Wu, Xiao-Yu; Ghoniem, Ahmed F.(Proceedings of the Combustion Institute, Elsevier BV, 2018-06-21)[Article]
In this paper, we demonstrate CO2 thermochemical reduction to CO in a La0.9Ca0.1FeO3-δ oxygen ion transport membrane reactor. For process intensification, we also show that methane can be used on the sweep side, producing two streams: a CO stream from CO2 reduction on the feed side, and a syngas stream on the other. We show that surface reactions are the rate-limiting steps for fuel-assisted CO2 reduction on a flat LCF-91 membrane. To improve productivity, we study how that adding catalytic porous layers can accelerate these steps and hence, increase the CO2-to-fuel conversion rates. Adding LCF-91 porous layers onto the membrane surface raised the oxygen flux by 1.4X. Secondly, different catalysts (Ce0.5Zr0.5O2 on the feed side and (La0.6Sr0.4)0.95Co0.2Fe0.8O3 on the sweep side) were added onto the porous layers to further accelerate the surface reaction rates. As a result, the oxygen flux was further increased especially at lower temperatures, e.g., at 850°C, oxygen flux was raised by one order of magnitude as compared to the unmodified membrane. Process intensification was tested on the latter membrane configuration, and the syngas produced on the sweep side had a H2:CO ratio very close to 2, ideal for production of fuels. Carbon species balance showed that higher methane concentration on the sweep side could lead to coke formation. Results also show that the selectivity to CO2 near the membrane surface is higher than that at the reactor outlet due to the availability of lattice oxygen and the favorable water-gas shift reactions.
Ravi, Vikash Kumar; Scheidt, Rebecca A; DuBose, Jeffrey; Kamat, Prashant V.(Journal of the American Chemical Society, American Chemical Society (ACS), 2018-06-21)[Article]
The suppression of halide ion exchange between CsPbBr3 and CsPbI3 nanocrystals achieved through capping with PbSO4–oleate has enabled us to deposit different perovskite nanocrystals as aligned arrays on the electrode surfaces without intermixing of species. The electrophoretic deposition of PbSO4–oleate-capped CsPbX3 (X = Cl, Br, I) nanocrystals suspended in hexane solution on mesoscopic TiO2 films allows the design of controlled architecture with single or multiple layers of perovskite films. The hierarchy in the assembly of these nanocrystals is seen first through the linearly organized nanocrystals in hexane followed by the deposition of larger linear rods ∼500 nm in length. Since most of the photophysical properties of nanocrystals are retained in these aligned arrays, we can design films with tunable luminescence including white color. The electrophoretic deposition of layered films of perovskites in a controlled fashion opens up new ways to design tandem perovskite solar cells and tunable display devices.
Gong, Shi-Jing; Gong, Cheng; Sun, Yu-Yun; Tong, Wen-Yi; Duan, Chun-Gang; Chu, Jun-Hao; Zhang, Xiang(Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, 2018-08-03)[Article]
Engineering the electronic band structure of material systems enables the unprecedented exploration of new physical properties that are absent in natural or as-synthetic materials. Half metallicity, an intriguing physical property arising from the metallic nature of electrons with singular spin polarization and insulating for oppositely polarized electrons, holds a great potential for a 100% spin-polarized current for high-efficiency spintronics. Conventionally synthesized thin films hardly sustain half metallicity inherited from their 3D counterparts. A fundamental challenge, in systems of reduced dimensions, is the almost inevitable spin-mixed edge or surface states in proximity to the Fermi level. Here, we predict electric field-induced half metallicity in bilayer A-type antiferromagnetic van der Waals crystals (i.e., intralayer ferromagnetism and interlayer antiferromagnetism), by employing density functional theory calculations on vanadium diselenide. Electric fields lift energy levels of the constituent layers in opposite directions, leading to the gradual closure of the gap of singular spin-polarized states and the opening of the gap of the others. We show that a vertical electrical field is a generic and effective way to achieve half metallicity in A-type antiferromagnetic bilayers and realize the spin field effect transistor. The electric field-induced half metallicity represents an appealing route to realize 2D half metals and opens opportunities for nanoscale highly efficient antiferromagnetic spintronics for information processing and storage.
