Academic literature on the topic 'Diffusion-controlled system'

Advanced research in Controlled/Modified Atmosphere storage systems has shown that open channels of different lengths and cross sectional areas, connected to an air tight storage chamber, are able to maintain variable stable gas concentrations which could be near optimal concentrations for CA/MA storage of various commodities.<br>This study was geared towards assessing the suitability of the diffusion channels in maintaining a desired gas concentration for CA storage of spinach. Initially, the respiratory behaviour of spinach was studied in gas sealed chambers (replicated four times) stored at four different temperatures, 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C. The respiration rate of spinach was 20 mgCO$ sb2$/kg.h, 66 mgCO$ sb2$/kg.h, 163 mgCO$ sb2$/kg.h and 271 mgCO$ sb2$/kg.h for 2$ sp circ$C, 8$ sp circ$C, 15$ sp circ$C and 23$ sp circ$C, respectively. A model was developed based on principles of enzymatic kinetics which could reliably predict the respiration rate of spinach at any given storage temperature.<br>Two other sets of experiments were carried in a cold room set at 2$ sp circ$C. (Abstract shortened by UMI.)

Au/PbSn joints are widely used in the microelectronics industry. Intermetallic formation in Au/60Sn-40wt. %Pb and in Au/62Sn-36Pb-2wt. %Ag systems has been studied in the temperature range 80°C-160°C using diffusion couples. Interdiffusion between Au films and 60Sn-40wt. %Pb solder doped with 2 wt. % zinc has also been studied but at 125°C only, also using diffusion couples. The intermetallic phases were identified by Energy Dispersive X-ray Analysis (EDAX) in the Scanning Electron Microscope (SEM) and found to be gold-tin compounds. The predominant phases were found to be AuSn4 and AuSn2 but all the phases predicted in that range of temperatures by the equilibrium phase diagram of the Au-Sn system were present in the couples after long annealing times. The kinetics of the intermetallic layers were determined and an activation energy for the growth of the layer of AuSn4 of 0.84 ± 0.02 eV was found. The effect of both silver and zinc on the growth rates of the intermetallic layers were determined. It was found that both additives reduce the intermetallic layer growth rates. In addition to the Au-Sn intermetallics, a compound layer of composition Au0.3Sn0.3Zn0.4 forms between the AuSn4 layer and the solder in the Au/PbSnZn system. The tensile strengths of the joints, before and after aging, were also evaluated and the weak bonds within the joints identified. It was found that the weak bonds within a Au/PbSn joint, with or without silver in the solder, were the intermetallic layer interfaces. The joint tensile strength is not weakened by the increase of the intermetallic layer thicknesses with aging time. Joint weakening occurs after degradation of the gold film of the joint, but that happens a long aging time after the depletion of the gold film. The joint made with the zinc containing solder was found to lose strength rapidly after aging. The weak area of the joint is the solder/wire interface.

Дисертація присвячена теоретичним та експериментальним дослідженням масообмінних процесів з твердою фазою у дво- та трифазних системах. Вирішена науково-технічна проблема дає змогу моделювати процеси сушіння, розчинення та екстрагування, використовувати нові методи їх інтенсифікації та розрахунку обладнання для їх проведення. Досліджено гідродинаміку, тепло- і масообмін та динаміку фільтраційного сушіння дисперсних матеріалів та визначено кінетичні коефіцієнти процесу. Досліджено розчинення полідисперсних сумішей у апараті періодичної дії за умови зміни рушійної сили та неперервне розчинення зернистого шару у вертикальному апараті. Досліджено екстрагування розчинної твердої фази з одинарних частинок та з шару зернистого матеріалу і визначено вихідні концентрації міді сульфату на виході з колонного апарату. Результати досліджень показали значну інтенсифікацію процесу розчинення та екстрагування в умовах постійного та періодичного вакуумування. Розроблено теорію масообмінного процесу у трифазній системі газ – рідина – тверде тіло. Показано можливість використання хемосорбційного процесу для очищення газового середовища від діоксиду сульфуру. Розглянуто процес розчинення твердих тіл, який супроводжується значним тепловим ефектом у зоні взаємодії. Наведено аналогію теплообміну та масообміну Для промислового розчинника складено математичну модель розчинення калійної солі. Запропоновано технологічну схему очищення газового середовища від діоксиду сірки.