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<jats:title>A traffic jam of air</jats:title> <jats:p>Persistent meandering of the jet stream can cause atmospheric blocking of prevailing eastward winds and result in weather extremes such as heat waves in the midlatitudes. Nakamura and Huang interpret the poorly understood origins of these systems as the meteorological equivalents of traffic congestion on a highway and show how they can be described by analogous mathematical theory. Climate change may affect the frequency of blocking as well as its geographic distribution, reflecting a simultaneous shift in the structure of the stationary atmospheric waves and the regional capacity of the jet stream.</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" issue="6397" page="42" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat0721">42</jats:related-article> </jats:p>

<jats:title>Covalent organic frameworks writ large</jats:title> <jats:p> Covalent organic framework (COF) materials have been difficult to characterize structurally and to exploit because they tend to form powders or amorphous materials. Ma <jats:italic>et al.</jats:italic> studied a variety of three-dimensional COFs based on imine linkages (see the Perspective by Navarro). They found that the addition of aniline inhibited nucleation and allowed the growth of crystals large enough for single-crystal x-ray diffraction studies. Evans <jats:italic>et al.</jats:italic> describe a two-step process in which nanoscale seeds of boronate ester–linked two-dimensional COFs can be grown into micrometer-scale single crystals by using a solvent that suppresses the nucleation of additional nanoparticles. Transient absorption spectroscopy revealed superior charge transport in these crystallites compared with that observed in conventional powders. </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" issue="6397" page="48" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat7679">48</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6397" page="52" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aar7883">52</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6397" page="35" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau1701">35</jats:related-article> </jats:p>

<jats:title>Covalent organic frameworks writ large</jats:title> <jats:p> Covalent organic framework (COF) materials have been difficult to characterize structurally and to exploit because they tend to form powders or amorphous materials. Ma <jats:italic>et al.</jats:italic> studied a variety of three-dimensional COFs based on imine linkages (see the Perspective by Navarro). They found that the addition of aniline inhibited nucleation and allowed the growth of crystals large enough for single-crystal x-ray diffraction studies. Evans <jats:italic>et al.</jats:italic> describe a two-step process in which nanoscale seeds of boronate ester–linked two-dimensional COFs can be grown into micrometer-scale single crystals by using a solvent that suppresses the nucleation of additional nanoparticles. Transient absorption spectroscopy revealed superior charge transport in these crystallites compared with that observed in conventional powders. </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" issue="6397" page="48" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat7679">48</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6397" page="52" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aar7883">52</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6397" page="35" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aau1701">35</jats:related-article> </jats:p>

<jats:title>A single-photon gate</jats:title> <jats:p> A long-standing goal in optics is to produce a solid-state alloptical transistor, in which the transmission of light can be controlled by a single photon that acts as a gate or switch. Sun <jats:italic>et al.</jats:italic> used a solid-state system comprising a quantum dot embedded in a photonic crystal cavity to show that transmission through the cavity can be controlled with a single photon. The single photon is used to manipulate the occupation of electronic energy levels within the quantum dot, which in turn changes its optical properties. With the gate open, about 28 photons can get through the cavity on average, thus demonstrating single-photon switching and the gain for an optical transistor. </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" issue="6397" page="57" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat3581">57</jats:related-article> </jats:p>

<jats:title>In search of the right diamond defect</jats:title> <jats:p> Certain defects in diamond are among the most promising physical implementations of qubits, the building blocks of quantum computers. However, identifying a defect with balanced properties is tricky: Nitrogen vacancy centers have a long lifetime but comparatively poor optical properties, whereas negatively charged silicon vacancy centers have the opposite characteristics. Rose <jats:italic>et al.</jats:italic> used careful materials engineering to stabilize the neutral charge state of silicon vacancy centers and found that they combine long coherence times with excellent optical properties. </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" issue="6397" page="60" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aao0290">60</jats:related-article> </jats:p>

<jats:title>Motion picture of a conical intersection</jats:title> <jats:p> In most chemical reactions, electrons move earlier and faster than nuclei. It is therefore common to model reactions by using potential energy surfaces that depict nuclear motion in a particular electronic state. However, in certain cases, two such surfaces connect in a conical intersection that mingles ultrafast electronic and nuclear rearrangements. Yang <jats:italic>et al.</jats:italic> used electron diffraction to obtain time-resolved images of CF <jats:sub>3</jats:sub> I molecules traversing a conical intersection in the course of photolytic cleavage of the C–I bond (see the Perspective by Fielding). </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" issue="6397" page="64" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat0049">64</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6397" page="30" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat6002">30</jats:related-article> </jats:p>

<jats:title>Cyclobutanes sourced right from ethylene</jats:title> <jats:p>Ethylene is one of the highest-volume commodity chemicals manufactured from fossil fuels. It is mainly used to make plastic, although its ready availability incentivizes its expanded use in pharmaceutical synthesis. Pagar and RajanBabu now report that a cobalt catalyst can couple ethylene with enynes (another comparatively inexpensive feedstock bearing carbon-carbon double and triple bonds) to make complex chiral molecules. Initially, the ethylene reacts with the enyne's triple bond to form an isolable cyclobutene compound. At longer reaction times, the same catalyst can add a second equivalent of ethylene enantioselectively to form cyclobutanes with a quaternary chiral carbon center.</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" issue="6397" page="68" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aat6205">68</jats:related-article> </jats:p>

<jats:title>Controlling zinc in the oceans</jats:title> <jats:p> Zinc, a key micronutrient for marine phytoplankton, has a global distribution remarkably similar to that of silicic acid, even though Zn and Si have very different biogeochemical cycles. Weber <jats:italic>et al.</jats:italic> investigated why this is so by combining model calculations and observations. They found that biological uptake in the Southern Ocean and reversible scavenging of Zn onto sinking particles both affect the distribution of Zn in the ocean. Thus, Zn and Si distributions will be affected differently by future changes in ocean temperature, pH, and carbon fluxes. </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" issue="6397" page="72" related-article-type="in-this-issue" vol="361" xlink:href="10.1126/science.aap8532">72</jats:related-article> </jats:p>