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Due to their ability to model complicated imaging physics, to compensate for imperfect data acquisition systems, and to exploit prior information regarding the to-be-imaged object, iterative image reconstruction algorithms can often produce higher quality images than analytical reconstruction methods. However, for three-dimensional (3-D) imaging tasks with large fields of view, iterative reconstruction methods can be computationally burdensome. A common cause for this is the need to repeatedly evaluate the forward operator and its adjoint. From the algorithmic perspective, one way to accelerate iterative algorithms is to substitute the adjoint operator with an unmatched approximation of it, which can be computed more efficiently. Previous works have investigated some of the impacts of employing unmatched backward operators in iterative algorithms. This paper extends the theoretical analysis of unmatched backward operators to a more general penalized least-squares framework that allows for complex eigenvalues and regularization. Additionally, a convergence condition for a Landweber-type algorithm employing an unmatched backward operator is presented and numerically corroborated. An unmatched backward operator is introduced to accelerate iterative image reconstruction in 3-D optoacoustic tomography, and it is investigated by use of experimental data.

Zeolite-based catalysts are usually utilized in the form of a composite with binders, such as alumina, silica, clay, and others. However, these binders are usually known to block the accessibility of the active sites in zeolites, leading to a decreased effective surface area and agglomeration of zeolite particles. The aim of this work is to utilize carbon nanostructures (CNS) as a binding material for nano-zeolite-Y particles. The unique properties of CNS, such as its high surface area, thermal stability, and flexibility of its fibrous structure, makes it a promising material to hold and bind the nano-zeolite particles, yet with a contemporaneous accessibility of the reactants to the porous zeolite structure. In the current study, a nano-zeolite-Y/CNS composite catalyst was fabricated through a ball milling approach. The catalyst possesses a high surface area of 834 m2/g, which is significantly higher than the conventional commercial cracking catalysts. Using CNS as a binding material provided homogeneous distribution of the zeolite nanoparticles with high accessibility to the active sites and good mechanical stability. In addition, CNS was found to be an effective binding material for nano-zeolite particles, solving their major drawback of agglomeration. The nano-zeolite-Y/CNS composite showed 80% conversion for hexadecane catalytic cracking into valuable olefins and hydrogen gas, which was 14% higher compared to that of pure nano-zeolite-Y particles.

Nanosized zeolite Y is used in various applications from catalysis in petroleum refining to nanofillers in water treatment membranes. Ball milling is a potential and fast technique to decrease the particle size of zeolite Y to the nano range. However, this technique is associated with a significant loss of crystallinity. Therefore, in this study, we investigate the effect of adding biodegradable and recyclable cellulose nanofibrils (CNFs) to zeolite Y in a wet ball milling approach. CNFs are added to shield the zeolite Y particles from harsh milling conditions due to their high surface area, mechanical strength, and water gel-like format. Different zeolite Y to CNFs ratios were studied and compared to optimize the ball milling process. The results showed that the optimal zeolite Y to CNFs ratio is 1:1 to produce a median particle size diameter of 100 nm and crystallinity index of 32%. The size reduction process provided accessibility to the zeolite pores and as a result increased their adsorption capacity. The adsorption capacity of ball-milled particles for methylene blue increased to 29.26 mg/g compared to 10.66 mg/g of the pristine Zeolite. These results demonstrate the potential of using CNF in protecting zeolite Y particles and possibly other micro particles during ball milling.

Ultrafiltration (UF) and nanofiltration (NF) membranes have attracted great research interest to treat dye wastewaters. However, UF membranes suffer from low dye rejection and NF membranes have low salt recovery. There is a tradeoff between the dye rejection and salt recovery in the UF and NF membranes. A novel membrane is required for dye rejection with high salt recovery. Herein, we report a novel UF conductive ceramic membrane made from nano-zeolite and carbon nanostructures (CNS) combined with an external electric potential to treat crystal violet (CV) dye/NaCl-Na2SO4 salt solution. The membrane showed trimodal hierarchical porosity, a water contact angle of ≈40°, good flexibility and high electrical conductivity. Voltages from 2 to 15 V were applied to the membrane acting as a cathode in a cross-flow filtration setup. High dye rejections ≈100% with a flux of 210 LMH at a voltage as low as 3 V were achieved. Contemporaneous dye degradation was observed with several intermediate compounds, identified through mass spectroscopy. It was observed that higher potentials produced nitrates/nitrites from organic intermediates as deduced from ion chromatography results. Donnan steric repulsion increased with higher potentials, leading to increased ion transfer resistance for anions and improved permeation for cations. Various permeate properties such as pH and conductivity were monitored, along with high salt recoveries, hence providing a huge advantage of using such a membrane for treating dye wastewaters with selective dye/salt rejection. The versatile properties, together with its facile fabrication process indicates tremendous prospect of zeolite/CNS membranes for multipurpose applications treating wastewaters containing charged molecules and ions.

