Deep flaws in weldments of aluminum and titanium

Surface flawed specimens of 2219-T87 and 6Al-4V STA titanium weldments were tested to determine static failure modes, failure strength, and fatigue flaw growth characteristics. Thicknesses selected for this study were purposely set at values where, for most test conditions, abrupt instability of the flaw at fracture would not be expected. Static tests for the aluminum weldments were performed at room, LN2 and LH2 temperatures. Titanium static tests for tests were performed at room and LH2 temperatures. Results of the static tests were used to plot curves relating initial flaw size to leakage- or failure-stresses (i.e. "failure" locus curves). Cyclic tests, for both materials, were then performed at room temperature, using initial flaws only slightly below the previously established failure locus for typical proof stress levels. Cyclic testing was performed on pairs of specimens, one with and one without a simulated proof test cycle. Comparisons were made then to determine the value and effect of proof testing as affected by the various variables of proof and operating stress, flaw shape, material thickness, and alloy

Summary Abstract: The oxidation of carbon monoxide on the Pt(110)-(1×2) surface: The influence of the adlayer composition on the reaction dynamics

We have developed and employed the technique of surface temperature modulation to examine the dynamics of the oxidation of Ca on the Pt(110)-(1×2) surface [2]. This technique permits a straightforward analysis of the energetics of elementary surface reactions even in the presence of strong nonlinearities, providing a decided advantage over competing techniques such as modulated molecular-beam reactive scattering. We shall emphasize here the coverage dependence of the kinetic rate parameters (Er and kr(2)Z)) that describe the elementary surface reaction CO(a) + O(a) → CO2 (g). These data will be compared briefly with results obtained previously concerning the coverage dependence of the energy retained in the translational [3] and internal [4,5] modes of the product CO2 molecule

Characterization of bacterial lipooligosaccharides by delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption ionization (MALDI) with a time-of-flight analyzer has been used to analyze bacterial lipooligosaccharides (LOS). Crude LOS preparations from pathogenic strains of Haemophilus influenzae and Haemophilus ducreyi and a commercial preparation of lipopolysaccharide from Salmonella typhimurium were treated with hydrazine to remove O-linked fatty acids on the lipid A moiety. The resulting O-deacylated LOS forms were water soluble and more amenable to cocrystallization with standard MALDI matrices such as 2,5-dihydroxybenzoic acid and 1-hydroxyisoquinoline. Under continuous extraction conditions, O-deacylated LOS yielded broad peaks with abundant salt adducts as well as forming prompt fragments through β-elimination of phosphoric acid, that is, [M-H3PO4-H]. However, when a time delay was used between ionization and extraction (“delayed extraction”) a significant improvement was seen in both mass resolution and the stability of the molecular ions against β-elimination of phosphoric acid, especially in the negative-ion mode. Both an external two-point calibration and an internal single-point calibration were used to assign masses, the latter of which provided the highest degree of accuracy (better than 0.01% in most cases). At higher laser powers, the LOS molecules cleave readily between the oligosaccharide and lipid A moieties yielding a number of prompt fragments. Postsource decay (PSD) analysis of selected molecular ions provided a set of fragments similar to those seen in the linear spectra, although they were more limited in number because they were derived from a single LOS-glycoform. Both the prompt and PSD fragments provided important structural information, especially in assigning the phosphate and phosphoethanolamine substitution pattern of the lipid A and oligosaccharide portions of LOS. Last, with the addition of ethylenediaminetetraacetic acid followed by pulsed sonication, the relatively insoluble (and impure) LOS preparations yielded MALDI spectra similar to the O-deacylated LOS, although these intact LOS preparations required higher laser powers to ionize and were generally more affected by competing impurities

Characterization of Chimeric Lipopolysaccharides from Escherichia coli Strain JM109 Transformed with Lipooligosaccharide Synthesis Genes (lsg) from Haemophilus influenzae

