Partial Coherence Research Articles

Investigation of longitudinal spatial coherence induced by a partially spatially coherent source

In this study, we report longitudinal spatial coherence (LSC) generated from an extended partially spatially coherent source. This treatment differs from traditional LSC studies, which consider the source to be strictly spatially incoherent. We found that the higher transverse spatial coherence (TSC) of the source resulted in a smaller longitudinal coherence length with strong modulations. In addition, the influence of propagation distance is studied through the position of the reference plane, which was not apparent in conventional LSC formulations. The result of the assumption of TSC and propagation distance is reduced LSC contrast, which may affect the quality of the resulting images. The spatial correlation between two transverse points on different planes is demonstrated to compensate for the degradation in longitudinal coherence caused due to some misalignment. Understanding the effects of parameters such as propagation distance and partial coherence of the source can help in designing optical systems to achieve optimal LSC contrast in optical imaging modalities.

Graph Analysis of TMS-EEG Connectivity Reveals Hemispheric Differences following Occipital Stimulation.

(1) Background: Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) provides a unique opportunity to investigate brain connectivity. However, possible hemispheric asymmetries in signal propagation dynamics following occipital TMS have not been investigated. (2) Methods: Eighteen healthy participants underwent occipital single-pulse TMS at two different EEG sites, corresponding to early visual areas. We used a state-of-the-art Bayesian estimation approach to accurately estimate TMS-evoked potentials (TEPs) from EEG data, which has not been previously used in this context. To capture the rapid dynamics of information flow patterns, we implemented a self-tuning optimized Kalman (STOK) filter in conjunction with the information partial directed coherence (iPDC) measure, enabling us to derive time-varying connectivity matrices. Subsequently, graph analysis was conducted to assess key network properties, providing insight into the overall network organization of the brain network. (3) Results: Our findings revealed distinct lateralized effects on effective brain connectivity and graph networks after TMS stimulation, with left stimulation facilitating enhanced communication between contralateral frontal regions and right stimulation promoting increased intra-hemispheric ipsilateral connectivity, as evidenced by statistical test (p < 0.001). (4) Conclusions: The identified hemispheric differences in terms of connectivity provide novel insights into brain networks involved in visual information processing, revealing the hemispheric specificity of neural responses to occipital stimulation.

Do volatilities in tourism arrivals and foreign aids matter for GDP volatility in Cambodia? Partial and vector coherence wavelet models

The purpose of this research note is to investigate the nexus between volatility in international tourist arrivals, volatility in foreign aids and gross domestic product (GDP) volatility in Cambodia over the period of 1993–2018 by using partial and vector coherence wavelet models. The partial wavelet coherence models show that volatility in tourist arrival has strong impacts on GDP volatility across all time and frequency domains. Secondly, we find from the vector wavelet coherence plots strong and significant coherence between GDP volatility and volatility in overseas development assistance to Cambodia across all time and frequency domains.

Characteristics of multi-channel intermuscular directional coupling based on time-varying partial directional coherence analysis

The human body transmits directional information between muscles during upper limb movements, and this will be particularly evident when the dominant muscle changes during movement transitions. By capturing the electromyography (EMG) signals of wrist flexion and extension continuous transition movements, we investigated the characteristics of multichannel intermuscular directional coupling and directional information transmission, and consequently explored the control mechanism of Central nervous system (CNS) and the coordination mechanism of motor muscles. Multi-channel EMG was collected from 12 healthy subjects under continuous translational movements of wrist flexion and extension, and the time-varying biased directional coherence analysis (TVPDC) model was constructed using partial directional coherence analysis (PDC) frequency domain directionality to study the directional information transfer characteristics in the time–frequency domain, screen closely related muscle pairs and perform directional coupling significance analysis. Palmaris longus (PL) played a dominant role under wrist flexion movements(WF), Extensor Carpi Radialis (ECR) played a dominant role under wrist extension movements(WE), and the remaining muscles responded to them with information and Biceps Brachii (BB) played a responsive role throughout the movement; flexor pairs had the highest positive coupling values in the beta band during Conversion action1 (MC1) and WF phases, and extensor pairs had the highest positive coupling values in the gamma band during Conversion action2(MC2) phase and the highest coupling values in the beta band during WE phase. TVPDC can effectively analyze the multichannel intermuscular directional coupling and information transmission relationship of surface electromyography under wrist flexion and extension transition movements, providing a reference for exploring the control mechanism of CNS and abnormal control mechanism in patients with motor dysfunction in a new perspective.

