Numerical prediction of the propagation of elastic waves in longitudinally impacted rods: Applications to Hopkinson testing

Simple expressions, based on one-dimensional elastic wave theory, are established which permit prediction of normal force and particle velocity at cross-sections of a non-uniform linearly-elastic rod. The initial normal force and particle velocity at each cross-section of that rod must be known. In order to assess the validity of the assumptions, an experimental test on a cone-shaped rod is performed. Numerical results are provided for two different configurations: a rod shaped at one end in order to perform the Hopkinson three-point bend test and a rod heated at one end for a high temperature dynamic test. The given expressions are so easy to program that a common spreadsheet program is sufficient to implement and perform the calculation. They enable the influence of an impedance variation to be quantified a priori. In the case of the Hopkinson three-point bend test, the wave distortion is not very important if the rise time is long and the length of the shaped end is short. For a heated rod, the conventional Hopkinson treatment is not available when the temperature is too high. Some effects of an idealized quasi-static specimen for both Hopkinson three-point bend and non-uniform temperature are included.     

Relative Stabilities of Conserved and Non-Conserved Structures in the OB-Fold Superfamily

The OB-fold is a diverse structure superfamily based on a β-barrel motif that is often supplemented with additional non-conserved secondary structures. Previous deletion mutagenesis and NMR hydrogen exchange studies of three OB-fold proteins showed that the structural stabilities of sites within the conserved β-barrels were larger than sites in non-conserved segments. In this work we examined a database of 80 representative domain structures currently classified as OB-folds, to establish the basis of this effect. Residue-specific values were obtained for the number of Cα-Cα distance contacts, sequence hydrophobicities, crystallographic B-factors, and theoretical B-factors calculated from a Gaussian Network Model. All four parameters point to a larger average flexibility for the non-conserved structures compared to the conserved β-barrels. The theoretical B-factors and contact densities show the highest sensitivity. Our results suggest a model of protein structure evolution in which novel structural features develop at the periphery of conserved motifs. Core residues are more resistant to structural changes during evolution since their substitution would disrupt a larger number of interactions. Similar factors are likely to account for the differences in stability to unfolding between conserved and non-conserved structures.     

Rapid determination of shoot nitrogen status in rice using near infrared reflectance spectroscopy

Near infrared reflectance (NIR) spectroscopy is a rapid, cheap, simple technique which can be used to make quantitative analyses of the concentrations of nutrients in plant tissue. The application of NIR to determine nitrogen in rice was examined. The absorbance spectrum of rice (Oryza sativa L) shoot tissue was similar to that of the temperate cereal wheat even though rice tissue has a much higher silica content. A 19-filter NIR instrument was calibrated to estimate the nitrogen content of rice shoots with between 0·8 and 3·50% N by the Kjeldahl technique. The calibration model developed used three wavelengths to account for 96% of the variation in sample Kjeldahl nitrogen concentration. This model was validated using 67 samples comprising five rice varieties grown on farms in two seasons in southern New South Wales. The standard error of prediction of the model was 0·15% N. A tissue testing service using this NIR calibration is now operational for rice crops in southern New South Wales.     

Comparison of sampling methods for microbiological testing of beef animal rectal/colonal feces, hides, and carcasses

This study compared sampling methods for detecting Escherichia coli O157:H7 and Salmonella in beef cattle feces and on hides and carcasses and for enumerating E. coli biotype I counts (ECC) on carcasses. Fecal samples were collected by rectal/colonal palpation and colonal sponge swabbing. Hides were sampled by sponge swabbing three sites, hair clipping, excision, rinsing, and gauze swabbing, whereas carcasses were sampled by three-site thoracic and pattern-mark sponge swabbing and tissue excision. Overall, irrespective of sampling method, 36.7, 13.3, and 0.0% of lots contained at least one E. coli O157:H7-positive hide, fecal, and carcass sample, respectively, while the corresponding prevalence of Salmonella was 70.0, 16.7, and 6.7%, respectively. For hide sampling, excision and gauze swabbing yielded the fewest (13.3%) E. coli O157:H7-positive samples, while hair clipping and sponge swabbing yielded the most (23.3%). None of the carcass-sampling methods detected E. coli O157:H7 or differed (P > 0.05) in their ability to enumerate ECC. Colonal swabbing was the most effective (10.0%) method for detecting E. coli O157:H7 in feces. No differences (P > 0.05) in Salmonella prevalence were observed between carcass-sampling methods, although three-site sponge swabbing and tissue excision detected the most (3.3%). Hide rinsing was the most effective (P < 0.05) Salmonella detection method (63.3%), but dangers associated with its application may preclude its use by industry; there were no differences (P > 0.05) among other hide-sampling methods. No differences (P > 0.05) in Salmonella detection were observed between fecal-sampling methods. Overall, three-site sponge swabbing was the most feasible and effective sampling method for the detection of E. coli O157:H7 and Salmonella on hides and carcasses.     

