关键词： Vibrational spectroscopy   vibrational configuration interaction   selected configuration interaction  

摘要： Recently, a selected vibrational configuration interaction method was introduced where the selection of the vibrational basis was performed using the heat-bath algorithm (VHCI). This method was adapted from the heat-bath configuration interaction (HCI) method used to solve the electronic Schrodinger equation. The selection algorithm in electronic HCI exploits the fact that most nonzero Hamiltonian matrix elements correspond to a double electronic excitation from one determinant to another and have values equal to the two-electron molecular orbital integrals such that they can be computed once, sorted, stored, and easily accessed later using a dictionary data structure. However, the Hamiltonian matrix elements in VHCI are more complicated than their electronic HCI counterparts, which lead to the possibility of different VHCI implementations. We explore one such implementation. The most significant differences compared to the original VHCI implementation is that we (i) explicitly compute all one- and two-quanta excitations, (ii) include all occupation-number contributions to the Hamiltonian matrix elements, and (iii) add individual Hartree product basis functions to the variational space rather than multiple basis functions as determined by operator products. We apply the new VHCI algorithm to ethylene oxide and naphthalene and achieve good accuracy relative to previous results at a modest computational cost.

关键词： Positron-electron annihilation   Positrophilic electrons   Electronegativity   Average Doppler shift  

摘要： In this study, we calculated the theoretical gamma-ray spectra of the first 36 representative elements in groups 1, 2, and 13-18. We found that the width of these atoms' gamma-ray spectra is proportional to the value of the corresponding Rahm's electronegativity (Eg). Based on this, we present a new explanation of the width of the gamma-ray spectra. We also define a new physical quantity, average Doppler shift (ADS). ADS can quantitatively verify that positrophilic electrons in the positron-electron annihilation process are valence electrons. ADS also can express some characteristics of the gamma-ray spectra such as the full width at half maximum (FWHM), and even more general than FWHM in some cases. Both the FWHM and ADS of the gamma-ray spectra in light elements agree with the corresponding Rahm's electronegativity values, respectively. ADS provides strong evidence in favour of Rahm's electronegativity scale. It is expected that this will be useful for understanding the mechanism of the positron-electron annihilation process. (C) 2021 Elsevier B.V. All rights reserved.

关键词： boundary layer structure   turbulent boundary layers  

摘要： The statistical properties of prograde spanwise vortex cores and internal shear layers (ISLs) are evaluated for a series of high-Reynolds-number turbulent boundary layers. The considered flows span a wide range of both Reynolds number and surface roughness. In each case, the largest spanwise vortex cores in the outer layer of the boundary layer have size comparable to the Taylor microscale lambda(T), and the azimuthal velocity of these large vortex cores is governed by the friction velocity u(tau). The same scaling parameters describe the average thickness and velocity difference across the ISLs. The results demonstrate the importance of the local large-eddy turnover time in determining the strain rate confining the size of the vortex cores and shear layers. The relevance of the turnover time, and more generally the Taylor microscale, can be explained by a stretching mechanism involving the mutual interaction of coherent velocity structures such as uniform momentum zones with the evolving shear layers separating the structures.

关键词： Remanufacturing   batch processing   periodic policies   threshold policies   stochastic process   disposal  

摘要： This article examines a fundamental lot-sizing problem which arises in the context of a make-to-order remanufacturing environment. The problem setting is characterized by a stochastic used-item return process along with a stochastic remanufactured-item demand process faced by a remanufacturer. We explicitly take into account for all relevant costs, including the fixed costs (associated with remanufacturing of used-items and dispatching of remanufactured-item orders in batches) and inventory-related cost (associated with used-item inventory holding costs and remanufactured-item order waiting costs). We propose five batching policies inspired by shipment consolidation practice (three periodic policies and two threshold policies). For the purpose of computing policy parameters, we develop analytical models that are aimed at minimizing the long-run average expected total cost of the remanufacturer. Since the underlying cost expressions are not analytically tractable, we propose easily computable approximations that lead to closed-form expressions for obtaining policy parameters. A careful numerical investigation demonstrates that the resulting policy parameters are highly effective approximations. Then, we extend the policies by considering disposal options when needed. For this extension, an effective parameter-based approximation approach is developed for computational purposes, and additional numerical experiments demonstrate the effectiveness of the proposed approach.

