车载经纬仪的静态指向误差补偿

为了降低载车平台变形对经纬仪静态测角精度的影响,补偿较大变形产生的测角误差,实现移动站弹道测量,分析了平台变形对光电经纬仪静态测角误差影响的基本原理,利用固定在方位轴轴心的倾角传感器测量出因平台变形而导致的经纬仪工作基准面中心点与水平面变化的夹角,并计算其测量坐标系的变化量。建立了平台中心变形角的底部轮廓图,经过有限的平台变形采样,存入计算机,在计算机中以方位、俯仰角为输入变量建立二维查找表,通过插值计算全方位角和全俯仰角的平台变形量,进行事后补偿。实验结果表明,该方法能够有效地补偿因平台变形而带来最大为142″的测角误差,使方位测角精度提高44″,俯仰测量精度提高8.5″。该方法为实现高精度车载光电测量提供了一种有效的途径。     

Abrasion behaviour of polymeric textiles for endovascular stent-grafts

Endovascular aneurysm repair (EVAR) is a type of endovascular surgery used to treat abdominal aortic aneurysms (AAA). The prosthesis used for the purpose, called stent-grafts, are made of polymeric materials reinforced by metallic stents. The polymers used for the graft construction are usually woven PET fibres or extruded ePTFE. After implantation and due to blood flow and to the relative motion between the stent and the graft, abrasion, erosion and fatigue of the graft material can occur, leading to fibre separation/fracture and perforation of the graft. In this paper, abrasion wear tests results are presented for three different materials used in stent–grafts, using the Martindale method. Mass loss as function of wear cycles is presented. Scanning electron microscopy, before and after tests was used to analyse the materials surface. ePTFE specimens presented ruptures between 45,000 and 55,000 cycles and PET specimens at 70,000 cycles. PET-LP (low profile) specimens did not reveal any rupture until 150,000 cycles. These results show an increased life resistance, due to different wear mechanisms of PET-LP fabric, when compared with ePTFE and PET fabric for vascular prosthesis applications.     

An investigation of the flow field within patient-specific models of an abdominal aortic aneurysm under steady inflow conditions

The flow fields within three patient-specific models of an abdominal aortic aneurysm (AAA) were investigated under steady laminar inflow conditions over a range of Reynolds numbers. Each model extended from the renal arteries to downstream of the iliac bifurcation. The aneurysms (referred to as models A, B, and C) are mature, with D/d ratios of 1.83, 1.57, and 1.95 respectively. The mass flowrates in each of the iliac arteries were equal. Using flow visualization it was observed that the flow proximally in the aneurysm was characterized by a primary jet that separated from either the posterior wall or the lateral wall or both, producing large recirculating zones. The primary jet impinged either normally or obliquely upon the anterior or right lateral wall in the distal half of the aneurysm, the flow distally in the aneurysm having been greatly disturbed. Measurements of the turbulence intensity along the median lumen centre-line showed that in each model the onset of transition and full turbulence occurred at Reynolds numbers much lower than those previously measured in idealized models. Computational fluid dynamics showed substantial differences in the velocity and stress fields when using the shear stress transport turbulence model as opposed to a laminar viscous model. It was also observed that turbulence was largely produced along the shear layers surrounding the primary jet and, in particular, at interfaces between the jet and the recirculating zones. In conclusion, turbulence may be expected to exist at Reynolds numbers typically encountered within an AAA, and it must be taken account of in an analysis of the flow field.     

Method for the study of the three-dimensional orientation of the nuclei of myocardial cells in fetal human heart by means of confocal scanning laser microscopy

A series of three-dimensional image analysis tools are used to measure the three-dimensional orientation of nuclei of myocardial cells. Confocal scanning laser microscopy makes it possible to acquire series of sections up to 100 μm inside thick tissue sections. A mean orientation vector of unit length is calculated for each segmented nucleus. The global orientation statistics are obtained by calculating the vectorial sum of the nuclear unit vectors. The final orientation is expressed by a mean azimuth angle, an elevation angle and a measure of the angular homogeneity. The method is illustrated for two different regions of the myocardium (interventricular septum and papillary muscle) of a normal human fetal heart. This quantitative method will be used to assess and calibrate the information provided by polarized light microscopy.     

