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<jats:p>The technological goal of optimizing the controlled deposition of atomic monolayers is simplified by studying models of deposition of larger colloids.</jats:p>

<jats:title>Making Connections</jats:title> <jats:p> Genetic interaction profiles highlight cross-connections between bioprocesses, providing a global view of cellular pleiotropy, and enable the prediction of genetic network hubs. <jats:bold> Costanzo <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="425" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1180823">425</jats:related-article> ) performed a pairwise fitness screen covering approximately one-third of all potential genetic interactions in yeast, examining 5.4 million gene-gene pairs and generating quantitative profiles for ∼75% of the genome. Of the pairwise interactions tested, about 3% of the genes investigated interact under the conditions tested. On the basis of these data, a reference map for the yeast genetic network was created. </jats:p>

<jats:title>Iapetus Revealed</jats:title> <jats:p> The striking appearance of Saturn's moon Iapetus—half black and half white—has puzzled astronomers for over three centuries. Now <jats:bold>Spencer and Denk</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="432" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177132">432</jats:related-article> , published online 10 December) present an explanation for this asymmetry: A thermally controlled runaway migration of water ice triggered by exogenic deposition of dark material on the moon's leading darker side, which faces the direction of motion of the moon in its orbit around Saturn. This mechanism is unique to Iapetus because it rotates slowly enough to allow large temperature variations to arise, it is small enough to allow long-range migration of water, and there is a source of dust to trigger the process. In a related paper, <jats:bold> Denk <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="435" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177088">435</jats:related-article> , published online 10 December) present data derived from the Cassini Imaging Science Subsystem that reveal that both dark and bright materials on the leading side of Iapetus are redder than their trailing-side counterparts. This asymmetry results from the deposition of dust and debris from other moons in the saturnian system—the very same process that initiates the thermal segregation proposed above. </jats:p>

<jats:title>Iapetus Revealed</jats:title> <jats:p> The striking appearance of Saturn's moon Iapetus—half black and half white—has puzzled astronomers for over three centuries. Now <jats:bold>Spencer and Denk</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="432" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177132">432</jats:related-article> , published online 10 December) present an explanation for this asymmetry: A thermally controlled runaway migration of water ice triggered by exogenic deposition of dark material on the moon's leading darker side, which faces the direction of motion of the moon in its orbit around Saturn. This mechanism is unique to Iapetus because it rotates slowly enough to allow large temperature variations to arise, it is small enough to allow long-range migration of water, and there is a source of dust to trigger the process. In a related paper, <jats:bold> Denk <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="435" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177088">435</jats:related-article> , published online 10 December) present data derived from the Cassini Imaging Science Subsystem that reveal that both dark and bright materials on the leading side of Iapetus are redder than their trailing-side counterparts. This asymmetry results from the deposition of dust and debris from other moons in the saturnian system—the very same process that initiates the thermal segregation proposed above. </jats:p>

<jats:title>Miniature Transport Engineers</jats:title> <jats:p> In its vegetative phase, the slime mold <jats:italic>Physarum polycephalum</jats:italic> “slimes” its way through the world seeking food. As it explores, it links previously found food sources with tubular structures. <jats:bold> Tero <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="439" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177894">439</jats:related-article> ) report that if food sources are deposited on a plate in a pattern corresponding in miniature to the positions of the cities that surround Tokyo, the resulting network of <jats:italic>Physarum</jats:italic> tubules that develops is rather similar in structure to the railroad network that connects the Japanese cities. A model was produced that describes the adaptive network development displayed by the slime mold. This biologically inspired model might provide insight into how to implement properties like resistance of transport systems to local failures into similar human-designed systems. </jats:p>

