Polar Transformation Research Articles

Geochemical matrix differently affects the response of internal standards and target analytes for pesticide transformation products measured in groundwater samples

Electrospray ionization (ESI) is the most common technique in liquid chromatography coupled to tandem mass spectrometry (LC-MS-MS) allowing for sensitive detection of polar compounds with online water concentration. The technique is popular in groundwater monitoring programs and has permitted great progress in the detection and quantification of polar pesticide transformation products (TP) in recent years. However, ESI is also known to be prone to matrix effects. The common solution to this potential bias is the use of labelled internal standards. Unfortunately, these are not available for all target compounds, which leads to the linkage of target compounds to non-homologue internal standards with unknown consequences for quantification in variable geochemical settings. We investigated these matrix effects for polar TP with a molecular mass range of 225–350 Da and logDpH7 between −0.27 and −1.7 as well as for parent compounds with logDpH3 between 0.84 and 3.22. The acquired internal standards were tested on a gradient of DOC, anions, conductivity and inorganic carbon with a set of ten carefully chosen groundwater samples. Internal standards that were measured in positive ionization mode proved to be insensitive to geochemical variations while those that were measured in negative ionization mode showed reduced response with increasing anion concentration. All pairs of internal standards and target analytes were investigated for deviating matrix effects using standard addition experiments. Positive ionization compounds and target compounds with deuterated homologues showed little deviation while non-homologue pairs in negative mode proved to be strongly biased. Although bias was up to factor five for some compounds it was remarkably stable over the entire gradient studied, suggesting an identical suppression mode at varying matrix levels for different compounds. We advocate the conduct of standard addition experiments if homologue internal standards are not available.

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

The results of studying the waveforms of longitudinal and transverse photocurrent pulses generated in thin, semitransparent CuSe/Se films as a function of the angle of incidence (α) of a femtosecond laser beam at linear and circular polarizations are presented. It has been established that the durations of unipolar longitudinal photocurrent pulses at linear and circular polarizations of laser pumping do not depend on the angle α. It is shown that the evolution of the temporal profile of the helicity-sensitive transverse photocurrent with a change in α strongly depends on polarization. At linear polarization, the shape of the unipolar pulses remains virtually constant; however, at circular polarization, the generation of unipolar and bipolar pulses is possible, with the waveforms strongly depending on the angle α. The influence of the incidence angle on the waveforms of transverse photocurrent pulses is explained by the transformation of linear and circular polarization into an elliptical upon the refraction of light at the air/semitransparent film interface and by the interplay of photocurrents arising due to linear and circular surface photogalvanic effects in the film. The presented findings can be utilized to develop polarization and incidence angle-sensitive photovoltaic devices.

Experimental Study on a Self-Phase-Shifting Cross Vibrator Plasma Antenna Array

The study designs a type of plasma antenna array with four quartz fluorescent lamps, which can be classified into linear polarization and circular polarization (CP). The antenna arrays are designed into a self-phase-shifting cross shape, and the kHz alternating current power supplies are adopted in the proposed antenna arrays. Experimental results show that the cross vibrator antenna can realize not only impedance and pattern reconstruction, but also the polarization transformation. Moreover, the horizontal polarization, vertical polarization, and CP can be mutually transformed into each other by changing the vibrator operation mode. It is noted that we can easily transform the left-hand circular polarization and right-hand circular polarization into each other via modifying vibrator length and plasma density. Compared with a conventional metal antenna with the same shape, polarization conversion can be realized in an easier yet faster way via the help of self-phase-shifting plasma antenna array.

A Simple Method to Design Wideband Circularly Polarized Spherical Multibeam Luneburg Lens Antenna

This letter presents a simple method to design the wideband circularly polarized spherical multibeam Luneburg lens (LL) antenna by using three-dimensional (3-D)-printing. The conventional 3-D-printed spherical LL is divided into many cells and each cell is filled by the unit cell with different filling ratios, which breaks the circular symmetry of the LL. The proposed method divides the LL into many layers, and the profile surface equation of each layer is calculated by the ordinary least square method to keep the rotation symmetry of the LL. Then, according to the proposed circularly polarized implement method, the transformation of linear polarization to circular polarization can be realized by selecting a proper radius of LL. The simulated and measured results show that the axial ratios of the proposed multibeam LL antenna are less than 3 dB with good impedance performance and more than 13.8 dBi gain in a relative bandwidth of 31.6%, which demonstrates the validity and simplicity of the presented method.

