加速度传感器动态校准系统不确定度评估方法的研究

针对加速度传感器动态校准获取其工作频带的过程中,因校准系统存在测试不确定度导致传感器校准不准确的问题,设计了某型号加速度传感器的动态校准试验,以试验数据为依据提出了系统不确定度评估方法。通过对冲击试验台为冲击激励源构成的动态校准系统测试过程中几个主要误差源的分析,结合文中提出的系统不确定度评估方法计算出校准系统的测试标准不确定为1.77%,扩展不确定度为3.54%。对比测量仪器特性评定相关指标可知该校准系统符合工程校准需要,而该评估方法的提出对校准系统的不确定度评估有一定的现实指导意义。     

Second harmonic generation of metal nanoparticles under tightly focused illumination

The near-field and far-field second harmonic(SH) responses of a metal spherical nanoparticle placed in the focal region of a highly focused beam are investigated by using the calculation model based on three-dimensional finite-difference time-domain(FDTD) method. The results show that off-axis backward-propagating SH response can be reinforced by tightly focusing, due to the increase of the relative magnitude of the longitudinal field component and the phase shift along the propagation direction.     

多元掺杂尖晶石型Li1.02MxMn2-xQyO4-y正极材料的电化学特性

The effect of doping on the electrochemical performance was studied for spinel type Li_1.02M_xMn_2-xQ_yO_4-y used as cathode material in lithium-ion battery. TG/DTA curves of the precursor(the raw materials) doped with different elements were studied. The spinel materials Li_1.02Mn₂O₄, Li_1.02Co_0.02Cr_0.01La_0.01Mn_1.96F_0.02O_3.98, Li_1.02Co_0.02Cr_0.01 La_0.01Mn_1.96Cl_0.02O_3.98, Li_1.02Co_0.02La_1.02Mn_1.97Cl_0.02O_3.98, Li_1.02Co_0.02Cr_0.01Mn_1.97O₄, were prepared by solid-state reaction method after the pretreatment of conversion under low temperature and uniform mixing. X-ray diffraction patterns showed that all the samples had perfect spinel structure. SEM indicated that the particles of the samples had uniform size and were distributed evenly. The results of the charge/discharge curves showed that Li_1.02Co_0.02Cr_0.01La_0.01Mn_1.96F_0.02O_3.98 had better performance than other materials according to the inhibition of decline of reversible capacity of spinel Li_1.02M_xMn_2-xQ_yO_4-y. Therefore, cycle performance had been improved so obviously that 93.9% of the initial capacity were preserved after 100 cycles. Furthermore, electrochemical impedance tests were carried out with the spinel Li_1.02Co_0.02Cr_0.01La_0.01Mn_1.96F_0.02O_3.98 as working electrode, Lithium as counter electrode and reference electrode. Results showed that this material possessed good charge/discharge reversible capability and had the lowest impedance in 3.95～4.25 V range (on the stage of charge / discharge).     

十八烷基离子液体杂化固相微萃取整体柱用于检测咖啡中的多环芳烃

以自制的1-十八烷基-3-(γ-三乙氧基硅基丙基)咪唑溴盐离子液体(C18IL)、二苯基二甲氧基硅烷(DDS)和四乙氧基硅烷(TEOS)为功能单体,采用溶胶-凝胶法制备了烷基咪唑基离子液体管内固相微萃取整体柱(C18IL in-tube SPME).以多环芳烃为分析对象,考察了C_(18)IL含量对C_(18)IL in-tube SPME萃取性能的影响,并对萃取条件进行了优化.建立了基于C_(18)IL in-tube SPME-气相色谱(GC-FID)的分析方法,用于检测萘、芴、菲、荧蒽和芘5种多环芳烃.该方法的检出限(S/N=3)为0.007~0.072μg/L,定量限(S/N=10)为0.023~0.24μg/L,日内和日间精密度(RSD)除菲类多环芳烃外均小于10%.将该方法用于检测咖啡中5种多环芳烃,3个不同浓度下的加标回收率为85.79%~103.42%.     

HAT循环性能分析研究

本文着重分析研究最近刚提出的并联型Brayton和Rankine联合循环——HAT循环。由于效率、环保及成本等优势,它将成为跨世纪的新颖热力循环。 一、HAT循环概念 图1为热力系统图。水在中冷器C_1、后冷器C_2及热水器H中加热升温后从饱和器S     

土壤分类的模糊集成算法与应用

土壤是一个多性状的连续体,其分类的首选方法是模糊聚类分析.但是模糊聚类分析中现有的基于模糊等价关系的动态聚类法和模糊c-均值法各有利弊,采用其中一种方法聚类肯定存在不足.为此集成两种聚类方法的优点,避其缺点,提出了用基于模糊等价关系的动态聚类方法和方差分析方法确定聚类数目和初始聚类中心,再用模糊c-均值法决定最终分类结果的集成算法,并将其应用到松花江流域土壤分类中,得到了较为切合实际的分类结果.     

