Angular Correlation Research Articles

Densely sampled light field reconstruction with transformers

Densely sampled light fields (LFs) are critical for their further applications, such as digital refocus and depth estimation. However, it is costly and time-consuming to capture them. LF reconstruction, which aims at reconstructing a densely sampled LF from a sparsely sampled one, has attracted extensive attention of researchers. Although existing methods have achieved significant progress, these methods synthesize novel views, either through depth estimation and image warping, which depend heavily on the accuracy of the depth maps and are prone to cause artifacts at occluded regions, or by stacking multi-layer convolutions to learn the inherent structure of the LF, which will result in blurring results due to limited receptive fields when processing scenes with large disparities. We propose a transformer-based neural network for LF reconstruction (termed as LFRTR). Specifically, two novel transformers are introduced, namely angular transformer and spatial transformer. The former can fully explore angular information and correlations among different views, whereas the latter can capture local and non-local spatial texture information within each view. Moreover, dense skip connections are employed to enhance information flow between different layers. Thanks to the inherent global modeling ability of self-attention, the proposed LFRTR can reconstruct high-quality densely sampled LF in complex scenarios, such as large disparity, occlusion, and reflection. Experimental results on both synthetic and real-world LF datasets show that the proposed LFRTR outperforms other state-of-the-art methods in terms of both visual and numerical evaluations.

Multifrequency Wireless Channel Measurements and Characterization in Large Indoor Office Environments

This paper performs extensive channel measurements and characteristics analysis to investigate large-scale fading (LSF) and small-scale fading (SSF) of wireless local area network (WLAN) channels in large indoor office environments. Multi-frequency single-input single-output (SISO) channel measurements are conducted at 3, 5.5, and 6.5 GHz under the same conditions to explore the frequency dependence of LSF, delay spread (DS), and K-factor (KF). Then, SISO channel measurements with different half-power beamwidths (HPBWs) of antennas are performed at 5.5 GHz in access point (AP) to user equipment (UE) and AP to AP scenarios. The effects of antenna HPBW on LSF, DS, and KF are investigated, thereby inspiring the AP deployment in high density (HD) scenarios. Finally, 32×64 multiple-input multiple-output (MIMO) channel measurements at 5.5 GHz are conducted to study the SSF of the time non-stationarity and multi-link correlation. The time non-stationarity, including the parameters drifting and cluster evolution caused by the movement of the UE, is verified by measurement results. Multi-link correlations are illustrated from perspectives of the angular power spectral density (APSD) and correlation matrix collinearity (CMC). The results show that the distance between users and separation angle can affect the multi-link correlation.

An Effective Method for Antenna Radiation Pattern Reconstruction Based on Phaseless Measurement in a Reverberation Chamber

It has been shown that the angular correlation of the antenna can be obtained by rotating it in a reverberation chamber (RC) and the radiation pattern of the antenna under test (AUT) can be reconstructed from the measured correlation coefficients using spherical wave decomposition. However, the correlation coefficient needs to be obtained by measuring the complex-valued S-parameters in an RC, which is no longer applicable to active antenna tests where the phase information is unavailable. To solve this problem, we propose an antenna radiation pattern reconstruction method based on phaseless measurement in an RC. In this method, the power correlation coefficient of AUT is calculated using the signal amplitude received by the antenna at different angles. According to the relationship between complex correlation coefficient and power correlation coefficient of the AUT, the nonlinear least squares method is used to reverse the spherical wave coefficients and reconstruct the antenna radiation pattern. Simulations and measurements are carried out in RC and anechoic chamber, which demonstrated the feasibility and applicability of the proposed method.

Construction of St. Benedict

The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the University of Notre Dame Nuclear Science Laboratory. It is designed to measure the beta-neutrino angular correlation parameter in superallowed mixed beta-decay transitions between mirror nuclei in order to extract the Fermi-to-Gamow Teller mixing ratio and test theoretical corrections entering in the determination of the Vud element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix. St. Benedict includes a large volume gas catcher to thermalize the radioactive ion beam from TwinSol, a differentially-pumped extraction system, a radiofrequency quadrupole ion cooler and buncher, and a Paul trap for the observation and detection of the β decay products. The status of each of these components will be presented.