关键词： Heat treatment furnace   Natural gas   Hydrogen   Fuel blend   Combustion   NOx  

摘要： The present study investigates the application of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces and their economic potential for decreasing carbon dioxide emissions in this field of application. Doing so, a detailed technological analysis of several influencing parameters on the heating system was performed as well as a consideration of furnace heating technology challenges. Starting with an evaluation of the main thermophysical properties of the blends and their corresponding flue gases, requirements for the heating systems were identified. Potential ways of decreasing flue gas losses and increasing the heat transfer are shown. In the radiant tube application, an increased overall combustion efficiency of about 1.2% was measured at 40 vol% hydrogen in the fuel gas. Influences on the air to gas ratio control system of the furnace is a further important point, which was considered in this study. Two commonly used control systems were evaluated concerning their capabilities to regulate the gas flow rates of blends with varying hydrogen contents and combustion properties, such as Wobbe Index. This is important, since it shows the capability to retrofit existing furnaces. Two types of burners were tested with different natural gas/hydrogen blends. This includes an open jet burner with air-staged and flameless combustion operation modes. A recuperative burner for radiant tube application was considered as well in these tests. Doing so, the nitrogen oxide formation of both systems under different operating conditions and different fuel blends were evaluated. An increase by about 10% at air-staged combustion and about 100% at flameless combustion was measured by a hydrogen content of 40 vol% in comparison to pure natural gas firing. Finally, the additional fuel costs of natural gas hydrogen blends and different cases are presented in an economic analysis. The driving force for the use of hydrogen as a fuel is the price of the CO2

关键词： Natural gas   Unconventional hydrocarbon reservoirs   Maturity   Migration   Overpressure  

摘要： Understanding fluid distribution within the most prolific low-permeability hydrocarbon reservoir of the Western Canadian Sedimentary Basin (WCSB), the Montney Formation, continues to be a challenge due to the complex history of hydrocarbon migration, which includes thermal alteration of hydrocarbons that migrated before maximum burial as well as more recent migration due to uplifting in the Eocene. In this study, we have assessed the occurrence of methane, ethane, and propane using parameters that are based on the possibility of molecular interconversion between C1-C3 alkanes. This approach allowed us to identify the boundary between two hydrocarbon plays within the Montney Formation based on the composition coefficient Q, and the compositional factors (C2H6)2 and (CH4).(C3H8), which are less susceptible to methane migration [particularly (C2H6)2]. One play is located primarily in Alberta and includes unconventional and conventional hydrocarbon fields;the second play is located exclusively in British Columbia and consists of unconventional hydrocarbon fields. Our new approach enables the identification of main hydrocarbon migration zones within conventional and unconventional sections (e.g. northeast, southeast, and central-west). Additionally, we used the C2/C3 ratio as a maturity indicator in the Montney Formation, which facilitates the identification of overpressure zones (to the southwest) and target areas for natural gas liquids (NGL) production (based on an estimated 1.5 %Ro). The assessment we have conducted can be further explored in other low-permeability hydrocarbon reservoirs.

关键词： Integrated coastal management   Trade-off evaluation   Socioeconomic benefit measurement   Sea area use and cover   Xiamen  

摘要： We develop a systematic approach for evaluating the trade-offs between different policies governing coastal land and sea area uses under an integrated coastal management (ICM) programme. The analytical framework includes multiple marine industry sectors (e.g., port, shipping and coastal tourism) as well as social and environmental sectors (e.g., employment and ecosystem services). The net benefit measure captures social, economic and environmental effects. We apply our analytical model to Xiamen, China, using empirical data from 2011 to 2015. Results of the case study show that the implementation of land and sea use policies under the ICM framework has led to a significant increase (over 7%) in annual net benefit. Thus, the Xiamen ICM programme has improved the efficiency of marine resource use. As an adaptive management approach, the introduction of revised marine function zoning scheme under an ICM framework may help to achieve sustainable development.

