Effect of K+ Force Fields on Ionic Conductivity and Charge Dynamics of KOH in Ethylene Glycol

Predicting ionic conductivity is crucial for developing efficient electrolytes for energy storage and conversion and other electrochemical applications. An accurate estimate of ionic conductivity requires understanding complex ion-ion and ion-solvent interactions governing the charge transport at the molecular level. Molecular simulations can provide key insights into the spatial and temporal behavior of electrolyte constituents. However, such insights depend on the ability of force fields to describe the underlying phenomena. In this work, molecular dynamics simulations were leveraged to delineate the impact of force field parameters on ionic conductivity predictions of potassium hydroxide (KOH) in ethylene glycol (EG). Four different force fields were used to represent the K+ ion. Diffusion-based Nernst-Einstein and correlation-based Einstein approaches were implemented to estimate the ionic conductivity, and the predicted values were compared with experimental measurements. The physical aspects, including ion-aggregation, charge distribution, cluster correlation, and cluster dynamics, were also examined. A force field was identified that provides reasonably accurate Einstein conductivity values and a physically coherent representation of the electrolyte at the molecular level.

Pathway toward Scalable Energy-Efficient Li-Mediated Ammonia Synthesis

Lithium-mediated ammonia synthesis (LiMAS) is an emerging electrochemical method for NH3 production, featuring a meticulous three-step process involving Li+ electrodeposition, Li nitridation, and Li3N protolysis. The essence lies in the electrodeposition of Li+, a critical phase demanding current oscillations to fortify the solid-electrolyte interface (SEI) and ensure voltage stability. This distinctive operational cadence orchestrates Li nitridation and Li3N protolysis, profoundly influencing the NH3 selectivity. Increasing N2 pressure enhances the NH3 faradaic efficiency (FE) up to 20 bar, beyond which proton availability controls selectivity between Li nitridation and Li3N protolysis. The proton donor, typically alcohols, is a key factor, with 1-butanol observed to yield the highest NH3 FE. Counterion in the Li salt is also observed to be significant, with larger anions (e.g., exemplified by BF4-) improving SEI stability, directly impacting LiMAS efficacy. Notably, we report a peak NH3 FE of ∼70% and an NH3 current density of ∼-100 mA/cm2 via a delicate balance of process conditions, encompassing N2 pressure, proton donor, Li salt, and their respective concentrations. In contrast to the recent literature, we find that the theoretical maximum energy efficiency of LiMAS hinges significantly on the proton source, with LiMAS utilizing H2O calculated to have a maximum achievable energy efficiency of 27.8%. Despite inherent challenges, a technoeconomic analysis suggests high-pressure LiMAS to be more feasible than both ambient LiMAS and a modified green Haber-Bosch process. Our analysis finds that, at a 100 mA/cm2 NH3 current density and a 6 V cell voltage, LiMAS delivers green NH3 at an all-inclusive cost of $456 per ton, significantly lower than conventional cost barriers. Our economic analysis underscores high-pressure LiMAS as a potentially transformative technology that may revolutionize large-scale NH3 production, paving the way for a sustainable future.

Engineering advancements in microfluidic systems for enhanced mixing at low Reynolds numbers

Mixing within micro- and millichannels is a pivotal element across various applications, ranging from chemical synthesis to biomedical diagnostics and environmental monitoring. The inherent low Reynolds number flow in these channels often results in a parabolic velocity profile, leading to a broad residence time distribution. Achieving efficient mixing at such small scales presents unique challenges and opportunities. This review encompasses various techniques and strategies to evaluate and enhance mixing efficiency in these confined environments. It explores the significance of mixing in micro- and millichannels, highlighting its relevance for enhanced reaction kinetics, homogeneity in mixed fluids, and analytical accuracy. We discuss various mixing methodologies that have been employed to get a narrower residence time distribution. The role of channel geometry, flow conditions, and mixing mechanisms in influencing the mixing performance are also discussed. Various emerging technologies and advancements in microfluidic devices and tools specifically designed to enhance mixing efficiency are highlighted. We emphasize the potential applications of micro- and millichannels in fields of nanoparticle synthesis, which can be utilized for biological applications. Additionally, the prospects of machine learning and artificial intelligence are offered toward incorporating better mixing to achieve precise control over nanoparticle synthesis, ultimately enhancing the potential for applications in these miniature fluidic systems.