金属规则表面形貌影响二次电子产额的解析模型

表面形貌是影响二次电子发射特性的重要因素, 但目前仍缺乏刻画这一影响规律的解析模型. 本文通过分析发现表面结构的遮挡作用是影响二次电子发射特性的主要因素. 基于二次电子以余弦角分布出射的规律, 提出了建立表面形貌参数与二次电子产额之间定量关系的方法, 并以矩形槽和三角槽为例, 建立了电子正入射和斜入射时的一代二次电子产额的解析模型. 将推导的解析模型与Monte Carlo模拟结果和实验结果进行了比较, 结果表明本文建立的模型能够正确反映规则表面形貌的二次电子产额. 本文的模型对于反映常用规则结构影响二次电子出射的规律以及指导通过表面结构调控二次电子发射特性都具有参考价值.     

单压过热蒸汽余热锅炉变工况解析解

主要符号说明符号：Cp比热DT温差F换热面积G工质流量H比焓值K换热系数L汽化潜热Q换热量Re余热回收率T温度Tg1烟气在蒸发器出口处的温度保热系数下标：a接近点e出口参数E省煤器g烟气d进口参数p节点B蒸汽V蒸发器B水0设计工况参数1序言余热锅炉是动力装置中余热回收的主要设备,由于余热锅炉的烟气侧热源变动大,因此在热力系统分析时,经常要对余热锅炉的各种工况的性能作出预报。余热锅炉变工况计算方法很多,但公开发表的文献较少。其中基于已知余热锅炉各部件详细尺寸,用类似于锅炉校核计算的方法进行变工况计算是比较精确的方法l…     

Ca~(2+)掺杂对SmFeO_3的介电、铁磁特性及磁相变温度的影响

采用固相反应法制备Sm_(1-x)Ca_xFeO_3(x=0,0.1,0.2,0.3)样品,研究Ca~(2+)掺杂对SmFeO_3介电性能、铁磁性及磁相变温度的影响.X射线衍射图谱分析表明:所有样品的主衍射峰与SmFe03相符合且具有良好的晶体结构.随着x的增加,SmFeO_3样品的晶粒尺寸由原来的0.5μm逐渐增大到2μm.当f=1 kHz时,Sm_(1-x)Ca_xFeO_3(x=0.1,0.2,0.3)样品的ε_r分别是SmFe03的5倍、3倍和2.6倍,而tgσ增大一个数量级.在3T磁场作用下,SmFe03样品的M-H呈线性,随着x的增加,M-H逐渐趋向饱和,Sm_(1-x)Ca_xFeO_3(x=0.1,0.2,0.3)样品的M_r分别是SmFeO_3的20倍、31倍和68倍.X射线光电子能谱分析表明:Fe~(2+)和Fe3+共存于Sm_(1-x)Ca_xFeO_3样品中,Fe~(2+)/Fe~(3+)比例随着x的增加而增大,证明Ca~(2+)掺杂增加了Fe~(2+)的含量,形成Fe~(2+)—O~(2-)—Fe~(3+)超交换作用,增强SmFe03的铁磁特性.测量了Sm_(1-x)Ca_xFeO_3样品在外加磁场为1000 Oe(1 Oe=79.5775 A/m)的M-T变化关系,观测到其自旋重组温度(T_(SR))和尼尔温度(T_N)分别为438 K和687 K,发现SmFe03样品的T_(SR)和T_N均随着x的增加向低温方向移动,当x=0.3时,自旋重组现象消失.这主要是SmFeO_3样品磁结构的稳定性和Fe~(3+)—O~(2-)—Fe~(3+)及Sm~(3+)—O~(2-)—Fe~(3+)超交换三者共同作用的结果.     

An efficient multipaction suppression method in microwave components for space application

Multipaction,caused by the secondary electron emission phenomenon,has been a challenge in space applications due to the resulting degradation of system performance as well as the reduction in the service life of high power components.In this paper we report a novel approach to realize an effective increase in the multipaction threshold by employing micro-porous surfaces.Two micro-porous structures,i.e.,a regular micro-porous array fabricated by photolithography pattern processing and an irregular micro-porous array fabricated by a direct chemical etching technique,are proposed for suppressing the secondary electron yield(SEY) and multipaction in components,and the benefits are validated both theoretically and experimentally.These surface processing technologies are compatible with the metal plating process,and offer substantial flexibility and accuracy in topology design.The suppression effect is quantified for the first time through the proper fitting of the surface morphology and the corresponding secondary emission properties.Insertion losses when using these structures decrease dramatically compared with regular millimeter-scale structures on high power dielectric windows.SEY tests on samples show that the maximum yield of Ag-plated samples is reduced from 2.17 to 1.58 for directly chemical etched samples.Multipaction testing of actual C-band impedance transformers shows that the discharge thresholds of the processed components increase from 2100 W to 5500 W for photolithography pattern processing and 7200 W for direct chemical etching,respectively.Insertion losses increase from 0.13 d B to only 0.15 d B for both surface treatments in the transmission band.The experimental results agree well with the simulation results,which offers great potential in the quantitative anti-multipaction design of high power microwave components for space applications.