A Proposed Framework for Simulation Based Learning of Inheritance

Different types of serious games have been used in elucidating computer science areas such as computer games, mobile games, Lego-based games, virtual worlds and webbased games. Different evaluation techniques have been conducted like questionnaires, interviews, discussions and tests. Simulation have been widely used in computer science as a motivational and interactive learning tool. This paper aims to evaluate the possibility of successful implementation of simulation in computer programming modules. A framework is proposed to measure the impact of serious games on enhancing students understanding of key computer science concepts. Experiments will be held on the EEECS of Queen’s University Belfast students to test the framework and attain results.

Uplink Performance of Conventional and Massive MIMO Cellular Systems with Delayed CSIT

This work studies the uplink of a cellular network with zero-forcing (ZF) receivers under imperfect channel state information at the base station. More specifically, apart from the pilot contamination, we investigate the effect of time variation of the channel due to the relative users' movement with regard to the base station. Our contributions include analytical expressions for the sum-rate with finite number of BS antennas, and also the asymptotic limits with infinite power and number of BS antennas, respectively. The numerical results provide interesting insights on how the user mobility degrades the system performance which extends previous results in the literature.

I/Q imbalance in two-way AF relaying: Power allocation and performance analysis

We investigate the performance of dual-hop two-way amplify-and-forward (AF) relaying in the presence of inphase and quadrature-phase imbalance (IQI) at the relay node. In particular, the effective signal-to-interference-plus-noise ratio (SINR) at both sources is derived. These SINRs are used to design an instantaneous power allocation scheme, which maximizes the minimum SINR of the two sources under a total transmit power constraint. The solution to this optimization problem is analytically determined and used to evaluate the outage probability (OP) of the considered two-way AF relaying system. Both analytical and numerical results show that IQI can create fundamental performance limits on two-way relaying, which cannot be avoided by simply improving the channel conditions.

Design and Flux-Weakening Control of an Interior Permanent Magnet Synchronous Motor for Electric Vehicles

Permanent magnet synchronous motors (PMSMs) provide a competitive technology for EV traction drives owing to their high power density and high efficiency. In this paper, three types of interior PMSMs with different PM arrangements are modeled by the finite element method (FEM). For a given amount of permanent magnet materials, the V-shape interior PMSM is found better than the U-shape and the conventional rotor topologies for EV traction drives. Then the V-shape interior PMSM is further analyzed with the effects of stator slot opening and the permanent magnet pole chamfering on cogging torque and output torque performance. A vector-controlled flux-weakening method is developed and simulated in Matlab to expand the motor speed range for EV drive system. The results show good dynamic and steady-state performance with a capability of expanding speed up to four times of the rated. A prototype of the V-shape interior PMSM is also manufactured and tested to validate the numerical models built by the FEM.

Rational Function Interpolation of Electromagnetic Transfer Functions of High-Speed Interconnect Systems from Discrete Time-Domain and Frequency-Domain Data

We present new methodologies to generate rational function approximations of broadband electromagnetic responses of linear and passive networks of high-speed interconnects, and to construct SPICE-compatible, equivalent circuit representations of the generated rational functions. These new methodologies are driven by the desire to improve the computational efficiency of the rational function fitting process, and to ensure enhanced accuracy of the generated rational function interpolation and its equivalent circuit representation. Toward this goal, we propose two new methodologies for rational function approximation of high-speed interconnect network responses. The first one relies on the use of both time-domain and frequency-domain data, obtained either through measurement or numerical simulation, to generate a rational function representation that extrapolates the input, early-time transient response data to late-time response while at the same time providing a means to both interpolate and extrapolate the used frequency-domain data. The aforementioned hybrid methodology can be considered as a generalization of the frequency-domain rational function fitting utilizing frequency-domain response data only, and the time-domain rational function fitting utilizing transient response data only. In this context, a guideline is proposed for estimating the order of the rational function approximation from transient data. The availability of such an estimate expedites the time-domain rational function fitting process. The second approach relies on the extraction of the delay associated with causal electromagnetic responses of interconnect systems to provide for a more stable rational function process utilizing a lower-order rational function interpolation. A distinctive feature of the proposed methodology is its utilization of scattering parameters. For both methodologies, the approach of fitting the electromagnetic network matrix one element at a time is applied. It is shown that, with regard to the computational cost of the rational function fitting process, such an element-by-element rational function fitting is more advantageous than full matrix fitting for systems with a large number of ports. Despite the disadvantage that different sets of poles are used in the rational function of different elements in the network matrix, such an approach provides for improved accuracy in the fitting of network matrices of systems characterized by both strongly coupled and weakly coupled ports. Finally, in order to provide a means for enforcing passivity in the adopted element-by-element rational function fitting approach, the methodology for passivity enforcement via quadratic programming is modified appropriately for this purpose and demonstrated in the context of element-by-element rational function fitting of the admittance matrix of an electromagnetic multiport.

