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<jats:title>Majoranas Arrive</jats:title> <jats:p> When a negatively charged electron meets a positron—its positively charged antiparticle—they annihilate each other in a flash of gamma rays. A Majorana fermion, on the other hand, is a neutral particle, which is its own antiparticle. No sightings of a Majorana have been reported in the elementary particle world, but recently they have been proposed to exist in solid-state systems and suggested to be of interest as a quantum computing platform. <jats:bold> Mourik <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="1003" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222360">1003</jats:related-article> , published online 12 April; see the cover; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="989" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1223302">Brouwer</jats:related-article> </jats:bold> ) set up a semiconductor nanowire contacted on each end by a normal and a superconducting electrode that revealed evidence of Majorana fermions. </jats:p>

<jats:title>Tiny Tinny Bumps</jats:title> <jats:p> One challenge in moving to three-dimensional integrated circuit architectures is the need for aligned interconnects to join neighboring layers. <jats:bold> Hsiao <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="1007" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216511">1007</jats:related-article> ) applied rapid stirring to the direct current electroplating of copper to produce films with oriented copper grains that have a high density of nanotwin defects. The resulting material was an excellent platform for the growth of copper-tin intermetallic compounds in the form of arrays of microbumps potentially suitable for the soldering of electronic components. </jats:p>

<jats:title>Growing in Liquid</jats:title> <jats:p> The ability to control the growth of materials at the nanometer scale is key to nanotechnology. Materials grown in liquids, however, are difficult to track on a particle-by-particle basis during growth. Two studies used an in situ liquid cell to follow the formation of larger nanoparticles or nanorods grown in solvents using high-resolution transmission electron microscopes. <jats:bold> Liao <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="1011" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219185">1011</jats:related-article> ) watched platinum iron nanorods form from kinked chains of connected nanoparticles that gradually reoriented and straightened to form rigid rods. <jats:bold> Li <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="1014" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219643">1014</jats:related-article> ) observed the coalescence of iron oxyhydroxide nanoparticles through an oriented attachment mechanism, whereby two similar particles rotated until their corresponding crystal lattices aligned. </jats:p>

<jats:title>Growing in Liquid</jats:title> <jats:p> The ability to control the growth of materials at the nanometer scale is key to nanotechnology. Materials grown in liquids, however, are difficult to track on a particle-by-particle basis during growth. Two studies used an in situ liquid cell to follow the formation of larger nanoparticles or nanorods grown in solvents using high-resolution transmission electron microscopes. <jats:bold> Liao <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="1011" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219185">1011</jats:related-article> ) watched platinum iron nanorods form from kinked chains of connected nanoparticles that gradually reoriented and straightened to form rigid rods. <jats:bold> Li <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="1014" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219643">1014</jats:related-article> ) observed the coalescence of iron oxyhydroxide nanoparticles through an oriented attachment mechanism, whereby two similar particles rotated until their corresponding crystal lattices aligned. </jats:p>

<jats:title>Maximizing Molecular Pore Diameters</jats:title> <jats:p> Amorphous materials, such as activated carbon, can have pore diameters of several nanometers, but the synthesis of ordered structures with very large pore diameters is often thwarted by the creation of interpenetrating networks or difficulties in removing guest molecules. <jats:bold> Deng <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="1018" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220131">1018</jats:related-article> ) avoided these problems in the synthesis of metal-organic frameworks (MOFs) with very large diameters (some exceeding 3 nanometers) by using a combination of short and very long linking groups. The compounds formed channels almost 10 nanometers in diameter that could be visualized by electron microscopy and that were large enough to accommodate protein molecules. </jats:p>

<jats:title>Subterranean Eruption Clues</jats:title> <jats:p> Volcano monitoring relies upon detecting changing physical conditions around an active source, such as increased seismicity or ground deformation; however, relating these behaviors to magmatic processes below ground remains challenging. The geochemical signatures of erupted magmatic crystals, including chemically distinct zones formed during growth and cooling, provide clues as to the conditions of the magma chamber prior to the eruption. Through a combination of chemical analysis of orthopyroxene crystals and chronometry based on diffusion, <jats:bold> Saunders <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="1023" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220066">1023</jats:related-article> ) were able to link the magmatic processes and seismic events leading up to and during the 1980–1986 series of eruptions at Mount St. Helens, USA. The seismic events corresponded to earthquakes caused by magma degassing and ground movement—events of which are routinely detected with geophysical instruments. </jats:p>