Electrospun tungsten oxide/nickel tungstate (WO3/NiWO4) composite nanofibers were tested for photoelectrochemical (PEC) performance under visible light irradiation under three voltages, 1.6, 1.8 and 2.0 V with reference to Ag/AgCl electrode in 0.5 M H2SO4. It was found that the photocurrent density of this novel nanostructure fiber is about 70% higher than the pristine electrospun WO3 fibers under similar conditions. WO3/NiWO4 heterojunction was identified within the fiber through high-resolution transmission electron microscopy imaging. The fibrous form is expected to provide greater exposure to the WO3/NiWO4 heterojunctions for the photocatalytic reaction. This heterojunction within the fibrous form is expected to provide a higher photoanode performance due to a lower charge-transfer resistance than the pristine WO3 fibers as also confirmed through the electrochemical impedance spectra. Interestingly, calcination of these composite fibers at 800 °C instead at 550 °C increased the percentage of NiWO4 phase, yet with a contemporaneous increase in larger crystallites of metal tungstate. The latter was responsible for giving lower photocurrents which helped in understanding the PEC performance with respect to material structure for the composite fiber under the current study.

Novel crystalline nickel–tungsten oxide composite fibers were synthesized for the first time, to the best of our knowledge, through the electrospinning method using nickel acetate and ammonium metatungstate as precursor solutions. Fibers with five different Ni:W molar ratios, 2:1, 1:1, 1:2, 3:1 and 1:3, were prepared. After calcination, the produced fibers were composed of tungsten oxide (WO3), nickel oxide (NiO) and nickel tungstate (NiWO4). Fiber morphology and structure were studied using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Selected fibers were investigated for electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H2SO4 and 0.1 M KOH electrolytes. The electrospun composite fibers showed good electrocatalytic activity compared to pure NiO and WO3 fibers with an overpotential of 80 mV and 60 mV in acidic and basic media, respectively. Low Tafel slopes were also registered as 50.27 mV/dec and 41.29 mV/dec in H2SO4 and KOH, respectively. The presence of NiWO4 compound, formed during the composite fabrication, was responsible for improving the electrocatalytic performance of the fibrous catalyst.

The utilization of seawater for drinking purposes is limited by the high specific energy consumption (SEC) (kW-h/m3) of present desalination technologies; both thermal and membrane-based. This is in turn exasperated by high water production costs, adding up to the water scarcity around the globe. Most technologies are already working near their thermodynamic limit, while posing challenges in further SEC reductions. Understanding the current energy status and energy breakdowns of leading desalination technologies will further help in realizing limitations and boundaries imposed while working for improved system performances. This paper comprehensively reviews the energy requirements and potential research areas for reduced SEC of various thermal, membrane-based and emerging desalination technologies. For thermal desalination processes, which consume a large chunk of energy for heating, renewable energy sources can be a viable option for bringing down the energy requirements. Hence, this review also focuses on the potential of desalination-renewable energy integrations. The review extends beyond conventional energy reduction possibilities to utilizing novel, advanced membranes and innovative techniques for energy offsets. The future of desalination for optimized energy requirements is projected to include ultra-high permeability membranes, fouling resistant membranes, hybrid systems, and renewable-energy driven desalination.

Membrane fouling is a major drawback in membrane-based separation processes. In this work, periodic electrolytic membrane cleaning was used for the first time on ceramic-based electrically conductive membranes made from nano-zeolite and carbon nanostructures (CNS). Highly conductive nano zeolite/CNS, hydrophilic microfiltration membranes were fabricated through vacuum filtration, with PVDF as a binder for improved mechanical strength. Membrane cross-section revealed a uniform nano-zeolite distribution within the CNS. The membrane was subjected to periodic electrolysis during the filtration of yeast and sodium alginate (SA) as model foulants. High flux recoveries were obtained, with flux increasing to 95% and 90% for yeast and SA after the first cycle compared to without electrolysis. Subsequent increase in flux was observed thereafter each cleaning cycle reducing the concentration boundary layer. The composite membrane possessed high electrical conductivity and good electrocatalytic behavior for hydrogen evolution, which enabled membrane surface cleaning through the generation of hydrogen bubbles which led to the sweeping away of the foulant layer during the electrocatalytic cleaning between each filtration cycle. The membrane also showed good anti-microbial properties with low bacterial proliferation for both gram-positive and gram-negative bacteria. These electro-ceramic self-cleaning membranes hold immense potential in several types of separation processes where ceramic membranes are a choice of material, and where bio-fouling is a predominant factor for flux decline.