Spatio-temporal Variations in PM2.5and Its Influencing Factors in the Yangtze River Delta Urban Agglomeration

To coordinate the contradiction between economic development and environmental pollution and achieve the sustainable development of the economy and society, the spatio-temporal variations in PM2.5 were analyzed based on PM2.5 concentration and meteorological data of the Yangtze River Delta (YRD) urban agglomeration. Wavelet transform coherence (WTC), partial wavelet coherence (PWC), and multiple wavelet coherence (MWC) were used to analyze the multi-scale coupling oscillation between PM2.5 and meteorological factors in the time-frequency domain. The results showed that:① the concentration of PM2.5 in the YRD decreased from northwest to southeast, and the spatial range with high PM2.5 concentration decreased annually. The spatial distribution characteristics of the seasonal average PM2.5 concentration were similar to those of the annual average PM2.5 concentration. PM2.5 concentration exhibited the seasonal variation characteristics of high in winter, low in summer, and transitioning between spring and autumn. ② PM2.5 concentration decreased from 2015 to 2021, and the compliance rate increased. The difference in annual average PM2.5 concentration was decreased with dynamic convergence characteristics. The convergence of PM2.5 concentration in summer was greater than that in winter. During the whole study period, the daily average PM2.5 concentration showed a "U" distribution, and the proportion of days with excellent and good PM2.5 levels were 49.72% and 41.45%, respectively. ③ The wavelet coherence between PM2.5 and meteorological factors was different in different time-frequency domains. The main factors affecting PM2.5 were different in different time-frequency scales. At all time-frequency scales, WTC and PWC showed that wind speed and temperature were the best explanatory variables of PM2.5 variation, respectively. ④ The larger the time-frequency scale, the stronger the interaction of multi-factor combinations to explain PM2.5 variations. The synergistic effect of temperature and wind speed could better explain the variation in PM2.5. These results can provide reference for air pollution control in the YRD.

A study of the effects of Gaussian distribution of coherence length of source on the diffraction of partial temporal coherence beam from multi slits: Theory and simulation

First, we have generalized the notion of Franhoufer diffraction of temporal coherent light from a single slit to the case of arbitrary n-slits. The diffraction pattern is investigated for different values of recently (Koushki and Alavi, 2019) introduced parameter η “decoherence parameter”. It is shown that for multi-slits, the temporal decoherence effects appear for η≥1 i.e., the coherence length is shorter that the size of the slits. Results of our study reproduce the previous studies for perfect temporal case, when coherence length tends to infinity. Then to bring the problem closer to reality, we do not fix the coherence length and consider a Gaussian distribution function for it. Numerical study of the effects of coherence parameters of Gaussian distribution on far field diffraction pattern is performed.

Does market sentiment and global uncertainties influence ESG-oil nexus? A time-frequency analysis

This study investigates the influence of market sentiment and global uncertainties on the ESG-oil nexus for ten developed and eleven emerging countries from 4/1/2016 to 1/31/2023. Using bi-variate, partial and multiple wavelet coherence analysis, this study finds some insightful results: First, the ESG-oil nexus shows higher coherency, specifically during the health crisis period of COVID-19. Second, there is a diffusion of coherency between the networks, while controlling market sentiment (VIX and OVX) and global risks (EPU and OFR-FSI). Lastly, we find that the interaction effect of oil and uncertainties intensified the coherency. These results signal that market sentiment and global uncertainties are significant drivers influencing the ESG-oil nexus. The findings are important from a portfolio management and risk diversification perspective.

Disentangling local and global climate drivers in the population dynamics of mosquito-borne infections.

