Decomposition mechanisms of nuclear-grade cationic exchange resin by advanced oxidation processes:Statistical molecular fragmentation model and DFT calculations

The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this paper,a simplified model of cationic exchange resin is proposed,and the degradation processes of cationic resin monomer initiated by hydroxyl radicals(·OH)are clarified by combining statistical molecular fragmentation(SMF)model and density functional theory(DFT)calculations.The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation.The meta-position of the sulfonic group on the benzene ring is the most active site,and the benzene ring without the sulfonic group has a certain reactivity.The C11-C14 and C17-C20 bonds,on the carbon skeleton,are the most easily broken.It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation,carbon skeleton cleavage and benzene ring separation.The decomposition mechanisms found through the combination of physical models and chemical calculations,provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.

New approach to assess sperm DNA fragmentation dynamics： Fine-tuning mathematical models

Background： Sperm DNA fragmentation（sDF） has been proved to be an important parameter in order to predict in vitro the potential fertility of a semen sample. Colloid centrifugation could be a suitable technique to select those donkey sperm more resistant to DNA fragmentation after thawing. Previous studies have shown that to elucidate the latent damage of the DNA molecule, sDF should be assessed dynamically, where the rate of fragmentation between treatments indicates how resistant the DNA is to iatrogenic damage. The rate of fragmentation is calculated using the slope of a linear regression equation. However, it has not been studied if s DF dynamics fit this model. The objectives of this study were to evaluate the effect of different after-thawing centrifugation protocols on sperm DNA fragmentation and elucidate the most accurate mathematical model（linear regression, exponential or polynomial） for DNA fragmentation over time in frozen-thawed donkey semen.Results： After submitting post-thaw semen samples to no centrifugation（UDC）, sperm washing（SW） or single layer centrifugation（SLC） protocols, sD F values after 6 h of incubation were significantly lower in SLC samples than in SW or UDC.Coefficient of determination（R-2） values were significantly higher for a second order polynomial model than for linear or exponential. The highest values for acceleration of fragmentation（aSDF） were obtained for SW, fol owed by SLC and UDC.Conclusion： SLC after thawing seems to preserve longer DNA longevity in comparison to UDC and SW. Moreover,the fine-tuning of models has shown that sDF dynamics in frozen-thawed donkey semen fit a second order polynomial model, which implies that fragmentation rate is not constant and fragmentation acceleration must be taken into account to elucidate hidden damage in the DNA molecule.

PROGRESSIVE FRAGMENT MODELING OF FAILURE WAVE IN CERAMICS UNDER PLANAR IMPACT LOADING

Polycrystalline ceramics have heterogeneous meso-structures which result in high singularity in stress distribution. Based on this, a progressive fragment model was proposed which describes the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave was characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from collapse of original pores. Numerical simulation of the free surface velocity was performed in good agreement with planar impact experiments on 92.93% aluminas at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.

A Model Comparison Study of Fragment Production in 140 A MeV 58,64Ni+9Be Reactions

The cross sections of fragments produced in the 140 A MeV58,64Ni＋9 Be projectile fragmentation reactions are calculated by using the antisymmetrized molecular dynamics （AMD） model, the modified statistical abrasion- ablation （SAA） model, and the empirical EPAX2/EPAX3 formulae. The Gogny-gO interaction is taken as the effective nucleon-nucleon interaction in the AMD calculation, and the decays of fragments obtained from the AMD results are calculated by using the GEMINI code. The calculated cross sections of fragments are compared.

Assessment of forest geospatial patterns over the three giant forest areas of China

Geospatial patterns of forest fragmentation over the three traditional giant forested areas of China （Northeastern, southwestern and Southern China） were analyzed comparatively and reported based on a 250-m resolution land cover dataset. Specifically, the spatial patterns of forest fragmentation were characterized by combining geospatial metrics and forest fragmentation models. The driving forces resulting in the differences of the forest spatial patterns were also investigated. Results suggested that forests in southwest China had the highest severity of forest fragmentation, followed by south region and northeast region. The driving forces of forest fragmentation in China were primarily the giant population and improper exploitation of forests. In conclusion, the generated information in the study provided valuable insights and implications as to the fragmentation patterns and the conservation of hiodiversity or genes, and the use of the chosen geospatial metrics and forest fragmentation models was quite useful for depicting forest fragmentation patterns.

Numerical assessment of spacing–burden ratio to effective utilization of explosive energy

The spacing–burden(S/B) ratio plays significant role on rock fragmentation and proper utilization of explosive energy to minimize the undesirable damage.Low S/B ratio generates fine fragments due to pressure rings coalescence of two blast holes,whereas boulder generations were observed above optimum S/B ratio.Both conditions are not acceptable because of wastage of explosive energy.Therefore,to resolve this issue,a numerical model study was conducted to optimize the S/B ratio and to envisage its effect on rock fragmentation based on utilization of explosive energy.Finite element simulation tool was used to see the extent of two blast hole influence area variation with varying S/B ratio.The better results were obtained at S/B ratio of 1:2 with optimum utilization of peak explosive energy.The performance was observed based on peak kinetic energy,peak pressure,radial and hoop stresses on centre of the two blast holes,where pressure rings coalescence.

An Isoratio Method and an Isoratio Scaling Phenomenon in Heavy-Ion Collisions

An isoratio method is proposed to study the chemical potential of neutrons(protons) from the yield ratio of isotopes(isotones) differing in neutron-excess(I = N- Z). The measured fragments in the 140 A MeV ^(40),^(48) Ca and^(58),^(64) Ni +~9Be reactions, as well as those in the simulated^(58),^(64) Ni +~9Be reactions by using the antisymmetric molecular dynamics(AMD) model plus the secondary decay model gemini, have been adopted to perform the isoratio analysis.The results of the isoratio method verify that they are similar to that of the well known isoscaling method. The isoratio scaling phenomenon suggested by the isoratio method has also been found in the measured data and the fragments simulated by the AMD + gemini models.