关键词： Aircraft   Aviation   Fuels   Energy   Exergy   Solid oxide fuel cell   Turbofan  

摘要： This paper presents a unique hybrid type aircraft propulsion system which combines a commercial turbofan system with a solid oxide fuel cell system. Thermodynamic analyses and parametric studies are collectively performed to investigate the compatibility and applicability of the proposed system as well as its performance through the energetic and exergetic efficiencies to determine how the efficiencies are affected by varying the operating conditions. Hydrogen, methane, methanol, ethanol, and dimethyl ether with different combinations are chosen as alternative fuels to replace kerosene, which is a traditional, fossil-based fuel. It is found that the net power of the solid oxide fuel cell is 944 kW with an electric efficiency of 87.0%. A maximum thermal efficiency of 32.3% and exergetic efficiency of 43.9% were achieved using 75% methane and 25% hydrogen fuel. The maximum overall thermal and exergetic efficiencies of the hybrid turbofan are 48.1% and 54.4%, respectively, using 75% methanol and 25% hydrogen fuel, which reduce carbon emissions by 65% compared to the fossil fuels. Therefore, the hybrid turbofan aircraft engine can increase the turbofan performance. In addition, a fuel mixture of 60% ethanol and 40% hydrogen can increase the performance by 5% and reduce carbon emissions by 73%.

关键词： Miscellaneous electric loads   U   S   national energy consumption   Energy savings potential   Buildings   End uses   Forecast  

摘要： Over time, miscellaneous electric loads (MELs) are expected to increase both in magnitude and share of residential and commercial building energy consumption. This trend is most apparent in North America, but it is also occurring in Japan and Europe. However, the contribution of MELs to building energy use is not currently well understood, both because the products in this category are transforming rapidly and the definition and classification of MELs is ambiguous. This study estimated the national energy consumption of 36 MELs using best-available data and found them to comprise 12% of delivered electricity to the U.S. residential and commercial building sectors. If 26 of these MELs were replaced with the most energy-efficient product models available on the market, their energy consumption could be halved to 6% of delivered electricity. National energy models will better account for building energy consumption by incorporating the MELs data collected and analyzed for this study, leading to improved policy decisions. (c) 2021 Elsevier B.V. All rights reserved.

关键词： Alternative jet fuel   Gas-to-liquid   Microscopic spray   Elevated ambient gas temperature   Phase doppler anemometry  

摘要： The volatile characteristics of alternative Gas-to-Liquid (GTL) jet fuel and conventional Jet A-1 fuel are significantly different due to their chemical composition variations. This difference can have a strong influence on the atomization performance at elevated ambient gas temperature conditions. Because the atomization process plays a vital role in fuel distribution inside the combustor, which ultimately affects heat release and emission patterns. The objective of the present work is to investigate the effects of ambient gas temperature and nozzle pressure differential on the non-reacting, microscopic spray performance of the alternative jet fuel using a pressure-swirl nozzle, and then, compare these effects to those of Jet A-1 fuel. Specifically, this study investigates the droplet size, velocity and distribution, by employing the Phase Doppler Anemometry technique to measure these parameters at several radial and axial locations downstream of the nozzle exit. The effect of ambient gas temperatures is studied at 300, 350, and 400 K at two nozzle pressure differentials, 300 and 900 kPa, while maintaining a constant ambient gas pressure and fuel temperature. Results show that, in the region investigated, there is a significant difference between the spray performances of GTL and Jet A-1 at elevated operating conditions. The outcomes of this study will add new knowledge to the limited scientific literature on the effect of ambient gas conditions on the local spray parameters of alternative jet fuel.