Snap-on Adaptor for Microtiter Plates to Enable Continuous-Flow Microfluidic Screening and Harvesting of Crystalline Materials

Microtiter plate assay is a conventional and standard tool for high-throughput (HT) screening that allows the synthesis, harvesting, and analysis of crystals. The microtiter plate screening assays require a small amount of solute in each experiment, which is adequate for a solid-state crystal analysis such as X-ray diffraction (XRD) or Raman spectroscopy. Despite the advantages of these high-throughput assays, their batch operational nature results in a continuous decrease in supersaturation due to crystal nucleation and growth. Continuous-flow microfluidic mixer devices have evolved as an alternate technique for efficiently screening crystals under controlled supersaturation. However, such a microfluidic device requires a minimum of two inlets per micromixer to create cyclonic flow, thereby creating physical limitations for implementing such a device for HT screening. Additionally, the monolithic design of these microfluidic devices makes it challenging to harvest crystals for post-screening analysis. Here, we develop a snap-on adapter that can be reversibly attached to a microtiter plate and convert it into a continuous-flow microfluidic mixer device. The integration of the snap-on adapter with a flow distributor and concentration gradient generator provides greater control over screening conditions while minimizing the number of independent inlets and pumps required. The three-dimensional (3D)-printed snap-on adaptor is plugged into a 24-well plate assay to demonstrate salt screening of naproxen crystals. Different naproxen salts are crystallized using four different salt formers (SFs)-sodium hydroxide, potassium hydroxide, pyridine, and arginine-and four different solvents-ethanol, methanol, isopropyl alcohol, and deionized water. The wells are further inspected under an optical microscope to identify their morphological forms and yields. The crystals are then harvested for solid-state characterization using XRD and Fourier transform infrared spectroscopy, followed by measurement of their dissolution rates. The flexibility of the snap-on adapter to fit on a wide range of microtiter plates and the ease in harvesting and analyzing crystals postscreening are two significant advantages that make this device versatile for various applications.

Determination of spinal tracer dispersion after intrathecal injection in a deformable CNS model

Background: Traditionally, there is a widely held belief that drug dispersion after intrathecal (IT) delivery is confined locally near the injection site. We posit that high-volume infusions can overcome this perceived limitation of IT administration. Methods: To test our hypothesis, subject-specific deformable phantom models of the human central nervous system were manufactured so that tracer infusion could be realistically replicated in vitro over the entire physiological range of pulsating cerebrospinal fluid (CSF) amplitudes and frequencies. The distribution of IT injected tracers was studied systematically with high-speed optical methods to determine its dependence on injection parameters (infusion volume, flow rate, and catheter configurations) and natural CSF oscillations in a deformable model of the central nervous system (CNS). Results: Optical imaging analysis of high-volume infusion experiments showed that tracers spread quickly throughout the spinal subarachnoid space, reaching the cervical region in less than 10 min. The experimentally observed biodispersion is much slower than suggested by the Taylor-Aris dispersion theory. Our experiments indicate that micro-mixing patterns induced by oscillatory CSF flow around microanatomical features such as nerve roots significantly accelerate solute transport. Strong micro-mixing effects due to anatomical features in the spinal subarachnoid space were found to be active in intrathecal drug administration but were not considered in prior dispersion theories. Their omission explains why prior models developed in the engineering community are poor predictors for IT delivery. Conclusion: Our experiments support the feasibility of targeting large sections of the neuroaxis or brain utilizing high-volume IT injection protocols. The experimental tracer dispersion profiles acquired with an anatomically accurate, deformable, and closed in vitro human CNS analog informed a new predictive model of tracer dispersion as a function of physiological CSF pulsations and adjustable infusion parameters. The ability to predict spatiotemporal dispersion patterns is an essential prerequisite for exploring new indications of IT drug delivery that targets specific regions in the CNS or the brain.