Identifying climate drivers is essential to understand and predict epidemics of mosquito-borne infections whose population dynamics typically exhibit seasonality and multiannual cycles. Which climate covariates to consider varies across studies, from local factors such as temperature to remote drivers such as the El Niño-Southern Oscillation. With partial wavelet coherence, we present a systematic investigation of nonstationary associations between mosquito-borne disease incidence and a given climate factor while controlling for another. Analysis of almost 200 time series of dengue and malaria around the globe at different geographical scales shows a systematic effect of global climate drivers on interannual variability and of local ones on seasonality. This clear separation of time scales of action enhances detection of climate drivers and indicates those best suited for building early-warning systems.

Differences in Axial Length and Anterior Chamber Depth among Keratoconic, Myopic and Emmetropic Eyes

Purpose: To report variation of the axial length (AL) and anterior chamber depth (ACD) among keratoconic (KC) eyes compared to myopic and emmetropic eyes in an African population sample. Study Design: Cross sectional observational. Place and Duration of Study: Al-Faisal Eye Hospital at Khartoum state of Sudanfrom January 2022 to September 2022. Methods: One-hundred and twenty-four eyes of 62 patients were divided into KC group (n =17, eyes=34), myopic group (n=28, eyes=56), and an age/gender matched emmetropic group (n=17, eyes =34). Central corneal thickness (CCT) was measured using ultrasonic pachymeter, AL, ACD and keratometry readings (K-reading) were recorded for each patient using non-contact partial coherence interferometry with an IOL Master. Results: Mean age of the sample population was 22.27± 6.05 (range; 10 – 40 years). KC patients had the highest spherical equivalent of refraction (SER) (-6.19±3.91 dioptres), highest k-reading (48.98±5.68 dioptres) and the thinnest CCT. Myopic participants had a longer AL compared to other refractive error groups (AL=24.99±2.39, p&lt;0.001). KC patients exhibited a larger ACD in comparison to emmetropes and myopes (ACD=3.6?9±0.26, p&lt;0.001). Among all participants, SER exhibited the highest correlation with AL (r=-0.71, p&lt;0.001) followed by a weaker correlation with ACD (r=-0.26, p=0.003). However, among KC patients, SER exhibited a weaker correlation with AL compared to myopes (r=-0.55, p=0.001), and a higher correlation with ACD compared to myopes (r=-0.38, p=0.03). Conclusion: ACD and corneal curvature were the most significantly detrimental parameters in KC. KC participants demonstrated a lower correlation between SER and AL and higher correlation between SER and ACD.

Revisiting the Nexus between Turkish Tourism Index Returns and Economic Policy Uncertainty: Partial Wavelet Coherence Analysis

This study reevaluates the well-documented negative relationship between the Turkish tourism index stock returns and economic policy uncertainty (EPU) indices using a wide range of EPU indices that span from 1997 to 2003. The aim of the paper is to find out whether EPU indices a have particular importance for the tourism companies’ stock returns or they end up with the same consequences regardless of the sector. To this end, Partial Wavelet Coherence analysis is conducted using the BIST 100 and the real effective exchange rate indices as conditioning variables. Results show that the negative relationship between the EPU indices and Turkish tourism index returns tends to disappear when controlled for the BIST 100 index returns. EPUs are shown to have no particular effect on the excess stock return performance of Turkish tourism companies. The policy uncertainties in Europe (particularly in France and, to a lesser extent in Germany) become effective only after controlling also for the changes in real effective exchange rates.

Affectivity in mental disorders: an enactive-simondonian approach

AbstractSeveral enactive-phenomenological perspectives have pointed to affectivity as a central aspect of mental disorders. Indeed, from an enactive perspective, sense-making is an inherently affective process. A question remains on the role of different forms of affective experiences (i.e., existential feelings, atmospheres, moods, and emotions) in sense-making and, consequently, in mental disorders. This work elaborates on the enactive perspective on mental disorders by attending to the primordial role of affectivity in the self-individuation process. Inspired by Husserl’s genetic methodology and Simondonian philosophy of individuation, sense-making is described as the process of progressive concretization and structuration of the self-world structures that support the intentionality of conscious experiences. Accordingly, affectivity is described as the force that anticipates a partial self-world coherence in sense-making. Structurally different types of affective experiences are integrated into the genetic picture and, on this basis, a reinterpretation and classification of certain mental disorders, such as schizophrenia, depression, and the anxiety spectrum, is provided. In this way, this work contributes to a phenomenologically informed enactive account of mental disorders as disorders of affectivity.

