2,338 research outputs found
Indirect low-thrust trajectory optimization with gridded ion thruster model
No full textThe work deals with indirect optimization of minimum-time and minimum-fuel interplanetary trajectories when gridded ion thruster models are considered. Using an accurate model of solar electric propulsion is beneficial in preliminary mission design, and allows including operational constraints. The maximum thrust and the specific impulse are expressed as a function of thruster input power, which is achieved by means of point-fitting lines that match the performance capabilities of the thrusters. Minimum-time and minimum-fuel problems are formulated to be solved by indirect optimization. In order to increase the accuracy and robustness of the shooting procedure, analytic Jacobians are derived, and a hybrid switching detection technique is used to improve the integration accuracy for minimum-fuel problems. Two examples of Earth-to-Mars transfer and Near-Earth rendezvous mission using the realistic NASA's Evolutionary Xenon Thruster (NEXT) are given to substantiate the feasibility and effectiveness of the proposed method
Multi-component body composition models: recent advances and future directions.
No full textThis overview examines concepts related to a category of body composition methods generally referred to as multi-component models, that is, those models that include three or more components
Coexistence of trapped and free excess electrons in SrTiO3
No full textThe question whether excess electrons in SrTiO3 form free or trapped carriers is a crucial aspect for the electronic properties of this important material. This fundamental ambiguity prevents a consistent interpretation of the puzzling experimental situation, where results support one or the other scenario depending on the type of experiment that is conducted. Using density functional theory with an on-site Coulomb interaction U, we show that excess electrons form small polarons if the density of electronic carriers is higher than approximate to 10(20) cm(-3). Below this value, the electrons stay delocalized or become large polarons. For oxygen-deficient SrTiO3, small polarons confined to Ti3+ sites are immobile at low temperature but can be thermally activated into a conductive state, which explains the metal-insulator transition observed experimentally
Six-compartment body composition model: inter-method comparisons of total body fat measurement.
No full textTo compare 16 currently used total body fat methods to a six-compartment criterion model based on in vivo neutron activation analysis
Study on the Influence of ZM Modifier on the Rheological Properties and Microstructural Characteristics of Asphalt
No full textAs traffic load continuously rises and climatic conditions increasingly vary, the performance of conventional base asphalt can no longer satisfy the needs of modern road engineering in low-temperature cracking resistance, high-temperature stability, and long-term durability. Therefore, the development of novel and efficient asphalt modifiers holds significant engineering value and practical importance. In this study, modified asphalt was prepared using varying dosages of ZM modifier (direct-injection asphalt mixture modified polymer additive). A series of experiments was executed to assess its influence on asphalt properties. First, fundamental property tests were implemented to determine the regulating effect of the ZM modifier on basic physical performances, like the softening point and penetration of the base asphalt. Penetration tests at different temperatures were performed to calculate the penetration index, thereby assessing the material’s temperature sensitivity. Subsequently, focusing on temperature as a key factor, tests on temperature sweep, and multiple stress creep recovery (MSCR) were implemented to delve into the deformation resistance and creep recovery behavior of the modified asphalt under high-temperature conditions. In addition, bending beam rheometer (BBR) experiments were introduced to attain stiffness modulus and creep rate indices, which were applied to appraise the low-temperature rheological performance. Aside from Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) was utilized to explore the mechanism by which the ZM modifier influences the asphalt’s functional group composition and microstructure. Our findings reveal that the ZM modifier significantly increases the asphalt’s softening point and penetration index, reduces penetration and temperature sensitivity, and enhances high-temperature stability. Under high-temperature conditions, the ZM modifier adjusts the viscoelastic balance of asphalt, hence enhancing its resistance to flow deformation and its capacity for creep recovery. In low-temperature environments, the modifier increases the stiffness modulus of asphalt and improves its crack resistance. FTIR analyses reveal that the ZM modifier does not introduce new functional groups, indicating a physical modification process. However, by enhancing the cross-linked structure and increasing the hydrocarbon content within the asphalt, it strengthens the adhesion between the asphalt and aggregates. Overall, the asphalt’s performance improvement positively relates to the dosage of the ZM modifier, providing both theoretical basis and experimental support for its application in road engineering
ZM Solid Catalysts for Synthesis of 1-Butoxy-2-Propanol with High Selectivity
No full textThis document explains and demonstrates the problem of butanol and propylene oxide propoxylation, ZrO2 load active alkali metal oxides MgO the catalytic propoxylation method, analyzed a new type of catalyst activity and selectivity. The results show that the synthesis of ZM complex oxide as a catalyst for the reaction of butanol substrate, through the catalytic reaction of propylene oxide, selective access to the propylene glycol ether, High selectivity synthesis 1-butoxy-2-propanol. Synthesis of complex oxide catalyst ZM series in the course of the performance of the primary ether good selectivity, Primary ether, second ether ratio greater than 12, and the catalytic activity is also high (about 90% of all).</jats:p
Text-To-Visual Speech in Chinese Based on Data-Driven Approach
No full textWang ZM, Cai LH, AI HZ. Text-To-Visual speech in Chinese based on data-driven approach. Journal o
Vacancy clusters at domain boundaries and band bending at the SrTiO3(110) surface
No full textAntiphase domain boundaries (APDBs) in the (n x 1) (n = 4,5) reconstructions of the SrTiO3(110) surface were studied with scanning tunneling microscopy, x-ray photoemission spectroscopy, and density functional theory (DFT) calculations. Two types of APDBs form on each reconstruction; they consist of TixOy vacancy clusters with a specific stoichiometry. The presence of these clusters is controlled by the oxygen pressure during annealing. The structural models of the vacancy clusters are resolved with DFT, which also shows that their relative stability depends on the chemical potential of oxygen. The surface band bending can be tuned by controlling the vacancy clusters at the domain boundaries
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