The flowability of fine powders in reduced gravity conditions

The extrapolation of Qian’s semi-theoretical relationship for the transition between cohesive and non-cohesive powder fluidization behavior into regions of low gravity is studied and a validation experiment employing fluidization is discussed. The fluidization experiment utilized fine glass and alumina powders in a fluidized bed and was flown onboard NASA’s reduced gravity aircraft. The transition region between cohesive and non-cohesive behavior is determined for the glass and alumina powders at gravity levels of 1.8, 1.0, 0.38, and 0.16 g. The results are compared to Qian’s model and show fair agreement. The fluidization experiment limitations are discussed and a rotating drum experiment that will reduce the experiment uncertainty, provide quantifiable results, and is suitable for flight onboard NASA’s reduced gravity aircraft is proposed. The rotating drum technique determines the characteristic frequency of the powder’s center of area to detect avalanching. The concept is validated by comparing the characteristic frequency obtained from analyzing a cohesive powder to the characteristic frequency obtained from analyzing a flowable powder.     

Influence of oxygen content on grain growth in Pr–Fe–B/Nd–Fe–B sintered magnets

An investigation into the effects of intermediate/variable final oxygen contents, in relation to the resultant microstructures and final magnetic properties of Pr–Fe–B- and Nd–Fe–B-type magnets in the as-sintered state has been undertaken. For low oxygen contents the Pr–Fe–B and Nd–Fe–B sintered magnets exhibited excessive grain growth on sintering. A high oxygen content resulted in the elimination of abnormal grain growth for both materials, on sintering, where the level of oxygen contamination appeared to affect the grain growth process, although not the grain growth mechanism. Differences, however, in grain growth behaviour for the Pr–Fe–B and Nd–Fe–B sintered magnets have been observed. A changing oxygen content resulted in a variable grain size and grain size distribution for both the Pr–Fe–B and Nd–Fe–B sintered magnets, resulting in a progressive change in intrinsic coercivity, with oxygen content.     

Assessment of non-uniform malathion distribution for insect control in a commercial wheat silo

Experimental (non-uniform) and conventional malathion treatments of wheat, stored in 2000 tonne vertical steel bins were compared. For the experimental treatment, grain pretreated with malathion at 750–800 ppm was added to an untreated grain stream during inloading of a silo, so that pretreated grain comprised about 1% of the bulk. Conventional treatment consisted of continuous spraying of a similar grain stream with an emulsion of malathion. Mean overall malathion levels of approximately 5–6 ppm were obtained in both silos.Distribution of insecticide in the two treatments was compared by assaying groups of 25 grains taken from each bin. Significantly increased non-uniformity of distribution of insecticide was found in the experimental treatment which was considered to account for the greater persistence of malathion residues.Bioassays to indicate the potential of adult Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) to develop infestations were conducted on wheat from the experimental and conventional treatments throughout their respective 10 and 8 months storage periods. Results indicated effective suppression of T. castaneum infestation throughout the storage periods in both silos. After 6 months storage, the conventional treatment did not prevent infestation by S. oryzae, whereas the experimental treatment remained effective throughout the 10 months storage period; suggesting that the proposed method has the economic advantage of eliminating retreatment.     

Sub-discretized surface model with application to contact mechanics in multi-body simulation

