Coherence Volume Research Articles

Enhancement of Fluorescence Resonance Energy Transfer by Coherent Coupling In-Between Surface Plasmon and Volume Plasmon Polariton

Enhancement of Fluorescence Resonance Energy Transfer by Coherent Coupling In-Between Surface Plasmon and Volume Plasmon Polariton

Refined speckle contrast estimation in OCT based on compensation of scattering-related distortions of speckle pattern parameters

Abstract Speckle contrast (SC) parameters in optical coherence tomography (OCT) scans are formed by the interplay of several factors—local level of optical wave backscattering by the material inhomogeneities, parameters of spatial distribution of the latter and the degree of cumulative optical wave attenuation during its fourth-and-back propagation. For the optical wavelengths used in OCT, this attenuation is usually dominated by the influence of scattering in the visualized turbid tissues rather than by absorption. For sufficiently high concentrations of scatterers (at least a few scatterers in the coherence volume) characterized by comparable scattering strengths and a fairly homogeneous distribution in space, the interference of locally scattered waves should be characterized by a Rayleigh distribution of speckle amplitudes, for which the local SC tends to 0.52. Equivalently, in terms of speckle intensities, the local SC tends to unity. Local spatial inhomogeneities or strongly uneven scattering strengths lead to the appearance of increased values of SC, which may serve as a diagnostic feature of some tissue components in OCT images. At the same time, in comparison to surface speckles formed by coherent-light scattering from rough surfaces, OCT-beam attenuation during its fourth-and-back propagation may introduce intensity inhomogeneities in OCT scans even for homogeneous tissue areas. This effect results in artefactual distortion of the visible SC in comparison with the above-mentioned expected value. Moreover, the presence of individual strong scatterers may additionally non-locally distort SC values due to the appearance of elongated shadows below such scatterers, which causes lateral inhomogeneities in OCT scans. Here, we propose a refined SC parameter, which is cleaned from distorting scattering-related effects in both axial and lateral directions. Depth-resolved estimation of the optical attenuation coefficient is used to restore attenuation-free OCT scans, for which the refined SC is estimated. The efficiency of the proposed approach is demonstrated using both digital OCT phantoms with highly controlled properties and experimental OCT data.

Implications of in-ice volume scattering for radio-frequency neutrino experiments

Over the last three decades, several experimental initiatives have been launched with the goal of observing radio-frequency signals produced by ultra-high energy neutrinos (UHEN) interacting in solid media. Observed neutrino event signatures comprise impulsive signals with duration of order the inverse of the antenna+system bandwidth (∼10 ns), superimposed upon an incoherent (typically white noise) thermal noise spectrum. Whereas bulk volume scattering (VS) of radio-frequency (RF) signals is well-studied within the radio-glaciological communities, polar ice-based neutrino-detection experiments have thus far neglected VS in their signal projections. As discussed herein, coherent volume scattering (CVS, for which the phase of the incident signal is preserved during scattering) generated by in-ice neutrino interactions may similarly produce short-duration signal-like power, albeit with a slightly extended time structure, and thereby enhance neutrino detection rates, whereas incoherent (randomized phase) volume scattering (IVS) will persist for O(100 ns), appearing similar to thermal white noise and therefore reducing the measured Signal-to-Noise Ratio (SNR) of neutrino signals. Herein, we present the expected voltage profiles resulting from in-ice volume scattering as a function of the molecular scattering cross-section, for both CVS and IVS, and assess their impact on UHEN experiments. VS contributions are currently only weakly constrained by extant data; stronger limits may be obtained with dedicated calibration experiments.

A next-generation, histological atlas of the human brain and its application to automated brain MRI segmentation.

Magnetic resonance imaging (MRI) is the standard tool to image the human brain in vivo. In this domain, digital brain atlases are essential for subject-specific segmentation of anatomical regions of interest (ROIs) and spatial comparison of neuroanatomy from different subjects in a common coordinate frame. High-resolution, digital atlases derived from histology (e.g., Allen atlas [7], BigBrain [13], Julich [15]), are currently the state of the art and provide exquisite 3D cytoarchitectural maps, but lack probabilistic labels throughout the whole brain. Here we present NextBrain, a next-generation probabilistic atlas of human brain anatomy built from serial 3D histology and corresponding highly granular delineations of five whole brain hemispheres. We developed AI techniques to align and reconstruct ~10,000 histological sections into coherent 3D volumes with joint geometric constraints (no overlap or gaps between sections), as well as to semi-automatically trace the boundaries of 333 distinct anatomical ROIs on all these sections. Comprehensive delineation on multiple cases enabled us to build the first probabilistic histological atlas of the whole human brain. Further, we created a companion Bayesian tool for automated segmentation of the 333 ROIs in any in vivo or ex vivo brain MRI scan using the NextBrain atlas. We showcase two applications of the atlas: automated segmentation of ultra-high-resolution ex vivo MRI and volumetric analysis of Alzheimer's disease and healthy brain ageing based on ~4,000 publicly available in vivo MRI scans. We publicly release: the raw and aligned data (including an online visualisation tool); the probabilistic atlas; the segmentation tool; and ground truth delineations for a 100 μm isotropic ex vivo hemisphere (that we use for quantitative evaluation of our segmentation method in this paper). By enabling researchers worldwide to analyse brain MRI scans at a superior level of granularity without manual effort or highly specific neuroanatomical knowledge, NextBrain holds promise to increase the specificity of MRI findings and ultimately accelerate our quest to understand the human brain in health and disease.