Membrane performance is a region of growing research interest, where new functional nanomaterials are continually sought. In this study, nano zeolite type-Y was prepared through a unique ball milling process. The produced zeolite has a high surface area, and abundant flow channels with a well-defined pore structure facilitating water passage, but at the same time restricting the passage of contaminants through the molecular sieving effect. Polysulfone (PSf) membranes were prepared through phase inversion with nano-Y loadings from 0.2 to 1.5 wt%. Membranes were characterized for their structure, morphology, thermal stability and porosity. The developed membranes were tested for micellar enhanced ultrafiltration (MEUF) cationic dye rejections. The addition of nano-Y affected both the flux and dye rejection of the membranes. Optimum performance was obtained at 0.4 wt% nano-Y loading, giving a rejection of 99.5% and a corresponding flux of 105 L m−2 h−1. The static contact angle measurements indicate that membrane hydrophilicity increased with progressive nano-Y additions until 0.4 wt%, after which the membrane showed no further change in hydrophilic character. The obtained effects of nano-Y addition on membrane performance was attributed to the well-connected 3-D microporous structure in which the nano zeolite provided preferential water pathways though its nanoporous hydrophilic channels. Whereas, the high dye rejection was attributed to the fact that nano-Y zeolite is negatively charged and, as a result, provided resistance to the negatively charged micelles, and further restricted its passage through the microporous zeolite structure.

This paper reviews various functional materials used in desalination. Desalination of the abundant seawater resource has emerged as a promising technology to meet the current fresh water demands. For improved performance, often functional materials such as photocatalysts, electrocatalysts, photothermal materials, sorbents, antibacterial materials and magnetic materials are utilized in thermal, membrane-based and other desalination technologies. With an aim to provide an insight on the existing research on functional materials and the purpose behind using such in desalination, this review collates different research studies of various functional properties and the subsequent materials utilized for those properties. New generation materials such as carbon nanotubes (CNTs) and graphene form a major part, where they exhibit multiple functionalities with improved water transport properties, and thus have been deemed as very attractive enhancers to the desalination technology. Nevertheless, most of the functional materials, such as nano-TiO2, nano-zeolites, graphene, CNTs and magnetic nanoparticles suffer from several limitations such as specialized synthesis techniques, agglomeration, leaching and environmental and health concerns. This review focuses on such challenges and suggests improvements for enhanced incorporation of these in the desalination technology. Lastly, emerging new technologies, advanced fabrication methods and novel functional hybrid materials are reviewed to equip the readers with the latest research trends. Thus, a comprehensive review is essential which will provide current and future researchers an insight on the importance and significance of utilizing functional materials in various desalination technologies.

Recent progress in reverse osmosis (RO) technology is not limited to RO membrane materials, module designs and RO process optimization. It involves prior feed treatment which directly impacts RO system performance. The ongoing challenges of membrane fouling in RO membranes can be addressed by increasing the operational efficiency through the use of correct pretreatment options which can mitigate organic and inorganic fouling by selectively rejecting contaminants prior to reaching the RO unit. Highly polluted water resources have put critical stress on the existing conventional pretreatment techniques, whereby membrane pretreatment has emerged as a promising alternative. This paper provides an overview of the development and current trends in conventional and non-conventional RO pretreatment techniques whereby the techniques are critically reviewed to inform readers of potential improvements in such areas. This paper addresses the major drawbacks of conventional pretreatment methods which have necessitated the use of membrane pretreatment techniques. Special attention is given to microfiltration, ultrafiltration and nanofiltration methods and their development in terms of advanced membrane materials based on ceramics and self-cleaning membranes. Studies from laboratory scale standalone systems, pilot scale and large scale integrated systems for performance, cost and ecological analysis have been reviewed to familiarize readers with the many factors which need to be analyzed for selection of the appropriate pretreatment method(s). The critical review in this paper will help researchers focus more on the areas which have room for further development for cost-effective and advanced RO pretreatment techniques.