Angular Correlations in the β Decay of ^{8}B: First Tensor-Current Limits from a Mirror-Nucleus Pair.

We present the first measurement of the α-β-ν angular correlation in the Gamow-Teller β^{+} decay of ^{8}B. This was accomplished using the Beta-decay Paul Trap, expanding on our previous work on the β^{-} decay of ^{8}Li. The ^{8}B result is consistent with the V-A electroweak interaction of the standard model and, on its own, provides a limit on the exotic right-handed tensor current relative to the axial-vector current of |C_{T}/C_{A}|^{2}<0.013 at the 95.5% confidence level. This represents the first high-precision angular correlation measurements in mirror decays and was made possible through the use of an ion trap. By combining this ^{8}B result with our previous ^{8}Li results, we demonstrate a new pathway for increased precision in searches for exotic currents.

Primordial non-Gaussianity with angular correlation function: integral constraint and validation for DES

ABSTRACT Local primordial non-Gaussianity (PNG) is a promising observable of the underlying physics of inflation, characterized by $f_{\rm NL}^{\rm loc}$. We present the methodology to measure $f_{\rm NL}^{\rm loc}$ from the Dark Energy Survey (DES) data using the two-point angular correlation function (ACF) with scale-dependent bias. One of the focuses of the work is the integral constraint (IC). This condition appears when estimating the mean number density of galaxies from the data and is key in obtaining unbiased $f_{\rm NL}^{\rm loc}$ constraints. The methods are analysed for two types of simulations: ∼246 goliat-png N-body small area simulations with fNL equal to −100 and 100, and 1952 Gaussian ice-cola mocks with fNL = 0 that follow the DES angular and redshift distribution. We use the ensemble of goliat-png mocks to show the importance of the IC when measuring PNG, where we recover the fiducial values of fNL within the 1σ when including the IC. In contrast, we found a bias of ΔfNL ∼ 100 when not including it. For a DES-like scenario, we forecast a bias of ΔfNL ∼ 23, equivalent to 1.8σ, when not using the IC for a fiducial value of fNL = 100. We use the ice-cola mocks to validate our analysis in a realistic DES-like set-up finding it robust to different analysis choices: best-fitting estimator, the effect of IC, BAO damping, covariance, and scale choices. We forecast a measurement of fNL within σ(fNL) = 31 when using the DES-Y3 BAO sample, with the ACF in the 1 deg &amp;lt; θ &amp;lt; 20 deg range.

A SiPM-based dual and triple coincidence system for positron annihilation lifetime measurement

Positron annihilation lifetime (PAL) spectroscopy is a powerful non-destructive method to study defects in materials. Silicon photomultipliers (SiPMs) have emerged as promising photodetector alternatives for PAL systems. However, further research is needed to fully optimize SiPM arrays for PAL applications. In this study, a dual and triple coincidence system has been developed based on four 1 × 4 SiPM arrays with resistor-chain readout, and initial results of PAL measurement have been obtained. A pixel-by-pixel time shift correction method was proposed and successfully applied using triple γ coincidence for summing 128 PAL spectra in one measurement. The system provides position, timing, and energy information for both 1275 and 511 keV γ-rays. The use of SiPM arrays and the pixel-by-pixel time shift correction method have enabled precise and reliable measurements of PALs in single-crystal silicon and yttria-stabilized zirconia samples. The developed SiPM-array-based PAL system also offers a technical solution to measure angular correlations of positron annihilation radiation, with the potential for further improvements.

Testing entanglement of annihilation photons

We present a new experimental study of the quantum entanglement of photon pairs produced in positron-electron annihilation at rest. Each annihilation photon has an energy that is five orders of magnitude higher than the energy of photons in optical experiments. It provides a unique opportunity for controlled Compton pre-scattering of initial photons before the polarization measurements. The experimental setup includes a system of Compton polarimeters to measure the angular correlations of annihilation photons in initial and thus prepared pre-scattered states. For the first time, a direct comparison of the polarization correlations of initial and pre-scattered annihilation photons has been carried out. The angular distributions of scattered in polarimeters photons turned out to be the same for both types of events. Moreover, the correlation function in the Bell’s inequality is also the same for both states. We discuss the implications of our results for quantum measurement theory and for the quantum-entangled positron emission tomography.