Did real economic uncertainty drive risk connectedness in the oil–stock nexus during the COVID-19 outbreak? A partial wavelet coherence analysis

This study explores the impact of real economic policy (business condition risk) on the oil–stock nexus risk connectedness during the COVID-19 pandemic. It uses multivariate wavelet coherency and partial wavelet coherency methods to isolate the effects of global risk indices, such as the US economic uncertainty index, the crude oil volatility index, and the geopolitical risk index, on risk connectedness. The study is based on daily data from January 2018 to December 2020 and finds a strong impact of real economic uncertainty indices on risk connectedness, with time-varying and frequency-sensitive patterns. The results also show that during the COVID-19 crisis, higher coherencies between oil and equity volatilities exist at lower frequencies. This research provides useful insights for regulators and portfolio diversifiers.

Quantifying the scale-dependent relationships of PM2.5 and O3 on meteorological factors and their influencing factors in the Beijing-Tianjin-Hebei region and surrounding areas

To investigate the variations of PM2.5 and O3 and their synergistic effects with influencing factors at different time scales, we employed Bayesian estimator of abrupt seasonal and trend change to analyze the nonlinear variation process of PM2.5 and O3. Wavelet coherence and multiple wavelet coherence were utilized to quantify the coupling oscillation relationships of PM2.5 and O3 on single/multiple meteorological factors in the time-frequency domain. Furthermore, we combined this analysis with the partial wavelet coherence to quantitatively evaluate the influence of atmospheric teleconnection factors on the response relationships. The results obtained from this comprehensive analysis are as follows: (1) The seasonal component of PM2.5 exhibited a change point, which was most likely to occur in January 2017. The trend component showed a discontinuous decline and had a change point, which was most likely to appear in February 2017. The seasonal component of O3 did not exhibit a change point, while the trend component showed a discontinuous rise with two change points, which were most likely to occur in July 2018 and May 2017. (2) The phase and coherence relationships of PM2.5 and O3 on meteorological factors varied across different time scales. Stable phase relationships were observed on both small- and large-time scales, whereas no stable phase relationship was formed on medium scales. On all-time scales, sunshine duration was the best single variable for explaining PM2.5 variations and precipitation was the best single variable explaining O3 variations. When compared to single meteorological factors, the combination of multiple meteorological factors significantly improved the ability to explain variations in PM2.5 and O3 on small-time scales. (3) Atmospheric teleconnection factors were important driving factors affecting the response relationships of PM2.5 and O3 on meteorological factors and they had greater impact on the relationship at medium-time scales compared to small- and large-time scales.

Deterministic vortices evolving from partially coherent fields

Optical vortices—lines of zero intensity around which the field phase has a circulating or helical structure—have become important tools for many applications such as imaging, trapping, and communications. It has long been assumed, however, that there is an intrinsic conflict between optical vortices and partial coherence, in that a vortex is a deterministic phase structure, and a partially coherent field has a randomly fluctuating phase. In most cases, a vortex imposed on a partially coherent field evolves into a singularity of the two-point correlation function. We demonstrate, however, that it is possible to construct a beam that has no deterministic vortices in the source plane yet evolves such a deterministic vortex at a specified propagation distance.