Microkinetic insights into the role of catalyst and water activity on the nucleation, growth, and dissolution during COF-5 synthesis

The chemical pathway for synthesizing covalent organic frameworks (COFs) involves a complex medley of reaction sequences over a rippling energy landscape that cannot be adequately described using existing theories. Even with the development of state-of-the-art experimental and computational tools, identifying primary mechanisms of nucleation and growth of COFs remains elusive. Other than empirically, little is known about how the catalyst composition and water activity affect the kinetics of the reaction pathway. Here, for the first time, we employ time-resolved in situ Fourier transform infrared spectroscopy (FT-IR) coupled with a six-parameter microkinetic model consisting of ∼10 million reactions and over 20 000 species. The integrated approach elucidates previously unrecognized roles of catalyst pK_a on COF yield and water on growth rate and size distribution. COF crystalline yield increases with decreasing pK_a of the catalysts, whereas the effect of water is to reduce the growth rate of COF and broaden the size distribution. The microkinetic model reproduces the experimental data and quantitatively predicts the role of synthesis conditions such as temperature, catalyst, and precursor concentration on the nucleation and growth rates. Furthermore, the model also validates the second-order reaction mechanism of COF-5 and predicts the activation barriers for classical and non-classical growth of COF-5 crystals. The microkinetic model developed here is generalizable to different COFs and other multicomponent systems.

Achievements, Challenges, and Perspectives on Nitrogen Electrochemistry for Carbon-Neutral Energy Technologies

Unrestrained anthropogenic activities have severely disrupted the global natural nitrogen cycle, causing numerous energy and environmental issues. Electrocatalytic nitrogen transformation is a feasible and promising strategy for achieving a sustainable nitrogen economy. Synergistically combining multiple nitrogen reactions can realize efficient renewable energy storage and conversion, restore the global nitrogen balance, and remediate environmental crises. Here, we provide a unique aspect to discuss the intriguing nitrogen electrochemistry by linking three essential nitrogen-containing compounds (i.e., N₂ , NH₃ , and NO₃ ^- ) and integrating four essential electrochemical reactions, i.e., the nitrogen reduction reaction (N₂ RR), nitrogen oxidation reaction (N₂ OR), nitrate reduction reaction (NO₃ RR), and ammonia oxidation reaction (NH₃ OR). This minireview also summarizes the acquired knowledge of rational catalyst design and underlying reaction mechanisms for these interlinked nitrogen reactions. We further underscore the associated clean energy technologies and a sustainable nitrogen-based economy.

In-line measurement of liquid-liquid phase separation boundaries using a turbidity-sensor-integrated continuous-flow microfluidic device

Liquid-liquid phase separation (LLPS), also known as oiling-out, is the appearance of the second liquid phase preceding the crystallization. LLPS is an undesirable phenomenon that can occur during the crystallization of active pharmaceutical ingredients (APIs), proteins, and polymers. It is typically avoided during crystallization due to its detrimental impacts on crystalline products due to lowered crystallization rate, the inclusion of impurities, and alteration in particle morphology and size distribution. In situ monitoring of phase separation enables investigating LLPS and identifying the phase separation boundaries. Various process analytical technologies (PATs) have been implemented to determine the LLPS boundaries prior to crystallization to prevent oiling out of compounds. The LLPS measurements using PATs can be time-consuming, expensive, and challenging. Here, we have implemented a fully integrated continuous-flow microfluidic device with a turbidity sensor to quickly and accurately evaluate the LLPS boundaries for a β-alanine, water, and IPA mixture. The turbidity-sensor-integrated continuous-flow microfluidic device is also placed under an optical microscope to visually track and record the appearance and disappearance of oil droplets. Streams of an aqueous solution of β-alanine, pure solvent (water), and pure antisolvent (IPA or ethanol) are pumped into the continuous-flow microfluidic device at various flow rates to obtain the compositions at which the solution becomes turbid. The onset of turbidity is measured using a custom-designed, in-line turbidity sensor. The LLPS boundaries can be estimated using the turbidity-sensor-integrated microfluidic device in less than 30 min, which will significantly improve and enhance the workflow of the pharmaceutical drug (or crystalline material) development process.

