Phase Filter Research Articles

A Range-Based Monte Carlo Box Algorithm for Mobile Nodes Localization in WSNs

Fast and accurate localization of randomly deployed nodes is required by many applications in wireless sensor networks (WSNs). However, mobile nodes localization in WSNs is more difficult than static nodes localization since the nodes mobility brings more data. In this paper, we propose a Range-based Monte Carlo Box (RMCB) algorithm, which builds upon the Monte Carlo Localization Boxed (MCB) algorithm to improve the localization accuracy. This algorithm utilizes Received Signal Strength Indication (RSSI) ranging technique to build a sample box and adds a preset error coefficient in sampling and filtering phase to increase the success rate of sampling and accuracy of valid samples. Moreover, simplified Particle Swarm Optimization (sPSO) algorithm is introduced to generate new samples and avoid constantly repeated sampling and filtering process. Simulation results denote that our proposed RMCB algorithm can reduce the location error by 24%, 14% and 14% on average compared to MCB, Range-based Monte Carlo Localization (RMCL) and RSSI Motion Prediction MCB (RMMCB) algorithm respectively and are suitable for high precision required positioning scenes.

OAM interferometry: the detection of the rotational Doppler shift.

In this paper, we propose a new type of rotational Doppler shift measurement based on the OAM of light which is capable of measuring the rotation of a point source in the plane orthogonal to the observer line of sight. By analysing the correlations between OAM states of light emitted by rotating sources, the rotational Doppler shift, and hence the rate of rotation, can be measured. We demonstrate that an OAM interferometer capable of extracting the rotational Doppler shift from OAM correlations can be constructed from a standard OAM modesorter combined with a phase filter.

Generation of an ultralong pure longitudinal magnetization needle with high axial homogeneity using an azimuthally polarized beam modulated by pure multi-zone plate phase filter

Based on the vector diffraction theory and the inverse Faraday effect in the magneto-optic film, light-induced magnetization distributions, for a high numerical aperture focusing configuration with an azimuthally polarized beam modulated by an optimized pure multi-zone plate phase filter, are investigated. By making use of the compeletely destructive interference of its inter circle with the π phase shift between adjacent sub-annuli, and the capability to extend the constructive interference in the propagating direction through its narrow outer annulus modulated by three misplaced helical phases, an ultralong () magnetization needle with both transverse super-resolution () and uniform axial field strength is achieved in the focal region. The perfect magnetization needle and the accessible method give a guide for ultrahigh density magnetic storage, fabricating magnetic lattices for spin wave operation, as well as atomic trapping.

Immiscible phase filter extraction and equivalent amplification of genotypes 1–6 of hepatitis C RNA: The building blocks for point-of-care diagnosis

The lack of hepatitis C virus (HCV) diagnostic tests designed for use in decentralized settings is a major obstacle for providing access to treatment and prevention services particularly in low and middle income countries. Here we describe the development and validation of two building blocks of the HCV Quant Assay, a test in development for point-of-care use: 1) an RT-qPCR assay with noncompetitive internal control that equivalently detects the 6 major HCV genotypes and 2) an automated sample prep method using immiscible phase filter technology. This novel assay has wide dynamic range of HCV quantification and a limit of detection of 30IU/ml with 200μl specimen volume. In a preliminary study of 61 clinical specimens, the HCV Quant Assay demonstrated 100% sensitivity and specificity and gave comparable viral load results across 4 logs of IU/ml when compared to the Abbott RealTime HCV Assay.

Creation of optical chain in the focal region of high NA lens of tightly focused higher order Gaussian beam

Based on vectorial diffraction theory, the interference effect of phase filter to generate multiple optical focal spot in the focal region of high numerical aperture (NA) objective lens on tightly focused transversely polarized Laguerre Gaussian beam is studied numerically. Basically the incident beam will generate a focal spot in the focal region, in order to change the focal structure, the diffractive optical element (DOE) (Phase filter) is introduced. Upon optimizing and tunning the angles of DOE the multiple focal spot in the subwavelength scale is generated in the focal region of high NA objective lens. Such kind of subwavelength focal spot segment may find wide applications in optical traps, biological application, atmospheric sciences and optical manipulation technology.

Focusing properties of Lorentz-Gaussian beam with azimuthally-variant phase filters

Optical vortex attracts many researchers for its interesting properties and promising applications. Focusing properties of the linearly polarized Lorentz-Gaussian beam with azimuthally-variant phase filters were investigated by vector diffraction theory. Results show that the focal intensity distributions can be altered considerably by phase variation parameter of phase filter and the beam parameters, changing phase variation parameter of the phase mask, focal shift, focal switch and focal split may occur, simultaneously, the focal shift direction may change. Moreover, altering phase variation parameter will change the energy distributions of maximum intensity peak and other small intensity peaks. And novel focal patterns also evolve considerably, such as from only one peak to multiple peaks. The focal pattern evolution principle is different with different beam parameter. The tunable focal shift can be used to construct controllable optical tweezers. In practice, azimuthally-variant phase filters can be implemented through phase-only spatial light modulator, which can conveniently alter the wavefront phase distribution of the incident laser beam in the control of computer.