Surgical Tool Segmentation with Pose-Informed Morphological Polar Transform of Endoscopic Images

This paper presents a tool-pose-informed variable center morphological polar transform to enhance segmentation of endoscopic images. The representation, while not loss-less, transforms rigid tool shapes into morphologies consistently more rectangular that may be more amenable to image segmentation networks. The proposed method was evaluated using the U-Net convolutional neural network, and the input images from endoscopy were represented in one of the four different coordinate formats (1) the original rectangular image representation, (2) the morphological polar coordinate transform, (3) the proposed variable center transform about the tool-tip pixel and (4) the proposed variable center transform about the tool vanishing point pixel. Previous work relied on the observations that endoscopic images typically exhibit unused border regions with content in the shape of a circle (since the image sensor is designed to be larger than the image circle to maximize available visual information in the constrained environment) and that the region of interest (ROI) was most ideally near the endoscopic image center. That work sought an intelligent method for, given an input image, carefully selecting between methods (1) and (2) for best image segmentation prediction. In this extension, the image center reference constraint for polar transformation in method (2) is relaxed via the development of a variable center morphological transformation. Transform center selection leads to different spatial distributions of image loss, and the transform-center location can be informed by robot kinematic model and endoscopic image data. In particular, this work is examined using the tool-tip and tool vanishing point on the image plane as candidate centers. The experiments were conducted for each of the four image representations using a data set of 8360 endoscopic images from real sinus surgery. The segmentation performance was evaluated with standard metrics, and some insight about loss and tool location effects on performance are provided. Overall, the results are promising, showing that selecting a transform center based on tool shape features using the proposed method can improve segmentation performance.

Arbitrary spatially variant polarization by unitary transformations in a common path interferometer

We introduce a novel, common path interferometric technique, for generating hybrid spatially variant polarized fields and Poincaré beams. The technique is based on unitary polarization transformations employing a single spatial light modulator in a Sagnac-like common path interferometer. This technique allows generating arbitrary fields as a superposition of orthogonal elliptically polarized vortex basis with opposite handedness. We demonstrate the generation of such fields theoretically and verify it experimentally for azimuthal and spiral polarization. As an example of application, we generated a radially polarized ring-shaped field and characterize it by Stokes polarimetry.

Bidirectional Deep Learning of Polarization Transfer in Liquid Crystals with Application to Quantum State Preparation

Accurate control of light polarization represents a core building block in polarization metrology, imaging, and optical and quantum communications. Voltage-controlled liquid crystals offer an efficient way of polarization transformation. However, common twisted nematic liquid crystals are notorious for lacking an accurate theoretical model linking control voltages and output polarization. An inverse model, which would predict control voltages required to prepare a target polarization, is even more challenging. Here we report both the direct and inverse models based on deep neural networks, radial basis functions, and linear interpolation. We present an inverse-direct compound model solving the problem of control voltages ambiguity. We demonstrate one order of magnitude improvement in accuracy using deep learning compared to the radial basis function method and two orders of magnitude improvement compared to the linear interpolation. Errors of the deep neural network model also decrease faster than the other methods with an increasing number of training data. The best direct and inverse models reach the average infidelities of $4 \times 10^{-4}$ and $2 \times 10^{-4}$, respectively, which is the accuracy level not reported yet. Furthermore, we demonstrate local and remote preparation of an arbitrary single-photon polarization state using the deep learning models. The results will impact the application of twisted-nematic liquid crystals, increasing their control accuracy across the board. The presented bidirectional learning can be used for optimal classical control of complex photonic devices and quantum circuits beyond interpolation.

Twisted Two-Dimensional Material Stacks for Polarization Optics.

The ability to control the light polarization state is critically important for diverse applications in information processing, telecommunications, and spectroscopy. Here, we propose that a stack of anisotropic van der Waals materials can facilitate the building of optical elements with Jones matrices of unitary, Hermitian, non-normal, singular, degenerate, and defective classes. We show that the twisted stack with electrostatic control can function as arbitrary-birefringent wave-plate or arbitrary polarizer with tunable degree of non-normality, which in turn give access to plethora of polarization transformers including rotators, pseudorotators, symmetric and ambidextrous polarizers. Moreover, we discuss an electrostatic-reconfigurable stack which can be tuned to operate as four different polarizers and be used for Stokes polarimetry.

