A numerical study of dynamic capillary pressure effect for supercritical carbon dioxide‐water flow in porous domain

Numerical simulations for core‐scale capillary pressure (P^c)‐saturation (S) relationships have been conducted for a supercritical carbon dioxide‐water system at temperatures between 35°C and 65°C at a domain pressure of 15 MPa as typically expected during geological sequestration of CO₂. As the P^c‐S relationships depend on both S and time derivative of saturation ( ) yielding what is known as the “dynamic capillary pressure effect” or simply “dynamic effect,” this work specifically attempts to determine the significance of these effects for supercritical carbon dioxide‐water flow in terms of a coefficient, namely dynamic coefficient (τ). The coefficient establishes the speed at which capillary equilibrium for supercritical CO₂ (scCO₂)‐water flow is reached. The simulations in this work involved the solution of the extended version of Darcy's law which represents the momentum balance for individual fluid phases in the system, the continuity equation for fluid mass balance, as well as additional correlations for determining the capillary pressure as a function of saturation, and the physical properties of the fluids as a function of temperature. The simulations were carried out for three‐dimensional cylindrical porous domains measuring 10 cm in diameter and 12 cm in height. τ was determined by measuring the slope of a best‐fit straight line plotted between (1) the differences in dynamic and equilibrium capillary pressures against (2) the time derivative of saturation (dS/dt), both at the same saturation value. The results show rising trends for τ as the saturation values reduce, with noticeable impacts of temperature at 50% saturation of aqueous phase. This means that the time to attain capillary equilibrium for the CO₂‐water system increases as the saturation decreases. From a practical point of view, it implies that the time to reach capillary equilibrium during geological sequestration of CO₂ is an important factor and should be accounted for while simulating the flow processes, for example, to determine the CO₂ storage capacity of a geological aquifer. In this task, one would require both the fundamental understanding of the dynamic capillary pressure effects for scCO₂‐water flow as well as τ values. These issues are addressed in this article. © 2014 American Institute of Chemical Engineers AIChE J 60: 4266–4278, 2014     

Dynamic effects in capillary pressure relationships for two‐phase flow in porous media: Experiments and numerical analyses

Well defined experiments and numerical analyses are conducted to determine the importance of dynamic effect in capillary pressure relationships for two‐phase flow in porous media. Dynamic and quasi‐static capillary pressure‐saturation (P^c‐S_w) and, ?S_w/?t‐t curves are determined. These are then used to determine the dynamic effects, indicated by a dynamic coefficient (τ) in the porous domains which establishes the speed at which flow equilibrium (?S_w/?t = 0) is reached. τ is found to be a nonlinear function of saturation which also depends on the medium permeability. Locally determined τ seems to increase as the distance of the measurement point from the fluid inlet into the domain increases. However, the functional dependence τ‐S_w follows similar trends at different locations within the domain. We argue that saturation weighted average of local τ‐S_w curves can be defined as an effective τ‐S_w curve for the whole domain which follows an exponential trend too. © 2012 The Authors. AIChE Journal, published by Wiley on behalf of the AIChE. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. AIChE J, 58: 3891–3903, 2012     

Structured singular value of a repeated complex full-block uncertainty

The structured singular value (SSV), or $\mu$, is used to assess the robust stability and performance of an uncertain linear time-invariant system. Existing algorithms compute upper and lower bounds on the SSV for structured uncertainties that contain repeated (real or complex) scalars and/or nonrepeated complex full-blocks. This paper presents algorithms to compute bounds on the SSV for the case of repeated complex full-blocks. This specific class of uncertainty is relevant for the input-output analysis of many convective systems, such as fluid flows. Specifically, we present a power iteration to compute the SSV lower bound for the case of repeated complex full-blocks. This generalizes existing power iterations for repeated complex scalars and nonrepeated complex full-blocks. The upper bound can be formulated as a semi-definite program (SDP), which we solve using a standard interior-point method to compute optimal scaling matrices associated with the repeated full-blocks. Our implementation of the method only requires gradient information, which improves the computational efficiency of the method. Finally, we test our proposed algorithms on an example model of incompressible fluid flow. The proposed methods provide less conservative bounds as compared to prior results, which ignore the repeated full-block structure.     