Angular correlation of the two gamma rays produced in the thermal neutron capture on gadolinium-155 and gadolinium-157

Abstract The ANNRI-Gd collaboration studied in detail the single γ-ray spectrum produced from the thermal neutron capture on 155Gd and 157Gd in our previous publications. Gadolinium targets were exposed to a neutron beam provided by the Japan Spallation Neutron Source (JSNS) in J-PARC, Japan. In the present analysis, one new additional coaxial germanium crystal was used in combination with the 14 germanium crystals in the cluster detectors to study the angular correlation of the two γ rays emitted in the same neutron capture. We present for the first time angular correlation functions for two γ rays produced during the electromagnetic cascade transitions in the (n, γ) reactions on 155Gd and 157Gd. As expected, we observe mild angular correlations for the strong, but rare transitions from the resonance state to the two energy levels of known spin-parities. Contrariwise, we observe negligibly small angular correlations for arbitrary pairs of two γ rays produced in the majority of cascade transitions from the resonance state to the dense continuum states.

Improvement of double photon emission Compton imaging using angular and polarization correlations in cascade photons

A Compton camera is a gamma ray imaging system that produces images by superposing Compton cones calculated from Compton kinematics. However, the reconstructed images exhibit a high background. In this study, the angular correlation and polarization correlation were used to decrease the background. 111In, which emits 171 keV and 245 keV cascade gamma rays, was imaged using Compton camera modules in the ring structure. The 3D list-mode ordered subset expectation maximization method was used to reconstruct the images. Probability modeling of events reflecting angular and polarization correlations was applied to the image-reconstruction algorithm. The results were compared with those of a typical Compton camera method using only 245 keV Compton cones. The sensitivity of the proposed method was 1.03% of that of the typical method. However, compared to the typical method, the application of angular and polarization correlations improved the signal-to-background ratio. The proposed method is expected to be useful in capturing low-background images wherein a ring-type Compton camera and cascade photon-emitting nuclides can be used.

Collimator design for gamma-ray cascade angular correlations in medical imaging

In recent decades, Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) have become workhorses of molecular imaging. The main drawback of these modalities is that they resort to statistical methods of image reconstruction, as the location of the individual nuclei emitting radiation is not accessible. To remedy this situation, we embarked on a project to introduce a new modality of nuclear medical imaging which exploits the non-collinear angular correlations of nuclear gamma-ray cascades subsequent to beta decays. This modality, if effective, determines the location of each decay nucleus. We have retrofitted the small animal PET assembly of RIKEN-Kobe (Japan) with tungsten+PLA (polylactic acid) collimators. The chosen material is inexpensive, amenable to three-dimensional (3D) printing, and has good photon attenuation properties. We included the collimator geometry in GATE (Geant4 Application for Tomographic Emission) simulations and developed algorithms for image reconstruction with medical isotope candidates viz., 111In and 43K. Our preliminary simulations show that data acquisition with a 2 MBq source for 900 s is sufficient to reproduce the source geometry with high resolution. This report summarizes our progress to date and the plans for the near future.

Fragmentation Dynamics of CO2q+ (q = 2, 3) in Collisions with 1 MeV Proton

The fragmentation dynamics of the CO2q+ (q = 2, 3) molecular ions formed under the impact of 1 MeV protons is studied using a recoil ion momentum spectrometer equipped with a multi-hit time- and position-sensitive detector. Both two-body and three-body fragmentation channels arising from the doubly and triply ionized molecular ions of CO2 are identified and analyzed. Kinetic energy release (KER) distributions have been obtained for various channels. With the help of Dalitz plots and Newton diagrams concerted and sequential processes have been assigned to observed fragmentation channels. In addition, angular correlations are used to determine the molecular geometry of the precursor molecular ion. It is found that the symmetric breakup into C+ + O+ + O+ involves asymmetric stretching of the molecular bonds in CO23+ prior to dissociation via concerted decay implying the fact that collisions with 1 MeV proton induces an asynchronous decay in CO2.