In this work, a hydrocracking catalyst, nano zeolite Y-NiO-WO3 is reshaped into nanofibrous form. This novel composite fiber show good mechanical strength together with a uniform elemental distribution for both the acidic and hydrogenation components as confirmed through scanning transmission electron microscopy. The catalyst is tested for n-heptane hydrocracking in a continuous flow fixed-bed reactor at reaction temperatures of 350 °C and 400 °C with a time on stream of 180 minutes. The fibers produced from nano zeolite-Y show superior performance with a total conversion of 98.81 wt% and 96.8 wt% at 350 °C and 400 °C respectively. In addition, a low amount of coke (0.40 wt% and 1.05 wt% at 350 °C and 400 °C respectively) was formed with the nano zeolite Y fibers. This superior performance is related to the enhanced accessibility due to the nanofiber shape where the non-woven mesh/network of catalytic fibers prevents the agglomeration of the nanoparticles. Agglomeration is a major cause of hindered accessibility of the reactants to the catalyst active sites. The zeolite particle size, and the shape of the fibrous catalyst, together with its mesoporous character (as confirmed through BET analysis) enhances diffusion and improves accessibility for the reactants to react on the catalytic active sites as proven by the high total n-heptane conversions and high hexane and iso hexane selectivity for n-heptane hydrocracking.

Since its inception in the 19th century, microfiltration (MF) has evolved as a membrane-based separation technology for treating various effluents and wastewaters. This review aims to familiarize its readers with general and specific research trends on various topics in MF. The level of research interest has been measured by the number of publications in that area for each year. An increasing research trend was observed from the number of publications since 2009 to 2018 with MF as the major topic. During the past decade, MF articles have spanned in about 150 different journals, with The Journal of Membrane Science, Desalination and Separation and Purification Technology being the major ones. Major topics of interest include membrane fabrication and modification, waste water treatment and fouling studies, while a significant research increase was seen in various fabrication methods and MF application in the food sector. MF modeling still remains a topic which needs further research output, and has experienced a decline over the past years. Several potential research areas are also identified in this review which will help future researchers to materialize their efforts into the right direction.

Zeolite based membranes have been extensively studied over the past decade for enhanced reverse osmosis (RO) performances. In this study, poly vinyl alcohol (PVA)-networked cellulose (NC) membranes incorporated with nano zeolite-Y were prepared through a facile slip casting approach using various nano zeolite-Y loadings from 0.05 to 1.0 wt%. The nano zeolite was prepared through a unique ball milling process. Membrane hydrophilicity was seen to increase with increase in zeolite loading, while improved tensile strength (8.7 MPa) and tensile modulus (67 MPa) were obtained on small zeolite additions of 0.05 wt%. No prominent peak shifts were observed in differential scanning calorimeter (DSC) testifying to the thermal stability of the membranes. Membranes were tested for RO using 25,000 mg/L NaCl solution. Optimum RO performance was achieved for 0.5 wt% nano zeolite registering a salt rejection (Rs) of 99.52% with a flux increase of 34.2% compared to the bare PVA-NC membranes. Thus, addition of nano-Y to the polymer matrix provides preferential water pathways which facilitate water flow through the membrane. In addition, the irregular crystal morphology of the nano-Y, the size exclusion principle and the ion exchange mechanism provided a high salt rejection for the PVA-NC-nano Y membranes.

MHD visco elastic Fluid flow and heat transfer over a stretching surface in presence of viscous dissipation, internal heat generation or absorption and work due to deformation has been investigated. The flow is influenced by linearly stretching sheet, in presence of heat generation/absorption of the wall. The problem has been solved numerically by shooting technique with fourth order RUNGE-KUTTA integration scheme. Heat Transfer analysis has been carried out for both prescribed surface temperature (PST) and prescribed power law heat flux (PHF) to get the effect of visco –elasticity (k1),Eckert number (Ec), heat source /sink (), and Prandle number (Pr) in presence and absence of magnetic field (Mn).

We study three-body recombination in two dimensions for systems interacting via short-range two-body interactions in the regime of large scattering lengths. Using the adiabatic hyperspherical representation, we derive semi-analytical formulas for three-body recombination in both weakly and deeply bound diatom states. Our results demonstrate the importance of long-range corrections to the three-body potentials by showing how they alter the low-energy and scattering length dependence of the recombination rate for both bosonic and fermionic systems, which exhibit suppressed recombination if compared to the three-dimensional case. We verify these results through numerical calculations of recombination for systems with finite-range interactions and supporting a few two-body bound states. We also study finite-range effects for the energies of the universal three-identical-bosons states and found a slow approach to universal predictions as a function of the scattering length., 11 pages, 7 figures