Circumferential variation in mechanical characteristics of porcine descending aorta

Arterial characterization of healthy descending thoracic aorta (DTA) is indispensable in determining stress distributions across wall thickness and different regions that may be responsible for aorta inhomogeneous dilation, rupture, and dissection when aneurysm occurs. Few studies have shown the inhomogeneity of DTA along the aorta tree considering changes in circumferential direction. The present study aims to clarify the circumferential regional characterization of DTA. Porcine DTA tissues were tested according to region and orientation using uniaxial tension. For axial test, results show that the difference in circumferential direction was mainly in collagen fiber modulus, where the anterior collagen fiber modulus was significantly lower than the posterior quadrant. For circumferential test, the difference in circumferential direction was mainly in the recruitment parameter, where the circumferential stiffness is significantly higher in the posterior region at physiological maximum stress. The proximal posterior quadrant and left quadrant showed significantly lower axial collagen fiber stiffness than the right and anterior quadrants, which may be a factor in aneurysm development. Furthermore, the constitutive parameters for similar detailed regions can be used by biomedical engineers to investigate improved therapies and thoroughly understand the initial stage of aneurysm development. The regional collagen fiber modulus can help improve our understanding of the mechanisms of arterial dilation and aortic dissection.     

3D reconstruction of elastin fibres in coronary adventitia

A 3D reconstruction of individual fibres in vascular tissue is necessary to understand the microstructure properties of the vessel wall.  The objective of this study is to determine the 3D microstructure of elastin fibres in the adventitia of coronary arteries.  Quantification of fibre geometry is challenging due to the complex interwoven structure of the fibres.  In particular, accurate linking of gaps remains a significant challenge, and complex features such as long gaps and interwoven fibres have not been adequately addressed by current fibre reconstruction algorithms.  We use a novel line Laplacian deformation method, which better deals with fibre shape uncertainty to reconstruct elastin fibres in the coronary adventitia of five swine. A cost function, based on entropy and Euler Spiral, was used in the shortest path search. We find that mean diameter of elastin fibres is 1.67 ± 1.42 m and fibre orientation is clustered around two major angles of 8.9? and 81.8?.  Comparing with CT‐FIRE, we find that our method gives more accurate estimation of fibre width.  To our knowledge, the measurements obtained using our algorithm represent the first investigation focused on the reconstruction of full elastin fibre length.  Our data provide a foundation for a 3D microstructural model of the coronary adventitia to elucidate the structure–function relationship of elastin fibres.     

Wall expansion assessment of an intracranial aneurysm model by a 3D Digital Image Correlation System

Intracranial aneurysm is a local dilatation of an intracranial artery with high risk of rupture and death. Although it is generally accepted that the weakening of the arterial wall is the main cause for the rupture of an aneurysm, it still no consensus about the reasons for its creation, expansion and rupture. In particular, what is the role played by the blood flow in these phenomena. In this way, the aim of this work is the in vitro mechanical assessment of the wall expansion, namely the displacements, deformations and strains occurring in a saccular intracranial aneurysm model, when subjected to different flow rates. To obtain new insights into the mechanisms involved in the aneurysm rupture, a 3D-Vic™ Digital Image Correlation System was used and validated with a finite element analysis. The wall expansion results have revealed that the displacements, deformations and principal strains are directly related to the internal pressure caused by the fluid on the wall of the aneurism. These findings were especially observed in the weakened areas of the aneurysm model, where the wall was thinner. Furthermore, the technique used in this study has shown to be a potential method to validate numerical simulations of aneurysms, allowing the future performance of more complex and realistic haemodynamic studies.     

