非线性基线长度约束在北斗测姿中的应用

针对传统无约束LAMBDA(least-squares ambiguity decorrelation adjustment)算法中整周模糊度求解成功率不高的问题,提出一种利用基线约束的整数最小二乘快速求解整周模糊度的方法,并将其应用到北斗姿态测量系统中.该方法利用基线长度作为先验信息,将无约束的整数最小二乘扩展为非线性约束的最小二乘,并采用正交映射方法求解其约束解;同时在模糊度求解过程中,根据搜索空间的特性,先确定其上下界范围,再对模糊度残差范围限定,减少模糊度搜索过程中的候选解,最后采用迭代增加模糊度空间法和约束最小二乘求解对模糊度候选解筛选.实验采用单频北斗接收机实时数据对该算法的有效性进行验证,结果表明,在单频单历元条件下,该算法有效降低计算量,将姿态角求解成功率提高30%左右.     

基于改进型最小二乘搜索的 GNSS 姿态测量方法

结合全球卫星导航系统(global navigation satellite system,GNSS)用于姿态测量具有基线已知的特点,提出了一种改进型最小二乘搜索算法:将整周模糊度分为基本组和剩余组,在伪距精度和基线长度约束条件下确定出基本模糊度组的搜索空间;然后根据模糊度与基线俯仰角、航向角的关系,并以俯仰、航向角度组合作为联系基本组和剩余组的中间变量,通过搜索基本模糊度组来确定出剩余模糊度组合;最后利用最小二乘解算基线矢量,在二次残差比值检验条件下,完成整周模糊度的固定及姿态解算.实验结果表明,改进算法不仅有效减小了模糊度的搜索空间,而且缩短了模糊度初始化时间,具有较高的测姿精度,适用于GNSS姿态测量.     

模糊度二维搜索的姿态测量改进算法

值域算法由于采用遍历姿态角的方式建立搜索空间,从而会造成初始化时间较长的问题,故提出了一种基于窄巷组合的模糊度二维搜索算法:首先基于卫星空间几何关系对参考星与两颗主星间的窄巷主模糊度范围进行约束,利用其与姿态角之间的关系推得全体候选姿态角,从而以一种非遍历且不遗漏正确候选姿态角的途径得到搜索范围。然后基于值域二维搜索模型求解各候选姿态角相对应的窄巷模糊度浮点解,就近取整后依次采用模糊度整数特性法、基线先验信息法以及基线残差平方和最小准则固定整周模糊度。试验结果表明:文中算法相比原算法,不仅初始化时间由先前的153 s缩短至76 s,而且姿态精度总体提高近15%。     

基于 MEMS 辅助的单基线北斗融合测姿算法

载体的姿态信息是导航的重要参数,随着北斗卫星导航系统（Beidou navigation satellite system,BDS）和微机电系统（micro-electro-mechanical systems,MEMS）惯性传感器的发展与完善,高精度、低成本、自主化的融合测姿技术具有广阔的应用前景,因此,提出MEMS辅助单基线北斗融合测姿算法。根据MEMS惯性传感器解算出的姿态信息确定基线向量的搜索范围,从而辅助模糊度函数法（ambiguity function method,AFM）减小整周模糊度搜索空间,提高整周模糊度快速求解的成功率和计算效率。将BDS输出的姿态角信息作为观测信息,对MEMS陀螺仪解算出的姿态信息进行实时校正,实现BDS和MEMS传感器二者的数据融合算法。通过实测数据仿真验证,该算法能够解决信号失锁带来的整周模糊度求解困难的问题,并且测姿系统能在遮挡和动态等复杂环境下提供高质量姿态测量结果。     