Machine Learning-Driven, Sensor-Integrated Microfluidic Device for Monitoring and Control of Supersaturation for Automated Screening of Crystalline Materials

Integrating sensors in miniaturized devices allow for fast and sensitive detection and precise control of experimental conditions. One of the potential applications of a sensor-integrated microfluidic system is to measure the solute concentration during crystallization. In this study, a continuous-flow microfluidic mixer is paired with an electrochemical sensor to enable in situ measurement of the supersaturation. This sensor is investigated as the predictive measurement of the supersaturation during the antisolvent crystallization of l-histidine in the water-ethanol mixture. Among the various metals tested in a batch system for their sensitivity toward l-histidine, Pt showed the highest sensitivity. A Pt-printed electrode was inserted in the continuous-flow microfluidic mixer, and the cyclic voltammograms of the system were obtained for different concentrations of l-histidine and different water-to-ethanol ratios. The sensor was calibrated for different ratios of antisolvent and concentrations of l-histidine with respect to the change of the measured anodic slope. Additionally, a machine-learning algorithm using neural networks was developed to predict the supersaturation of l-histidine from the measured anodic slope. The electrochemical sensors have shown sensitivity toward l-histidine, l-glutamic acid, and o-aminobenzoic acid, which consist of functional groups present in almost 80% of small-molecule drugs on the market. The machine learning-guided electrochemical sensors can be applied to other small molecules with similar functional groups for automated screening of crystallization conditions in microfluidic devices.

Autocatalysis and Oriented Attachment Direct the Synthesis of a Metal-Organic Framework

Synthesis of porous, covalent crystals such as zeolites and metal-organic frameworks (MOFs) cannot be described adequately using existing crystallization theories. Even with the development of state-of-the-art experimental and computational tools, the identification of primary mechanisms of nucleation and growth of MOFs remains elusive. Here, using time-resolved in-situ X-ray scattering coupled with a six-parameter microkinetic model consisting of ∼1 billion reactions and up to ∼100 000 metal nodes, we identify autocatalysis and oriented attachment as previously unrecognized mechanisms of nucleation and growth of the MOF UiO-66. The secondary building unit (SBU) formation follows an autocatalytic initiation reaction driven by a self-templating mechanism. The induction time of MOF nucleation is determined by the relative rate of SBU attachment (chain extension) and the initiation reaction, whereas the MOF growth is primarily driven by the oriented attachment of reactive MOF crystals. The average size and polydispersity of MOFs are controlled by surface stabilization. Finally, the microkinetic model developed here is generalizable to different MOFs and other multicomponent systems.

Selective desolvation in two-step nucleation mechanism steers crystal structure formation

The two-step nucleation (TSN) theory and crystal structure prediction (CSP) techniques are two disjointed yet popular methods to predict nucleation rate and crystal structure, respectively. The TSN theory is a well-established mechanism to describe the nucleation of a wide range of crystalline materials in different solvents. However, it has never been expanded to predict the crystal structure or polymorphism. On the contrary, the existing CSP techniques only empirically account for the solvent effects. As a result, the TSN theory and CSP techniques continue to evolve as separate methods to predict two essential attributes of nucleation - rate and structure. Here we bridge this gap and show for the first time how a crystal structure is formed within the framework of TSN theory. A sequential desolvation mechanism is proposed in TSN, where the first step involves partial desolvation to form dense clusters followed by selective desolvation of functional groups directing the formation of crystal structure. We investigate the effect of the specific interaction on the degree of solvation around different functional groups of glutamic acid molecules using molecular simulations. The simulated energy landscape and activation barriers at increasing supersaturations suggest sequential and selective desolvation. We validate computationally and experimentally that the crystal structure formation and polymorph selection are due to a previously unrecognized consequence of supersaturation-driven asymmetric desolvation of molecules.