The mechanics of contact between rough and imperfectly spherical adhesive powder grains are often complicated by a variety of factors, including several which vary over sub-grain length scales. These include several traction factors that vary spatially over the surface of the individual grains, including high energy electron and acceptor sites (electrostatic), hydrophobic and hydrophilic sites (electrostatic and capillary), surface energy (general adhesion), geometry (van der Waals and mechanical), and elasto-plastic deformation (mechanical). For mechanical deformation and reaction, coupled motions, such as twisting with bending and sliding, as well as surface roughness add an asymmetry to the contact force which invalidates assumptions for popular models of contact, such as the Hertzian and its derivatives [H. Hertz, Über die Berührung fester elastische körper. Journal für die reine und angewandte Mathematik 1882; 92: 156-171; R.D. Mindlin, Compliance of elastic bodies in contact. Journal of Applied Mechanics 1949; 71: 259-268; R.D. Mindlin, H. Deresiewicz, Elastic spheres in contact under varying oblique forces. Journal of Applied Mechanics 1953; 20: 269-286], for the non-adhesive case, and the JKR [K.L. Johnson, K. Kendall, A.D. Roberts, Surface energy and the contact of elastic solids. Proceedings of the Royal Society of London 1971; 324: 301-313] and DMT [B.V. Derjaguin, V.M. Muller, Y.P. Toporov, Effect of contact deformations on the adhesion of particles. Journal of Colloid and Interface Science 1975; 53: 314-326] models for adhesive contacts. Though several contact laws have been offered to ameliorate these drawbacks, they are often constrained to particular loading paths (most often normal loading) and are relatively complicated for computational implementation. This paper offers a simple and general computational method for augmenting contact law predictions in multi-body simulations through characterization of the contact surfaces using a hierarchically-defined surface sub-discretization. For the case of adhesive contact between powder grains in low-stress regimes, this technique can allow a variety of existing contact laws to be resolved across scales, allowing for moments and torques about the contact area as well as normal and tangential tractions to be resolved. This is especially useful for multi-body simulation applications where the modeler desires statistical distributions and calibration for parameters in contact laws commonly used for resolving near-surface contact mechanics. The approach is verified against analytical results for the case of rough, elastic spheres.     

Opinion organization in a heterogeneous population.

The intercorrelations among the responses of 1,029 persons to 25 items from the 1948 Elmira Voting Study questionnaires were analyzed by Thurstone's group centroid method. The analysis was repeated in three segments of the population that were contrasted on the basis of formal education. Two factors or attitudes, together, accounted for 23% of the variance for the 25 items. These were a factor associated with the expression of hostile attitudes toward outgroups and expectations of war and depression; and a factor associated with the identification with a political party or social class. These factors appear most clearly delineated in that segment of the population which has had some college education. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mode of failure, interference tendencies, and achievement imagery.

The relative effects upon addition performance of failure to reach goals set by the subject himself and failure to reach goals set by the experimenter are studied, as well as the relative performance of groups differing in scores on the Interfering Tendency Questionnaire (IT) and the Achievement Imagery (AI) scale of the Iowa Picture Interpretation Test. The major findings were as follows: (1) There was no overall difference in the effects of the two failure procedures. High AI Ss showed greater improvement following failure to reach goals they had set for themselves while low AI Ss showed greater improvement following failure to reach experimenter set goals. (2) Under failure conditions, low IT Ss were superior, while under non failure conditions, high IT Ss were superior. (3) High AI Ss worked significantly faster than low AI Ss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preliminary investigation of bioadvantaged polymers as sustainable alternatives to petroleum-derived polymers for asphalt modification

Due to recent volatility in the petroleum market, the possibility of using sustainable alternative materials as substitutes has gained great interest and viability. The purpose of this research is fourfold: to demonstrate how bioadvantaged polymers are produced using non-food soybean oil and showcase their economic and environmental value; to evaluate how they perform rheologically in asphalt against commonly used petroleum-derived polymers; to optimize the formulation of the bioadvantaged polymer for warm climate regions pavement applications based on the grading results, and to verify the modification effects of optimized bioadvantaged polymer by running performance grade tests. The study on economic and environmental implications demonstrated that poly(styrene-acrylated epoxidized soybean oil) (PS-PAESO) is more cost-effective, environmentally friendly, and safer to produce than styrene-butadiene (SB) polymer. The commercially produced petroleum-derived SB diblock polymer was used for comparison, while the laboratory produced bioadvantaged polymers were targeted at 1.25 MDa molecular weight of PS-PAESO diblock copolymers that consist of PAESO with various polystyrene (PS) molecular weights and contents. The effectiveness and rheological performance of the polymer modified asphalt binders were evaluated through binder investigations. Rheology test results indicated that the bioadvantaged polymers improved the stiffness, elasticity, and rutting resistance of the neat asphalt binder. Best-fit prediction models were developed through response surface modeling to optimize the PS-PAESO formulation in terms of PS content and molecular weight and the models were verified to be highly accurate based on the grading results. It was found that lower polystyrene content in PS-PAESO polymer could be beneficial in the improvement of critical high temperatures.