5,294 research outputs found
Simplified Optimization Model for Low-Thrust Perturbed Rendezvous Between Low-Eccentricity Orbits
Trajectory optimization of low-thrust perturbed orbit rendezvous is a crucial
technology for space missions in low Earth orbits, which is difficult to solve
due to its initial value sensitivity, especially when the transfer trajectory
has many revolutions. This paper investigated the time-fixed perturbed orbit
rendezvous between low-eccentricity orbits and proposed a priori quasi-optimal
thrust strategy to simplify the problem into a parametric optimization problem,
which significantly reduces the complexity. The optimal trajectory is divided
into three stages including transfer to a certain intermediate orbit,
thrust-off drifting and transfer from intermediate orbit to the target orbit.
In the two transfer stages, the spacecraft is assumed to use a parametric law
of thrust. Then, the optimization model can be then obtained using very few
unknowns. Finally, a differential evolution algorithm is adopted to solve the
simplified optimization model and an analytical correction process is proposed
to eliminate the numerical errors. Simulation results and comparisons with
previous methods proved this new method's efficiency and high precision for
low-eccentricity orbits. The method can be well applied to premilitary analysis
and high-precision trajectory optimization of missions such as in-orbit service
and active debris removal in low Earth orbits
High-energy electronic excitations in SrIrO observed by Raman scattering
Spin-orbit interaction in SrIrO leads to the realization of the
= 1/2 state and also induces an insulating behavior. Using
large-shift Raman spectroscopy, we found two high-energy excitations of the
d-shell multipletat at 690 meV and 680 meV with and symmetry
respectively. As temperature decreases, the and peaks narrow,
and the peak shifts to higher energy while the energy of the
peak remains the same. When 25 of Ir is substituted with Rh the
peak softens by 10 but the peak does not. We show that both
pseudospin-flip and non-pseudosin-flip dd electronic transitions are Raman
active, but only the latter are observed
Reverse Diffusion Monte Carlo
We propose a Monte Carlo sampler from the reverse diffusion process. Unlike
the practice of diffusion models, where the intermediary updates -- the score
functions -- are learned with a neural network, we transform the score matching
problem into a mean estimation one. By estimating the means of the regularized
posterior distributions, we derive a novel Monte Carlo sampling algorithm
called reverse diffusion Monte Carlo (rdMC), which is distinct from the Markov
chain Monte Carlo (MCMC) methods. We determine the sample size from the error
tolerance and the properties of the posterior distribution to yield an
algorithm that can approximately sample the target distribution with any
desired accuracy. Additionally, we demonstrate and prove under suitable
conditions that sampling with rdMC can be significantly faster than that with
MCMC. For multi-modal target distributions such as those in Gaussian mixture
models, rdMC greatly improves over the Langevin-style MCMC sampling methods
both theoretically and in practice. The proposed rdMC method offers a new
perspective and solution beyond classical MCMC algorithms for the challenging
complex distributions.Comment: 44 pages, 16 figures, ICLR 202
Two highly similar DEAD box proteins, OsRH2 and OsRH34, homologous to eukaryotic initiation factor 4AIII, play roles of the exon junction complex in regulating growth and development in rice
Accession numbers and proteins homologous to eIF4A. (DOCX 18 kb
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