When does a longer shut-in lead to a larger radius of investigation?

While the concept of radius of investigation is better understood for drawdown tests, its applicability to buildup tests is less certain. For example, a rule of thumb is that “one cannot see a particular feature in a buildup unless the radius of investigation during the preceding flow period has seen that feature”. In this paper, we clearly illustrate that the radius of investigation of a buildup can be larger than that of its previous flow period.Another common contention is that the radius of investigation of a buildup is limited by noise dominating the late-time pressure behavior. Oliver [Oliver, D.S., 1990. The averaging process in permeability estimation from well-test data. SPEFE. pp. 319–324.] and later Thompson and Reynolds [Thompson, L.G. and Reynolds, A.C, 1997. Well testing for radially heterogeneous reservoirs under single and multiphase flow conditions. SPEFE. pp. 57–64.] defined the radius of investigation based on the distance from the well to the region of the reservoir which has the greatest impact on the pressure derivative. We have used this approach to calculate the derivative and show that the ratio of noise to the signal from the reservoir does not necessarily increase. While many situations exist when radius of investigation of a build-up test is limited by the preceding flow period and noise, we show that when data is sampled appropriately, the radius of investigation of a buildup can easily go beyond that of the preceding flow period, and demonstrate when this may remain unaffected by noise.     

Application of ultrasonic irradiation for well deliverability improvement in gas-condensate reservoirs

In gas condensate reservoirs the process of condensation around the wellbore, when the pressure falls below the dewpoint, creates a condensate bank that can drastically reduce well productivity, requiring additional expensive wells to maintain the production level. Conventional remedial methods relying on removing the condensate bank are not generally long lasting, requiring repeated treatment.In this paper we present results of a study on the feasibility of using ultrasonic energy to alleviate the above problem by reducing the flow resistance in this region. Ultrasonic excitation of gas condensate systems was visually examined using high-pressure glass capillary tubes and micromodels with realistic pore patterns, simulating pores of a reservoir rock.Capillary tube experiments demonstrated that ultrasound radiation caused the gas-condensate interface to oscillate. In addition to destabilising the static equilibrium position of the interface, this oscillation also causes local mixing effects at the interface, lowering the effective liquid/gas interfacial tension. Results of our flow experiments in high-pressure glass micromodels showed that a significant amount of condensate was mobilised and recovered as a result of the application of ultrasound energy. We also show theoretically, that the radiation pressure caused by ultrasound waves exerts a net force on a fluid/fluid interface placed along the line of propagation of the wave. This force is a function of the phase difference between the applied acoustic field and the oscillation of the interface with the force being maximum at the resonance frequency.     

Production of Chlorosulfonated Rubber from Postconsumer Polyethylene and Evaluation of Produced Rubber Properties

In order to convert the postconsumer polyethylene to a valuable product, chlorosulfonation of virgin and highly degraded polyethylene has been carried out in the solution phase under atmospheric pressure. Produced chlorosulfonated polyethylene samples from virgin and degraded HDPE are compounded and cured at different temperatures and their mechanical properties are determined. The results show that degradation of used polyethylene does not have noticeable negative effects on the final mechanical properties of produced chlorosulfonated rubbers. Therefore, it can be concluded that chlorosulfonation can be considered as an effective new method for polyolefin recycling.     

Optimal robust control of drug delivery in cancer chemotherapy: A comparison between three control approaches

During the drug delivery process in chemotherapy, both of the cancer cells and normal healthy cells may be killed. In this paper, three mathematical cell-kill models including log-kill hypothesis, Norton–Simon hypothesis and E_max hypothesis are considered. Three control approaches including optimal linear regulation, nonlinear optimal control based on variation of extremals and H_∞-robust control based on μ-synthesis are developed. An appropriate cost function is defined such that the amount of required drug is minimized while the tumor volume is reduced. For the first time, performance of the system is investigated and compared for three control strategies; applied on three nonlinear models of the process. In additions, their efficiency is compared in the presence of model parametric uncertainties. It is observed that in the presence of model uncertainties, controller designed based on variation of extremals is more efficient than the linear regulation controller. However, H_∞-robust control is more efficient in improving robust performance of the uncertain models with faster tumor reduction and minimum drug usage.     

