On the Elastic Vibration Model for High Length-Diameter Ratio Rocket with Attitude Control System

An elastic vibration model for high length diameter ratio spinning rocket with attitude control system which can be used for trajectory simulation is established. The basic theory of elastic dynamics and vibration dynamics were both used to set up the elastic vibration model of rocket body. In order to study the problem more conveniently, the rocket's body was simplified to be an even beam with two free ends. The model was validated by simulation results and the test data.

Uncertainty of Slope Length Derived from Digital Elevation Models of the Loess Plateau, China

Although many studies have investigated slope gradient uncertainty derived from Digital Elevation Models(DEMs), the research concerning slope length uncertainty is far from mature. This discrepancy affects the availability and accuracy of soil erosion as well as hydrological modeling. This study investigates the formation and distribution of existing errors and uncertainties in slope length derivation based on 5-m resolution DEMs of the Loess Plateau in the middle of China. The slope length accuracy in three different landform areas is examined to analyse algorithm effects. The experiments indicate that the accuracy of the flat test area is lower than that of the rougher areas. The value from the specific contributing area(SCA) method is greater than the cumulative slope length(CSL), and the differences between these two methods arise from the shape of the upslope area. The variation of mean slope length derived from various DEM resolutions and landforms. The slope length accuracy decreases with increasing grid size and terrain complexity at the six test sites. A regression model is built to express the relationship of mean slope length with DEM resolution less than 85 m and terrain complexity represented by gully density. The results support the understanding of the slope length accuracy, thereby aiding in the effective evaluation of the modeling effect of surface process.

Effect of calibration data series length on performance and optimal parameters of hydrological model

In order to assess the effects of calibration data series length on the performance and optimal parameter values of a hydrological model in ungauged or data-limited catchments （data are non-continuous and fragmental in some catchments）, we used non-continuous calibration periods for more independent streamflow data for SIMHYD （simple hydrology） model calibration. Nash-Sutcliffe efficiency and percentage water balance error were used as performance measures. The particle swarm optimization （PSO） method was used to calibrate the rainfall-runoff models. Different lengths of data series ranging from one year to ten years, randomly sampled, were used to study the impact of calibration data series length. Fifty-five relatively unimpaired catchments located all over Australia with daily precipitation, potential evapotranspiration, and streamflow data were tested to obtain more general conclusions. The results show that longer calibration data series do not necessarily result in better model performance. In general, eight years of data are sufficient to obtain steady estimates of model performance and parameters for the SIMHYD model. It is also shown that most humid catchments require fewer calibration data to obtain a good performance and stable parameter values. The model performs better in humid and semi-humid catchments than in arid catchments. Our results may have useful and interesting implications for the efficiency of using limited observation data for hydrological model calibration in different climates.

Mathematical model of determination of die bearing length in design of aluminum profile extrusion die

Based on the finite element simulation of profile extrusion process, the effect of local extrusion ratio, die bearing area and the distance between extrusion cylindrical center and local die orfice center on mental flow velocity was investigated. The laws of deformed metal flow on profile extrusion process were obtained. The smaller the local extrusion ratio, the faster the metal flow velocity; the smaller the area of die bearing, the faster the metal flow velocity; the smaller the distance of position of local die orifice(the closer the distance of position of local die orifice from extrusion cylindrical axis), the faster the metal flow velocity. The effect of main parameters of die structure on metal flow velocity was integrated and the mathematical model of determination of die bearing length in design of aluminum profile extrusion die was proposed. The calculated results with proposed model were well compared with the experimental results. The proposed model can be applied to determine die bearing length in design of aluminum profile extrusion die.

A Combined-Power Model for the Distribution of Axial Force in Shaft Anchor along Its Length

The theoretical results of axial force distribution models differ greatly from tests because of the complication of the rock type material. A three-parameter combined-power model is proposed by curves fitting the test data recorded from the pull tests on anchoring bars used in different engineering projects. Based on the comparison of the mechanical characteristics of shaft anchors and prestressed tendons, a two-parameter combined-power function model for prestressed tendons is proposed. The bounded length derived from the model and the suggested values of the parameters are also proposed. Compared with the Gaussian model, the three-parameter combined-power model is more precise and simple in expression. Results also suggest that the bounded length calculated from the average stress method is not safe enough.

