Prediction of yield and long‐term failure of oriented polypropylene: Kinetics and anisotropy

The time‐dependent yield and failure behavior of off‐axis loaded uniaxially oriented polypropylene tape is investigated. The yield and failure behavior is described with an anisotropic viscoplastic model. A viscoplastic flow rule is used with an equivalent stress, based on Hill's anisotropic yield criterion, and the Eyring flow theory combined with a critical equivalent strain definition. This model is based on factorization of the rate and draw ratio dependence and is capable of quantitatively predicting the rate, angle and draw ratio dependence of the yield stress as well as time‐to‐failure in various off‐axis tensile loading conditions characterized solely from the transverse direction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2026–2035, 2009     

The signal/noise of an HMBC spectrum can depend dramatically upon the choice of acquisition and processing parameters

The effect of various acquisition and processing parameters on the sensitivity of HMBC spectra for typical organic molecules has been systematically investigated. For molecules in the 200–600 molecular weight range, an acquisition time of 0.2 to 0.4 s, a recycle time of no more than 1.0 s, optimization for ⁿJ_CH = 8 Hz and 512 time increments (with two‐ to fourfold linear prediction) are recommended. Some form of sine bell weighting along f₂ and either Gaussian or sine bell weighting along f₁ is suggested. The use of a 0.1‐s acquisition time and/or Gaussian or exponential weighting along f₂ can result in dramatic sensitivity loss, particularly for correlation peaks involving protons with complex splitting patterns, and should be avoided. Copyright © 2009 John Wiley & Sons, Ltd.     

Measurement of turbulent wall velocity gradients using cylindrical waves of laser light

A new optical instrument has been developed for direct measurement of instantaneous velocity gradients at the bounding wall. Light emerging from two tiny optical slits in the surface is used to form a fan of fringes in the region very near the wall. Doppler frequency of the light scattered by the seed particles is directly proportional to the velocity gradient. The system has been used to measure the statistics of the streamwise and spanwise velocity gradients in a turbulent boundary layer. The streamwise and spanwise rms fluctuations were found to be 38% and 11% of the mean streamwise value respectively. The latter result is subject to a large uncertainty.List of symbols a slit width - B transfer function of the instrument - B ^* normalized transfer function - path-averaged value of the normalized transfer function - c constant in logarithmic velocity profile - C _f skin friction coefficient - d _f fringe spacing - f ₁,f₂ frequencies at the downstream and upstream slits resp. - f _d heterodyne Doppler frequency of the signal - g(t) instantaneous wall velocity gradient - G Clauser shape factor - mean wall velocity gradient - g rms value of the wall velocity gradient - H boundary layer shape factor - i, j, k unit vectors along x, y, z axes - wavenumber of laser light - L major axis of the elliptic cross-section of the laser sheet at the slit - l length of each slit - N number of cycles in a signal - N ₀ number of cycles without frequency-shifting - n difference of the unit vectors u ₁and u ₂ - P power transmitted through a slit - P _o power incident on a slit - Re ₁ Reynolds number based on displacement thickness and free-stream velocity - Re ₂ Reynolds number based on momentum thickness and free-stream velocity - S spacing between the slits - S ^* normalized spacing between the slits - u streamwise velocity - u ₁,u₂ unit vectors along the local directions of propagation of the two cylindrical waves - u _l linear term in the streamwise velocity profile - u _nl nonlinear terms in the streamwise velocity - u _nl ^* normalized value of nonlinear streamwise velocity - u _nl ^* mean streamwise velocity - u friction velocity - u⁺ mean velocity normalized with friction velocity - v velocity component normal to the wall - v ^* normal velocity normalized with streamwise velocity - V velocity vector - w spanwise component of velocity - W minor axis of the elliptic cross-section of the laser sheet at the slit - x streamwise distance - ± x _m limiting values of streamwise distance for a signal - x ^* normalized streamwise distance - x ^* normalized value of x _m - y normal distance - y ⁺ normal distance normalized with friction length scale - z spanwise distance - z ⁺ spanwise distance normalized with friction length scale - half-spreading angle of the cylindrical waves - boundary layer thickness in Coles' profile - ₁ displacement thickness of the boundary layer - ₂ momentum thickness of the boundary layer - ₃ energy thickness of the boundary layer - constant in logarithmic velocity profile - wavelength of laser light - kinematic viscosity - coefficient of wake function in Coles' profile Currently at LSTM, Universitat Erlangen-Nürnberg, Cauerstraße 4, W-8520 Erlangen, BRD     