Le questionnaire d'évaluation des relations parent/enfant (QéRPE): Une validation fran?aise de l'Egna Minnen Betr?ffende Uppfostran (EMBU).

Parents influence a child's development and his or her success in academic, sports or musical matters. Their support is essential for success. However, some of their behaviours may also have a negative impact. We need to better define parent/child relationships and their influence on the success and well-being of the child. Questionnaires are helpful in this respect, but few valid tools in French exist. Those available do not focus on evaluating dimensions central to child development. This article is aimed at validating the French translation of the EMBU questionnaire (Egna Minnen Betr?ffende Uppfostran, Perris, Jacobsson, Lindstr??m, von Knorring & Perris, 1980), the Questionnaire d'évaluation des relations parents/enfant (QéRPE), Questionnaire to Evaluate Parent/Child Relationships. It assesses the levels of parental support, overprotection and rejection experienced by children. We applied it to relationships between parents and sports-lovers. We tested the factorial structure (exploratory and confirmatory analyses) and the internal consistency of the QéRPE, and conducted external validation. Our results demonstrated that the psychometric qualities of the QéRPE are very acceptable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization and kinetics of gastric emptying of peptides derived from milk proteins in the preruminant calf.

The gastric emptying kinetics of peptides derived from milk protein were studied in vivo in preruminant calves by collecting and characterizing the whole effluent leaving the stomach for 12 h after ingestion of crude skim milk. Peptides were isolated by reversed-phase HPLC and identified. Particular attention was paid to biologically active peptides and to peptides that could be precursors of biologically active sequences. A gastrin inhibitor, the caseinomacropeptide, was emptied from the stomach only during the first 0.5 h of digestion and rapidly hydrolysed. Precursors of immunostimulatory peptides from alpha s1- and beta-caseins were emptied throughout digestion in the gastric effluent. A precursor of beta-casomorphins (peptide 58-93 of beta-casein) was emptied from the stomach 3.5 h after the meal when it was taken on an empty stomach. From this precursor, peptides that may be resistant to hydrolysis by intestinal peptidase were obtained after in vitro hydrolysis by pancreatic enzymes. A phosphopeptide (fragment 110-142 of alpha s1-casein) was also found in digesta after a few hours of digestion. When the meal was not taken on an empty stomach, these peptides were emptied in the first digesta at a low concentration. The potential activity of these peptides is discussed. The results support the hypothesis that active sequences could still be present in the gut after the action of pancreatic enzymes.     

Modelling transdermal delivery of high molecular weight drugs from microneedle systems

In the past few years, a number of microneedle designs have been proposed for transdermal drug delivery of high molecular weight drugs. However, most of them do not increase the drug permeability in skin significantly. In other cases, designs developed based on certain criteria (e.g. strength of the microneedles) have failed to meet other criteria (e.g. drug permeability in skin, throughputs of the drugs, etc.). It is obvious therefore that in order to determine the 'optimum' design of these microneedles, the effect of different factors (e.g. length of the microneedle, surface area of the patch, etc.) along with various transport properties of drug transport behaviour using microneedles should be determined accurately. Appropriate mathematical models for drug transport from these systems into skin have the potential to resolve some of these issues. To address this, a parametric analysis for transdermal delivery of a high molecular weight drug from a microneedle is presented in this paper. The simulations have allowed us to identify the significance of various factors that influence the drug delivery while designing microneedle arrays. A scaling analysis is also done which shows the functional dependence of drug concentration on other variables of skin and microneedle arrays.     

Avoidance of churn rate through temporal centralization in Chord

In this paper we have introduced a concept called temporal centralization to handle high churn rate without disturbing the original decentralized architecture of Peer-to-Peer overlay system. The frequent joining/leaving of nodes in a P2P system costs high. We know that the well-known structured system like Chord handles query in O(logn), but node joining/leaving is O(logn)², where n is the number of nodes available in the system. Therefore, with high churn rate, it is hard to maintain the cost of routing table. In our approach, updation of all routing tables are not done immediately after a node joining the system. We introduce the concept of temporal centralization to Chord protocol that reduces the churn rate retaining the same number of steps for query processing. The simulation results show the improvement of performance of P2P network reducing transient node population.     