Cybersecurity: A Statistical Predictive Model for the Expected Path Length

The object of this study is to propose a statistical model for predicting the Expected Path Length (expected number of steps the attacker will take, starting from the initial state to compromise the security goal—EPL) in a cyber-attack. The model we developed is based on utilizing vulnerability information along with having host centric attack graph. Utilizing the developed model, one can identify the interaction among the vulnerabilities and individual variables (risk factors) that drive the Expected Path Length. Gaining a better understanding of the relationship between vulnerabilities and their interactions can provide security administrators a better view and an understanding of their security status. In addition, we have also ranked the attributable variables and their contribution in estimating the subject length. Thus, one can utilize the ranking process to take precautions and actions to minimize Expected Path Length.

Minimum Description Length Methods in Bayesian Model Selection: Some Applications

Computations involved in Bayesian approach to practical model selection problems are usually very difficult. Computational simplifications are sometimes possible, but are not generally applicable. There is a large literature available on a methodology based on information theory called Minimum Description Length (MDL). It is described here how many of these techniques are either directly Bayesian in nature, or are very good objective approximations to Bayesian solutions. First, connections between the Bayesian approach and MDL are theoretically explored;thereafter a few illustrations are provided to describe how MDL can give useful computational simplifications.

Estimation on principal component of multi-collinearity Gauss-Markov model based on minimum description length

Gauss-Markov model is frequently used in data analysis; the analysis and estimation of its parameters is always a hot issue. Based on the information theory and from the viewpoint of optimal information on description—minimum description length, this paper discusses a case: where there is multi-collinearity in the coefficient matrix, principal component estimation is used to estimate and select the original parameters, so as to reduce its multi-collinearity and improve its credibility. From the viewpoint of minimum description length, this paper discusses the approach of selecting principal components and uses this approach to solve a practical problem.

Nonlinear mixed-effects height to crown base and crown length dynamic models using the branch mortality technique for a Korean larch( Larix olgensis ) plantations in northeast China

Korean larch(Larix olgensis)is one of the main tree species for aff orestation and timber production in northeast China.However,its timber quality and growth ability are largely infl uenced by crown size,structure and shape.The majority of crown models are static models based on tree size and stand characteristics from temporary sample plots,but crown dynamic models has seldom been constructed.Therefore,this study aimed to develop height to crown base(HCB)and crown length(CL)dynamic models using the branch mortality technique for a Korean larch plantation.The nonlinear mixed-eff ects model with random eff ects,variance functions and correlation structures,was used to build HCB and CL dynamic models.The data were obtained from 95 sample trees of 19 plots in Meng JiaGang forest farm in Northeast China.The results showed that HCB progressively increases as tree age,tree height growth(HT growth)and diameter at breast height growth(DBH growth).The CL was increased with tree age in 20 years ago,and subsequently stabilized.HT growth,DBH growth stand basal area(BAS)and crown competition factor(CCF)signifi cantly infl uenced HCB and CL.The HCB was positively correlated with BAS,HT growth and DBH growth,but negatively correlated with CCF.The CL was positively correlated with BAS and CCF,but negatively correlated with DBH growth.Model fi tting and validation confi rmed that the mixed-eff ects model considering the stand and tree level random eff ects was accurate and reliable for predicting the HCB and CL dynamics.However,the models involving adding variance functions and time series correlation structure could not completely remove heterogeneity and autocorrelation,and the fi tting precision of the models was reduced.Therefore,from the point of view of application,we should take care to avoid setting up over-complex models.The HCB and CL dynamic models in our study may also be incorporated into stand growth and yield model systems in China.