<br>Диссертация посвящена теоретичесим и эспериментальным исследованиям масоообменных процессов с твердой фазой в дво- и трифазных системах. Решеная научно-техническая проблема дает возможность моделировать процессы сушки, растворения и экстрагирования, использовать новые методы их интенсификации и рассчета оборудования для их проведения. Исследовано гидродинамику, тепло- и массообмен и динаміку фільтрационной сушки дисперсных материалов и определено кинетические коэффициенты процесса. Исследовано. растворение полидисперсных смесей в аппарате периодического действия при условии изменения движущей силы и неперывное растворение зернистого слоя в вертикальном аппарате. Исследовано экстрагирование растворимой твердой фазы с одиночных частиц и со слоя зернистого материала и определено выходные концентрации меди сульфата на выходе с колонного аппарата. Результаты исследований показали значительную интенсификацию процесса растворения и экстрагирования в условиях постоянного и периодического вакуумированя. Розработано теорию масоообменного процесса у трифазной системе газ – жидкость – твердое тело. Показано возможность использования хемосорбционного процесса для очистки газовой среды от диоксида сульфура. Рассмотрено дифузионно контролированый процесс растворения твердых тіл, который сопровождается значительным тепловым эффектом в зоне взаимодействия. Наведено аналогию теплообмена и массообмена. Для промышленного растворителя составлено математическую модель растворения калійной соли. Запропонировано технологическую схему очищения газовой среды от диоксида серы.<br>The dissertation is devoted to theoretical and experimental researches of mass transfer processes with solid phase in two- and three-phase systems, which are the actual scientific and applied problem for processes of chemical technology. The solved scientific and technical problem enables to simulate mass transfer processes of drying, dissolution and extraction, to use new methods of their intensification and calculation of equipment for their implementation. Hydrodynamics, heat and mass transfer and the dynamics of filtration drying of dispersed materials were studied and the kinetic coefficients for the substances involved in the process were determined. Theoretically and experimentally was investigated the dissolution of polydisperse mixtures in a periodic action apparatus under conditions of change in motive force. The particle distribution function is represented by their diameters and the function change with the dissolution time is shown. The graphic integration method was used to determine the mass soluble particle during the theoretical analysis of the dissolution of the polydisperse mixture depending on the dimensionless time. Experimentally was investigated the continuous direct solubility of a stationary granular layer in a vertical apparatus and determined the concentrations at certain heights of a layer. A mathematical model of the dissolution process is made and its solution is presented. The theoretical algorithm for calculating of concentrations and dimensionless diameter is presented. The dissolution of solids in the stationary layer of the granular material is accompanied by non-stationary phenomena, which complicate the calculation of the dissolution. The results of experimental researches showed significant intensification of the process of extracting of sulphate cuprum in conditions of constant and periodic vacuuming. Effective diffusion coefficients were determined and was shown the possibility of increasing of the extraction rate up to 6 times compared to the external mechanical mixing of medium. The theory of the mass transfer process in the three-phase gas-liquid-solid system was developed, and each mass transfer stage was studied: physical absorption, mass deduction, diffusion-controlled chemical dissolution. The possibility of application of chemisorption process to purify the gas environment from sulphur dioxide is shown. The mathematical models of the non-stationary heat transfer process with a superficial heat source are developed, which allows to determine the temperature in solids and liquid media. An analogy of heat transfer and mass transfer is shown, which is determined by the same hydrodynamic situation in the reaction zone. For the industrial solvent a mathematical model for dissolving potassium salt is developed. The technological scheme of purification of gas medium from sulphur dioxide in a three-phase system is proposed on the basis of conducted researches.