Axial length acquisition success rates and agreement of four optical biometers and one ultrasound biometer in eyes with dense cataracts

BackgroundTo evaluate the axial length acquisition success rates and agreement between various biometric parameters obtained with different biometers in dense cataracts.MethodsFifty-one eyes were measured using Anterion®, Argos® and IOLMaster® 700 swept-source optical coherence tomography (SS-OCT) biometers, a Pentacam® AXL partial coherence interferometry (PCI) biometer, and an OcuScan® RxP ultrasound biometer. We measured keratometry (K1, flattest keratometry and K2, steepest keratometry), white-to-white (WTW), anterior chamber depth (ACD), lens thickness (LT) and axial length. Cataracts were classified according to the Lens Opacities Classification System III grading system, the dysfunctional lens index (DLI) and Pentacam® nucleus staging (PNS) metrics. Percentage of acquisition success rate and a Bland–Altman analysis for the agreement between biometers were calculated.ResultsThe mean LOCS III score was 3.63 ± 0.92, the mean DLI was 2.95 ± 1.30 and the mean PNS was 2.36 ± 1.20. The acquisition success rates for the Anterion®, Argos®, IOLMaster® 700, Pentacam® AXL and OcuScan® RxP biometers were 94.12%, 100%, 98.04%, 60.78% and 100%, respectively. There were significant differences in the success rates between biometers (P = 0.014). There were statistically significant differences between biometers for all parameters evaluated (P < 0.05). The range of the limit of agreement (LoA) for all comparisons of K1 and K2 were > 1.00 D. The LoA for WTW ranged from 0.095 to 1.050 mm. The LoA for ACD and LT ranged from 0.307 to 0.114 mm and from 0.378 to 0.108 mm, respectively. The LoA for axial length ranged from 0.129 to 2.378 mm.ConclusionsAmong optical biometers, those based on SS-OCT technology are more successful at measuring axial length in eyes with dense cataracts.Trial Registration: The study was registered with the National Institutes of Health (clinical trial identifier NCT05239715, http://www.clinicaltrials.gov).

Clarifying the relationship between annual maximum daily precipitation and climate variables by wavelet analysis

Analyzing the temporal hydrological response of regional precipitation to climate variables is critical for improving precipitation prediction and understanding the underlying mechanism. We study the potential relationship between the annual maximum daily precipitation (RX1day) in Guangdong Province and 21 climate variables, including the length of the day of the earth's rotation (LOD), Niño 3.4, and Pacific Decadal Oscillation (PDO). Wavelet coherence (WTC), partial wavelet coherence (PWC), and multiple wavelet coherence (MWC) are used to identify possible individual, independent, and coupled relationships between the RX1day and climate variables. The analysis results show that Tropical Southern Atlantic Index (TSA), Niño 3.4, Southern Oscillation Index (SOI), Western Pacific Index (WP), Tripole Index for the Interdecadal Pacific Oscillation (TPI), North Pacific pattern (NP), Atlantic Multidecadal Oscillation (AMO), and Tropical Northern Atlantic Sea Surface Temperatures Index (TNA) are important driving forces influencing RX1day in Guangdong. After excluding the influence of Niño 3.4 and PDO, PWC accurately explains the influence of a single climate variable on RX1day. A single climate variable is insufficient to describe the influence on RX1day, but MWC accurately reflects the combined influence of different climate variables on RX1day. Our work emphasizes the use of PWC and MWC to reveal the independent and combined influences of climate variables on RX1day on different time scales. This study provides new insights into selecting the optimum predictive factors of RX1day.

Design of Fourier ptychographic illuminator for single full-FOV reconstruction.

Fourier ptychographic microscopy (FPM) is a spatial-temporal-modulation high-throughput imaging technique via a sequential angle-varied LED illumination. Therefore, the illuminator is one of the key components and the design of this illuminator is significant. However, because of the property of spherical wave, partial coherence, and aperture-induced vignetting, the acquired images must be processed in blocks first, and rely on parallel reconstruction via a graphics processing unit (GPU). The high cost makes it unappealing compared with commercial whole slide imaging system via a low-cost central processing unit (CPU). Especially, the vignetting severely destroys the space-invariant model and induces obvious artifacts in FPM, which is the most difficult problem. The conventional method is to divide the field of view (FOV) into many tiles and omit those imperfect images, which is crude and may discards low frequency information. In this paper, we reevaluated the conditions of vignetting in FPM. Through our analysis, the maximum side length of FOV is 0.759 mm for a single full-FOV reconstruction via a 4×/0.1 NA objective and a 4 mm spacing LED array in theory, while almost 1.0 mm can be achieved in practice due to the tolerance of algorithm. We found that FPM system can treat the vignetting coefficient Vf below 0.1 as brightfield images and Vf lager than 0.9 as darkfield images, respectively. We reported an optimized distribution for designing an illuminator without vignetting effect according to the off-the-shelf commercial products, which can reconstruct full FOV in one time via a CPU. By adjusting the distribution of LED units, the system could retrieve the object with the side length of FOV up to 3.8 mm for a single full-FOV reconstruction, which achieves the largest FOV that a typical 4×/0.1 NA objective with the field number of 22 mm can afford.