Comparison of Slope Length Factor Extraction in Hillslope Soil Erosion Model with Different DEM Resolutions

In this study, non-cumulative slope length(NCSL) calculation method and spatial analytical calculation(SAC) method were respectively applied to extract slope length and slope length factor from 10 sample areas, which are located in Ansai County, north Shaanxi Province. The comparison of computation precision between variable DEM resolutions showed that NCSL was superior to SAC entirely. And the results were best when the DEM resolutions were 5 and 10 m. Besides, the results of slope length factor were nearly the same under the two conditions. So DEM of 10 m resolution can be used to extract slope length.

Efficiency of employing fiber-based finite-length plastic hinges in simulating the cyclic and seismic behavior of steel hollow columns compared with other common modelling approaches

The accuracy and effi ciency of the modelling techniques utilized to model the nonlinear behavior of structural components is a signifi cant issue in earthquake engineering. In this study, the suffi ciency of three diff erent modelling techniques that can be employed to simulate the structural behavior of columns is investigated. A fi ber-based fi nite length plastic hinge (FB-FLPH) model is calibrated in this study. In order to calibrate the FB-FLPH model, a novel database of the cyclic behavior of hollow steel columns under simultaneous axial and lateral loading cycles with varying amplitudes is used. By employing the FB-FLPH model calibrated in this study, the interaction of the axial force and the bending moment in columns is directly taken into account, and the deterioration in the cyclic behavior of these members is implicitly considered. The superiority of the calibrated FB-FLPH modelling approach is examined compared with the cases in which conventional fi ber-based distributed plasticity and concentrated plasticity models are utilized. The effi ciency of the enumerated modelling techniques is probed when they are implemented to model the columns of a typical special moment frame in order to prove the advantage of the FB-FLPH modelling approach.

基于空间句法的矿井应急疏散研究与应用

地下矿井作业危险,空间拓扑结构复杂,因而矿山安全事故时有发生,合理的应急疏散路线规划以及疏散指示布置,能够有效提高井下人员的逃生效率,降低人员伤亡与财产损失。结合某地下矿井实例,基于空间句法和GIS网络分析搭建地下矿井巷道网络模型,从逃生人员的空间认知角度出发,利用标准化角度选择度值选取巷道网络模型中的前景网络和背景网络作为主要避险通道,为应急疏散指示标志布置提供参考;考虑巷道宽度、巷道类型、巷道坡度等巷道基础属性信息,并结合空间句法指标——标准化角度整合度,构建巷道网络应急脆弱模型,顾及巷道空间单元的稳定性,规划井下人员的最优认知路径,进而实现了多目标的地下矿井紧急疏散路线规划。该研究不仅能够为地下矿井的巷道布局设计提供建议,还可为地下矿井的应急疏散路线规划辅助决策、应急预案制定提供理论依据,同时为紧急避险系统的建设与完善提供新的思路。

An Econometric Analysis of Hospital Length of Stay for Cataract Operations in Japan by the Box-Cox Transformation Model and Hausman Tests: Evaluation of the 2010 Revision of the Medical Payment System

The Japanese medical costs for cataract treatments reached 270 billion yen in fiscal year 2012. Since the length of stay (LOS) in hospital is much longer than other major countries, controlling the medical costs by reducing LOS becomes an important issue in Japan. In this paper, we evaluated the effects of the 2010 revision of the Japanese medical payment system (DPC/PDPS) on LOS for cataract operations. The Box-Cox transformation model, Nawata’s estimators and Hausman tests were used in the analysis. To evaluate the effects, we analyzed a dataset obtained from 34 DPC hospitals (Hp1-34) where one-eye cataract operations were performed both before (April 2008-March 2010) and after (April 2010-March 2012) the 2010 revision and there were more than 500 patients. The dataset contained information from 32,593 patients. We did not admit the effect of the 2010 revision in this study, and there were large differences LOS among hospitals, even after removing the influences of factors such as patient characteristics and types of principal diseases.

