Published Article / Under-performance and failure in first year accounting is a problem experienced in many higher education institutions world-wide as well as in South Africa. Literature shows that the problem is relatively well researched. Most of the research has taken place within the quantitative paradigm and in many cases focused on a search for determinants of possible success and / or failure in the subject or the factors contributing to the situation. The findings of all these research projects are varied and often inconclusive. It also becomes clear that the contexts of the studies are diverse, which makes it difficult for institutions and concerned lecturers to apply the findings in their specific situations. In this article the authors provide an overview of some of the most prominent research findings on factors determining or influencing success / failure in the field. They also attempt to organise these findings in a digestible way for the concerned lecturer and interested researcher. This is followed by a report on the first phase of an investigation into possible factors contributing to the low performance levels of students at a South African higher education institution. The unit of analysis is the first year accounting class of the first author (a lecturer at the institution). The research is quantitative in nature and statistical analyses are employed. In addition to factors such as age, gender, matric performance in key subjects, M-scores, class attendance and nationality, the investigation also looked at the levels of learning approach of the students as a possible determinant of success or failure. The findings are compared with the findings from literature and the implications of the research are discussed.

In this dissertation we obtain an e cient hybrid numerical method for the solution of stochastic di erential equations (SDEs). Speci cally, our method chooses between two numerical methods (Euler and Milstein) over a particular discretization interval depending on the value of the simulated Brownian increment driving the stochastic process. This is thus a new1 adaptive method in the numerical analysis of stochastic di erential equation. Mauthner (1998) and Hofmann et al (2000) have developed a general framework for adaptive schemes for the numerical solution to SDEs, [30, 21]. The former presents a Runge-Kutta-type method based on stepsize control while the latter considered a one-step adaptive scheme where the method is also adapted based on step size control. Lamba, Mattingly and Stuart, [28] considered an adaptive Euler scheme based on controlling the drift component of the time-step method. Here we seek to develop a hybrid algorithm that switches between euler and milstein schemes at each time step over the entire discretization interval, depending on the outcome of the simulated Brownian motion increment. The bias of the hybrid scheme as well as its order of convergence is studied. We also do a comparative analysis of the performance of the hybrid scheme relative to the basic numerical schemes of Euler and Milstein. / Mathematical Sciences / M.Sc. (Applied Mathematics)

Submitted in fulfillment of the academic requirements for the Masters Degree in Technology: Chemistry, Durban University of Technology, 2008. / The thermodynamic properties of binary liquid mixtures involving ionic liquids (ILs) with alcohols were determined. ILs are an important class of solvents since they are being investigated as environmentally benign solvents, because of their negligible vapour pressure, and as potential replacement solvents for volatile organic compounds (VOCs) currently used in industries. Alcohols were chosen for this study because they have hydrogen bonding and their interaction with ILs will help in understanding the intermolecular interactions. Also, their thermodynamic properties are used for the development of specific chemical processes. The excess molar volumes of binary mixtures of {1-ethyl-3-methylimidazolium ethylsulfate + methanol or 1-propanol or 2-propanol}, {trioctylmethylammonium bis (trifluoromethyl-sulfonyl) imide + methanol or ethanol or 1-propanol}, {1-buty-3-methylimidazolium methylsulfate + methanol or ethanol or 1-propanol} were calculated from experimental density values, at T = (298.15, 303.15 and 313.15) K. The Redlich-Kister smoothing polynomial was fitted to the excess molar volume data. The partial molar volumes of the binary mixtures {1-ethyl-3-methylimidazolium ethylsulfate + methanol or 1-propanol or 2-propanol}, {trioctylmethylammonium bis (trifluoromethyl-sulfonyl) imide + methanol or ethanol or 1-propanol}, {1-buty-3-methylimidazolium methylsulfate + methanol or ethanol or 1-propanol} were calculated from the Redlich-Kister coefficients, at T = (298.15, 303.15 and 313.15) K. This information was used to better understand the intermolecular interactions with each solvent at infinite dilution. iii The isentropic compressibility of {trioctylmethylammonium bis (trifluoromethyl-sulfonyl) imide + methanol or ethanol or 1-propanol}, were calculated from the speed of sound data at T = 298.15 K. / National Research Fundation ; Durban University of Technology

