RESEARCH HIGHLIGHTS THIS WEEKATMO SPHERIC SCIEN C E

JULIEN COURCHET

Aerosols suppress
hurricanes
Aerosol particles from humanactivities could have lowered
the number of tropical storms
over the Atlantic Ocean during
the twentieth century.
Natural aerosols such as
dust particles are thought
to influence hurricane
activity, but the effects ofanthropogenic aerosols areunclear. A team led by Nick
Dunstone at the Met Office
Hadley Centre in Exeter, UK,modelled the frequency ofNorth Atlantic tropical storms
with simulations that either
incorporated or excludedchanges in man-madeaerosols. The model suggeststhat as levels of anthropogenic
aerosols increased in the earlier
part of the century, tropicalstorm activity dropped; aerosol
declines at the end of thecentury increased storms.
The authors attribute this tothe effect of aerosols on clouds.
By brightening clouds andcausing them to stick aroundfor longer, aerosols coolsurface temperatures and shiftcirculation patterns in a waythat suppresses hurricanes.
Nature Geosci. http://dx.doi.
org/10.1038/ngeo1854 (2013)

MATERIALS SCIENCE

Droplets move tosofter substrates

ROBERT STYLE

Liquid droplets dripped ontoa silicone gel will move fromthin, stiff regions to thick,springy ones.
This intriguing behaviour,
reported by Eric Dufresne
at Yale University in New
Haven, Connecticut, and hiscolleagues, occurs becauseof the physics of surface
tension. A droplet tends
to spread out over a thick,deformable surface, but rears
up into a spherical shapeat thinner, stiffer places.
A similar phenomenon
occurs in biology, but inreverse: cells tend to moveto stiffer parts of a substrate,
a process called durotaxis.
The biological movement
is thought to involve thecell actively sensing its
environment and using
actin–myosin fibres tocontrol locomotion. The
liquid durotaxis can beused to generate patternsof droplets (pictured)
without chemical or thermal
gradients and might beuseful in microfluidics, theauthors speculate.
Proc. Natl Acad. Sci. USA
http://dx.doi.org/10.1073/
pnas.1307122110 (2013)

A PPL I ED PH YSI CS

Metamaterial wall
amplifies soundSound waves can squeeze
through holes smaller
than their wavelength in a
specially fabricated wall.
Metamaterials are
artificial materials precisely
engineered from metals orplastics to have structuresthat manipulate sound or
light waves. Such materials
have already been used todirect light waves throughseemingly impassible
openings. To accomplish
such ‘extraordinarytransmission’ with sound,
Sam Lee at Yonsei University
in Seoul, South Korea, andhis colleagues stretchedpieces of plastic film acrosstiny perforations in a thinmetal plate. Incoming sound

COMMUNITYCHOICEThe most viewed
papers in science
G E N E T I C E NG I NE E R I N GComprehensive fly library
A method that can systematically generate
fruitflies to overexpress particular genes
on dev.biologists.
will help researchers to explore geneorg in May
function in the model organism.
Konrad Basler at the University of Zurich, Switzerland, andhis colleagues developed a scalable method to overexpress
genes at known sites in the genome of the fruitfly Drosophila.
They coupled a system that allows controlled gene expression
with one that allows site-specific integration of a newly
introduced gene. The researchers used the technology toestablish a library of 1,149 fly strains. The approach could
be used to efficiently explore effects of overexpression
in a comprehensive set of fly genes and to complement
experiments with knockout flies, in which particular genes
are disabled or deleted, the authors say.

✪ HIGHLY READ

Development 140, 2434–2442 (2013)

waves of a selected frequency
resonated with the film,
causing air to flow as if itwere massless and funnel asmuch as 97% of the soundthrough the holes. The soundwas intensified within theholes by a factor of up to5,700, and thus could be usedin sensitive detectors, theresearchers suggest.
Phys. Rev. Lett. 110, 244302(2013)NE U R OS CI E N CE

Enzyme duo elicit
nerve branching
A pair of enzymes control
where synapses formin neurons by guiding
the transport of energyproducing organelles called
mitochondria.
A team led by Franck
Polleux at the Scripps
Research Institute in La Jolla,
California, identified two
enzymes that are required
for axons (the long messagetransmitting stalks ofneurons) to branch and form
synapses with other neurons.
When these enzymes wereoverexpressed in neurons,
mitochondria moving down
the axon, along microtubules,
were immobilized at thepoint where axons would
form synapses. Higher levelsof these enzymes boosted
axon branching (pictured),
whereas lower levels
reduced it.
The researchers suggestthat the two enzymes
work together to tellmitochondria where to stopand thus where synapses
will form. Mitochondrialtransport could factor in
the development of a wide
range of disorders, including
autism, through its effects
on synapse formation, theauthors say.
Cell http://dx.doi.org/10.1016/j.
cell.2013.05.021 (2013)

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