Post-shock thermochemistry in hypervelocity CO2 and air flow

This work represents ongoing efforts to study high-enthalpy carbon dioxide flows in anticipation of the upcoming Mars Science Laboratory (MSL) and future missions to the red planet. The work is motivated by observed anomalies between experimental and numerical studies in hypervelocity impulse facilities for high enthalpy carbon dioxide flows. In this work, experiments are conducted in the Hypervelocity Expansion Tube (HET) which, by virtue of its flow acceleration process, exhibits minimal freestream dissociation in comparison to reflected shock tunnels. This simplifies the comparison with computational result as freestream dissociation and considerable thermochemical excitation can be neglected. Shock shapes of the MSL aeroshell and spherical geometries are compared with numerical simulations incorporating detailed CO2 thermochemical modeling. The shock stand-off distance has been identified in the past as sensitive to the thermochemical state and as such, is used here as an experimental measurable for comparison with CFD and two different theoretical models. It is seen that models based upon binary scaling assumptions are not applicable for the low-density, small-scale conditions of the current work. Mars Science Laboratory shock shapes at zero angle of attack are also in good agreement with available data from the LENS X expansion tunnel facility, confi rming results are facility-independent for the same type of flow acceleration, and indicating that the flow velocity is a suitable first-order matching parameter for comparative testing. In an e ffort to address surface chemistry issues arising from high-enthalpy carbon dioxide ground-test based experiments, spherical stagnation point and aeroshell heat transfer distributions are also compared with simulation. Very good agreement between experiment and CFD is seen for all shock shapes and heat transfer distributions fall within the non-catalytic and super-catalytic solutions. We also examine spatial temperature profiles in the non-equilibrium relaxation region behind a stationary shock wave in a hypervelocity air Mach 7.42 freestream. The normal shock wave is established through a Mach reflection from an opposing wedge arrangement. Schlieren images confirm that the shock con guration is steady and the location is repeatable. Emission spectroscopy is used to identify dissociated species and to make vibrational temperature measurements using both the nitric oxide and the hydroxyl radical A-X band sequences. Temperature measurements are presented at selected locations behind the normal shock. LIFBASE is used as the simulation spectrum software for OH temperature-fitting, however the need to access higher vibrational and rotational levels for NO leads to the use of an in-house developed algorithm. For NO, results demonstrate the contribution of higher vibrational and rotational levels to the spectra at the conditions of this study. Very good agreement is achieved between the experimentally measured NO vibrational temperatures and calculations performed using an existing state-resolved, three-dimensional forced harmonic oscillator thermochemical model. The measured NO A-X vibrational temperatures are significantly higher than the OH A-X temperatures.