Dissertation submitted in fulfilment of the requirements for the Masters Degree in Technology: Chemistry, Durban University of Technology, 2009. / The activity coefficients at infinite dilution ( γ13 ) were calculated for alkanes, alkenes, cycloalkanes, alkynes, ketones, alcohols and aromatic compounds from gas liquid chromatography (glc) measurements at three temperatures (303.15 and 313.15 and 323.15) K. The γ13 values were calculated from the retention data for two ionic liquids (ILs) with the same cation but different anions. The ionic liquids: [methyltrioctylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium thiosalicylate] were used as the stationary phase. The γ13 data for methyltrioctylammonium thiosalicylate were higher than for methyltrioctylammonium bis(trifluoromethylsulfonyl)imide. For each temperature and each ionic liquid, γ13 values were determined for two columns and the average γ13 values were used for the calculation of the partial molar excess enthalpies at infinite dilution, H E 1 Δ , using the Gibbs-Helmholtz equation. Graphs of In γ13 vs 1/T were plotted to determine H E 1 Δ at T = 303.15 K. The selectivity, S12 , value for the hexane/benzene separation was calculated from the ratio of the avarage γ13 values to determine the suitability of the ILs as an entrainer for extractive distillation in the separation of aromatic and aliphatic compounds.The S12 values were also compared to the literature values for other ionic liquids. It was found that the longer chain alkyl group attached to the cation or anion gave lower S12 values. Both ILs have S12 values greater than one and in theory can be used as an entrainer for the hexane/ benzene separation. The capacities at infinite dilutions, k1 , were also calculated from the inverse of the avarage γ13 values for each IL at each temperature. / National Research Fund; Postgraduate Development and Support Directorate.

Submitted in fulfillment of the requirements of the Degree of Doctor of Technology: Chemistry, Durban University of Technology, 2010. / The thermodynamic properties of mixtures involving ionic liquids (ILs) with alcohols or alkyl acetate or nitromethane at different temperatures were determined. The ILs used were methyl trioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]+[Tf2N]-) and 1-butyl-3- methylimidazolium methyl sulphate [BMIM]+[MeSO4]-. The ternary excess molar volumes (􀜸􀬵􀬶􀬷 E ) for the mixtures {methyl trioctylammonium bis (trifluoromethylsulfonyl)imide + methanol or ethanol + methyl acetate or ethyl acetate}and (1- butyl-3-methylimidazolium methylsulfate + methanol or ethanol or 1-propanol + nitromethane) were calculated from experimental density values, at T = (298.15, 303.15 and 313.15) K and T = 298.15, respectively. The Cibulka equation was used to correlate the ternary excess molar volume data using binary data from literature. The 􀜸􀬵􀬶􀬷 E values for both IL ternary systems were negative at each temperature. The negative contribution of 􀜸􀬵􀬶􀬷 E values are due to the packing effect and/or strong intermolecular interactions (ion-dipole) between the different molecules. The density and speed of sound of the binary solutions ([MOA]+[Tf2N]- + methyl acetate or ethyl acetate or methanol or ethanol), (methanol + methyl acetate or ethyl acetate) and (ethanol + methyl acetate or ethyl acetate) were also measured at T = ( 298.15, 303.15, 308.15 and 313.15) K and at atmospheric pressure. The apparent molar volume, Vφ , and the apparent molar isentropic compressibility, κφ , were evaluated from the experimental density and speed of sound data. A Redlich-Mayer type equation was fitted to the apparent molar volume and apparent molar isentropic compressibility data. The results are discussed in terms of solute-solute, solute- solvent and solvent-solvent interactions. The apparent molar volume and apparent molar isentropic compressibility at infinite dilution, 􀜸φ 􀬴 and κφ 􀬴, respectively of the binary solutions have been calculated at each temperature. The 􀜸φ 􀬴 