Capacitive deionization, CDI, has emerged as an attractive alternative for water desalination. Electrodes based on Hierarchically porous carbons, HPCs, consistently show promising electrosorption performance. However, the typically low mesopore fraction and broad pore size distribution limit their utilization in practical applications. Here we report the CDI performance of a series of HPCs synthesized via ice templation possessing a high fraction of mesopore volume (85–93% of total porosity) and tight control over the amount and the size of mesopores (∼6 nm). Electrochemical measurements indicate high rate capability (82% salt retention) and outstanding cycling stability performance (100% capacitance retention over 600 cycles at 0.76 A g−1). In the CDI experiments, the HPCs display high salt capacity (up to ∼ 13 mg g−1) and consistently outperform other high surface areas commercial carbons. The existence of high fraction of mesoporosities enables better utilization of the accessible surfaces of HPCs where the introduction of micropores leads to more than 80% increase in the salt capacity. The HPCs reported here can serve as model electrode systems in studies to delineate the impact of mesoporosity (pore size and volume) on CDI performance and they may pave the way for practical CDI applications.
Lentz, S. J.; Churchill, J. H.; Davis, K. A.(Journal of Physical Oceanography, American Meteorological Society, 2018-05-31)[Article]
A primary challenge in modeling flow over shallow coral reefs is accurately characterizing the bottom drag. Previous studies over continental shelves and sandy beaches suggest surface gravity waves should enhance the drag on the circulation over coral reefs. The influence of surface gravity waves on drag over four platform reefs in the Red Sea is examined using observations from 6-month deployments of current and pressure sensors burst sampling at 1 Hz for 4–5 min. Depth-average current fluctuations U′ within each burst are dominated by wave orbital velocities uw that account for 80%–90% of the burst variance and have a magnitude of order 10 cm s−1, similar to the lower-frequency depth-average current Uavg. Previous studies have shown that the cross-reef bottom stress balances the pressure gradient over these reefs. A bottom stress estimate that neglects the waves (ρCdaUavg|Uavg|, where ρ is water density and Cda is a drag coefficient) balances the observed pressure gradient when uw is smaller than Uavg but underestimates the pressure gradient when uw is larger than Uavg (by a factor of 3–5 when uw = 2Uavg), indicating the neglected waves enhance the bottom stress. In contrast, a bottom stress estimate that includes the waves [ρCda(Uavg + U′)|Uavg + U′|)] balances the observed pressure gradient independent of the relative size of uw and Uavg, indicating that this estimate accounts for the wave enhancement of the bottom stress. A parameterization proposed by Wright and Thompson provides a reasonable estimate of the total bottom stress (including the waves) given the burst-averaged current and the wave orbital velocity.
Lindell, David B.; O'Toole, Matthew; Wetzstein, Gordon(2018 IEEE International Conference on Computational Photography (ICCP), Institute of Electrical and Electronics Engineers (IEEE), 2018-05-31)[Conference Paper]
Active imaging at the picosecond timescale reveals transient light transport effects otherwise not accessible by computer vision and image processing algorithms. For example, analyzing the time of flight of short laser pulses emitted into a scene and scattered back to a detector allows for depth imaging, which is crucial for autonomous driving and many other applications. Moreover, analyzing or removing global light transport effects from photographs becomes feasible. While several transient imaging systems have recently been proposed using various imaging technologies, none is capable of acquiring transient images at interactive framerates. In this paper, we present an imaging system that records transient images at up to 25 Hz. We show several transient video clips recorded with this system and demonstrate transient imaging applications, including direct-global light transport separation and enhanced depth imaging.
Kittaneh, Omar A.; Shehata, Mohamed; Majid, M. A.(2018 15th Learning and Technology Conference (L&T), Institute of Electrical and Electronics Engineers (IEEE), 2018-05-31)[Conference Paper]
Beyond energy saving, LED connected lighting systems allows for real-time data streaming, generating intelligence and creation of intelligent buildings systems. Lifetime experiments is crucial for such a connected system, as early termination would lead to big errors in estimating the lifetime model parameters, and late termination would waste time and cost. In this paper sup-entropy is applied in quantifying the amount of information in censored solid state lighting (SSL) luminaire experimental data that has Weibull distribution with respect to complete data. We use a quantity called efficiency of the censored sample as an indicator of the quality and goodness of the censoring scheme. This allowed us to determine the suitable termination time of the experiment subject to a desired efficiency. An intensive simulation study is conducted to validate our procedure.