Intelligent spraying robot for building walls with mobility and perception

Currently, wall mortar spraying relies on manual labour, which leads to high labour costs and low construction efficiency. In view of this, an intelligent spraying robot for building walls is developed. The retractable robot structure is designed to resolve the contradiction between the small robot size and the large single working range. A surface-to-surface parallel adjustment algorithm, based on laser ranging, is utilized to keep the robot parallel to the wall during spraying. A polar coordinate transformation method, based on LiDAR data, is used to enable the robot to automatically identify areas which do not need to be sprayed. The results of the experiments show that the robot can adjust its posture in 8 s with angle errors of less than 1° and that the robot can successfully identify windows or doors on walls. The wall spraying experiment proves that the spraying robot can automatically realize the wall mortar spraying.

Compact 2-step Septulum Polarization Converters for Radars and Satellite Systems

This article presents the results of analysis, numerical simulations and optimization of new narrowband guide septulum polarization converters. Orthomode duplexers and polarization converter designs based on septulums are widely used in modern microwave systems with orthogonal circularly polarized signals. Septulum guide polarizer is an effective compact device, which transforms right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic modes into linearly polarized ones. At the same time it divides RHCP and LHCP modes and directs them to two different rectangular guides with high signal discrimination to each other. Thus, a septulum-based guide device integrates performance of a polarization transformer and of an orthomode duplexer. The main electromagnetic characteristics of the polarization converter were simulated in software based on the finite elements method in the frequency domain. The proposed design of a compact narrowband guide polarization converter has a septulum with two steps. Several designs of septulum polarization converters were developed and compared for different relative bandwidths of 5%, 10%, and 15%. The comparative investigation of the obtained designs was carried out. Main electromagnetic characteristics of optimal septulum polarization converters were compared. These include return losses, cross-polarization discrimination, ellipticity parameter, and ports discrimination. It was demonstrated that in 5% fractional bandwidth a compact 2-stepped septulum polarization converter has return losses greater than 22 dB. Its cross-polarization discrimination and ports discrimination are greater than 25 and 27 dB. Developed compact septulum polarization converters can be applied in modern antenna systems for radars and satellite communication systems.

A Blend of Analytical and Numerical Methods to Compute Orthogonal Image Moments over a Unit Disk

Accurate image moment computation is critical because they are used in a variety of fields, including image reconstruction and object recognition. Orthogonal polynomials are frequently used to compute moments due to their numerous intersecting and important theoretical properties. In polar coordinate systems, orthogonal polynomials such as the Polar Harmonic Fourier Transform (PHFT) and Polar Harmonic Transformation (PHT) are defined. However, the images are defined by a Cartesian coordinate system. To obtain image moments, a double integration over a unit circle over the product of the PHFT or PHT and the image function must be performed. The choice of double integration techniques and domain for the double integral has a significant effect on the precision of the computed moments. We have proposed a method for using the entire unit circle as an integration domain in this study, for image reconstruction. We used the PHFT and PHT to apply this technique to computing moments for the reconstruction. The proposed method outperforms other state-of-the-art methods, including Gaussian quadrature numerical integration method (GQM) and zeroth order approximation (ZOA) on variety of scenarios using three benchmarked image sets. We have demonstrated experimentally that this technique significantly improves the accuracy of image moments in higher order moments, as measured by reduced mean squared error (MSE). Additionally, the proposed method significantly improved the moment’s rotational (an improvement of 1-3% as compared to GQM and an improvement of 37-93% as compared to ZOA) and scaling invariance (an improvement of 0-500% as compared to GQM and an improvement of 3-7000% as compared to ZOA).

An effective metasurface-based linear and circular polarization converter for C- and X-band applications

In this study, a reflection-mode metasurface-based linear and circular polarization converter is designed for common microwave frequencies (C-band (5.85–8.20 GHz) and X-band (8.20–12.40 GHz)). The proposed polarization converter possesses a right-handed circular polarization (RHCP) capability in the 5.35–5.94 GHz frequency range and a left-handed circular polarization conversion (LHCP) capability in the 8.88–12.03 GHz frequency range. Besides its circular polarization converter capability, it demonstrates linear polarization transformation in the 4.61–4.85 GHz and 6.86–7.78 GHz frequency ranges with a polarization converter rate (PCR) greater than 90%. The design provides an oblique incidence performance up to 45° with 80% PCR value in linear polarization. The CST Microwave Studio (a commercial 3D electromagnetic simulator) was used to obtain simulation results of the design. For validation, the designed converter was first fabricated using the conventional circuit-board method, and then its reflection coefficient was measured by a microwave measurement setup calibrated by the thru-reflect-line method. A good agreement was observed between simulated and experimental results. Finally, the proposed converter design was compared with other converter designs in the literature to examine its effectiveness.

