Numerical computation of nonlinear oscillatory two‐immiscible magnetohydrodynamic flow in dual porous media system: FTCS and FEM study

The transient Hartmann magnetohydrodynamic flow of two immiscible fluids flowing through a horizontal channel containing two porous media with oscillating lateral wall mass flux is studied. A two‐dimensional spatial model is developed for two fluids, one of which is electrically conducting and the other is electrically insulating. Both the fluid regimes are driven by a common pressure gradient. A Darcy‐Forchheimer drag force model is used to simulate the porous media effects on the flow in both the fluid regimes. Special boundary conditions are imposed at the interface. The governing second‐order nonlinear partial differential dimensionless equations are obtained for each region using a set of transformations. The resulting transport equations are controlled by the Hartmann hydromagnetic parameter (Ha), viscosity ratio parameter (α), two Darcy numbers (Da ₁ and Da ₂), two Forchheimer numbers (Fs ₁ and Fs ₂), two Reynolds numbers (Re ₁ and Re ₂), frequency parameter ( εA) associated with the transpiration (lateral wall flux) velocity and a periodic frequency parameter ( ω*t*). Numerical forward time/central space finite‐difference solutions are obtained for a wide range of the governing parameters. Bench marking is performed with a Galerkin finite‐element method (MAGNETO‐FEM), and the results are found to be in excellent agreement. Applications of the model include magnetic cleanup operations in coastal/ocean seabed oil spills and electromagnetic purification of petroleum reservoir fluids.     

A semi-analytical solution for a two-dimensional capacitance model in solute transport

A two-dimensional capacitance model is presented for the analysis of solute transport in heterogeneous porous media where the transport processes are affected by mass transfer between the flowing volume in macropores and the stagnant volume in micropores. The semi-analytical solutions for both penetrating and nonpenetrating sources are obtained using double Laplace transforms and numerical inversions. The modeling results reveal the strong influences of dispersive and convective properties of porous media in the transverse direction on the overall transport that cannot be replicated by the current one-dimensional transport models. The solution may provide a useful tool to interpret some transport situations within common field geometries.     

Electrically Conductive Carbon Nanofiber Composites with High-Density Polyethylene and Glass Fibers

Carbon nanofibers are being investigated for incorporation into composites to improve mechanical, thermal, and electrical properties. The difficulties in making such composites are issues of dispersion of the nanofiber and wetting of the nanofibers by the matrix. The processing methods developed to date tend to be complex, involving multiple steps. This paper reports on a study to make electrically conductive composites with small volume fraction of vapor-grown carbon nanofibers (VGCF). The matrix is a high-density polyethylene (HDPE); the effect of adding glass fibers to this composite is also studied. Certain types of the VGCF fibers did not produce conductive composites with standard mixing techniques; however, VGCF nanofibers heat treated with a post-processing surface treatment produced conductive composites without extensive or vigorous dispersion techniques. The results indicate that surface treatments and dispersion methods are important factors in producing conductive composites. It is demonstrated that small volume fractions of nanofiber can be used to produce conductive composites without extensive processing steps.     

Differential effects of hypoxia with age on the chick embryonic heart. Changes in membrane potential, intracellular K and Na, K efflux and glycogen

The effects of hypoxia on different parameters of cell membrane function were studied in 7 and 19 day chick embryonic hearts. The following changes were observed: 1. Transmembrane potential: A depolarization of the cell membrane and a decrease in the duration and in the overshoot of the action potential. 2. Intracellular ion concentrations: A decrease in (K)i and an increase in (Na)i. Cellular Ca-content remained constant. 3. K efflux: An increase in the rate coefficient, which was larger in stimulated preparations. These changes were more pronounced in 19 day than in 7 day hearts. The effects of hypoxia were increased by simultaneous substrate depletion and counteracted by an excess external glucose. We conclude that: 1. The 19 day hearts are more sensitive to oxygen lack than the 7 day hearts. The difference can be correlated with the observation that the younger hearts are able to consume more glycogen during hypoxia. 2. The changes of the resting membrane potential and the overshoot of the action potential correlate with changes in respectively (K)i and (Na)i. 3. An increase in the background K current may be an important factor in explaining the shortening of the action potential during hypoxia.     

