基于Hamilton-Jacobi-Bellman方程求解保险业最优投资策略

在经典复合泊松模型中，保险公司将资金投入一个风险投资过程和一个无风险投资过程.当索赔的分布确定后，运用随机控制中的HJB方程最小化保险公司的破产概率，在已知投资规模或投资组合的情况下求解二者中的另一项，进而得到最优投资策略并讨论各种策略的运用对破产概率的影响.解决保险公司的投资资金分配问题，在实际应用中具有一定的参考价值.     

二元立木材积方程的检验与更新方法探讨

森林蓄积是森林资源监测的重要指标,用于森林蓄积估计的立木材积表作为行业标准已经颁布使用了30多年,需要进行检验、修订或更新。以东北落叶松(Larix)和南方马尾松(PinusMassoniana)立木材积数据为例,探讨二元立木材积方程的检验和更新方法。结果表明:采用回归方程的适应性检验方法,可以对原来的二元立木材积方程的适应性进行检验;两个树种原来的材积方程存在明显的系统偏差,总相对偏差和平均系统偏差均达到了10%左右,已经不再适用于现阶段的森林蓄积量估计;新建立的两个树种的二元立木材积方程,其平均预估误差都在3%以内,达到了预定的精度要求。     

Vermicompost and humic fertilizer improve coastal saline soil by regulating soil aggregates and the bacterial community

Soil salinity, poor soil structure and macronutrient deficiencies are three important limitations responsible for poor crop yields in coastal saline soils. Here we used humic fertilizer and vermicompost to ameliorate salt-induced stress by regulating the soil bacterial community and aggregates in different growth stages of winter wheat. Soil salinity, aggregates, nutrient availability, the soil bacterial community from next-generation high-throughput sequencing, and wheat yield were determined in this study. The results indicated that humic fertilizer and vermicompost could efficiently alleviate salt accumulation (by 16.8–41.1 and 13.3–42.7%, respectively) in topsoil by inhibiting resalinization and increase the proportion of soil macroaggregates (by 26.7–85.9 and 31.6–105.5%, respectively) in the wheat growth stages. Skermanella, Arthrobacter and Sphingomonas were the dominant genera in the study soil. Humic fertilizer and vermicompost could improve soil total N (by 4.7–15.6 and 2.4–25.2%, respectively), available P (by 15.9 and 7.3–64.4%, respectively), and exchangeable K (by 3.9–18.4 and 0.7–12.1%, respectively) by increasing the abundance of Arthrobacter and Pedobacter, consequently improving shoot biomass (by 41.1 and 52.8%, respectively) and grain yield (by 45.1 and 60.2%, respectively) of wheat. Therefore, vermicompost and humic fertilizer ameliorate salt-induced stress in coastal saline soil through the integrated improvement of soil physical, chemical and biological properties.     

依赖于参数的泛函微分方程正周期解的存在性

考虑依赖于参数的泛函微分方程x′(t)=-a(t)g(x(t))x(t)+λb(t)f(t,x(t-τ_1(t)),x(t-τ_2(t)),…,x(t-τ_n(t))).利用不动点定理,得到了上述方程正周期解存在的充分条件。     

大海林林业局落叶松人工林削度方程的研究

以大海林林业局太平沟林场不同年龄、不同密度及不同立地条件的落叶松人工林为研究对象，采用非线性回归模型的参数估计方法拟合5个削度方程，通过计算每个削度方程的拟合统计量来确定最优削度方程模型；最后通过独立检验样本数据对5个模型进行检验，验证模型Ⅲ为最优削度方程。     

测度链上一类滞后动力微分方程的解的性质

本文在测度链上研究了一类滞后动力微分方程的解的性质,得到了微分方程的解的零点分布定理。     

Fisher方程的孤子解

利用一维波动方程的解具有行波解形式的特解的特点，给出行波解的形式．通过变量替换，再引入双曲正切函数作为独立变量，并利用双曲正切函数其独特的微分特性，给出一组变换，将Fisher方程简化为常微分方程，由此得出它的解．此解可做为物理学中非线性方程的实例．尽管不是所有的非线性波动方程都可以用此法来处理，但它缩短了线性和非线性波动理论之间的距离。     

Nitrous oxide emissions following seasonal freeze-thaw events from arable soils in Northeast China

