Microstructure and Creep Behavior of Silicon Nitride and SiAlONs

Microstructural evolution of silicon nitride (Si₃N₄) and SiAlON materials and its influence on creep resistance is reviewed. Grain size, grain morphology, and the ratio of α- to β-phase grains play a part in resistance to creep. The glassy, intergranular phase typically has the strongest influence on creep. Creep data are usually obtained using uniaxial tensile or compressive tests, where creep in tension is controlled by cavitation and grain boundary sliding controls creep in compression. The impression creep methodology is also reviewed. An additional creep mechanism, dilation of the SiAlON grain structure, was found to be active in impression creep.     

A tall tower study of Missouri winds

This paper summarizes the results of a study of wind speeds observed at heights up to 150 m above ground level around Missouri. This is an amalgamation of four projects that allowed a total of eleven tall communication towers to be instrumented with wind observation equipment across the State of Missouri. This provided an assessment of the wind resource and the characteristics of the seasonal and diurnal cycles of wind in different areas of Missouri at the heights of utility scale wind turbines. Comparisons were also made to wind speeds predicted at these levels from a previously published wind map.The main finding was that the observed winds at each tower were smaller than those presented in the wind map. The discrepancy is most likely to be due to underestimation of the surface roughness and turbulence leading to an overestimation of near-surface wind shear. However, the wind shear, as expressed by the shear parameter was consistently greater than the ‘standard’ value of 1.4. The reconciliation of these two apparently contradictory findings is that the shear varies with the height at which it is measured. In wind resource assessment, wind shear is usually observed below 50 m and is tacitly assumed to be constant with height when used to extrapolate winds to higher levels. The author advocates the use of the friction velocity as a measure of shear in wind power applications in preference to the shear parameter that is usually used. This is because the shear parameter has a velocity bias that can also manifest as a bias with height or season. As wind power resource assessment is starting to use taller towers than the standard 50 m, intercomparison of site resources and extrapolation to turbine heights can be compromised if the shear parameter is used.     

Hybrid finite-volume/transported PDF simulations of a partially premixed methane-air flame

A hybrid finite-volume (FV)/transported probability density function (PDF) method is used for the simulation of a partially premixed flame with detailed chemistry. The FV code is implemented to handle detailed chemistry implicitly with no subgrid closure. A partially premixed methane-air flame is simulated to illustrate the need for closure. The PDF scheme is then substituted to handle the species transport using a subgrid mixing model. The algorithmic modifications to the PDF code are discussed in the context of a generalized structured grid solution technique. A multi-step particle transport algorithm is used to eliminate grid dependence of the time step. A detailed chemistry mechanism (GRI-2.11) is handled using in situ adaptive tabulation. It is shown that with simple modifications, the Interaction by Exchange with the Mean mixing model is able to predict the flame quite accurately. Mean profiles and conditional means obtained using the 49-species GRI-2.11 and 53-species GRI-3.0 mechanisms and the 16-species Augmented Reduced Mechanism are compared with the experimental data from the Sandia D flame. It is shown that with the mixing model, good agreement with the experimental data is achieved. Also the effect of the value of the mechanical-to-scalar time-scale ratio used in the mixing model is analyzed. The effect of the model constants in the dissipation equation for the turbulence model and the effect of radiation on flame predictions are also discussed.     

Study of proteolysis during the processing of a dry fermented pork sausage

Dry pork sausage was formulated, fermented and dried for 41 days. Gross composition was determined and proteolysis was monitored by assaying the following N fractions: water-soluble nitrogen (WSN), salt-soluble nitrogen (SSN), ultrafiltration (UF) permeates of WSN and SSN, phosphotungstic acid (PTA)-soluble and -insoluble fractions and free amino acids. Meat and sausages, water- and salt-insoluble components, UF-retentates of WSN and SSN were assessed by SDS-PAGE at different stages of ripening.

The amount of WSN, WSN permeate, PTA-soluble N and free amino acids increased during processing, while the SSN and PTA-insoluble N decreased. The electrophoretic studies demonstrated that proteolysis of the heavy myosin chain, -actinin and actin was most prominent. The increased insolubility of meat proteins was confirmed by SDS-PAGE.     

