Showing papers by "Missouri University of Science and Technology published in 2022"

Multi-walled carbon nanotube supported manganese selenide as a highly active bifunctional OER and ORR electrocatalyst

Abstract: A manganese selenide and multiwalled carbon nanotube-based composite shows promising bifunctional electrocatalytic activity for the oxygen evolution and oxygen reduction reactions with superior stability and lower overpotential for both OER and ORR.

A Three-Winding Coupled Inductor-Based Interleaved High-Voltage Gain DC–DC Converter for Photovoltaic Systems

Abstract: In this article, an interleaved high-voltage gain dc–dc converter is proposed for use with photovoltaic (PV) systems. By integrating two three-winding coupled inductors (CIs) with switched capacitor cells, the voltage gain is further extended. Through passive diode-capacitor clamp circuits, the energy stored in the leakage inductances is absorbed; additionally, the voltage stress of the power switches is clamped to a value far lower than the output voltage, which enables designers to select switches with low-voltage ratings. Due to the interleaved structure of the proposed converter, the input current has a small ripple, which leads to the increased lifespan of the PV panels. In addition, the current stress on the components is reduced. Thanks to the leakage inductances of the CIs, the zero-current switching condition is intrinsically provided for the diodes; accordingly, the adverse impact of the diodes’ reverse-recovery is alleviated. The operating principles, steady-state analyses, and design considerations of the proposed converter are presented in this article. A comparison with other similar converters is carried out to verify the merits of the proposed converter. Finally, the theoretical analyses are confirmed through the experimental results of a 400-W prototype with an output voltage of 400 V.

Digital fabrication of eco-friendly ultra-high performance fiber-reinforced concrete

Abstract: A 3D-printable ultra-high performance fiber reinforced concrete (3DP-UHPFRC) has been developed recently by the authors. This material shows high compressive and flexural strengths accompanied by deflection-hardening behavior, which allows digital fabrication of thin structures with noticeable reduction/elimination of conventional steel bars. However, the high cement content of the developed 3DP-UHPFRC (840 kg/m3) limits the material's environmental sustainability. This paper reports the development of an eco-friendly 3DP-UHPFRC by replacing high volume of the cement component of the mixture with fly ash (FA) and/or ground granulated blast-furnace slag (S). Three printable eco-friendly mixtures were prepared in which 60% of the cement was replaced by either 60% FA (S0F60) or 60% S (S60F0) or 30% FA and 30% S (S30F30). All mixtures had 30% silica fume (SF) content, by mass of binder. The fresh properties (i.e., extrudability, buildability, workability, and rheological parameters), the hardened properties (i.e., anisotropic compressive and flexural strengths), and the environmental impacts (i.e., global warming potential (GWP)) of the eco-friendly mixtures were measured and the results were compared with those of the control mixture made with SF but no FA or S (S0F0). The printable eco-friendly mixtures developed in this research have significantly higher environmental sustainability while retaining mechanical performance comparable to the 3DP-UHPFRC. A material efficiency index (MEI) was proposed to compare suitability of the eco-friendly mixtures against the control mixture. The MEI simultaneously considers multiple performance criteria including mechanical and rheological properties, and GWP. The order of MEIs of the mixtures was: S60F0 > S0F0 > S30F30 > S0F60.

A review on ICP powder plasma spheroidization process parameters

Abstract: Powder particles with spherical geometries have been found to result in better powder performance in different industries, especially Additive Manufacturing (AM), by fabricating more dense powder layers that consequently result in more desirable part properties with less defects. Plasma spheroidization process has shown an excellent capability in enhancing particle geometries of powders from a variety of materials, particle size distributions, and arbitrary initial particle geometries. The current review paper summarizes the previous conducted work on plasma spheroidization process to determine the effect of its process parameters on powder characteristics. The spheroidization process parameters, including powder feed rate, central, carrier, and sheath gas flow rates, gas mixtures, power, and chamber pressure are individually discussed. Also, the impact of these process parameters on powder characteristics, such as particle size distribution, particle trajectories, chemical impurity, microstructure, porosity, flowability, and densities are reviewed. A tradeoff among process parameters, spheroidization ratio, and evaporation rate was observed. Depending on particle size and material melting point, increasing particle residence time in exposure to plasma first increased and then decreased the spheroidization ratio overall.