The design and realization of CoViD: a system for collaborative virtual 3D design

Many important decisions in the design process are made during fairly early on, after designers have presented initial concepts. In many domains, these concepts are already realized as 3D digital models. Then, in a meeting, the stakeholders for the project get together and evaluate these potential solutions. Frequently, the participants in this meeting want to interactively modify the proposed 3D designs to explore the design space better. Today’s systems and tools do not support this, as computer systems typically support only a single user and computer-aided design tools require significant training. This paper presents the design of a new system to facilitate a collaborative 3D design process. First, we discuss a set of guidelines which have been introduced by others and that are relevant to collaborative 3D design systems. Then, we introduce the new system, which consists of two main parts. The first part is an easy-to-use conceptual 3D design tool that can be used productively even by naive users. The tool provides novel interaction techniques that support important properties of conceptual design. The user interface is non-obtrusive, easy-to-learn, and supports rapid creation and modification of 3D models. The second part is a novel infrastructure for collaborative work, which offers an interactive table and several large interactive displays in a semi-immersive setup. It is designed to support multiple users working together. This infrastructure also includes novel pointing devices that work both as a stylus and a remote pointing device. The combination of the (modified) design tool with the collaborative infrastructure forms a new platform for collaborative virtual 3D design. Then, we present an evaluation of the system against the guidelines for collaborative 3D design. Finally, we present results of a preliminary user study, which asked naive users to collaborate in a 3D design task on the new system.     

Evidence of irradiation‐induced crosslinking in miscible blends of poly(vinyl chloride)/epoxidized natural rubber in presence of trimethylolpropane triacrylate

Electron‐beam initiated crosslinking of a poly(vinyl chloride)/epoxidized natural rubber blend (PVC/ENR), which contained trimethylolpropane triacrylate (TMPTA), was carried out over a range of irradiation doses (20–200 kGy) and concentrations of TMPTA (1–5 phr). The gelation dose was determined by a method proposed by Charlesby. It was evident from the gelation dose, resilience, hysteresis, glass‐transition temperature (T_g), IR spectroscopy, and scanning electron microscopy studies that the miscible PVC/ENR blend underwent crosslinking by electron‐beam irradiation. The acceleration of crosslinking by the TMPTA was further confirmed in this study. Agreement of the results with a theory relating the T_g with the distance between crosslinks provided further evidence of irradiation‐induced crosslinking. The possible mechanism of crosslinking induced by the irradiation between PVC and ENR is also proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1914–1925, 2001     

Novel Nano Structure for Green Energy Harvesting at 10 μm Thermal Radiation

In recent years, the potential of renewable green energy sources has been extensively studied. The proven technology which is photovoltaic solar cells strictly depends on daylight and produces low-efficiently. To overcome the restrictions, one technology studied is through harvesting the thermal radiation energy which can provide a 24-hour energy source. The continuity of energy sources promises very good energy conversion especially for military applications. This article presents a new structure that can harvest the abundant thermal radiation energy into usable energy at the wavelength of 10 m. A rectangular structure with a perturbation slit was designed to integrate with a rectifier circuit for green energy conversion. The slit tunnel junction guided the electromagnetic field into a junction where the energy could be collected and converted. An enhancement factor of approximately 110.6 can be achieved by a perturbation slit length of 1.0 m. The results extracted from the proposed design promise a better candidate to overcome the disadvantages of photovoltaic solar cells for energy harvesting devices.     

Policy and market barriers to energy storage providing multiple services

Policy and market conditions remain the primary barriers to stacking energy storage services, reducing its cost-competitiveness with traditional technologies. This article explores two cases that show how treating energy storage as a traditional asset class providing either market-remunerated or regulated services limits its profitability, and how changing market rules creates regulatory risk that could be mitigated through stacking services.     

Interface-tuned epoxy/clay nanocomposites

Though interface has been known for a critical role in determining the properties of conventional composites, its role in polymer nanocomposites is still fragmented and in its infancy. This study synthesized a series of epoxy/clay nanocomposites with different interface strength by using three types of modifiers: ethanolamine (denoted ETH), Jeffamine^® M2070 (M27) and Jeffamine^® XTJ502 (XTJ). XTJ created a strong interface between clay layers and matrix because it bridged the layers with matrix by a chemical reaction as proved by Fourier transform infrared spectroscopy; M27 produced an intermediate interface strength due to the molecular entanglement between grafted M27 chains and matrix molecules; the interface made by ETH was weak because neither chemical bridging nor molecular entanglement was involved. The studies of mechanical and thermal properties and morphology at a wide range of magnification show that the strong interface promoted the highest level of exfoliation and dispersion of clay layers, and achieved the most increment in Young’s modulus, fracture toughness and glass transition temperature (T_g) of matrix. With ∼1.3 wt% clay, the critical strain energy release rate G_1c of neat epoxy improved from 179.0 to 384.7 J/m, 115% improvement and T_g enhanced from 93.7 to 99.7 °C, 6.4% improvement.