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1.
数码望远镜实现了数码相机与望远镜的有机组合,因此可用评价数码相机成像质量的指标——分辨率来评价数码望远镜的成像质量。但国际标准的数码相机分辨率检测如果不加改进,很难直接应用于数码望远镜的分辨率检测中。为此,提出了采用平行光管来测试数码望远镜分辨率的新方法,并在理论推导可行的基础上对单个数码望远镜进行了重复实验,最后采用自行编制的软件自动判读分辨率,测得数码望远镜的水平分辨率均值为814LW/PH,标准差为24LW/PH。结果表明,实验重复性好、可靠性较高,且采用软件自动判读分辨率比人工目视判读更客观、准确。 相似文献
2.
Consumer-grade digital cameras with or without external filters are recognized as a cost-effective method of vegetation monitoring. These cameras could produce time series information related to biophysical properties of vegetation. This paper evaluates the use of low-cost external filters with digital cameras for assessing vegetation indices (VIs). The system was implemented for ground-based (handheld) remote sensing in assessing biophysical properties of vegetation like plant phenology and Chlorophyll content. It also has high potential for above-canopy measurement using low-altitude remote sensing (LARS). In this study the modified cameras were used to capture near-infrared (NIR), red-edge (RE), and red (R) bands using proposed external filters. We use the low-cost NIR-R and NIR-RE external filters with modified cameras and tested the cameras performance using custom chamber under different illumination. Based on our findings, a method was proposed for enhancing the value of VI, which comprised the extracted DN of two broadbands like NIR and R. New ranges of broadband in red edge area (REhigh and RElow) are proposed as alternative bands in estimating Chlorophyll content. In addition, evaluation and implementation for assessing VIs are detailed in this study. 相似文献
3.
Holographic storage of three-dimensional image and data using photopolymer and polymer dispersed liquid crystal films 下载免费PDF全文
We present holographic storage of three-dimensional(3D) images and data in a photopolymer film without any applied electric field.Its absorption and diffraction efficiency are measured,and reflective analog hologram of real object and image of digital information are recorded in the films.The photopolymer is compared with polymer dispersed liquid crystals as holographic materials.Besides holographic diffraction efficiency of the former is little lower than that of the latter,this work demonstrates that the photopolymer is more suitable for analog hologram and big data permanent storage because of its high definition and no need of high voltage electric field.Therefore,our study proposes a potential holographic storage material to apply in large size static 3D holographic displays,including analog hologram displays,digital hologram prints,and holographic disks. 相似文献
4.
The computational efficiency and measurement accuracy of the digital image correlation (DIC) have become more and more important in recent years. For the three-dimensional DIC (3D-DIC), these issues are much more serious. First, there are two cameras employed which increases the computational amount several times. Second, because of the differences in view angles, the must-do stereo correspondence between the left and right images is equivalently a non-uniform deformation, and cannot be weakened by increasing the sampling frequency of digital cameras. This work mainly focuses on the efficiency and accuracy of 3D-DIC. The inverse compositional Gauss–Newton algorithm (IC-GN2) with the second-order shape function is firstly proposed. Because it contains the second-order displacement gradient terms, the measurement accuracy for the non-uniform deformation thus can be improved significantly, which is typically one order higher than the first-order shape function combined with the IC-GN algorithm (IC-GN1), and 2 times faster than the second-order shape function combined with the forward additive Gauss–Newton algorithm (FA-GN2). Then, based on the features of the IC-GN1 and IC-GN2 algorithms, a high-efficiency and high-accuracy measurement strategy for 3D-DIC is proposed in the end. 相似文献
5.
Summary The first-principle dynamics of IVAP-originated two-level systems is developed with reference to phonon-scattering and thermally
activated processes. It is shown that the anomalous coupling term βδ, appearing in the phonon-IVAP interaction, originates
from the elastic polarity ξ characteristic of the IVAP-like defects. The formal expressions for the quantities of interest,
such as the resonant-scattering rate of phonons and the time-dependent density of TLS states, are given analytically. Since
the tunnelling-atom theory is a limit case (β=0) of the present general approach, a point-by-point comparison with the standard
formalism of tunnelling-originated TLS is performed.