Multilevel memory and artificial synaptic plasticity in P(VDF-TrFE)-based ferroelectric field effect transistors

Multilevel data memory and artificial synaptic plasticity in poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] ferroelectric field effect transistors were demonstrated. The dynamics of ferroelectric polarization transformation modulate potential of transistor channel, and adjust the electric field of the P(VDF-TrFE) ferroelectric film by potential along channel direction, thus realizing the multilevel nonvolatile memory state. The artificial synaptic plasticity of transistor is simulated, and the long-term plasticity of excited/inhibited postsynaptic current, paired impulse facilitation/inhibition, and spike-rate-dependent plasticity is realized. In long-term potentiation/depression simulation of devices, the conductivity symmetry and linearity are improved by setting the amplitude of the pulse increments. In addition, the vector-matrix multiplication operation was performed in a crossbar array. This work demonstrates the scheme to develop the P(VDF-TrFE) transistors-based multilevel memory and neural morphological computing.

Stochastic Stability and Bifurcation of Centrifugal Governor System Subject to Color Noise

This paper presents a detailed investigation of stochastic stability and complex dynamics of a centrifugal governor system with approximately uniform color noise. The centrifugal governor system excited by noise is transformed into Itö equation using polar coordinate transformation and stochastic average method. According to the boundary conditions of attraction and repulsion, the stochastic stability is ensured. In addition, analyses concerning the influence of parameter variation and validity are carried out by employing numerical method. The results manifest that the effects of noise intensity and correlation time on stationary probability density are opposite. The amplitudes of probability density finally tend to a limit value, and the only limit cycle appears, which shows that when the bifurcation occurs, the trivial solution of the system converges to a limit cycle with a higher probability. Finally, the two-dimensional parameter bifurcation analysis of the centrifugal governor system subject to color noise excitation is studied. An interesting distribution characteristic is found that the periodic region is organized according to the sequence of Stern–Brocot trees, and this typical characteristic is a universal characteristic of the system on the two parameter planes. Furthermore, it is concluded that based on the largest Lyapunov exponent diagram and bifurcation diagram in two-dimensional parameter plane, the effects of noise intensity and correlation time on the periodic oscillation state are opposite, but both of them can transform the quasi-periodic oscillation into periodic oscillation. It should be emphasized that with the increase of noise intensity, the coexisting oscillation behavior of the centrifugal governor system will change, which is manifested by the destruction of coexisting attractors and the generation of chaotic attractors.

General Lossless Polarization and Phase Transformation Using Bilayer Metasurfaces

AbstractMetasurface optical elements enable wavefront control and polarization manipulation with subwavelength resolution. Metasurfaces made of linearly birefringent meta‐atoms such as rectangular nanoposts are commonly used to control phase and polarization, but a single layer of these meta‐atoms cannot implement transformations with elliptically polarized or circularly polarized eigenstates (i.e., chiral transformations). Here, it is shown that two cascaded metasurface layers comprising linearly birefringent meta‐atoms provide sufficiently many degrees of freedom to implement arbitrary unitary phase and polarization transformations. A systematic design method for such metastructures is described and used to design a bifocal metalens that cannot be implemented by a single layer of birefringent meta‐atoms. The presented design and implementation techniques introduce a systematic approach for realizing the most general form of lossless polarization and phase transformations using metasurfaces with high efficiency.

A new scheme of polar Fast Fourier Transform Code for iris recognition through symbolic modelling approach

The rich random structure of the iris, non-invasiveness and temporal stability properties makes it one of the most powerful biometric trait for person identification. Iris recognition techniques have demonstrated very low false acceptance rates and very high matching efficiency in large iris datasets. However, iris recognition systems face several challenges including non-uniform lighting conditions, occlusion of the eye by the eyelid, variation of head pose (causes dimensional inconsistencies of iris part), the reflection of surrounding objects and many others. The paper has addressed some of the reported issues of iris recognition technique by exploring new feature extraction technique and devising a new symbolic modelling approach for feature representation and classification, along with other classification techniques namely k-NN, SVM and PNN. The symbolic approach employed in the proposed research to represent iris feature reduces the dimensionality of feature space and also reduces the actual time required for iris recognition. The symbolic approach with new feature extraction technique has attained recognition accuracy of 100%, 98.26%, 99.25% and 96.67% on CASIA 1.1, CASIA 4.0 Interval, SGGSIE&T and the newly formed VISA Iris datasets respectively. Additionally, authors deployed previous algorithms and their findings of the results are discussed in comparison with proposed techniques.

