Evidence for electron-electron interaction in topological insulator thin films

We consider in our work high quality single crystal thin films of Bi2Se3, grown by molecular beam epitaxy, both with and without Pb doping. Our ARPES data demonstrate topological surface states with a Fermi level lying inside the bulk band gap in the Pb doped filims. Transport data show weak localization behavior, as expected for a 2D system, but a detailed analysis within the standard theoretical framework of diffusive transport shows that the temperature and magnetic field dependences of resistance cannot be reconciled in a theory that neglects inter-electron interactions. We demonstrate that an excellent account of quantum corrections to conductivity is achieved when both disorder and interaction are taken into account. These results clearly demonstrate that it is crucial to include electron electron interaction for a comprehensive understanding of diffusive transport in topological insulators.Comment: Submitted to Phys. Rev.

Fleet-Level Environmental Assessments for Feasibility of Aviation Emission Reduction Goals

13-C-AJFE-PU-013This is an open access paper under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) license https://creativecommons.org/licenses/by/4.0/. Please cite this article as: Ogunsina, K.E., Chao, H., Kolencherry, N.J., Jain, S., Moolchandani, K.A., DeLaurentis, D., & Crossley, W.A. (2022). Fleet-Level Environmental Assessments for Feasibility of Aviation Emission Reduction Goals. ArXiv, https://doi.org/10.48550/arXiv.2210.11302The International Air Transport Association (IATA) is one of several organizations that have presented goals for future CO2 emissions from commercial aviation with the intent of alleviating the associated environmental impacts. These goals include attaining carbon-neutral growth in the year 2020 and total aviation CO2 emissions in 2050 equal to 50% of 2005 aviation CO2 emissions. This paper presents the use of a simulation-based approach to predict future CO2 emissions from commercial aviation based upon a set of scenarios developed as part of the Aircraft Technology Modeling and Assessment project within ASCENT, the FAA Center of Excellence for Alternative Jet Fuels and the Environment. Results indicate that, in future scenarios with increasing demand for air travel, it is difficult to reduce CO2 emissions in 2050 to levels equal to or below 2005 levels, although neutral CO2 growth after 2020 may be possible. Presented at the Council of Engineering Systems Universities (CESUN) conference in 201

A Multi-fidelity Approach to Address Multi-objective Constrained Mixed-discrete Nonlinear Programming Problems with Application to Greener Aircraft Design

Engineering problems often involve solving constrained multi-objective Mixed-Discrete Nonlinear Programming (MDNLP) problems. These problems are inherently difficult to solve given the presence of multiple competing objectives, nonlinear objective and constraint functions, mixed-discrete type design variables, and expensive analysis tools. This work presents a multi-fidelity approach that addresses all these features together and exhibits its efficacy to solve constrained multi-objective MDNLP problems within a reasonable computational budget. The work addresses the high computational cost drawback associated with a previously developed hybrid multi-objective optimization approach\u27\u27 that combines a Genetic Algorithm (GA) with the gradient-based Sequential Quadratic Programming (SQP) algorithm. The multi-fidelity hybrid algorithm in this work employs surrogate models to provide low-fidelity approximations of the objective and constraint functions that are fast to evaluate. The gradient-based SQP algorithm uses these surrogate models in a goal attainment formulation. The combination of the GA with SQP then finds a diverse set of designs representing the best possible trade-off solutions for the multi-objective problem. For this thesis, the author initially pursues both Kriging and Radial Basis Function (RBF) surrogate modeling techniques, with their respective application to test problems (three-bar and ten-bar truss constrained, multi-objective, MDNLP problems) determining their feasibility of implementation in the multi-fidelity approach. The test problem results indicate that using RBF technique makes use of the hybrid approach more feasible as compared to using the Kriging technique. The results show a reduction of at least 98% in the high-fidelity\u27\u27 function evaluations with respect to the previously-developed hybrid approach, along with a reduction of at least 89% in the computational runtime. Subsequently, the multi-fidelity approach using RBF surrogate models is employed to solve a complex aerospace engineering problem used in previous studies - a \u27greener\u27 aircraft design problem - posed as a constrained multi-objective MDNLP problem. The resulting non-dominated design solutions are comparable to those obtained using the previously-developed hybrid approach. The result indicates a compromise that exists between the number of high-fidelity\u27\u27 evaluations performed and the ability of the multi-fidelity hybrid algorithm to find as diverse non-dominated designs as possible (indicating the spread of the Pareto frontier). This work also suggests a preliminary approach to choose the population size for the multi-objective multi-fidelity hybrid algorithm, so that the algorithm finds a satisfactory spread for the Pareto frontier at a reasonable computational cost

