The Pros (and Cons) of Plugging In
- Jake Yeston
The adage out of sight, out of mind has some resonance as the first big crop of plug-in hybrid cars hits the road in the United States. People see and sometimes smell gasoline; plugging a car into a socket may make it seem like the energy is conjured from the ether. Of course, power plants actually bear the burden, and Peterson et al. are among the growing number of researchers gauging the implications. They have examined the net effect on carbon, nitrogen, and sulfur emissions of replacing a fraction of the cars in a number of Eastern and Midwestern U.S. states with plug-in hybrids. They modeled several different scenarios, such as when cars were charged and whether carbon dioxide emissions were priced or captured and sequestered. For a 10% hybrid fleet scenario, they found significant reductions in CO2 emissions across the board, and NOx reductions in most cases. The principal drawback was an increase in sulfur dioxide emissions as demand for coal combustion rose.
Environ. Sci. Technol. 45, 10.1021/es102464y (2011).
- Applied Physics
A Sharper Focus
- Ian S. Osborne
Imaging techniques are rarely applied in ideal environments. Ultrasound imaging, for instance, is hindered by scattering from tissue, bone, and other surrounding organs, which often blur the images. The same is true for terahertz body scanners, wherein scattering from clothing or designed concealers may obscure detection. Scattering from random scatterers creates speckle noise in the backscattered signal that results in an overall deterioration in image quality. Montaldo et al. show that this speckle noise can be controlled and mitigated by a time-reversed scattering process using a time-domain array of transmitters and receivers. By sending in pulses of ultrasound from the array and tweaking the timing at each array element, the signals at the receivers are fed back to the transmitters, and the timing is iteratively adjusted to effectively steer the pulses to focus on a desired point. The improved imaging capability is demonstrated in a phantom for ultrasound but should be extendable to other frequency regimes for radar and communication applications.
Phys. Rev. Lett. 106, 54301 (2011).
Brother, Can You Share a Hollow?
- Sacha Vignieri
Tree hollows are a key resource for numerous forest-dwelling species. Hollow reductions that result from forest harvest and management practices are a significant threat to forest species worldwide. Although the reduction of hollows has generally been followed by a decline in dependent species, two species of Australian possum (Gymnobelidus leadbeateri and Trichosurus cunninghami) have not followed this trend. By tracking the denning behavior of individuals of known genetic relatedness, Banks et al. show that this resilience is largely due to a change in social behavior. When hollows are plentiful, possums use a large number of dens, have overlapping home ranges, and prefer to share hollows with unrelated individuals. When hollows are scarce, the animals show increased aggression and defense of hollows and instead prefer to nest with relatives. Thus, when resources are scarce, animals obtain an inclusive fitness benefit of sharing with relatives and excluding nonrelatives, whereas when resources are plentiful, inclusive fitness is less important than other considerations, such as inbreeding or pathogen avoidance.
Proc. R. Soc. London Ser. B 278, 10.1098/rspb.2010.2657 (2011).
- Jake Yeston
In principle, dimeric molecules may seem easier to synthesize than lower-symmetry compounds of comparable size. After all, both halves can be generated together and then conveniently coupled at the end. In practice, the coupling step often poses a tremendous challenge—all the more frustrating because it comes after long and meticulous preparation of the penultimate monomer. Such was the case with the polycyclic core of lomaiviticin, an organic natural product of exploratory pharmaceutical interest. The compound comprises two identical tetracyclic frameworks linked by a C-C bond and two C-O bonds; an especially unusual feature is the presence in each half of a diazo group, ordinarily a highly reactive substituent. Herzon et al. have now succeeded in assembling the lomaiviticin framework (without the pendant sugars in the natural product) using 11 steps, perhaps the hardest of which proved to be the formation of that central C-C bond. After an extensive search, the authors discovered that a trivalent manganese complex bearing three fluorinated acetylacetonate ligands was a uniquely selective oxidant for the coupling reaction (though the bacterial solution to the same challenge remains somewhat mysterious).
J. Am. Chem. Soc. 133, 10.1021/ja200034b (2011).
- Plant Sciences
- Pamela J. Hines
During reproduction, some genes in the offspring are “imprinted”: They contain inherited epigenetic markings that promote specific expression of either the maternal or paternal allele. Genetic imprinting can be viewed within the parental conflict theory, which postulates that females allocate resources equally to all offspring, whereas males favor the expression of genes that maximize resource use by individual offspring. In Arabidopsis, a few imprinted genes are known to be expressed in the endoderm, which is the portion of the seed that will nourish the growing embryo. Hsieh et al. have now surveyed the gene expression landscape of the Arabidopsis endoderm and found 43 imprinted genes in the endoderm, 34 maternally expressed and 9 paternally expressed. The genes that maternal and paternal sources disagreed over encode transcription factors, hormone signaling components, and regulators of chromatin modification and small RNA pathways. The Arabidopsis embryo, on the other hand, reflected an inner peace, with no imprinted genes identified.
Proc. Natl. Acad. Sci. U.S.A. 108, 1755 (2011).
No Damaged Daddies
- Beverly A. Purnell
Cells have evolved mechanisms to protect against damaged DNA, including the induction of apoptotic cell death. Such protection is especially important in germline cells in order to ensure the evolutionary stability of a species. The p53 homolog, p63, functions to protect the female germ line by promoting apoptosis of oocytes with damaged DNA. Beyer et al. sought to determine whether p63 also functions in the male germ line and identified p63 isoforms that are expressed in the human testis. Male germ cell-associated transcriptionally active p63 (GTAp63) is encoded by the p63 gene with a long terminal repeat (LTR), the result of an integration event of the endogenous retrovirus ERV9 LTR, inserted upstream. Spermatogenic precursors, but not mature spermatozoa, expressed GTAp63, which induced the expression of proapoptotic genes upon DNA damage. Analysis of primate DNA showed conservation of the LTR insertion in great apes and humans, which suggests that the insertion occurred recently in evolution. Besides ensuring germline genomic integrity, p63 may also act as a tumor suppressor: Examination of tissue from human testicular cancers revealed a loss of p63 expression.
Proc. Natl. Acad. Sci. U.S.A. 108, 10.1073/pnas.1016201108 (2011).
Pulsing Once Again
- Maria Cruz
Just as seismic waves allow scientists to study Earth's interior, stellar oscillations can tell us about the interior of stars. Cataclysmic variables are binary systems in which an extremely dense star, or white dwarf, accretes material from another star; in a dozen such cases so far, the white dwarf is known to pulsate. As their name suggests, cataclysmic variables can experience sudden outbursts—with the brightness of the entire system sometimes increasing by several orders of magnitude—when the accreted material undergoes thermonuclear fusion on the white dwarf's surface. The extent to which these events affect the white dwarf's interior is not completely understood.
The white dwarf in the cataclysmic variable SDSS J074531.92+453829.6 was shown to have stopped pulsating 1 year after its first recorded outburst, suggesting that it was heated to temperatures beyond those at which pulsations can occur. Now, 3 years after the outburst, Mukadam et al. show that the pulsations have resumed and that their properties, which depend on fundamental parameters such as the density, pressure, and temperature in the stellar interior, are similar to those of the pre-outburst pulsations. This white dwarf has thus cooled down to its previous state, with no signs of its interior having been perturbed by the outburst.
Astrophys. J. 728, L33 (2011).