Stress Analysis of Soil Beneath Wheel for Planetary Rover by Using Discrete Element Method

Modeling the interaction between rover's wheel and soft terrain is of great importance in predicting or evaluating wheel performance for lunar and planetary rovers. The current wheel-soil interaction models predict or evaluate wheel performance under certain conditions. However, most of them do not consider the soil flow and deformation, and thus, they cannot capture the physical phenomena of wheel-soil interaction. Developing a new model that includes such physical phenomena contributes to the improvement of prediction accuracy. To develop such a model, it is necessary to analyze soil flow and deformation beneath the wheel. This study analyzes the stress distributions in the soil and soil flow fields beneath the grouser wheel by performing experiments using the discrete element method (DEM) with the particle simulation tool "Sir partsival". In addition to the single wheel simulation, two simple test simulations - an angle of repose test and a shear test - are performed to confirm the soil flow fields and stress distributions in the soil. In the field of fluid dynamics, (shear) stress generally exists along high gradients of flow velocity. These two tests confirm if the soil stress shows the same trend. The wheel simulations are performed under several slip conditions to investigate their influences on soil flow characteristics. The shape of the soil flow region - the shape of the slip line - can be divided into two patterns depending on the slip conditions. The stress increases along the slip line in all simulations. The findings of this study contribute to understanding the relationship between soil velocity field and stress distribution in the soil

Soil Flow Analysis for Planetary Rovers Based on Particle Image Velocimetry and Discrete Element Method

Planetary rovers commonly have grouser wheels to improve locomotion performance on deformable terrains such as the surfaces of the Moon or Mars. The biggest difference between the wheel with grousers and without grousers is soil behavior underneath the wheel since the grousers shovel the sand. Hence, analyzing soil flow gives us beneficial information on wheel-soil interaction. The detailed investigation for micro-scale soil behavior and gravity effect, which are difficult to see in the laboratory test, contributes to further understanding of wheel-soil interaction mechanics. This paper presents a two-dimensional discrete element method (DEM) simulation to analyze soil flow beneath the grouser wheel. The soil flow in the simulation is validated by comparing it with that of the measurements, which is visualized by particle image velocimetry (PIV). The comparison results are discussed from four perspectives: 1) wheel slip ratio, 2) traces formed behind the wheel travels, 3) entrance and leaving angles of the grousers, 4) soil velocity field. The results indicate that DEM could describe the soil deformation. This work would contribute to further investigations of the state inside the soil by using developed DEM simulation

Roles of bulk γ(L)-Bi₂MoO₆ and surface β-Bi₂Mo₂O₉ in the selective catalytic oxidation of C₃H₆

γ(L)-Bi₂MoO₆ (L: low temperature phase) catalysts, whose surface compositions have a Mo/Bi ratio above = 0.5, exhibited high selectivity in the partial oxidation of C₃H₆, while catalysts with Mo/Bi surface ratios near or below = 0.5 exhibited low selectivity. γ(L)-phase catalysts which have Mo/Bi surface ratios greater than = 0.5, were demonstrated to form β-Bi₂Mo₂O₉ on their surface. An interaction between the β- and γ(L)-phases was observed in these catalysts’ UV–vis spectra at 430 nm. The new β-phase material seems to grow along b-axis of γ(L)-phase, i.e., perpendicular to MoO₂–Bi₂O₂ layers. Structure visualizations revealed that the α-Bi₂Mo₃O₁₂, β-, and γ(H)-phases, which are selective catalysts, contain twin Mo tetrahedral structures, and that their Mo and Bi ions lie on the same plane. The pure γ(L)-phase does not contain this structure. A model for the very rapid transfer of oxygen between the γ(L)- and β-phases is discussed in relation to the kinetics of C₃H₆ oxidation.ArticleJournal of molecular catalysis. A, Chemical. 318(1-2):94-100 (2010)journal articl

Smoking Cessation after Discharge among Japanese Patients with Established Ischemic Heart Disease: A Prospective Cohort Study

In this prospective cohort study for Japanese patients with established ischemic heart disease (IHD), the authors investigated the rate of success of smoking cessation 3 months after hospital discharge and its related factors. The subjects included 90 current smokers admitted for IHD. A total of 58 subjects (64%) had quit smoking for 3 months after being discharged. In comparison with subjects with acute myocardial infarction, those with stable angina (SA) showed a significantly lower frequency of smoking cessation (relative risk of resuming smoking (95% confidence interval):2.06 (1.09, 3.92), p=0.036). This relationship remained significant even after controlling for sex, age, and scores of the Fagerstrom Test for Nicotine Dependence (adjusted odds ratio:3.39 (1.01, 11.37), p=0.048). However, it became insignificant when hospital admission followed by emergency medical service (EMS) care was additionally adjusted (adjusted odds ratio:2.48 (0.36, 16.97), p=0.356). The smoking cessation rate in this study was identical to that observed in studies conducted in Japan prior to the recent social changes with regard to tobacco use. SA still appears to be a risk factor for smoking resumption after discharge. Experiencing EMS care would be an intermediate variable in this relationship.</p

Strong ice-ocean interaction beneath Shirase Glacier Tongue in East Antarctica

Mass loss from the Antarctic ice sheet, Earth’s largest freshwater reservoir, results directly in global sea-level rise and Southern Ocean freshening. Observational and modeling studies have demonstrated that ice shelf basal melting, resulting from the inflow of warm water onto the Antarctic continental shelf, plays a key role in the ice sheet’s mass balance. In recent decades, warm ocean-cryosphere interaction in the Amundsen and Bellingshausen seas has received a great deal of attention. However, except for Totten Ice Shelf, East Antarctic ice shelves typically have cold ice cavities with low basal melt rates. Here we present direct observational evidence of high basal melt rates (7–16 m yr−1) beneath an East Antarctic ice shelf, Shirase Glacier Tongue, driven by southward-flowing warm water guided by a deep continuous trough extending to the continental slope. The strength of the alongshore wind controls the thickness of the inflowing warm water layer and the rate of basal melting

MicroRNA-133 regulates the expression of GLUT4 by targeting KLF15 and is involved in metabolic control in cardiac myocytes

GLUT4 shows decreased levels in failing human adult hearts. We speculated that GLUT4 expression in cardiac muscle may be fine-tuned by microRNAs. Forced expression of miR-133 decreased GLUT4 expression and reduced insulin-mediated glucose uptake in cardiomyocytes. A computational miRNA target prediction algorithm showed that KLF15 is one of the targets of miR-133. It was confirmed that over-expression of miR-133 reduced the protein level of KLF15, which reduced the level of the downstream target GLUT4. Cardiac myocytes infected with lenti-decoy, in which the 3′UTR with tandem sequences complementary to miR-133 was linked to the luciferase reporter gene, had decreased miR-133 levels and increased levels of GLUT4. The expression levels of KLF15 and GLUT4 were decreased at the left ventricular hypertrophy and congestive heart failure stage in a rat model. The present results indicated that miR-133 regulates the expression of GLUT4 by targeting KLF15 and is involved in metabolic control in cardiomyocytes