Modeling Hybrid-Electric Aircraft and their Fleet-Level Co2Emission Impacts

With rising concerns over commercial aviation’s contribution to global carbon emissions, there exists a tremendous pressure on the aviation industry to find advanced technological solutions to reduce its share of CO2 emissions. Single-aisle (or narrowbody) aircraft are the biggest contributors to CO2emissions by number of operations, insisting a need to reduce / eliminate their aircraft-level fuel consumption as soon as possible. A potential solution for this is to operate fully-electric single-aisle aircraft; however, the limitations of the current (and predicted future) battery technology is forcing the industry to explore hybrid-electric aircraft as a possible mid-term solution. Modeling hybrid-electric aircraft comes with its own challenges due to the presence of two different propulsion sources – gas turbine engines (powered by Jet-A fuel) and electric motors (powered by batteries). Since traditional sizing approaches and legacy sizing tools do not seem to work well for hybrid-electric aircraft, this work presents a “flight-mechanicsbased” conceptual sizing tool for hybrid-electric aircraft, set up as a Multidisciplinary Design Optimization (MDO) toolbox. Some of the key features of the sizing tool include concurrently sizing the electric motors and downsizing the gas turbine engines while meeting the oneengine-inoperative (OEI) and top-of-climb constraints, and re-sizing the fuselage to account for the volumetric constraints associated with required batteries. Current work considers a parallel hybrid-electric single-aisle aircraft with a 900 nmi design range, with electric power augmentation (with electric motors operating at full throttle) available only for the takeoff and climb segments when sizing the aircraft. Four hybrid-electric propulsion technology cases are considered, and the resulting hybrid-electric aircraft show 15.0% to 22.5% reduction in fuel burn compared to a Boeing 737-800 aircraft. Another challenge with modeling hybrid-electric aircraft is determining their off-design performance characteristics (considering a different payload or mission range, or both). This work presents an energy management tool – set up as a nonlinear programming optimization problem – to minimize the fuel burn for a payload-range combination by identifying the optimal combination of throttle settings for the gas turbine engines and the electric motors during takeoff, climb, and cruise, along with identifying an optimal flight path. The energy management tool enables fuel savings of at least of 2%, with actual savings ranging from 142.1 lbs to 276.1 lbs per trip for a sample route (LGA–ORD) at a 80% load factor. Although the hybrid-electric aircraft sizing and performance analysis studies show encouraging results about the potential reduction in carbon emissions at an aircraft level, the future fleet-level carbon emissions are not expected to reduce proportionally to these aircraft level emission reductions. This work predicts the fleet-level environmental impacts of future single-aisle parallel hybrid-electric aircraft by modeling the behavior of a profit-seeking airline (with a mixture of conventional all Jet-A fuel burning and hybrid electric aircraft in its fleet) using the Fleet-Level Environmental Evaluation Tool (FLEET). FLEET’s modelbased predictions rely upon historically-based information about US-touching airline routes and passenger demand served by US flag-carrier airlines from the Bureau of Transportation Statistics to initiate model-based predictions of future demand, aircraft fleet mix, and aircraft operations

Modeling Hybrid-Electric Aircraft and their Fleet-Level CO₂ Emission Impacts

   With rising concerns over commercial aviation’s contribution to global carbon emissions, there exists a tremendous pressure on the aviation industry to find advanced technological solutions to reduce its share of CO2 emissions. Single-aisle (or narrowbody) aircraft are the biggest contributors to CO2 emissions by number of operations, insisting a need to reduce / eliminate their aircraft-level fuel consumption as soon as possible. A potential solution for this is to operate fully-electric single-aisle aircraft; however, the limitations of the current (and predicted future) battery technology is forcing the industry to explore hybrid-electric aircraft as a possible mid-term solution. Modeling hybrid-electric aircraft comes with its own challenges due to the presence of two different propulsion sources – gas turbine engines (powered by Jet-A fuel) and electric motors (powered by batteries). Since traditional sizing approaches and legacy sizing tools do not seem to work well for hybrid-electric aircraft, this work presents a “flight-mechanics-based” conceptual sizing tool for hybrid-electric aircraft, set up as a Multidisciplinary Design Optimization (MDO) toolbox. Some of the key features of the sizing tool include concurrently sizing the electric motors and downsizing the gas turbine engines while meeting the one-engine-inoperative (OEI) and top-of-climb constraints, and re-sizing the fuselage to account for the volumetric constraints associated with required batteries. Current work considers a parallel hybrid-electric single-aisle aircraft with a 900 nmi design range, with electric power augmentation (with electric motors operating at full throttle) available only for the takeoff and climb segments when sizing the aircraft. Four hybrid-electric propulsion technology cases are considered, and the resulting hybrid-electric aircraft show 15.0% to 22.5% reduction in fuel burn compared to a Boeing 737-800 aircraft. Another challenge with modeling hybrid-electric aircraft is determining their off-design performance characteristics (considering a different payload or mission range, or both). This work presents an energy management tool – set up as a nonlinear programming optimization problem – to minimize the fuel burn for a payload-range combination by identifying the optimal combination of throttle settings for the gas turbine engines and the electric motors during takeoff, climb, and cruise, along with identifying an optimal flight path. The energy management tool enables fuel savings of at least of 2%, with actual savings ranging from 142.1 lbs to 276.1 lbs per trip for a sample route (LGA–ORD) at a 80% load factor. Although the hybrid-electric aircraft sizing and performance analysis studies show encouraging results about the potential reduction in carbon emissions at an aircraft level, the future fleet-level carbon emissions are not expected to reduce proportionally to these aircraft level emission reductions. This work predicts the fleet-level environmental impacts of future single-aisle parallel hybrid-electric aircraft by modeling the behavior of a profit-seeking airline (with a mixture of conventional all Jet-A fuel burning and hybrid electric aircraft in its fleet) using the Fleet-Level Environmental Evaluation Tool (FLEET). FLEET’s model-based predictions rely upon historically-based information about US-touching airline routes and passenger demand served by US flag-carrier airlines from the Bureau of Transportation Statistics to initiate model-based predictions of future demand, aircraft fleet mix, and aircraft operations. Using the aircraft performance coefficients from the energy management tool to represent the behavior of a single-aisle parallel hybrid-electric aircraft, the FLEET simulation predicts the changes in the fleet-wide carbon emissions due to the introduction of this new aircraft in an airline fleet in the year 2035. By 2055, FLEET results predict that the fleet-wide CO2 emissions with hybrid-electric aircraft in the fleet mix are at least 1.2% lower than the fleet-wide CO2 emissions of a conventional (all Jet-A fuel burning) aircraft-only airline. The rather limited reduction in emissions is an attribute of the reduced range capability and higher operating cost of the hybrid-electric aircraft (relative to a conventional aircraft of similar size). This causes the airline to change the usage, acquisition and retirement of its conventional aircraft when hybrid-electric aircraft are available; this is most notable to serve passenger demand on certain predominantly single-aisle service routes that cannot be flown by the future single-aisle hybrid-electric aircraft. </p