The Biochemistry of Phytocannabinoids and Metabolic Engineering of Their Production in Heterologous Systems

The medicinal properties of cannabis and the its legal status in several countries and jurisdictions has spurred the massive growth of the cannabis economy around the globe. The value of cannabis stems from its euphoric activity offered by the unique phytocannabinoid tetrahydrocannabinol (THC). However, this is rapidly expanding beyond THC owing to other non-psychoactive phytocannabinoids with new bioactivities that will contribute to their development into clinically useful drugs. The discovery of the biosynthesis of major phytocannabinoids has allowed the exploration of their heterologous production by synthetic biology, which may lead to the industrial production of rare phytocannabinoids or novel synthetic cannabinoid pharmaceuticals that are not easily offered by cannabis plants. This review summarizes the biosynthesis of major phytocannabinoids in detail, the most recent development of their metabolic engineering in various systems, and the engineering approaches and strategies used to increase the yield.     

A case study in engineering model validation using new wavelet‐based methods

Simulation model validation is an important part of simulation development and use. An emerging challenge is the examination of functional data systems and the validation of the simulations built to represent them. While validation methods do exist, there is a gap in the engineering and statistical approaches used for functional model validation. This case study demonstrates the use of recently developed methods based on the use of wavelets to bridge the engineering‐statistical gap in functional simulation model validation. Two methods are used to provide insight regarding model validity, and a third method is used to identify areas of system‐simulation disagreement when model validity fails to hold.     

Evaluation of a thin-slot formalism for finite-differencetime-domain electromagnetics codes

A thin-slot formalism proposed by Gilbert and Holland (1981) for use with finite-difference time-domain (FDTD) electromagnetics codes has been evaluated in both two and three dimensions. This formalism allows narrow slots to be modeled in the wall of a scatterer without reducing the spatial grid size to the slot width. In two dimensions, the evaluation involves the calculation of the total fields near two infinitesimally thin coplanar strips separated by a gap. A method-of-moments (MoM) solution of the same problem serves as a benchmark for comparison. Results in two dimensions show that up to 10 percent error can be expected in total electric and magnetic fields both near (λ/40) and far (1 λ) from the gap. In three dimensions, the evaluation is similar. The finite-length slot is placed in a finite plate and an MoM surface patch solution is used for the benchmark. These data show that slightly larger errors can be expected     

Measurement of nonlinearity in chemical process control systems: The steady state map

Most chemical processes exhibit some degree of nonlinearity, and when selecting an appropriate controller design approach it is important to understand the extent of this nonlinearity. In this paper a quantitative measure of steady-state process nonlinearity is proposed. Drawing from results for nonlinear regression, the curvature is decomposed into tangential and normal components. It is shown that the tangential curvature can be reduced or eliminated by transforming the control inputs, whereas the normal curvature can be reduced or eliminated only by a combination of state feedback and transformations. The problem of scaling is addressed by identifying a “region of interest”, and scale-independent measures of curvature are proposed. Nonlinearity is measured both as root mean squared curvature and directional curvature. The importance of curvature in the foward and inverse steady-state maps is discussed, and a transformation suggested by the curvature arrays is presented. This transformation reduces the static nonlinearity in the process, and can be used to improve the controller performance. Application of the proposed techniques is illustrated using chemical process examples.