Seasonal soil freeze-thaw events may enhance soil nitrogen transformation and thus stimulate nitrous oxide(N_2O)emissions in cold regions.However,the mechanisms of soil N_2O emission during the freeze-thaw cycling in the field remain unclear.We evaluated N_2O emissions and soil biotic and abiotic factors in maize and paddy fields over 20 months in Northeast China,and the structural equation model(SEM)was used to determine which factors affected N_2O production during non-growing season.Our results verified that the seasonal freeze-thaw cycles mitigated the available soil nitrogen and carbon limitation during spring thawing period,but simultaneously increased the gaseous N_2O-N losses at the annual time scale under field condition.The N_2O-N cumulative losses during the non-growing season amounted to 0.71 and 0.55 kg N ha~(–1) for the paddy and maize fields,respectively,and contributed to 66 and 18%of the annual total.The highest emission rates(199.2–257.4μg m~(–2) h~(–1))were observed during soil thawing for both fields,but we did not observe an emission peak during soil freezing in early winter.Although the pulses of N_2O emission in spring were short-lived(18 d),it resulted in approximately80%of the non-growing season N_2O-N loss.The N_2O burst during the spring thawing was triggered by the combined impact of high soil moisture,flush available nitrogen and carbon,and rapid recovery of microbial biomass.SEM analysis indicated that the soil moisture,available substrates including NH_4~+and dissolved organic carbon(DOC),and microbial biomass nitrogen(MBN)explained 32,36,16 and 51%of the N_2O flux variation,respectively,during the non-growing season.Our results suggested that N_2O emission during the spring thawing make a vital contribution of the annual nitrogen budget,and the vast seasonally frozen and snow-covered croplands will have high potential to exert a positive feedback on climate change considering the sensitive response of nitrogen biogeochemical cycling to the freeze-thaw disturbance.     

一种简便确定支腿纵横跨距的方法

文章通过对合力轨迹圆方程的研究,提出了一种简便快捷确定支腿纵横跨距的新方法,此方法可适用于固定底盘支腿且有回转结构上车的工程机械产品。     

Assessment of Phosphorus Requirements of Wheat on Different Textured Alluvial Soils through Freundlich Type Equations

Once soil solution phosphorus (P) level optimum for plant growth is identified, P adsorption isotherms or their equations can further be used to estimate fertilizer P rates required to adjust this desired soil solution P level to obtain maximum yield. Surface soil samples were collected from a farmer's field area and research area. An adsorption study was conducted on Ustic Endoaquerts (S₁ soil), Typic Calciargids (S₂ soil), and Typic Torripsamments (S₃ soil) to develop the Freundlich-type equations. Phosphorus adsorption data were obtained by equilibrating 10-g soil samples in 100 mL of 0.01 M calcium chloride (CaCl₂) containing various amounts of monopotassium phosphate (KH₂PO₄). Values of 1/n (slope) ranged from 0.4827 to 0.6452 L kg^?1. Based on 1/n values, it was inferred that each of the two S₁ and S₃ soils was homogeneous and S₂ was not. The K_F (mg P kg^?1) values of S₁, S₂, and S₃ soils were 92.45, 55.81, and 23.38, respectively. The highest amount of P (92.45 mg kg^?1) was adsorbed at unit EPC in S₁ soil, whereas the lowest amount (23.38 mg P kg^?1) was adsorbed in S₃ soil. Thereafter, 11 P fertilizer doses were calculated by these Freundlich-type equations to adjust different estimated soil solution P levels that were designated as treatments (0.05 to 0.90 mg L^?1). Then field experiments on wheat (cv. Inqalab-91) were conducted according to a randomized complete block design (RCBD) on these soils to determine internal (plant tissue), external (soil solution), and fertilizer P requirements. Maximum wheat gain yield (Mg ha^?1) was 6.82 with T₅ (0.25 mg P L^?1) on S₁ soil, 5.96 with T₅ (0.25 mg P L^?1) on S₂ soil, and 4.97 with T₇ (0.40 mg P L^?1) on S₃ soil that was obtained by application of 196 kg P₂O₅ ha^?1 on S₁ soil, 142 kg P₂O₅ ha^?1 on S₂ soil, and 78 kg P₂O₅ ha^?1 on S₃ soil. Internal P concentration (%) associated with 95% of maximum wheat yield at booting stage was 0.32 in S₁, 0.21 in S₂, and 0.33 in S₃ soil. In straw, it was 0.123% in S₁, 0.080% in S₂, and 0.108% in S₃ soil. The internal P requirement of wheat grain was 0.39% in S₁, 0.40% in S₂, and 0.37% in S₃ soil. External soil solution P requirement (ESPR) for 95% of maximum yield of wheat was 0.45 mg L^?1 in S₁ soil, 0.34 mg L^?1 in S₂ soil, and 0.44 mg L^?1 in S₃ soil. Quantity of P₂O₅ corresponding to ESPR values were 217 kg ha^?1 on S₁, 123 kg ha^?1 on S₂, and 60 kg ha^?1 on S₃ soil. Putting ESPR values in the respective Freundlich-type equation, P fertilizer rates (kg P₂O₅ ha^?1) were estimated that were 282 on S₁, 167 on S₂, and 83 on S₃ soil; Practically, 262, 156, and 78 kg P₂O₅ ha^?1 was applied in the field to adjust soil solution P level (mg L^?1) at 0.40 (T₇), 0.30 (T₆), and 0.40 (T₇) in S₁, S₂, and S₃ soil, respectively, that are somewhat less than determined ESPR values. Phosphorous doses applied to achieve a desired EPAS value or estimated from graphs against predicted ESPR values, or calculated from corresponding Freundlich-type equations using desired ESPR values are in close proximity to one another. Therefore, any of the techniques can be used interchangeably to estimate the P fertilizer requirement for optimum wheat yield.