Previously, we reported the expression of chimeric lipopolysaccharides (LPS) in Escherichia coli strain JM109 (a K-12 strain) transformed with plasmids containing Haemophilus influenzae lipooligosaccharide synthesis genes (lsg) (Abu Kwaik, Y., McLaughlin, R. E., Apicella, M. A., and Spinola, S. M. (1991) Mol. Microbiol. 5, 2475–2480). In this current study, we have analyzed the O-deacylated LPS and free oligosaccharides from three transformants (designated pGEMLOS-4, pGEMLOS- 5, and pGEMLOS-7) by matrix-assisted laser desorption ionization, electrospray ionization, and tandem mass spectrometry techniques, along with composition and linkage analyses. These data show that the chimeric LPS consist of the complete E. coli LPS core structure glycosylated on the 7-position of the non-reducing terminal branch heptose with oligosaccharides from H. influenzae. In pGEMLOS-7, the disaccharide Gal13 3GlcNAc13 is added, and in pGEMLOS-5, the structure is extended to Gal134GlcNAc133Gal133GlcNAc13. PGEMLOS-5 LPS reacts positively with monoclonal antibody 3F11, an antibody that recognizes the terminal disaccharide of lacto-N-neotetraose. In pGEMLOS-4 LPS, the 3F11 epitope is apparently blocked by glycosylation on the 6-position of the terminal Gal with either Gal or GlcNAc. The biosynthesis of these chimeric LPS was found to be dependent on a functional wecA (formerly rfe) gene in E. coli. By using this carbohydrate expression system, we have been able to examine the functions of the lsg genes independent of the effects of other endogenous Haemophilus genes and expressed proteins

A facility to remotely assemble radioisotope thermoelectric generators

Radioisotope Thermoelectric Generators (RTGs) are electrical power sources that use heat from decaying radioisotopes to directly generate electrical power. The RTG assembly process is performed in an inert atmosphere inside a large glovebox, which is surrounded by radiation shielding to reduce exposure to neutron and gamma radiation from the radioisotope heat source. In the past, allowable dose rate limits have allowed direct, manual assembly methods; however, current dose rate limits require a thicker radiation shielding that makes direct, manual assembly infeasible. To minimize RTG assembly process modifications, telerobotic systems are being investigated to perform remote assembly tasks. Telerobotic systems duplicate human arm motion and incorporate force feedback sensitivity to handle objects and tools in a human-like manner. A telerobotic system with two arms and a three-dimensional (3-D) vision system can be used to perform remote RTG assembly tasks inside gloveboxes and cells using unmodified, normal hand tools

Summary Abstract: The hydrogenolysis of alkanes over single-crystalline surfaces of iridium: The influence of surface structure on the catalytic selectivity

We have investigated the hydrogenolysis of various short-chain alkanes on the Ir(111) and Ir(110)-(1×2) surfaces. A striking correlation has been discovered between the selectivity for ethane production from the hydrogenolysis of n-butane over Ir catalysts and the concentration of low-coordination-number metal surface atoms. This result is best interpreted as a manifestation of the occurrence of a particular adsorbed reaction intermediate on the Ir(11O)-(1×2) surface, namely, a metallacyc1e pentane. The formation of this intermediate is sterically forbidden on the Ir(111) surface

Women candidates and councillors in Scottish local government, 1974-2012

While significant attention has been paid to the levels of representation of women in both the Westminster Parliament and the Scottish Parliament, much less considered has been given to the position within local government. This article addresses that deficit for Scotland. It shows that for twenty-five years following the reorganisation of local government in Scotland in 1974 there was a slow but relatively steady increase in the numbers of female candidates and councillors, although more recently this appears to have since plateaued somewhat, together with a similar increase in the number of women councillors taking up more senior roles in Scotland’s councils. The article analyses the representation of women in Scottish local government over the period from 1974 to 2012 against the backdrop of significant change in Scotland, including a further restructuring of local government and the introduction of the Single Transferable Vote for council elections, the creation of the Scottish Parliament, the rise of the SNP and the decline of the Conservative Party

Comparative studies of alkane activation by low-index surfaces of iridium and platinum

The interaction of alkanes with low-index surfaces of iridium at low temperatures and pressures has been studied in our laboratory by thermal desorption mass spectrometry and low-energy electron diffraction. While the reconstructed (110)-(1 × 2) surface of iridium initiates dissociative chemisorption of ethane and all higher alkanes at 125 K in the low coverage limit, similar reactions with the close-packed (111) surface occur readily only at defect sites. Thus, surface geometry influences strongly the activation barriers to C-H bond scission in alkanes on iridium surfaces