Investigation of copper oxide impregnants prepared from various precursors for respirator carbons

Copper oxide impregnated activated carbon was prepared by three methods and studied as a respirator carbon. Using techniques such as dynamic flow testing, X-ray diffraction (XRD), thermal analysis, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), copper oxide impregnants, derived from different sources such as basic copper carbonate (Cu₂CO₃(OH)₂), copper nitrate (Cu(NO₃)₂) and copper chloride (CuCl₂) reacted with sodium hydroxide (NaOH), have been studied. Dynamic flow tests performed using sulfur dioxide (SO₂), ammonia (NH₃) and hydrogen cyanide (HCN) challenge gases allow the determination of the stoichiometric ratio of reaction (SRR) between challenge gas and impregnant. Thermal gravimetric analysis experiments showed that an inert heating environment was required when thermally decomposing the Cu(NO₃)₂ impregnant to CuO to avoid damaging the activated carbon substrate. SEM has been used to investigate dispersal and particle size of the impregnant on the activated carbon. XRD permits the identification of crystalline and amorphous phases as well as the grain size of the impregnant. XRD analysis of samples before and after exposure to SO₂ has allowed the active impregnant in SO₂ adsorption to be identified. The relationship between SRR, impregnant loading and grain size is discussed. Methods to improve impregnant distribution are presented and their impact discussed.     

Spanwise variations in nominally two-dimensional rough-wall boundary layers

Laboratory experiments have been conducted in two separate boundary layer facilities to investigate steady spanwise variations in mean velocity discovered during studies of developing flows over regular arrays of large roughness elements. Regular spanwise variation was found with a steady wavelength, moderated by the growing boundary layer, which was an integer multiple of the repeating unit of roughness. Amplitude variations greater than ±5% in the mean were found over the roughness and greater than ±10% in turbulence quantities. Due to the dominating nature of this phenomena throughout the layer, care should be taken in undertaking local measurements aimed at identifying flow variations caused by roughness heterogeneity.     

Determination of MDL 201,012 at femtomole/millilitre levels in human plasma by liquid chromatography with electrochemical detection.

A sensitive and selective liquid chromatographic method to quantitate MDL 201,012 in human plasma was developed and validated. MDL 201,012 (I), diethyl-MDL 201,012 (internal standard, II) and desmethyldiol-MDL 201,012 (masking agent, III) were isolated from basified plasma (2 mL) by solid phase extraction using Bond-Elut C-18 cartridges. Endogenous components were selectively removed prior to eluting the analytes from the sorbent. Components were separated using on-line LC column switching with a cyanopropyl precolumn and a phenyl analytical column. The analytical column effluent was monitored electrochemically at a glassy carbon electrode at a potential of +1025 mV vs. Ag/AgCl. Peak-height ratios were proportional to the amount of MDL 201,012 added to plasma over the range 125-7500 pg/mL MDL 201,012. Absolute recovery of MDL 201,012 from human plasma was > 94% across the calibration range. The minimum quantitation limit was 125 pg/mL. Assay precision (%RSD) ranged from 5.2 to 13% based on the analysis of quality control standards containing 125, 250, 500, 1000, 2500, 5000 and 7500 pg/mL MDL 201,012. Corresponding assay accuracy (% relative error) was +/- 8.5%. The method has been successfully used to quantitate MDL 201,012 in samples from acute dose tolerance studies in human volunteers.