<jats:title>Dissecting Fermion Interactions</jats:title> <jats:p> Electrons, protons, and other building blocks of our universe belong to a class of particles we call fermions. Different interfermion interactions give rise to different forms of matter. In the strongly interacting resonant regime, however, fermionic systems have thermodynamic properties that depend only on the interparticle spacing and scaled temperature. <jats:bold> Horikoshi <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="442" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183012">442</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5964" page="419" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185570">Marwan</jats:related-article> </jats:bold> ) precisely characterize the thermodynamics in this universal regime for a system of ultracold fermionic lithium atoms. Analysis of a large number of trapped-gas density profiles confirms that the results depend neither on trap geometry nor the absolute temperature of the gas. The results are relevant to studies of all strongly interacting fermionic systems, including neutron stars and nuclear matter. </jats:p>

<jats:title>Colloids as Models</jats:title> <jats:p> Colloids are often used as analogs for atoms in order to study crystallization kinetics or glassy dynamics using particles that are much easier to observe and that move on much slower time scales. <jats:bold> Ganapathy <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="445" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179947">445</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5964" page="423" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1184947">Einstein and Stasevich</jats:related-article> </jats:bold> ) consider whether the analogous behavior extends to the growth of epitaxial films, a technique that is used in manufacturing. Controlling the rate of addition of the colloidal particles allowed the mapping of diffusional pathways during film nucleation and growth on a patterned substrate. The same relationships used to describe atomistic growth could be applied to the colloidal systems, but certain growth barriers such as those found at step edges and corners were controlled by diffusion rather than energetics. </jats:p>

<jats:title>How to Get a Date</jats:title> <jats:p> Radiometric dating relies on measuring the abundance of a radioactive isotope and/or its decay products. By knowing a decay rate and an isotopic starting abundance—both assumed to be constant—an age is determined. Using high-resolution mass spectrometry, <jats:bold> Brennecka <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="449" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1180871">449</jats:related-article> , published online 31 December; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5964" page="422" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1183755">Connelly</jats:related-article> </jats:bold> ) show that the known starting abundance of <jats:sup>238</jats:sup> U and <jats:sup>235</jats:sup> U isotopes in meteorites, which decay into <jats:sup>206</jats:sup> Pb and <jats:sup>207</jats:sup> Pb, respectively, is actually quite variable. Trace amounts of <jats:sup>247</jats:sup> Cm in the early solar system may have unexpectedly contributed additional <jats:sup>235</jats:sup> U, skewing the ratio. Pb-Pb dating, the method commonly used to date early solar system materials, may thus need a correction of up to 5 million years. </jats:p>

<jats:title>The Long and Short of It</jats:title> <jats:p> Semi-arid forests cover close to 18% of Earth's land surface. If climate change were to stimulate carbon accumulation in these areas, resulting changes in the forests could both promote climate cooling and warming: On one hand, forest growth would draw CO <jats:sub>2</jats:sub> from the atmosphere, providing a cooling effect on climate; on the other, as forests grew and became more dense, their albedo would decrease, which would warm climate. <jats:bold>Rotenberg and Yakir</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="451" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1179998">451</jats:related-article> ; see the Perspective by <jats:bold>Schimel</jats:bold> ) now report that a shift in peak photosynthetic activities from summer to early spring would, indeed, cause carbon accumulation by the forests, but that a suppression of reflected longwave radiation effect would complement the better-known (shortwave) albedo effect, doubling the amount of potential warming. Several decades of carbon accumulation would thus be necessary to counteract these radiative changes. </jats:p>

<jats:title>Stormy Weather</jats:title> <jats:p> One of the most active questions about the effects of global warming is whether, and how, it might affect the frequency and the strength of hurricanes. Some studies have suggested that warming will bring fewer, and less energetic, hurricanes, while others have claimed that we can expect more intense storms. <jats:bold> Bender <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="454" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1180568">454</jats:related-article> ; see the news story by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5964" page="399" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.2010.327.5964.327_399">Kerr</jats:related-article> </jats:bold> ) explore the influence of global warming on hurricane dynamics over the Atlantic Ocean with a state-of-the-art hurricane prediction model. The model predicts that the annual total number of hurricanes in the 21st century will be less than now, but also that the number of the most intense storms per year will increase. The largest increase of the most intense hurricane frequency is predicted in the western Atlantic, which suggests that Hispaniola, the Bahamas, and the Southeast coast of the United States could be at greater risk. </jats:p>