This work was partially supported by Ministero della Pubblica Istruzione. 相似文献
6.
High resolution digital holography 总被引:11,自引:0,他引:11
In digital Fresnel holography, present specifications of charge-coupled device cameras require the incident beams to be quasi-parallel. That implies large speckle grain size and low lateral resolution in reconstructed images. Better lateral resolutions are demonstrated in our work, down to 8 μm, allowing the observation of sub-millimetre objects by digital holography. The experimental set-up built samples the incident light distribution with a definition of 500 pixels mm−1. The maximum acceptable angle is then widened and the hologram recording and reconstruction distances are drastically reduced, as well as the speckle size. Interferometric holography was implemented for the measurement of the deformation of a sub-millimetre silicon cantilever and results in phase-contrasts imaging are also reported. The design of dedicated complementary metal-oxide-semiconductor active pixel sensor cameras is also discussed. 相似文献
7.
Three Dimensional digital image correlation(3D-DIC) has been widely used by industry, especially for strain measurement. The traditional 3D-DIC system can accurately obtain the whole-field 3D deformation. However, the conventional 3D-DIC system can only acquire the displacement field on a single surface, thus lacking information in the depth direction. Therefore, the strain in the thickness direction cannot be measured. In recent years, multiple camera DIC (multi-camera DIC) systems have become a new research topic, which provides much more measurement possibility compared to the conventional 3D-DIC system. In this paper, a multi-camera DIC system used to measure the whole-field thickness strain is introduced in detail. Four cameras are used in the system. two of them are placed at the front side of the object, and the other two cameras are placed at the back side. Each pair of cameras constitutes a sub stereo-vision system and measures the whole-field 3D deformation on one side of the object. A special calibration plate is used to calibrate the system, and the information from these two subsystems is linked by the calibration result. Whole-field thickness strain can be measured using the information obtained from both sides of the object. Additionally, the major and minor strain on the object surface are obtained simultaneously, and a whole-field quasi 3D strain history is acquired. The theory derivation for the system, experimental process, and application of determining the thinning strain limit based on the obtained whole-field thickness strain history are introduced in detail. 相似文献
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一种基于亮度直方图的自动曝光控制方法 总被引:5,自引:0,他引:5
自动曝光控制是现代相机和摄像机必备功能之一。提出一种基于亮度直方图的自动曝光控制算法。基于人类视觉系统(HVS)的视觉注意机制,可认为直方图中大而陡峭的峰值区域对应于图像中的不感兴趣区域。算法寻找直方图中最大的两个峰值区域,并依据峰值区域的大小确定它们中像素亮度的加权值,从而计算图像的加权亮度均值。像素亮度的加权值与其所属峰值区域的大小之间的关系由一组二次型曲线描述,二次型曲线的参量是由图像的背景亮度决定,其中背景亮度由自动曝光系统参量计算得到。在实际应用中采用了模糊逻辑确定最大的两个峰值区域的加权值。实验结果表明该算法对各种场景均能进行有效的自动曝光控制。 相似文献
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Digital holography is a widely used method for displacement measurement in coherent optical metrology. An obvious limit of the method is that too large displacements result in dense fringes, so the fringes are practically invisible. The maximum number of contour fringes in displacement measurement is limited, because the cameras are discrete devices and sampling theory plays an important role. Because of the limited measurement range, compensation methods are promising tools for practical measurements. It can be shown that the practical measurement range can be extended above the Nyquist sampling limit. Compensation methods can be digital, because digital holographic interferometry operates with images recorded with a digital camera. In our research work the upper measurement range of fringe compensation method was examined. Our goal was to perform automatic compensation even if the displacement is higher than the measurement range of the basic method. The operation of the automatic fringe compensation method was based on the combination of two types of out-of-plane displacement measurements with different sensitivities. 相似文献
13.
