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<jats:p>Gravity field measurements by the Cassini spacecraft suggest that Titan's interior was too cold for the primordial mixture of ice and rock to melt and fully separate.</jats:p>

<jats:p>Changes in ocean chemistry could exacerbate global warming by raising the atmospheric concentration of nitrous oxide, a potent greenhouse gas.</jats:p>

<jats:title>Spite and Altruism</jats:title> <jats:p> Many social animal species can exhibit altruism—the loss of their own individual fitness to help others. One of the most extreme examples is that of the social insects (bees and ants) where, in a colony of related individuals, only a few reproduce. The nonreproductive individuals contribute to the success of the young of these individuals thereby increasing their collective fitness. Spite occurs when an individual damages its own fitness to harm another's. This negative form of altruism can arise if the victim is less related to the perpetrator than an average member of the population. <jats:bold>West and Gardner</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1341" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1178332">1341</jats:related-article> ) review the current literature on the origins and maintenance of altruism and spite and the associated phenomenon of greenbeards. Greenbeards use a visible inherited character to signal relatedness and spur altruism. Greenbeard genes provide a mechanism to link the genes that encode cooperative behavior with those that cause cooperators to associate. These traits maybe an ornament or a type of behavior, and they may result in altruistic or spiteful behavior. </jats:p>

<jats:title>Thalidomide Teratogenicity Target</jats:title> <jats:p> In the late 1950s and early 1960s, thalidomide was prescribed to pregnant women as a cure for morning sickness, but it was then found to have developmental defects, most obviously, stunted limbs in thousands of babies. Although its use was banned worldwide, thalidomide has since been found to be a valuable treatment for a range of cancers, inflammatory disorders, and leprosy. Several hypotheses have been proposed, but the mechanism of action of thalidomide is unknown. Using zebrafish and chicken as animal models, <jats:bold> Ito <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="1345" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177319">1345</jats:related-article> ) show that the protein cereblon is a primary target of thalidomide. Thalidomide exerts teratogenic effects by binding to cereblon and inhibiting associated enzymatic activity important for limb development. Knowing the mechanism of action of thalidomide should encourage the search for thalidomide derivatives without teratogenic activity. </jats:p>

<jats:title>Solar Meridional Flow</jats:title> <jats:p> The surface of the Sun is composed of plasma that exhibits observable flow patterns. The weakest flow pattern occurs along meridional lines from the equator toward the poles. <jats:bold>Hathaway and Rightmire</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1350" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1181990">1350</jats:related-article> ) measured the meridional flow using observations taken with the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory between 1996 and 2009 and found that meridional flow varied with the solar cycle, such that flow was faster during the 2004–2009 minimum than during the 1996–1997 minimum. This finding provides further evidence that the last solar minimum was peculiar by comparison with previous cycles. </jats:p>

<jats:title>Scattered and Coupled</jats:title> <jats:p> Cavity electrodynamics explores the coupling of light with matter—ideally, that of a single photon with a single atom. Typically, this requires that the photon and the atom be confined to increase the likelihood of interaction, but scattering of light is an unavoidable product of an engineered device and is usually considered to be detrimental because it leads to loss of the photons from the cavity. <jats:bold> Sapienza <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="1352" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1185080">1352</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="5971" page="1333" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1187084">Wiersma</jats:related-article> </jats:bold> ) saw extreme light scattering as an opportunity for the spontaneous generation of localized modes of light that can be exploited to induce light-matter coupling. Thus, working with a process where scattering is considered a resource rather than a nuisance, as in this case, may prove useful for realizing robust quantum information devices. </jats:p>

<jats:title>Nanoparticles, Lightly Twisted</jats:title> <jats:p> The helical structures that are widespread in natural macromolecules result from well-coordinated bonding interactions and affect their physical properties in striking ways. To obtain helical nanoparticles, <jats:bold> Srivastava <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="1355" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1177218">1355</jats:related-article> , published online 11 February) slowly oxidized cadmium-tellurium under visible light and assembled ribbons of nanostructure. The ribbons were persuaded to twist into helices because they were doped with cadmium sulfide nanoparticles, which underwent surface oxidation and caused localized stresses that could only be relieved by a conformational change. The pitch of the twisted ribbons that were produced could be controlled by the intensity of illumination applied. This behavior offers promise for application in the development of materials with interesting optical properties. </jats:p>

<jats:title>Slightly Cracked</jats:title> <jats:p> While there are detailed theories to explain the propagation of a crack in the bulk of a material, our understanding of cracking breaks down near the tip of the crack. Experimentally, it is very hard to observe the propagation of a crack at the tip region because it tends to move very quickly. <jats:bold> Livne <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="1359" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1180476">1359</jats:related-article> ) approached this problem by working with a polyacrylamide gel in which cracks progress slowly enough to monitor them. A hierarchy of linear and nonlinear regions was observed through which energy is transported before being dissipated by the growing crack. How stresses are distributed during cracking will determine whether the resulting failure will be brittle or ductile. </jats:p>

<jats:title>An Electrochemical Landscape</jats:title> <jats:p> Electrochemical detection is an analytical method that has been used for a wide range of purposes, including trace chemical analysis, glucose and neurotransmitter monitoring, DNA and protein detection, and electrocatalysis. Scanning electrochemical microscopy maps changes in the local electrochemical current along a surface in a serial way, but serial probing can disrupt the process under study. <jats:bold> Shan <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="1363" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186476">1363</jats:related-article> ) show that optical measurements of surface plasmon resonances can be used as a less disruptive way of determining the concentration of electrochemically active species on gold-coated glass slides and their current density. This method can be used for a wide range of applications from analyzing DNA and protein microarrays and enzyme-amplified biosensors to probing the activities of cells. </jats:p>

<jats:title>Titan Through to the Core</jats:title> <jats:p> Gravity measurements acquired from orbiting spacecraft can provide useful information about the interior of planets and their moons. <jats:bold> Iess <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="1367" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1182583">1367</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="5971" page="1338" related-article-type="in-this-issue" vol="327" xlink:href="10.1126/science.1186255">Sohl</jats:related-article> </jats:bold> ) used gravity data from four flybys of the Cassini spacecraft past Saturn's moon, Titan, to model the moon's gravity field and probe its deep interior structure. Their analysis implies that Titan is a partially differentiated body with a core consisting of a mix of ice and rock or hydrated silicates. </jats:p>