A generalized stress correction scheme for the Maxwell elasto-brittle rheology: impact on the fracture angles and deformations

The Maxwell elasto-brittle (MEB) rheology uses a damage parameterization to represent the brittle fracture of sea ice without involving plastic laws to constrain the sea ice deformations. The conventional MEB damage parameterization is based on a correction of super-critical stresses that binds the simulated stress to the yield criterion but leads to a growth of errors in the stress field. A generalized damage parameterization is developed to reduce this error growth and to investigate the influence of the super-critical stress correction scheme on the simulated sea ice fractures, deformations and orientation of linear kinematic features (LKFs). A decohesive stress tensor is used to correct the super-critical stresses towards different points on the yield curve. The sensitivity of the simulated sea ice fractures and deformations to the decohesive stress tensor is investigated in uniaxial compression experiments. Results show that the decohesive stress tensor influences the growth of residual errors associated with the correction of super-critical stresses, the orientation of the lines of fracture and the short-term deformation associated with the damage, but it does not influence the long-term post-fracture sea ice deformations. We show that when ice fractures, divergence first occurs while the elastic response is dominant, and convergence develops post-fracture in the long term when the viscous response dominates – contrary to laboratory experiments of granular flow and satellite imagery in the Arctic. The post-fracture deformations are shown to be dissociated from the fracture process itself, an important difference with classical viscous plastic (VP) models in which large deformations are governed by associative plastic laws. Using the generalized damage parameterization together with a stress correction path normal to the yield curve reduces the growth of errors sufficiently for the production of longer-term simulations, with the added benefit of bringing the simulated LKF intersection half-angles closer to observations (from 40–50 to 35–45∘, compared to 15–25∘ in observations).

Iterative Lambert’s Trajectory Optimization for Extrasolar Bodies Interception

Interception of extrasolar objects is one of the major current astrophysical objectives since it allows gathering information on the formation and composition of other planetary systems. This paper develops a tool to design optimal orbits for the interception of these bodies considering the effects of different perturbation sources. The optimal trajectory is obtained by solving a Lambert’s problem that gives the required initial impulse. A numerical integration of a perturbed orbital model is calculated. This model considers the perturbations of the joint action of the gravitational potentials of the Solar System planets and the solar radiation pressure. These effects cause a deviation in the orbit that prevents the interception from taking place, so an iterative correction scheme of the initial estimated impulse is presented, capable of modifying the orbit and achieving a successful interception in a more realistic environment.

Design and Analysis of Asynchronous Sampling Duty Cycle Corrector

This paper presents a duty cycle correction scheme based on asynchronous sampling and associated settling analysis. The proposed duty cycle corrector circuit consumes less power and area compared to other corrector circuits due to the low-frequency operation of asynchronous sampling. However, the settling behavior of an asynchronous sampling duty cycle corrector is limited in some operation conditions, which degrades its robustness and performance. This paper, therefore, performs analysis on the settling behavior of the asynchronous sampling in various operating conditions and proposes a control scheme to avoid the lagged settling. To verify the proposed duty cycle corrector and its analysis, a prototype design is implemented in a 40-nm CMOS process and its performance is verified by post-layout simulations. The proposed duty cycle corrector achieved very small duty cycle errors (less than 0.8%) and consumed 540 uW per one DCC unit.

Timing Fluctuation Correction of A Femtosecond Regenerative Amplifier

We report on the long-term correction of a timing fluctuation between the femtosecond regenerative amplifier and the reference oscillator for the seed 100 PW laser system in the Station of Extreme Light (SEL). The timing fluctuation was characterized by a noncollinear balanced optical cross-correlator that maps the time difference to the sum frequency intensity of the amplifier and oscillator laser pulses. A feedback loop was employed to correct the timing jitter by adjusting the time delay line in the amplifier beam path. The timing fluctuation was reduced to 1.26 fs root-mean-square from hundreds of fs over 10 hours. Benefitting from excellent performance and long-term stability, this timing jitter correction scheme, as a component of optical synchronization in the 100 PW laser facility, will be integrated into SEL.

Study on the optical spectra of the oxygen vacancy in ZnWO4 crystal

ZnWO4 is easy to color, which will reduce the luminous efficiency of the crystal and limit the application of the crystal. In order to study the origin of the color in the crystal, in this paper, the effects of the oxygen vacancy on the optical properties for the ZnWO4 crystal have been studied based on the density functional theory (DFT). The hybrid functional method (HSE) and the finite-size correction scheme (FNV) are used to correct the band edge problem and eliminate the artificial interaction of the charged defects, respectively. On the basis of the corrected defect formation energy, we obtain the optical spectra of the [Formula: see text] and [Formula: see text] centers containing electron-phonon coupling. The calculated absorption and luminescence peaks are at 2.54 eV and 0.79 eV for the [Formula: see text] center and at 2.98 eV and 1.09 eV for the [Formula: see text] center, respectively. The calculated absorption band of the [Formula: see text] center is close to the experimental value of 2.48 eV (500 nm), so we speculate that the coloring of the ZnWO4 crystal is related to the [Formula: see text] center. Meanwhile, the existence of oxygen vacancy makes ZnWO4 crystal to have self-absorption and to increase decay time, which greatly affects the scintillation properties of the crystal.

Atmospheric Correction of DSCOVR EPIC: Version 2 MAIAC Algorithm

The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) provides multispectral images of the sunlit disk of Earth since 2015 from the L1 orbit, approximately 1.5 million km from Earth toward the Sun. The NASA’s Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm has been adapted for DSCOVR/EPIC data providing operational processing since 2018. Here, we describe the latest version 2 (v2) MAIAC EPIC algorithm over land that features improved aerosol retrieval with updated regional aerosol models and new atmospheric correction scheme based on the ancillary bidirectional reflectance distribution function (BRDF) model of the Earth from MAIAC MODIS. The global validation of MAIAC EPIC aerosol optical depth (AOD) with AERONET measurements shows a significant improvement over v1 and the mean bias error MBE = 0.046, RMSE = 0.159, and R = 0.77. Over 66.7% of EPIC AOD retrievals agree with the AERONET AOD to within ± (0.1 + 0.1AOD). We also analyze the role of surface anisotropy, particularly important for the backscattering view geometry of EPIC, on the result of atmospheric correction. The retrieved BRDF-based bidirectional reflectance factors (BRF) are found higher than the Lambertian reflectance by 8–15% at 443 nm and 1–2% at 780 nm for EPIC observations near the local noon. Due to higher uncertainties, the atmospheric correction at UV wavelengths of 340, 388 nm is currently performed using a Lambertian approximation.