Integrated Design of Moon-to-Earth Transfer Trajectory Considering Re-Entry Constraints

The exploration of the Moon has always been a hot topic. The determination of the Moon-to-Earth transfer opportunity and the design of the precise transfer trajectory play important roles in manned Moon exploration missions. It is still a difficult problem to determine the Moon-to-Earth return opportunity for accurate atmospheric re-entry and landing, through which the actual return trajectory can be easily obtained later. This paper proposes an efficient integrated design method for Moon-to-Earth window searching and precise trajectory optimization considering the constraints of Earth re-entry and landing. First, an analytical geometry-based method is proposed to determine the state of the re-entry point according to the landing field and re-entry constraints to ensure accurate landing. Next, the transfer window is determined with the perilune heights, which are acquired by inversely integrating the re-entry state under the simplified dynamics as criterion. Then, the precise Moon-to-Earth trajectory is quickly obtained by a three-impulse correction. Simulations show the accuracy and efficiency of the proposed method compared with methods such as the patched-conic method and provide an explicit reference for future Moon exploration missions

Layer-Controlled Synthesis of a Silanol-Graphene Oxide Nanosheet Composite Forward Osmosis Membrane by Surface Self-Assembly

More and more two-dimensional materials, such as graphene, are used in water separation membrane synthesis. Among the main influencing factors, surface properties and the interface structure of multilayers are the two crucial factors to the membrane separation performance. In the present paper, a silanol ((SiO3)(x)) and graphene oxide nanosheet composite (GO-(SiO3)(x)) was used to synthesize a skin like forward osmosis (FO) membrane for desalination by a surface layer-by-layer self-assembly method. We tested the separation performance of the FO membranes using DI water and 1.5 M NaCl aqueous solutions as feed and draw solutions, respectively. The results show that the molecular size and particle morphology of (SiO3)(x) grafted onto GO nanosheets play main roles in the water flux of the composite membrane. Based on this property and the self-assembly method, we can control the number of composite layers and the space between the GO nanosheets. Simultaneously, we have introduced a new concept: dilutive "skin layer concentration polarization (SLCP)" and the concentrative external concentration polarization (ECP) effect at the membrane surface are considered. The FO membrane synthesized in the current study exhibits a high level of water flux (above 30 L.m(-2).h(-1)), and the salt retention capacity of the membranes increases as the number of composite layers increases. Thus, in this article, we find a way to create suitable water channels for separation of salt/water in a FO process by controlling the GO-(SiO3)(x) content and size

The role of phase transfer catalysts on properties of polyamide thin-film composite forward osmosis membranes

In this article, 1,3,5-benzenetricarbonyl trichloride (TMC), m-phenylenediamine (MPD) and phase transfer catalysts (PTCs) were used to produce polyamide thin-film composite (TFC) forward osmosis (FO) membranes through interfacial polymerization (IP) reaction. The effects of dodecyl trimethyl ammonium chloride (DTAC), sodium dodecyl sulphate (SDS) and dodecyl dimethyl betaine (BS12) on the polyamide molecular aggregation structures, surface morphology and FO separation performance of the membranes were systematically investigated. In the FO process, concentrated 1.0 M NaCl aqueous solution was chosen as the draw solution and 0.1 M NaCl aqueous solution was used as the feed solution (at room temperature). Separation performance included the water flux (J(w)) and reverse salt rejection (reverse solute flux, RS). The experiment proved that PTCs can regulate the molecular chain aggregation state and surface morphology of polyamide, which can lead to a relatively definite improvement in water flux (11.5 L m(-2) h(-1)) (DTAC-polyamide). Simultaneously, the polyamide surface morphology was found to play a major role in the water permeability of the FO membrane rather than the density of the skin layer (i.e., degree of cross-linking), and we found that a relatively smooth surface is more conducive to weakening the external concentration polarization (ECP) phenomenon that occurs in the FO process. We attribute this mechanism on polyamide to the size effect and charge interaction of PTCs. In the current study, the balanced effect of the synergistic interaction of the molecular structure and rough surface of polyamide on FO separation performance should be comprehensively considered

Preparation of the regular polyhedral single-crystalline SrTiO3 particles with exposing different crystal facets

Strontium titanate (SrTiO3) has risen and drawn more and more attention of the researchers duo to its excellent photocatalytic activity based on the anisotropic charge transport theory. In this work, we first produced the regular polyhedral single-crystalline SrTiO3 particles with multiple crystal facets exposing include the {1 0 0}, {1 1 0} and {1 1 1} by one-step hydrothermal method. This SrTiO3 exhibited improved photocatalytic activity compared with that only exposing {1 0 0} crystal facet. Simultaneously, the SrTiO3 crystal growing process had been discussed. The single-crystalline SrTiO3 particles may provide a new basic material for the SrTiO3 application in photocatalysis. (C) 2021 Elsevier B.V. All rights reserved

Effects of Irrigation and Nitrogen Fertilization on Seed Yield, Yield Components, and Water Use Efficiency of Cleistogenes songorica

