Dominica has been recognized for its landscape containing hundreds of rivers and receiving high rainfall, and "our water belongs to the world," or so says many Dominican citizens, and their government. A schism exists in the understanding of the water resources of Dominica. Local perceptions are in conflict with regional climate change data. Where climate change research has found Dominica to be high risk for water quality and quantity, locals maintain the mindset that there is an overabundance of the resource. Local epistemologies influence governmental water management practices, which presently focus on exportation of the resource. In efforts of economic development, while trusting that there is a surplus of water, Dominica leases billions of gallons of water each year to foreign companies. A popular conception on the island is that there is an abundance of water, and therefore, it should be shared globally. This unique social construction of Dominican water has been a foundation leading to the sale of billions of gallons of fresh water to international corporations. However, the bulk exportation of water is occurring in the context of climate change, and thus, the availability of water will be impacted by changes in annual rainfall, sea level rise, increased temperatures, and more severe hurricanes. The purpose of this study is to gain a better understanding of how the social understanding of water in Dominica was constructed, and what this means in relation to resource exportation and climate change. This research-based paper explores Dominican perceptions of water abundance and sustainability.

We study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a strong coverage dependence of the adsorption energy. For the case of reduced surface, our results show that it may not be energetically favorable for water to oxidize oxygen vacancy site at the surface. Instead, oxygen vacancies tend to result in water more strongly binding to the surface. The result of this attractive water-vacancy interaction is that the apparent concentration of oxygen vacancies at the surface is enhanced in the presence of water. Finally, we discuss this problem with reference to recent experimental and theoretical studies of vacancy clustering at the (111) ceria surface. We also describe the simulation results for the structure and dynamics of liquid water using the SIESTA electronic structure approach. We find that the structure of water depends strongly on the particular basis set used. Applying a systematic approach to varying the basis set, we find that the basis set which results in good agreement with experimental binding energies for isolated water dimers also provides a reasonable description of the radial distribution functions of liquid water. We show that the structure of liquid water varies in a systematic fashion with the choice of basis set. Comparable to many other first-principle studies of liquid water using gradient-corrected density functionals, the liquid is found to be somewhat overstructured. The possibility of further improvements through a better choice of the basis set is discussed. We find that while improvements are likely to be possible, application to large-scale systems will require use of a computational algorithm whose computational cost scales linearly with system size. Finally, we study the molecular and atomic adsorption of oxygen on the gold nano-clusters. We show multiple stable and metastable structures for atomically and molecularly adsorbed oxygen to the gold cluster. We plan to predict the reaction pathway and calculate activation energy barrier for desorption of molecular oxygen from the atomically adsorbed gold cluster which is very important for any catalytic reaction occurring using gold nanoparticles.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Accurate water usage information is very important for municipalities in order to provide accurate billing information for high volume water users. Meter reading are currently obtained by sending a person out to every meter to obtain a manual reading. This is very costly with regards to time and money, and it is also very error prone. In order to improve on this system, an image based telemetry system was developed that can be retrofitted on currently installed bulk water meters. Images of the meter dials are captured and transmitted to a central server where they are further processed and enhanced. Character recognition is performed on the enhanced images in order to extract meter readings. Through tests it was found that characters can be recognised to 100% accuracy for cases which the character recognition software has been trained, and 70% accuracy for cases which is was not trained. Thus, an overall recognition accuracy of 85% was achieved. These results can be improved upon in future work by statistically analysing results and utilizing the inherent heuristic information from the meter dials. Overall the feasibility of the approach was demonstrated and a way forward was indicated. / AFRIKAANSE OPSOMMING: Dit is belangrik vir munisipaliteite om akkurate water verbruikingssyfers te hê sodat hulle akkurate rekeninge aan hoë volume water gebruikers kan stuur. Tans besoek ’n persoon fisies elke meter om meterlesings te verkry. Dit is egter baie oneffektief ten opsigte van tyd en geld. Die metode is ook baie geneig tot foute. Ten einde te verbeter op hierdie stelsel was ’n beeld gebaseerde telemetrie stelsel ontwerp wat geïnstalleer word op huidig geïnstalleerde hoë volume water meters. Beelde van die meters word na ’n sentrale bediener gestuur waar dit verwerk word en die beeld kwaliteit verbeter word. Karakter herkenning sagteware word gebruik om die meter lesings te verkry vanuit die verbeterde beelde. Deur middel van toetse is gevind dat karakters herken kan word tot op 100% graad van akkuraatheid in gevalle waar die karakter herkenning sagteware opgelei is, en 70% akkuraatheid vir gevalle waarvoor dit nie opgelei was nie. Dus was ’n algehele herkennings akkuraatheid van 85% behaal. Hierdie resultate kan verbeter word in die toekoms deur die resultate statisties te analiseer en die inherente heuristieke inligting van die meter syfers te benutting. Ten slotte, in die tesis was die haalbaarheid van die benadering gedemonstreer en ’n weg vorentoe vir toekomstige werk aangedui.

