Mathematical modelling and control of agitated extraction columns

Liquid-liquid extraction has long been known as a unit operation that plays an important role in industry. This process is well known for its complexity and sensitivity to operation conditions. This thesis presents an attempt to explore the dynamics and control of this process using a systematic approach and state of the art control system design techniques. The process was studied first experimentally under carefully selected. operation conditions, which resembles the ranges employed practically under stable and efficient conditions. Data were collected at steady state conditions using adequate sampling techniques for the dispersed and continuous phases as well as during the transients of the column with the aid of a computer-based online data logging system and online concentration analysis. A stagewise single stage backflow model was improved to mimic the dynamic operation of the column. The developed model accounts for the variation in hydrodynamics, mass transfer, and physical properties throughout the length of the column. End effects were treated by addition of stages at the column entrances. Two parameters were incorporated in the model namely; mass transfer weight factor to correct for the assumption of no mass transfer in the. settling zones at each stage and the backmixing coefficients to handle the axial dispersion phenomena encountered in the course of column operation. The parameters were estimated by minimizing the differences between the experimental and the model predicted concentration profiles at steady state conditions using non-linear optimisation technique. The estimated values were then correlated as functions of operating parameters and were incorporated in·the model equations. The model equations comprise a stiff differential~algebraic system. This system was solved using the GEAR ODE solver. The calculated concentration profiles were compared to those experimentally measured. A very good agreement of the two profiles was achieved within a percent relative error of ±2.S%. The developed rigorous dynamic model of the extraction column was used to derive linear time-invariant reduced-order models that relate the input variables (agitator speed, solvent feed flowrate and concentration, feed concentration and flowrate) to the output variables (raffinate concentration and extract concentration) using the asymptotic method of system identification. The reduced-order models were shown to be accurate in capturing the dynamic behaviour of the process with a maximum modelling prediction error of I %. The simplicity and accuracy of the derived reduced-order models allow for control system design and analysis of such complicated processes. The extraction column is a typical multivariable process with agitator speed and solvent feed flowrate considered as manipulative variables; raffinate concentration and extract concentration as controlled variables and the feeds concentration and feed flowrate as disturbance variables. The control system design of the extraction process was tackled as multi-loop decentralised SISO (Single Input Single Output) as well as centralised MIMO (Multi-Input Multi-Output) system using both conventional and model-based control techniques such as IMC (Internal Model Control) and MPC (Model Predictive Control). Control performance of each control scheme was. studied in terms of stability, speed of response, sensitivity to modelling errors (robustness), setpoint tracking capabilities and load rejection. For decentralised control, multiple loops were assigned to pair.each manipulated variable with each controlled variable according to the interaction analysis and other pairing criteria such as relative gain array (RGA), singular value analysis (SVD). Loops namely Rotor speed-Raffinate concentration and Solvent flowrate Extract concentration showed weak interaction. Multivariable MPC has shown more effective performance compared to other conventional techniques since it accounts for loops interaction, time delays, and input-output variables constraints.

The impact of brand owner on consumers' brand perceptions : a development of Heider's Balance Theory

Studies have shown that the brand “owner” is very influential in positioning the brand and when the brand “owner” ceases his or her active role the brand will be perceived differently by the consumers. Balance Theory (HBT), a cognitive psychological theory, studies the triadic relationships between two persons and an entity and predicts that when a person’s original perception of the relationship is disturbed, the person restructures to a new balanced perception. Consequently, this research was undertaken to: conceptualize the brand owner’s impact on consumer’s brand perception; test the applicability of both the static and dynamic predictions of the Heider’s Balance Theory in brand owner-consumer-brand relation (OCB); construct and test a model of brand owner-consumer-brand relation; and examine if personality has an influence on OCB. A discovery-oriented approach was taken to understand the selected market segment, the ready-to-wear and diffusion lines of international designer labels. Chinese Brand Personality Scale, fashion proneness and hedonic and utilitarian shopping scales were developed, and validated. 51 customers were surveyed. Both traditional and extended methods used in the Balance Theory were employed in this study. Responses to liked brand have been used to test and develop the model, while those for disliked brand were used for test and confirmation. A “what if’ experimental approach was employed to test the applicability of dynamic HBT theory in OCB Model. The hypothesized OCB Model has been tested and validated. Consumers have been found to have separate views on the brand and the brand owner; and their responses to contrasting ethical and non-ethical news of the brand owner are different. Personality has been found to have an influence and two personality adapted models have been tested and validated. The actual results go beyond the prediction of the Balance Theory. Dominant triple positive balance mode, dominant negative balance mode, and mode of extreme antipathy have been found. It has been found that not all balanced modes are good for the brand. Contrary to Heider’s findings, simply liking may not necessarily lead to unit relation in the OCB Model.