改进型单频非遍历值域姿态测量算法

非遍历值域搜索算法利用二维模糊度搜索范围压缩了姿态角搜索空间,由于二维模糊度搜索空间较大,造成压缩姿态角搜索空间效率较低,提出了一种采用多约束条件以提高压缩姿态角搜索空间效率的方法。选取仰角最高的4颗卫星作为主星,采用最小二乘搜索算法利用单个历元观测数据确定三维模糊度搜索空间,结合基线长度及低成本微机电系统(micro electrical mechanical system,MEMS)提供的俯仰角信息对三维模糊度搜索空间进行筛选,取仰角最高的3颗卫星构成二维模糊度搜索空间,将其代入搜索模型解算整周模糊度候选值,采用残差比例检验法进行模糊度固定。试验结果表明,相比于原算法,姿态角搜索数目由576组降至8组,残差比峰值由16增至1 279,固定所需时长从35 s缩短至单个历元。     

GPS单频单历元定姿算法性能分析与改进方法

为了提高LAMBDA在单频单历元情况下的性能和成功率,对该定姿算法的性能进行了理论研究,分析了影响搜索效率的因素,并提出了一种新的求解模型.将未知的整周模糊度拟合成噪声,能够显著提高搜索效率,同时利用模糊度存在范围等约束条件对原算法的成功率进行了改善.实验表明:相比于原算法,改进算法能够有效减少GPS姿态解算的时间,同...     

基于基线约束及递推多历元的改进GNSS定姿技术

在GNSS单频姿态测量技术中,利用单差载波相位和码相位结合模型以及CLAMBDA算法(带有基线约束的最小二乘降相关平差算法)解算整周模糊度可以达到较好的定姿结果,但解算成功率不高。针对这一问题,提出了一种多基线三角形约束的递推多历元方法。三角形基线约束主要针对副基线,利用它可以使CLAMBDA算法得出的整周模糊度更准确。而递推多历元则保证了在此时刻没有解出整周模糊度时仍然可以计算出姿态角,主、副基线都适用。2种方法结合,进一步提高了姿态解算的成功率。对副基线的解算进行了验证,实验证明,这种方法将副基线的成功率提高到99.7%以上。     

低成本u-blox接收机单频BDS RTK定位性能评估

针对低成本u-blox接收机的单频BDS(BeiDou Navigation Satellite System)观测数据,分别采用经典LAMBDA算法和附有基线长约束的CLAMBDA算法对其定位精度进行分析评估。实测数据结果表明,针对低精度观测数据CLAMBDA算法相比于LAMBDA算法可以显著提高模糊度的正确固定率;当模糊度固定正确时两种算法在基线解算精度方面差异相对较小:在静态观测环境下均可达到水平0.5 cm、高程1 cm的定位精度,在动态环境下解算结果稍差,也能达到水平1 cm、高程2 cm的定位精度。     

一种改进的CIR法用于单历元模糊度解算

针对级联整周模糊度解算（CIR）法在载波相位和伪距观测噪声很大的场合,模糊度固定成功率很低这一问题,提出了一种改进的CIR法,该算法以CIR法为基础,利用排序和连续（逆）乔里斯基降相关法对每步最小二乘法求得的模糊度浮点解和协方差矩阵进行降相关,最后采用改进的最近点搜索（MAEVZ）法固定整周模糊度.仿真实验表明,在伪距观测噪声为2.0 m,载波相位观测噪声为0.03周的短基线环境下,CIR法单历元整周模糊度解算成功率已经低于5%,无法正确固定整周模糊度,而改进的CIR法单历元整周模糊度解算成功率仍能达到90%以上.      

利用零空间约束的GPS双差整周模糊度动态求解

针对非专用全球定位系统(GPS)导航型接收机,利用零空间约束动态求解GPS初始整周模糊度.对单个历元的双差载波相位观测方程进行零空间变换,避免了实时变化的三维位置参数求解;用精度衰减因子(XDOP)准则选取3个独立的双差整周模糊度,并根据GPS干涉仪测姿原理以基线长度来确定整周模糊度的搜索区间,通过基线长度约束进一步使搜索范围大大降低,模糊度最终采用多种检验方法联合确认.用Garmin25导航型单频接收机构成单基线,求解整周模糊度后在2-D平面上求解航向角,与航向参考对照后表明,采用该方法可在多个历元动态解算出整周模糊度,此时计算航姿精度可达到1°.     