Concurrent validation of magnetic and inertial measurement units in estimating upper body posture during gait

We assessed the concurrent validity of commercially available magnetic and inertial measurement units (MIMUs) for estimating mean postural angles for head flexion, thorax flexion and shoulder girdle elevation during gait in seven healthy individuals. Postural angles estimated with the MIMUs were compared with angles calculated using marker data from a gold standard motion capture system. Coefficients of determination of mean postural angles between measurement systems were 0.82 for head flexion, 0.58 for thorax flexion, and 0.77 for shoulder girdle elevation. Bland–Altman analysis showed good agreement between measurement systems. Intraclass correlation coefficients were 0.9 for head flexion, 0.73 for thorax flexion, and 0.87 for shoulder girdle elevation. Root mean square errors were less than 3° between measurement systems for all body segments. The present findings suggest that the MIMUs tested in this study are valid for estimating head flexion, thorax flexion and shoulder girdle elevation during gait.     

Polarizing light microscopy of intestine and its relationship to mechanical behaviour

The polarizing optical microscope has been used to observe morphologically the effect of stress on rat and bovine intestine. Collagen fibres about 6 μm in diameter were found to be biaxially oriented at approximately +30° and ?30° to the longitudinal direction. The fibres are arranged in layers with the fibres in each layer densely packed in parallel undulating arrays. The undulations give rise to the extinction pattern observed in the polarizing optical microscope. The initial response to stress is straightening of the fibres. Gradual straightening of the fibres is related to the increasing stiffness of the tissue observed in the stress-strain relationship. Once the fibres are straightened, the biaxial orientation of the fibres produces higher strength in the longitudinal direction than in the transverse direction. This organization of intestinal collagen fibres has not been reported previously and is not observed in other biaxial tissues such as skin and aorta. Thus, intestine is a unique tissue for studying the relationships of mechanical behaviour to structure and organization of collagen.     

基于大气偏振模式的三维姿态信息获取

现有的偏振光导航方法提供的二维方向信息不能满足导航的实际需求,因此,本文提出了一种利用大气偏振模式获取三维姿态信息的方法,选取太阳作为空间显著特征点,利用大气偏振模式信息计算出载体在两次不同状态下的太阳空间位置信息,通过建立姿态变换矩阵获得了载体的三维姿态信息。最后,对不同天气条件、不同太阳空间位置、不同波段以及天空被部分遮挡情况下太阳空间位置计算的误差分布情况进行了仿真分析和实际测量。实验结果显示,当天空有气溶胶粒子分布时,蓝色波段下的计算误差最小,方位角和高度角的误差分别为1.50°和2.10°;当观测视场中有树木遮挡时,方位角和高度角的平均误差分别为0.91°和1.97°,由此表明本文方法能够有效提取太阳的空间位置,获得载体的三维姿态信息,并满足实际导航的需求。     

Physico-chemical characterization of functional electrospun scaffolds for bone and cartilage tissue engineering

Mimicking the zonal organization of the bone-cartilage interface will aid the production of functional osteochondral grafts for regeneration of skeletal joint defects. This study investigates the potential of the electrospinning technique to build a three-dimensional construct recapitulating the zonal matrix of this interface. Poly(lactic-co-glycolic acid) (PLGA) and PLGA-collagen solutions containing different concentrations of hydroxyapatite nanoparticles (nHAp) were electrospun on a thin layer of phosphate buffer saline solution spread on the collector in order to facilitate membrane detachment and recovery. Incorporation of increasing amounts of nHAp in PLGA solutions did not affect significantly the average diameter of the fibres, which was about 700 nm. However, in the presence of collagen, fibres with diameters below 100 nm were generally observed and the number of these fibres was inversely proportional to the ratio PLGA:collagen and proportional to the content of nHAp. PLGA membranes were rather hydrophobic, although the aqueous drop contact angles progressively fell from 125 degrees to 110 degrees when the content of nHAp was increased from 0 per cent to 50 per cent (w/v). PLGA-collagen membranes were more hydrophilic with contact angles between 60 degrees and 110 degrees; the values being proportional to the ratio PLGA:collagen and the content of nHAp. Also, the addition of nHAp from 0 per cent to 50 per cent (w/v) in the absence of collagen resulted in decreasing dramatically both the Young's modulus (Ym), from 34.3 +/- 1.8 MPa to 0.10 +/- 0.06 MPa, and the ultimate tensile strain (epsilon max), from a value higher than 40 per cent to 5 per cent. However, the presence of collagen together with nHAp allowed the creation of membranes much stiffer, although more brittle, as shown for membranes made with a ratio 8:2 and 10 per cent of nHAp, for which Ym = 70.0 +/- 6.6 MPa and epsilon max = 7 per cent.     