A Hybrid Approach for Solving Constrained Multi-Objective Mixed-Discrete Nonlinear Programming Engineering Problems

Several complex engineering design problems have multiple, conflicting objectives and constraints that are nonlinear, along with mixed discrete and continuous design variables; these problems are inherently difficult to solve. This chapter presents a novel hybrid approach to find solutions to a constrained multi-objective mixed-discrete nonlinear programming problem that combines a two-branch genetic algorithm as a global search tool with a gradient-based approach for the local search. Hybridizing two algorithms can provide a search approach that outperforms the individual algorithms; however, hybridizing the two algorithms, in the traditional way, often does not offer advantages other than the computational efficiency of the gradient-based algorithms and global exploring capability of the evolutionary-based algorithms. The approach here presents a hybridization approach combining genetic algorithm and a gradient-based approach with improved information sharing between the two algorithms. The hybrid approach is implemented to solve three engineering design problems of different complexities to demonstrate the effectiveness of the approach in solving constrained multi-objective mixed-discrete nonlinear programming problems

The 750 GeV threshold to a new particle world

We show how an excess in the diphoton channel can be the effect of neither a resonance nor an end-point in a cascade decay, but rather of a threshold for virtual production of a pair of extra quarks, each with half of peak invariant mass, onsetting in both the $gg$-initiated production and the $\gamma\gamma$-induced decay of an off-shell $Z$ boson. For our analysis we consider as paradigmatic example the 750 GeV excess previously seen at the end of 2015 with the Run 2 data of the LHC but not confirmed with 2016 data

Evaluation of efficiency of complete dentures using bps, lecutonite & acrylic materials: An original research

Introduction: Type of materials used in fabrication of denture base has an effect on dimension during denture base material processing and other factors related to clinical use. The study aims were to assess the efficiency of complete dentures made using bps, lecutonite &amp; acrylic materials. Material and Methods: Ninety patients were selected to construct complete dentures with bps, lecutonite &amp; acrylic materials denture base materials. They were randomly divided into three groups: group 1, patients with bps; group 2, patients with heat curing acrylic resin fabricated by injection moulding technique and conventional methods; and group 3, patients with lecutonite. The dimensional changes were assessed using digital caliper. Results: After the twelfth month, injection moulding acrylic resin had significantly the highest dimensional change followed by the lecutonite. There were no significant differences in the dimensions between the three types of denture base materials at normal mouth temperature, while, after hot tea drinking at 45∘C, the dimensional change was significantly the highest in cobalt chrome metallic denture base group. Conclusion: BPS denture base has stable dimension compared to denture bases fabricated of lecutonite, acrylic resin but it was more affected by altered mouth temperature

Fleet-Level Environmental Assessments for Feasibility of Aviation Emission Reduction Goals

The International Air Transport Association (IATA) is one of several organizations that have presented goals for future CO2 emissions from commercial aviation with the intent of alleviating the associated environmental impacts. These goals include attaining carbon-neutral growth in the year 2020 and total aviation CO2 emissions in 2050 equal to 50% of 2005 aviation CO2 emissions. This paper presents the use of a simulation-based approach to predict future CO2 emissions from commercial aviation based upon a set of scenarios developed as part of the Aircraft Technology Modeling and Assessment project within ASCENT, the FAA Center of Excellence for Alternative Jet Fuels and the Environment. Results indicate that, in future scenarios with increasing demand for air travel, it is difficult to reduce CO2 emissions in 2050 to levels equal to or below 2005 levels, although neutral CO2 growth after 2020 may be possible