Desenvolvimento de um método para correção de curvas de desempenho em bombas centrífugas submersas operando com fluidos viscosos

Electrical Submersible Pump (ESP) is used as an artificial lift technique. However, pumping viscous oil is generally associated with low Reynolds number flows. This condition leads to a performance degradation respect to the performance expected from the regular operation with water that most of the centrifugal pumps are originally designed for. These issues are considered in this investigation through a numerical study of the flow in two different multistage, semi-axial type ESPs. This investigation is carried out numerically using a Computational Fluid Dynamics (CFD) package, where the transient RANS equations are solved numerically. The turbulence is modeled using the SST model. Head curves for several operating conditions are compared with manufacturer’s curves and experimental data for a three-stage ESP, showing good agreement for a wide range of fluid viscosities and rotational speeds. Dimensionless numbers (n, n, n e Re) are used to investigate performance degradation of the ESPs. In addition, flow phenomena through the impellers of the ESPs are investigated using flow field from numerical results. Results show that performance degradation is directly related to rotational Reynolds number, Re. In addition, it was verified that performance degradation occurs for constant normalized specific speedn, which shows that performance degradation occurs similarly for different centrifugal pumps. Moreover, experimental data and numerical results agreed with a correlation from literature between head and flow correction factors proposed by Stepanoff (1967). A definition of modified Reynolds number was proposed and relates the head correction factor to viscosity. A correlation between head correction factor and the modified Reynolds number was proposed, which agreed well with numerical and experimental data. Then, a method to predict performance degradation based on the previous correlations was proposed. This method was compared with others from literature. In general, results and conclusions from this work can also be useful to bring more information about the flow of highly viscous fluids in pumps, especially in semi-axial, multistage ESPs.

A study of the electrical basis for the inhibition and excitation in autonomically innervated smooth muscle