Motion control analysis of a parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS)

This paper presents motion control architectures for a parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS) that enable it to achieve milli/micro-manipulations under the constraint of moving through a fixed penetration point or so-called remote centre-of-motion (RCM) point without any mechanical constraint. Two control structures suitable for minimally invasive surgery operations with submillimeter accuracy and for minimally invasive microsurgery operations with the desired accuracy in micron range are proposed. The control algorithm also applies orientation constraints preventing the tip from orienting around the instrument axis due to the robot movements as well as a minimum displacement constraint to minimise the movements of the parallel micropositioning robot. Experiments were performed and the results are analysed in this paper to verify accuracy and effectiveness of the proposed control algorithm for both cases of minimally invasive surgery and microsurgery operations. The experimental results present good accuracy and performance of the control algorithm. The numerical modelling and graphical simulations were also carried out and the results are also provided that demonstrate the correlation between the experimental results and physical responses.     

Mathematical simulation of nitrogen interactions in soils

Four mathematical models were evaluated for their ability to describe the fate of nitrogen (N) in the soil environment. The first model is a general one which accounts for convective-dispersive N transport under transient water flow conditions with active N uptake by plants. Model II considers N transport to be only of the convective type, whereas model III considers N uptake as a passive process. In contrast, model IV considers N transport under conditions of steady water flow in the soil. Experimental data from lysimeter studies for two soils showed that the convective model (II) and the steady state model (IV) are inferior in describing N transport in comparison to models I and III. It is concluded that transient water flow in the soil system as well as the convective dispersive transport mechanisms must be considered for reliable simulation of N behavior in the soil environment.     

A new multi-level trust management framework (MLTM) for solving the invalidity and sparse problems of user feedback ratings in cloud environments

Choosing a trusted cloud service provider (CSP) is a major challenge for cloud users (CUs) in the cloud environment, as many CSPs offer cloud services (CSs) with the same functionality. Trust evaluation of CSPs is often based on information from quality of service (QoS) monitoring and CUs’ feedback ratings. Despite the volume of feedback ratings received in trust management systems, the quality of feedback storage is very low, as many CUs do not send their feedback ratings when using CSs. Additionally, a percentage of existing feedback ratings may not be valid, since some malicious CUs send unfair feedback ratings to change the trust evaluation results. As these lead to poor data quality, the accuracy of trust evaluation results might be affected. To overcome these limitations, this paper proposes a new multi-level trust management framework, which completes previous frameworks by defining new components to improve the data quality of feedback storage. In our framework, new components were defined to solve the invalidity and sparse problems of feedback storage. Certainly, the trust assessment of CSP would be more accurate based on high-quality feedback ratings. The performance of the MLTM was evaluated using two different datasets based on a real Quality of Web Services dataset (QWS) and an artificial data set (Cloud-Armor), whose quality was reduced for the purpose of this study. Analytical values revealed that our proposed approach significantly outperformed other approaches even with the poor data quality of feedback storage.

     

Numerical simulation of mass transfer in gas–liquid hollow fiber membrane contactors for laminar flow conditions

This study presents a numerical simulation using computational fluid dynamics (CFD) of momentum and mass transfer in a hollow fiber membrane contactor for laminar flow conditions. Axial and radial diffusion inside the fiber, through the membrane, and within the shell side of the membrane contactor were considered in the mass transfer equations. The simulation results were compared with the experimental data obtained from literature for CO₂ absorption in pure water. The simulation results indicated that the removal of CO₂ increased with increasing liquid flow rate in the shell side. On the other hand, increasing temperature and gas flow rate in the tube side have an opposite effect.     

On the synthetic dataset generation for IPTV services based on user behavior

Multimedia Tools and Applications - The adoption of the paradigm shift from push-based media broadcasting to pull-based media streaming has seen a significant growth in the recent decade. IPTV is...