Remote Sensing Inversion of Nitrogen Nutrition Status of Apple Tree Leaves during Stopping Period of Spring Shoots

The nutrient inversion model of apple leaves was established by spectral analysis technology to provide technical support for the fine management of apple trees.In Shuangquan Town,Changqing District,Jinan City,Shandong Province,the Fuji apple trees with stopping period of spring shoots were taken as research objects.The spectral reflectance and nitrogen content of apple leaves were measured by ASD Field Spec 4 portable ground object spectrometer.Analyzed the correlation between leaf nitrogen content and spectral reflectance.The sensitive wavelengths with high correlation coefficient were select by fractional differential algorithm,and the optimal vegetation index was constructed and screened out.Partial Least Square Regression(PLSR),Support Vector Machine(SVM)and Random Forests(RF)method were used to construct an inversion model of leaf nitrogen content.The results show that the RF model based on fractional differential second-order treatment is the best inversion model for the nitrogen content of leaves during stopping period of spring shoots.The modeling accuracy determination coefficient R2 reached 0.891,RMSE was 0.0841,and RPD was 2.1396.The determination coefficient R2 of the fitting results of the verification set was 0.617,RMSE was 0.1251,and RPD was 1.7105.The inversion model established by RF method is effective in monitoring the nitrogen content in apple leaves,which provides a theoretical basis for monitoring the growth of apple by hyperspectral technology.

Weak wide-band signal detection method based on small-scale periodic state of Duffing oscillator

The conventional Duffing oscillator weak signal detection method, which is based on a strong reference signal, has inherent deficiencies. To address these issues, the characteristics of the Duffing oscillator＇s phase trajectory in a small- scale periodic state are analyzed by introducing the theory of stopping oscillation system. Based on this approach, a novel Duffing oscillator weak wide-band signal detection method is proposed. In this novel method, the reference signal is discarded, and the to-be-detected signal is directly used as a driving force. By calculating the cosine function of a phase space angle, a single Duffing oscillator can be used for weak wide-band signal detection instead of an array of uncoupled Duffing oscillators. Simulation results indicate that, compared with the conventional Duffing oscillator detection method, this approach performs better in frequency detection intervals, and reduces the signal-to-noise ratio detection threshold, while improving the real-time performance of the system.

Numerical simulation of transient flow performance during different periods in centrifugal pumpNumerical simulation of transient flow performance during different periods in centrifugal pump

The instantaneous variations of the hydraulic characteristics take place in centrifugal pumps during their start-up,shutdown and other variable speed operations.In this paper,the variable speed method was proposed to simulate the transient internal flow field and the external performance of the pump during starting and stopping periods.The terms of accelerations due to variable speeds in the flow governing equations were analyzed in a multiple reference of frame(MRF).A transient CFD simulation was performed for a typical centrifugal pump by using ANSYS-CFX with the standard k-εturbulence model.The entire simulation process was composed of four stages:start-up,normal run,shutdown and post-shutdown.The function of rotating speed with regard to time was set by CEL language directly into the impeller domain in the pre-processor of the software to conduct variable speed simulation.The variations of the flow field in the centrifugal pump were obtained from the transient simulation.The changing laws of flow rate,head and other performance parameters over time were also analyzed and summarized.

H0i-Eigenwave Characteristics of a Periodic Iris-Loaded Circular Waveguide

H0i-eigenwave characteristics of a periodic iris-loaded circular waveguide (PICW) are examined, as concerns the ei-genmode behavior vs arbitrary variations of the geometric parameters and the Bragg bandwidths vs the parameter of filling extremums.