Polarization-independent wavelength-tunable flat-top comb filter based on quarter-wave polarization transformation

By harnessing quarter-wave polarization transformation, we propose a polarization-independent wavelength-tunable flat-top fiber comb filter composed of a polarization beam splitter, two polarization-maintaining fiber segments of equal length, a set of a half-wave plate and a quarter-wave plate (QWP), and dual QWPs, the simplest polarization controller. Using the Jones calculus, we derived the polarization-independent filter transmittance and sought the possible loci of the orientation angles (OAs) of the four waveplates as the functions of the transmittance phase (ϕ). With these OA loci, flat-top transmission spectra were calculated for eight ϕ values from 0° to 315° (increment: 45°), which manifests the frequency tunability of the filter. This theoretical prediction was also experimentally verified by using a broadband light source and optical spectrum analyzer. Eight measured flat-top transmission spectra were spaced 0.1 nm apart in wavelength as predicted, and the wavelength-tuning linearity was high enough to exhibit an adjusted R 2 value of ∼0.99925.

Co-Circular Polarization Reflector Revisited: Reflection Properties, Polarization Transformations, and Matched Waves

The variety of electromagnetic impedance boundaries is wide since the impedance boundary condition can have a two-dimensional matrix nature. In this article, a particular class of impedance boundary conditions is treated: a boundary condition that produces the so-called co-circular polarization reflector (CCPR). The analysis focuses on the possibilities of manipulating the polarization of the electromagnetic wave reflected from the CCPR surface as well as the so-called matched waves associated with it. The characteristics of CCPR and its special cases (perfectly anisotropic boundary (PAB) and soft-and-hard surface (SHS)) are compared against more classical lossless boundaries: perfect electric, perfect magnetic, and perfect electromagnetic conductors (PEC, PMC, and PEMC).

Analysis of waveguide polarizers using equivalent network and finite elements methods

Current research is dedicated to the development of new theoretical model for guide polarization converter with irises. New created model is derived based on the equivalent circuits and transmission line representations. Specific feature of the model consists in the possibility of account of irises thickness in the simulations by approximate single-mode method. Using equivalent lumped elements of the circuits we obtained general scattering matrices of the polarization transformer for fundamental modes of vertical and horizontal linear polarizations. Besides, numerical simulations and optimization of the device were carried out by finite elements method. Good agreement of obtained optimal sizes and polarization characteristics is observed. Provided by the polarizer phase difference between two orthogonal polarizations falls within range 90°±5° in the operating Ku-band. Calculated ellipticity coefficient is better than 1.5 dB. Developed model can be applied for designing of new waveguide polarization converters, filters and other waveguide components with irises.

High-resolution DTM-based estimation of geomorphometric parameters of selected putative martian scoria cones

Some previous studies have identified a number of features on Mars that are thought to be scoria cones. Since (terrestrial) scoria cones have special significance that they are monogenetic volcanoes, i.e. the volcanic edifice is created by a single eruptive event. The process usually produces fairly symmetrical cones, making them a target for morphometric research. In this study, we investigated features that were interpreted as scoria cones (or mud volcanoes), which are included in the HiRiSE database of stereopairs and thus, high-resolution DTMs can be generated for their area. We have computed DTMs using the tools of NASA Ames Stereo Pipeline and USGS ISIS system and calculated classic (cone width, cone height, crater width) and other volcano-geomorphometric indices and derivatives based on the elevation data. Polar Coordinate Transformation (PCT) images have been calculated in order to analyze the symmetry of the cones. Spatial Elliptical Fourier Descriptors (SEFD) have been computed to model the outer contours and the crater rims. The parameters (especially those of the fitted ellipses) are analyzed in order to visualize the orientation and extent of the properties of the cones. The classic relationship of the cone widths and cone heights can also be established for the Martian scoria cones. However, while for the terrestrial cases, a factor of 0.20–0.22 has been determined in the last decades, for the analyzed putative Martian scoria cones this factor is below 0.2, according to our calculations, they are in the range of 0.16–0.19. The analysis of the elevations of the cone contours reveals that in most of the cases the pre-eruptional surface could have been subhorizontal and flat. The fitted ellipses of SEFD method have a remarkably constant ratio of the lengths of the semimajor and semiminor axes, both for the outlines and for the crater rims. Although the contours and rims are slightly elliptical in most cases, our results show a high degree of symmetry in the selected cones. This symmetry is considered to be due to two main reasons: first, it is the result of a selection effect, as only those cone-shaped features are included in the study that are very probably scoria cones, and second, due to the different Martian conditions from those on Earth, in certain cases there is degradation on these cones, with e.g. at most minor mass movement traces modifying the high degree of symmetry.