Experimental quantification and DEM simulation of micro-macro behaviors of granular materials using x-ray tomography imaging

A non-invasive experimental method and a clustering DEM model were developed in this study to investigate micro-macro behaviors of real granular materials with irregular particle shape configurations. The investigated behaviors include global deformations, failure strengths and residual strengths, stress and strain distributions, local coordination number, local void ratio, particle kinematics, and fabric orientation distributions. The experimental method includes an approach to automatically identify and recognize multiple particles using x-ray computed tomography imaging (XCT) and an enhanced approach to digitally represent microstructures of granular materials. The digitally represented microstructure can be directly employed for numerical simulation setup. A compression test and a direct shear test on coarse aggregates were conducted and analyzed using this method. The experimental measurements were applied for the evaluation of DEM simulations. The clustering DEM model provided in this study extends the conventional DEM model by incorporating actual microstructure of materials into simulations. Real irregular particles were represented by clusters of balls in the clustering DEM model while spherical particles were employed in the conventional DEM model. The PFC3D commercial software was applied for 3D DEM simulations of the compression test and the direct shear test. Compared to the conventional DEM model, the clustering DEM model demonstrated a better capability of predicting both the micro and macro behaviors of granular materials, including dilation, strength, particle kinematics, and fabric evolution. Fabric distribution was investigated for both the conventional DEM model and the clustering DEM model. The clustering DEM model described the fabric distribution of actual materials more precisely. This feature enabled it to simulate micro-macro behaviors of materials more accurately. A theoretic stress-fabric tensor relationship was also evaluated using the simulated stress and fabric distributions based on the actual microstructure of a real material. This relationship incorporated the anisotropic microstructure characteristics of the material. Whether it can better describe behaviors of granular materials was evaluated in this study. Generally, this research provides a more inherent understanding of granular materials through both DEM simulations and experimental validations

Progress in generation kinetics studies of coal-derived gases

Hydrocarbon-generation kinetics is of applicable significance in the study of coal-derived gas pool formation. Its research progress in recent years includes: in combination with geothermal history, it is used as a tool to evaluate source rocks dynamically and depict the change of source kitchen with geological time; according to the carbon isotope fractionation kinetics, a more precise model of identifying coal-derived gas is developed, which contains the kinetic relationship among gas compounds; the combination of compositional kinetics and carbon isotopic kinetics leads to the study method of accumulation processes of coal-derived gases, which is constrained precisely by multi kinetic indices; with the reservoir records, generation kinetics is used to study the whole gas life including generation, charge and alteration. The problems that need investigation are generation kinetics of coal-derived gas at low maturity, pressure effects on gas generation, minerals and water influences, and kinetics of residual soluble organic matter at high maturity. Key words: coal, natural gas, coal-derived gas, generation kinetics, progres

Estimating multiple option Greeks simultaneously using random parameter regression

The derivatives of option prices with respect to underlying parameters are commonly referred to as Greeks, and they measure the sensitivities of option prices to these parameters. When the closed-form solutions for option prices do not exist and the discounted payoff functions of the options are not sufficiently smooth, estimating Greeks is computationally challenging and could be a burdensome task for high-dimensional problems in particular. The aim of this paper is to develop a new method for estimating option Greeks by using random parameters and least-squares regression. Our approach has several attractive features. First, just like the finite-difference method it is easy to implement and does not require explicit knowledge of the probability density function and the pathwise derivative of the underlying stochastic model. Second, it can be applied to options with discontinuous discounted payoffs as well as options with continuous discounted payoffs. Third, and most importantly, we can estimate multiple derivatives simultaneously. The performance of our approach is illustrated for a variety of examples with up to fifty Greeks estimated simultaneously. The algorithm is able to produce computationally efficient results with good accuracy

Symmetrically Related Construction and Optical Properties of Two Noncentrosymmetric 3D Iodides of d¹⁰ Cation (Cu⁺, Ag⁺) Based on the <i>N</i>‑Benzylpyridinium and Its Supramolecular Interactions