The aim of this thesis was to investigate the electrical and mechanical responses to inhibitory non-adrenergic noncholinergic (NANC) nerve stimulation in the bovine retractor penis muscle (BRP) and compare them with those to an inhibitory extract made from this muscle. The extract may contain the NANC inhibitory transmitter of the BRP and possibly of other smooth muscles. Because of species differences in the electrical response to NANC nerves in the rat and rabbit anococcygeus the effects of the extract on these tissues was also investigated. Prior to the investigation of the extract, both the excitatory and inhibitory responses to field stimulation in the BRP, and the effects of passive membrane potential displacement were studied using conventional intra- or extracellular (sucrose gap) recording techniques. The majority of cells in the BRP were electrically quiescent independent of the resting tone. The most frequent (in approximately 25% of preparations) form of spontaneous activity, oscillations in membrane potential and tone, may represent a pacemaker activity. The BRP had cable properties; the time constant and space constant indicated a high membrane resistance. In the absence of tone, field stimulation of the BRP evoked excitatory junction potentials (ejps) in every cell impaled and contractions, graded with the strength, frequency and number of pulses; spikes were not observed. Guanethidine (1-3 x 10-5M) abolished the ejps and contractions, confirming their adrenergic origin. Noradrenaline added exogenously depolarised and contracted the muscle. These effects were blocked by the a-adrenoceptor antagonists, phentolamine and prazosin. However, phentolamine (2.5x 10-6M) inhibited the contraction without reducing the ejp significantly. These effects may be independent of adrenoceptor blockade or the ejp may be mediated by a substance other than noradrenaline (e.g. ATP) released from adrenergic nerves. Prazosin (1.4 x lO-6M) failed to block either the ejp or contraction, indicating the possible existence of two types of adrenoceptor in the BRP; one activated by neuronally-released and the other by exogenously-added noradrenaline. ATP, a contaminant in the extract, also depolarised and contracted the BRP. Physostigmine reduced whilst atropine enhanced the ejps and contractions without similarly affecting the response to exogenous noradrenaline. This confirmed the presence of a cholinergic inhibitory innervation acting on the excitatory adrenergic fibres (Klinge and Sjostrand, 1977). TEA (1 x lO-4M) enhanced the ejp and contraction. Higher concentrations (0.5 to 10 x 10-3M) depolarised, increased the tone and evoked electrical and mechanical oscillations but no spikes. The depolarisation and contraction to exogenous noradrenaline were not enhanced, indicating that TEA acts on the adrenergic nerves. Some post-synaptic effect to block K+ channels also seems likely. The relationship between ejp amplitude and membrane potential in the double sucrose gap was linear and indicated a reversal potential more positive than -30mV. Electrotonic pulse amplitude decreased during the ejp, indicating an increased membrane conductance. Ejps and contractions were reduced following the replacement of the NaCl of the Krebs solution with sodium glutamate. This may be due to the effects of glutamate itself (e.g. Ca2+ chelation) rather than reduction in the membrane Cl- gradient. Tone usually developed spontaneously and was accompanied by membrane depolarisation (from -53 to -45mV) which may open voltage-dependent channels, causing Ca2+ entry and/or its release from intracellular binding sites. Field stimulation produced inhibitory potentials (ijps) and relaxations graded with the strength and number of pulses but showing little frequency dependence. Rebound depolarisation and contraction often followed the ijp and relaxation. Tetrodotoxin (3 x IO-6M), but not adrenergic or cholinergic antagonists, abolished the ijp and relaxation, confirming their non-adrenergic non-cholinergic neurogenic nature. The extract, prepared and acid-activated as described by Gillespie, Hunter and Martin (1981), hyperpolarised and relaxed the BRP, as did sodium nitroprusside and adenosine triphosphate (ATP). Unlike the activated extract or sodium nitroprusside, desensitisation to ATP occurred rapidly and without any change in the inhibitory electrical or mechanical responses to field stimulation. The ijp and relaxation in the BRP were insensitive to apamin but abolished by oxyhaemoglobin (4-8 x 10-6M), as were the responses to extract and sodium nitroprusside. In TEA (10-2M), field stimulation evoked relaxations with no accompanying electrical change. The ijp may be unconnected with or additional to another mechanism producing relaxation. The relationship between membrane potential and ijp in the BRP was non-linear. Ijp amplitude was initially increased during membrane potential displacement from -45mV to approximately -60mV. Thereafter (-60 to -l03mV) the ijp was reduced. Ijps were abolished at -27 and -103mV; reversal was not observed. The hyperpolarisation to extract was also enhanced during passive displacement of the membrane potential to more negative values (-57mV). Membrane resistance increased during the ijp. The extract produced inconsistent changes in membrane resistance, possibly because of the presence of more than one active component. K+ withdrawal failed to enhance the ijp or hyperpolarisation to extract and 20mM K+ did not abolish the the ijp at membrane potentials exceeding EK (-49mV). Thus, the ijp or hyperpolarisation to extract are unlikely to be mediated by an increased K+ conductance. Reducing the Cl- abolished the hyperpolarisation to field stimulation and extract. This occurred more quickly than the anticipated reduction in the Cl- gradient and may be due to Ca2+ chelation by the anion substitute (glutamate or benzenesulphonate) or blockade of the resting conductance which is normally inactivated by the transmitter. Ouabain (1-5x 10-5M), which reduces both the Na+ and Cl- gradients, abolished the ijp, implicating either of these ions as the ionic species involved. In the rat and rabbit anococcygeus, field stimulation and extract each reduced guanethidine-induced tone. This was unaccompanied in the majority of cells in the rat by any significant electrical response. In the remaining cells, inhibition of the membrane potential oscillations occurred. The rabbit anococcygeus differed in that inhibition of the electrical oscillations was observed in every cell exhibiting this behaviour. However, the majority of cells in the rabbit were electrically quiescent and showed only small hyperpolarisations to field stimulation and no electrical response to extract. Apamin (1 x 10-7M) failed to block the electrical and mechanical response to field stimulation in the rabbit but did inhibit transiently that to extract. The latter effect may be due to the initial excitatory effects of apamin. The similarities between the electrical effects of the extract and those of inhibitory nerve stimulation in the BRP, rat and rabbit anococcygeus muscles are generally consistent with their being mediated by the same active component. Moreover, the ijp in the BRP shows properties which have not been reported in other non-adrenergic noncholinergically innervated smooth muscles.

