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<jats:p> Compressibilities were determined for four pseudobrookite-type magnesium titanate (MgTi <jats:sub>2</jats:sub> O <jats:sub>5</jats:sub> ) samples with different degrees of Mg-Ti disorder. Compressibilities of <jats:italic>a</jats:italic> and <jats:italic>c</jats:italic> axes in disordered MgTi <jats:sub>2</jats:sub> O <jats:sub>5</jats:sub> were 10% and 7% greater, respectively, than those of a relatively ordered sample. The estimated bulk moduli for fully ordered and disordered MgTi <jats:sub>2</jats:sub> O <jats:sub>5</jats:sub> are 167 ± 1 and 158 ± 1 gigapascals, respectively. This difference is an order of magnitude greater than that predicted by bulk modulus–volume systematics. Cation order, in addition to composition and structure information, is thus important when documenting the elasticity of crystalline phases. Elastic constants of mantle silicates that are subject to pressure-induced cation ordering must be reevaluated. </jats:p>

<jats:p> Satellite observations by the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) have produced global measurements of hydroxyl (OH) in the atmosphere. These observations reveal a sharp peak in OH density near an altitude of 65 to 70 km and are thus consistent with observations from the Halogen Occultation Experiment (HALOE) on the NASA Upper Atmosphere Research Satellite (UARS), which showed an unexplained H <jats:sub>2</jats:sub> O layer at the same level. Analysis of stratopause (about 50 kilometers) OH measurements and coincident ozone observations from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment reveals that the catalytic loss of ozone attributable to odd-hydrogen chemistry is less than that predicted with standard chemistry. Thus, the dominant portion of the ozone deficit problem in standard models is a consequence of overestimation of the OH density in the upper stratosphere and lower mesosphere. </jats:p>

<jats:p>The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.</jats:p>

<jats:p>Numerical simulations of homogeneous crystal nucleation with a model for globular proteins with short-range attractive interactions showed that the presence of a metastable fluid-fluid critical point drastically changes the pathway for the formation of a crystal nucleus. Close to this critical point, the free-energy barrier for crystal nucleation is strongly reduced and hence, the crystal nucleation rate increases by many orders of magnitude. Because the location of the metastable critical point can be controlled by changing the composition of the solvent, the present work suggests a systematic approach to promote protein crystallization.</jats:p>

<jats:p> The linear and nonlinear (χ <jats:sup>(2)</jats:sup> ) optical responses of Langmuir monolayers of organically functionalized silver quantum dots were measured as a continuous function of interparticle separation under near-ambient conditions. As the distance between metal surfaces was decreased from 12 to ∼5 angstroms, both quantum and classical effects were observed in the optical signals. When the separation was less than 5 angstroms, the optical second-harmonic generation (SHG) response exhibited a sharp discontinuity, and the linear reflectance and absorbance began to resemble those of a thin metallic film, indicating that an insulator-to-metal transition occurred. This transition was reversible. </jats:p>

<jats:p>Dendrimers constitute a class of polymers with unique properties and applications resulting from the presence of internal voids and of a large number of functionalities on the surface. The development of a macromolecular chemistry within the cavities of dendrimers is illustrated here. Two examples of construction of six dendrimer units within the cascade structure of a main dendrimer are reported. The preparation of these multidendritic systems involves the regioselective modification of the framework of the central dendrimer to create internal reactive centers, followed by the stepwise synthesis of the six dendritic macromolecules.</jats:p>

<jats:p>Infants' long-term retention of the sound patterns of words was explored by exposing them to recordings of three children's stories for 10 days during a 2-week period when they were 8 months old. After an interval of 2 weeks, the infants heard lists of words that either occurred frequently or did not occur in the stories. The infants listened significantly longer to the lists of story words. By comparison, a control group of infants who had not been exposed to the stories showed no such preference. The findings suggest that 8-month-olds are beginning to engage in long-term storage of words that occur frequently in speech, which is an important prerequisite for learning language.</jats:p>

<jats:p>Mature single-positive (SP) T lymphocytes enter a “resting” state in which they are proliferatively quiescent and relatively resistant to apoptosis. The molecular mechanisms regulating this quiescent phenotype were unknown. Here it was found that the expression of a Kruppel-like zinc finger transcription factor, lung Kruppel-like factor (LKLF), is developmentally induced during the maturation of SP quiescent T cells and rapidly extinguished after SP T cell activation. LKLF-deficient T cells produced by gene targeting had a spontaneously activated phenotype and died in the spleen and lymph nodes from Fas ligand–induced apoptosis. Thus, LKLF is required to program the quiescent state of SP T cells and to maintain their viability in the peripheral lymphoid organs and blood.</jats:p>

<jats:p> The cause of neurodegeneration in Huntington's disease (HD) is unknown. Patients with HD have an expanded NH <jats:sub>2</jats:sub> -terminal polyglutamine region in huntingtin. An NH <jats:sub>2</jats:sub> -terminal fragment of mutant huntingtin was localized to neuronal intranuclear inclusions (NIIs) and dystrophic neurites (DNs) in the HD cortex and striatum, which are affected in HD, and polyglutamine length influenced the extent of huntingtin accumulation in these structures. Ubiquitin was also found in NIIs and DNs, which suggests that abnormal huntingtin is targeted for proteolysis but is resistant to removal. The aggregation of mutant huntingtin may be part of the pathogenic mechanism in HD. </jats:p>

<jats:p>A distant relative of catalase that is specialized for metabolism of a fatty acid hydroperoxide was identified. This heme peroxidase occurs in coral as part of a fusion protein, the other component of which is a lipoxygenase that forms the hydroperoxide substrate. The end product is an unstable epoxide (an allene oxide) that is a potential precursor of prostaglandin-like molecules. These results extend the known chemistry of catalase-like proteins and reveal a distinct type of enzymatic construct involved in the metabolism of polyunsaturated fatty acids.</jats:p>