Time-frequency Analysis of Time-varying Plasma’s Influences on PCM-FM Signal

In the process of hypersonic flight vehicle reentry, plasma sheath form on the aircraft surface because of atmospheric friction. Due to the changes of vehicle speed, posture and height , the atmospheric turbulence and non-uniform ablation, the influence of such factors makes the formed plasma sheath has time-varying characteristics. Statistical properties of telemetry PCM-FM signal change with the plasma’s parameters after the signal propagate through the time-varying plasma, and the PCM-FM signal become non-stationary random signal. In order to study the influence of time-varying plasma to PCM-FM signal, the time-frequency analysis is carried out on the output signal using short-time Fourier transform. Analysis results show that the time-varying plasma’s influence on the PCM-FM signal perform as amplitude attenuation and phase stray. Increasing the carrier frequency can reduce the influence of amplitude attenuation and improve the quality of the signal to a certain extent. But phase-stray phenomenon still exist, and can be solved by other methods such as phase filtering.

Synthetic aperture common-path digital holographic microscopy with spiral phase filter

This paper describes a synthetic aperture common-path digital holographic microscopy through phase-shifting in a rotating spiral phase filter (SPF) to strengthen axial phase accuracy and fully utilize frequency coverage to improve of the spatial resolution. A phase-type liquid crystal on a silicon spatial light modulator was employed to generate an SPF on the Fourier plane of the digital holographic microscopy system. Subsequently, the scattering wave passing through the spiral phase plate and the reference wave generated through the center of phase plate as a spatial filter were used for the interference process, thereby completing the recording of the on-axis digital hologram. The common-path digital holographic microscopy system integrated with synthetic aperture imaging can be applied for Fresnel hologram recording and numerical focusing on objects without being affected by environmental vibration and coherence, thereby improving the spatial resolution and axial phase accuracy.

Leveraging set relations in exact set similarity join

Exact set similarity join, which finds all the similar set pairs from two collections of sets, is a fundamental problem with a wide range of applications. The existing solutions for set similarity join follow a filtering-verification framework, which generates a list of candidate pairs through scanning indexes in the filtering phase, and reports those similar pairs in the verification phase. Though much research has been conducted on this problem, set relations, which we find out is quite effective on improving the algorithm efficiency through computational cost sharing, have never been studied. Therefore, in this paper, instead of considering each set individually, we explore the set relations in different levels to reduce the overall computational costs. First, it has been shown that most of the computational time is spent on the filtering phase, which can be quadratic to the number of sets in the worst case for the existing solutions. Thus we explore index-level set relations to reduce the filtering cost to be linear to the size of the input while keeping the same filtering power. We achieve this by grouping related sets into blocks in the index and skipping useless index probes in joins. Second, we explore answer-level set relations to further improve the algorithm based on the intuition that if two sets are similar, their answers may have a large overlap. We derive an algorithm which incrementally generates the answer of one set from an already computed answer of another similar set rather than compute the answer from scratch to reduce the computational cost. Finally, we conduct extensive performance studies using 21 real datasets with various data properties from a wide range of domains. The experimental results demonstrate that our algorithm outperforms all the existing algorithms across all datasets and can achieve more than an order of magnitude speedup against the state- of-the-art algorithms.

Filter based phase distortions in extracellular spikes.

Extracellular recordings are the primary tool for extracting neuronal spike trains in-vivo. One of the crucial pre-processing stages of this signal is the high-pass filtration used to isolate neuronal spiking activity. Filters are characterized by changes in the magnitude and phase of different frequencies. While filters are typically chosen for their effect on magnitudes, little attention has been paid to the impact of these filters on the phase of each frequency. In this study we show that in the case of nonlinear phase shifts generated by most online and offline filters, the signal is severely distorted, resulting in an alteration of the spike waveform. This distortion leads to a shape that deviates from the original waveform as a function of its constituent frequencies, and a dramatic reduction in the SNR of the waveform that disrupts spike detectability. Currently, the vast majority of articles utilizing extracellular data are subject to these distortions since most commercial and academic hardware and software utilize nonlinear phase filters. We show that this severe problem can be avoided by recording wide-band signals followed by zero phase filtering, or alternatively corrected by reversed filtering of a narrow-band filtered, and in some cases even segmented signals. Implementation of either zero phase filtering or phase correction of the nonlinear phase filtering reproduces the original spike waveforms and increases the spike detection rates while reducing the number of false negative and positive errors. This process, in turn, helps eliminate subsequent errors in downstream analyses and misinterpretations of the results.