传统的迈克尔逊干涉仪只能简单地呈现光的干涉图像,并不能生动体现光的波动特性及其形貌特征,且测量过程繁琐。针对这些问题,提出了一种基于数字全息技术的新型迈克尔逊干涉仪实验装置。该装置采用2个CCD相机代替传统迈克尔逊干涉仪中的平面反射镜,并引入与球面光相干的平面参考光与球面光发生干涉,利用数字全息技术直接获取2个CCD记录面上的球面光复振幅信息,然后通过最小二乘拟合获取球面波参数,并对球面光复振幅进行解调得到居中后的球面光复振幅,最后通过数字干涉的方法实现两球面光的干涉。实验结果表明,该装置能实时生动地显示入射球面光的三维图像和两球面光的干涉图像,同时根据拟合得到的参数能便捷地测量透明等厚介质的折射率,实验中测量了3种不同材料的折射率,其误差均能控制在±5%以内,有较高的测量精度。 相似文献
14.
为提高数字全息再现像视角,提出一种基于滤波成像的数字全息技术来实现大视角的三维物体面型测量.利用离轴像面数字全息技术,通过在4F相干图像处理系统的空间频谱面处放置可移动的低通滤波器,使满足CCD分辨率的物光波与参考光波干涉形成全息图,并控制低通滤波及成像区域分别记录不同谱段的子全息图.再现时,首先对子全息图进行数字傅里叶变换,重构对应频谱段,并对频谱段进行拼接形成完整的物光频谱|而后通过数字再现获得大视角的数字全息再现像.利用该方法测量了圆柱形表面(光滑的缝纫针)的三维形貌,并取得了较好的实验结果. 相似文献
15.
C. Schick 《The European physical journal. Special topics》2010,189(1):3-36
Calorimetry is an effective analytical tool to characterize the glass transition and phase transitions under confinement.
Calorimetry offers a broad dynamic range regarding heating and cooling rates, including isothermal and temperature modulated
operation. Today 12 orders of magnitude in scanning rate can be covered by combining different types of calorimeters. The
broad dynamic range, comparable to dielectric spectroscopy, is especially of interest for the study of kinetically controlled
processes like crystallization or glass transition.
Accuracy of calorimetric measurements is not very high. Commonly it does not reach 0.1% and often accuracy is only a few percent.
Nevertheless, calorimetry can reach high sensitivity and reproducibility. Both are of particular interest for the study of
confined systems. Low addenda heat capacity chip calorimeters are capable to measure the step in heat capacity at the glass
transition in nanometer thin films. The good reproducibility is used for the study of glass forming materials confined by
nanometer sized structures, like porous glasses, semicrystalline structures, nanocomposites, phase separated block copolymers,
etc. Calorimetry allows also for the frequency dependent measurement of complex heat capacity in a frequency range covering
several orders of magnitude.
Here I exclusively consider calorimetry and its application to glass transition in confined materials. In most cases calorimetry
reveals only a weak dependence of the glass transition temperature on confinement as long as the confining dimensions are
above 10 nm. Why these findings contradict many other studies applying other techniques to similar systems is still an unsolved
problem of glass transition in confinement. 相似文献
16.
为了实现多摄像机之间同步曝光积分。对摄像机同步的原理和方法进行了研究。结合动态目标多目摄像测量方法设计并实现了同步采集系统,提出了通过编程控制将一种通用的数字输出模块USB-4711A作为同步触发信号发生器,该设备具有USB接口,支持即插即用。利用Visual C++平台开发了控制程序,能够根据图像采集频率和摄像机触发电平调节同步触发信号的周期和波形。经过验证.所设计的同步采集系统同步精度较高,同步误差小于10μs,并且具有设备简单、使用方便、成本低等优点,提供了一种通用的多摄像机同步解决方案。 相似文献
17.