Patterned microfluidic devices for rapid screening of metal-organic frameworks yield insights into polymorphism and non-monotonic growth

Metal-organic frameworks (MOFs) are porous crystalline structures that are composed of coordinated metal ligands and organic linkers. Due to their high porosity, ultra-high surface-to-volume ratio, and chemical and structural flexibility, MOFs have numerous applications. MOFs are primarily synthesized in batch reactors under harsh conditions and long synthesis times. The continuous depletion of metal ligands and linkers in batch processes affects the kinetics of the oligomerization reaction and, hence, their nucleation and growth rates. Therefore, the existing screening systems that rely on batch processes, such as microtiter plates and droplet-based microfluidics, do not provide reliable nucleation and growth rate data. Significant challenges still exist for developing a relatively inexpensive, safe, and readily scalable screening device and ensuring consistency of results before scaling up. Here, we have designed patterned-surface microfluidic devices for continuous-flow synthesis of MOFs that allow effective and rapid screening of synthesis conditions. The patterned surface reduces the induction time of MOF synthesis for rapid screening while providing support to capture MOF crystals for growth measurements. The efficacy of the continuous-flow patterned microfluidic device to screen polymorphs, morphology, and growth rates is demonstrated for the HKUST-1 MOF. The effects of solvent composition and pH modulators on the morphology, polymorphs, and size distribution of HKUST-1 are evaluated using the patterned microfluidic device. Additionally, a time-resolved FT-IR analysis coupled with the patterned microfluidic device provides quantitative insights into the non-monotonic growth of MOF crystals with respect to the progression of the bulk oligomerization reaction. The patterned microfluidic device can be used to screen crystals with a longer induction time, such as proteins, covalent-organic frameworks, and MOFs.

On-the-spot quenching for effective implementation of cooling crystallization in a continuous-flow microfluidic device

Illustrated is a microfludic cooling crystallization device that can effectively screen polymorphs, growth rates, and morphology of crystalline materials.

2D High-Entropy Transition Metal Dichalcogenides for Carbon Dioxide Electrocatalysis

High-entropy alloys combine multiple principal elements at a near equal fraction to form vast compositional spaces to achieve outstanding functionalities that are absent in alloys with one or two principal elements. Here, the prediction, synthesis, and multiscale characterization of 2D high-entropy transition metal dichalcogenide (TMDC) alloys with four/five transition metals is reported. Of these, the electrochemical performance of a five-component alloy with the highest configurational entropy, (MoWVNbTa)S₂ , is investigated for CO₂ conversion to CO, revealing an excellent current density of 0.51 A cm^-2 and a turnover frequency of 58.3 s^-1 at ≈ -0.8 V versus reversible hydrogen electrode. First-principles calculations show that the superior CO₂ electroreduction is due to a multi-site catalysis wherein the atomic-scale disorder optimizes the rate-limiting step of CO desorption by facilitating isolated transition metal edge sites with weak CO binding. 2D high-entropy TMDC alloys provide a materials platform to design superior catalysts for many electrochemical systems.