Studies of turbulent flows in continuous casting of steel with and without magnetic field

This thesis develops and tests various transient and steady-state computational models such as direct numerical simulation (DNS), large eddy simulation (LES), filtered unsteady Reynolds-averaged Navier-Stokes (URANS) and steady Reynolds-averaged Navier-Stokes (RANS) with and without magnetic field to investigate turbulent flows in canonical as well as in the nozzle and mold geometries of the continuous casting process. The direct numerical simulations are first performed in channel, square and 2:1 aspect rectangular ducts to investigate the effect of magnetic field on turbulent flows. The rectangular duct is a more practical geometry for continuous casting nozzle and mold and has the option of applying magnetic field either perpendicular to broader side or shorter side. This work forms the part of a graphic processing unit (GPU) based CFD code (CU-FLOW) development for magnetohydrodynamic (MHD) turbulent flows. The DNS results revealed interesting effects of the magnetic field and its orientation on primary, secondary flows (instantaneous and mean), Reynolds stresses, turbulent kinetic energy (TKE) budgets, momentum budgets and frictional losses, besides providing DNS database for two-wall bounded square and rectangular duct MHD turbulent flows. Further, the low- and high-Reynolds number RANS models (k-ε and Reynolds stress models) are developed and tested with DNS databases for channel and square duct flows with and without magnetic field. The MHD sink terms in k- and ε-equations are implemented as proposed by Kenjereš and Hanjalić using a user defined function (UDF) in FLUENT. This work revealed varying accuracies of different RANS models at different levels. This work is useful for industry to understand the accuracies of these models, including continuous casting. After realizing the accuracy and computational cost of RANS models, the steady-state k-ε model is then combined with the particle image velocimetry (PIV) and impeller probe velocity measurements in a 1/3rd scale water model to study the flow quality coming out of the well- and mountain-bottom nozzles and the effect of stopper-rod misalignment on fluid flow. The mountain-bottom nozzle was found more prone to the longtime asymmetries and higher surface velocities. The left misalignment of stopper gave higher surface velocity on the right leading to significantly large number of vortices forming behind the nozzle on the left. Later, the transient and steady-state models such as LES, filtered URANS and steady RANS models are combined with ultrasonic Doppler velocimetry (UDV) measurements in a GaInSn model of typical continuous casting process. LES-CU-LOW is the fastest and the most accurate model owing to much finer mesh and a smaller timestep. This work provided a good understanding on the performance of these models. The behavior of instantaneous flows, Reynolds stresses and proper orthogonal decomposition (POD) analysis quantified the nozzle bottom swirl and its importance on the turbulent flow in the mold. Afterwards, the aforementioned work in GaInSn model is extended with electromagnetic braking (EMBr) to help optimize a ruler-type brake and its location for the continuous casting process. The magnetic field suppressed turbulence and promoted vortical structures with their axis aligned with the magnetic field suggesting tendency towards 2-d turbulence. The stronger magnetic field at the nozzle well and around the jet region created large scale and lower frequency flow behavior by suppressing nozzle bottom swirl and its front-back alternation. Based on this work, it is advised to avoid stronger magnetic field around jet and nozzle bottom to get more stable and less defect prone flow.

Three-dimensional kinetic simulations of active suspensions: effect of chemotaxis and steric interaction

In this work, the effects of chemotaxis and steric interactions in active suspensions are analyzed by extending the kinetic model proposed by Saintillan and Shelley [1, 2]. In this model, a conservation equation for the active particle configuration is coupled to the Stokes equation for the flow arising from the force dipole exerted by the particles on the fluid. The fluid flow equations are solved spectrally and the conservation equation is solved by second-order finite differencing in space and second-order Adams-Bashforth time marching. First, the dynamics in suspensions of oxytactic run-and-tumble bacteria confined in thin liquid films surrounded by air is investigated. These bacteria modify their tumbling behavior by making temporal comparisons of the oxygen concentration, and, on average, swim towards high concentrations of oxygen. The kinetic model proposed by Saintillan and Shelley [1, 2] is modified to include run-and-tumble effects and oxygentaxis. The spatio-temporal dynamics of the oxygen and bacterial concentration are analyzed. For small film thicknesses, there is a weak migration of bacteria to the boundaries, and the oxygen concentration is high inside the film as a result of diffusion; both bacterial and oxygen concentrations quickly reach steady states. Above a critical film thickness (approximately 200 micron), a transition to chaotic dynamics is observed and is characterized by turbulent-like 3D motion, the formation of bacterial plumes, enhanced oxygen mixing and transport into the film, and hydrodynamic velocities of magnitudes up to 7 times the single bacterial swimming speed. The simulations demonstrate that the combined effects of hydrodynamic interactions and oxygentaxis create collective three-dimensional instabilities which enhances oxygen availability for the bacteria. Our simulation results are consistent with the experimental findings of Sokolov et al. [3], who also observed a similar transition with increasing film thickness. Next, the dynamics in concentrated suspensions of active self-propelled particles in a 3D periodic domain are analyzed. We modify the kinetic model of Saintillan and Shelley [1, 2] by including an additional nematic alignment torque proportional to the local concentration in the equation for the rotational velocity of the particles, causing them to align locally with their neighbors (Doi and Edwards [4]). Large-scale three- dimensional simulations show that, in the presence of such a torque both pusher and puller suspensions are unstable to random fluctuations and are characterized by highly nematic structures. Detailed measures are defined to quantify the degree and direction of alignment, and the effects of steric interactions on pattern formation will be presented. Our analysis shows that steric interactions have a destabilizing effect in active suspensions.