Integrated direct air capture and oxidative dehydrogenation of propane with CO2 at isothermal conditions

Abstract: Developing routes of utilizing CO2 emissions is important for long-term environmental preservation, as storing such emissions underground will eventually become unsustainable. One way of utilizing CO2 emissions is as a light-oxidant feedstock for oxidative dehydrogenation of propane (ODHP) to propylene. However, the adsorption and reaction steps typically occur at widely different temperatures, meaning that the thermal gradients – and by extension process energy requirements – are often unreasonably high. In recent years, dual-functional materials (DFMs) – i.e., materials comprised of a high temperature adsorbent phase alongside a heterogeneous catalyst – have been employed for combined CO2 adsorption and utilization over one material within a single bed using a reduced thermal gradient. However, these materials have never been formed into practical contactors and have never been applied to ODHP applications. Therefore, in this study we manufactured the first-generation of DFM adsorbent/catalyst monoliths, comprised of CaO (adsorbent) and M@ZSM-5 (M = V-, Ga-, Ti-, or Ni-oxide) heterogeneous catalysts, using our novel direct metal-oxide 3D printing technique. The monoliths were vigorously characterized using N2 physisorption, C3H8-DRIFTS, NH3-TPD, Py-FTIR, H2-TPR, XRD, XPS, and elemental mapping and were assessed for CO2 capture/ODHP utilization at 600–700 oC. The adsorption/catalysis experiments revealed that these materials can perform both processes effectively at 600 oC, with reduced propylene yield at higher temperature, which eliminated the need for a thermal gradient between the adsorption and catalysis steps. Between the various samples, the Ti-doped monolith generated the best balance of CO2 conversion (76%) and propylene selectivity (39%), due to the high dispersion of TiO2, favorable redox properties and controlled acidity of the dopant. However, it was also found that varying the metal dopant could be used to control the heuristics of CO2/C3H8 conversion, C3H6 selectivity, and C3H6 yield, meaning that the manufacturing process outlined herein represents a promising way of tuning the chemical properties of structured DFM adsorbent/catalyst materials. More importantly, this study establishes a promising proof-of-concept for 3D printing as a facile means of structuring these exciting composite materials and expands DFMs to the previously unexplored application of ODHP.

Depth-targeted energy delivery deep inside scattering media

Abstract: Diffusion makes it difficult to predict and control wave transport through a medium. Overcoming wave diffusion to deliver energy into a target region deep inside a diffusive system is an important challenge for applications, but also represents an interesting fundamental question. It is known that coherently controlling the incident wavefront allows diffraction-limited focusing inside a diffusive system, but in many applications, the targets are significantly larger than a focus and the maximum deliverable energy remains unknown. Here we introduce the ‘deposition matrix’, which maps an input wavefront to the internal field distribution, and we theoretically predict the ultimate limit on energy enhancement at any depth. Additionally, we find that the maximum obtainable energy enhancement occurs at three-fourths the thickness of the diffusive system, regardless of its scattering strength. We experimentally verify our predictions by measuring the deposition matrix in two-dimensional diffusive waveguides. The experiment gives direct access to the internal field distribution from the third dimension, and we can excite the eigenstates to enhance or suppress the energy within an extended target region. Our analysis reveals that such enhancement or suppression results from both selective transmission-eigenchannel excitation and constructive or destructive interference among these channels. Optimally depositing optical energy into an extended region of a diffusive medium, such as biological tissue, is a challenging task. A matrix that maps the incoming wavefront to the field distribution inside the material can predict the energy enhancement that occurs at a given depth.

Improving I/O Performance for Exascale Applications Through Online Data Layout Reorganization

Abstract: The applications being developed within the U.S. Exascale Computing Project (ECP) to run on imminent Exascale computers will generate scientific results with unprecedented fidelity and record turn-around time. Many of these codes are based on particle-mesh methods and use advanced algorithms, especially dynamic load-balancing and mesh-refinement, to achieve high performance on Exascale machines. Yet, as such algorithms improve parallel application efficiency, they raise new challenges for I/O logic due to their irregular and dynamic data distributions. Thus, while the enormous data rates of Exascale simulations already challenge existing file system write strategies, the need for efficient read and processing of generated data introduces additional constraints on the data layout strategies that can be used when writing data to secondary storage. We review these I/O challenges and introduce two online data layout reorganization approaches for achieving good tradeoffs between read and write performance. We demonstrate the benefits of using these two approaches for the ECP particle-in-cell simulation WarpX, which serves as a motif for a large class of important Exascale applications. We show that by understanding application I/O patterns and carefully designing data layouts we can increase read performance by more than 80 percent.