Structure, dynamics and reactivity of the hydrated electron Frank Uhlig In this work, one of the products of ionization of water, namely the hydrated electron, has been investigated. The hydrated electron is a key-intermediate in aqueous radiation chemistry. Although known to exist for over 50 years, its structure remained elusive and under discussion up to the present day. We show in this work, that we can obtain a faithful picture of the hydrated electron, its equilibrium structure, dynamics after attachment to water, and its reactivity, using ab initio methods. To this end, small cluster models and extended bulk and slab geometries of water including an excess electron have been investigated.

A liquid Cooled below its normal freezing temperature is known as a supercooled liquid. On further cooling, supercooled liquids crystallize to thermodynamically stable, ordered structures. Alternatively, if the cooling rate is fast enough, the crystallization may be avoided altogether. Below a particular temperature during rapid cooling the liquid will solidify into a disordered, amorphous phase -also known as the glassy phase of matter. This particular temperature is termed the ”glass transition temperature” (Tg). Unlike a crystalline solid, a glass is neither a thermodynamically stable phase nor does it possess long range molecular ordering. Very slow structural relaxation (in the time scale of ∼ 100 s) is always present in the glassy phase. Thus, this phase is often referred to as a metastable phase of matter. Experimental and theoretical studies related to the behavior of supercooled liquids are the subject matter of many investigations for the last few decades [1]. These studies find their applications in diverse fields such as geology, cryopreservation, glaciology and atmospheric science. However, properties of supercooled liquids and the corresponding amorphous phase are not completely understood at present, particularly for hydrogen bonded (H-bonded) systems. This thesis concerns both the crystallization and the glass formation process of H-bonded systems. The systems of interest are water, the commonly accepted universal solvent, and the aqueous binary mixture of glycerol and water. The technique of molecular probing is often used to study the cooperativety and rotational diffusion of supercooled liquids and for determination of the glass transition temperature. For the present set of work, a molecular probe technique called spin probe ESR is extensively used. Electron paramagnetic resonance or electron spin resonance (EPR/ESR) measures the electronic energy level separation and is well known for the high sensitivity. All of the systems studied in the present set of work are diamagnetic. This issue is circumvented by dissolving paramagnetic spin probe molecules, which are usually organic free radicals with one N-O group, into the systems. Spin probes are added in very low concentrations (~10-3M) to minimize the effect on the host system and also to avoid mutual interactions between them. The unpaired electron delocalized in the direction of the N-O bond serves as the paramagnetic center required for an ESR experiment. The splitting of electron energy level due to the external magnetic field (Zeeman splitting) can give rise to resonance absorption of energy if exposed to a microwave of appropriate frequency. There is also a magnetic coupling (hyperfine) between the spin of the unpaired electron and nuclear spin of the nearby nitrogen atom. The hyperfine coupling splits each electron energy levels, to the first order, symmetrically into three levels. The transitions between these levels -subject to appropriate selection rules -give rise to the ESR spectrum [2]. The spectral shape in a magnetic field sweep ESR experiment appears complex if randomly oriented spin probes are dispersed in an amorphous or polycrystalline solid matrix. The high degree of mobility in probe molecules, present in a liquid solution, can average out the individual anisotropy of magnetic tensors to get a spectrum of three equally spaced liens. Experiments can be performed spanning a spin probe reorientation timescale of 10-7-10-12 s typically in the temperature range of 4.2 -300K. In chapter one we have given a brief overview of the supercooled liquids and the phase transitions related to the present work. Particular emphasis has been given to the dynamical features of the supercooled liquid close to its glass transition temperature and their classification based on the degree of ’fragility’ [3]. Brief general introductions of the systems studied in each of the following chapters are also provided. Then, the details of ESR spectroscopy and a quantum mechanical picture of the method of spin probe ESR have been discussed [4]. A separate section has been devoted to the numerical and analytical methods used to analyze the spectrum to extract information related to the spin probe dynamics [5]. The chapter concludes with a description of the ESR spectrometer. In chapter two we have studied the glass transition and dynamics of the supercooled water by the method of spin probe ESR. The vitrification has been done by direct exposure of the bulk water sample, doped with the spin probe TEMPOL, to the liquid helium flow. The vitrified matrix turns into the ultraviscous liquid above the putative glass transition temperature of ~136 K which further transforms to cubic ice (Ic) above TX ~150 K. The supercooled fraction of water, along with the spin probes which are treated as impurities by the crystallized surroundings, remain trapped inside the veins or triple junctions of the ice grains which serve as the interfacial reservoir of impurities in a polycrystalline ice matrix. The spectra for the entire