Non-dimensional analysis on blast wave propagation in foam concrete:Minimum thickness to avoid stress enhancement

Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.

Soil Fertility Comparison between Rotations of Tobacco-Rice (TR) and Rape-Rice (RR)

Tobacco-planting plays an important role in ensuring the high-quality tobacco raw materials supply and the local social and economic development in Chenzhou City. In recent years whether tobacco-planting is better for the maintenance and improvement of soil fertility than other crop-planting has been highly concerned. In this study, 16 soil fertility indicators and soil integrated index (IFI) were compared by 21 pairs of fields in Chenzhou city under the rotations of tobacco-rice (TF) and rice-rice (RR), and results showed that, comparing the mean values of soil fertility indicators, the contents of OM, TN, AN, AK, S and IFI were extremely significantly higher in TR than those in RR (p < 0.01), the contents of Cu, Ca, Mg and Fe were significantly higher in TR than those in RR (p < 0.05), but Mn content was significantly lower in TR than those in RR (p < 0.05). Meanwhile the contents of TP, TK and AP were insignificantly higher in TR than those in RR, and the contents of B, Mo and Zn were insignificantly lower in TR than those in RR. The above significant differences in soil fertility indicators were mainly due to relatively higher fertilizer inputs and less nutrient removal during tobacco-growing season than during rape-growing season, the net increase of N, P2O5 and K2O are 8.61, 5.25 and 24.89 kg per 667 m2 respectively in tobacco-growing season, while the net decrease of N, P2O5 and K2O are 8.88, 4.70 and 4.62 kg per 667 m2 respectively in rape-growing season. C.V. of soil fertility indicators and IFI were meanly lower in TR (52.25% and 15.95%, respectively) than those in RR (63.07% and 22.12%, respectively). Comparatively, tobacco-planting can improve soil fertility better than rape-planting when rotated with late rice in Chenzhou city. For tobacco-planting, Mg fertilizer should be applied for 23.8% TR fields, while more N, K, Ca, Mg, S and B fertilizers should be applied for 42.86%, 23.81%, 14.29%, 47.62%, 80.95% and 47.62% RR fields, respectively.

Study on Chemical Characteristics of Rainfall in Tobacco-Growing Regions of Chenzhou, Hunan Province

In order to clarify the chemical properties of rainfall in typical tobacco areas in Chenzhou City, Hunan Province, and analyze its potential for soil and flue-cured tobacco planting, rainfall samples in 2020 were collected by rainfall instruments in Fangyuan Town and Aoquan Town of Guiyang County, and the chemical properties that are closely related to the quality of flue-cured tobacco were determined, such as pH, EC, total nitrogen (TN), nitrate nitrogen (), ammonium nitrogen () and ion concentrations (K+, Na+, Ca2+, Mg2+, , Al3+, , Cl−,). The results show that the pH values of rainfall samples at Fangyuan and Aoquan monitoring sites are in the range of 4.92 - 6.17 and 4.93 - 5.69 respectively, with an average of 5.27 and 5.27 respectively. The acid rain characteristic is very obvious, which is mainly dominated by . The variation of rainfall EC has seasonal characteristics. EC is low from January to September, in the range of 6.09 - 56.72 and 11.83 - 30.93 μS/cm respectively, besides, it is high from October to December, in the range of 102.63 - 174.60 and 25.05 - 86.37 μS/cm respectively. The annual deposition of TN was 22.19 and 20.76 kg/hm2/yr respectively, which were higher than that in the western regions with less human disturbance, but lower than or equal to that in the developed agricultural regions in eastern China. The proportion of in the annual deposition of TN was higher than that of at two monitoring sites, with an average of 56.51% and 38.86% respectively. Ammonia volatilization from agricultural activities contributed more to rainfall nitrogen content. The ratios of ammonium nitrogen to nitrate nitrogen deposition at two monitoring points were 1.84, 1.81, 1.86 and 1.34, 1.46, and 1.29 during the whole year, summer and autumn, winter and spring respectively. The ratio is higher in summer and autumn than in winter and spring. The weighted average equivalent concentrations of the main ions at two monitoring sites were 238.88 μeq/L and 211.21 μeq/L respectively, and the orders of the ion concentrations were slightly different. Both the concentrations of and are higher, while Mg2+, and Al3+ are lower. , and are mainly from human activities with a contribution rate between 91.90% and 99.35%. Ca2+ mainly comes from soil and ground dust, besides, Cl− and Mg2+ mainly come from marine sources and K+ mainly comes from terrestrial sources. In general, the acidic rainfall and higher concentration are beneficial to reducing the high pH value of soil in Aoquan tobacco area and improving the quality of flue-cured tobacco. Higher concentrations of and in rainfall are not conducive to the improvement of flue-cured tobacco quality, because of the high content of soil available sulfur in Chenzhou tobacco area and the characteristics of flue-cured tobacco’s preference for ammonium.