Dissimilar pixel counting based impulse detector for two-phase mixed noise removal

Mixed noise is a challenging noise model due to its statistical complexity. A new two-phase denoising method based on an impulse detector using dissimilar pixel counting is proposed in this paper. This method consists of two stages: detection and filtering. For the detection phase, average difference scheme is proposed to distinguish whether two neighboring pixels are similar or not, and then the number of dissimilar pixels is compared with a threshold to locate the outlier point in noisy image. An iterative framework is used for detection accuracy with the least numbers of iteration. For the filtering phase, an extended trilateral filter is used to remove the mixture of Gaussian and impulse noise, which are treated differently depending on the guidance matrix from the detection phase. Extensive experimental results demonstrate that the proposed method exhibits better noise detection capability and outperforms many existing two-phase mixed noise removal methods in both quantitative evaluation and visual quality.

Three-dimensional super-resolution longitudinal magnetization spot arrays

We demonstrate an all-optical strategy for realizing spherical three-dimensional (3D) super-resolution (∼λ3/22) spot arrays of pure longitudinal magnetization by exploiting a 4π optical microscopic setup with two high numerical aperture (NA) objective lenses, which focus and interfere two modulated vectorial beams. Multiple phase filters (MPFs) are designed via an analytical approach derived from the vectorial Debye diffraction theory to modulate the two circularly polarized beams. The system is tailored to constructively interfere the longitudinal magnetization components, while simultaneously destructively interfering the azimuthal ones. As a result, the magnetization field is not only purely longitudinal but also super-resolved in all three dimensions. Furthermore, the MPFs can be designed analytically to control the number and locations of the super-resolved magnetization spots to produce both uniform and nonuniform arrays in a 3D volume. Thus, an all-optical control of all the properties of light-induced magnetization spot arrays has been demonstrated for the first time. These results open up broad applications in magnetic-optical devices such as confocal and multifocal magnetic resonance microscopy, 3D ultrahigh-density magneto-optic memory, and light-induced magneto-lithography.

Detecting sexual predators in chats using behavioral features and imbalanced learning

AbstractThis paper presents a system developed for detecting sexual predators in online chat conversations using a two-stage classification and behavioral features. A sexual predator is defined as a person who tries to obtain sexual favors in a predatory manner, usually with underage people. The proposed approach uses several text categorization methods and empirical behavioral features developed especially for the task at hand. After investigating various approaches for solving the sexual predator identification problem, we have found that a two-stage classifier achieves the best results. In the first stage, we employ a Support Vector Machine classifier to distinguish conversations having suspicious content from safe online discussions. This is useful as most chat conversations in real life do not contain a sexual predator, therefore it can be viewed as a filtering phase that enables the actual detection of predators to be done only for suspicious chats that contain a sexual predator with a very high degree. In the second stage, we detect which of the users in a suspicious discussion is an actual predator using a Random Forest classifier. The system was tested on the corpus provided by the PAN 2012 workshop organizers and the results are encouraging because, as far as we know, our solution outperforms all previous approaches developed for solving this task.

Tunable compensation of GVD-induced FM-AM conversion in the front end of high-power lasers.

Group velocity dispersion (GVD) is one of the main factors leading to frequency modulation (FM) to amplitude modulation (AM) conversion in the front end of high-power lasers. In order to compensate the FM-AM modulation, the influence of GVD, which is mainly induced by the phase filter effect, is theoretically investigated. Based on the theoretical analysis, a high-precision, high-stability, tunable GVD compensatory using gratings is designed and experimentally demonstrated. The results indicate that the compensator can be implemented in high-power laser facilities to compensate the GVD of fiber with a length between 200-500 m when the bandwidth of a phase-modulated laser is 0.34 nm or 0.58 nm and the central wavelength is in the range of 1052.3217-1053.6008 nm. Due to the linear relationship between the dispersion and the spacing distance of the gratings, the compensator can easily achieve closed-loop feedback controlling. The proposed GVD compensator promises significant applications in large laser facilities, especially in the future polarizing fiber front end of high-power lasers.

InSAR phase filtering using spatially adapted total generalized variation

ABSTRACTPhase filtering is an important processing step in interferometric synthetic aperture radar (InSAR) measurement. It is a difficult task to achieve noise reduction and fringe preservation simultaneously. To solve the dilemma, a new noise reduction scheme for InSAR phase images is introduced based on total generalized variation (TGV). The TGV regularization has been mathematically proven to be able to preserve edges while still imposing high-order smoothness in homogeneous regions. Combined with the characteristics of phase image, a spatially adapted TGV model is used as a regularizer in phase filtering. The regularization parameters are adaptively selected according to the coherence and local phase image features. The presented model is realized in the complex domain in order to avoid the effect of phase wrapping. Experiment results from simulated and real data sets demonstrate the effectiveness of this algorithm.