The impact and estimation of uncertainty correlation for multi-angle polarimetric remote sensing of aerosols and ocean color

Abstract. Multi-angle polarimetric (MAP) measurements contain rich information for characterization of aerosol microphysical and optical properties that can be used to improve atmospheric correction in ocean color remote sensing. Advanced retrieval algorithms have been developed to obtain multiple geophysical parameters in the atmosphere–ocean system, although uncertainty correlation among measurements is generally ignored due to lack of knowledge on its strength and characterization. In this work, we provide a practical framework to evaluate the impact of the angular uncertainty correlation from retrieval results and a method to estimate correlation strength from retrieval fitting residuals. The Fast Multi-Angular Polarimetric Ocean coLor (FastMAPOL) retrieval algorithm, based on neural-network forward models, is used to conduct the retrievals and uncertainty quantification. In addition, we also discuss a flexible approach to include a correlated uncertainty model in the retrieval algorithm. The impact of angular correlation on retrieval uncertainties is discussed based on synthetic Airborne Hyper-Angular Rainbow Polarimeter (AirHARP) and Hyper-Angular Rainbow Polarimeter 2 (HARP2) measurements using a Monte Carlo uncertainty estimation method. Correlation properties are estimated using autocorrelation functions based on the fitting residuals from both synthetic AirHARP and HARP2 data and real AirHARP measurement, with the resulting angular correlation parameters found to be larger than 0.9 and 0.8 for reflectance and degree of linear polarization (DoLP), respectively, which correspond to correlation angles of 10 and 5∘. Although this study focuses on angular correlation from HARP instruments, the methodology to study and quantify uncertainty correlation is also applicable to other instruments with angular, spectral, or spatial correlations and can help inform laboratory calibration and characterization of the instrument uncertainty structure.

Improved FIFRELIN de-excitation model for neutrino applications

The precise modeling of the de-excitation of Gd isotopes is of great interest for experimental studies of neutrinos using Gd-loaded organic liquid scintillators. The FIFRELIN code was recently used within the purposes of the STEREO experiment for the modeling of the Gd de-excitation after neutron capture in order to achieve a good control of the detection efficiency. In this work, we report on the recent additions in the FIFRELIN de-excitation model with the purpose of enhancing further the de-excitation description. Experimental transition intensities from the EGAF database are now included in the FIFRELIN cascades, in order to improve the description of the higher energy part of the spectrum. Furthermore, the angular correlations between $$\gamma $$ rays are now implemented in FIFRELIN, to account for the relative anisotropies between them. In addition, conversion electrons are now treated more precisely in the whole spectrum range, while the subsequent emission of X rays is also accounted for. The impact of the aforementioned improvements in FIFRELIN is tested by simulating neutron captures in various positions inside the STEREO detector. A repository of up-to-date FIFRELIN simulations of the Gd isotopes is made available for the community, with the possibility of expanding for other isotopes which can be suitable for different applications.

Deep Constrained Spherical Deconvolution for Robust Harmonization.

Diffusion weighted magnetic resonance imaging (DW-MRI) captures tissue microarchitecture at millimeter scale. With recent advantages in data sharing, large-scale multi-site DW-MRI datasets are being made available for multi-site studies. However, DW-MRI suffers from measurement variability (e.g., inter- and intra-site variability, hardware performance, and sequence design), which consequently yields inferior performance on multi-site and/or longitudinal diffusion studies. In this study, we propose a novel, deep learning-based method to harmonize DW-MRI signals for a more reproducible and robust estimation of microstructure. Our method introduces a data-driven scanner-invariant regularization scheme to model a more robust fiber orientation distribution function (FODF) estimation. We study the Human Connectome Project (HCP) young adults test-retest group as well as the MASiVar dataset (with inter- and intra-site scan/rescan data). The 8th order spherical harmonics coefficients are employed as data representation. The results show that the proposed harmonization approach maintains higher angular correlation coefficients (ACC) with the ground truth signals (0.954 versus 0.942), while achieves higher consistency of FODF signals for intra-scanner data (0.891 versus 0.826), as compared with the baseline supervised deep learning scheme. Furthermore, the proposed data-driven framework is flexible and potentially applicable to a wider range of data harmonization problems in neuroimaging.

