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Yes / Fresh water is crucial for life, supporting human civilizations and ecosystems, and its production is one of the global issues. To cope with this issue, we evaluated the performance and cost of a solar-powered direct contact membrane distillation (DCMD) unit for fresh water production in Karachi, Pakistan. The solar water heating system (SWHS) was evaluated with the help of a system advisor model (SAM) tool. The evaluation of the DCMD unit was performed by solving the DCMD mathematical model through a numerical iterative method in MATLAB software®. For the SWHS, the simulation results showed that the highest average temperature of 55.05 ◦C and lowest average temperature of 44.26 ◦C were achieved in May and December, respectively. The capacity factor and solar fraction of the SWHS were found to be 27.9% and 87%, respectively. An exponential increase from 11.4 kg/m2 ·h to 23.23 kg/m2 ·h in permeate flux was observed when increasing the hot water temperatures from 44 ◦C to 56 ◦C. In the proposed system, a maximum of 279.82 L/day fresh water was produced in May and a minimum of 146.83 L/day in January. On average, the solar-powered DCMD system produced 217.66 L/day with a levelized water cost of 23.01 USD/m3 / This research was funded by the Researcher’s Supporting Project Number (RSP-2021/269), King Saud University, Riyadh, Saudi Arabia.

Three types of nonlinear optical spectroscopies, ultrafast two-dimensional infrared (2DIR) spectroscopy, transient infrared (IR) absorption/pump-probe spectroscopy, and sum-frequency generation (SFG) vibrational spectroscopy, are used to investigate molecular structure and dynamics in two distinct classes of materials. First, 2DIR and pump-probe spectroscopies are used to study ultrafast rotational and vibrational energy relaxation in dense gaseous and supercritical fluid solutions, special solvation effects near the critical point, and the evolution of cooperative, liquid-phase dynamics as a function of density for two different solvent systems. 2DIR’s demonstrated capabilities offer a unique tool for identifying co-existing free rotor and liquid-like populations within the same fluid sample, evaluating the adequacy of isolated binary collision (IBC) relaxation descriptions in dense gas and near-liquid density fluids, and learning about how solute-solvent intermolecular properties separately influence rotational and vibrational relaxation in these dynamic and heterogeneous environments. Analysis of the density-dependent 2DIR and pump-probe spectra of a quasi-free rotor (asymmetric stretch rovibrational band of N2O) in SF6 and Xe provides timescales for rotational energy relaxation rates (1 – 3 collisions), but much slower vibrational energy relaxation rates. A critical slowing effect on the rate of rotational relaxation is identified, and liquid-like solvation is observed in dense gaseous solutions at state points lower than the critical density. Solvent-dependent differences in energy relaxation and IBC model breakdown, as well as applications of this 2DIR methodology to other high density and supercritical solution dynamics and descriptions are discussed. In a second nonlinear spectroscopy project, SFG is used to study the role of substrate type, gold or silver, and surface roughness on the parity odd-even effect in n-alkanethiolate (n = 10 – 16) self-assembled monolayers (SAMs), materials of potential importance to molecular scale electronics. SFG methyl vibrational transition intensities, frequencies, and linewidths display parity and metal dependence attributable to the orientational differences of the interfacial ethyl group, which inverts for SAMs on Ag substrates relative to SAMs on Au. Substrate roughness, an often-underreported experimental parameter, is shown here to affect the extent of odd-even methyl orientation anisotropy, and this SFG analysis establishes a new roughness limit for the appearance of odd-even effects on Ag substrates.

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The structure/function relationship between bacteria and biocidal molecules in the vapor or solution phase is well-understood. However, the fundamental structure/function relationship between covalently-bound biocidal surface molecules and bacteria is not. While a number of antibacterial surfaces have been reported, detailed analysis of the molecular scale surface structure has not been performed. The lack of structural knowledge makes it difficult to determine how alterations to the surface affect the viability of the bacteria. Most of the antibacterial surfaces reported to date are composed of polymer systems. Controlling the properties of large surface-bound molecules like polymers is difficult. Self-assembled monolayers, or SAMs, of alkanethiols on gold have been used extensively in the past 20 years as model surfaces for investigation of a large breadth of surface phenomena. SAMs allow for control of the molecular scale surface structure and are amenable to a great number of characterization techniques. The primary objective of the work in this study is to establish the use of SAMs as a tool to investigate the fundamental relationship between surface structure and bacteria viability. The surfaces were characterized before interaction with bacteria by reflection-absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). Determination of the viability of Escherichia coli on the surfaces was performed via the antibacterial assay. In the assay, a culture of E. coli was sprayed onto the surfaces using a chromatography sprayer. After addition of growth agar and overnight incubation, the number of colony forming units on the surface were counted. Statistical analyses were performed to compare the number of colony forming units on different surfaces. Surfaces were characterized after the assay by RAIRS. The RAIR spectra indicated that no significant change to the well-ordered alkane chain configuration was evident. The structural stability shown by the SAMs will allow for their use in future studies to determine fundamental relationship between surface structure and bacteria viability. / Master of Science

The acoustic microscope is an efficient non-invasive tool that can explore the acoustic properties and the related mechanical microstructure of a wide diversity of materials, including biomedical and biological samples, which are, nowadays, among the most intriguing targets for investigations. In the presented work, an acoustic microscope with vector contrast is used to image and characterize the acousto-mechanical properties of chitosan, an abundant natural derivative of chitin known to be a biodegradable, nontoxic and versatile biopolymer that suits many biomedical applications such as its usage in tissue engineering. The work also presents key measurements for the study of the acousto-mechanical properties that are subject to variations during the life span of red blood cells (RBCs). The characteristic signature of fixed cells from groups of three different ages, fractionated according to mass density, is obtained from the acoustic microscope images. The analysis of these data enabled the quantitative comparisons between the acousto-mechanical properties (velocity and attenuation of ultrasound propagating in the cells, mass density, and bulk modulus of compression). Comparison of the contrasts in the acoustic micrographs for the cells of the different age groups is exploited to generate a model that determines the age of the individual cells in a sample of red blood cells collected from a healthy person. The dependence of the parameters of the cells including density, velocity and attenuation of longitudinal polarized ultrasonic waves travelling in the cells on the age of the cell is also presented. The output signal in dependence on the thickness of the sample, the so called V(d), represented as polar graph was exploited as the method of analysis of the data extracted from the acoustic micrographs imaged with ultrasound of a center frequency of 1.2 GHz. This procedure allows for the extraction of the quantitative information from a single image in magnitude and phase contrast and allows for height profiling with so called super resolution, relating to resolution below the diffraction limit, based on the developed modeling, beside of other advantages concerning the acoustic characterization of biomedical and biological samples. This method and the applications are presented and discussed together with the developed or adapted modeling.