Advanced continuous-flow microfluidic device for parallel screening of crystal polymorphs, morphology, and kinetics at controlled supersaturation

A flow-controlled microfluidic device for parallel and combinatorial screening of crystalline materials can profoundly impact the discovery and development of active pharmaceutical ingredients and other crystalline materials. While the existing continuous-flow microfluidic devices allow crystals to nucleate under controlled conditions in the channels, their growth consumes solute from the solution leading to variation in the downstream composition. The materials screened under such varying conditions are less reproducible in large-scale synthesis. There exists no continuous-flow microfluidic device that traps and grows crystals under controlled conditions for parallel screening. Here we show a blueprint of such a microfluidic device that has parallel-connected micromixers to trap and grow crystals under multiple conditions simultaneously. The efficacy of a multi-well microfluidic device is demonstrated to screen polymorphs, morphology, and growth rates of l-histidine via antisolvent crystallization at eight different solution conditions, including variation in molar concentration, vol% of ethanol, and supersaturation. The overall screening time for l-histidine using the multi-well microfluidic device is ∼30 min, which is at least eight times shorter than the sequential screening process. The screening results are also compared with the conventional 96-well microtiter device, which significantly overestimates the fraction of stable form as compared to metastable form and shows high uncertainty in measuring growth rates. The multi-well microfluidic device paves the way for next-generation microfluidic devices that are amenable to automation for high-throughput screening of crystalline materials.

Organophilicity of Graphene Oxide for Enhanced Wettability of ZnO Nanorods

Interfacing two-dimensional graphene oxide (GO) platelets with one-dimensional zinc oxide nanorods (ZnO) would create mixed-dimensional heterostructures suitable for modern optoelectronic devices. However, there remains a lack in understanding of interfacial chemistry and wettability in GO-coated ZnO nanorods heterostructures. Here, we propose a hydroxyl-based dissociation-exchange mechanism to understand interfacial interactions responsible for GO adsorption onto ZnO nanorods hydrophobic substrates. The proposed mechanism initiated from mixing GO suspensions with various organics would allow us to overcome the poor wettability (θ ∼ 140.5°) of the superhydrophobic ZnO nanorods to the drop-casted GO. The addition of different classes of organics into the relatively high pH GO suspension with a volumetric ratio of 1:3 (organic-to-GO) is believed to introduce free radicals (-OH and -COOH), which consequently result in enhancing adhesion (chemisorption) between ZnO nanorods and GO platelets. The wettability study shows as high as 75% reduction in the contact angle (θ = 35.5°) when the GO suspension is mixed with alcohols (e.g., ethanol) prior to interfacing with ZnO nanorods. The interfacial chemistry developed here brings forth a scalable tool for designing graphene-coated ZnO heterojunctions for photovoltaics, photocatalysis, biosensors, and UV detectors.

Steelmaking in India - new evidence from microscopic and archaeometallurgical analysis from middle Ganga plain, Balirajgarh

The present study deliberates on the archaeometallurgical examination of 2300 years old excavated iron nail from India's middle Ganga plain of Balirajgarh. The nail was subjected to multianalytical investigations in order to determine the raw materials used, manufacturing technology and preservation state. The combined analytical techniques optical microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX), Vickers hardness and X-ray diffractometry shed light towards the characterisation and use of the iron artefact. Special attention was paid for qualitative and quantitative analysis of slag inclusions, metal matrix and corrosion products. The presence of heterogeneous microstructure and inclusion of impurities suggests that nail has been produced through the direct process and work hardened. The noncorroded nail is made of hypereutectoid steel and used for building purpose. The study is important to understand the role of technology in the evolution of cultural changes in India that also provides archaeometric data on the method used in the forging work.

Continuous-flow, well-mixed, microfluidic crystallization device for screening of polymorphs, morphology, and crystallization kinetics at controlled supersaturation

