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<jats:title>Topological protection for lasers</jats:title> <jats:p> Ideas based on topology, initially developed in mathematics to describe the properties of geometric space under deformations, are now finding application in materials, electronics, and optics. The main driver is topological protection, a property that provides stability to a system even in the presence of defects. Harari <jats:italic>et al.</jats:italic> outline a theoretical proposal that carries such ideas over to geometrically designed laser cavities. The lasing mode is confined to the topological edge state of the cavity structure. Bandres <jats:italic>et al.</jats:italic> implemented those ideas to fabricate a topological insulator laser with an array of ring resonators. The results demonstrate a powerful platform for developing new laser systems. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aar4003">eaar4003</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aar4005">eaar4005</jats:related-article> </jats:p>

<jats:title>Daily transcription cycling in the baboon</jats:title> <jats:p> Much of our knowledge about the important effects of circadian rhythms in physiology comes from studies of mice, which are nocturnal. Mure <jats:italic>et al.</jats:italic> report transcriptional profiles from many tissues and brain regions in baboons over a 24-hour period (see the Perspective by Millius and Ueda). The results emphasize how extensive rhythmic expression is, with more than 80% of protein-coding genes involved. They also highlight unanticipated differences between the mouse and baboon in the cycling of transcripts in various tissues. The findings provide a comprehensive analysis of circadian variation in gene expression for a diurnal animal closely related to humans. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aao0318">eaao0318</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6381" page="1210" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aat3211">1210</jats:related-article> </jats:p>

<jats:p> Huang and Xu argue that the <jats:italic>cyclo</jats:italic> -N <jats:sub>5</jats:sub> <jats:sup>–</jats:sup> ion in (N <jats:sub>5</jats:sub> ) <jats:sub>6</jats:sub> (H <jats:sub>3</jats:sub> O) <jats:sub>3</jats:sub> (NH <jats:sub>4</jats:sub> ) <jats:sub>4</jats:sub> Cl we described in our report is theoretically unfavorable and is instead protonated. Their conclusion is invalid, as they use an improper method to assess the proton transfer in a solid crystal structure. We present an in-depth experimental and theoretical analysis of (N <jats:sub>5</jats:sub> ) <jats:sub>6</jats:sub> (H <jats:sub>3</jats:sub> O) <jats:sub>3</jats:sub> (NH <jats:sub>4</jats:sub> ) <jats:sub>4</jats:sub> Cl that supports the results in the original paper. </jats:p>

<jats:p> Zhang <jats:italic>et al</jats:italic> . (Reports, 27 January 2017, p. 374) reported synthesis of a <jats:italic>cyclo</jats:italic> -N <jats:sub>5</jats:sub> <jats:sup>–</jats:sup> ion putatively stabilized in a solid-state salt by hydrogen bonding from surrounding counterions. We performed theoretical calculations suggesting that HN <jats:sub>5</jats:sub> would be favored over the anion in the reported pentazolate salt via proton transfer. </jats:p>

<jats:title>Topological protection for lasers</jats:title> <jats:p> Ideas based on topology, initially developed in mathematics to describe the properties of geometric space under deformations, are now finding application in materials, electronics, and optics. The main driver is topological protection, a property that provides stability to a system even in the presence of defects. Harari <jats:italic>et al.</jats:italic> outline a theoretical proposal that carries such ideas over to geometrically designed laser cavities. The lasing mode is confined to the topological edge state of the cavity structure. Bandres <jats:italic>et al.</jats:italic> implemented those ideas to fabricate a topological insulator laser with an array of ring resonators. The results demonstrate a powerful platform for developing new laser systems. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aar4003">eaar4003</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aar4005">eaar4005</jats:related-article> </jats:p>

<jats:p>The tragic shooting at a school in Parkland, Florida, last month triggered another round of proposals from local, state, and federal policymakers about controlling firearm-related violence without violating broad interpretations of the rights to keep and bear arms provided by the U.S. Constitution. Unfortunately, there is only very sparse scientific evidence that can help figure out which policies will be effective. Earlier this month, the RAND Corporation released a comprehensive analysis on gun policy in the United States,* and among its conclusions is that too few policies and outcomes have been the subject of rigorous scientific investigation. Even the seemingly popular view that violent crime would be reduced by laws prohibiting the purchase or possession of guns by individuals with mental illness was deemed to have only moderate supporting evidence. If the nation is serious about getting firearm-related violence under control, it must rise above its aversion to providing financial support for firearm-related research, and the scientific community will have to expeditiously carry out the needed research.</jats:p>

<jats:p>A roundup of weekly science policy and related news.</jats:p>

<jats:p>Advanced stone tools, pigment, and extensive networks emerged as environment changed.</jats:p>