Measurement of angular correlation changes in double-photon emission nuclides using ultrasound irradiation

Our group has been developing DPECT (Double Photon Emission CT) to enhance nuclear medicine diagnostics using cascade nuclides that emit multiple gamma rays simultaneously. It is possible to detect the local environment around the nuclide by examining the angular correlation of the emitted cascade gamma-rays. In this study, with the goal of developing a new imaging method combining ultrasound and nuclear medicine, we investigated the effect of ultrasound on cascade gamma-ray emission and found that the angular correlation could be changed by a micro-electric field around 111In in an aqueous solution caused by ultrasound irradiation. Using 8 × 8 array of GAGG scintillators as a detector and Hamamatsu Photonics 8 × 8 MPPCs as a photomultiplier, eight detectors were used and arranged in a ring shape to surround the point source 111In from 360° direction. For the readout system, using a dynamic ToT board, read out its channel information, energy information as ToT signal, and detection time information simultaneously and independently concerning gamma-ray detection. We measured the angular correlation change with four types of ultrasound intensities of 0.05 V, 0.10 V, 0.15 V, and 0.20 V input voltage, and found that the gamma-ray emission angle distribution decreased by about up to 5% around the 90° direction and increased by about up to 5% around 0° and 180° for an ultrasound with an input voltage of 0.15 V or higher.

Multiparametric Quantitative Analysis of Photodamage to Skin Using Optical Coherence Tomography.

Ultraviolet (UV) irradiation causes 90% of photodamage to skin and long-term exposure to UV irradiation is the largest threat to skin health. To study the mechanism of UV-induced photodamage and the repair of sunburnt skin, the key problem to solve is how to non-destructively and continuously evaluate UV-induced photodamage to skin. In this study, a method to quantitatively analyze the structural and tissue optical parameters of artificial skin (AS) using optical coherence tomography (OCT) was proposed as a way to non-destructively and continuously evaluate the effect of photodamage. AS surface roughness was achieved based on the characteristic peaks of the intensity signal of the OCT images, and this was the basis for quantifying AS cuticle thickness using Dijkstra's algorithm. Local texture features within the AS were obtained through the gray-level co-occurrence matrix method. A modified depth-resolved algorithm was used to quantify the 3D scattering coefficient distribution within AS based on a single-scattering model. A multiparameter assessment of AS photodamage was carried out, and the results were compared with the MTT experiment results and H&E staining. The results of the UV photodamage experiments showed that the cuticle of the photodamaged model was thicker (56.5%) and had greater surface roughness (14.4%) compared with the normal cultured AS. The angular second moment was greater and the correlation was smaller, which was in agreement with the results of the H&E staining microscopy. The angular second moment and correlation showed a good linear relationship with the UV irradiation dose, illustrating the potential of OCT in measuring internal structural damage. The tissue scattering coefficient of AS correlated well with the MTT results, which can be used to quantify the damage to the bioactivity. The experimental results also demonstrate the anti-photodamage efficacy of the vitamin C factor. Quantitative analysis of structural and tissue optical parameters of AS by OCT enables the non-destructive and continuous detection of AS photodamage in multiple dimensions.

First Evidence of Axial Shape Asymmetry and Configuration Coexistence in Zn74 : Suggestion for a Northern Extension of the N=40 Island of Inversion

The excited states of N=44 ^{74}Zn were investigated via γ-ray spectroscopy following ^{74}Cu β decay. By exploiting γ-γ angular correlation analysis, the 2_{2}^{+}, 3_{1}^{+}, 0_{2}^{+}, and 2_{3}^{+} states in ^{74}Zn were firmly established. The γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2_{2}^{+}, 3_{1}^{+}, and 2_{3}^{+} states were measured, allowing for the extraction of relative B(E2) values. In particular, the 2_{3}^{+}→0_{2}^{+} and 2_{3}^{+}→4_{1}^{+} transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the N=40 gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize ^{74}Zn in its ground state. Furthermore, an excited K=0 band with a significantly larger softness in its shape is identified. A shore of the N=40 "island of inversion" appears to manifest above Z=26, previously thought as its northern limit in the chart of the nuclides.