The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

Basic science and early clinical trial evidence suggest the safe diuretic drug amiloride, may exert a neuroprotective effect in multiple sclerosis (MS) through blockade of the acid sensing ion channel. Neuroprotective treatments are a key unmet need in multiple sclerosis. Optic neuritis (ON) is a discrete CNS inflammatory event leading to neuro-axonal injury in the optic nerve and retina. The optic nerve is part of the visual system, one of the most functionally and structurally eloquent systems in the central nervous system, which affords a number of unique modalities to assess neurodegeneration and neuroprotection. The visual system can be classified into two parts, the anterior and posterior visual systems, which are defined by the lateral geniculate nucleus, where the two components synapse. The extent of neurodegeneration following ON in the anterior visual system can be imaged in vivo through scanning laser polarimetry (GDx) and optical coherence tomography (OCT). The posterior visual system can be imaged by quantitative and functional magnetic resonance imaging (MRI) of the brain, giving insights into white matter structural integrity and cortical plasticity over time. Combining these modalities in a longitudinal study, allows assessment of the impact of neurodegeneration in the anterior visual system on neurodegeneration downstream in the posterior visual system and on changes in functional connectivity over time in the visual cortex. Furthermore, in the clinical trial setting the neuroprotective effect of any intervention both on direct anterior neurodegeneration and downstream processes can be assessed. The functional relevance of changes in all of these biomarkers can be tested through a number of visual measures, including low contrast visual acuity. In MS, the contribution of transsynaptic neurodegeneration to the global neuronal loss experienced by patients is an area of incomplete understanding. In addition, the role of the visual cortex, through neuroplasticity, in aiding visual recovery from optic neuritis, is unclear. To address these issues, this thesis reports the results of the first clinical trial of amiloride in ON, and shows that despite the pre- and early clinical evidence of neuroprotection of amiloride, no neuroprotective benefit was found. It goes on to explore reasons for this lack of effect including the finding of early retinal neurodegeneration in ON, and the need for early recruitment windows in the future. From there, it makes a detailed assessment of the longitudinal changes in retinal OCT for 12 months following ON, including a novel finding of the temporal evolution of inner nuclear layer swelling, previously reported only cross-sectionally. Next, for the first time macular retinal neurodegeneration is shown to influence diffusion tensor MRI derived measures of white matter integrity in the optic radiations, indicating transsynaptic neurodegeneration. Finally, longitudinal changes in resting state functional connectivity following ON are found in the visual system for the first time. The interaction between this cortical functional, retinal neurodegeneration and visual recovery is probed.

The fate of the carbon and nitrogen in dairy farm effluent (DFE) applied onto soil was investigated through laboratory experiments and field lysimeter studies. They resulted in the development and testing of a complex carbon (C) and nitrogen (N) simulation model (CaNS-Eff) of the soil-plant-microbial system. To minimise the risk of contamination of surface waters, regulatory authorities in New Zealand promote irrigation onto land as the preferred treatment method for DFE. The allowable annual loading rates for DFE, as defined in statutory regional plans are based on annual N balance calculations, comparing N inputs to outputs from the farming system. Little information is available, however, to assess the effects that these loading rates have on the receiving environment. It is this need, to understand the fate of land-applied DFE and develop a tool to describe the process, that is addressed in this research. The microbially mediated net N mineralisation from DFE takes a central role in the turnover of DFE, as the total N in DFE is dominated by organic N. In a laboratory experiment, where DFE was applied at the standard farm loading rate of 68 kg N ha⁻¹, the net C mineralisation from the DFE was finished 13 days after application and represented 30% of the applied C, with no net N mineralisation being measured by Day 113. The soluble fraction of DFE appeared to have a microbial availability similar to that of glucose. The low and gradually changing respiration rate measured from DFE indicated a semi-continuous substrate supply to the microbial biomass, reflecting the complex nature and broad range of C compounds in DFE. The repeated application of DFE will gradually enhance the mineralisable fraction of the total soil organic N and in the long term increase net N mineralisation. To address the lack of data on the fate of faecal-N in DFE, a ¹⁵N-labelled faecal component of DFE was applied under two different water treatments onto intact soil cores with pasture growing on them. At the end of 255 days, approximately 2% of the applied faecal ¹⁵N had been leached, 11 % was in plant material, 11 % was still as effluent on the surface, and 40% remained in the soil (39% as organic N). Unmeasured gaseous losses and physical losses from the soil surface of the cores supposedly account for the remaining ¹⁵N (approximately 36%). Separate analysis of the total and ammonium nitrogen contents and ¹⁵N enrichments of the DFE and filtered sub-samples (0.5 mm, 0.2µm) showed that the faecal-N fraction was not labelled homogeneously. Due to this heterogeneity, which was exacerbated by the filtration of DFE on the soil surface, it was difficult to calculate the turnover of the total faecal-N fraction based on ¹⁵N results. By making a simplifying assumption about the enrichment of the ¹⁵N in the DFE that infiltrated the soil, the contribution from DFE-N to all plant available N fractions including soil inorganic N was estimated to have been approximately 11 % of the applied DFE-N. An initial two-year study investigating the feasibility of manipulating soil water conditions through controlled drainage to enhance denitrification from irrigated DFE was extended a further two years for this thesis project. The resulting four-year data set provided the opportunity to evaluate the sustainability of DFE application onto land, an extended data set against which to test the adequacy of CaNS-Eff, and to identify the key processes in the fate of DFE irrigated onto soil under field conditions. In the final year of DFE irrigation, 1554 kg N ha⁻¹ of DFE-N was applied onto the lysimeters, with the main removal mechanism being pasture uptake (700 kg N ha⁻¹ yr⁻¹ removed). An average of 193 kg N ha⁻¹ yr⁻¹ was leached, with 80% of this being organic N. The nitrate leaching decreased with increasing soil moisture conditions through controlled drainage. At the high DFE loading rate used, the total soil C and N, pH and the microbial biomass increased at different rates over the four years. The long-term sustainability of the application of DFE can only be maintained when the supply of inorganic N is matched by the demand of the pasture. The complex simulation model (CaNS-Eff) of the soil-plant-microbial system was developed to describe the transport and transformations of C and N components in effluents applied onto the soil. The model addresses the shortcomings in existing models and simulates the transport, adsorption and filtration of both dissolved and particulate components of an effluent. The soil matrix is divided into mobile and immobile flow domains with convective flow of solutes occurring in the mobile fraction only. Diffusion is considered to occur between the micropore and mesopore domains both between and within a soil layer, allowing dissolved material to move into the immobile zone. To select an appropriate sub-model to simulate the water fluxes within CaNS-Eff, the measured drainage volumes and water table heights from the lysimeters were compared to simulated values over four years. Two different modelling approaches were compared, a simpler water balance model, DRAINMOD, and a solution to Richards' equation, SWIM. Both models provided excellent estimation of the total amount of drainage and water table height. The greatest errors in drainage volume were associated with rain events over the summer and autumn, when antecedent soil conditions were driest. When soil water and interlayer fluxes are required at small time steps such as during infiltration under DFE-irrigation, SWIM's more mechanistic approach offered more flexibility and consequently was the sub-model selected to use within CaNS-Eff. Measured bromide leaching from the lysimeters showed that on average 18% of the bromide from an irrigation event bypassed the soil matrix and was leached in the initial drainage event. This bypass mechanism accounted for the high amount of organic N leached under DFE-irrigation onto these soils and a description of this bypass process needed to be included in CaNS-Eff. Between 80 and 90% of the N and C leached from the lysimeters was particulate (> 0.2 µm in size), demonstrating the need to describe transport of particulate material in CaNS-Eff. The filtration behaviour of four soil horizons was measured by characterising the size of C material in a DFE, applying this DFE onto intact soil cores, and collecting and analyzing the resulting leachate using the same size characterisation. After two water flushes, an average of 34% of the applied DFE-C was leached through the top 0-50 mm soil cores, with a corresponding amount of 27% being leached from the 50-150 mm soil cores. Most of the C leaching occurred during the initial DFE application onto the soil. To simulate the transport and leaching of particulate C, a sub-model was developed and parameterised that describes the movement of the effluent in terms of filtering and trapping the C within a soil horizon and then washing it out with subsequent flow events. The microbial availability of the various organic fractions within the soil system are described in CaNS-Eff by availability spectra of multiple first-order decay functions. The simulation of microbial dynamics is based on actual consumption of available C for three microbial biomass populations: heterotrophs, nitrifiers and denitrifiers. The respiration level of a population is controlled by the amount of C that is available to that population. This respiration rate can vary between low level maintenance requirements, when very little substrate is available, and higher levels when excess substrate is available to an actively growing population. The plant component is described as both above and below-ground fractions of a rye grass-clover pasture. The parameter set used in CaNS-Eff to simulate the fate of DFE irrigated onto the conventionally drained lysimeter treatments over three years with a subsequent 10 months non-irrigation period was derived from own laboratory studies, field measurements, experimental literature data and published model studies. As no systematic calibration exercise was undertaken to optimise these parameters, the parameter set should be considered as "initial best estimates" and not as a calibrated data set on which a full validation of CaNS-Eff could be based. Over the 42 months of simulation, the cumulative drainage from CaNS-Eff for the conventionally drained DFE lysimeter was always within the 95% CI of the measured value. On the basis of individual drainage bulking periods, CaNS-Eff was able to explain 92% of the variation in the measured drainage volumes. On an event basis the accuracy of the simulated water filled pore space (WFPS) was better than that of the drainage volume, with an average of 70% of the simulated WFPS values being within the 95% CI for the soil layers investigated, compared to 