Development of a Cryogenic Detector for Coherent Neutrino Nucleus Scattering

In Coherent Neutrino Nucleus Scattering (CNNS) the neutrinos interact coherently with all nucleons leading to a cross section which is much larger than for all other neutrino interactions. Because of the small momentum transfer as well as the small recoil energy in CNNS, and the relatively low count rate, a low energy threshold and a large target mass (several hundred grams) are required to observe CNNS. Our aim is to build a cryodetector for that purpose. Such a cryodetector, installed in the vicinity of a nuclear power plant, could probe new physics like non-standard neutral current interactions or a neutrino magnetic moment. We describe the results of three detectors, with Ge absorbers of 0.8 and 3.2 g and with a CaWO₄ absorber of 10 g. For Ge (0.8 g) an energy threshold of 0.43 keV and an energy resolution of 0.27 keV at ∼6 keV could be reached. We demonstrate that surface roughness effects deteriorate both threshold and resolution. For the 10 g CaWO₄ absorber we obtained 0.27 keV and 0.35 keV for threshold and energy resolution at ∼6 keV respectively.      

On the possibility of eliminating the energy threshold for electron detection in semiconductor detectors

A method of eliminating the energy threshold for electron detection in semiconductor devices is described. The class of devices used for the detection and measurement of electron emission is sufficiently large, including electrostatic analyzers, gas-filled devices, microchannel plates, etc. An alternative to these types of devices for electron detection is offered by semiconductor radiation detectors based on the p-n junctions, which are widely used in the spectrometry of nuclear particles including medium-and high-energy electrons (10² keV and above). These detectors are obviously advantageous in comparison to the devices of other types, but there are several factors hindering the use of semiconductor detectors for the detection and analysis of low-energy electrons (in the kiloelectronvolt range). We propose an approach that allows the energy threshold for electron detection in semiconductor detectors to be eliminated by means of preliminary acceleration of the detected particles in an electrostatic field created between the emitter and the detector. This approach removes the basic factor limiting the use of semiconductor detectors in a number of diagnostic methods based on the analysis of electron emission, such as the extended X-ray absorption fine structure (EXAFS), surface EXAFS, and X-ray absorption near-edge structure (XANES) techniques.     

Method of target detection in images by moment analysis of correlation peaks

Automatic target detection and recognition in images often is attempted by use of a linear correlation filter (matched filter), whose output is interpreted by a single pointwise detector (detection based on only one point). I examine a technique for significantly improving the performance of this target detection approach by supplementing the pointwise detector with several neighborhood correlation peak detectors (detection based on a domain of many points extending over much of the peak). The neighborhood detectors extract peak shape information through a moment analysis of correlation plane peaks. I describe the design of statistically quasi-optimal correlation peak discriminators based on second-order geometric moments.     

Demonstration of feasibility of operating a silicon ZIP detector with 20 eV threshold

100-g silicon detectors (known as “ZIPs,” Z-resolving Ionization and Phonon detectors) developed by the Cryogenic Dark Matter Search Experiment have been tested at charge bias voltages of up to 200 V/cm, significantly above their usual operating range (3–6 V/cm). Thermal gain factors in excess of 50 were observed due to the primary ionization drifting in the large applied field, with only minimal increase in phonon noise. The observed thermal gain corresponds to an intrinsic threshold of 20 eV, resulting in detectors that have direct application for use in a neutrino magnetic moment measurement based on a 40-MCi tritium source.     

Comparison of automatic target recognition system performance with full- and reduced-resolution correlators

The performance of an automatic target recognition (ATR) system with full- and reduced-resolution correlators was compared. In addition, the ATR system performance with reduced-resolution filter sets designed by use of multiresolution analyasis (MA) and downsampling (DS) techniques was also compared. It was discovered that results obtained at the optical correlator subsystem level, pertaining to the relative merits of the MA and the DS techniques, could not be extrapolated to the system level. This was because target signature differences between the test and the training imagery were discovered to have a greater influence on system performance than the choice of filter design technique. In addition, it was found that, for the case in which the target signature and the reduced-resolution filter were of the same size, there was some degradation in the receiver-operating-characteristic curve for reduced resolution compared with full. Nevertheless, this was deemed to have no practical significance, and thus the use of reduced-resolution optical correlators for ATR merits serious consideration.     

Distortion-invariant pattern recognition with Fourier-plane nonlinear filters

The use of nonlinear techniques in the Fourier plane of pattern-recognition correlators can improve the correlators' performance in terms of discrimination against objects similar to the target object, correlation-peak sharpness, and correlation noise robustness. Additionally, filter designs have been proposed that provide the linear correlator with invariance properties with respect to input-signal distortions and rotations. We propose simple modifications to presently known distortion-invariant correlator filters that enable these filter designs to be used in a nonlinear correlator architecture. These Fourier-plane nonlinear filters can be implemented electronically, or they may be implemented optically with a nonlinear joint transform correlator. Extensive simulation results are presented that illustrate the performance enhancements that are gained by the unification of nonlinear techniques with these filter designs.     