Analysis of Length of Stay (LOS) Data from the Medical Records of Tertiary Care Hospital in Saudi Arabia for Five Diagnosis Related Groups: Application of Cox Prediction Model

Background: One of the main objectives of hospital managements is to control the length of stay (LOS). Successful control of LOS of inpatients will result in reduction in the cost of care, decrease in nosocomial infections, medication side effects, and better management of the limited number of available patients’ beds. The length of stay (LOS) is an important indicator of the efficiency of hospital management by improving the quality of treatment, and increased hospital profit with more efficient bed management. The purpose of this study was to model the distribution of LOS as a function of patient’s age, and the Diagnosis Related Groups (DRG), based on electronic medical records of a large tertiary care hospital. Materials and Methods: Information related to the research subjects were retrieved from a database of patients admitted to King Faisal Specialist Hospital and Research Center hospital in Riyadh, Saudi Arabia between January 2014 and December 2016. Subjects’ confidential information was masked from the investigators. The data analyses were reported visually, descriptively, and analytically using Cox proportional hazard regression model to predict the risk of long-stay when patients’ age and the DRG are considered as antecedent risk factors. Results: Predicting the risk of long stay depends significantly on the age at admission, and the DRG to which a patient belongs to. We demonstrated the validity of the Cox regression model for the available data as the proportionality assumption is shown to be satisfied. Two examples were presented to demonstrate the utility of the Cox model in this regard.

一种杆长可调的多功能铰链四杆机构模型的设计

设计出一款多功能铰链四杆机构,可使不同机构类型在同一模型上实现。阐述了设计原理,完成了杆长调节机构、限位装置、杆长锁紧装置、机架、多功能连接装置、铅笔固定滑块机构的设计,通过数字化模型呈现其功能。

考虑杆件尺寸相关性的受电弓运动可靠性分析

为分析杆件尺寸参数的关联特性对机构运动可靠性的影响规律,提出一种基于Cholesky法则的机构运动可靠性分析方法。首先,根据机构运动学原理构建机构运动学方程;其次,结合有效长度理论,建立考虑运动副间隙的杆件有效长度模型,在此基础上,引入Archard磨损模型量化运动周期对杆件有效长度的影响,通过蒙特卡罗法获取不同运动周期下的杆件尺寸样本数据并计算样本相关系数,进而利用Cholesky法则完成不同运动周期下的杆件样本数据重构,并结合可靠性理论对机构运动可靠性进行评估;最后,以受电弓机构为例,验证了所提方法的有效性。计算分析结果表明:杆件样本数据关联性由于运动副间隙的存在而增强,并随运动副间隙的增加愈加显著;与传统分析方法相比,基于Cholesky法则的机构运动可靠性指标存在一定程度降幅,能够为实际机构可靠性评估提供更为安全的参考价值。

锚杆岩体界面载荷传递规律及锚固长度设计

为揭示巷道围岩锚固界面脱粘失效机理,量化锚杆支护设计参数,采用三线性粘结滑移模型进行理论分析,对轴向载荷作用下锚固脱粘失效全过程中,锚固段界面剪应力、锚杆轴力分布演化规律以及界面极限锚固力进行研究,根据锚固段长度不同,得到两种界面剪应力分布演化类型。研究结果表明:当锚固长度较短时,界面剪应力存在全长软化阶段;当锚固长度较长时,界面剪应力存在弹性-软化-滑移三段共存阶段。锚固粘结界面弹性段、软化段、摩擦段内的剪应力分别呈现双曲余弦函数衰减分布、余弦函数上升分布、均匀分布规律,锚杆轴力随界面剪应力分布演化呈现多种形态的衰减分布规律。根据锚固界面模型解析计算获得极限锚固力,当不考虑脱粘摩擦力时,极限锚固力随锚固长度的增加趋近于某一固定值;当考虑脱粘摩擦力时,增加锚固长度能够持续提高锚固界面安全系数。研究成果可为锚固机制分析、锚杆支护参数设计提供理论参考。

