基于Radon逆变换的CT系统图像重建研究

笔者基于Radon逆变换研究了CT系统成像及重建的问题,并利用粒子群优化算法对标定参数及CT图像重构进行了优化,建立了相应的系统模型。利用Matlab进行仿真检验,结果表明笔者所建立的模型可以较准确确定CT系统的相关信息,并且在图像重构时有较高的准确度。

求解结构特征对的改进矢量逆迭代法

将矢量逆迭代法与结构拓扑变化法结合起来 。

电弧喷涂设备的现状与展望

简要介细了电弧喷涂设备的现状和发展概况。分析了电弧喷涂电源和电弧喷涂枪的研究进展。表明逆变化、智能化是电弧喷涂电源发展的必然趋势 ;电弧喷涂枪将朝着高速。

计算有限元结构特征值的D值迭代法

对前期研究中提出的广义逆拓扑变化理论作了进一步研究。引入了一个新概念——D值,并得到了静力结构拓扑变化法中D值的有界性质、单调性质以及D值随特征值的变化性质,据此提出了一个求解特征值的新方法,称之为D值迭代法。该方法具有精度和收敛速度与相邻特征值之比无关的特点,具有一定的理论意义和实用价值。

路面不平度模型对车辆侧翻瞬态响应的影响分析

精准的路面不平度模型可以提高车辆在瞬态响应的估算精度。结合国标中的标准路面谱和路面形貌自相似性特点,利用傅里叶逆变换法和正方形细分法分别建立平整路面、二维路面和三维路面模型。在双移线、鱼钩工况和角阶跃典型工况下,对比分析不同路面不同平度模型下横向载荷转移率(LTR)、侧向加速度、横摆角速度和侧倾角4个瞬态响应的区别。其中三维路面模型对各响应影响最大,车辆侧翻时其各响应的数值达到侧翻阈值。验证了多维度路面模型建立的可行性,为车辆侧翻瞬态响应研究提供了理论基础。

太阳能小屋的设计

针对提高太阳能光伏能源系统的发电效率问题,参考2012年全国大学生数学建模比赛B题部分数据,利用面积约束对各表面光伏电池的组合铺设及逆变器的选取建立数学模型并进行简化分析处理,通过多元优化对影响目标函数的变量进行合理赋值得到最优解,从而实现光伏能源的高效利用。

体大虑周与思深意远——《读黔阳县志》

清代章学诚在《文史通义·诗论篇》中说:“《文心》体大而虑周,《诗品》思深而意远。”这虽是评论刘勰的《文心雕龙》,钟嵘的《诗品》而言,但我认为对纂修二十四卷,几十万字的《黔阳县志》(以下简称《县志》)来说,“兹事体大”,为能做到“体大虑周”,“思深意远”,也是难能可贵的。《县志》在这方面却迈出了可喜的步伐。现就个人阅读所得,略陈一隅之见,以就正于领导、方家。

同园环境中不同海拔中华蟾蜍的心脏相对大小:海塞规则是否适合外温动物?

海塞规则(Hesse’s rule)是指物种内不同种群或近缘种间的心脏相对大小随海拔或纬度梯度增加而增加。该生物地理规则的实验证据来源于内温动物,是否适用于外温动物仍不清楚。本研究采集了不同海拔的中华蟾蜍Bufo gargarizans进行同园实验,比较心脏及其功能关联器官(肝脏、脾脏、肺脏、肾脏、脂肪体)的相对干重,对海塞规则进行检验。结果显示,中华蟾蜍心脏、肝脏、肺脏、肾脏和脂肪体的相对干重均随海拔增加而减小,与海塞规则预测相反,这提示外温性脊椎动物可能通过降低能量代谢需求以适应高海拔环境。

Monotonicity of the tail dependence for multivariate t-copula

This paper considers the upper orthant and extremal tail dependence indices for multivariate t-copula. Where, the multivariate t-copula is defined under a correlation structure. The explicit representations of the tail dependence parameters are deduced since the copula of continuous variables is invariant under strictly increasing transformation about the random variables, which are more simple than those obtained in previous research. Then, the local monotonicity of these indices about the correlation coefficient is discussed, and it is concluded that the upper extremal dependence index increases with the correlation coefficient, but the monotonicity of the upper orthant tail dependence index is complex. Some simulations are performed by the Monte Carlo method to verify the obtained results, which are found to be satisfactory. Meanwhile, it is concluded that the obtained conclusions can be extended to any distribution family in which the generating random variable has a regularly varying distribution.

Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean

The North Equatorial Countercurrent(NECC) is an important zonal fl ow in the upper circulation of the tropical Pacifi c Ocean, which plays a vital role in the heat budget of the western Pacifi c warm pool. Using satellite-derived data of ocean surface currents and sea surface heights(SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacifi c Ocean was investigated. It was found that the intensity(INT) and axis position(Y_(CM)) of the surface NECC exhibit strikingly different seasonal fl uctuations in the upstream(128°–136°E) and downstream(145°–160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and Y CM are greatly infl uenced by variations of the Mindanao Eddy, Mindanao Dome(MD), and equatorial Rossby waves to its south. Both INT and YC M also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacifi c and local wind forcing in the western Pacifi c Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacifi c Ocean. Those in the MD region are especially important in modulating the Y CM of the downstream NECC. In addition to the SSH-related geostrophic fl ow, zonal Ekman fl ow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions refl ect the high complexity of regional ocean dynamics.

Redox Controllable Switch of Crystalline Phase and Physical Property in SrVO_x Epitaxial Films

Transition-metal oxides have attracted much attention due to its abundant crystalline phases and intriguing physical properties. However, some of these compounds are difficult to be fabricated directly in film form due to the ease of valence variation of transition-metal elements.In this work, we reveal the reversible structural transition between SrVO3 and Sr2V2O7 films via thermal treatment in oxygen atmosphere or in vacuum. Based on this, Sr2V2O7 epitaxial films are successfully synthesized and studied. Property characterizations show that the semitransparent and metallic SrVO3 could reversibly switch into transparent and insulating Sr2V2O7, implying potential applications in controllable electronic and optical devices.

Modular Multilevel Inverter with Maximum Power Point Tracking for Grid Connected Photovoltaic Application

A single-phase modular multilevel inverter based photovoltaic system for grid connection is proposed. This photovoltaic system utilizes two conversion stages： a boost converter for tracking the maximum power point and a modular multilevel inverter used as an interfacing unit. The maximum power point tracking is achieved with a fuzzy logic controller, and the modular multilevel inverter regulates the DC link voltage and synchronizes the grid voltage and current in order to achieve unity power factor operation. The proposed system provides high dynamic performance and power quality injected into the grid. The validity of the proposed system is confirmed by simulations.

Unique two-way free-standing thermo-and photo-responsive shape memory azobenzene-containing polyurethane liquid crystal network

In this work,azobenzene-containing polyurethane liquid crystal networks(PULCN(AZO)s)were synthesized using a one-pot strategy to demonstrate excellent two-way free-standing thermo-/photo-responsive shape memory effects.Based on the step-growth nature of hydroxyls and isocyanates,the architectures of the networks were adjusted by controlling the stoichiometries of chemical materials.A uniform monodomain sample was prepared by external stress relaxation via a reversible addition reaction of a dynamic carbamate bond.Two independent transition temperatures assigned to glass transition temperature/melting temperature and liquid crystal phase transition temperature were employed to thermally trigger triple shape memory effects and two-way autonomous actuation.In addition,taking advantage of the trans-cis photoisomerization of azobenzene,the programmed network showed a reversible bending and unbending shape change upon irradiation by visible light at450 and 550 nm,respectively.Coupling the autonomously thermo-induced contraction/extension actuation and reversible photo-induced bending/unbending behaviors of PULCN(AZO)s in one system will expand their potential applications in emerging multifunctional devices.

L_1 adaptive controller design for hypersonic formation flight

The design of an L_1 adaptive controller for hypersonic formation flight is presented. The traditional leader/wingman formation control problem is considered, with focused attention on dealing with the input disturbance and parametric variations, both of which are intrinsic properties of the system that result in undesired control performance. A proportional-derivative control scheme based on nonlinear dynamic inversion is implemented as the baseline controller, and an L_1 adaptive controller is augmented to the baseline controller to attenuate the effects of input disturbance and parametric variations. Simulation results illustrate the effectiveness of the proposed control scheme.