The Becker-Döring equations with monomer input, competition and inhibition

We investigate the Becker-Döring model of nucleation with three generalisations; an input of monomer, an input of inhibitor and finally, we allow the monomers to form two morphologies of cluster. We assume size-independent aggregation and fragmentation rates. Initially we consider the problem of constant monomer input and determine the steady-state solution approached in the large-time limit, and the manner in which it is approached. Secondly, in addition to a constant input of monomer we allow a constant input of inhibitor, which prevents clusters growing any larger and this removes them from the kinetics of the process; the inhibitor is consumed in the action of poisoning a cluster. We determine a critical ratio of poison to monomer input below which the cluster concentrations tend to a non-zero steady-state solution and the poison concentration tends to a finite value. Above the critical input ratio, the concentrations of all cluster sizes tend to zero and the poison concentration grows without limit. In both cases the solution in the large-time limit is determined. Finally we consider a model where monomers form two morphologies, but the inhibitor only acts on one morphology. Four cases are identified, depending on the relative poison to monomer input rates and the relative thermodynamic stability. In each case we determine the final cluster distribution and poison concentration. We find that poisoning the less stable cluster type can have a significant impact on the structure of the more stable cluster distribution; a counter-intuitive result. All results are shown to agree with numerical simulation.

Physical Design Methodologies for Low Power and Reliable 3D ICs

As the semiconductor industry struggles to maintain its momentum down the path following the Moore's Law, three dimensional integrated circuit (3D IC) technology has emerged as a promising solution to achieve higher integration density, better performance, and lower power consumption. However, despite its significant improvement in electrical performance, 3D IC presents several serious physical design challenges. In this dissertation, we investigate physical design methodologies for 3D ICs with primary focus on two areas: low power 3D clock tree design, and reliability degradation modeling and management. Clock trees are essential parts for digital system which dissipate a large amount of power due to high capacitive loads. The majority of existing 3D clock tree designs focus on minimizing the total wire length, which produces sub-optimal results for power optimization. In this dissertation, we formulate a 3D clock tree design flow which directly optimizes for clock power. Besides, we also investigate the design methodology for clock gating a 3D clock tree, which uses shutdown gates to selectively turn off unnecessary clock activities. Different from the common assumption in 2D ICs that shutdown gates are cheap thus can be applied at every clock node, shutdown gates in 3D ICs introduce additional control TSVs, which compete with clock TSVs for placement resources. We explore the design methodologies to produce the optimal allocation and placement for clock and control TSVs so that the clock power is minimized. We show that the proposed synthesis flow saves significant clock power while accounting for available TSV placement area. Vertical integration also brings new reliability challenges including TSV's electromigration (EM) and several other reliability loss mechanisms caused by TSV-induced stress. These reliability loss models involve complex inter-dependencies between electrical and thermal conditions, which have not been investigated in the past. In this dissertation we set up an electrical/thermal/reliability co-simulation framework to capture the transient of reliability loss in 3D ICs. We further derive and validate an analytical reliability objective function that can be integrated into the 3D placement design flow. The reliability aware placement scheme enables co-design and co-optimization of both the electrical and reliability property, thus improves both the circuit's performance and its lifetime. Our electrical/reliability co-design scheme avoids unnecessary design cycles or application of ad-hoc fixes that lead to sub-optimal performance. Vertical integration also enables stacking DRAM on top of CPU, providing high bandwidth and short latency. However, non-uniform voltage fluctuation and local thermal hotspot in CPU layers are coupled into DRAM layers, causing a non-uniform bit-cell leakage (thereby bit flip) distribution. We propose a performance-power-resilience simulation framework to capture DRAM soft error in 3D multi-core CPU systems. In addition, a dynamic resilience management (DRM) scheme is investigated, which adaptively tunes CPU's operating points to adjust DRAM's voltage noise and thermal condition during runtime. The DRM uses dynamic frequency scaling to achieve a resilience borrow-in strategy, which effectively enhances DRAM's resilience without sacrificing performance. The proposed physical design methodologies should act as important building blocks for 3D ICs and push 3D ICs toward mainstream acceptance in the near future.