考虑锈蚀损伤的黏结滑移本构模型

为合理反映钢筋锈蚀后黏结滑移性能劣化对钢筋混凝土(RC)结构抗震性能的影响,在既有黏结应力分布模式的基础上,推导得到钢筋应力-滑移关系,进而通过分析锈蚀对混凝土与钢筋界面黏结滑移机理的影响,建立考虑钢筋锈蚀损伤的黏结滑移本构模型。基于已有拉拔试验结果,与仅考虑纵筋锈蚀率影响的Cheng模型进行对比,验证所建模型的合理性与准确性。基于OpenSees有限元平台,采用纤维梁柱单元和零长度截面单元串联的方式,将所建钢筋黏结滑移模型嵌套于零长度截面单元的钢筋本构中,建立可考虑黏黏结滑移的锈蚀损伤纤维梁柱模型,并通过6根锈蚀RC柱拟静力试验结果验证模型的准确性,结果发现所提考虑黏结滑移的锈蚀RC纤维梁柱模型计算所得滞回曲线与试验滞回曲线吻合良好,累计耗能最大误差不超过15%。此外,通过参数分析研究影响锈蚀钢筋滑移量的因素,结果表明屈服滑移量与极限滑移量随体积配箍率的增大而明显减小,随混凝土保护层与钢筋直径之比(c/d)增大而变化的幅度较小。

基于多段压裂缝-井筒耦合流动模型的页岩油水平井段长度优化研究

长水平井段和大规模体积压裂是页岩油开发的关键技术,受储层特征、压裂规模的影响,不同区块的最佳水平井段长度存在差异,需综合考虑油藏渗流和长水平井井筒流动来优选水平井段长度。北美海相页岩连续性好,相对均质,油层巨厚,长水平井段对提高单井生产效率起决定性作用,而中国陆相页岩非均质性强,平面变化快,薄互层发育,需确定合理水平井段长度实现单井提产,获得经济效益。因此,准确表征页岩油藏渗流-长水平段井筒流动对页岩油产能评价和合理水平井段长度的确定至关重要。在五区线性流的基础上,综合考虑页岩基质启动压力梯度、复杂裂缝网络非均质及应力敏感特征,建立了页岩油水平井多段压裂缝-井筒耦合流动模型,并利用摄动变换、Laplace变换对模型求解。基于多段压裂缝-井筒耦合流动模型,开展了产量评价与预测,实现了复杂裂缝网络参数反演,论证了储层厚度、裂缝条数对合理页岩油水平井段长度的影响规律,在此基础上构建了页岩油水平井段长度优化图版。结果表明,对于厚层页岩,裂缝条数是影响合理水平井段长度的主控因素。将上述模型应用于实际区块,确定了不同区块在目前储层条件下的合理水平井段长度,该研究为明确不同类型页岩油储层合理水平井段长度的确定提供理论依据。

皮肤科住院患者多重耐药菌感染风险诺莫图预测模型的建立与验证

目的通过分析皮肤科住院患者多重耐药菌(MDRO)感染风险的影响因素建立诺莫图预测模型,并进行验证。方法选取2018年1月—2022年6月皮肤科住院患者8950例作为研究对象,统计其MDRO感染发生情况,采用Lasso-Logistic回归分析法筛选MDRO感染影响因素,构建诺莫图预测模型,并验证预测模型预测MDRO感染的价值。结果8950例皮肤科住院患者发生MDRO感染782例,发生率为8.74%。多因素Logistic回归分析显示年龄、免疫性皮肤疾病、侵入性操作、糖尿病、住院天数、长期应用糖皮质激素/免疫抑制剂、抗生素联用、C反应蛋白(CRP)为皮肤科住院患者MDRO感染的独立危险因素(P<0.01);采用R软件rms程序建立皮肤科住院患者MDRO感染的诺莫图预测模型,该模型预测风险能力指数为0.920,校准度为0.885;受试者工作特征曲线分析显示,该模型预测MDRO感染的曲线下面积为0.945(95%CI:0.903,0.991),敏感度为0.905,特异度为0.918。结论皮肤科住院患者MDRO感染风险较高,影响因素包括年龄、免疫性皮肤疾病、侵入性操作、糖尿病、住院天数、长期应用糖皮质激素/免疫抑制剂、抗生素联用、CRP,根据上述因素构建的诺莫图预测模型具有较高的预测效能。