values for the binary v systems ([MOA]+[Tf2N]- + methyl acetate or ethyl acetate or methanol or ethanol) and (methanol + methyl acetate or ethyl acetate) and (ethanol + methyl acetate or ethyl acetate) are positive and increase with an increase in temperature. For the (methanol + methyl acetate or ethyl acetate) systems 􀜸φ 􀬴 values indicate that the (ion-solvent) interactions are weaker. The κφ 􀬴 is both positive and negative. Positive κφ 􀬴, for ([MOA] + [Tf2N]- + ethyl acetate or ethanol), (methanol + ethyl acetate) and (ethanol + methyl acetate or ethyl acetate) can be attributed to the predominance of solvent intrinsic compressibility effect over the effect of penetration of ions of IL or methanol or ethanol. The positive κφ 􀬴 values can be interpreted in terms of increase in the compressibility of the solution compared to the pure solvent methyl acetate or ethyl acetate or ethanol. The κφ 􀬴 values increase with an increase in temperature. Negative κφ 􀬴, for ([MOA] + [Tf2N]- + methyl acetate or methanol), and (methanol + methyl acetate) can be attributed to the predominance of penetration effect of solvent molecules into the intra-ionic free space of IL or methanol molecules over the effect of their solvent intrinsic compressibility. Negative κφ 􀬴 indicate that the solvent surrounding the IL or methanol would present greater resistance to compression than the bulk solvent. The κφ 􀬴 values decrease with an increase in the temperature. The infinite dilution apparent molar expansibility, 􀜧φ 􀬴 , values for the binary systems (IL + methyl acetate or ethyl acetate or methanol or ethanol) and (methanol + methyl acetate or ethyl acetate) and (ethanol + methyl acetate or ethyl acetate) are positive and decrease with an increase in temperature due to the solution volume increasing less rapidly than the pure solvent. For (IL + methyl acetate or ethyl acetate or methanol or ethanol) systems 􀜧φ 􀬴 indicates that the interaction between (IL + methyl acetate) is stronger than that of the (IL + ethanol) or (IL + methanol) or (IL + ethyl acetate) solution. For the (methanol + methyl acetate or ethyl acetate) systems 􀜧φ 􀬴 values vi indicate that the interactions are stronger than (ethanol + methyl acetate or ethyl acetate) systems. / National Research Foundation; Durban University of Technology

Dissertation was submitted in fulfilment of the academic requirement for the Masters Degree in Technology: Chemistry, Durban University of Technology, 2011. / In this work, the binary and ternary excess molar volumes have been calculated from the density, ρ, measurements using an Anton Paar (DMA 38) vibrating tube digital densimeter. One component of the ternary systems studied was an ionic liquid. The ionic liquid used is methyl trioctylammonium bis(trifluoromethylsulfonyl)imide [MOA]+[Tf2N]-. Binary excess molar volumes were obtained for (1-butanol + ethyl acetate) and (2-butanol + ethyl acetate) systems at T = (298.15, 303.15, and 313.15) K. Ternary excess molar volumes were obtained for the mixtures {[MOA]+[Tf2N]- + 2-propanol or 1-butanol or 2-butanol + ethyl acetate} at T = (298.15, 303.15, and 313.15) K. The Redlich-Kister equation was fitted to the calculated binary excess molar volume data to obtain the fitting parameters which were used to calculate the partial molar volumes at infinite dilution. The calculated partial molar volume was used to better understand the intermolecular interactions of each component at infinite dilution. The Redlich-Kister parameters were also used in the Cibulka equation and the Cibulka equation was used to correlate the ternary excess molar volume data to give the fitting parameters. The binary excess molar volumes,VmE , for the (1-butanol + ethyl acetate) and (2-butanol + ethyl acetate) are positive at each temperature over the entire composition range. At high mole fractions of the alcohol for the binary systems (2-propanol or 1-butanol or 2-butanol + ethyl acetate), VmE is positive again, similar to the Cibulka ternary correlation. The positive V E m values are due to the breaking of intermolecular interactions in the pure components during the mixing process. The ternary excess molar volume,V E 123 , values are negative for all mole fractions. The negative values are due to a more efficient packing and/ or attractive intermolecular interactions in the mixtures than in the pure liquid. There is also a contraction in volume which can be attributed to electron-donor-acceptor type interactions between the ionic liquid and 2-propanol or 1-butanol or 2-butanol as well as ethyl acetate. / National Research Foundation.

