Toughenability of Nylon-6 with CaCO3 filler particles: new findings and general principles

The mechanical behavior of Nylon-6 blends modified by two types of CaCO₃ particles of 0.7 and 3.5 μm diameter with particle volume fractions ranging from 0.05 to 0.28 was studied between −30 and 60°C in slow tension, and at 20°C in bending impact. Additional experiments were also carried out at 20°C to determine the plane stress fracture toughness of the blends in Single-Edge-Cracked-Plate configurations; all fracture behavior was followed extensively by SEM fractography.

Experiments demonstrated that the particles are attached to the matrix only through a differential thermal–contraction–pressure and particle separation preceded plastic response in all instances. As a consequence of the above ease in debonding, the yield strengths of the blends drop systematically with increasing particle concentration.

In slow tension all blends showed a well defined plastic stretching response following necking, but the stable post-necking stretch was severely limited by an overabundance of large particle clusters which acted as super-critical flaws to initiate premature termination of stretching. The present findings show that in these blends with their high plastic resistances, critical flaw sizes that trigger brittle response are in the range of 8–12 μm, well under the sizes of many of the particle clusters encountered in the blends.

In contrast with the attractively tough response of the rubber modified Nylon-6 blends of Murato lu et al. [Polymer 36 (1995) 921; Polymer 36 (1995) 4771] all present blends showed only disappointing brittle behavior under Izod impact conditions. This was traced to the development of substantial levels of triaxial tensile stresses arising from only partial separation of rigid particles from the matrix in the early phases of impact response.

Based on the new findings a number of general principles on toughenability with both compliant and rigid particle modification are presented and supported by simple micro mechanical models.     

Very High Volume Aerosol Sampling with a Novel Drum Centrifuge

For chemical analysis of trace compounds, comparatively large amounts of dust have to be collected. If good time resolution is required, very high sampling flow rates are mandatory. The operating principle of the drum centrifuge built to cope with these requirements is based on particle deposition on the inner surface of a porous rotating drum. Due to the rotation, a pressure gradient draws the aerosol into the bore of the axis and from there radially outward through a number of holes into the drum. The aerosol then moves to the periphery of the double-walled drum, which consists of two 0.15-mm-thick metal sheets with 1-mm spacing. Each of these metal sheets is perforated by several rows of small slits resulting in porosity of 16%. The slits in the inner and outer sheet are displaced, so that the particles will be strongly deflected on their way out of the rotating drum. Under the combined action of centrifugal forces and strong streamline deflection in the displaced slits of the two thin-walled drums, the particles are deposited. Flow rate as a function of rpm and collection efficiency as a function of particle size were determined experimentally. For simplicity, only the flow field of two (nonrotating) displaced slits was mathematically analyzed. The resulting 2-D solution of the Navier-Stokes equation was used for deterministic limiting trajectory calculations in the case of large particles. Diffusional motion of small particles was allowed for by Monte Carlo trajectory calculation. The calculated deposition efficiencies agree satisfactorily with the experimental results. At 3000 rpm a flow rate of 1200 m³/hr and efficiencies of 91% for 2.1-μm particles, 75% for 0.6-μm particles, and 48% for 0.04-μm particles were obtained. For easy extraction of the collected particulate matter, the device is equipped with an ultrasonic cleaning bath.     

Ultrafine Particle Deposition in a Human Tracheobronchial Cast

The deposition of 0.20, 0.15, and 0.04 μm diameter particles was measured in a human central airway cast using a variable larynx with cyclic inspiratory flow. Data were compared with theoretical predictions for deposition from laminar flow for the first seven airway generations. With the exception of tracheal deposition, which on average exceeded predictions by a factor of 9, the measured deposition was about twice that predicted. The enhanced deposition is attributable to secondary swirling flows. Less enhancement is observed at higher inspiratory flow rates as turbulence increases. The surface density of particles deposited at bifurcations was approximately 20% greater than along the airway lengths. This increased deposition at bifurcations should be considered when calculating tissue dose for particles which act before the initial deposit is removed by clearance processes.     

Controlled telescopic reinforcement system of fabric-cement composites — Durability concerns

The study objective was to modify the microstructure of AR glass strand to induce a controlled mode of telescopic bonding during service life, by using sub-micron particles absorbed between the filaments of the strand. Two groups of fillers were used: (i) pozzolanic fillers (silica fume) with 50 nm and 200 nm particle sizes; and (ii) polymeric fillers (polystyrene-based polymers), with two glass transition temperatures (− 6 °C and 100 °C). Composites were prepared using fabric reinforcement and tested for tensile behavior. Composite properties could be controlled by addition of fillers into the glass bundle, and the magnitude and efficiency of the modification was highly dependent on the filler type, structure, and properties. The best performance was obtained with silica fume fillers having relatively large 200 nm particles.     