Ultrasound computed tomography (USCT) holds great promise for improving the detection and management of breast cancer. Because they are based on the acoustic wave equation, waveform inversion-based reconstruction methods can produce images that possess improved spatial resolution properties over those produced by ray-based methods. However, waveform inversion methods are computationally demanding and have not been applied widely in USCT breast imaging. In this work, source encoding concepts are employed to develop an accelerated USCT reconstruction method that circumvents the large computational burden of conventional waveform inversion methods. This method, referred to as the waveform inversion with source encoding (WISE) method, encodes the measurement data using a random encoding vector and determines an estimate of the sound speed distribution by solving a stochastic optimization problem by use of a stochastic gradient descent algorithm. Both computer-simulation and experimental phantom studies are conducted to demonstrate the use of the WISE method. The results suggest that the WISE method maintains the high spatial resolution of waveform inversion methods while significantly reducing the computational burden.

The dissociation of an H2+ molecular-ion beam by linearly polarized, carrier-envelope-phase-tagged 5 fs pulses at 4×10(14) W/cm2 with a central wavelength of 730 nm was studied using a coincidence 3D momentum imaging technique. Carrier-envelope-phase-dependent asymmetries in the emission direction of H+ fragments relative to the laser polarization were observed. These asymmetries are caused by interference of odd and even photon number pathways, where net zero-photon and one-photon interference predominantly contributes at H+ + H kinetic energy releases of 0.2-0.45 eV, and net two-photon and one-photon interference contributes at 1.65-1.9 eV. These measurements of the benchmark H2+ molecule offer the distinct advantage that they can be quantitatively compared with ab initio theory to confirm our understanding of strong-field coherent control via the carrier-envelope phase.

We present a study of multiphoton dissociative ionization from molecules. By solving the time-dependent Schr\"{o}dinger equation for H$_2^+$ and projecting the solution onto double continuum scattering states, we observe the correlated electron-nuclear ionization dynamics in detail. We show --- for the first time --- how multiphoton structure prevails as long as the energies of all fragments are accounted for. Our current work provides a new avenue to analyze strong-field fragmentation that leads to a deeper understanding of the correlated molecular dynamics., Comment: 1 Letter with 4 figures, 1 supplemental material

We discuss the strong-field dynamics of HeH${}^{+}$, the simplest stable heteronuclear molecule, focusing on identifying a laser regime for which there is a sufficient dissociation signal for experimental measurement. We numerically solve the time-dependent Schr\"odinger equation to obtain total dissociation probabilities, kinetic-energy release spectra, and momentum distributions for wavelengths from 800 to 2400 nm. The suitability of this simple system as a prototype for understanding the strong-field nuclear dynamics of heteronuclear dissociation is discussed.

We describe a pump-probe scheme with which the spatial asymmetry of dissociating molecular fragments --- as controlled by the carrier-envelope phase of an intense few-cycle laser pulse --- can be enhanced by an order of magnitude or more. We illustrate the scheme using extensive, full-dimensional calculations for dissociation of H$_2^+$ and include the averaging necessary for comparison with experiment., 5 pages, 4 figues

We report the first experimental observation of nonadiabatic field-free orientation of a heteronuclear diatomic molecule (CO) induced by an intense two-color (800 and 400 nm) femtosecond laser field. We monitor orientation by measuring fragment ion angular distributions after Coulomb explosion with an 800 nm pulse. The orientation of the molecules is controlled by the relative phase of the two-color field. The results are compared to quantum mechanical rigid rotor calculations. The demonstrated method can be applied to study molecular frame dynamics under field-free conditions in conjunction with a variety of spectroscopy methods, such as high-harmonic generation, electron diffraction, and molecular frame photoelectron emission.

We present the first experimental observation of dynamic field-free orientation of a heteronuclear molecule (CO) induced by intense two color (800 and 400 nm) femtosecond laser pulses. We have used the two color pulse as pump to orient the molecules and a more intense 800 nm pulse as probe to measure the angular distributions. In addition to dynamic alignment seen in time dependence of , we observe clear orientation in traces, which revives with the rotational period and can be reversed by changing the relative phase of the two colors. We studied the dependence of degree of orientation on the pump pulse intensity, and compared the results with theoretical calculations.

The carrier-envelope phase (CEP) of few-cycle laser pulses can be used to control the strong-field dynamics of atoms and molecules. To study CEP effects in H2+, we have solved the time-dependent Schodinger equation including nuclear vibration and rotation as well as electronic excitation, only ionization is excluded. Including nuclear rotation is essential to obtaining results directly comparable with experiment such as the momentum distribution. We show that the momentum distribution is quite sensitive to the CEP.