temperature range have been analyzed with the help of in-depth computation by modelling the reorientation of TEMPOL in terms of the jump angle θs and the rotational correlation time τ [5]. This model, based on a homogeneous mobility scenario of the spin probe, works nicely except in the temperature range of 140-180 K. Dynamical heterogeneity (DH) is apparent in this temperature range and a more mobile (fast) component, as compared to the one corresponding to the very slow dynamics of TEMPOL at lower temperatures (slow), is observed. The relative weight of the fast and the slow component changes with temperature and above ~180 K the entire spectrum changes into the motionally narrowed triplet. The temperature dependence of the slow component of τ shows a change in slope at a temperature close to the putative glass transition temperature of water. The fast component of τ exhibits a fragile, i.e. non-Arrhenius character at high temperature with a crossover to a strong, i.e. Arrhenius behavior below ~225 K, close to the hypothesized fragile-to-strong crossover (FSC) for water at TFSC ~228 K. The breakdown of the Debye-Stokes-Einstein (DSE) law is observed when the τ values are combined with the available viscosity data of water to evaluate the DSE ratio, paralleling the SE breakdown which has recently been observed in nanoconfined water [6]. The dynamical heterogeneity is thought to be closely associated with the static structural heterogeneities of supercooled water. The existence of large scale structural fluctuations spanning a range of low-and high-density phases of liquid water have been associated with the heterogeneous dynamics sensed by TEMPOL. Motivated by the Arrhenius like behavior of the slow component, it has been identified with the low density liquid (LDL). The fragile nature of the fast component at high temperature may be identified with that of the high density liquid (HDL) which is the predominant fraction in liquid or weakly supercooled water [6]. Chapter three reports the studies on freezing and dynamics of the supercooled water trapped inside the veins of a polycrystalline ice matrix by dissolving spin probes TEMPO and TEMPOL into it. When a millimolar spin probe aqueous solution is cooled below the freezing point of water, the spin probes -driven by the mechanism described above migrate to the liquid environment inside the ice veins. Local concentration of the probe molecules inside the veins can go up to 1-10 M [7]. Bulk crystallization is evident in differential scanning calorimetry (DSC) studies whereas the liquid environment of the spin probe below the bulk freezing is confirmed by its narrow triplet ESR spectrum. A sudden collapse of this narrow triplet into a single broad line indicates the freezing of the trapped water fraction which usually happens well below the DSC freezing point for both the probes. The spin probe detected freezing point of this interstitial water is found to be largely dependent on the properties and the amount of the dissolved probe molecules. An explanation is sought in terms of the ’destructuring effect’ on the tetrahedral ordering of the water H-bond network by both the high local concentration of the spin probes and the hydrogen bond strength, formed between the water and the spin probe molecules through the polar groups of the latter [8, 9]. These two factors are thought to play important roles in determining the reorientational dynamics of the spin probe molecules, as well. The rotational correlation times of the two probes exhibit a crossover owing to the different mobility of their salvation shells in the more ordered supercooled water. The observed relaxation behavior of this confined water using the probe TEMPO, which has little effect on water H-bond network, is found in agreement with the previous experimental investigations on water confined in a nanochannel [10]. In chapter four, the glass transition, relaxation and the free volume of the glycerol-water (G-W) system are studied over the glycerol concentration range of 5 -85 mol% with TEMPO as the spin probe. G-W mixture is intrinsically inhomogeneous due to the well established phase segregation below a critical glycerol concentration of 40 mol%. In the inhomogeneous regime the water molecules tend to form cooperative domains besides the mesoscopic G-W mixture [11]. Samples are quenched by rapid cooling down to 4.2 K inside the spectrometer cryostat. Spectra were recorded on slow heating of the sample in the temperature range of 130 -305 K. The glass transition temperature is correlated to the sharp transition of the extrema separation of the ESR spectrum. The glass transition temperatures are found to follow a concentration dependence which is closely associated to the mesoscopic inhomogeneities of the G-W system. The steady enhancement in fragility of the G-W system with the addition of water is evident from the temperature dependence of the spin probe correlation time τ for the entire concentration range. In the temperature range of 283 -303 K, the DSE law is followed i.e. the spin probe reorientation process is found to be strongly coupled to the system viscosity. In this regime, the τ values have been used along with the available viscosity data to calculate the effective volume V of the spin probe for the entire concentration range. The spin probe effective volume is a measure of the available free volume of the host matrix. A drastic change in the quantity is seen in the vicinity of the 40 mol% glycerol concentration owing to a similar structural change of the matrix due to the formation of mesoscopic scale inhomogeneities below the critical concentration [12]. The thesis concludes with a discussion about the possible future directions of research.