Lowe, A.; Thomas, L.M.; Satija, A.; Lucht, R.P.; Masri, A.R.(Proceedings of the Combustion Institute, Elsevier BV, 2018-07-31)[Article]
This paper presents temperature measurements in turbulent dilute and dense spray flames using single-laser-shot chirped-probe-pulse femtosecond coherent anti-Stokes Raman spectroscopy (CPP-fs-CARS). This ultrafast technique, with a repetition rate of 5 kHz, is applied to the piloted Sydney Needle Spray Burner (SYNSBURNTM). The burner system features air-blast atomization of liquid injected from a needle that can be translated within a co-flowing air stream. The pilot-stabilized spray flames can range between the two extremes of dense and dilute by physically translating the needle tip relative to the burner's exit plane. The CPP-fs-CARS set-up has achieved integration times of 3 picoseconds (ps) as well as spatial resolution of approximately 800 µm along beam propagation and 60 µm in the transverse dimension. Brief details of the technique, calibration, correction of interferences, and spectral fitting processes are presented along with estimates of the associated error. The measurements are compared against well-established, line Raman–Rayleigh data for temperature collected in a turbulent CH4/air jet diffusion flame, which is largely non-sooting. At peak gaseous flame temperatures of up to 2512 K, the relative accuracy and precision were 2.8% and ±3.4%, respectively. Measurements in turbulent spray flames are shown after applying the relevant corrections based on non-resonant background (NRB) behavior and camera saturation effects on the shape of the CARS signal spectrum. Preliminary mapping of the temperature fields demonstrates the wealth of information available in this dataset which will provide insights into the spatio-temporal structure of spray flames once relevant statistical analysis is applied.
Liu, Zhiguang; Du, Huifeng; Li, Jiafang; Lu, Ling; Li, Zhi-Yuan; Fang, Nicholas X.(Science Advances, American Association for the Advancement of Science (AAAS), 2018-07-06)[Article]
Kirigami enables versatile shape transformation from two-dimensional (2D) precursors to 3D architectures with simplified fabrication complexity and unconventional structural geometries. We demonstrate a one-step and on-site nano-kirigami method that avoids the prescribed multistep procedures in traditional mesoscopic kirigami or origami techniques. The nano-kirigami is readily implemented by in situ cutting and buckling a suspended gold film with programmed ion beam irradiation. By using the topography-guided stress equilibrium, rich 3D shape transformation such as buckling, rotation, and twisting of nanostructures is precisely achieved, which can be predicted by our mechanical modeling. Benefiting from the nanoscale 3D twisting features, giant optical chirality is achieved in an intuitively designed 3D pinwheel-like structure, in strong contrast to the achiral 2D precursor without nano-kirigami. The demonstrated nano-kirigami, as well as the exotic 3D nanostructures, could be adopted in broad nanofabrication platforms and could open up new possibilities for the exploration of functional micro-/nanophotonic and mechanical devices.
Tu, Zhengyuan; Zachman, Michael J.; Choudhury, Snehashis; Khan, Kasim A.; Zhao, Qing; Kourkoutis, Lena F.; Archer, Lynden A.(Chemistry of Materials, American Chemical Society (ACS), 2018-07-25)[Article]
Approaches for regulating electrochemical stability of liquid electrolytes in contact with solid-state electrodes are a requirement for efficient and reversible electrical energy storage in batteries. Such methods are particularly needed in electrochemical cells in which the working potentials of the electrodes lie well outside the thermodynamic stability limits of the liquid electrolyte. Here we study electrochemical stability of liquids at electrolyte/electrode interfaces protected by a nanometer-thick, high-electrical band gap ceramic phase. We report that well-designed ceramic interphases extend the oxi-dative stability limits for both protic and aprotic liquid electrolytes, in some cases by as much as 1.5V. It is shown further that such interphases facilitate stable electrodeposition of reactive metals such as lithium at high Coulombic efficiency and in electrochemical cells subject to extended galvanostatic cycling at a high current density of 3 mA cm-2 and at capacities as high as 3 mAh cm-2. High-resolution cryo-FIB-SEM characterization reveals that solid/compact Li electrodeposits anchored by the ceramic interphase are the source of the enhanced Li deposition stability. The results enable a proof-of-concept ‘an-ode-free’ Li metal rechargeable battery in which Li initially provided in the cathode is the only source of lithium in the cell.
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