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<jats:p> Some corals release their gametes all at once, dramatically increasing the chances of any one gamete being fertilized. In a report in this issue, Clifton <jats:italic>et al</jats:italic> . ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1116" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5303.1116" xlink:type="simple">1116</jats:related-article> ) demonstrate that a seaweed, <jats:italic>Halimeda</jats:italic> , also engages in synchronous spawning. Hay's Perspective discusses the natural history of these seaweeds and their efficient use of time in their growth and reproduction. </jats:p>

<jats:p> Cells can die in two ways: in a disorderly, destructive process called necrosis or by programmed cell death (or apoptosis), an orderly series of biochemical events that neatly eliminate the cell. Four reports in this week's issue by Chinnaiyan ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1122" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5303.1122" xlink:type="simple">1122</jats:related-article> ), Wu ( <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1126" related-article-type="in-this-issue" vol="275" xlink:href="10.1126/science.275.5303.1126" xlink:type="simple">1126</jats:related-article> ), Yang (p. 1129), and Kluck (p. 1132) elucidate two critical steps in the biochemical cascade of programmed cell death. In his Perspective, Golstein describes how these demonstrations—that the <jats:italic>Caenorhabditis elegans</jats:italic> protein CED-4 directly contacts CED-3 and CED-9 and that Bcl-2 causes release of cytochrome c from mitochondria—advance our understanding of programmed cell death. </jats:p>

<jats:p> The complex phase diagram of high-critical temperature ( <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> ) superconductors can be deduced from an <jats:italic>SO</jats:italic> (5) symmetry principle that unifies antiferromagnetism and <jats:italic>d</jats:italic> -wave superconductivity. The approximate <jats:italic>SO</jats:italic> (5) symmetry has been derived from the microscopic Hamiltonian, and it becomes exact under renormalization group flow toward a bicritical point. This symmetry enables the construction of a <jats:italic>SO</jats:italic> (5) quantum nonlinear σ model that describes the phase diagram and the effective low-energy dynamics of the system. This model naturally explains the basic phenomenology of the high- <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> superconductors from the insulating to the underdoped and the optimally doped region. </jats:p>

<jats:p>The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and “conducting wires” in a very flexible and convenient manner.</jats:p>

<jats:p> Pentacoordinate hydrogen atoms were identified by single-crystal neutron diffraction analysis of [N(CH <jats:sub>3</jats:sub> ) <jats:sub>4</jats:sub> ] <jats:sub>3</jats:sub> [H <jats:sub>2</jats:sub> Rh <jats:sub>13</jats:sub> (CO) <jats:sub>24</jats:sub> ]. The hydrogen atoms are located in square pyramidal cavities of the Rh <jats:sub>13</jats:sub> cluster, in positions almost coplanar with the Rh <jats:sub>4</jats:sub> faces on the surface of the cluster. They are slightly displaced inward, toward the central rhodium atom of the cluster, with average H-Rh(central) and H-Rh(surface) distances of 1.84(2) and 1.97(2) angstroms, respectively. This result shows that hydrogen, which normally forms only one bond, can be attached to five other atoms simultaneously in a large metal cluster. </jats:p>

<jats:p> Optical detection and spectroscopy of single molecules and single nanoparticles have been achieved at room temperature with the use of surface-enhanced Raman scattering. Individual silver colloidal nanoparticles were screened from a large heterogeneous population for special size-dependent properties and were then used to amplify the spectroscopic signatures of adsorbed molecules. For single rhodamine 6G molecules adsorbed on the selected nanoparticles, the intrinsic Raman enhancement factors were on the order of 10 <jats:sup>14</jats:sup> to 10 <jats:sup>15</jats:sup> , much larger than the ensemble-averaged values derived from conventional measurements. This enormous enhancement leads to vibrational Raman signals that are more intense and more stable than single-molecule fluorescence. </jats:p>

<jats:p>Continuous monitoring of submillisecond free-solution dynamics of individual rhodamine-6G molecules and 30-base single-stranded DNA tagged with rhodamine was achieved. Fluorescence images were recorded from the same set of isolated molecules excited either through the evanescent field at the quartz-liquid interface or as a thin layer of solution defined by micron-sized wires, giving diffraction-limited resolution of interconnected attoliter volume elements. The single-molecule diffusion coefficients were smaller and the unimolecular photodecomposition lifetimes were longer for the dye-DNA covalent complex as compared with those of the dye molecule itself. Unlike bulk studies, stochastic behavior was found for individual molecules of each type, and smaller diffusion coefficients were observed.</jats:p>