evacuating a home due to the explosion risk—and the wells were muddy and foaming. (A nearby river even began bubbling a few months later.)
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Hot, young stars and cosmic pillars of gas and dust seem to crowd into NGC 7822. At the edge of a giant molecular cloud toward the northern constellation Cepheus, the glowing star forming region lies about 3,000 light-years away. Within the nebula, bright edges and dark shapes are highlighted in this colorful skyscape. The image includes data from narrowband filters, mapping emission from atomic oxygen, hydrogen, and sulfur into blue, green, and red hues. The atomic emission is powered by energetic radiation from the hot stars, whose powerful winds and radiation also sculpt and erode the denser pillar shapes. Stars could still be forming inside the pillars by gravitational collapse, but as the pillars are eroded away, any forming stars will ultimately be cutoff from their reservoir of star stuff. This field spans around 40 light-years at the estimated distance of NGC 7822.Micro-electromechanical systems, or MEMS, may not be on your mind, but there could be some in your pocket.
The post MEMS pack big punch in tiny package has been published on Technology Org.