Reversible magnetocaloric effect and refrigeration capacity enhanced by two successive magnetic transitions in DyB2

A large and reversible magnetocaloric effect is found in the compound DyB2, which is associated with two successive mag- netic transitions： a spin-reorientation-like transition followed by a ferromagnetic-paramagnetic transition. These two transitions appreciably enlarge the magnetic-refrigeration temperature window and yield a huge refrigeration capacity of 610 J kg^-1, with a maximum magnetic entropy change -ASmax of 17 J kg^-1K^-1, at a magnetic-field change of 5 T. The corresponding values for low magnetic-field change of 2 T are 193 J kg^-1 and 7.4 J kg-lK^-1, respectively.

Experimental investigations of a prototype reversible pump turbine in generating mode with water head variations

Influences of water head variations on the performances of a prototype reversible pump turbine are experimentally studied in generating mode within a wide range of load conditions(from 25% to 96% of the rated power). The pressure fluctuations of the reversible pump turbine at three different water heads(with non-dimensional values being 0.48, 0.71 and 0.90) are measured and compared based on the pressure data recorded in the whole flow passage of the turbine. Furthermore, effects of monitoring points and load variations on the impeller-induced unstable behavior(e.g. blade passing frequency and its harmonics) are quantitatively discussed. Our findings reveal that water head variations play a significant role on the pressure fluctuations and their propagation mechanisms inside the reversible pump turbine.

Reversible phase transition of the 1:1 complex between 18-crown-6 and n-propylammonium triiodide

Solid-state structure of the crystalline 1：1 complex [C3H10N（18-crown-6）]＋[I3] （1） between 18-crown-6 and n-propylammonium triiodide has been determined at 293 and 93 K, respectively, showing a change from monoclinic P21/m to monoclinic P21/a. Crystal structural analysis shows that in addition to van der Waals＇ forces, conventional N-H..-O hydrogen bonds are the key interactions. Measurements of unit cell parameters versus temperature show that the values of one of the three axes and the crystal volume change abruptly and remarkably at 220 K, indicating a first-order phase transition. The lack of the mirror plane in the low temperature structure is the most important differences between the two structural forms. Dif- ferential scanning calorimetry （DSC） measurement confirms that I undergoes a reversible phase transition at about 220 K with a thermal hysteresis of 3.5 K. The relatively large latent heat makes 1 a good candidate for phase change materials. The phase transition is accompanied by an anomaly of dielectric constant during heating and cooling process near the phase transition temperature.

Inverse Problem and Variation Method to Optimize Cascade Heat Exchange Network in Central Heating System

Urban heating in northern China accounts for 40% of total building energy usage. In central heating systems, heat is often transferred from heat source to users by the heat network where several heat exchangers are installed at heat source, substations and terminals respectively. For given overall heating capacity and heat source tempera- tore, increasing the terminal fluid temperature is an effective way to improve the thermal performance of such cascade heat exchange network for energy saving. In this paper, the mathematical optimization model of the cas- cade heat exchange network with three-stage heat exchangers in series is established. Aim at maximizing the cold fluid temperature for given hot fluid temperature and overall heating capacity, the optimal heat exchange area dis- tribution and the medium fluids＇ flow rates arc determined through inverse problem and variation method. The preliminary results show that the heat exchange areas should be distributed equally for each heat exchanger. It al- so indicates that in order to improve the thermal performance of the whole system, more heat exchange areas should be allocated to the heat exchanger whore flow rate difference between two fluids is relatively small. This work is important for guiding the optimization design of practical cascade heating systems.

Reversible photoswitching self-assembly of azobenzene-functionalized hyperbranched polyglycerol induced by host-guest chemistry

Reversible assembly and disassembly of rodlike large complex micelles have been achieved by applying photoswitching of supramolecular inclusion and exclusion of azobenzene-functionalized hyperbranched polyglycerol and acyclodextrin as driv ing force, promising a versatile system for selfassembly switched by light. Hydrogennuclear magnetic resonance （H NMR） and Fourier transform infrared （FTIR） spectroscopy were applied to characterize the azobenzenefunctionalized hyperbranched polyglycerol. Atomic force microscopy （AFM）, transmission electron microscopy （TEM） and dynamic laser light scattering （DLS） were employed to investigate and track the morphology of the rodlike large complex micelles before and after irradiation of UV light.