Tight focusing properties of phase modulated transversely polarized sinh Gaussian beam

We studied the tight focusing properties of an azimuthally polarized sinh-Gaussian beam phase modulated with multi belt vortex phase filter on the basis of the vector diffraction theory. The sinh-Gaussian beam can be considered as superposition of a series of eccentric Gaussian beams and it is observed that focusing such a beam with a properly designed dedicated vortex phase filter generates many novel focal patterns including transversely polarized optical needle of extended focal depth with sub wavelength scale lateral resolution and mutiple focal spots with different axial seperation distance. We expect that such a focal patterns are usefull in applications such as semiconductor inspection and multiple optical trapping.

Hypercomplex polynomial wavelet-filter bank transform for color image

Starting from a link with the discrete polynomial decomposition, we propose an extension of the non-uniform filter bank framework to vector-valued signals to carry out a non marginal color wavelet transform. Recently quaternions or Clifford algebras have been used to perform color image processing. This paper uses the embedding of color information into the imaginary part of a Quaternion. From this coding strategy, discrete Hypercomplex 2D polynomial transform is presented as generalizing the real polynomial transform to the Hypercomplex domain. We illustrate how this numerical approach can be used to define Wavelet filter bank transform for color image, with piecewise Hypercomplex polynomial. From this, the connection between discrete polynomial representation and multiscale, filter bank algorithm already defined for Grayscale image is described and the proposed color representation is discussed. This new hypercomplex polynomial-wavelet transform has an extra parameter: an imaginary unit quaternion corresponding to a privileged color direction. This new color representation satisfies the conditions of orthogonality, perfect reconstruction and linear phase filter. Moreover, a link between hypercomplex polynomial projections and discrete multiscale differentiators is studied. We also give a practical study of this new Hypercomplex transform in the contexts of image denoising, which validates the interest of our construction.

Pre-computed Region Guardian Sets Based Reverse kNN Queries

Given a set of objects and a query q, a point p is q’s Reverse k Nearest Neighbour (RkNN) if q is one of p’s k-closest objects. RkNN queries have received significant research attention in the past few years. However, we realize that the state-of-the-art algorithm, SLICE, accesses many objects that do not contribute to its RkNN results when running the filtering phase, which deteriorates the query performance. In this paper, we propose a novel RkNN algorithm with pre-computation by partitioning the data space into disjoint rectangular regions and constructing the guardian set for each region R. We guarantee that, for each q that lies in R, its RkNN results are only affected by the objects in R’s guardian set. The advantage of this approach is that the results of a query $$q\in R$$ can be computed by using SLICE on only the objects in its guardian set instead of using the whole dataset. Besides, we raise two new useful variants of RkNN and propose algorithms. Our comprehensive experimental study on synthetic and real the proposed approaches are the most efficient algorithms for RkNN and its variants.

Image Retrieval using GA Optimized Gabor Filter

Objective: A Hybrid content based image retrieval method is proposed in this paper. This method extracts color, tuned texture and shape features of the images in three successive phases. Methodology: In proposed system, color features are extracted using color histogram method in the first phase. The tuned texture features are extracted by employing GA optimized Gabor filters in second phase. Finally, shape features are extracted using the polygonal fitting algorithm. The best match output images of each phase are given as input images to the next phase to obtain ‘S’ best match images out of ‘N’ database images. Findings: The novelty of proposed system is that it employs a tunable filter that is tuned with the query image dynamically. The tuning of Gabor filter is implemented using GA in second phase. The proposed method shows improved retrieval rate in terms of average recall and average precision compared to the existing systems. The computation complexity is also found to be less than other existing methods. Applications: It can be employed in numerous fields such as medical, satellite, multimedia, and surveillance imaging systems, etc. where the retrieval of related images from huge databases is critical task for analysis.

Improved Goldstein Interferogram Filter Based on Local Fringe Frequency Estimation

The quality of an interferogram, which is limited by various phase noise, will greatly affect the further processes of InSAR, such as phase unwrapping. Interferometric SAR (InSAR) geophysical measurements’, such as height or displacement, phase filtering is therefore an essential step. In this work, an improved Goldstein interferogram filter is proposed to suppress the phase noise while preserving the fringe edges. First, the proposed adaptive filter step, performed before frequency estimation, is employed to improve the estimation accuracy. Subsequently, to preserve the fringe characteristics, the estimated fringe frequency in each fixed filtering patch is removed from the original noisy phase. Then, the residual phase is smoothed based on the modified Goldstein filter with its parameter alpha dependent on both the coherence map and the residual phase frequency. Finally, the filtered residual phase and the removed fringe frequency are combined to generate the filtered interferogram, with the loss of signal minimized while reducing the noise level. The effectiveness of the proposed method is verified by experimental results based on both simulated and real data.