PROPAGATION BEHAVIORS OF SHEAR HORIZONTAL WAVES IN PIEZOELECTRIC-PIEZOMAGNETIC PERIODICALLY LAYERED STRUCTURES

This paper investigates shear horizontal （SH） waves propagating in a periodically layered structure that consists of piezoelectric （PE） layers perfectly bonded with piezomagnetic （PM） layers alternately. The explicit dispersion relations are derived for the two cases when the propagation directions of SH waves are normal to the interface and parallel to the interface, respectively. The asymptotic expressions for dispersion relations are also given when the wave number is extremely small. Numerical results for stop band effect and phase velocity are presented for a periodic system of alternating BaTiO3 and Terfenol-D layers. The influence of volume fraction on stop band effect and dispersion behaviors is discussed and revealed.

FILTERING CHARACTERISTICS AND EXPERIMENTAL INVESTIGATION OF ONE-DIMENSIONAL PERIODIC RODS

Passive periodic structures exhibit unique dynamic characteristics that make the passive periodic structures act as mechanical filters for wave propagation. As a result, wave can propagate along the periodic structures only within specific frequency bands called the pass bands and wave propagation is completely blocked within other frequency bands called the “stop bands”. A theoretical method based on the transfer matrix formulation is developed in order to effectively investigate the influence of periodicity, variable geometry and material properties on the wave propagation characteristics of one-dimensional periodic rod. Several numerical examples are presented in order to illustrate their unique tunable filtering and localization characteristics. The experiments are conducted to verify the numerical predictions and to demonstrate the capability of the wavelet transform as a very powerful tool to uniquely identify and compare the energy distribution both in the time and frequency domain. The flexibility that the spectral width and location of the pass and stop bands can be tuned by introducing intentional variation in geometric and material properties for the individual substructure or cell is identified completely by both numerical predictions and experimental results. The results demonstrate the potential of such one-dimensional periodic structure in controlling the dynamics of wave propagation as a mechanical filter such as engine mount, gearbox support strut and other applications.

癫痫缓解期患儿减停药后复发的相关因素分析

目的:分析癫痫缓解期的患儿减停药后复发相关危险因素。方法:选择2020年1月—2021年2月喀什地区第一人民医院收治的癫痫缓解期患儿110例作为研究对象,根据患儿减停药后复发情况分为复发组与未复发组。收集患儿一般资料以及疾病特征资料,利用单因素与多因素Logistic回归分析复发相关因素。结果:110例患儿减停药后复发23例,复发率为20.91%。应用多因素Logistic回归分析显示,年龄<6岁、初始发病年龄<7岁、合并颅内病灶、停药前癫痫发电、停用药物时间<6个月均是癫痫缓解期患儿减停药后复发的独立危险因素。结论:癫痫缓解期患儿减停药后复发因素较多,因此需了解复发危险因素,采取合理防范措施,改善患儿预后。

泥岩盖层压力封闭的演化特征及其研究意义

在深入研究泥岩盖层压力封闭形成机制的基础上，分析了泥岩盖层压力封闭油气的机理及其演化特征，提出了泥岩 盖层压力封闭形成的起始时期和终止时期的概念，建立了确定方法。通过比较泥岩盖层压力封闭形成时期与烃源岩大量 排气期的早晚，提出了泥岩盖层压力封闭有效性的概念，并建立了其研究方法，应用于松辽盆地三肇凹陷青山口组泥岩盖 层压力封闭形成时期及有效性研究中，其结果表明泥岩盖层压力封闭的有效性好坏对天然气的聚集成藏具有重要意义。

核主泵停机过渡过程瞬态水动力特性研究

为研究核主泵停机过渡过程中瞬态水的动力特性,通过Pro/E软件对核主泵内部流道进行三维造型,利用雷诺时均N-S方程和RNGk-ε方程,应用计算流体力学软件CFX对核主泵叶轮流道内的停机过渡过程瞬态涡变和径向力进行数值模拟计算。结果表明:叶轮出口涡量小于进口涡量,且叶轮出口涡量受叶轮与导叶动静干涉影响而呈大幅的周期性波动。在泵体与出口管交接处的涡量变化较大,与导叶出口方向相反方向处的涡量变化最大。对比3种停机惰转过渡过程中惰转模型可知,带惰轮惰转模型的径向力呈周期性波动逐渐减小;线性惰转模型与带惰轮惰转模型的径向力变化趋势类似,但其变化幅度少于线性惰转模型径向力变化幅度,t/T=0.6～1时,其径向力变化幅度接近零;常规惰转模型的径向力呈现不规律变化,t/T约为0.25时出现极大值,对核主泵的可靠运行产生较大影响。