Two noncentrosymmetric compounds, namely, [<i>N</i>-Bz-Py]₂­[Cu₆I₈] (<b>1</b>) and [<i>N</i>-Bz-Py]₄­[Ag₉I₁₃] (<b>2</b>) (<i>N</i>-Bz-Py⁺ = <i>N</i>-benzylpyridinium), with three-dimensional open frameworks, were synthesized solvothermally via in situ benzylation of pyridine. <b>1</b> is constructed from 3-connected Cu₃I₇ secondary building units (SBUs) with chiral (10,3)-a topology, while the occluded <i>N</i>-Bz-Py⁺ forms a complementary supramolecular (10,3)-a net via π–π interactions. <b>2</b> is characteristic of acentric connections of trimeric Ag₃I₈ and hexamer Ag₆I₁₂ SBU, while <i>N</i>-Bz-Py⁺ in the channels aggregates into asymmetrically supramolecular chains via π–π interactions. Remarkable structural correlations imply the unique amplification and transfer of asymmetric information from V-shaped <i>N</i>-Bz-Py⁺ to organic supramolecular nets and inorganic frameworks, which are confirmed by their second harmonic generation responses. Adsorption spectra reveal their semiconductive nature (2.52 eV for <b>1</b> and 3.02 eV for <b>2</b>) and interesting reversible thermochromism for <b>1</b> based on the intermolecular charge transfer

Functional identity drives tree species richness-induced increases in litterfall production and forest floor mass in young tree communities

- Forest floor accumulation is a key process that influences ecosystem carbon cycling. Despite evidence suggesting that tree diversity and soil carbon are positively correlated, most soil carbon studies typically omit the response of the forest floor carbon to tree diversity loss. - Here, we evaluated how tree species richness affects forest floor mass and how this effect is mediated by litterfall production and forest floor decay rate in a tree diversity experiment in a subtropical forest. - We observed that greater tree species richness leads to higher forest floor accumulation at the soil surface through increasing litterfall production – positively linked to functional trait identity (i.e. community-weighted mean functional trait) rather than functional diversity – and unchanged forest floor decay. Interestingly, structural equation modelling revealed that this lack of overall significant tree species richness effect on forest floor decay rate was due to two indirect and opposite effects cancelling each other out. Indeed, tree species richness increased forest floor decay rate through increasing litterfall production while decreasing forest floor decay rate by increasing litter species richness. - Our reports of greater organic matter accumulation in the forest floor in species-rich forests suggest that tree diversity may have long-term and important effect on ecosystem carbon cycling and services

The immunosuppression effects of deforolimus (ridaforolimus, AP23573) on allograft organ transplantation

Abstract Objects We conducted this study to confirm the immunosuppression effect of Deforolimus in heart allotransplantation and find its mechanism. Material and methods We used vitro methods to confirm the immunosuppression of Deforolimus in T cell subgroups. Then, we conducted heart allotransplantation from BALB/c donors to C57BL/6 recipients with the oral administration of Deforolimus or blank solvent to contrast the immunosuppression effect in vivo. We used the flow cytometry（）, clone anergy test, ELISA (enzyme‐linked immunosorbent assay), apoptosis test, and lymphocyte translation (LT) to find the mechanism of Deforolimus’ immunosuppressive action. Results Studies in vitro demonstrated that Deforolimus had immunosuppressive action. Studies in vivo demonstrated that Deforolimus could inhibit the immune system of the heart allotransplantation recipients to extend the recipients’ life. The mechanisms of Deforolimus’ immunosuppressive action included induction of Tregs (regulatory T cells), induction of T cells anergy, and decreasing proportion of T cells in spleens and lymph nodes. Conclusion Deforolimus suppressed the immunological rejection of mouse cardiac allotransplantation which laid the foundation of Deforolimus applying to solid organ allotransplantation