Screening of crystal polymorphs and morphology and measurement of crystallization kinetics in a controlled supersaturated environment is crucial for the development of crystallization processes for pharmaceuticals, agrochemicals, semiconductors, catalysts, and other specialty chemicals. Most of the current tools including microtiter plates and droplet-based microfluidic devices suffer from depleting supersaturation in small compartments due to nucleation and growth of crystals. Such variation in supersaturation not only affects the outcome but also leads to impediments during the scale-up of the crystallizer. Here we develop an innovative technique using H-shaped and cyclone mixer designs to study crystallization at constant supersaturation maintained by a continuous flow of solution. While the H-shaped design can be used to screen crystals with slower kinetics, the cyclone mixer is better suited for crystals with faster kinetics. The polymorphs and morphology of o-aminobenzoic acid (o-ABA) at different supersaturations are analyzed using the cyclone mixer design and compared with the microtiter plate. While the polymorphs and morphology of o-ABA are affected by depleting supersaturation in a microtiter plate, the cyclone mixer design consistently screened stable and metastable polymorphs. These novel devices will also play an important role in supporting the FDA's initiative to spur innovation in continuous manufacturing for the advancements in drug development.

Effects of temperature and gas-liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2 reduction electrocatalysts

In the last few years, there has been increased interest in electrochemical CO₂ reduction (CO2R). Many experimental studies employ a membrane separated, electrochemical cell with a mini H-cell geometry to characterize CO2R catalysts in aqueous solution. This type of electrochemical cell is a mini-chemical reactor and it is important to monitor the reaction conditions within the reactor to ensure that they are constant throughout the study. We show that operating cells with high catalyst surface area to electrolyte volume ratios (S/V) at high current densities can have subtle consequences due to the complexity of the physical phenomena taking place on electrode surfaces during CO2R, particularly as they relate to the cell temperature and bulk electrolyte CO₂ concentration. Both effects were evaluated quantitatively in high S/V cells using Cu electrodes and a bicarbonate buffer electrolyte. Electrolyte temperature is a function of the current/total voltage passed through the cell and the cell geometry. Even at a very high current density, 20 mA cm^-2, the temperature increase was less than 4 °C and a decrease of <10% in the dissolved CO₂ concentration is predicted. In contrast, limits on the CO₂ gas-liquid mass transfer into the cells produce much larger effects. By using the pH in the cell to measure the CO₂ concentration, significant undersaturation of CO₂ is observed in the bulk electrolyte, even at more modest current densities of 10 mA cm^-2. Undersaturation of CO₂ produces large changes in the faradaic efficiency observed on Cu electrodes, with H₂ production becoming increasingly favored. We show that the size of the CO₂ bubbles being introduced into the cell is critical for maintaining the equilibrium CO₂ concentration in the electrolyte, and we have designed a high S/V cell that is able to maintain the near-equilibrium CO₂ concentration at current densities up to 15 mA cm^-2.

Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure

Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels

Thermodynamic, achievable, and realistic efficiency limits of solar-driven electrochemical conversion of water and carbon dioxide to fuels are investigated as functions of light-absorber composition and configuration, and catalyst composition. The maximum thermodynamic efficiency at 1-sun illumination for adiabatic electrochemical synthesis of various solar fuels is in the range of 32-42%. Single-, double-, and triple-junction light absorbers are found to be optimal for electrochemical load ranges of 0-0.9 V, 0.9-1.95 V, and 1.95-3.5 V, respectively. Achievable solar-to-fuel (STF) efficiencies are determined using ideal double- and triple-junction light absorbers and the electrochemical load curves for CO2 reduction on silver and copper cathodes, and water oxidation kinetics over iridium oxide. The maximum achievable STF efficiencies for synthesis gas (H2 and CO) and Hythane (H2 and CH4) are 18.4% and 20.3%, respectively. Whereas the realistic STF efficiency of photoelectrochemical cells (PECs) can be as low as 0.8%, tandem PECs and photovoltaic (PV)-electrolyzers can operate at 7.2% under identical operating conditions. We show that the composition and energy content of solar fuels can also be adjusted by tuning the band-gaps of triple-junction light absorbers and/or the ratio of catalyst-to-PV area, and that the synthesis of liquid products and C2H4 have high profitability indices.

Effects of electrolyte, catalyst, and membrane composition and operating conditions on the performance of solar-driven electrochemical reduction of carbon dioxide

Identified optimal cell design and operating conditions for efficient solar-driven electrochemical reduction of CO₂. Developed a method to predict polarization losses from the experimental data.