Staying in nursing:what factors determine whether nurses intend to remain employed?

Aim. To test a model of eight thematic determinants of whether nurses intend to remain in nursing roles. Background. Despite the dramatic increase in the supply of nurses in England over the past decade, a combination of the economic downturn, funding constraints and more generally an ageing nursing population means that healthcare organizations are likely to encounter long-term problems in the recruitment and retention of nursing staff. Design. Survey. Method. Data were collected from a large staff survey conducted in the National Health Service in England between September-December 2009. A multi-level model was tested using MPlus statistical software on a sub-sample of 16,707 nurses drawn from 167 healthcare organizations. Results. Findings were generally supportive of the proposed model. Nurses who reported being psychologically engaged with their jobs reported a lower intention to leave their current job. The perceived availability of developmental opportunities, being able to achieve a good work-life balance and whether nurses' encountered work pressures were also influencing factors on their turnover intentions. However, relationships formed with colleagues and patients displayed comparatively small relationships with turnover intentions. Conclusion. The focus at the local level needs to be on promoting employee engagement by equipping staff with the resources (physical and monetary) and control to enable them to perform their tasks to standards they aspire to and creating a work environment where staff are fully involved in the wider running of their organizations, communicating to staff that patient care is important and the top priority of the organization. © 2012 Blackwell Publishing Ltd.

Recent and Miocene carbonate sediments from Indonesia. Available in 2 volumes.

Mapping and sediment sampling in reefs of the Pulau Seribu group (southwest Java Sea) shows the existence of ten physiographic zones and subzones represented by seven lithofacies. Reefs in the northern part of the archipelago are smaller, more closely spaced and morphologically sim pler than those in the south. This pattern is attributed to differences in subsidence rate. A th reedimensional model is proposed for the evo lution of these reefs but borehole data are requi red to test this model. Miocene limestones are described in detail from hydrocarbon reservoirs in the Batu Raja Formation of the same area. Brief comparisons a re made with surface outcrops of approximately coeval carbonate developments. The lithofacies developed within these limestones reflect variations in hydrodynam ic regime and basement topography . Ele\le.n diagenetic processes affected the Batu Raja limestones and the dist ribution of these is primarily related to sealevel fluctuations. Early diagenesis was marine and characterised by micritisation and preCipitation of fibrous and bladed cements. Dolomitisat ion occurred in the mixed- water zone and its variable intensity is attributed to the configuration of the carbonate body relative to this zone. Subsequently the limestones were subjected to freshwater phreatic zone diagenesis resulting in dissolution and cementation, and a t a late stage underwent burial compaction. Secondary porosity, which \ar9e1.y determines the suitability of these limestones as hydrocarbon reserVOirs, is a function of the variable intensity of dissolution and cementation, burial compaction, dolomitisation and possibly micrite neomorphism. The sedimentary processes that generated the Batu Raja buildups are inferred f rom comparisons with the Pulau Seribu and other Recent analogues. The contrasting pinnacle form of the Pulau Seribu patch reefs compared with the low relief of the Batu Raja buUdups results from differences in the initial substrate topography and subsequent subsidence rate

Determinants of sponsorship fit:a multilevel analysis

Sponsorship fit is frequently mentioned and empirically examined as a success factor of sponsorship. While sponsorship fit has been considered as a determinant of sponsorship success, little knowledge exists about the antecedents of sponsorship fit. In the present paper, individual and firm-level antecedents of sponsorship fit are examined in a single hierarchical linear model. Results show that sponsorship fit is influenced by the perception of benefits, the firm’s regional identification, sincerity, relatedness to the sponsored activity, and its dominance. On a partnership level, results show that contract length contributes to sponsorship fit while contract value is found to be unrelated.

Determinants of B2B e-commerce adoption in Saudi Arabian firms

Business-to-business (B2B) electronic commerce (e-commerce) has become an increasingly important initiative among organisations. The factors affecting the adoption decisions have been well-documented but there is a paucity of empirical studies that examine the adoption of e-commerce in developing economies in the Arab world. The aim of our study is to provide insights into the salient e-commerce adoption issues by focusing on Saudi Arabian businesses. We developed a conceptual model for B2B e-commerce adoption incorporating six factors. Survey data from 450 businesses were used to test the model and hypotheses. The analysis demonstrates that, (1) when e-commerce preliminary adoption is investigated, organizational IT readiness, management support and regulatory environment emerge as the strongest factor, (2) pressure from customers may not have much effect on the preliminary adoption of e-commerce by companies, but does significantly influence on the utilisation of e-commerce by firms, and (3) Saudi Arabia has a strong ICT infrastructure for supporting e-commerce practices. Taken together, these findings on the multi-dimensionality of e-commerce adoption show that preliminary adoption and utilisation of ecommerce are not only different measures of ecommerce adoption, but also have different determinants. The implications of the findings are discussed and suggestions for future inquiry are presented.