Performance of Φ-Sulfo Fatty Methyl Ester Sulfonate Versus Linear Alkylbenzene Sulfonate,Secondary Alkane Sulfonate and α-Sulfo Fatty Methyl Ester Sulfonate

Sulfoxidation of fatty acid methyl esters with SO_2, O₂ and ultraviolet light of appropriate wavelength, has led to the synthesis of methyl esters sulfonates or sulfoxylates, known as Φ-MES, because of the possible random position of SO₃ group in the alkyl chain. Aqueous solutions based on the sulfoxylated methyl ester of palmitic acid (Φ-MES C16) have been studied and compared to the leading types of surfactants used today: linear alkylbenzene sulfonate (LAS) secondary alkane sulfonate (SAS) and α-sulfo fatty methyl ester sulfonate (α-MES) with regard to solubility, performance and skin compatibility. The experimental results obtained indicate that Φ-MES C16 can be regarded as a potential component of detergent formulations and most likely also of body care products.

Pore generation in asymmetric polymeric membranesCorrelation with solvent mobilities

Summary Analyzing videomicroscopy observations, this work deals with macrovoids detected through the skin of asymmetric polymeric membranes. The circle-like images of the macrovoids were found to form two-dimensional random patterns ; these were characterized from the mean distance, <λ>, determined between nearest neighboring images. Starting from polyetherimide or polyacrylonitrile solutions, each solution cast as a film was immersed in a water bath, at room temperature ; <λ> was shortened either by increasing the solvent concentration in the casting solution or by decreasing the solvent concentration in the bath (non-solvent of the polymer). This study was based on the assumption that the formation of the macrovoid pattern may be correlated to the interface instability resulting from the current of solvent diffusing towards the bath and initiated by the immersion of the polymer solution. Master curves, involving <λ>, the solvent concentrations in the polymeric solutions or in the bath and the solvent diffusion coefficients, measured prior to the immersion of the solution in the bath, were drawn. Diffusion coefficients were measured using a pulsed magnetic field gradient method. Received: 6 November 1998/Revised version: 9 February 1999/Accepted: 9 February 1999     

The effects of altitude on heavy-duty diesel truck on-road emissions

On-road measurements of carbon monoxide, hydrocarbons, and nitric oxide from 5772 heavy-duty diesel trucks at five locations in the United States and Europe show slightly increasing emissions with increasing altitude. The result for nitric oxide showed a statistically significant increase of 4.1 +/- 1 gNO/kg of fuel consumed/km increase in altitude. The increases for CO and HC were also statistically significant.     

What the public thinks about the tobacco industry and its products

Objectives: To assess public attitudes toward the tobacco industry and its products, and to identify predictors of attitudes supportive of tobacco industry denormalisation.

Design: Population based, cross sectional survey.

Setting: Ontario, Canada.

Subjects: Adult population (n = 1607).

Main outcome measures: Eight different facets of tobacco industry denormalisation were assessed. A denormalisation scale was developed to examine predictors of attitudes supportive of tobacco industry denormalisation, using bivariate and multivariate analyses.

Results: Attitudes to the eight facets of tobacco industry denormalisation varied widely. More than half of the respondents supported regulating tobacco as a hazardous product, fining the tobacco industry for earnings from underage smoking, and suing tobacco companies for health care costs caused by tobacco. Majorities also thought that the tobacco industry is dishonest and that cigarettes are too dangerous to be sold at all. Fewer than half of the respondents thought that the tobacco industry is mostly or completely responsible for the health problems smokers have because of smoking and that tobacco companies should be sued for taxes lost from smuggling. In particular, less than a quarter thought that the tobacco industry is most responsible for young people starting to smoke. Non-smoking, knowledge about health effects caused by tobacco, and support for the role of government in health promotion were independent predictors of support for tobacco industry denormalisation.

Conclusions: Although Ontarians are ambivalent toward tobacco industry denormalisation, they are supportive of some measures. Mass media programmes aimed at increasing support for tobacco industry denormalisation and continued monitoring of public attitudes toward this strategy are needed.

     

On cost-aware monitoring for self-adaptive load sharing

Monitoring is an essential part of any self-adaptive management loop. While providing the necessary information for making management decisions, monitoring itself incurs a cost in terms of the system and network resources committed to this management task. Thus, one can pose a generic question: what is the right amount of monitoring that maximizes its utility for management? This question turns out to be difficult to answer in general. In this paper we focus on quantifying the utility of monitoring for self-adaptive load sharing, where a stream of jobs arrives at a collection of n identical servers. We propose a novel model, that we dubbed an Extended Supermarket Model (ESM) to study the tradeoff between the usefulness of the monitoring information and the cost of obtaining it. We show that for each service request rate, there exists an optimal number of servers that should be monitored to obtain minimal average service time at an optimal cost. Using these findings, we present self-adaptive load-sharing algorithms both for centralized and fully distributed settings and evaluate these algorithms using simulations and a real testbed. Our results show that in realistic scenarios, where monitoring cost is not negligible, the self-adaptive load balancing is clearly superior to any cost-oblivious load-sharing mechanisms. We also demonstrate that in a fully distributed setting, where no dedicated monitoring component is employed, our self-adaptive heuristics perform very well with respect to the current common practice.