混流泵停机过程的瞬态水力特性分析研究

针对混流泵在不同转速下停机过程中的瞬态水力特性进行了试验研究,并对试验结果进行了讨论。介绍了用于瞬态水力性能测试的试验设备以及试验方法,不同转速下停机过程的瞬态水力特性,并尝试用三次多项式拟合的方法模拟停机过程的流量—扬程曲线。试验结果显示了在停机瞬间泵的流量和扬程迅速下降,管路能量亦急剧降低,但在这一过程中无噪音和气泡产生,由此提出了瞬态工作泵的停机阶段操作方法。同时,试验结果亦显示了三次多项式拟合曲线与实际测量曲线能基本符合。试验和计算结果可在瞬态工作特性方面为瞬态离心式水泵的设计和实际使用打下基础。

采用自调式激振器的高方平筛停车阶段分析

为了消除高方平筛在停车阶段的共振现象,采用了一种新型的自调偏心距式惯性激振方式,并对系统停车过程进行了动力学建模和数值模拟。考虑电机制动时的机械特性和滚动轴承摩擦,在MATLAB中得到了偏心距不变和偏心距自调2种激振方式下停车过程的数值解,分析了自调式激振器中初始偏心距、刚度和阻尼对停车时间的影响规律。结果表明:采用合适参数设置的自调式激振器能大幅度减少设备停车阶段的最大瞬态振幅和停车时间。该文结果对于提高高方平筛及惯性式振动机械的工作性能和寿命具有参考价值。

比赛前后优秀女子赛艇运动员体成分与AT4功率的变化特点及其相关性研究

以优秀女子赛艇W8+运动员为研究对象,探讨优秀女子公开级赛艇运动员在赛前训练和赛后停训及恢复训练阶段体成分和AT4功率的变化情况和相关性特点。结果:瘦体重和骨骼肌质量在赛前训练和赛后停训阶段呈显著下降,恢复训练5周后较赛前训练后期显著升高,但仍显著低于赛前训练初期水平;体脂%在赛前训练和停训及恢复训练阶段均呈连续显著升高趋势;AT4功率在赛前和恢复训练6周后变化不显著,仅与体脂%呈中度负相关(P<0.01)。结论:AT4功率和体成分各指标在赛前训练和停训阶段易出现不良变化,且较难改善,较高的体脂%可能是限制运动水平提高的重要因素之一。

自调式激振器对高方平筛停车阶段共振的影响

为了使高方平筛在停车阶段获得较为稳健的减振效果,对采用自调式惯性激振的高方平筛停车过程进行了动力学建模和数值模拟。在考虑三相异步电机制动时的机械特性和滚动轴承摩擦的前提下,建立筛体、悬吊装置和自调式激振装置所组成系统的非线性动力学模型,运用4阶Runge-Kutta数值算法得到了偏心距不变式和偏心距自调式两种激振方式下停车过程的数值解。分析了自调式激振装置中初始偏心距、刚度和阻尼等对停车时间的影响规律。结果表明:只有在合适的参数匹配下,自调式激振方式才能获得较好的减振效果;适中的初始偏心距是提高减振稳健性的关键因素。所得结果对于振动机械中自调式激振装置的设计具有参考价值。

一维光子晶体的电磁波理论及实现方法

对一维光子晶体的电磁波理论及周期介质中的 Bloch波解做了详细的推导 ,给出了光子晶体中的禁带存在的理论依据 ,并以此分析了禁带的特征 .同时 ,对一维光子晶体的光学理论做了阐释 ,并应用于一维光子晶体的设计实践 .列举了两个多层周期介质膜的禁带特性 .最后对光子晶体的应用和制造前景做了展望 .