The present paper develops a Statistical Mechanics approach to the inherent states of glassy systems and granular materials
by following the original ideas proposed by Edwards for granular media. We consider three lattice models (a diluted spin glass,
a system of hard spheres under gravity and a hard-spheres binary mixture under gravity) introduced to describe glassy and
granular systems. They are evolved using a “tap dynamics” analogous to that of experiments on granular media. We show that
the asymptotic states reached in such a dynamics are not dependent on the particular sample history and are characterized
by a few thermodynamical parameters. We assume that under stationarity these systems are distributed in their inherent states
satisfying the principle of maximum entropy. This leads to a generalized Gibbs distribution characterized by new “thermodynamical”
parameters, called “configurational temperatures” (related to Edwards compactivity for granular materials). Finally, we show
by Monte Carlo calculations that the average of macroscopic quantities over the tap dynamics and over such distribution indeed
coincide. In particular, in the diluted spin glass and in the system of hard spheres under gravity, the asymptotic states
reached by the system are found to be described by a single “configurational temperature”. Whereas in the hard-spheres binary
mixture under gravity the asymptotic states reached by the system are found to be described by two thermodynamic parameters,
coinciding with the two configurational temperatures which characterize the distribution among the inherent states when the
principle of maximum entropy is satisfied under the constraint that the energies of the two species are independently fixed.
Received 19 March 2002 and Received in final form 14 June 2002 相似文献
18.
The paper presents an introduction on the pure grid method for deformation measurements in experimental mechanics. The pure grid method involves that the grid images are processed separately, and subsequently the results of these separate processings are substrated from each other in order to obtain a quantified deformation indication.The recording and processing of the grid images are currently performed photonically by means of digital image measurement systems. The basic data processing relations and set-ups of four different applicabilities of the photonical, pure grid method are presented in this paper. The applicabilities are discussed. Strains can be measured with errors smaller than 200 micro strain and displacements with errors smaller than
of the diameter of the object as visible in the grid image. These figures can be improved substantially by future application of high resolving-power CCD cameras. Two examples are shown. The paper also contains an extensive bibliography for further explorations. 相似文献
19.
A. Herrmann L. Schimmele J. Mössinger M. Hirscher H. Kronmüller 《Applied Physics A: Materials Science & Processing》2001,72(2):197-208
The effective long-range long-time tracer diffusivity Deff for interstitial diffusion of hydrogen through heterogeneous systems was studied theoretically for model systems consisting
of isolated grains of material G embedded in a matrix of material M. Different solubilities of hydrogen in these two materials
as well as different diffusivities are allowed for. Additionally, modified diffusion barriers at the phase boundaries were
included in the diffusion model. The effect of different sizes, arrangements, and forms of the grains was also considered.
Deff was determined by Monte Carlo (MC) simulations on simple lattice models of the systems described above. An equilibrium distribution
of hydrogen atoms among the two constituent materials was assumed. Our main interest was focused on whether and how Deff may be related to mesoscopic or macroscopic quantities characterizing the heterogeneous system and its constituent materials,
such as the volume fractions of the two materials, the fraction of lattice sites in the immediate vicinity of the phase boundary,
the hydrogen concentrations cG and cM in the grains and in the matrix and the respective hydrogen diffusivities DG(cG) and DM(cM). In order to obtain good estimates for these relations in terms of analytic formulas, we attempted to model a heterogeneous
system by a network of diffusion elements connected in series and in parallel, in analogy to an electric network. The properties
of the basic connections, in parallel and in series, were studied on layered structures, for which analytic expressions for
Deff could be derived. The network formulas for different grain–matrix systems were tested by comparing with results of MC simulations.
In general, the network formulas describe the corresponding MC results for Deff fairly well. It was found that differences in the hydrogen solubilities in the two phases as well as modified energy barriers
at the phase boundaries may have dramatic effects on Deff.
Received: 19 September 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
20.
V.B. Markov 《Optics & Laser Technology》1996,28(4):319-325
Possible applications of holography for cultural heritage study, demonstration and restoration, particularly in practical museum applications, are discussed. In this respect two main applications of holography are of interest: display holography and technical holography. The latter includes holographic NDT methods, three-dimensional measurements of objects, memory systems, and so on. 相似文献