An investigation into the adoption of electronic business in Saudi Arabia using technology-organisation-environment framework

Despite the proliferation of e-business adoption by organisations and the world-wide growth of the e-business phenomenon, there is a paucity of empirical studies that examine the adoption of e-business in the Middle East. The aim of our study is to provide insights into the salient e-business adoption issues by focusing on Saudi Arabian businesses. We developed a conceptual model for electronic business (e-business) adoption incorporating ten factors based on the technology-organization-environment framework. Survey data from 550 businesses were used to test the model and hypotheses. We conducted confirmatory factor analysis to assess the reliability and validity of constructs. The findings of the study suggest that firm technology competence, size, top management Support, technology orientation, consumer readiness, trading partner readiness and regulatory support are important antecedents of e-business adoption and utilisation. In addition, the study finds that, competitive pressure and organisational customer and competitor orientation is not a predictor for e-business adoption and utilisation. The implications of the findings are discussed and suggestions for future inquiry are presented.

E-business adoption in Saudi Arabian private sector

Despite the proliferation of e-business adoption by organisations and the world-wide growth of the e-business phenomenon, there is a paucity of empirical studies that examine the adoption of e-business in the Middle East. The aim of our study is to provide insights into the salient e-business adoption issues by focusing on Saudi Arabian businesses. We developed a conceptual model for electronic business (e-business) adoption incorporating nine factors. Survey data from 550 businesses were used to test the model and hypotheses. The findings of the study suggest that firm's technological readiness, top management Support, technology orientation, consumer readiness, trading partner readiness and regulatory support are important facilitators of e-business adoption. In addition, the study finds that, competitive pressure and organisational customer and competitor orientation is not a predictor for e-business adoption. The implications of the findings are discussed and suggestions for future inquiry are presented.

The influence of brand equity on consumer responses

Purpose: The purpose of this paper is to propose and test a model to better understand brand equity. It seeks to investigate the effects of this construct on consumers' responses using data from two European countries. Design/methodology/approach: Hypotheses were tested using structural equation modeling (SEM). Measurement invariance and stability of the model across the two national samples was assessed using multigroup confirmatory factor analysis. Findings: Results indicate that brand equity dimensions inter-relate. Brand awareness positively impacts perceived quality and brand associations. Brand loyalty is mainly influenced by brand associations. Finally, perceived quality, brand associations and brand loyalty are the main drivers of overall brand equity. Findings also corroborate the positive impact of brand equity on consumers' responses. In addition, the general framework proposed is found to be empirically robust across the studied countries. Only a few differences are observed. Research limitations/implications: A limited set of product categories, brands and countries were used. Practical implications: Findings provide useful guidelines for brand equity management. Managers can complement financial metrics with consumer-based brand equity measures to track brand performance over time and to benchmark against other brands. Building brand equity generates more value for corporations since a more favourable consumer response results from positive brand equity. Originality/value: This study contributes to the scarce international brand equity literature by testing the proposed model using data from a sample of consumers in two European countries. It also enriches the brand equity literature by empirically examining the relationships among consumer-based brand equity dimensions and its effects on consumers' responses. © Emerald Group Publishing Limited.

Guiding local regression using visualisation

Solving many scientific problems requires effective regression and/or classification models for large high-dimensional datasets. Experts from these problem domains (e.g. biologists, chemists, financial analysts) have insights into the domain which can be helpful in developing powerful models but they need a modelling framework that helps them to use these insights. Data visualisation is an effective technique for presenting data and requiring feedback from the experts. A single global regression model can rarely capture the full behavioural variability of a huge multi-dimensional dataset. Instead, local regression models, each focused on a separate area of input space, often work better since the behaviour of different areas may vary. Classical local models such as Mixture of Experts segment the input space automatically, which is not always effective and it also lacks involvement of the domain experts to guide a meaningful segmentation of the input space. In this paper we addresses this issue by allowing domain experts to interactively segment the input space using data visualisation. The segmentation output obtained is then further used to develop effective local regression models.