Available Contents and Spatial Distribution of Soil Microelements of Tobacco Fields in Liupanshui City

The contents of soil microelements can affect the growth, yield and quality of tobacco, but it is not clear of the status quo of soil microelements in tobacco fields in Liupanshui city. In this study, soil samples of the plough layers (0 - 20 cm) were collected from January to March in 2021 from 500 typical tobacco fields in Liupanshui City (100, 180 and 220 fields in Zhongshan, Shuicheng and Panzhou, respectively), the particle size composition, pH, the contents of organic matter (OM), available boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) were measured and discussed. the results show that the mean contents of B, Cu, Fe, Mn, Mo and Zn are 0.92, 2.55, 66.47, 47.26, 0.39 and 3.96 mg/kg, respectively, and among which, B, Cu and Zn are at the high grades while Fe, Mn and Mo are at the very-high grades. There are significant differences in B, Fe and Zn among the three regions, while Cu is significantly different between Zhongshan and Shuicheng, Mn is significantly different between Panzhou with Zhongshan and Shuicheng, and Mo is significantly different between Zhongshan and Panzhou. The proportions of fields deficient in microelements are relatively low, no field is Fe-deficient, and the fields deficient in Mo, B, Cu, Zn and Mn are only account for 10.40%, 9.40%, 7.40%, 2.80% and 2.00% of the total fields respectively. B-deficient fields (green and light green colors, the same below) are mainly scattered in the northwest of Zhongshan and in the north and south of Panzhou, Cu-deficient fields mainly in the middle of Shuicheng and Panzhou, Mn-deficient fields mainly in northern Zhongshan, central Shuicheng and north of Panzhou. Mo-deficient fields are mainly in the middle of Shuicheng and the middle and east of Panzhou, while Zn-deficient fields are mainly in the middle of Shuicheng and the middle and east of Panzhou. Altitude is negatively correlated with Mn (P < 0.05), pH is negatively correlated with B (P < 0.05), Fe and Mn (P < 0.01), and OM is positively correlated with Fe and Zn (P < 0.01). Sand is negatively correlated with B (P < 0.05), Mn and Mo (P < 0.01), but positively correlated with Zn (P < 0.01). Silt is positively correlated with Mo (P < 0.05);clay is positively correlated with B (P < 0.05) and Mn (P < 0.01), but negatively correlated with Zn (P < 0.01). In conclusion, most of the fields do not need to apply micro-fertilizers in Liupanshui, but the fields deficient in microelements should be considered to use the corresponding fertilizers.

Study on Exchangeable Cation Determining Base Saturation Percentage of Soil in South China

Base saturation percentage (BSP) is an important soil chemical index in soil fertility and soil taxonomy. However, it is still unclear what exchangeable cation dominates BSP of soil in south China. Therefore, in this study, the data of BSPs and exchangeable H+, Al3+, Ca2+, Mg2+, K+ and Na+ of 109 and 45 horizon samples of 50 and 28 soil species in red soil and yellow soil groups in the Database of Chinese Soil Species were used to explore further the characteristics of BSPs and exchangeable cations as well as the correlation between BSPs and exchangeable cations. The results showed that the concentrations of exchangeable cations in both red soil and yellow soil groups were in an order of Al3+ (4.55 ± 1.47 and 4.22 ± 1.2 cmol(+)/kg) > Ca2+ (0.32 ± 0.21 and 0.36 ± 0.24 cmol(+)/kg) > H+ (0.23 ± 0.13 and 0.19 ± 0.10 cmol(+)/kg) > K+ (0.16 ± 0.09 and 0.16 ± 0.11 cmol(+)/kg) > Mg2+ (0.13 ± 0.09 and 0.11 ± 0.08 cmol(+)/kg) > Na+ (0.08 ± 0.06 and 0.11 ± 0.06 cmol(+)/kg). For red soil group, Al3+ concentration was significantly higher than those of other exchangeable cations, Ca2+ and H+ concentrations were significantly higher than those of K+, Mg2+ and Na+;while for yellow soil group, Ca2+, H+ and K+ concentrations were significantly higher than those of Mg2+ and K+. BSP of red soil group was codetermined by Ca2+, Al3+, Mg2+ and Na+, with the contributions of 33.81%, 19.82% and 14.49%, respectively;while BSP of yellow soil group was codetermined by Al3+, Ca2+, Mg2+, K+ and Na+, with the contributions of 24.91%, 21.55%, 19.91% and 14.21%, respectively. A higher concentration of exchangeable cation does not mean the higher importance of the cation to soil BSP.

