Solute and penetrant diffusion in swellable polymers: X. Swelling of multiethylene glycol dimethacrylate copolymers

The swelling behavior of copolymers containing 2-hydroxyethyl methacrylate and various multiethylene glycol dimethacrylates was examined at 25°C. These highly crosslinked copolymers show some hydrophilic behavior due to the hydroxyl groups of HEMA. Analysis of the swelling data indicates and anomalous water transport in the network, which depends on the degree of crosslinking attained according to the dimethacrylate comonomer molar fraction in the copolymerization feed. Thermomechanical analysis data were used to further characterize the network structure.     

The modified preconditioned simultaneous displacement (MPSD) method

In [4] it is shown that the Preconditioned Simultaneous Displacement (PSD) method when applied to σ₂-ordered systems of linear equations may be preferred over the Successive Overrelaxation (SOR) method in certain cases whereas it is undoubtedly superior over the symmetric SOR (SSOR) method. In this paper, we define a generalised form of PSD and the produced scheme, the Modified PSD (MPSD) method is considered for the solution of the linear system Au=b when A possesses a special form (σ₁-ordered). The analysis of convergence and the determination of optimum values for the involved parameters is presented. It is shown that if MPSD is combined with a work reduction scheme, then it may be considered competitive with SOR as the two methods possess the same rate of convergence at the optimum stage. Finally, it is proven that under these conditions PSD possesses a rate of convergence which is asymptotically twice as fast as SSOR, a result which is also valid for σ₂-ordered systems.     

A metric for quantifying the ripple effects among requirements

Software Quality Journal - During software maintenance, it is often costlier to identify and understand the artifacts that need to be changed, rather than to actually apply the change. In addition...     

Announcement: Howard Rosenbrock Prize 2021

Optimization and Engineering -     

Novel additively manufactured bio-inspired 3D structures for impact energy damping

Additive manufacturing enables the design of complicated structures that would not be feasible to manufacture otherwise. Novel bio-inspired 3D structures were digitally produced employing Voronoi tessellation techniques and manufactured by selective laser sintering from polyamide. Impact tests were performed to analyze the impact absorption capacity of these structures, while FEM modeling offered insights on the fracture mechanisms and the prediction of the material response, which proved to be highly sensitive to strain rate. The results show a considerable impact attenuation in the case of 80% porosity and strut radius of 0.5 mm, encountering small transmitted peak force and smooth deceleration.     

Description of a GIS-based rockfall hazard assessment methodology and its application in mountainous sites

Bulletin of Engineering Geology and the Environment - In Western Greece, rockfalls occur every year in residential areas and on public roads, causing considerable societal and economic damage. As a...     

Electromagnetic analysis of coupling and guiding phenomena in elliptical cross-section parallel waveguides with rotated symmetry planes

Rigorous electromagnetic analysis methods, based on the Green's function method along with the method of moments, are utilized to analyze coupling, guiding, and polarization phenomena in elliptic cross-section parallel waveguides. The analysis is carried out for the general case of closely spaced elliptic fibers of arbitrary orientation of the ellipses' axes. Numerical results are presented for the cases of 0 degrees and 45 degrees angles between axes, as well as for the single elliptical fiber and closely spaced circular dielectric waveguides. The possibility of using this type of coupling structure in quantum signal processing applications is examined.     

Conversion of yeast by hydrothermal treatment under reducing conditions

In the work reported here, baker’s yeast (Saccharomyces cerevisiae) was used as feed for the production of liquid biofuels in a continuous one-step process under hydrothermal conditions in the presence of excess hydrogen and K₂CO₃. The yeast conversion experiments were performed in an up-flow reactor under near-critical water conditions (T 330–450 °C, p 20–32 MPa). The products consisted of three phases, an oil-like organic phase, a gaseous phase, and an aqueous phase. Higher concentrations of organic carbon in the process resulted in a higher product yield. The heating value of the organic phase was up to 38.6 MJ/kg. Liquefaction of yeast without any addition of K₂CO₃ also resulted in liquid oil, but the quality and the yield of the oil product were lower. A reaction temperature of 400 °C was found to be optimal for the oil yield and quality.     

Catalytic conversion of waste biomass by hydrothermal treatment

The purpose of the work presented here is the production of liquid biofuels from wet organic waste matter in a continuous one-step catalytic process under hydrothermal conditions. The catalytic reaction of wet organic matter at near-critical water conditions (T > 300 °C, p > 22.1 MPa) is used to produce a mixture of combustible organics which can be used as liquid biofuel. In order to achieve a good product quality in a continuous one-step process, two catalysts were applied, a homogeneous potassium carbonate catalyst and a heterogeneous ZrO₂ catalyst. In addition, the reaction mixture was recirculated. The continuous flow of concentrated waste biomass feed at low flow rates and recirculation of the hot reaction mixture were the most challenging obstacles to overcome. The scale of the plant (0.1 l reactor volume) allowed for a variation of the feed, reaction temperature, and recirculation rate in order to optimise the process conditions. Still, the product quantity obtained was sufficient to perform a analytical characterisation. The experimental results confirmed the feasibility of the process. Hydrothermal treatment of waste biomass, after dewatering, resulted in a biocrude oil of high calorific value.