Two-beam-coupling correlator for synthetic aperture radar image recognition with power-law scattering centers preenhancement

Synthetic radar image recognition is an area of interest for military applications including automatic target recognition, air traffic control, and remote sensing. Here a dynamic range compression two-beam-coupling joint transform correlator for detecting synthetic aperture radar targets is utilized. The joint input image consists of a prepower-law, enhanced scattering center of the input image and a linearly synthesized power-law-enhanced scattering center template. Enhancing the scattering center of both the synthetic template and the input image furnishes the conditions for achieving dynamic range compression correlation in two-beam coupling. Dynamic range compression (a) enhances the signal-to-noise ratio, (b) enhances the high frequencies relative to low frequencies, and (c) converts the noise to high frequency components. This improves the correlation-peak intensity to the mean of the surrounding noise significantly. Dynamic range compression correlation has already been demonstrated to outperform many optimal correlation filters in detecting signals in severe noise environments. The performance is evaluated via established metrics such as peak-to-correlation energy, Horner efficiency, and correlation-peak intensity. The results showed significant improvement as the power increased.     

Bistatic SAR ATR

With the present revival of interest in bistatic radar systems, research in that area has gained momentum. Given some of the strategic advantages for a bistatic configuration, and technological advances in the past few years, large-scale implementation of the bistatic systems is a scope for the near future. If the bistatic systems are to replace the monostatic systems (at least partially), then all the existing usages of a monostatic system should be manageable in a bistatic system. A detailed investigation of the possibilities of an automatic target recognition (ATR) facility in a bistatic radar system is presented. Because of the lack of data, experiments were carried out on simulated data. Still, the results are positive and make a positive case for the introduction of the bistatic configuration. First, it was found that, contrary to the popular expectation that the bistatic ATR performance might be substantially worse than the monostatic ATR performance, the bistatic ATR performed fairly well (though not better than the monostatic ATR). Second, the ATR performance does not deteriorate substantially with increasing bistatic angle. Last, the polarimetric data from bistatic scattering were found to have distinct information, contrary to expert opinions. Along with these results, suggestions were also made about how to stabilise the bistatic-ATR performance with changing bistatic angle. Finally, a new fast and robust ATR algorithm (developed in the present work) has been presented.     

System-on-chip design for ultrasonic target detection using split-spectrum processing and neural networks

Ultrasonic detection and characterization of targets concealed by scattering noise is remarkably challenging. In this study, a neural network (NN) coupled to split-spectrum processing (SSP) is examined for target echo visibility enhancement using experimental measurements with input signal-to-noise ratio around 0 dB. The SSP-NN target detection system is trainable and consequently is capable of improving the target-to-clutter ratio by an average of 40 dB. The proposed system is exceptionally robust and outperforms the conventional techniques such as minimum, median, average, geometric mean, and polarity threshold detectors. For realtime imaging applications, a field-programmable gate array (FPGA)-based hardware platform is designed for system-onchip (SoC) realization of the SSP-NN target detection system. This platform is a hardware/software co-design system using parallel and pipelined multiplications and additions for highspeed operation and high computational throughput.     

Integrated approach for automatic target recognition using a network of collaborative sensors

We introduce what is believed to be a novel concept by which several sensors with automatic target recognition (ATR) capability collaborate to recognize objects. Such an approach would be suitable for netted systems in which the sensors and platforms can coordinate to optimize end-to-end performance. We use correlation filtering techniques to facilitate the development of the concept, although other ATR algorithms may be easily substituted. Essentially, a self-configuring geometry of netted platforms is proposed that positions the sensors optimally with respect to each other, and takes into account the interactions among the sensor, the recognition algorithms, and the classes of the objects to be recognized. We show how such a paradigm optimizes overall performance, and illustrate the collaborative ATR scheme for recognizing targets in synthetic aperture radar imagery by using viewing position as a sensor parameter.     

