Bayesian spatio-temporal modelling for forecasting ground level ozone concentration levels

Accurate, instantaneous and high resolution spatial air-quality information can better inform the public and regulatory agencies of the air pollution levels that could cause adverse health effects. The most direct way to obtain accurate air quality information is from measurements made at surface monitoring stations across a study region of interest. Typically, however, air monitoring sites are sparsely and irregularly spaced over large areas. That is why, it is now very important to develop space-time models for air pollution which can produce accurate spatial predictions and temporal forecasts.This thesis focuses on developing spatio-temporal models for interpolating and forecasting ground level ozone concentration levels over a vast study region in the eastern United States. These models incorporate output from a computer simulation model known as the Community Multi-scale Air Quality (Eta-CMAQ) forecast model that can forecast up to 24 hours in advance. However, these forecasts are known to be biased. The models proposed hereare shown to improve upon these forecasts for a two-week study period during August 2005.The forecasting problems in both hourly and daily time units are investigated in detail. A fast method, based on Gaussian models is constructed for instantaneous interpolation and forecasts of hourly data. A more complexdynamic model, requiring the use of Markov chain Monte Carlo (MCMC) techniques, is developed for forecasting daily ozone concentration levels. A set of model validation analyses shows that the prediction maps that are generated by the aforementioned models are more accurate than the maps based solely on the Eta-CMAQ forecast data. A non-Gaussian measurement error model is also considered when forecasting the extreme levels of ozone concentration. All of the methods presented are based on Bayesian methods and MCMC sampling techniques are used in exploring posterior and predictive distributions

Structural Modelling And Analysis Of The Behavioural Dynamics Of Foreign Exchange Rate [HG3851. Y51 2006 f rb].

Tesis ini berkaitan dengan Kadar Wang Pertukaran Asing (KWPA) yang dihasilkan oleh satu regime urusniaga bebas. Pada amnya, kita mengkaji Pemodelan Struktur dan Analisis Tingkahlaku Dinamik Kadar Pertukaran Wang Asing. This thesis deals specifically with the foreign exchange rates that resulted from free float regimes. In general, we study the structural modelling and analysis of the behavioural dynamics of foreign exchange rates

Disrupting Desalination: Novel Energy Efficient Technologies for Hypersaline Brines

Management and treatment of hypersaline brines, e.g., produced water from oil and gas extraction, zero liquid discharge effluent, and flue gas desulfurization wastewater, are of growing environmental importance. Prevailing practice of distilling brines is highly energy-intensive and costly because the evaporation of water is enthalpically unfavorable. Here, we present two novel technologies for hypersaline desalination: cascading osmotically mediated reverse osmosis (COMRO) and temperature swing solvent extraction (TSSE). The first technology, COMRO, utilizes the novel design of bilateral countercurrent reverse osmosis stages to lessening the osmotic pressure difference across the membrane, thereby simultaneously depressing the hydraulic pressure needed and reducing energy demand. The second technology, TSSE, is membrane-less, not based on evaporative phase-change, and utilizes low-grade waste heat to drive the separation. Working principles of the technologies are presented, the desalination performance are examined, and implications for the treatment of hypersaline brines are discussed

The impacts of oil shocks on Malaysia's GDP growth

This paper suggests that instrumental variable regression is a good alternative to nonlinear specification model when estimating the impacts of oil shocks on GDP growth in Malaysia

Comparison of Energy Efficiency and Power Density in Pressure Retarded Osmosis and Reverse Electrodialysis

Pressure retarded osmosis (PRO) and reverse electrodialysis (RED) are emerging membrane-based technologies that can convert chemical energy in salinity gradients to useful work. The two processes have intrinsically different working principles: controlled mixing in PRO is achieved by water permeation across salt-rejecting membranes, whereas RED is driven by ion flux across charged membranes. This study compares the energy efficiency and power density performance of PRO and RED with simulated technologically available membranes for natural, anthropogenic, and engineered salinity gradients (seawater–river water, desalination brine–wastewater, and synthetic hypersaline solutions, respectively). The analysis shows that PRO can achieve both greater efficiencies (54–56%) and higher power densities (2.4–38 W/m2) than RED (18–38% and 0.77–1.2 W/m2). The superior efficiency is attributed to the ability of PRO membranes to more effectively utilize the salinity difference to drive water permeation and better suppress the detrimental leakage of salts. On the other hand, the low conductivity of currently available ion exchange membranes impedes RED ion flux and, thus, constrains the power density. Both technologies exhibit a trade-off between efficiency and power density: employing more permeable but less selective membranes can enhance the power density, but undesired entropy production due to uncontrolled mixing increases and some efficiency is sacrificed. When the concentration difference is increased (i.e., natural → anthropogenic → engineered salinity gradients), PRO osmotic pressure difference rises proportionally but not so for RED Nernst potential, which has logarithmic dependence on the solution concentration. Because of this inherently different characteristic, RED is unable to take advantage of larger salinity gradients, whereas PRO power density is considerably enhanced. Additionally, high solution concentrations suppress the Donnan exclusion effect of the charged RED membranes, severely reducing the permselectivity and diminishing the energy conversion efficiency. This study indicates that PRO is more suitable to extract energy from a range of salinity gradients, while significant advancements in ion exchange membranes are likely necessary for RED to be competitive with PRO

