Measurement of calcium and titanium from 47sc by instrumental neutron activation analysis

A procedure is outlined for measuring calcium and titanium from ⁴⁷Sc by instrumental neutron activation analysis. Precise calcium measurements obtained from ⁴⁷Sc are compared with measurements based on ⁴⁷Ca and ⁴⁹Ca. The method is particularly suitable for low levels (ca. 1%) of calcium.     

Resonance-enhanced multiphoton ionisation photoelectron spectroscopy of the ClO radical: the C 2 sigma- state

A (2 + 1) one-colour resonance-enhanced multiphoton ionisation study is carried out on the C 2 sigma- state of the ClO radical in the one-photon energy range 29,500-31,250 cm-1. The ClO radical is produced by one-photon photolysis of ClO2 employing 359.2 nm photons derived from a separate laser. In this way a significant concentration of vibrationally excited ClO in its spin-orbit split X 2 pi omega (omega = 3/2 or 1/2) electronic ground state is produced. In addition to mass-resolved excitation spectra, kinetic-energy resolved photoelectron spectra for the X 3 sigma-(v+)<--C 2 sigma-(v' = 3-5) transitions are measured. These transitions are not completely Frank-Condon diagonal, and indicate a decrease in bond length on removal of the Rydberg electron from the C 2 sigma- state. In addition to an unambiguous assignment of the C 2 sigma- state, valuable information is obtained on the degree of vibrational excitation with which the nascent ClO radical is formed in the photolysis of ClO2. Analysis of the photoelectron spectra is supported by Franck-Condon calculations based on potential energy curves either from experimental spectroscopic parameters, or obtained by theoretical ab initio methods.     

Covariate and Newton–Raphson adjustments for a normal correlation coefficient when the variances are known

When the maximum likelihood estimator is computationally inconvenient, covariate and Newton–Raphson adjustment often provide algebraically explicit yet still asymptotically efficient estimators. The bivariate normal correlation coefficient with known variances is used to show that these methods may produce singularities that render the adjusted estimators unstable.     

Photoelastic determination of stresses in multiple-pin connectors

The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic- and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown.     

On the power of Wilks' U-test for MANOVA

Let V₁,…, V_m, W₁,…, W_n be independent p × 1 random vectors having multivariate normal distributions with common nonsingular covariance matrix Σ and with EW_α = 0, α = 1,…, n. In this canonical form of the multivariate linear model, the problem is to test H: EV_αazμ_α = 0, α = 1,…, m vs K: not H. It is shown that when the rank of the noncentrality matrix (μ₁…μ_m) Σ^?1 (μ₁…μ_m) is one, the power of Wilks' U-test (the likelihood ratio test) strictly decreases with the dimension p and the hypothesis degrees of freedom m. This generalizes results known for the noncentral F-test in the univariate case.     

Reducing shoplifting by investment in security

We consider a single retailer with a given potential revenue, who sells a product that is subject to shoplifting. In order to decrease losses due to shoplifting and to maximize his profit, the retailer can invest in security measures. In particular, we assume that the retailer purchases security services from a single security supplier. The security supplier decides which price to charge the retailer for these services, with the purpose of maximizing his own profit, and the retailer decides on the quantity of security services to purchase. We address this problem using a game theoretic approach, where the retailer competes with the supplier—the leader—who specifies first the service price. The retailer responds by deciding how much to invest in security. We study the conditions under which both players are profitable and the extent to which double marginalization affects the supply chain performance.     

Piezoelectricity of uniaxially stretched poly(vinylidene fluoride) corona poled at elevated temperature

X-ray diffraction, thermally stimulated depolarization, and piezoelectric current measurements have been carried out on uniaxially stretched poly(vinylidene fluoride) film, corona poled both negatively and positively at room temperature and at 90°C. Corona poling at elevated temperature considerably enhances the piezoelectric constant and is a more efficient way of charging the film than conventional thermal poling. Advantages over the latter are discussed.     

Effects of madelung potentials at surfaces of ZnO on photoemission spectra and work functions

Madelung potentials have been calculated for sites in and near polar and nonpolar, primitive and reconstructed surfaces of wurtzite ZnO. Surface versus bulk potential differences result in electron binding energy differences which should be observable in photoemission spectra even on nonpolar surfaces. In polar planes, the average site charges in the outermost ion layer are “naturally” reduced relative to charges in the crystal interior, and observable effects should be larger. Results for polar surfaces of singly bonded atoms are indicative of the Madelung potential effects expected for dense layers of chemisorbed species. These potentials are especially sensitive to details of charge transfer. If a crystal has uniform site charges except for the above-mentioned charge reduction on polar surfaces, there exist surface dipoles which would cause considerably greater variation in work function from one crystal face to another than that observed experimentally; this discrepancy is resolved if, in the outermost cation-anion layer, charges are further reduced to three-quarters to one-half the “natural” values.     

Phage display-derived inhibitor of the essential cell wall biosynthesis enzyme MurF

Background  

To develop antibacterial agents having novel modes of action against bacterial cell wall biosynthesis, we targeted the essential MurF enzyme of the antibiotic resistant pathogen Pseudomonas aeruginosa. MurF catalyzes the formation of a peptide bond between D-Alanyl-D-Alanine (D-Ala-D-Ala) and the cell wall precursor uridine 5'-diphosphoryl N-acetylmuramoyl-L-alanyl-D-glutamyl-meso-diaminopimelic acid (UDP-MurNAc-Ala-Glu-meso-A2pm) with the concomitant hydrolysis of ATP to ADP and inorganic phosphate, yielding UDP-N-acetylmuramyl-pentapeptide. As MurF acts on a dipeptide, we exploited a phage display approach to identify peptide ligands having high binding affinities for the enzyme.     

Hopping conduction in “pure” polypropylene

A recently developed theory of steady-state conduction in high-density polyethylene is applied to “pure” polypropylene (PP) in the temperature range 50–93°C. Morphological changes occur in PP, including a disordered-amorphous to monoclinic-amorphous transition between 50 and 80°C, where, with increasing temperature T, free volume increases, and decreases with decreasing amorphous fraction. The latter competing processes lead to large increases in hopping site separation, λ, in the transition region, followed either by saturation or a maximum in λ vs. T. We speculate that segmental and/or main chain molecular motions lower apparent activation energies, are “pinned“ by applied field, and impeded by dangling bonds in regions surrounding the surfaces of crystallites. Our analysis is semi-quantitative only, because the latter mechanisms have not been adequately quantified, and the relative contributions of each are unknown. Measurements were carried out on heated and cooled disordered-amorphous, and 106°C, 17-h annealed, 43% crystalline samples. Hopping distances, obtained from measured current vs. applied field characteristics, ranged from 1.2 to 5.2 nm. Apparent activation energies up to 1.80 eV were obtained from In (I/T) vs. (1/T) plots. Remarkable plateaus in the temperature range of the transition were observed in these plots, implying some carrier conduction with near zero activation energy. Possible explanations for the latter, and the electronic nature of the carriers are given. X-ray and density flotation measurements enabled crystallinity determinations. © 1994 John Wiley & Sons, Inc.