When to use the Bonferroni correction

PURPOSE: The Bonferroni correction adjusts probability (p) values because of the increased risk of a type I error when making multiple statistical tests. The routine use of this test has been criticised as deleterious to sound statistical judgment, testing the wrong hypothesis, and reducing the chance of a type I error but at the expense of a type II error; yet it remains popular in ophthalmic research. The purpose of this article was to survey the use of the Bonferroni correction in research articles published in three optometric journals, viz. Ophthalmic & Physiological Optics, Optometry & Vision Science, and Clinical & Experimental Optometry, and to provide advice to authors contemplating multiple testing. RECENT FINDINGS: Some authors ignored the problem of multiple testing while others used the method uncritically with no rationale or discussion. A variety of methods of correcting p values were employed, the Bonferroni method being the single most popular. Bonferroni was used in a variety of circumstances, most commonly to correct the experiment-wise error rate when using multiple 't' tests or as a post-hoc procedure to correct the family-wise error rate following analysis of variance (anova). Some studies quoted adjusted p values incorrectly or gave an erroneous rationale. SUMMARY: Whether or not to use the Bonferroni correction depends on the circumstances of the study. It should not be used routinely and should be considered if: (1) a single test of the 'universal null hypothesis' (Ho ) that all tests are not significant is required, (2) it is imperative to avoid a type I error, and (3) a large number of tests are carried out without preplanned hypotheses.

Synthesis and evaluation of N-(3-oxo-2,3-dihydro-1H-pyrazol-4-yl)-1H-indole-carboxamides as cholecystokinin antagonists

The structure-activity relationship optimization of the pyrazoline template 3a resulted in novel 3-oxo-1,2-diphenyl-2,3-dihydro-1H-pyrazol-4-yl)-indole carboxamides 4a-4e. These non-peptidal CCK ligands have been shown to act as potent CCK 1 ligands in a [125]I-CCK-8 receptor binding assay. The best amides (4c and 4d) of this series displayed an IC50 of 20/25 CCK 1 for the CCK 1 receptor. In a subsequent in-vivo evaluation using various behaviour pharmacological assays, an anxiolytic effect of these novel 3-oxo-1,2-diphenyl-2,3-dihydro-1H-pyrazol-4-yl)-indole carboxamides was found at high doses in the elevated plus-maze. In the despair swimming test, a model for testing antidepressants, an ED50 of 0.33/0.41 mg kg -1 was determined for amide 4c/4d and the antidepressant effect had a magnitude comparable to desimipramine. © 2006 The Authors.

A finite element approach to modelling the hydrological regime in horizontal subsurface flow constructed wetlands for wastewater treatment

A Finite Element Analysis (FEA) model is used to explore the relationship between clogging and hydraulics that occurs in Horizontal Subsurface Flow Treatment Wetlands (HSSF TWs) in the United Kingdom (UK). Clogging is assumed to be caused by particle transport and an existing single collector efficiency model is implemented to describe this behaviour. The flow model was validated against HSSF TW survey results obtained from the literature. The model successfully simulated the influence of overland flow on hydrodynamics, and the interaction between vertical flow through the low permeability surface layer and the horizontal flow of the saturated water table. The clogging model described the development of clogging within the system but under-predicted the extent of clogging which occurred over 15 years. This is because important clogging mechanisms were not considered by the model, such as biomass growth and vegetation establishment. The model showed the usefulness of FEA for linking hydraulic and clogging phenomenon in HSSF TWs and could be extended to include treatment processes. © 2011 Springer Science+Business Media B.V.

Uneasy lies the head that bears the trust:the effects of feeling trusted on emotional exhaustion

The construct of feeling trusted reflects the perception that another party is willing to accept vulnerability to one's actions. Although this construct has received far less attention than trusting, the consensus is that believing their supervisors trust them has benefits for employees' job performance. Our study challenges that consensus by arguing that feeling trusted can be exhausting for employees. Drawing on Stevan Hobfoll's conservation of resources theory, we develop a model in which feeling trusted fills an employee with pride a benefit for exhaustion and performance while also increasing perceived workload and concerns about reputation maintenance burdens for exhaustion and performance. We test our model in a field study using a sample of public transit bus drivers in London, England. Our results suggest that feeling trusted is a double-edged sword for job performance, bringing with it both benefits and burdens. Given that recommendations for managers generally encourage placing trust in employees, these results have important practical implications.

Investigation of factors influencing loyalty – The role of involvement, perceived risk and knowledge

Our research aimed to reveal the effects that can be observed during the buying process of food products and can influence the decisions of customers. We focused on the role of enduring involvement in customers’ behavioural loyalty, that is, the repurchase of food brands. To understand this relationship in a more sophisticated way, we involved two mediating constructs in our conceptual model: perceived risk and perceived knowledge of food products. The data collection was carried out among undergraduate students in frame of an online survey, and we used SPSS/AMOS software to test the model. The results only partly supported our hypothesis, although the involvement effects on loyalty and the two mediating constructs were strong enough, loyalty couldn’t be explained well by perceived risk and knowledge. The roles of further mediating/moderating variables should be determined and investigated in the next section of the research series.