44% for the drainage volumes. Overall the hydrological component of CaNS-Eff, which is based on the SWIM model, could be considered as satisfactory for the purposes of predicting the soil water status and drainage volume from the conventionally drained lysimeter treatment for this study. The simulated cumulative nitrate leaching of 4.7 g NO₃-N m⁻² over the 42 months of lysimeter operation was in good agreement to the measured amount of 3.0 (± 2.7) g NO₃-N m⁻². Similarly, the total simulated ammonium leaching of 2.7g NH₄- N m⁻² was very close to the measured amount of 2.5 (± 1.35) g NH₄- N m⁻² , however the dynamics were not as close to the measured values as with the nitrate leaching. The simulated amount of organic N leached was approximately double that measured, and most of the difference originated from the simulated de-adsorption of the dissolved fraction of organic N during the l0-month period after the final DFE irrigation. The 305 g C m⁻² of simulated particulate C leached was close to the measured amount of 224 g C m⁻² over the 31 months of simulation. The dissolved C fraction was substantially over-predicted. There was good agreement in the non-adsorbed and particulate fractions of the leached C and N in DFE. However, the isothermic behaviour of the adsorbed pools indicated that a non-reversible component needed to be introduced or that the dynamics of the de-adsorption needed to be improved. Taking into account that the parameters were not calibrated but only "initial best estimates", the agreement in the dynamics and the absolute amounts between the measured and simulated values of leached C and N demonstrated that CaNS-Eff contains an adequate description of the leaching processes following DFE irrigation onto the soil. The simulated pasture N production was in reasonable agreement with the measured data. The simulated dynamics and amounts of microbial biomass in the topsoil layers were in good agreement with the measured data. This is an important result as the soil microbial biomass is the key transformation station for organic materials. Excepting the topsoil layer, the simulated total C and N dynamics were close to the measured values. The model predicted an accumulation of C and N in the topsoil layer as expected, but not measured. Although no measurements were available to compare the dynamics and amounts of the soil NO₃-N and NH₄-N, the simulated values appear realistic for an effluent treatment site and are consistent with measured pasture data. Considering the large amount of total N and C applied onto the lysimeters over the 42 months of operation (4 t ha⁻¹ of N and 42 t ha⁻¹0f C), the various forms of C and N in dissolved and particulate DFE as well as in returned pasture, and that the parameters used in the test have not been calibrated, the simulated values from CaNS-Eff compared satisfactorily to the measured data.

The electro–mechanical connection between under bump metallization (UBM) and solder in flip–chip bonding is achieved by the formation of brittle intermetallic compounds (IMCs) during the soldering process. These IMCs continue to grow in the solid–state during storage at room temperature and service at an elevated temperature leading to degradation of the contacts. In this thesis, the diffusion–controlled growth mechanism of the phases and the formation of the Kirkendall voids at the interface of UBM (Cu, Ni, Au, Pd, Pt) and Sn (bulk/electroplated) are studied extensively. Based on the microstructural analysis in SEM and TEM, the presence of bifurcation of the Kirkendall marker plane, a very special phenomenon discovered recently, is found in the Cu–Sn system. The estimated diffusion coefficients at these marker planes indicate one of the reasons for the growth of the Kirkendall voids, which is one of the major reliability concerns in a microelectronic component. Systematic experiments using different purity of Cu are conducted to understand the effect of impurities on the growth of the Kirkendall voids. It is conclusively shown that increase in impurity enhances the growth of voids. The growth rates of the interdiffusion zone are found to be comparable in the Cu–Sn and the Ni–Sn systems. EPMA and TEM analyses indicate the growth of a metastable phase in the Ni–Sn system in the low temperature range. Following, the role of Ni addition in Cu on the growth of IMCs in the Cu–Sn system is studied based on the quantitative diffusion analysis. The analysis of thermodynamic driving forces, microstructure and crystal structure of Cu6Sn5 shed light on the atomic mechanism of diffusion. It does not change the crystal structure of phases; however, the microstructural evolution, the diffusion rates of components and the growth of the Kirkendall voids are strongly influenced in the presence of Ni. Considering microstructure of the product phases in various Cu/Sn and Cu(Ni)/Sn diffusion couples, it has been observed that (i) phases have smaller grains and nucleate repeatedly, when they grow from Cu or Cu(Ni) alloy, and (ii) the same phases have elongated grains, when they grow from another phase. A difference in growth rate of the phases is found in bulk and electroplated diffusion couples in the Au–Sn system. The is explained in AuSn4 based on the estimated tracer diffusion coefficients, homologous temperature of the experiments, grain size distribution and crystal structure of the phase. The growth rates of the phases in the Au–Sn system are compared with the Pd–Sn and the Pt–Sn systems. Similar to the Au–Sn system, the growth rate of the interdiffusion zone is found to be parabolic in the Pd–Sn system; however, it is linear in the Pt–Sn system. Following, the effect of addition of Au, Pd and Pt in Cu is studied on growth rate of the phases. An analysis on the formation of the Kirkendall voids indicates that the addition of Pd or Pt is deleterious to the structure compared to the addition of Au. This study indicates that formation of voids is equally influenced by the presence of inorganic as well as organic impurities.