Simple,efficient location‐based routing for data center network using IP address hierarchy

Increasing demand and sophistication of applications deployed on data centers resulted in various designs for data center networks (DCNs). One of the major challenges in the design of DCNs is the design of routing protocol that scales to support millions of servers that a typical DCN hosts. Many alternative routing protocols are proposed to overcome the scalability problem of conventional routing protocols such as Open Shortest Path First and Routing Information Protocol. These alternative protocols that use topology characteristics of DCN are broadly classified as source routing and location‐based routing. In the process of fixing the scalability problem, these protocols introduced additional complexities such as large network control overhead and reprogramming of network elements. The extra control overhead in these protocols is the result of their effort to determine the relative location of the end hosts in a given topology. Further, existing location‐based routing is not entirely location based and covers only the latter half of a route. In our work, we present a new location‐based routing based on IP address hierarchy that (a) does not need any additional network control plane and management planes, (b) deployable on proven network technologies, and (c) covers entire path of the route. We establish the correlation between topology design and address assignments that helps determining the location of an end host directly from the address assigned to it. We demonstrate our proposed location‐based routing on an existing proven architecture for DCN, BCube‐IP and on our proposed architecture 4‐4, 1‐4. We give proper justification for proposing 4‐4, 1‐4, a better design for our proposed location‐based routing. Copyright © 2016 John Wiley & Sons, Ltd.     

Direct electrochemistry of dinuclear CuA fragment from cytochrome c oxidase of Thermus thermophilus at surfactant modified glassy carbon electrode

Cytochrome c oxidase is ubiquitous enzyme involved in the terminal step of respiratory electron transfer process. The unique binuclear copper center containing bis-dithiolato bridges form a valance delocalized [Cu^1.5+-Cu^1.5+] state of the metal center located at the subunit II of cytochrome c oxidase. This metal center acts as the electron entry site of the enzyme and accepts electrons from cytochrome c. Direct electrochemistry of this binuclear copper center containing the water soluble protein obtained by genetically truncating the membrane bound part of the subunit II from Thermus thermophilus was achieved by favorable orientation of the protein on glassy carbon electrode surface promoting efficient electron transfer in the presence of various surfactants. Very reproducible, Nernstian responses are obtained with Cu_A. The redox potential and the electrochemical response were enhanced prominently in case of cationic surfactant CTAB indicating that the nature of the surfactant has a significant effect on the microenvironment of the protein-electrode interface. The results have been used to understand the mechanism of electron transfer from cytochrome c to the copper center during the enzymatic reaction.     

A prognostic approach for non-punch through and field stop IGBTs

Development of prognostic approaches for insulated gate bipolar transistors (IGBTs) is of interest in order to improve availability, reduce downtime, and prevent failures of power electronics. In this study, a prognostic approach was developed to identify anomalous behavior in non-punch through (NPT) and field stop (FS) IGBTs and predict their remaining useful life. NPT and FS IGBTs were subjected to electrical–thermal stresses until their failure. X-ray analysis performed before and after the stress tests revealed degradation in the die attach. The gate–emitter voltage (V_GE), collector–emitter voltage (V_CE), collector–emitter current (I_CE), and case temperature were monitored in situ during the experiment. The on-state collector–emitter voltage (V_CE(ON)) increased and the on-state collector–emitter current (I_CE(ON)) decreased during the test. A Mahalanobis distance (MD) approach was implemented using the V_CE(ON) and I_CE(ON) parameters for anomaly detection. Upon anomaly detection, the particle filter algorithm was triggered to predict the remaining useful life of the IGBT. The system model for the particle filter was obtained by a least squares regression of the V_CE(ON) at the mean test temperature. The failure threshold was defined as a 20% increase in V_CE(ON). The particle filter approach, developed using the system model based on the V_CE(ON), was demonstrated to provide mean time to failure estimates of IGBT remaining useful life with an error of approximately 20% at the time of anomaly detection.