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41.
Reinhold Kleiner Dieter Koelle John Clarke 《Journal of Low Temperature Physics》2007,149(5-6):230-260
We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving
the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing
the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function
of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and dissipative
regimes, characterized by an inductance parameter β′
L
≡2π
LI
0/Φ
0≈1; L is the loop inductance, I
0 the critical current of the Josephson junction, and Φ
0 the flux quantum. In this regime, the lowest (intrinsic) values of noise energy are a factor of about 2 above previous estimates
based on analytical approaches. However, several other analytical predictions, such as the inverse proportionality of the
noise energy on the tank circuit quality factor and the square of the coupling coefficient between the tank circuit and the
SQUID loop, could not be well reproduced. The optimized intrinsic noise energy of the rf SQUID is superior to that of the
dc SQUID at all temperatures. Although for technologically achievable parameters this advantage shrinks, particularly at low
thermal fluctuation levels, we give examples for realistic parameters that lead to a noise energy comparable to that of the
dc SQUID even in this regime.
相似文献
42.
Intelligent multisensor surveillance systems consist of several types of sensors, which are installed on fixed and mobile devices. These components provide a huge quantity of information that has to be contrasted, correlated and integrated in order to recognize and react on special situations. These systems work in highly dynamic environments, with severe security and robustness requirements. All these characteristics imply the need for distributed solutions. In these solutions, scattered components can decide and act with some degree of autonomy (for instance, if they become isolated), or cooperate and coordinate for a complete tracking of special situations. In order to cope with these requirements and to better structure the solution, we have decided to design surveillance system control as a multiagent system. This is done by applying an agent-orientated methodology, which is assessed with concrete scenarios. 相似文献
43.
44.
实时跟踪控制系统中的数字滤波技术 总被引:2,自引:0,他引:2
在高精度的实时跟踪控制系统中,由探测器等其他一些因素给系统带来的噪声将不容忽视,数字滤波将是滤除噪声的有效手段,,由于系统实时性和采样频率的要求,本文介绍几种时跟踪系统中常用的数字滤波方法,并对它们在实时跟踪系统中的作用进行了和比较。 相似文献
45.
46.
用工控机组成了油田注水站数据采集系统.给出了系统的组成及测量方法,并讨论了系统的可靠性等问题. 相似文献
47.
48.
概述了反射式光纤传感器的发展。讨论了这类光纤传感器理论分析中所采用的纤端出射光场光强径向均匀分布的假设。给出了纤端出射场的光通量分布函数,并以全光路补偿反射式光纤探头为例,建立了补偿机理的理论分析方法,给出了传感特性调制函数的解析表达式。最后,简要分析了这类光纤传感器的温度稳定性问题。 相似文献
49.
本文介绍一种噪声图象的滤波方法 ,它不需要先验的图象模型 ,而且也不会损伤边界和细小的细节 ,在相加性和相乘性噪声的情况下 ,计算与边界方向有关的子集的局部平均值和方差 ,相应地沿着边界方向的噪声就被去掉 ,同时对边界有一定的增强效果 相似文献
50.
Impacts of spectral band difference effects on radiometric cross-calibration between satellite sensors in the solar-reflective spectral domain 总被引:2,自引:0,他引:2
In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on an investigation of radiometric calibration errors due to differences in spectral response functions between satellite sensors when attempting cross-calibration based on near-simultaneous imaging of common ground targets in analogous spectral bands, a commonly used post-launch calibration methodology. Twenty Earth observation imaging sensors (including coarser and higher spatial resolution sensors) were considered, using the Landsat solar reflective spectral domain as a framework. Scene content was simulated using spectra for four ground target types (Railroad Valley Playa, snow, sand and rangeland), together with various combinations of atmospheric states and illumination geometries. Results were obtained as a function of ground target type, satellite sensor comparison, spectral region, and scene content. Overall, if spectral band difference effects (SBDEs) are not taken into account, the Railroad Valley Playa site is a “good” ground target for cross calibration between most but not all satellite sensors in most but not all spectral regions investigated. “Good” is defined as SBDEs within ± 3%. The other three ground target types considered (snow, sand and rangeland) proved to be more sensitive to uncorrected SBDEs than the RVPN site overall. The spectral characteristics of the scene content (solar irradiance, surface reflectance and atmosphere) are examined in detail to clarify why spectral difference effects arise and why they can be significant when comparing different imaging sensor systems. Atmospheric gas absorption features are identified as being the main source of spectral variability in most spectral regions. The paper concludes with recommendations on spectral data and tools that would facilitate cross-calibration between multiple satellite sensors. 相似文献