AI and Global Science and Technology Assessment

Strength in science & technology (S&T) is the foundation of a nation's economic power, so an effective, automated means of continually assessing this strength is critical to understanding a country's economic status. Six essays on global S&T assessment present various research frameworks, computational methods, issues, and results relative to knowledge mapping, scientometrics, information visualization, digital libraries, and multilingual knowledge management.     

Silver sulfide as a staining agent for scanning electron microscopy of nylon 6/MXD6 blends

BACKGROUND: In transmission and scanning electron microscopy imaging, the ability to obtain sufficient contrast between the components of a blend when they are both of a similar chemical structure still remains problematic. This paper investigates the domain morphology of a polymer blend containing two polyamides, nylon 6 and the semi‐aromatic polyamide poly(m‐xylene adipamide) (MXD6), using scanning electron microscopy in backscattered electron imaging mode. The efficiency of three staining agents, ruthenium tetroxide, phosphotungstic acid and silver sulfide, in obtaining optimum phase contrast between the two polymers is discussed. RESULTS: The use of silver sulfide as a staining agent was found to be a fast and reliable approach which required basic sample preparation and provided excellent compositional contrast between the phases present in the nylon 6/MXD6 blends compared to the other staining agents. CONCLUSIONS: The technique described in this paper is believed to be a novel and versatile method that has the potential to further improve the ability to study complex polymer blends where one polymer contains an aromatic ring. Copyright © 2009 Society of Chemical Industry     

Short communication: The effect of centrifugation and resuspension on the recovery of Mycoplasma species from milk

Low sensitivity of a single bulk tank milk culture is a major limitation for detection of mycoplasma organisms. We hypothesized that sedimentation of Mycoplasma spp. in a milk sample by centrifugation followed by resuspension in a small volume of fluid before agar plating would increase the ability to detect Mycoplasma spp. compared with direct conventional culture. The experiment was conducted to determine recovery of Mycoplasma spp. from milk as affected by 1) treatment (centrifugation vs. conventional method); 2) 2 species (Mycoplasma bovis and Mycoplasma californicum and 4 strains for each species); and 3) 4 different concentrations of Mycoplasma spp. (1,000, 100, 10, and 1 cfu/mL). A 5-mL portion of mycoplasma suspension from each strain was inoculated into 45 mL of fresh bulk tank milk to achieve concentrations of 1,000, 100, 10, and 1 cfu/mL. Treatment samples were vigorously mixed and centrifuged at 5,000 × g for 30 min. Control samples were vigorously mixed. All samples were plated on modified Hayflick agar. Plates were incubated at 37°C and 5% CO₂ for 5 d. Mean (±SE) log₁₀ mycoplasma counts (cfu/mL) in the treatment groups (1.91 ± 0.15) were higher than those in the control groups (1.70 ± 0.16). Recovery of at least 1 mycoplasma colony on agar culture was 100% in both treatment and control groups at high, medium, and low concentrations. At the lowest concentration, recovery of at least 1 mycoplasma colony on agar culture in treatment and control groups was 75% (n = 12/16) and 18.75% (n = 3/16), respectively. Centrifugation of milk followed by suspension in a smaller volume of saline before conventional culture increased the ability to detect mycoplasma microorganisms in the milk sample compared with controls. Recovery by centrifugation appeared best at the lowest concentration where detection of a positive sample was 4 times more likely than when conventional methods were used.     

Flexural behaviour and strength of cold-formed steel L-headers

Cold-formed steel headers are structural components used over wall openings in cold-formed steel residential and light commercial construction. Recently, there has been an increased interest in cold-formed L-headers among homebuilders primarily due to their ease of installation and low material cost. The findings from an extensive laboratory testing program, of full-scale single and double cold-formed steel L-headers are presented in this paper. The objective of the research was to investigate the flexural behaviour and strength of L-headers under both gravity and uplift loads. Based on the results improved ultimate strength design expressions and new deflection expressions for a wide range of L-header assemblies have been proposed.