Hydrocode modeling of the spallation process during hypervelocity impacts: Implications for the ejection of Martian meteorites

Hypervelocity ejection of material by impact spallation is considered a plausible mechanism for material exchange between two planetary bodies. We have modeled the spallation process during vertical impacts over a range of impact velocities from 6 to 21 km/s using both grid- and particle-based hydrocode models. The Tillotson equations of state, which are able to treat the nonlinear dependence of density on pressure and thermal pressure in the strongly shocked matter, were used to study the hydrodynamic and thermodynamic response after impacts. The effects of material strength and gravitational acceleration were not considered. A two-dimensional time-dependent pressure field within a 1.5-fold projectile radius from the impact point was investigated in cylindrical coordinates to address the generation of spalled material. A resolution test was also performed to reject ejected materials with peak pressures that were too low due to artificial viscosity. The relationship between ejection velocity veject and peak pressure Ppeak was also derived. Our approach shows that late stage acceleration in an ejecta curtain occurs due to the compressible nature of the ejecta, resulting in an ejection velocity that can be higher than the ideal maximum of the resultant particle velocity after passage of a shock wave. We also calculate the ejecta mass that can escape from a planet like Mars (i.e., veject higher than 5 km/s) that matches the petrographic constraints from Martian meteorites, and which occurs when Ppeak from 30-50 GPa. Although the mass of such ejecta is limited to from 0.1-1 percent of the projectile mass in vertical impacts, this is sufficient for spallation to have been a plausible mechanism for the ejection of Martian meteorites. Finally, we propose that impact spallation is a plausible mechanism for the generation of tektites.Comment: 67 pages, 28 figures, accepted for publication in Icaru

ICE6Gavg(GPS) GIA-induced changes in Stokes coefficients

Besides studies of sea level change and mantle rheology, reliable GIA (Glacial Isostatic Adjustment) models are necessary as a background model to correct the widely used GRACE (Gravity Recovery and Climate Experiment) monthly gravity solutions to determine sub-secular, non-viscous variations. Based on spherical harmonic analyses, we developed a method using degree-dependent weighting to assimilate GPS (Global Positioning System) derived crustal uplift rates into GIA model predictions, via which the good global pattern of GIA model predictions and better local resolution of GPS solutions are both retained. Some systematic errors in global GPS uplift rates were also corrected during that spherical harmonic analyses. Further, we used the refined GIA uplift rates to infer the GIA-induced rates of Stokes coefficients (complete to degree/order 120) relying on the accurate relationship between GIA vertical surface deformation and gravitational potential changes. The results may serve as a GIA-correction model for GRACE time-variable gravity data

Additional file 5 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 5: Fig S4. Subgroup analyses stratified by patient and operative variables in patients without preoperative anemia

Additional file 2 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 2: Fig S1. Restricted cubic spline function curves of the unadjusted and adjusted relationship between Hemoglobin drop and AKI probability. Shaded areas represent 95% confidence intervals

Additional file 1 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 1: Table S1. Definitions of variables. Table S2. Postoperative events. Table S3. Improvement of Hemoglobin drop in full models for classification. Table S4. Sensitivity analyses. Multivariable logistic regression with surgery duration adjustment. Table S5. Sensitivity analyses. Multivariable logistic regression with exclusion of patients with Intraoperative hypotension. Table S6. Sensitivity analyses. Multivariable logistic regression with preoperative hemoglobin mean level within three months instead of the hemoglobin value tested closest to the date of surgery. Table S7. Patient characteristics and operative variables in cohorts by hemoglobin drop more or no more than 43 g/L after propensity score weighting

Additional file 3 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 3: Fig S2. Timeliness between perioperative hemoglobin level and corresponding creatinine. The red line represented minimum hemoglobin level, with its corresponding red axis on the left. In plots A and B, the blue line represented creatinine level, with their corresponding blue axis on the right; in plots C and D, the blue line represented creatinine increment with their corresponding blue axis. Creatinine level changed simultaneously with hemoglobin level within five postoperative days. After day 5, this phenomenon disappeared

Chiral Diols: A New Class of Additives for Direct Aldol Reaction Catalyzed by l-Proline

Nine C2 symmetric diols have been examined as additives in the l-proline-catalyzed direct aldol reaction with significant improvement in enantioselectivity, conversion efficiency, and yield. Loading of 1 mol % of (S)-BINOL leads to the desired products in up to 98% ee and 90% yield. A transition state is proposed

Additional file 4 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 4: Fig S3. Timeliness between perioperative hemoglobin drop and corresponding creatinine. The red line represented maximum hemoglobin drop, with its corresponding red axis on the left. In plots A and B, the blue line represented creatinine level, with their corresponding blue axis on the right; in plots C and D, the blue line represented creatinine increment with their corresponding blue axis

Additional file 6 of Threshold heterogeneity of perioperative hemoglobin drop for acute kidney injury after noncardiac surgery: a propensity score weighting analysis

Additional file 6: Fig S5. Subgroup analyses stratified by patient and operative variables in patients with preoperative anemia

Reaction Path Force Matching: A New Strategy of Fitting Specific Reaction Parameters for Semiempirical Methods in Combined QM/MM Simulations

We present a general strategy of reparametrizing semiempirical (SE) methods against <i>ab initio</i> (AI) methods for combined quantum mechanical and molecular mechanical (QM/MM) simulations of specific chemical reactions in condensed phases. The resulting approach, designated Reaction Path Force Matching (RP-FM), features cycles of sampling configurations along a reaction path on an efficient SE/MM potential energy surface (PES) and adjusting specific reaction parameters (SRPs) in the SE method such that the atomic forces computed at the target AI/MM level are reproduced. Iterative applications of the RP-FM cycle make possible achieving the accuracy of AI/MM simulations without explicitly sampling the computationally expensive AI/MM PES. The bypassed sampling, nevertheless, is implicitly accomplished through the aid of the efficient SE-SRP/MM PES, on which the target-level reaction path is expected to be obtained upon convergence. We demonstrate the effectiveness of the RP-FM procedure for a symmetric proton transfer reaction in the gas phase and in solution. The remarkable agreements between the RP-FM optimized SE-SRP methods and the target AI method on various properties, including energy profiles, potential of mean force free energy profiles, atomic forces, charge populations, and solvation effects, suggest that RP-FM can be used as an efficient and reliable strategy for simulating condensed-phase chemical reactions