Performance Limiting Effects in Power Generation from Salinity Gradients by Pressure Retarded Osmosis

Pressure retarded osmosis has the potential to utilize the free energy of mixing when fresh river water flows into the sea for clean and renewable power generation. Here, we present a systematic investigation of the performance limiting phenomena in pressure retarded osmosis—external concentration polarization, internal concentration polarization, and reverse draw salt flux—and offer insights on the design criteria of a high performance pressure retarded osmosis power generation system. Thin-film composite polyamide membranes were chemically modified to produce a range of membrane transport properties, and the water and salt permeabilities were characterized to determine the underlying permeability-selectivity trade-off relationship. We show that power density is constrained by the trade-off between permeability and selectivity of the membrane active layer. This behavior is attributed to the opposing influence of the beneficial effect of membrane water permeability and the detrimental impact of reverse salt flux coupled with internal concentration polarization. Our analysis reveals the intricate influence of active and support layer properties on power density and demonstrates that membrane performance is maximized by tailoring the water and salt permeabilities to the structural parameters. An analytical parameter that quantifies the relative influence of each performance limiting phenomena is employed to identify the dominant effect restricting productivity. External concentration polarization is shown to be the main factor limiting performance at high power densities. Enhancement of the hydrodynamic flow conditions in the membrane feed channel reduces external concentration polarization and thus, yields improved power density. However, doing so will also incur additional operating costs due to the accompanying hydraulic pressure loss. This study demonstrates that by thoughtful selection of the membrane properties and hydrodynamic conditions, the detrimental effects that limit productivity in a pressure retarded osmosis power generation process can be methodically minimized to achieve high performance

Thermodynamic and Energy Efficiency Analysis of Power Generation from Natural Salinity Gradients by Pressure Retarded Osmosis

The Gibbs free energy of mixing dissipated when fresh river water flows into the sea can be harnessed for sustainable power generation. Pressure retarded osmosis (PRO) is one of the methods proposed to generate power from natural salinity gradients. In this study, we carry out a thermodynamic and energy efficiency analysis of PRO work extraction. First, we present a reversible thermodynamic model for PRO and verify that the theoretical maximum extractable work in a reversible PRO process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible constant-pressure PRO process is then examined. We derive an expression for the maximum extractable work in a constant-pressure PRO process and show that it is less than the ideal work (i.e., Gibbs free energy of mixing) due to inefficiencies intrinsic to the process. These inherent inefficiencies are attributed to (i) frictional losses required to overcome hydraulic resistance and drive water permeation and (ii) unutilized energy due to the discontinuation of water permeation when the osmotic pressure difference becomes equal to the applied hydraulic pressure. The highest extractable work in constant-pressure PRO with a seawater draw solution and river water feed solution is 0.75 kWh/m3 while the free energy of mixing is 0.81 kWh/m3—a thermodynamic extraction efficiency of 91.1%. Our analysis further reveals that the operational objective to achieve high power density in a practical PRO process is inconsistent with the goal of maximum energy extraction. This study demonstrates thermodynamic and energetic approaches for PRO and offers insights on actual energy accessible for utilization in PRO power generation through salinity gradients

Supporting Information: Unlocking High-Salinity Desalination with Cascading Osmotically Mediated Reverse Osmosis: Energy and Operating Pressure Analysis

Derivation of analytical expressions for specific energy requirement and operating pressures of COMRO, DPRO, and CF/OARO; analysis results of operating hydraulic pressures and specific energy consumption; analysis of alternative operating scheme for COMRO and DPRO; impacts of stage operating schemes on the specific energy requirement; and application of COMRO to treat ultrahigh salinity brine; Tables S1–6; Figures S1–S

Unlocking High-Salinity Desalination with Cascading Osmotically Mediated Reverse Osmosis: Energy and Operating Pressure Analysis

Current practice of using thermally driven methods to treat hypersaline brines is highly energy-intensive and costly. While conventional reverse osmosis (RO) is the most efficient desalination technique, it is confined to purifying seawater and lower salinity sources. Hydraulic pressure restrictions and elevated energy demand render RO unsuitable for high-salinity streams. Here, we propose an innovative cascading osmotically mediated reverse osmosis (COMRO) technology to overcome the limitations of conventional RO. The innovation utilizes the novel design of bilateral countercurrent reverse osmosis stages to depress the hydraulic pressure needed by lessening the osmotic pressure difference across the membrane, and simultaneously achieve energy savings. Instead of the 137 bar required by conventional RO to desalinate 70 000 ppm TDS hypersaline feed, the highest operating pressure in COMRO is only 68.3 bar (−50%). Furthermore, up to ≈17% energy saving is attained by COMRO (3.16 kWh/m3, compared to 3.79 kWh/m3 with conventional RO). When COMRO is employed to boost the recovery of seawater desalination to 70% from the typical 35–50%, energy savings of up to ≈33% is achieved (2.11 kWh/m3, compared to 3.16 kWh/m3 with conventional RO). Again, COMRO can operate at a moderate hydraulic pressure of 80 bar (25% lower than 113 bar of conventional RO). This study highlights the encouraging potential of energy-efficient COMRO to access unprecedented high recovery rates and treat hypersaline brines at moderate hydraulic pressures, thus extending the capabilities of membrane-based technologies for high-salinity desalination