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<jats:p> The number of threatened and endangered (T&amp;E) species in the United States is increasing monthly and critical habitat is constantly being destroyed. The number of newly listed T&amp;E species greatly outweighs the number recovered from threatened extinction, and the federal and state governments demonstrate little desire to step in on behalf of species at risk. These ecological crises faced by endangered species ( <jats:xref ref-type="bibr">1</jats:xref> ) may be exacerbated by the application of one aspect of the Endangered Species Act (ESA)—habitat conservation plans (HCPs). Many T&amp;E species will be at a crossroads over the next few years and the strength and use of the ESA will determine their fate. </jats:p>

<jats:p>The crystal structures of a germline antibody Fab fragment and its complex with hapten have been solved at 2.1 â„« resolution. These structures are compared with the corresponding crystal structures of the affinity-matured antibody, 48G7, which has a 30,000 times higher affinity for hapten as a result of nine replacement somatic mutations. Significant changes in the configuration of the combining site occur upon binding of hapten to the germline antibody, whereas hapten binds to the mature antibody by a lock-and-key fit mechanism. The reorganization of the combining site that was nucleated by hapten binding is further optimized by somatic mutations that occur up to 15 â„« from bound hapten. These results suggest that the binding potential of the primary antibody repertoire may be significantly expanded by the ability of germline antibodies to adopt more than one combining-site configuration, with both antigen binding and somatic mutation stabilizing the configuration with optimal hapten complementarity.</jats:p>

<jats:p> Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as ∼6 × 10 <jats:sup>8</jats:sup> objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ <jats:sub>20</jats:sub> and 1996 TL <jats:sub>66</jats:sub> , have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified. </jats:p>

<jats:p>Leaf physiognomy provides estimates of environmental parameters, including mean annual enthalpy, which is a thermodynamic parameter of the atmosphere that varies with altitude. Analyses of 12 mid-Miocene floras from western Nevada indicate that this part of the Basin and Range Province stood ∼3 kilometers above sea level at 15 to 16 million years ago, which is 1 to 1.5 kilometers higher than its present altitude. Much, if not all, of the collapse to present-day altitudes seems to have been achieved by ∼13 million years ago. The crust in much of this area has been extended and thinned throughout the past 40 to 50 million years, and the isostatic balance of a thinning crust requires subsidence, not uplift as suggested by previous paleobotanical work.</jats:p>

<jats:p> Anion femtosecond photoelectron spectroscopy was used to follow the dynamics of the I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> (Ar) <jats:sub>6</jats:sub> and I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> (Ar) <jats:sub>20</jats:sub> clusters subsequent to photodissociation of the I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> chromophore. The experiments showed that photodissociation of the I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> moiety in I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> (Ar) <jats:sub>6</jats:sub> is complete by approximately 200 femtoseconds, just as in bare I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> , but also that attractive interactions between the departing anion fragment and the solvent atoms persisted for 1200 femtoseconds. Photodissociation of I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> (Ar) <jats:sub>20</jats:sub> results in caging of the I <jats:sub>2</jats:sub> <jats:sup>−</jats:sup> followed by recombination and vibrational relaxation on the excited <jats:italic>Ã</jats:italic> <jats:sup>2</jats:sup> Π <jats:sub> <jats:italic>g</jats:italic> ,3/2 </jats:sub> and the ground <jats:italic>X̃</jats:italic> <jats:sup>2</jats:sup> Σ <jats:sub> <jats:italic>u</jats:italic> </jats:sub> <jats:sup>+</jats:sup> states; these processes are complete in 35 and 200 picoseconds, respectively. </jats:p>

<jats:p> Resonant two-photon ionization, ultraviolet hole-burning, and resonant ion-dip infrared (RIDIR) spectroscopy were used to assign and characterize the hydrogen-bonding topology of two conformers of the benzene-(water) <jats:sub>8</jats:sub> cluster. In both clusters, the eight water molecules form a hydrogen-bonded cube to which benzene is surface-attached. Comparison of the RIDIR spectra with density functional theory calculations is used to assign the two (water) <jats:sub>8</jats:sub> structures in benzene-(water) <jats:sub>8</jats:sub> as cubic octamers of <jats:italic>D</jats:italic> <jats:sub>2</jats:sub> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> and <jats:italic>S</jats:italic> <jats:sub>4</jats:sub> symmetry, which differ in the configuration of the hydrogen bonds within the cube. OH stretch vibrational fundamentals near 3550 wave numbers provide unique spectral signatures for these “molecular ice cubes.” </jats:p>

<jats:p>When ICl adsorbs on a clean silicon (111)-(7×7) surface, the reaction is chemically selective. This process has been studied with the use of scanning tunneling microscopy and Auger spectroscopy. The dominant mechanism is the formation of silicon monoiodide by abstraction and the ejection of the chlorine atoms back into the gas phase. This pathway is not only chemically selective but also the least exothermic of all the possible reaction mechanisms. Although atomic chemical selectivity in gas-phase reactions is quite common, atomic chemical selectivity is unexpected in gas-surface reactions on clean surfaces because of the high density of reactive sites.</jats:p>