Effects of Surface Relaxation on Enantiospecific Adsorption on Naturally Chiral Pt Surfaces

Many high Miller index metals surfaces are naturally chiral, offering opportunities for performing enantiospecific chemistry. Previous theoretical treatments of adsorption on these surfaces have used surfaces truncated from bulk crystals. This paper examines the effect of surface relaxation on enantiospecific adsorption on chiral Pt surfaces by using relaxed surface structures determined using density functional theory.     

Preparation and characterization of cellulose acetate organic/inorganic hybrid films

A series of organic/inorganic hybrid (OIH) films were prepared using cellulose acetate (CA) as the organic component and tetraethyl orthosilicate (TEOS) as the inorganic component. The chemical, morphological, and mechanical properties of these films were evaluated with a variety of analytical techniques. The results of these evaluations showed that crosslinked CA OIH films were formed during the sol-gel reactions. The structure of OIH films was very sensitive to the CA/TEOS ratio and film formation conditions. All of the films with added TEOS were two phase on a molecular level, i.e., inorganic TEOS domains surrounded by a CA matrix. Under some film formation conditions the presence of TEOS, a nonsolvent for CA, led to solvent/nonsolvent phase separation on the micron scale. © 1995 John Wiley & Sons, Inc.     

Adsorption of aroma chemicals on cotton fabric from aqueous systems

The adsorption of aroma chemicals on cotton fabric was studied relative to the surfactant concentration, surfactant type, water solubility, and fiber morphology. The adsorption increased with increasing surfactant concentration to a maximum near the critical micelle concentration, then decreased with further increases in surfactant concentration. The adsorption also was found to be highly dependent on the fiber surface area and pore structure; dramatic differences were observed between untreated and mercerized cotton fabric and are believed to be due to morphological differences. Cationic and anionic surfactants increased the aroma chemical adsorption, which varied with surfactant type, with cetyltrimethylammonium chloride (CTAC)>sodium dodecyl sulfate (SDS)>H₂O. Water solubility also influenced adsorption; in most cases, adsorption increased with water solubility. In addition, adsorption was also influenced by chemical structure and hydrophobic interactions. The adsorption of aroma chemicals on cotton fabric can be attributed to the aqueous solution being physically held in capillaries and pore structures within the fibular structure of cotton fiber and also to molecular interactions among the aroma chemical molecules, surfactants, and cotton substrate.     

Thermotropic phase properties of the hydroxyceramide/cholesterol system

The interaction of cholesterol with ceramides containing α-hydroxy fatty acyl chains (hydroxyceramides) has been studies as a foundation for characterizing the lipid bilayers of thestratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The lyophilized hydroxyceramides showed a broad melting region at 92°C. Hydroxyceramides dispersed in water produced a relatively narrow, thermotropic transition at 75°C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55°C. Upon immediate rescanning, this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between 40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation. The composition of isolated brain ceramides is being compared with that reported for thestratum corneum.     

Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Thermal runaway prevention in catalytic packed bed reactor by solid temperature measurement and Control

Magnetic crystallite thermometry has been used to measure the average nickel crystallite temperature in packed bed reactors during ethane hydrogenolysis, an exothermic reaction. The technique is based on the temperature dependence of the magnetic moment of dispersed nickel catalysts. Measurement of the average catalyst temperature is very useful for reactor control because of its shorter time constant compared with exit fluid temperature. Bed temperature control based on the exit fluid temperature, which has often been used as a control variable, is too slow to protect thermal runaway of the bed. The advantage of short time constant by measuring the average catalyst temperature has been incorporated with enhanced feedback control system to control the bed temperature and prevent the thermal runaway of the catalyst bed. An enhanced feedback control structure with supervisory action performed better than the classical proportional-integral control in runaway prevention when the two control schemes were compared with each other on the basis of the trippoint (incipient thermal runaway).     

Sub-wavelength resolution in air-coupled ultrasound images of spot welds

Resistance spot welds joining steel sheets were examined using air-coupled ultrasound at 1 MHz. Transmission C-scan images were obtained using two axially aligned transducers, with each focused on its adjacent surface of the specimen. Because of the enormous impedance mismatch between air and steel, the transmitted signal was exceedingly weak, requiring several hours to collect an image. Although the air-coupled images resembled the weld shapes as determined by an independent technique, surface topography introduced considerable image distortion. The smearing of the images was substantially less than the 5.9-mm wavelength in steel, with the steepness of the transition between welded and unwelded areas indicating a transverse resolution about 1 mm. Similarities to near-field imaging are mentioned as a possible explanation for the observed sub-wavelength resolution.     

Monitoring delamination of plasma-sprayed thermal barrier coatings by reflectance-enhanced luminescence

Plasma-sprayed thermal barrier coatings (TBCs) present a challenge for optical diagnostic methods to monitor TBC delamination, because the strong scattering exhibited by plasma-sprayed TBCs severely attenuates light transmitted through the TBC. This paper presents a new approach that indicates delamination in plasma-sprayed TBCs by utilizing a luminescent sublayer that produces significantly greater luminescence intensity from delaminated regions of the TBC. Freestanding coatings were produced with either a Eu-doped or Er-doped yttria-stabilized zirconia (YSZ) luminescent layer below a plasma-sprayed undoped YSZ layer. A NiCr backing layer was added to represent an attached substrate in some sections. For specimens with a Eu-doped YSZ luminescent sublayer, luminescence intensity maps showed excellent contrast between unbacked and NiCr-backed sections. Discernable contrast between unbacked and NiCr-backed sections was not observed for specimens with a Er-doped YSZ luminescent sublayer, because luminescence from Er impurities in the undoped YSZ layer overwhelmed luminescence originating from the Er-doped YSZ sublayer.     

Moving from the Consortium to the Reference Desk: Keeping Chat and Improving Reference at the MSU Libraries

The experience of the Mississippi State University (MSU) Libraries illustrates the challenges presented by moving from consortial to local chat, as well as an evaluation of the advantages of chat reference in an academic setting. Countering the consortial, instant-messaging model prevalent in virtual reference today, the MSU Libraries have found chat offers advantages in an academic community. Moving to a local setting, it was possible for the MSU Libraries to maintain quality control over chat transactions while building relationships with faculty and students across campus.