Irrigation and nitrogen (N) are two crucial factors affecting perennial grass seed production. To investigate the effects of irrigation and N rate on seed yield (SY), yield components, and water use efficiency (WUE) of Cleistogenes songorica (Roshevitz) Ohwi, an ecologically significant perennial grass, a four-year (2016–2019) field trial was conducted in an arid region of northwestern China. Two irrigation regimes (I1 treatment: irrigation at tillering stage; I2 treatment: irrigation at tillering, spikelet initiation, and early flowering stages) and four N rates (0, 60, 120, 180 kg ha−1) were arranged. Increasing amounts of both irrigation and N improved SY, evapotranspiration, WUE, and related yield components like fertile tillers m−2 (FTSM) and seeds spikelet−1. Meanwhile, no significant difference was observed between 120 and 180 kg N ha−1 treatments for most variables. The highest SY and WUE was obtained with treatment combination of I2 plus 120 kg N ha−1 with four-year average values of 507.3 kg ha−1 and 1.8 kg ha−1 mm−1, respectively. Path coefficient and contribution analysis indicated that FTSM was the most important yield component for SY, with direct path coefficient and contribution coefficient of 0.626 and 0.592. Overall, we recommend I2 treatment (three irrigations) together with 120 kg N ha−1 to both increase SY and WUE, especially in arid regions. Future agronomic managements and breeding programs for seed should mainly focus on FTSM. This study will enable grass seed producers, plant breeders, and government program directors to more effectively target higher SY of C. songorica

Perovskite Micro-Nano Cage SrTiO3: Formation Mechanism, Vacancy Analysis, and Exciton Dynamics

In the former research, we produced the regular polyhedron single-crystalline SrTiO3 particles with multiple crystal facets exposed by a one-step hydrothermal method. In this work, the dissolution process mechanism of SrTiO3 has been analyzed based on the evidence of the crystal structure and particle morphology with a completely new point of view. The anisotropic formation process of perovskite micro-nano cage SrTiO3 was primarily summarized, and the defective vacancy composition was analyzed. Simultaneously, based on femtosecond transient absorption spectroscopy, the exciton dynamic of SrTiO3 was deduced, and it will play a key role in improving the photoelectric properties of SrTiO3. Furthermore, the abundant defective vacancies promote the ability of SrTiO3 to oxidize Co species, which has a great advantage in the wastewater treatment processes

Effects of Irrigation and Nitrogen Fertilization on Seed Yield, Yield Components, and Water Use Efficiency of <i>Cleistogenes songorica</i>

Irrigation and nitrogen (N) are two crucial factors affecting perennial grass seed production. To investigate the effects of irrigation and N rate on seed yield (SY), yield components, and water use efficiency (WUE) of Cleistogenes songorica (Roshevitz) Ohwi, an ecologically significant perennial grass, a four-year (2016–2019) field trial was conducted in an arid region of northwestern China. Two irrigation regimes (I1 treatment: irrigation at tillering stage; I2 treatment: irrigation at tillering, spikelet initiation, and early flowering stages) and four N rates (0, 60, 120, 180 kg ha−1) were arranged. Increasing amounts of both irrigation and N improved SY, evapotranspiration, WUE, and related yield components like fertile tillers m−2 (FTSM) and seeds spikelet−1. Meanwhile, no significant difference was observed between 120 and 180 kg N ha−1 treatments for most variables. The highest SY and WUE was obtained with treatment combination of I2 plus 120 kg N ha−1 with four-year average values of 507.3 kg ha−1 and 1.8 kg ha−1 mm−1, respectively. Path coefficient and contribution analysis indicated that FTSM was the most important yield component for SY, with direct path coefficient and contribution coefficient of 0.626 and 0.592. Overall, we recommend I2 treatment (three irrigations) together with 120 kg N ha−1 to both increase SY and WUE, especially in arid regions. Future agronomic managements and breeding programs for seed should mainly focus on FTSM. This study will enable grass seed producers, plant breeders, and government program directors to more effectively target higher SY of C. songorica

Perovskite Micro-Nano Cage SrTiO3: Formation Mechanism, Vacancy Analysis, and Exciton Dynamics

In the former research, we produced the regular polyhedron single-crystalline SrTiO3 particles with multiple crystal facets exposed by a one-step hydrothermal method. In this work, the dissolution process mechanism of SrTiO3 has been analyzed based on the evidence of the crystal structure and particle morphology with a completely new point of view. The anisotropic formation process of perovskite micro-nano cage SrTiO3 was primarily summarized, and the defective vacancy composition was analyzed. Simultaneously, based on femtosecond transient absorption spectroscopy, the exciton dynamic of SrTiO3 was deduced, and it will play a key role in improving the photoelectric properties of SrTiO3. Furthermore, the abundant defective vacancies promote the ability of SrTiO3 to oxidize Co species, which has a great advantage in the wastewater treatment processes