A comparison of the measured and predicted flowfield in a patient-specific model of an abdominal aortic aneurysm

Numerical simulation is increasingly being used to predict the flowfield within patient-specific geometries of abdominal aortic aneurysms under physiologically realistic flow conditions. This paper reports on a comparison between the flowfield measured in vitro within a patient-specific model of a mature abdominal aortic aneurysm and that predicted using computational fluid dynamics (CFD). Visualization and traverses of axial velocity were obtained at a number of locations in the aneurysm region under both steady and physiologically realistic pulsatile flow conditions. Comparisons between the measured and predicted flowfield show good agreement throughout the aneurysm. Although turbulence was observed distal in the aneurysm during late diastole, best agreement was achieved using a simple laminar flow model.     

Automated quantification and reconstruction of collagen matrix from 3D confocal datasets

The geometrical structure of fibrous extracellular matrix (ECM) impacts on its biological function. In this report, we demonstrate a new algorithm designed to extract quantitative structural information about individual collagen fibres (orientation, length and diameter) from 3D backscattered‐light confocal images of collagen gels. The computed quantitative data allowed us to create surface‐rendered 3D images of the investigated sample.     

一种方位及俯仰可调控制平台的实现

微波接收机是射电望远镜中专门用于接收射电信号的设备,而强度校准的目的是将接收到的射电信号响应等效地转换为天文意义上的流量密度。由于毫米波校准还易受到大气吸收作用,因此对大气不透明度的测试尤为重要。文中通过搭建机械转动平台及其控制系统,可以精确实现7 mm 波段常温接收机在目标方位下进 行0°~ 90°俯仰扫描观测。通过控制软件并行记录在不同仰角下的接收机输出功率,结合大气辐射转移方程,采用非线性最小二乘拟合的方式,最终得到当前方位7 mm 波段实时的大气不透明度值,很好地实现了精确控制及自动测试功能。     

Influence of orientation and volume fraction of Aramid fabric on abrasive wear performance of polyethersulfone composites

In case of fabric reinforced composites of specialty polymers influence of orientation of fabric and its volume fraction on tribo-behaviour is sparingly studied. In our earlier work, we have reported on the influence of amount of Aramid fabric (AF) in polyethersulfone (PES) on abrasive wear performance. However, orientation effect of fabric with respect to abrading plane was not investigated. In this work three orientations of composites of PES containing Aramid (Kevlar 29) fabric with three concentrations 64, 72 and 83 wt.% were selected to study the influence on abrasive wear performance. Composites developed by compression molding technique were characterized for their mechanical and physical properties. The abrasive wear performance of the composites was evaluated by abrading 10 mm × 10 mm × 10 mm sample against silicon carbide (SiC) paper under various loads and two grades of abrasive papers. The fabric reinforcement enhanced the abrasive wear resistance of PES significantly (approximately 1.35–9.46 times depending on the operating conditions). It was observed that 83% fabric composite showed the highest resistance to abrasive wear and impact along with the best tensile strength and elongation properties. Its flexural strength and ILSS values, however, were the lowest. Sixty-four percent fabric composite, on the other hand, showed an exactly reverse trend among the three composites. Among the three orientations, fibres in normal and parallel (N–P) and normal and anti-parallel (N–AP) direction with respect to sliding plane proved to impart maximum wear resistance. N–P was best for light loads while N–AP was best for high loading conditions. Orientation parallel and anti-parallel (P–AP) was least beneficial in this respect. Moreover, the extent of improvement very much depended on the operating parameters such as grit size and load. Benefits endowed due to reinforcement were higher at less coarse grade paper. With increase in load, however, wear rate of composites with N–P orientation increased and for other two orientations it decreased. Thus, for severe operating conditions, N–AP orientation proved to be most beneficial. SEM studies proved supporting for understanding the influence of orientation on wear performance.     

