Stability experiments on the strongest columns and circular arches

Recent theories predict the cross-sectional shapes for the strongest, end-loaded column and the radially loaded arch whose neutral axis is circular. These tapered shapes have higher predicted load-carrying capacities than uniform columns or arches of equal weight and length or span. The purpose of the present experimental investigation was to study the stability of these configurations, modified so that no experimental model had the predicted cross-sectional area of zero where the bending moments vanished. Precise buckling loads were measured on metal models of tapered, pinned-end columns using strain gages and a unique modification of Southwell's method. The dynamic stability of these end-loaded columns under transverse vibrations was observed. Static stability tests were also performed on Plexiglas models of the strongest shaped circular arch and on the uniform circular arch of equal weight and span. The predicted buckling loads for the strongest shapes agreed reasonably well with measurements. The shaped circular arch, however, was found to be an inefficient design for loading applied uniformly across the span rather than in the radial direction.     

Attenuation of strain waves in core samples of three types of rock

Dynamic photoelasticity was employed to determine the velocity of longitudinal stress waves, dynamic modulus of elasticity and attenuation coefficients in rockcore samples 1 in. (25 mm) in diameter, 18 in. (0.46 m) long. Birefringent strips bonded to the core samples of Salem limestone, Charcoal granite and Berea sandstone provided all the data needed for the dynamic characterization of these rock types. The rods were dynamically loaded at one end with a lead-azide charge. A multiple-spark-gap camer was used to record the dynamic isochromatic-fringe patterns occurring in the birefringent strip. Of the three rock types investigated, the Berea sandstone exhibited the largest energy losses as characterized by an attenuation coefficient of 0.0910. Salem limestone and Charcoal granite exhibited much smaller losses with attenuation coefficients of 0.0196 and 0.0024, respectively. The extremely low-energy loss associated with Charcoal granite indicates that this material transmits stress waves as well as most metals.     

An IR study of the adsorption of water on Ru(001)

The strong OH stretch at 3400 cm^?1 (fwhm ～ 230 cm^?1) in the IR reflection absorption spectra of the system $\text{H}{}_2\text{O}\text{Ru(001)}$ at 85 K indicates the presence of hydrogen-bonded clusters. These clusters appear to form even at the lowest coverages. On the clean surface there is a linear relationship between integrated absorption intensity and coverage. The presence of small quantities of preadsorbed oxygen delays, however, the onset of absorption. It is thought that the oxygen atoms “bind” the water molecules, thus preventing cluster formation and in turn eliminating the intensity enhancement due to hydrogen bonding. Flash desorption spectra also indicate a second binding state when oxygen is coadsorbed. The relevance of these results to models of the electric double layer at the metal-electrolyte interface is discussed.     

Development of an in situ fiber optic Raman system to monitor hydrothermal vents

The development of a field portable fiber optic Raman system modified from commercially available components that can operate remotely on battery power and withstand the corrosive environment of the hydrothermal vents is discussed. The Raman system is designed for continuous monitoring in the deep-sea environment. A 785 nm diode laser was used in conjunction with a sapphire ball fiber optic Raman probe, single board computer, and a CCD detector. Using the system at ambient conditions the detection limits of SO(4)(2-), CO(3)(2-) and NO(3)(-) were determined to be approximately 0.11, 0.36 and 0.12 g l(-1) respectively. Mimicking the cold conditions of the sea floor by placing the equipment in a refrigerator yielded slightly worse detection limits of approximately 0.16 g l(-1) for SO(4)(-2) and 0.20 g l(-1) for NO(3)(-). Addition of minerals commonly found in vent fluid plumes also decreased the detection limits to approximately 0.33 and 0.34 g l(-1) respectively for SO(4)(-2) and NO(3)(-).     

Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.     

A Supramolecular Sorting Hat: Stereocontrol in Metal–Ligand Self‐Assembly by Complementary Hydrogen Bonding

A combination of self‐complementary hydrogen bonding and metal–ligand interactions allows stereocontrol in the self‐assembly of prochiral ligand scaffolds. A unique, non‐tetrahedral M₄L₆ structure is observed upon multicomponent self‐assembly of 2,7‐diaminofluorenol with 2‐formylpyridine and Fe(ClO₄)₂. The stereochemical outcome of the assembly is controlled by self‐complementary hydrogen bonding between both individual ligands and a suitably sized counterion as template. This hydrogen‐bonding‐mediated stereoselective metal–ligand assembly allows the controlled formation of nonsymmetric discrete cage structures from previously unexploited ligand scaffolds.     

Investigation of cold fusion in heavy water

An investigation of cold fusion of deuterium was performed by electrolyzing heavy water in a cell containing a palladium cathode while monitoring levels of tritium and neutron-capture gamma rays. No activity was detected that would indicate a sustained fusion reaction had taken place. Activities that were observed can be attributed to electrolytic enrichment and a normal cosmic-ray induced background.     

Spreading and fingering in a yield-stress fluid during spin coating

We study the deformation, spreading, and fingering of small droplets of a yield-stress fluid subjected to a centrifugal force on a rotating substrate. At low rotation rates and for small enough droplets, the droplets deform elastically but retain their essentially circular contact line. For large enough droplet volumes and rotation speeds, however, one or more fingers eventually form and grow at the edge of the drop. This fingering is qualitatively different from the contact line instability observed in other fluids, and appears to be a localized phenomenon that occurs when the stress at some point on the perimeter of the drop exceeds the yield stress.