The integration of services and products into solutions can open up new business opportunities for firms. This thesis concerns how firms can provide solutions that are perceived as high quality. Solutions are often provided over several years, which implies a changed customer relationship compared to product provisions. Since the solution aims to support the customer’s activities, firms face new challenges when introducing solutions. One challenge is to integrate all components and activities of the solution, and simultaneously support the customer’s activities. In addition, the firm must ensure that the solution and all of its parts are of high quality. Most of the existing research on quality is related to the management of a firm’s internal activities and the interaction during exchange. Within the research on quality, customer orientation means that a firm should manage the relevant product or service to meet customer requirements. When this is achieved, the product or service is of high quality. Since solutions are seen as services and products that are integrated as an outcome, as well as a customer relational process that aims to support the customer’s activities, firms have little to learn from previous research about the quality of solutions. The aim of this thesis is to increase knowledge about how to manage solution quality. The thesis combines insights from research on quality with research on solutions and servitization. Three research questions are answered. The first question concerns the content of solution quality; the second deals with how firms can, with support from interventions, meet the new challenges that arise from solution provision; and the third question concerns how customers can be involved to achieve solution quality. The research questions are answered through five papers based on literature studies and empirical data. The papers contribute to an increased knowledge of solution quality and how firms can work to achieve it. The results of the thesis suggest that solution quality is built on seven quality dimensions: reliability, communicability, internal consistency, empathy, approachability, tangibility, and adaptability. In addition, knowledge of processes and customer relationships are two prerequisites for the concept. These dimensions and prerequisites are supported by interventions that can provide a change. However, it has become evident that whatever intervention is used must be related to the dimensions that are supposed to be improved. Furthermore, customer involvement is argued to be an intervention to support the prerequisites for solution quality, especially during the solution  development. The results of this thesis extend the research on quality by increasing the knowledge of the solution quality concept and by changing the view of customers and their involvement during solution development. / Den här avhandlingen berör hur företag kan möjliggöra så att produkter och  tjänster, integrerade i så kallade helhetslösningar, kan levereras med hög kvalitet. Helhetslösningar levereras ofta över en längre tid vilket medför en förändrad kundrelation till skillnad mot när endast en produkt levereras. Helhetslösningar syftar till att stödja kunden i dess aktiviteter. Det medför att företagen möter nya utmaningar. En utmaning är att få den komplexa helhetslösningen, bestående av olika komponenter och aktiviteter, att passa ihop och samtidigt bidra till att stötta kundens aktiviteter. Dessutom behöver företagen säkerställa att helhetslösningen och alla dess delar har hög kvalitet. Tidigare forskning inom kvalitetsutveckling berör företags interna processer och aktiviteter. När man inom kvalitetsutveckling talar om kundorientering innebär det att företaget med interna medel ska arbeta för att möjliggöra så produkten eller tjänsten möter kundens specifikationer. När detta är uppnått har produkten eller tjänsten hög kvalitet. Företagen har här inga riktlinjer att följa när de ska leverera helhetslösningar som ska anpassas efter kundens aktiviteter och när en så tydlig kundrelation ska utvecklas. Det finns med andra ord ingen vägledning för vad som är kvalitet eller hur man möjliggör hög kvalitet på helhetslösningar. Den här avhandlingen visar vad som ingår i begreppet kvalitet när det gäller helhetslösningar (lösningskvalitet) samt hur företag kan möjliggöra det. Tre olika frågor har huvudsakligen behandlats. Den första frågan besvarar vad lösningskvalitet innehåller. Den andra berör hur företag med hjälp av åtgärder kan bidra till en förändring inom företaget för att möta de nya utmaningar som uppstår med att leverera helhetslösningar. Den tredje frågan berör på vilket sätt kunden kan involveras för att uppnå lösningskvalitet. För att besvara frågorna har ett antal studier baserade på empiriskt material genomförts, och fem artiklar har författats under forskningsprocessen. Artiklarna bidrar till att öka förståelsen för lösningskvalitet och hur företag kan arbeta för att uppnå det. Avhandlingens resultat visar att lösningskvalitet består av sju olika dimensioner: tillförlitlighet, kommunicerbarhet, intern överensstämmelse, empati, nåbarhet, påtaglighet, och anpassningsbarhet. Dessutom är kunskap om processer och kundrelationer två förutsättningar för att uppnå lösningskvalitet. Dimensionerna betraktas som riktmärken för lösningskvalitet som företag kan arbeta mot. Dimensionerna och förutsättningarna stöttas i sin tur av åtgärder som används för att bidra till den interna förändringen inom företaget. Resultaten visar dock att använda åtgärder inte alltid leder till en förändring. Endast noga utvalda åtgärder som relaterar till en specifik dimension möjliggör en förändring. Exempel på en möjlig åtgärd är kundinvolvering. Speciellt vid utveckling av helhetslösningar, betraktas kundinvolvering som en möjlig åtgärd för att stötta förutsättningarna till lösningskvalitet. Resultaten i den här avhandlingen bidrar huvudsakligen till en ökad kunskap om vad kvalitet är när det gäller helhetslösningar. Ytterligare ett bidrag är att föreslå kundens förändrade roll under utveckling och vid leverans av helhetslösningar för att uppnå lösningskvalitet.

Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: This study was initialized to introduce capillary electrophoresis (CE) as a useful technique in the analysis of fluid inclusions in quartz. lts advantages are low detection limits for the dissolved ionic content of the fluid, the small amount of sample (1 g or less) for a detailed qualitative and quantitative analysis, and the short time required to obtain results (one run for either cations or anions take approximately 10 minutes). The study area from which quartz veins were selected is situated within the Neoproterozoic Saldania belt. Syn- and post-tectonic S-, 1- and A-type granitoids from the Cape Granite Suite intruded the metamorphosed Malmesbury greywacke and pelites between 550 and 510 Ma. Additional periods of tectonism and metamorphism occurred during Cape Supergroup sedimentation (480 - 400 Ma) as well as Karoo sedimentation and the simultaneous Cape Orogeny (280 -215 Ma). The quartz-biotite±chlorite vems are hosted by Cape Granite as well as Malmesbury sediments. These barren quartz veins are part of two vein sets, one dipping at an angle between 15 and 500 to the S to SE and striking W, similar to Sn-mineralized quartz veins in the SW-cape, while the other is near-vertical and striking W to NW. Except for their orientation, no differences regarding associated minerals, inclusion characteristics or fluid chemistry indicated a difference in origin. Four fluid phases within a temperature range of 160 - 390 °C were identified as being largely late-magmatic and released from the underlying Cape Granite plutons, namely an early 370- 390 °C population, followed by the 310 - 360, 230 - 300 and lastly the 160 - 200 °C populations. Initiation of this fluid system occurred from at least SlOMa, after final granite intrusion, but the age of the final stage is unknown. Renewed fluid circulation occurred during a later period of metamorphism, possibly during the Cape Orogeny. These fluids had temperatures between 240 and 360°C and are of sedimentary origin, most likely released from the Malmesbury metamorphites. The technique of capillary electrophoresis has been evaluated for its application to bulk fluid inclusion analysis, and the crush-leach fluid extraction procedure of Bottrell, et al., (1988) optimized for CE analysis. Contamination factors were identified and minimized or eliminated, where possible. Bulk fluid inclusion chemistry obtained by CE was therefore proved to provide valuable information regarding the various fluid generations as long as inclusion populations are investigated individually to explain and correlate bulk data. / AFRIKAANSE OPSOMMING: Die doel van die studie was om te toon dat die tegniek van kapillêre elektroforese bruikbaar is in die analiese van vloeistofmsluitsels in kwarts. Die voordele van hierdie tegniek is lae deteksie limiete vir die opgeloste ioon inhoud van die vloeistof, die klein monstergrootte (< 1g) wat nodig is vir 'n omvattende kwalitatiewe en kwantitatiewe analise, en die kort tydsduur waarin resultate verkry word ('n katioon of anioon analise vir een monster duur lO minute). Die studie gebied waar kwarts are gemonster is, is binne die Neoproterosoïese Saldania Gordel geleë. Sin- en laat-tektoniese S-, I- en A-tipe graniete van die Kaapse Graniet Suite het die gemetamorfiseerde Malmesbury grouwakke en peliete tussen 550 en 510 Ma binnegedring. Latere periodes van tektonisme en metamorfose het tydens deponering van die Kaap Supergroep (480 - 400 Ma), en die gelyktydige episodes van Karoo sedimentasie en Kaapse Orogenese (280 - 215 Ma) plaasgevind. Die gasheer gesteentes vir die kwarts-biotiet±chloriet are is Kaapse Graniet sowel as Malmesbury sedimente. Hierdie ongemineraliseerde are is deel van twee aarstelsels, nl. een met 'n duik hoek tussen 15 en 50° S tot SO en 'n westelike strekking, soortgelyk aan die Sn- ,.gemineraliseerde are in die SW-Kaap, terwyl die ander stel are feitlik vertikaal is en W tot NW strek. Behalwe vir die verskil in oriëntasie was daar geen aanduiding, wat betref 'n verskil in geassosieerde minerale, vloeistofinsluitsel kenmerke of vloeistof chemie, dat hierdie twee aarstelsels van verskillende oorsprong is nie. Vier vloeistof fases binne 'n temperatuur gebied van 160 - 390 °C en 'n vloeistof saliniteit van 0 - 5.7 gewig % NaC1 ekw. is geïdentifiseer, met 'n laat-magmatiese assosiasie en vrygestel deur die onderliggende Kaapse Graniete. Dit behels 'n vroeë 370 - 390 °C populasie, gevolg deur die 310 - 360, 230 - 300 en laastens die 160 - 200 °C populasies. Inisiasie van hierdie sisteem kon moontlik rondom 510 Ma gelede plaasgevind het, maar die ouderdom van die finale fase is onbekend. Hernude vloeistof sirkulasie het tydens 'n later stadium van metamorfose onstaan, moontlik tydens die Kaapse Orogenese. Hierdie vloeistowwe het temperature tussen 240 en 360 °C en is van sedimentêre oorsprong waar dit moontlik deur metamorfose van die reeds gemetamorfiseerde Malmesbury gesteentes vrygestel is. Die tegniek van kapillêre elektroforese is vir die toepassing daarvan in die analise van vloeistof insluitsels in kwarts geëvalueer, terwyl die vloeistof vrystellingsmetode van Bottrell en Yardley (1988) vir hierdie tegniek geoptimaliseer is. Kontaminasie faktore is geïdentifiseer en verminder of uitgeskakel waar moontlik. Daar is getoon dat die vloeistof chemie, wat verteenwoordigend is van al die insluitsel populasies in 'n monster, wel bruikbaar is t.o.v. afsonderlike vloeistof generasies, solank elke populasie individueel bestudeer is om die omvattende chemiese data te verduidelik en met 'n enkele populasie te korrelleer.