On the effect of shear-thinning rheology on hemodynamic characteristics in basilar tip aneurysms with implication of two distinct flow patterns

Intra-aneurysmal hemodynamics such as wall shear stress and complex flow structures have been implicated as one of the important factors on the growth and risk of rupture of an aneurysm. In this study, the sensitivity of intra-aneurysmal blood flow dynamics to the shear-thinning rheological model is investigated by using the idealized geometries of a basilar tip aneurysm with two representative anterior-posterior (AP) tilting angles (2° and 30°). By choice of different rheological models, time-averaged hemodynamic factors such as wall shear stress, oscillatory shear index and relative residence time exhibited only minor effects. However, highly unstable flow present in idealized aneurysm model with 2° AP tilting angle facilitated an evident change in the instantaneous local flow dynamics with a considerable increase in effective viscosity. Nevertheless, the distinct hemodynamic phenotype, which characterizes the gross intraaneurysmal flow pattern, was independent of the choice of rheological model. This result suggests that the shear thinning viscous effect is of secondary importance in the gross hemodynamics in a basilar tip aneurysm but is appreciably enhanced on the instantaneous hemodynamics with unstable complex flow structures.     

An attitude sensing device

A device for sensing the attitude of an arbitrarily located object has been developed by the Polar Geophysical Institute, Kola Research Center, Russian Academy of Sciences, for carrying out geophysical research. The device is capable of determining three angular coordinates of an object: the angles of roll and pitch with respect to the Earth’s horizontal plane and the azimuth angle with respect to the direction toward the magnetic north. The measurement range of the azimuth is from −180° to 180° with an error of ≤1°. The angles of roll and pitch can be measured in the range from −60° to 60° with an error of ≤0.5°. The device is reliable and easy to operate.     

用于红外晶体双折射测量的单1/4波片法

提出了一种基于单1/4波片法的测量方法以实现红外波段光学晶体双折射光程差的精确测量。采用厚度差小于一个周期厚度的两个样品进行比对,有效克服了单1/4波片法测量厚度的限制。依照此原理研制了测试波长为3.39μm的晶体双折射测试设备。应用琼斯矩阵理论,推导了存在主要误差因素时的信号光强解析表达式,并由此分析了起偏器方位角误差、1/4波片定位精度、样品方位角偏差、检偏器旋转定位精度对测量结果的影响,综合评价了本测量方法的精度。实验结果表明,应用研制的设备实测标准1/4波片的双折射光程差误差为0.003 76μm,相对误差为0.44%,满足系统要求。得到的结果表明,采用基于单1/4波片法的新测量方法能够有效、精确测得红外晶体的双折射光程差。     

Calibration method of tilt and azimuth angles for alignment of TEM tomographic tilt series

This paper describes the calibration method of the tilt and azimuth angles of specimen using a digital protractor and a laser autocollimator for alignment of electron tomography. It also suggests an easy method to check whether the specimen is tilted by 180.0°, and whether the azimuth angle is 0.0°; the method involves the use of two images of a rod-shaped specimen collected before and after a 180.0° tilt. The method is based on the assumption that these images are symmetric about the tilt axis when the azimuth angle is 0.0°. In addition, we used an experiment to demonstrate the effect of the incorrect angles on reconstructed images and simulated the image quality against distance away from tilt axis.     

Contrast enhancement of negatively stained macromolecules and biomembranes by single sideband phase contrast interference.

A straightforward procedure is described for the production of contrast enhancement of negatively stained macromolecules and biological membranes by single sideband phase contrast interference (electron optical shadowing). The instrumental adjustment required to produce this type of phase contrast illumination is readily achieved by beam deflection from the strioscopic (dark field) mode. Part of the hollow cone of electrons from the annular condenser aperture that are unscattered by the specimen are permitted to pass through the objective aperture and interfere with the scattered beam. The electron optical shadowing effect is produced because only one side of the unscattered beam is used. Careful adjustment of the beam tilt control, with the ability to tilt in any azimuth, allows optimal illumination conditions to be achieved. The results presented show the increased image contrast obtained using as specimens the purified cylindrical macromolecule from human erythrocyte membranes, purified nuclear envelopes and collagen fibres.