Engineering, United Kingdom
Engineering, United Kingdom

Time filter

Source Type

Nezafati N.,Amirkabir University of Technology | Moztarzadeh F.,Amirkabir University of Technology | Hesaraki S.,Iranian Materials and Energy Research Center | Mozafari M.,Amirkabir University of Technology | And 4 more authors.
Key Engineering Materials | Year: 2012

Human beings are often infected by microorganisms in the living environment. Among various natural and inorganic substances, silver or silver ions have a powerful antibacterial activity. In the present study, the bioactivity and antibacterial activity of the SiO2-CaO-P 2O5-Ag2O was compared with that of its ternary counterpart glass system (as a control sample) in vitro. The molar ratio of silver oxide in the bioactive glass composition was considered as different amount (0.5%, 1% and 2%). The surface characterization was evaluated after soaking in simulated body fluid (SBF). The sharpest apatite peak in X-ray diffraction (XRD) analyse after 7 days soaking in SBF was observed for 2% Ag sample (2%Ag-BG). Hence, the antibacterial effects of 2%Ag-BG sample against 2 gram negatives bacterium were examined by agar plate test. The result showed that the amount of silver did not prevent the HAp formation. Also, the antibacterial properties of 2%Ag-BG sample indicated near 100% bactericidal ratio (according to the width of antibacterial halo). © (2012) Trans Tech Publications.

Paulen R.,TU Dortmund | Paulen R.,Center for Process Systems Engineering | Villanueva M.,Center for Process Systems Engineering | Chachuat B.,Center for Process Systems Engineering
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2013

This paper is concerned with guaranteed parameter estimation in nonlinear dynamic systems in a context of bounded measurement error. The problem consists of finding-or approximating as closely as possible-the set of all possible parameter values such that the predicted outputs match the corresponding measurements within prescribed error bounds. An exhaustive search procedure is applied, whereby the parameter set is successively partitioned into smaller boxes and exclusion tests are performed to eliminate some of these boxes, until a prespecified threshold on the approximation level is met. In order to enhance the convergence of this procedure, we investigate the use of optimization-based domain reduction techniques for tightening the parameter boxes before partitioning. We construct such bound-reduction problems as linear programs from the polyhedral relaxation of Taylor models of the predicted outputs. When applied to a simple case study, the proposed approach is found to reduce the computational burden significantly, both in terms of CPU time and number of iterations. © IFAC.

Siti-Ismail N.,Center for Process Systems Engineering | Siti-Ismail N.,Imperial College London | Samadikuchaksaraei A.,Center for Process Systems Engineering | Bishop A.E.,Imperial College London | And 2 more authors.
Tissue Engineering - Part C: Methods | Year: 2012

Application of stem cells for cell therapy of respiratory diseases is a developing field. We have previously established several protocols for the differentiation of embryonic stem cells (ESC) into alveolar epithelial cells, which require a high degree of operator interference and result in a low yield of target cells. Herein, we have shown that, by provision of a medium conditioned using A549 cells and by integration of classic steps of ESC differentiation into a single step through encapsulation in hydrogels (three-dimensional) and culture in a rotary bioreactor, murine ESC (mESC) could be directed to differentiate into distal respiratory epithelial cells. Type I and II pneumocytes (with a yield of 50% for type II) and Clara cells were demonstrated by the expression of aquaporin 5, surfactant protein C, and Clara cell secretory protein, respectively. We identified target cells as early as day 5 of culture and stably maintained our differentiated cells in vitro for 100 days. Electron microscopy demonstrated microvilli and intracellular lamellar bodies (LB), and fluorescent staining confirmed the active process of exocytosis of these LB in differentiated type II cells. When these cells were decapsulated and cultured in static conditions in flask cultures (two-dimensional), they retained their characteristic type II phenotype and morphology. In conclusion, our protocol offers integrated bioprocessing, shorter time of differentiation, lower cost, no use of growth factors, high reproducibility, and high phenotypic and functional stability, as well as being amenable to automation and being scalable, which would move this field closer to future clinical applications. © 2012, Mary Ann Liebert, Inc.

Alam-Nazki A.,Center for Process Systems Engineering | Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
BMC Systems Biology | Year: 2012

Background: Spatial signal transduction plays a vital role in many intracellular processes such as eukaryotic chemotaxis, polarity generation and cell division. Furthermore it is being increasingly realized that the spatial dimension to signalling may play an important role in other apparently purely temporal signal transduction processes. It is increasingly being recognized that a conceptual basis for studying spatial signal transduction in signalling networks is necessary.Results: In this work we examine spatial signal transduction in a series of standard motifs/networks. These networks include coherent and incoherent feedforward, positive and negative feedback, cyclic motifs, monostable switches, bistable switches and negative feedback oscillators. In all these cases, the driving signal has spatial variation. For each network we consider two cases, one where all elements are essentially non-diffusible, and the other where one of the network elements may be highly diffusible. A careful analysis of steady state signal transduction provides many insights into the behaviour of all these modules. While in the non-diffusible case for the most part, spatial signalling reflects the temporal signalling behaviour, in the diffusible cases, we see significant differences between spatial and temporal signalling characteristics. Our results demonstrate that the presence of diffusible elements in the networks provides important constraints and capabilities for signalling.Conclusions: Our results provide a systematic basis for understanding spatial signalling in networks and the role of diffusible elements therein. This provides many insights into the signal transduction capabilities and constraints in such networks and suggests ways in which cellular signalling and information processing is organized to conform to or bypass those constraints. It also provides a framework for starting to understand the organization and regulation of spatial signal transduction in individual processes. © 2012 Alam-Nazki and Krishnan; licensee BioMed Central Ltd.

Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
Industrial and Engineering Chemistry Research | Year: 2011

There has been a considerable effort in the past decade to understand different aspects of cellular processes from both a reverse engineering and, more recently, a synthetic perspective. In this article I provide a perspective on aspects of cellular signal processing which involve traditional chemical engineering elements (reactions, transport, control) and their variants, along with additional ingredients, sometimes combined in unusual ways. I also compare and contrast certain basic aspects of chemical engineering and cellular signal processing in areas of mutual overlap. © 2011 American Chemical Society.

Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London | Alam-Nazki A.,Center for Process Systems Engineering
Journal of Theoretical Biology | Year: 2011

Many important cellular processes rely on cellular responses to spatially graded signals. This response may be either attractive, indicating a positive bias, or repulsive indicating a negative bias. In this paper we consider cells which exhibit both repulsive and attractive gradient sensing responses and aim to uncover the underlying design principles and features of how the networks are wired which could allow a cell to exhibit both responses. We use a modular approach to examine different configurations which will allow for a cell to exhibit both responses and analyse how this depends on the basic characteristics of gradient sensing and downstream signal propagation. Overall our analysis provides insights into how gradient responses can be switched and the key factors which affect this switching. © 2010 Elsevier Ltd.

Suwanmajo T.,Center for Process Systems Engineering | Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
Journal of the Royal Society Interface | Year: 2013

Multi-site phosphorylation systems are repeatedly encountered in cellular biologyandmulti-sitemodification is a basic building blockofpost-translational modification. In this paper, we demonstrate how distributive multi-site modification mechanisms by a single kinase/phosphatase pair can lead to biphasic/ partial biphasic dose-response characteristics for the maximally phosphorylated substrate at steady state. We use simulations and analysis to uncover a hidden competing effect which is responsible for this and analyse how it may be accentuated.We build on this to analyse different variants of multi-site phosphorylation mechanisms showing that some mechanisms are intrinsically not capable of displaying this behaviour. This provides both a consolidated understanding of howand under what conditions biphasic responses are obtained in multi-site phosphorylation and a basis for discriminating between different mechanisms based on this. We also demonstrate how this behaviour may be combined with other behaviour such as threshold and bistable responses, demonstrating the capacity of multi-site phosphorylation systems to act as complex molecular signal processors. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

Alhajaj A.,Center for Process Systems Engineering | Mac Dowell N.,Center for Process Systems Engineering | Shah N.,Center for Process Systems Engineering
Energy Procedia | Year: 2013

An integrated whole-system model of a CO2 capture, transport and storage (CCTS) network was developed in order to design the optimum network linking CO2 sources (e.g., power stations) with potential sinks (e.g., depleted oil reservoirs). This work is multiscale in nature, employing models describing system behaviour and interactions through a range of length and timescales. We used our model to determine the optimum location and operating conditions of each CO2 capture process while giving full consideration to the whole-system behaviour. Further, researchers assume a cost associated with a pre-specified 90% degree of capture. However, an important result of designing and analysing cost optimal CCTS networks for the UAE was that the cost optimal degree of capture is a site specific factor that depends on the flue gas characteristics, proximity to transportation networks and adequate geological storage capacity. The results of this study indicated an optimum capture rate lower than the one obtained by looking into account the economies of the capture plant alone. This conclusion serves to underscore the importance of a whole-system analysis of potential CCTS networks.

Pistikopoulos E.N.,Center for Process Systems Engineering | Dominguez L.,Center for Process Systems Engineering | Panos C.,Center for Process Systems Engineering | Kouramas K.,Center for Process Systems Engineering | Chinchuluun A.,Center for Process Systems Engineering
Computational Management Science | Year: 2012

This paper presents an overview of recent theoretical and algorithmic advances, and applications in the areas of multi-parametric programming and explicit/multi-parametric model predictive control (mp-MPC). In multi-parametric programming, advances include areas such as nonlinear multi-parametric programming (mp-NLP), bi-level programming, dynamic programming and global optimization for multi-parametric mixed-integer linear programming problems (mp-MILPs). In multi-parametric/explicit MPC (mp-MPC), advances include areas such as robust multi-parametric control, multi-parametric nonlinear MPC (mp-NMPC) and model reduction in mp-MPC. A comprehensive framework for multi-parametric programming and control is also presented. Recent applications include a hydrogen storage device, a fuel cell power generation system, an unmanned autonomous vehicle (UAV) and a hybrid pressure swing adsorption (PSA) system. © 2012 Springer-Verlag.

Suwanmajo T.,Center for Process Systems Engineering | Krishnan J.,Center for Process Systems Engineering | Krishnan J.,Imperial College London
Journal of the Royal Society Interface | Year: 2015

Multi-site phosphorylation is ubiquitous in cell biology and has been widely studied experimentally and theoretically. The underlying chemical modification mechanisms are typically assumed to be distributive or processive. In this paper, we study the behaviour of mixed mechanisms that can arise either because phosphorylation and dephosphorylation involve different mechanisms or because phosphorylation and/or dephosphorylation can occur through a combination of mechanisms. We examine a hierarchy of models to assess chemical information processing through different mixed mechanisms, using simulations, bifurcation analysis and analytical work. We demonstrate how mixed mechanisms can show important and unintuitive differences from pure distributive and processive mechanisms, in some cases resulting in monostable behaviour with simple dose-response behaviour, while in other cases generating new behaviour-like oscillations. Our results also suggest patterns of information processing that are relevant as the number of modification sites increases. Overall, our work creates a framework to examine information processing arising from complexities of multi-site modification mechanisms and their impact on signal transduction. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Loading Center for Process Systems Engineering collaborators
Loading Center for Process Systems Engineering collaborators