The effect of dental restoration geometry and material properties on biomechanical behaviour of a treated molar tooth: A 3D finite element analysis.

Abstract: Objectives To test the hypothesis that restoration of class II mesio-occlusal-distal (MOD) cavities can be strengthened through judicious choice of restoration geometry and material properties. Methods An intact extracted human maxillary molar tooth was digitized, segmented, reconstructed, and four 3D restored tooth models were developed with four different restoration geometries: one straight, one single-curved, and two double-curved. Stress analysis was conducted for representative loading using finite element analysis, and maximum principal stresses were determined at the dentine-enamel and restoration-enamel junctions. A range of restorative material elastic moduli (5–80 GPa) and Poisson's ratios (0.25–0.35) were studied. Vertical loads of 400 N were applied on occlusal points, while the roots of the molar teeth, below the crevices, were supported in all directions. All the materials were modelled as homogeneous, isotropic, and elastic. Results The maximum principal stresses at the restoration-enamel junctions were strongly dependent on the MOD restoration geometries. Peak stresses occurred along the palatal surface of the restoration rather than the opposite buccal surface. Double-curved restorations showed the lowest peak stress at restoration-enamel junctions. Choice of the mechanical properties of restorative material in the range of 5–35 GPa further reduced stress concentrations on the enamel. Significance Class II MOD restorations may be stronger if designed with double-curved marginal geometries that can reduce stress concentrations. Designs with convex and concave geometries were particularly effective because they reduced stress concentrations dramatically. Results suggest that relatively minor changes to the geometry of a restoration can have a substantial effect on stress at the restoration-enamel junction and motivate future experimental analysis.

Combination of High pH and an Antioxidant Improves Chemical Stability of Two-Dimensional Transition-Metal Carbides and Carbonitrides (MXenes) in Aqueous Colloidal Solutions

Abstract: MXenes, a large family of two-dimensional (2D) transition-metal carbides/nitrides, have attracted increased attention in recent years because of their excellent electronic, mechanical, thermal, and optical properties. Studying chemical properties of MXenes is important to prolong the shelf life of their colloids and provide robust performance of MXenes in devices and applications. While the role of MXene reactivity with the environment, including water and components of air, is becoming more recognized, less is known about the role of parameters influencing the reactivity. In this work, we investigate the individual and combined effects of the pH and antioxidant on chemical stability of Ti2CTx, Ti3CNTx, and Ti3C2Tx MXenes using GC, XPS, UV-vis, and Raman spectroscopy. In contrast to indirect indicators of MXene degradation, such as film conductivity or performance in electrochemical energy storage systems, we focus on detection of reaction products as the most sensitive and direct way of monitoring the chemical transformations of MXenes. Based on our knowledge of MXene chemistry and interactions with the environment, we propose a combination of sodium hydroxide and sodium l-ascorbate to effectively slow down degradation of MXenes in colloidal solutions by suppressing their hydrolysis and oxidation reactions, respectively.

Complex Rupture and Triggered Aseismic Creep During the 14 August 2021 Haiti Earthquake From Satellite Geodesy

Abstract: The 2021 August 14 MW 7.2 Nippes, Haiti earthquake occurred 75 km west of the epicenter of the 2010 Leogane earthquake (Haiti) on the transpressive Caribbean - North America plate boundary. We present an updated fault map for Hispaniola and model coseismic and early postseismic fault slip using Interferometric Synthetic Aperture Radar and pixel offsets. We find the earthquake ruptured multiple segments of the Enriquillo-Plantain Garden Fault Zone. Slip occurred in two main sub-events on either side of a restraining bend at Pic Macaya, with ∼2.7 m of peak reverse-slip east of the bend. To the west, slip jumps the restraining bend and further ruptures with ∼1.2 m of left-lateral slip. Afterslip in the 4 days following the event occurred at shallow depth and adjacent to the coseismic rupture areas and reached the surface east of Pic Macaya.

Understanding Disputes in Modular Construction Projects: Key Common Causes and Their Associations

Abstract: Modularization is a well-known approach that can potentially mitigate many of the current construction industry’s challenges including, for example, poor productivity, shortages in skilled ...

Understanding Disputes in Modular Construction Projects: Key Common Causes and Their Associations

Abstract: AbstractModularization is a well-known approach that can potentially mitigate many of the current construction industry’s challenges including, for example, poor productivity, shortages in skilled ...