Exploring beam size measurement based on the Talbot effect at BEPCII.

Vertical beam size measurements were carried out at Beijing Electron-Positron Collider II (BEPCII) using a phase grating and an absorption grating based on the Talbot effect. The transverse coherence of synchrotron radiation is closely related to beam size. Due to the partial coherence of the synchrotron radiation source, the coherence length can be calculated by measuring the visibility decay of interferograms recorded at different distances behind the gratings. A vertical beam size of 68.19 ± 2 µm was obtained based on the relationship between the coherence length and beam size at the 3W1 beamline of BEPCII. A comparison of the vertical emittance derived from the grating Talbot method and the synchrotron radiation visible light interferometer method was presented. The vertical emittances from the two methods are 1.41 nm rad and 1.40 nm rad, respectively. The 0.1% difference indicates that the grating Talbot method for beam size measurement is reliable. This technique has great potential for small beam size measurement of fourth-generation synchrotron radiation light sources, considering its small diffraction limitation and simple experimental setups.

Comparison of Accuracy of 6 Modern Intraocular Lens Power Calculation Formulas.

To compare the accuracy of modern intraocular lens (IOL) power calculation formulas in predicting refractive outcomes after standard cataract surgery. The medical records of 203 eyes of 203 patients that received phacoemulsification and IOL implantation were retrospectively reviewed. Partial coherence interferometry was used to obtain the biometric values. The refractive outcomes of Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) 2.0, Hill-RBF 3.0, Hoffer QST, Kane, and PEARL-DGS formulas were evaluated. Axial length subgroup analysis was done separately. The correlations between the prediction error calculated by each formula and axial length (AL) and corneal power were also analyzed. Overall, there was no significant difference between the absolute prediction errors predicted by the six formulas after adjusting the mean prediction error (p = 0.058). AL subgroup analysis of absolute error also showed that there is no significant difference between the formulas. The BUII and Hill-RBF 3.0 formulas showed a higher percentage of eyes with PE within ±0.50 D compared to the Hoffer QST formula (p = 0.022 and p = 0.035). However, there was no significant difference after Bonferroni correction was applied. The BUII formula showed the highest IOL Formula Performance Index (FPI) and therefore the highest accuracy, followed by PEARL-DGS, EVO 2.0, Kane, Hill-RBF 3.0 and Hoffer QST formulas. Out of the six formulas, the prediction error calculated by the Hoffer QST was significantly correlated with the AL (p = 0.011). None of the prediction errors calculated by the six formulas showed correlation to the corneal power. Analysis of the prediction error showed that the 6 modern IOL power calculation formulas have comparable accuracy overall and across different ranges of axial length.

Pulsar polarization: a partial-coherence model

ABSTRACT The population of radio pulsars is observed to demonstrate certain polarization properties not explained by the conventional picture of pulsar polarization, namely frequency evolution of polarization, deviations of the linear polarization angle from a curve of geometric origins, and the presence of features in the circular polarization. We present the partial-coherence model as a way to explain the co-occurrence of these features and to provide an origin for circular polarization in radio pulsar profiles. We describe the mathematics of the model and demonstrate how it can explain these observed features, both on a population level and for the idiosyncrasies of individual pulsars. The partial coherence model can account for complex polarization behaviour, enabling improved access to information about pulsar geometries. We discuss the scientific implications of this for our understanding of pulsar radio emission and propagation.