Evaluation of steerable filter for detection of fibers in flowing suspensions

Steerable filters are concluded to be useful in order to determine the orientation of fibers captured in digital images. The fiber orientation is a key variable in the study of flowing fiber suspensions. Here, digital image analysis based on a filter within the class of steerable filters is evaluated for suitability of finding the position and orientation of fibers suspended in flowing suspensions. In sharp images with small noise levels, the steerable filter succeeds in determining the orientation of artificially generated fibers with well-defined angles. The influence of reduced image quality on the orientation has been quantified. The effect of unsharpness and noise is studied and the results show that the error in orientation is less than 1° for moderate levels. Images from two flow cases, one laminar shear flow and one turbulent, are also analyzed. The fiber orientation distribution is determined in the flow-vorticity plane. For the laminar case a comparison is made to a robust, but computationally more expensive, method involving convolutions with an oriented elliptic filter. A good agreement is found when comparing the resulting fiber orientation distributions obtained with the two methods. For the turbulent case, it is demonstrated that correct results are obtained and that the method can handle overlapping fibers.     

Ammonia synthesis and decomposition on a Ru-based catalyst modeled by first-principles

A recently published first-principles model for the ammonia synthesis on an unpromoted Ru-based catalyst is extended to also describe ammonia decomposition. In addition, further analysis concerning trends in ammonia productivity, surface conditions during the reaction, and macro-properties, such as apparent activation energies and reaction orders are provided. All observed trends in activity are captured by the model and the absolute value of ammonia synthesis/decomposition productivity is predicted to within a factor of 1–100 depending on the experimental conditions. Moreover it is shown: (i) that small changes in the relative adsorption potential energies are sufficient to get a quantitative agreement between theory and experiment (Appendix A) and (ii) that it is possible to reproduce results from the first-principles model by a simple micro-kinetic model (Appendix B).     

Behaviour of biaxial nematics in the presence of electric and magnetic fields

The behaviour of a biaxial nematic liquid crystal in the presence of electric and magnetic fields is discussed. In terms of the values of the magnetic susceptibilities and the dielectric permittivities, each biaxial nematic compound can be classified to belong to one of thirty-six different states. These states can be grouped together into three different classes, denoted by us as type A, B and C. The states belonging to each class exhibit a different qualitative behaviour in the presence of perpendicular electric and magnetic fields. While type A biaxial nematics always exhibit the same stable configuration in the presence of the fields, type B and C biaxial nematics exhibit two possible stable equilibrium configurations. Which of these is stable is determined by the magnitudes of the applied fields. The exchange of stability for type B systems can be modelled as a second order transition, while the exchange of stability for type C systems is of first order. In addition, the latter type can develop a bistable behaviour if certain conditions for the magnitudes of the electric and magnetic fields are fulfilled.     

An epitope in Coil 2B of cytokeratin 8

An immunological epitope has been located at the well preserved heptade discontinuity in Coil 2B of human cytokeratin 8, with the aid of synthetic peptides, antibodies to these and monoclonal antibodies to cytokeratins. CD revealed 37% alpha-helix in a 31-peptide.     

Kinetics and rate constants for the reaction of tri-n-butylgermanium hydride with methyl iodide and carbon tetrachloride. The combination of methyl and trichloromethyl radicals in solution.

The kinetics of the photoinitiated reductions of methyl iodide and carbon tetrachloride by tri-n-butylgermanium hydride in cyclohexane at 25°C have been studied and absolute rate constants have been measured. Rate constants for the combination of CH₃? and CCl₃? radicals are equal within experimental error and are also equal to the values found for the self-reactions of most non-polymeric radicals in low viscosity solvents, i.e. ～1–3 × 10⁹ M^?1 sec^?1. Rate constants for hydrogen atom abstraction by CH₃? and CCl₃? radicals are both ～1?2 × 10⁵ M^?1 sec^?1. Tri-n-butyltin hydride is about 10–20 times as good a hydrogen donor to alkyl radicals as is tri-n-butylgermanium hydride. The strength of the germanium–hydrogen bond, D(n-Bu₃Ge–H) is estimated to be approximately 84 kcal/mole.     

Die Photooxidation von Polypropylen-Monofilamenten. II. Physikalische Ver?nderungen und Mikrostruktur

Ohne Zusammenfassung     

A test of factorisation predictions for the fragmentation processes pp→π± at p momenta of 9.1 and 4.6 GeV/c

Relations have been derived between the invariant cross sections for various inclusive processes by assuming factorisation of the leading (pomeron) and non-leading (meson) trajectories. In this paper predictions for the invariant cross sections $\text{f(}\text{p}\text{p}\text{→π}{}^{\mathrm{\pm }}\text{)(2E}{}^1\text{/π√s)}\text{d}{}^2\text{σ/}\text{d}\text{x}\text{d}\text{p}{}^2{}_{\mathrm{\perp }}{}^2$ have been tested using data from $\text{p}\text{p}$interactions at 4.6 and 9.1 GeV/c.A large discrepancy between experiment and theory is apparent for the π^? data: in the π⁺ case the discrepancy is less marked but still present.     

An examination of the crystal structures present in nylon-6 fibers

The variety of wide-angle x-ray scattering (WAXS) patterns exhibited by nylon-6 fibers with different fabrication histories is rationalized using a model comprising three limiting structures, viz., an α, a γ, and a pleated α structure. The γ and pleated α structures both have a single broad reflection in the range 2θ = 19° ?25°, but differ in their annealing behavior. At 205° (in vacuo), the pleated α structure converts to the normal α structure by removal of the pleats, without breaking any hydrogen bonds. The γ structure, however, remains unchanged under this annealing condition since it is necessary to break all the hydrogen bonding in the structure to convert it to the α form. Different fabrication routes produce fibers which resemble the three ideal structures to varying extents. Fibers extruded at low speeds (and hence low spinline tension) resemble a mixed conventional α/pleated α structure with only a small γ component. Increasing the take-up speed (and hence the spinline tension) of the as-spun fiber, or in-line drawing of the low orientation fiber (without prior storage), increases the γ content. If drawing of the low orientation fiber takes place after several hours storage (off-line drawing), a largely α structure is produced. The intensity of the 020 reflection in the γ structure is shown to be very dependent on the degree of crystalline orientation in the sample.     

Polypropylene photo-stabilization by hindered secondary amines. A spectroscopic investigation

The conversion products from a commercially important photo-stabilizer based on 2,2,6,6-tetramethylpiperidine have been identified and quantified during the photo-oxidation of polypropylene. From a comparison with model compounds and model systems, direct evidence for the dominant involvement of grafted substituted hydroxylamine species was obtained by infra-red spectroscopy. Non-stabilizing conversion products, including N-acyloxy compounds, were also identified and the overall mechanism of photo-protection by hindered amine stabilizers is discussed.