Population Balance Modeling: Current Status and Future Prospects

Population balance modeling is undergoing phenomenal growth in its applications, and this growth is accompanied by multifarious reviews. This review aims to fortify the model's fundamental base, as well as point to a variety of new applications, including modeling of crystal morphology, cell growth and differentiation, gene regulatory processes, and transfer of drug resistance. This is accomplished by presenting the many faces of population balance equations that arise in the foregoing applications.

Switching in polaritonic-photonic crystal nanofibers doped with quantum dots

We have studied the acousto-optic effect in polaritonic nanofibers made by embedding a cylindrical polaritonic nanowire within a photonic crystal. Here the nanowire consists of either a phonon-polaritonic or an exciton-polaritonic material. The nanowire is doped with ensemble of noninteracting quantum dots. Quantum dots interact with the nanofiber via the exciton-polariton interaction. It is found that for the certain acoustic strain intensity the nanofiber has a localized-to-delocalized polariton transition similar to the metal-to-insulator transitions in doped semiconductors. It is also found that nanofiber has a transparent state due to the exciton-bound polariton coupling. The transparent state can be switched ON or OFF by the external acoustic strain intensity. These are very useful discoveries that can be used to fabricate new types of polaritonic nanoswitches and nanosensors.

Urban water tariff structure and cost recovery opportunities in India

Given the high level of capital investment and the history of government subsidized services, full cost pricing of water services has yet to take hold in India. As a result, it remains broadly underpriced leading to public perception that water is "free" The current tariff levels in India are too low to cover even operating costs. This paper examines the existing Indian urban water tariff models (fixed tariff, volumetric tariff, increasing block tariff etc.), their relevance and problems. It was found that none of the tariff structures could satisfy all the design objectives (cost recovery, economic efficiency, equity, affordability etc.). Also subsidies are not explicit and well targeted for poor population. There are several studies and issues that do demonstrate the opportunities for tariff increase and improved cost recovery. This paper highlights the results of such studies and brings out issues needing consideration. Improved cost recovery would lead to improved financial status of the water utilities. Also, subsidies, if designed suitably and well targeted, would serve the concerns of the economically weaker sections. Such reform process would eventually lead to socio-economic sustainability.

Using simulation to improve the operational efficiency of a multi-disciplinary clinic

A recent trend in health care is to provide patients with the benefits of multi-disciplinary care during a single clinic visit. The University of Michigan Breast Care Center is a leading example of a multi-disciplinary clinic which has served the Midwest United States since 1985. A hallmark of the Breast Care Center operation is a patient care conference immediately following the clinical evaluation sessions, where each case is discussed by a group of experts for immediate evaluation and generation of recommendations. The Center has experienced significant increases in the number of patient visits over the nine years since its inception. The patient mix, initially all new patients, has matured, and returning patients are now a significant portion of the clinic load. Unfortunately, the success of the Breast Care Center strained its smooth operation. Physicians were unable to attend the patient care conference because the clinical evaluation sessions were too busy, and this undermined the quality of the care recommendations generated. Patients were complaining about long waits in the Breast Care Center and delays in getting their next appointment. To examine these operational problems and to suggest corrective actions, a simulation study was conducted. This paper reports the results of this study. Our findings provide interesting insights into the operation and management of multi-disciplinary clinics.

Fine needle aspiration cytology, imprint cytology and tru-cut needle biopsy in breast lumps: a comparative evaluation

Fine needle aspiration cytology, imprint cytology and tru-cut needle biopsy were performed in 86 patients with breast lump and the results of these techniques were finally compared with the incisional or excisional biopsy in all the patients. Fine needle aspiration cytology had the sensitivity of 96.8% and specificity of 100%, the imprint cytology had the sensitivity of 98.4% and specificity of 100%. While the tru-cut needle biopsy had the sensitivity and specificity of 100% though in this technique 15 of 86 (17.4%) specimens were rejected as insufficient for any diagnosis.