Finite difference calculations of permeability in large domains in a wide porosity range.

Determining effective hydraulic, thermal, mechanical and electrical properties of porous materials by means of classical physical experiments is often time-consuming and expensive. Thus, accurate numerical calculations of material properties are of increasing interest in geophysical, manufacturing, bio-mechanical and environmental applications, among other fields. Characteristic material properties (e.g. intrinsic permeability, thermal conductivity and elastic moduli) depend on morphological details on the porescale such as shape and size of pores and pore throats or cracks. To obtain reliable predictions of these properties it is necessary to perform numerical analyses of sufficiently large unit cells. Such representative volume elements require optimized numerical simulation techniques. Current state-of-the-art simulation tools to calculate effective permeabilities of porous materials are based on various methods, e.g. lattice Boltzmann, finite volumes or explicit jump Stokes methods. All approaches still have limitations in the maximum size of the simulation domain. In response to these deficits of the well-established methods we propose an efficient and reliable numerical method which allows to calculate intrinsic permeabilities directly from voxel-based data obtained from 3D imaging techniques like X-ray microtomography. We present a modelling framework based on a parallel finite differences solver, allowing the calculation of large domains with relative low computing requirements (i.e. desktop computers). The presented method is validated in a diverse selection of materials, obtaining accurate results for a large range of porosities, wider than the ranges previously reported. Ongoing work includes the estimation of other effective properties of porous media.

Photoconductivity and electrical properties of diamond films grown by MPCVD

The electrical and photoconductive features of as-grown microwave-plasma-assisted chemical-vapour deposition (MPCVD) diamond films are studied in correlation with magnetic results obtained from electron paramagnetic resonance (EPR). Also, the morphology is analysed by atomic force microscopy (AFM) showing [111] crystals with a good uniformity of the deposit. The photoresponse as well the current-voltage features observed show an efficient photogeneration of carriers while the optoelectronic characteristics of the metal-diamond junction have an ideality factor of 1.6 together with a rectification ratio of about 10(4) at +/-2.5 V. The nature of the mechanisms responsible for the conduction is discussed. (C) 1998 Elsevier Science S.A.

Photoconductivity and electrical properties of diamond films grown by MPCVD

The electrical and photoconductive features of as-grown microwave-plasma-assisted chemical-vapour deposition (MPCVD) diamond films are studied in correlation with magnetic results obtained from electron paramagnetic resonance (EPR). Also, the morphology is analysed by atomic force microscopy (AFM) showing [111] crystals with a good uniformity of the deposit. The photoresponse as well the current-voltage features observed show an efficient photogeneration of carriers while the optoelectronic characteristics of the metal-diamond junction have an ideality factor of 1.6 together with a rectification ratio of about 10(4) at +/-2.5 V. The nature of the mechanisms responsible for the conduction is discussed. (C) 1998 Elsevier Science S.A.