李雅普诺夫稳定性理论在目标识别效果评估中的应用

针对目标识别效果的稳定性评估，建立了目标识别系统的动态模型，随后基于李雅普诺夫稳定性理论，给出了目标识别系统识别效果的动态稳定性分析并完成初步仿真。     

Radiation pressure and stability of interferometric gravitational-wave detectors

The effect of radiation pressure on the stability of Fabry-Perot cavities with hanging mirrors is investigated. Such cavities will form an integral part of the laser interferometric gravitational-wave detectors that are being constructed around the globe. The mirrors are hung by means of a pendulum suspension and are locked by servo controls. We assume a realistic servo-control transfer function that satisfies the standard stability criteria. We find that for positive offsets from the resonance of the cavity the system is stable. However, we show that for negative offsets instabilities can occur, although the servo system has the effect of increasing the instability threshold, compared with the nonservoed case. Conditions for stability are finally given, involving the finesse of the cavity, the input power, the mass of the mirrors, the servo gain, and the phase detuning from perfect resonance. Gravitational-wave detectors with arm cavities having a finesse as low as approximately 200 could exhibit instabilities. Some implications for the locking of these detectors are finally given.     

Optimum rotation-invariant filter for disjoint-noise scenes

We introduce an optimum matched filter for rotation-invariant pattern recognition in scenes with disjoint noise. The optimum filter maximizes the ratio between the correlation-peak intensity and the correlation-output energy; in order to ensure rotation invariance, we assume the filter to take the form of a circular-harmonic function. The performance of this new filter is tested by computer simulations with a variety of natural and artificial backgrounds. The results obtained from these tests show an excellent performance much better than the classical circular-harmonic function (the filter that maximizes the signal-to-noise ratio while maintaining rotation invariance).     

Fragment detection system for studies of exotic neutron-rich nuclei

We have developed a fragment detection system for use in studies of exotic, neutron-rich nuclei. Using a C-shaped dipole magnet, the system sweeps charged fragments and un-reacted beam particles through an angle before stopping them in an array of plastic scintillator detectors, recording time-of-flight and total energy. The system also includes a pair of silicon strip detectors to measure fragment angle of emergence from the target and energy loss for particle identification.     

高分辨率遥感图像飞机目标定位新算法

为了提高自动目标识别系统的准确性,本文提出了一种高分辨率遥感图像的飞机目标定位的新方法,即在图像分割后再进行一次"去除伪目标"的目标识别系统新策略.首先,利用先验知识采用重叠的面积均分法对图像分块,然后基于多次阈值自动分割方法对各块图像进行分割.针对大图像目标识别的分块策略和飞机目标分割不完全的实际情况,提出一种基于辅助直线的Radon变换飞机轴线检测方法,用于飞机目标的定位.最后,通过实验证明,当飞机目标分割不完全时,本文方法能有效的检测飞机目标.     

Convexity theorem for subthreshold stimuli in linear models of visual contrast detection

Under the general assumption that visual contrast detection occurs by a parallel array of linear detectors, either without probability summation or with probability summation of a commonly assumed type, it is shown that the set of functions representing subthreshold stimuli must be convex. Thus, for example, a planar plot of the threshold locus using multiples of any two functions as axes, must be convex (cannot bulge inward). If experimental evidence to the contrary were discovered, it would rule out detection by parallel linear detectors of the above type. One possible kind of such evidence would be an inward cusp of the threshold locus corresponding to one of a special class of stimuli to which the visual system might be specifically sensitive.     

Dosimetry of low energy ions by means of solid state nuclear track detectors

This paper concerns applications of solid state nuclear track detectors (SSNTDs) of the CR-39 type for measurements of ion streams emitted from the rod plasma injector (RPI). The main diagnostic tool was a Thomson-type mass spectrometer, To detect low energy ions use was made of an additional ion-acceleration system, which enabled the registration threshold to be lowered to about 25 keV. Simultaneously with the time-integrated measurements, time-resolved studies were performed of ion streams by means of Faraday-type collectors. It was shown that the investigated plasma-ion source generates also high energy ions, e.g. protons of energy of 2.6-3.7 MeV. For the analysis of the irradiated and etched CR-39 detectors use was made of a computerised system, which enabled determination of the dimensions of the registered tracks produced by low energy protons, deuterons and nitrogen ions. It has extended the known characteristics of the CR-39 detector.     

Optical correlation of images with signal-dependent noise using constrained-modulation filter devices

Images with signal-dependent noise present challenges beyond those of images with additive white or colored signal-independent noise in terms of designing the optimal 4-? correlation filter that maximizes correlation-peak signal-to-noise ratio, or combinations of correlation-peak metrics. Determining the proper design becomes more difficult when the filter is to be implemented on a constrained-modulation spatial light modulator device. The design issues involved for updatable optical filters for images with signal-dependent film-grain noise and speckle noise are examined. It is shown that although design of the optimal linear filter in the Fourier domain is impossible for images with signal-dependent noise, proper nonlinear preprocessing of the images allows the application of previously developed design rules for optimal filters to be implemented on constrained-modulation devices. Thus the nonlinear preprocessing becomes necessary for correlation in optical systems with current spatial light modulator technlogy. These results are illustrated with computer simulations of images with signal-dependent noise correlated with binary-phase-only filters and ternary-phase-amplitude filters.