数据库系统安全模型的设计

本文首先分析了有关数据库安全所需要解决的几个问题,并基于 discretion 和mandatory 存取策略,以及完整性和数据库加密策略,提出了一个较完整的数据库系统的安全模型。     

TURBO PROLOG 2.0开发环境的汉化

本文讨论了目前广泛使用的编译型逻辑程序设计语言TURBO PROLOG2.0开发环境的汉化问题。文中分析了TURBO PROLOG 2.0显示程序的一些特点以及目前使用的汉化版本存在的几个主要问题和汉化时应注意的几个问题,最后给出了2个典型程序段汉化的例子。     

野战防空作战系统的仿真策略

在分析野战防空作战系统特点的基础上,讨论该系统的仿真策略,提出了主动实体交替扫描的仿真策略,并给出了非形式化的描述。该方法体现了事件调度法和活动扫描法的优点,使之更适合于仿真带有对抗性离散事件系统,因此,对其它作战系统,尤其是战术C~3I 系统的仿真,也是适用的。     

野战防空C~3I与防空兵作战指挥控制

陆军防空兵自动化指挥系统已作为防空作战效能“倍增器”列入国家军装武器发展规划,并在近期可能交付防空部队使用。这一新装备、新技术的出现和发展必然会引起防空作战指挥的变化。在分析防空兵指挥自动化对防空作战指挥影响的基础上,对如何发挥防空兵自动化指挥的防空作战效能和防空兵指挥自动化需迫切解决的一些问题加以探讨。     

社会系统运行理论与我国现阶段政策的制定

本文阐述了社会系统运行理论的初步框架,并以其分析社会系统的组织化状态与政策在其自组织中的功能;在剖析不同类型经济系统利弊的基础上,提出了我国现阶段政策制定的基本思路。     

建筑消防设施施工中产生隐患研究

建筑消防设施施工质量的好坏,直接关系到消防设施能否正常运行。从消防给水管网、室内外消火栓系统、自动喷水灭火系统几个方面探讨了建筑消防工程施工中存在的问题,并分析了存在问题的原因,从监督管理、施工现场检查、消防设施检验中介机构作用的发挥、从业人员培训等方面提出预防建筑消防设施施工中产生隐患的措施。     

Prediction of concentration of toxic gases produced by detonation of commercial explosives by thermochemical equilibrium calculations

An adverse effect resulting from explosive mine blasts is the production of toxic nitrogen oxides (NO and NO₂) and carbon monoxide (CO). The empirical measurements of the concentration of toxic gases showed that it depends not only on the composition of an explosive and properties of its ingredients but also on several other parameters, such as volume of blasting chamber, explosive charge mass and design, confinement characteristics, surrounding atmosphere, etc. That explains why measured concentrations of toxic gases reported in literature significantly differ.In this paper, we discuss the possibility of theoretical prediction of the concentration of toxic gases by thermochemical equilibrium calculation applying two models: ideal detonation model and deflagration model. It can be demonstrated that thermochemical calculations can provide a good estimation of the measured concentrations and reproduce experimentally obtained effects of additives on the production of toxic gases. It was also found that the ideal detonation model applies to heavily confined explosive charges, while the deflagration model is more suitable for low detonation velocity explosives with light confinement.     

Numerical investigation of the failure mechanism of cubic concrete specimens in SHPB tests

Cylindrical specimens are commonly used in Split Hopkinson pressure bar (SHPB) tests to study the uniaxial dynamic properties of concrete-like materials.In recent years,true tri-axial SHPB equipment has also been developed or is under development to investigate the material dynamic properties under tri-axial impact loads.For such tests,cubic specimens are needed.It is well understood that static material strength obtained from cylinder and cube specimens are different.Conversion factors are obtained and adopted in some guidelines to convert the material strength obtained from the two types of specimens.Previous uniaxial impact tests have also demonstrated that the failure mode and the strain rate effect of cubic specimens are very different from that of cylindrical ones.However,the mechanical background of these findings is unclear.As an extension of the previous laboratory study,this study performs numerical SHPB tests of cubic and cylindrical concrete specimens subjected to uniaxial impact load with the validated numerical model.The stress states of cubic specimens in relation to its failure mode under different strain rates is analyzed and compared with cylindrical specimens.The detailed analyses of the numerical simulation results show that the lateral inertial confinement of the cylindrical specimen is higher than that of the cubic specimen under the same strain rates.For cubic specimen,the corners are more severely damaged because of the lower lateral confinement and the occurrence of the tensile radial stress which is not observed in cylindrical specimens.These results explain why the dynamic material strengths obtained from the two types of specimens are different and are strain rate dependent.Based on the simulation results,an empirical formula of conversion factor as a function of strain rate is proposed,which supplements the traditional conversion factor for quasi-static material strength.It can be used for transforming the dynamic compressive strength from cylinders to cubes obtained from impact tests at different strain rates.     

Dynamic modeling and parameter identification of a gun saddle ring

In this study, a theoretical nonlinear dynamic model was established for a saddle ring based on a dynamic force analysis of the launching process and the structure according to contact-impact theory. The ADAMS software was used to build a parameterized dynamic model of the saddle ring. A parameter identification method for the ring was proposed based on the particle swarm optimization algorithm. A loading test was designed and performed several times at different elevation angles. The response histories of the saddle ring with different loads were then obtained. The parameters of the saddle ring dynamic model were identified from statistics generated at a 50° elevation angle to verify the feasibility and accuracy of the proposed method. The actual loading history of the ring at a 70° elevation angle was taken as the model input. The response histories of the ring under these working conditions were obtained through a simulation. The simulation results agreed with the actual response. Thus, the effectiveness and applicability of the proposed dynamic model were verified, and it provides an effective method for modeling saddle rings.     

Study on dynamic response of multi-degree-of-freedom explosion vessel system under impact load

In order to study the dynamic response and calculate the axial dynamic coefficient of the monolayer cylindrical explosion vessel, the wall of vessel is simplified as a multi-degree-of-freedom (MDoF) undamped elastic foundation beam. Decoupling the coupled motion equation and using Duhamel's integrals, the solutions in generalized coordinates of the equations under exponentially decaying loads, square wave loads and triangular wave loads are calculated. These solutions are consistent in form with the solutions of single-degree-of-freedom (SDoF) undamped forced vibration simplified model. Based on the model, equivalent MDoF design method (also called MDoF dynamic coefficient method) of cylindrical explosion vessel is proposed. The traditional method can only predict the dynamic coefficient of torus portion around the explosion center, but this method can predict that of the vessel wall at any axial n dividing point position. It is verified that the prediction accuracy of this model is greatly improved compared with the SDoF model by comparing the results of this model with SDoF model and numerical simulation in different working conditions. However, the prediction accuracy decreases as the scaled distance decreases and approaches the end of the vessel, which is related to the accuracy of the empirical formula of the implosion load, the simplification of the explosion load direction, the boundary conditions, and the loading time difference.