Study on Climate Changes for Flue-Cured Tobacco Growth in Chenzhou City of Hunan Province

Chenzhou city is the most typical region of Nanling Hill Ecological Zone of flue-cured tobacco with of aroma style of burnt sweet and pure sweet in China and is the largest planting region of flue-cured tobacco in Hunan province. It is of significance to study the changes of climatic parameters with time because climate is the most important factor in determining the growth, yield and quality of flue-cured tobacco. In this study, the data of climatic parameters including cumulative sunshine hours(S), mean temperature (T) and cumulative precipitation (P)from 1952 to 2018 in Chenzhou were used to analyze their changes at the scales of year, whole field period and growing period of flue-cured tobacco. The results showed that at the scale of year, the cumulative S, mean T and cumulative P were ranged from 1029.0 h to 2072.1 h, from 17.1°C to 19.5°Cand from 897.1 mm to 2244.6 mm, with the means of 1449.7 h, 18.1°C and 1482.5 mm, respectively. At the scale of whole field period of flue-cured tobacco, the cumulative S, mean T and cumulative P were ranged from 298.1 h to 807.2 h, from 21.2°C to 23.9°C and from 416.7 mm to 1102.7 mm, with the means of 514.8 h, 22.3°C and 719.0 mm, respectively. At the scale of growing period of flue-cured tobacco, the annual cumulative S were ranged from 70.0 h to 257.2 h, from 77.3 h to 322.5 h and from 131.2 h to 300.3 h in the periods of rooting, flourishing and maturing with the means of 127.8 h, 190.4 h and 197.2 h, respectively. The mean temperatures were ranged from 14.2°C to 18.9°C, from 22.2°C to 26.1°C, and from 25.8°C to 29.6°C with the means of 16.4°C, 24.1°C and 28.0°C, respectively. The annual cumulative P were ranged from 69.9 mm to 553.9 mm, from 133.1 mm to 485.6 mm and from 46.4 mm to 356.8 mm in the periods of rooting, flourishing and maturing with the means of 262.5 mm, 299.9 mm and 153.9 mm, respectively. At the year scale, cumulative S annually decreased by 7.587 h, mean T annually increased by 0.02°C, while cumulative P changed irregularly with insignificantly increasing about by 0.184 mm annually. At the scale of whole field period of flue-cured tobacco, mean T annually increased by 0.0195°C, while both cumulative S and P changed irregularly with insignificantly decreasing by 1.64 h and 1.62 mm annually, respectively. At the scale of growing period of flue-cured tobacco, all climatic parameters changed irregularly except cumulative S in significant positive compound function in the maturing period. Meanwhile, the slight decreasing tendency of cumulative sunshine hours and the slight increasing tendency of cumulative precipitation are disadvantageous while the slight increasing tendency of cumulative precipitation in the maturing period is positive for the growth and quality of flue-cured tobacco.

Constitutive modelling of concrete material subjected to low-velocity projectile impact:insights into damage mechanism and target resistance

This paper presents a numerical study to improve the understanding of the complex subject of penetration and perforation of concrete targets impacted by low-velocity projectiles.The main focus is on the damage mechanisms and the major factors that account for the target resistance of the concrete.An improved continuous surface cap model recently proposed was employed.The model was first equipped with element erosion criteria and was adequately validated by comparisons with ballistic experiments.Comprehensive numerical simulations were carried out where the individual influence of tensile,shear,and volumetric behaviors(pore collapse)of a concrete target on its ballistic performance was investigated.Results demonstrated that cratering on the front face and scabbing on the rear face of the concrete target were mainly dominated by its tensile behavior.The major target resistance came from the second tunneling stage which was primarily governed by the shear and volumetric behaviors of the concrete.Particularly,this study captured the pore collapse-induced damage phenomenon during the high-pressure tunneling stage,which has been extensively reported in experiments but has usually been neglected in previous numerical investigations.