Two-particle angular correlations in e+e− collisions to hadronic final states in two reference coordinates at Belle

We present the analysis of two-particle angular correlations using coordinate systems defined with the conventional beam axis and the event thrust axis. We propose the latter as a good representation for the correlation structure interpretation in the e+e− collision system. The e+e− collisions to hadronic final states at center-of-mass energies of sqrt{s} = 10.52 GeV and 10.58 GeV are recorded by the Belle detector at KEKB. In this paper, results on the first dataset are supplementary to the previous Belle publication [1]. At the same time, the latter is the first two-particle correlation measurement at collision energy on the Υ(4S) resonance and is sensitive to its decay products. Measurements are reported as a function of the charged-particle multiplicity. Finally, a qualitative understanding of the correlation structure is discussed using a combination of Monte Carlo simulations and experimental data.

Vzaiemozviazok mizh problemamy zi somatychnym zdoroviam u ditei doshkilnoho viku ta porushenniamy psykhomotornoho rozvytku

Introduction. Multiple studies show the presence of interconnection between co-morbidity and psychomotor development disorders in children. The aim of the study. To identify the relationships between the problems with somatic health in preschool children (3-7 years old) and disorders of their psychomotor development. Materials and methods. Clinical and laboratory examination of 70 children was carried out in a randomized manner with preliminary stratification according to the presence of psychomotor development disorders regarding the somatic and infectious diseases and birth defects they had at the time of the examination and in the anamnesis. The examined group consisted of 70 children of preschool age (3-7 years) with psychomotor development disorders. Statistical processing included calculations using R. E. Fisher’s angular transformation and correlation analysis. Results. The results of the multiple conducted researches prove that the frequency of comorbidities, primarily somatic, in children with psychomotor development disorders is higher than in the general population. The combined influence of adverse environmental conditions, perinatal factors, nutritional disorders, nutritional behavior, reduced motor activity, neuroinflammation, immune response disorders, abnormalities in the quantitative and qualitative species composition of the intestinal microbiota, the phenomenon of an abnormally high microbial load on the organism, violations of interaction in the brain-gut axis, autonomic and mitochondrial dysfunctions, oxidative stress, sensory hypersensitivity, behavioral problems, sleep disorders, increased anxiety and irritability inherent in this children, can be the main reason for this. It is also worth to mention the presence of atopy and dyspeptic manifestations in many examined children, which, presumably, can be components of the food allergy complex of symptoms. It is worth noting, that in most of the subgroups we selected, there were children with physical development disorders, in all subgroups cases of infectious diseases were found in the anamnesis of children, as well as burdened family and allergic anamnesis, which can be caused by both adverse environmental factors and peculiarities, inherent in children with psychomotor development disorders. Among somatic diseases, respiratory ailments dominate in all studied subgroups. There is also a significant share of children with a burdened family and allergy history, atopic dermatitis, lesions of the ears and throat. We found full dependence, as well as medium strength and weak direct reliable correlation between somatic and infectious diseases, present in a significant part of the examined children with psychomotor development disorders, burdened allergic anamnesis and burdened family anamnesis (which conforms with a higher susceptibility to allergic diseases in children with psychomotor development disorders, in particular with mental retardation and ASD) in all subgroups, and also physical development disorders. It is necessary to include a personalized approach into the complex of rehabilitation of children with psychomotor development disorders, with simultaneous correction of existing comorbid pathological symptoms and neurological disorders, inherent in this category of children. Conclusions. Correlation between respiratory infections and a number of somatic and infectious diseases, disorders of physical development, burdened allergic and family history among the examined children in all the subgroups selected by us, which consists in the detection of complete dependence and a reliable correlation of varying strength, have been established.