<jats:title>New Digs</jats:title> <jats:p> Many studies predict range alterations among species in response to climate change. Species, however, cannot be thought of as truly independent entities, because they all exist as a part of an interacting community. Most discussions of such interactions have focused on the potential restrictions they might place on range expansion; however, <jats:bold> Pateman <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="1028" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216980">1028</jats:related-article> ) show that climate change has the potential to increase the number of species that can interact and thus facilitate expansion. British data collected by the general public on sightings of the Brown Argus butterfly and its host plants revealed an increased affiliation between the butterflies and a previously little-used group of plants. As summers warmed, populations associated with the new host were more productive than those associated with the more “traditional” host, which facilitated expansion of the butterflies into novel regions. </jats:p>

<jats:title>Finessing Crystal Analysis</jats:title> <jats:p> Protein crystallography has revolutionized our understanding of a whole variety of biological processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="986" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222162">Evans</jats:related-article> </jats:bold> ). In crystallography, the measure of agreement between the data and the calculated model is not on the same scale as the measure of data quality, making it challenging to choose an optimal high resolution limit beyond which the data should be discarded. Now, <jats:bold>Karplus and Diederichs</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1030" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218231">1030</jats:related-article> ) introduce a statistical model that assesses agreement of model and data accuracy on the same scale. Determining the structures of biological macromolecules by x-ray crystallography requires solving the phase problem. The two techniques that dominate phase evaluation (multi- and single-wavelength anomalous diffraction) rely on element-specific scattering from incorporated heavy atoms. <jats:bold> Liu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="1033" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218753">1033</jats:related-article> ) present procedures for routine structure determination of native proteins with no heavy atom incorporation. The technique, which relies on combining data from multiple crystals, was used to determine the structures of four native proteins, including a 1200-residue complex. </jats:p>

<jats:title>Finessing Crystal Analysis</jats:title> <jats:p> Protein crystallography has revolutionized our understanding of a whole variety of biological processes (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="986" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1222162">Evans</jats:related-article> </jats:bold> ). In crystallography, the measure of agreement between the data and the calculated model is not on the same scale as the measure of data quality, making it challenging to choose an optimal high resolution limit beyond which the data should be discarded. Now, <jats:bold>Karplus and Diederichs</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1030" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218231">1030</jats:related-article> ) introduce a statistical model that assesses agreement of model and data accuracy on the same scale. Determining the structures of biological macromolecules by x-ray crystallography requires solving the phase problem. The two techniques that dominate phase evaluation (multi- and single-wavelength anomalous diffraction) rely on element-specific scattering from incorporated heavy atoms. <jats:bold> Liu <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="1033" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218753">1033</jats:related-article> ) present procedures for routine structure determination of native proteins with no heavy atom incorporation. The technique, which relies on combining data from multiple crystals, was used to determine the structures of four native proteins, including a 1200-residue complex. </jats:p>

<jats:title>Human Argonaute Revealed</jats:title> <jats:p> RNA interference (RNAi) is mediated by Argonaute (Ago) proteins, which bind small regulatory RNAs that have sequence complementarity to target RNAs destined to be silenced. The structure of bacterial homologs of the Ago proteins, and fragments of eukaryotic Ago proteins, have provided initial insights into Ago function. Now, <jats:bold>Schirle and MacRae</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1037" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221551">1037</jats:related-article> , published online 26 April; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6084" page="985" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1223549">Kaya and Doudna</jats:related-article> </jats:bold> ) have determined the structure of the full-length human Ago protein bound to a single-stranded (ss) guide RNA. Within the bilobed structure, eight nucleotides of the ssRNA are visibly positioned in the RNA-guide, strand-binding site. The “seed” region of the ssRNA has its Watson-and-Crick base edges exposed to solvent, likely aiding target recognition. The location of two free tryptophans in the Piwi domain suggests a possible recruitment site for Ago-interacting proteins. </jats:p>