周期结构机械滤波器对浮筏隔振系统传递特性的影响

弹性波在周期性结构中传播时会形成特殊的阻带和通带结构。当弹性波的频率处于阻带范围内时,弹性波及振动是不允许传播的。根据这一性质,设计一种虚拟的周期结构机械滤波器,用于浮筏隔振系统中的下层隔振器和基座间,通过改变从机组到基座之间的传递特性,使浮筏隔振系统中与激励频率相近、并和舱段壳体振动相关的固有频率和激励频率错开。利用传递矩阵法研究浮筏隔振系统下层隔振器和基座间插入周期结构机械滤波器后的传递特性和动态响应,通过研究表明:当激励频率在周期结构的阻带之内时,基座的位移响应,力响应和功率流响应将大大减小。

一类具有潜伏期的随机禽流感模型的渐近性分析

研究了一类禽类患病系统具有潜伏期而人类染病系统受到随机白噪声干扰的随机禽流感模型的渐近性质.首先通过构造停时和Lyapunov函数及伊藤引理的方法得到了随机模型全局正解的存在唯一性.其次证明了在禽类患病种群灭绝的情形下,人类患病种群必将灭绝的结果;再次得到了禽类患病种群长期存在的前提下,由于随机因素的干扰,人类患病种群终将趋于灭绝的充分条件.最后通过数值模拟比较了人类染病种群在确定性和随机性系统中的发展趋势.

基于时段偏好的高速铁路列车停站和频率优化

优化高速铁路列车停站方案和开行频率应同时考虑旅客需求和运输企业效益,出发时段选择则是影响旅客需求分布的最重要因素。本文针对一条高速铁路客运走廊,研究基于时段偏好的列车停站和频率优化问题。分析了影响旅客出发时段偏好的2个主要因素,吸引度与排斥度。据此构建了高铁旅客出行阻抗函数,建立了一个双层规划模型,上层规划是以运营成本最小为目标的混合0-1规划模型,用于确定列车的停站和开行频率方案;下层规划是基于Wardrop用户平衡规则的客流分配模型,用于计算旅客在上层决策的停站和频率方案上的流量分配。根据模型特点设计了基于遗传算法的启发式方法,以兰西高铁走廊为背景实际求解了列车停站方案和开行频率,验证了本文方法的有效性。

黑麦草、白三叶安宁河流域的生长测定

在最冷的12月至2月对四川凉山州安宁河流域的黑麦草、白三叶进行生长测定,结果证实,在当地建高产人工草地可作当家品种,冬季无停止生长期,最低产量可在5000kg以上,放牧利用的停牧周期在一月以内为好,预计年刈割周期次数为6～8次。

具有射击域的武器系统的击发特性与精度

针对具有射击域的武器系统,研究其火控系统击发特性与精度。在分析随机穿越周期及滞留时间的基础上,得出了击发周期、允许射击时间及停射时间的分布特性及其均值。分析了加入射击域后以缩短允许射击时间为代价提高命中精度的实质,并定量的演绎了射击精度提高的程度。以靶场实测数据作为统计对象,验证了结论的可信性,为具有射击域的武器系统的论证、设计、检验提供了理论支持。

周期加筋板中的弯曲波传播

本文采用波动分析法分析了周期加筋板中的弯曲波传播,推导了周期加筋板的波传播方程,分析了振动频率和平面弯曲波入射角对传播常数的影响。研究表明:平面弯工波以某一角度入射周期加筋板时,随着频率的变化,会交错的出现弯曲波传递的穿透频段和阻塞频段;周期加筋板没有明显的穿透频段。本文的研究为周期加筋板应用于结构声传递途径的控制提供了理论基础。