White Matter Abnormalities in Major Depression Biotypes Identified by Diffusion Tensor Imaging

Identifying data-driven biotypes of major depressive disorder(MDD) has promise for the clarification of diagnostic heterogeneity. However, few studies have focused on white-matter abnormalities for MDD subtyping. This study included 116 patients with MDD and118 demographically-matched healthy controls assessed by diffusion tensor imaging and neurocognitive evaluation.Hierarchical clustering was applied to the major fiber tracts, in conjunction with tract-based spatial statistics, to reveal white-matter alterations associated with MDD.Clinical and neurocognitive differences were compared between identified subgroups and healthy controls. With fractional anisotropy extracted from 20 fiber tracts, cluster analysis revealed 3 subgroups based on the patterns of abnormalities. Patients in each subgroup versus healthy controls showed a stepwise pattern of white-matter alterations as follows: subgroup 1(25.9% of patient sample),widespread white-matter disruption;subgroup 2(43.1% of patient sample), intermediate and more localized abnormalities in aspects of the corpus callosum and left cingulate;and subgroup 3(31.0% of patient sample),possible mild alterations, but no statistically significant tract disruption after controlling for family-wise error. The neurocognitive impairment in each subgroup accompanied the white-matter alterations: subgroup 1, deficits in sustained attention and delayed memory;subgroup 2, dysfunction in delayed memory;and subgroup 3, no significant deficits. Three subtypes of white-matter abnormality exist in individuals with major depression, those having widespread abnormalities suffering more neurocognitive impairments, which may provide evidence for parsing the heterogeneity of the disorder and help optimize typespecific treatment approaches.

Neurocognitive Graphs of First-Episode Schizophrenia and Major Depression Based on Cognitive Features

Neurocognitive deficits are frequently observed in patients with schizophrenia and major depressive disorder(MDD). The relations between cognitive features may be represented by neurocognitive graphs based on cognitive features, modeled as Gaussian Markov random fields. However, it is unclear whether it is possible to differentiate between phenotypic patterns associated with the differential diagnosis of schizophrenia and depression using this neurocognitive graph approach. In this study, we enrolled 215 first-episode patients with schizophrenia(FES), 125 with MDD, and 237 demographically-matched healthy controls(HCs). The cognitive performance of all participants was evaluated using a battery of neurocognitive tests. The graphical LASSO model was trained with aone-vs-one scenario to learn the conditional independent structure of neurocognitive features of each group. Participants in the holdout dataset were classified into different groups with the highest likelihood. A partial correlation matrix was transformed from the graphical model to further explore the neurocognitive graph for each group. The classification approach identified the diagnostic class for individuals with an average accuracy of 73.41% for FES vs HC, 67.07% for MDD vs HC, and 59.48% for FES vs MDD. Both of the neurocognitive graphs for FES and MDD had more connections and higher node centrality than those for HC. The neurocognitive graph for FES was less sparse and had more connections than that for MDD.Thus, neurocognitive graphs based on cognitive features are promising for describing endophenotypes that may discriminate schizophrenia from depression.

PREDICTION OF PROJECTILE PENETRATION AND PERFORATION BY FINITE CAVITY EXPANSION METHOD WITH THE FREE-SURFACE EFFECT

With a target treated as the incompressible Tresca and Mohr-Coulomb material, by assuming that cavity expansion produces plastic-elastic and plastic-cracked-elastic response region, the decay function for the free-surface effect is constructed for metal and geological tar- gets, respectively. The forcing function for oblique penetration and perforation is obtained by multiplying the forcing function derived on the basis of infinite target assumption with the de- cay function. Then the projectile is modeled with an explicit transient dynamic finite element code and the target is represented by the forcing function as the pressure boundary condition. This methodology eliminates discretizing the target as well as the need for a complex contact algorithm and is implemented in ABAQUS explicit solver via the user subroutine VDLOAD. It is found that the free-surface effect must be considered in terms of the projectile deformation, residual velocity, projectile trajectory, ricochet limits and critical reverse velocity. The numerical predictions are in good agreement with the available experimental data if the free-surface effect is taken into account.

Finite Spherical Cavity Expansion Method for Layering Effect

A decay function for the layering effect during the projectile penetrating into layered targets is constructed, which is obtained via the theoretical solution of a dynamically expanding layered spherical cavity with finite radius in the layered targets that are assumed to be incom- pressible Mohr-Coulomb materials. By multiplying the decay function with the semi-empirical forcing functions that account for all the constitutive behavior of the targets, the forcing functions for the layered targets are obtained. Then, the forcing functions are used to represent the targets and are applied on the projectile surface as the pressure boundary condition where the projectile is modeled by an explicit transient dynamic finite element code. This methodology is implemented into ABAQUS explicit solver via the user subroutine VDLOAD, which eliminates the need for discretizing the targets and the need for the complex contact algorithm. In order to verify the proposed layering effect model, depth-of-penetration experiments of the 37 mm hard core pro-jectile penetrating into three sets of fiber concrete and soil layered targets are conducted. The predicted depths of penetration show good agreement with the experimental data. Furthermore, the influence of layering effect on projectile trajectory during earth penetration is investigated. It is found that the layering effect should be taken into account if the final position and trajectory of the projectile are the main concern.