This thesis deals with several aspects of the structure and dynamics of water molecules confined in nanoscopic pores. Water molecules confined in hydrophobic nanocavities exhibit unusual structural and dynamic properties. Confining walls of single-wall carbon nanotubes (SWCNTs) promote strong inter-water hydrogen bonding which in turn leads to several novel structural, dynamic and thermodynamic features not found in bulk water. Confined water molecules form ordered hydrogen-bonded networks, exhibit exceptionally high flow rates as compared to conventional flow in pipes, allow fast proton conduction and exhibit various other anomalous properties. Proteins are known to exploit some of the properties of confined water to perform certain physiological functions. Various properties of confined water can also be exploited in the design of nanofludic devices such as those for desalination and flow sensors. In addition, water molecules confined in SWCNTs and near graphene sheets serve as model systems to study various effects of confinement on the properties of liquids. In this thesis, we present the results of detailed molecular dynamics simulation studies of confined water molecules. In chapter 1, we summarize the findings of existing simulations and experimental studies of bulk and confined water molecules. We also highlight the significance of studying the structure and dynamics of confined water molecules in biological and biotechnological applications. Chapter 2 provides a brief ac-count of the methods and techniques used to perform the simulations described in subsequent chapters of the thesis. We also present a brief overview of the methods used to extract physical properties of water molecules from simulation data, with emphasis on the Two Phase Thermodynamics (2PT) method which we have used to compute the entropy of confined and bulk water molecules. In chapter 3, we discuss the thermodynamics of water entry in SWCNTs of various diameters. Experiments and computer simulations demonstrate that water spontaneously fills the interior of a carbon nanotube. Given the hydrophobic nature of the interior of carbon nanotubes and the strong confinement produced by narrow nanotubes, the spontaneous entry of water molecules in the pores of such nanotubes is surprising. To gain a quantitative thermodynamic understanding of this phenomenon, we use the recently developed Two Phase Thermodynamics (2PT) method to compute translational and rotational entropies of water molecules confined in SWCNTs and show that the increase in energy of a water molecule inside the nanotube is compensated by the gain in its rotational entropy. The confined water is in equilibrium with the bulk water and the Helmholtz free energy per water molecule of confined water is the same as that in the bulk within the accuracy of the simulation results. A comparison of translational and rotational spectra of water molecules confined in carbon nanotubes with those of bulk water shows significant shifts in the positions of spectral peaks that are directly related to the tube radius. These peaks are experimentally accessible and can be used to characterize water dynamics from spectroscopy experiments. We have also computed the free-energy transfer when a bulk water molecule enters a SWCNT for various temperatures and carbon-water interactions. We show that for reduced carbon-oxygen interaction, the free energy transfer is unfavourable and the SWCNT remains unoccupied for significant periods of time. As the temperature is increased, the free energy of confined water becomes unfavourable and reduced occupancy of water is observed. Bulk water exhibits many anomalous properties. No single water model is able to reproduce all properties of bulk water. Different empirical water models have been developed to reproduce different properties of water. In chapter 4, a comparative study of the structure, dynamics and thermodynamic proper-ties of water molecules confined in narrow SWCNTs, obtained from simulations using several water models including polarizable ones, is presented. We show that the inclusion of polarizability quantitatively affects the nature of hydro-gen bonding which governs different properties of water molecules. The SPC/E water model is shown to reproduce results in close agreement with those from polarizable water models with much less computational cost. In chapter 5, we report results obtained from simulations of the properties of water confined in the space between two planar surfaces. We consider three cases: two graphene surfaces, two Boron Nitride (BN) surfaces and one graphene and one BN surface. This is the first detailed study of the behaviour of water near extended BN surfaces. We show that the hydrophilic nature of the BN surface leads to several interesting effects on the dynamics of water molecules near it. We have observed a change in the activation energy, extracted from the temperature dependence of the translational and rotational dynamics, near 280K. This change in activation energy coincides with a change in the structure of the confined sheet of water, indicated by a sudden change in energy. We have also found signatures of glassy dynamics at low temperatures for all three cases, the glassy effects being the strongest for water molecules confined between two BN sheets. These results are similar to those of earlier studies in which novel phases of water have been found for water molecules confined between other surfaces at high pressure. In chapter 6, we have described our observation of a novel phenomenon exhibited by water molecules flowing through a SWCNT under a pressure gradient. We have shown that the flow induces changes in the orientation of the water molecules flowing through the nanotube. In particular, the dipole moments of the water molecules inside the nanotube get aligned along the axis of the nanotube under the effect of the flow. With increasing flow velocities, the net dipole moment first increases and eventually saturates to a constant value. This behaviour is similar to the Langevin theory of paramagnetism with the flow velocity acting as an effective aligning field. Preferential entry of water molecules with dipole moments pointing inward is shown to be the main cause of this effect. This observation provides a way to control the dipolar alignment of water molecules inside nano-channels, with possible applications in nanofluidic devices. Chapter 7 contains a summary of our main results and a few concluding re-marks.