Weighing of biomolecules, single cells and single nanoparticles in fluid

Nanomechanical resonators enable the measurement of mass with extraordinary sensitivity. Previously, samples as light as 7 zeptograms (1 zg = 10(-21) g) have been weighed in vacuum, and proton-level resolution seems to be within reach. Resolving small mass changes requires the resonator to be light and to ring at a very pure tone-that is, with a high quality factor. In solution, viscosity severely degrades both of these characteristics, thus preventing many applications in nanotechnology and the life sciences where fluid is required. Although the resonant structure can be designed to minimize viscous loss, resolution is still substantially degraded when compared to measurements made in air or vacuum. An entirely different approach eliminates viscous damping by placing the solution inside a hollow resonator that is surrounded by vacuum. Here we demonstrate that suspended microchannel resonators can weigh single nanoparticles, single bacterial cells and sub-monolayers of adsorbed proteins in water with sub-femtogram resolution (1 Hz bandwidth). Central to these results is our observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of our silicon crystal resonator. The combination of the low resonator mass (100 ng) and high quality factor (15,000) enables an improvement in mass resolution of six orders of magnitude over a high-end commercial quartz crystal microbalance. This gives access to intriguing applications, such as mass-based flow cytometry, the direct detection of pathogens, or the non-optical sizing and mass density measurement of colloidal particles.     

Observation of entanglement between a single trapped atom and a single photon

An outstanding goal in quantum information science is the faithful mapping of quantum information between a stable quantum memory and a reliable quantum communication channel. This would allow, for example, quantum communication over remote distances, quantum teleportation of matter and distributed quantum computing over a 'quantum internet'. Because quantum states cannot in general be copied, quantum information can only be distributed in these and other applications by entangling the quantum memory with the communication channel. Here we report quantum entanglement between an ideal quantum memory--represented by a single trapped 111Cd+ ion--and an ideal quantum communication channel, provided by a single photon that is emitted spontaneously from the ion. Appropriate coincidence measurements between the quantum states of the photon polarization and the trapped ion memory are used to verify their entanglement directly. Our direct observation of entanglement between stationary and 'flying' qubits is accomplished without using cavity quantum electrodynamic techniques or prepared non-classical light sources. We envision that this source of entanglement may be used for a variety of quantum communication protocols and for seeding large-scale entangled states of trapped ion qubits for scalable quantum computing.     

马来酸单十八酯的合成

以马来酸酐和正十八醇为原料 ,采用对甲苯磺酸作为催化剂合成了马来酸单十八酯。经实验确证了酯化的优化条件 ,获得了97.74 %的酯化率。     

Ultrahigh-quality silicon carbide single crystals

Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems.     

DNA typing from single hairs

The characterization of genetic variation at the DNA level has generated significant advances in gene and disease mapping, and in the forensic identification of individuals. The most common method of DNA analysis, that of restriction fragment length polymorphism (RFLP), requires microgram amounts of relatively undegraded DNA for multi-locus typing, and hundreds of nanograms for single-locus comparisons. Such DNA frequently cannot be obtained from forensic samples such as single hairs and blood stains, or from anthropological, genetic or zoological samples collected in the field. To detect polymorphic DNA sequences from single human hairs, we have used the polymerase chain reaction (PCR), in which specific short regions of a gene can be greatly amplified in vitro from as little as a single molecule of DNA. We have detected genetically variable mitochondrial and nuclear DNA sequences from the root region of shed, as well as freshly-plucked, single hairs; mitochondrial DNA (mtDNA) sequences have been detected in a sample from a single hair shaft. We have used three different means of DNA typing on these samples: the determination of amplified DNA fragment length differences, hybridization with allele-specific oligonucleotide probes, and direct DNA sequencing.