The semiconductor industry is continually challenged to maintain the trend identified in 1965 by Gordon Moore of increasing the density of transistors on an integrated circuit. These advances have been achieved by increasing the resolution that can be printed with photolithography, traditionally by decreasing the exposure wavelength. Decreasing the exposure wavelength from 193 nm, the current state of the art, presents significant technical challenges. To circumvent these challenges, resolution can be increased by enabling increases in numerical aperture (without changing the exposure wavelength), using immersion lithography. In immersion lithography, the air gap between the photoresist-coated wafer and lens is replaced with a high refractive index fluid. Immersion lithography has been demonstrated with water as the immersion fluid. With water immersion lithography at 193 nm, the maximum resolution that can be printed can be decreased from 65 nm to 45 nm. To enable further resolution increases, immersion fluids with a higher index than water are needed. The requirements for next generation high index fluids are: an index of refraction higher than water, high transparency, and physical properties similar to water. A variety of methods to identify a high index fluid were completed. First, the optical properties of aqueous solutions of metal cations with varying anions were tested. A series of linear, cyclic, and polycyclic alkanes were also studied, since saturated systems have electronic transitions at wavelengths less than 200 nm, to provide the necessary transparency at 193 nm. Large alkane groups were also incorporated into either the cation or anion of a salt to develop an aqueous solution with the optical properties of a saturated hydrocarbon. In addition to these empirical surveys, a modeling approach was used to develop “designer” absorbance spectra that would correspond to fluids with a high index and low absorbance at 193 nm. Additionally, in Appendix D, the results of an electrochemical study of the diffusion coefficient of ferrocene methanol in poly(ethylene glycol) diacrylate hydrogels of varying molecular weight and water content will be presented. The results of these mass transport studies can be used to qualitatively understand the mass transport characteristics of additional species in the hydrogel. / text

Un modèle physico-chimique prédictif a été développé pour représenter les propriétés d'équilibre dans des solutions aqueuses simples et mixtes. La partie physique du modèle utilise le modèle de contribution de groupes UNIFAC modifié par Larsen et al (1987), associé à un terme électrostatique issu du modèle Pitzer Debye-Hückel (Achard, 1992). La partie chimique, qui constitue l'originalité de ce travail, tient compte des interactions chimiques entre les molécules par un équilibre d'hydratation conduisant à la formation en une seule étape d'une nouvelle espèce n-hydratée dans le mélange. n, le nombre d'hydratation et K, la constante d'équilibre d'hydratation de l'espèce hydratée, sont les deux paramètres indépendants de cette partie chimique. La représentation des propriétés thermodynamiques des solutions aqueuses électrolytiques et non électrolytiques a conduit, dans un premier temps, à identifier les deux paramètres n et K ainsi que les paramètres d'interaction entre les ions et l'eau. Les valeurs des paramètres d'interaction et les groupes fonctionnels d'origine des espèces non électrolytiques n'ont pas été modifiés. De plus il n'y a pas eu d'introduction de nouveaux groupes fonctionnels. Dans un deuxième temps, le modèle développé a été utilisé pour prédire d'autres propriétés d'équilibre, telles que le pH, l'activité de l'eau, les températures de fusion et d'ébullition et la solubilité des solutés dans des mélanges aqueux binaires ternaires ou mixtes, contenant des espèces neutres (sucres, polyols) et/ou electrolytiques (sels, acides, bases)