Exceptionally Slow, Long-Range, and Non-Gaussian Critical Fluctuations Dominate the Charge Density Wave Transition.

(TaSe_{4})_{2}I is a well-studied quasi-one-dimensional compound long-known to have a charge-density wave (CDW) transition around 263K. We argue that the critical fluctuations of the pinned CDW order parameter near the transition can be inferred from the resistance noise on account of their coupling to the dissipative normal carriers. Remarkably, the critical fluctuations of the CDW order parameter are slow enough to survive the thermodynamic limit and dominate the low-frequency resistance noise. The noise variance and relaxation time show rapid growth (critical opalescence and critical slowing down) within a temperature window of ϵ≈±0.1, where ϵ is the reduced temperature. This is very wide but consistent with the Ginzburg criterion. We further show that this resistance noise can be quantitatively used to extract the associated critical exponents. Below |ϵ|≲0.02, we observe a crossover from mean-field to a fluctuation-dominated regime with the critical exponents taking anomalously low values. The distribution of fluctuations in the critical transition region is skewed and strongly non-Gaussian. This non-Gaussianity is interpreted as the breakdown of the validity of the central limit theorem as the diverging coherence volume becomes comparable to the macroscopic sample size. The large magnitude critical fluctuations observed over an extended temperature range, as well as the crossover from the mean-field to the fluctuation-dominated regime highlight the role of the quasi-one-dimensional character in controlling the phase transition.

Optical characterization of native aerosols from e-cigarettes in localized volumes.

Measuring the size distribution of aerosols typically requires processing a sample, specifically to adjust the particle concentration to an adequate level. Unfortunately, this manipulation can significantly alter the native composition of some aerosols, which can lead to unreliable or even unusable measurements. We demonstrate that coherence-gated dynamic light scattering is suitable to measure the size distribution of native aerosols without the need for sample processing. Another novel aspect of the present work is the first demonstration of these type of localized light-scattering-based measurements in aerial media. Measuring the size distribution reliably in optically dense aerosols is possible thanks to the interferometric amplification of single scattering in an optically isolated, picolitre-sized coherence volume. We carried out proof-of-concept experiments in aerosols from electronic cigarettes, which poses a challenge mainly due to their high concentration, volatility, and hygroscopicity. We generated aerosols using two common moisturizers, propylene glycol and glycerol, and measured their particle size distribution as a function of the burning power. The aerosols generated in the presence of glycerol are more polydisperse and have larger particles with increasing burning power. This unique characterization of native aerosols can provide valuable information for dosimetry and hosting sites in the respiratory system.

Fast fetal head compounding from multi-view 3D ultrasound.

The diagnostic value of ultrasound images may be limited by the presence of artefacts, notably acoustic shadows, lack of contrast and localised signal dropout. Some of these artefacts are dependent on probe orientation and scan technique, with each image giving a distinct, partial view of the imaged anatomy. In this work, we propose a novel method to fuse the partially imaged fetal head anatomy, acquired from numerous views, into a single coherent 3D volume of the full anatomy. Firstly, a stream of freehand 3D US images is acquired using a single probe, capturing as many different views of the head as possible. The imaged anatomy at each time-point is then independently aligned to a canonical pose using a recurrent spatial transformer network, making our approach robust to fast fetal and probe motion. Secondly, images are fused by averaging only the most consistent and salient features from all images, producing a more detailed compounding, while minimising artefacts. We evaluated our method quantitatively and qualitatively, using image quality metrics and expert ratings, yielding state of the art performance in terms of image quality and robustness to misalignments. Being online, fast and fully automated, our method shows promise for clinical use and deployment as a real-time tool in the fetal screening clinic, where it may enable unparallelled insight into the shape and structure of the face, skull and brain.

Effect of magnetic field on recombination dynamics in random electron systems

The evolution of localized electron states with increasing magnetic field is studied using time-resolved photoluminescence in GaAs/AlGaAs short-period superlattices, in which electrons are localized due to quantum interference between electron waves multiply scattered by the short-range potential of a random interface roughness. The nature of electronic states, extended or localized, is fundamentally related to the rate of their recombination, which is determined by the exciton coherence volume. Localization reduces the volume of exciton coherence, thereby decreasing the recombination rate. Correspondingly, the recombination rate in insulating samples turned out to be much lower than in metallic ones. Moreover, in insulating samples, the recombination rate increased with increasing temperature and magnetic field, which was found consistent with the temperature and magnetic field dependences of the electrical resistance. The observed increase in the recombination rate is attributed to the break-down of the quantum interference, leading to delocalization.

An alternative for tracing the path between supply and use tables in current and constant prices

Supply and use tables (SUT) in constant prices ensure coherent volume and price information across economic accounts. They are needed to appropriately measure technological change and connect physical and monetary models. To estimate SUTs in constant prices, researchers normally apply commodity-specific deflators to SUTs. From an economics perspective, deflators are undoubtedly cell-specific since exchanges of a commodity occur in different markets and institutional contexts. RAS can be used to calculate such cell-specific deflators. But deflating SUTs via RAS can become impossible due to excessive information requirements. This article revisits Path-RAS and applies it to build SUTs in constant prices. Our methodology lowers information requirements, enables cell-specific deflators, and avoids ad hoc adjustments. Additional information about specific industries or products can be included if existing and non-conflicting. We provide an empirical application based on the current 27 European Union countries to explore the accuracy of our estimations considering different information scenarios.

Low-order fault identification method of Putaohua oil layer of X block in Songliao Basin

With the exploration and development of oil fields to the later stage, the distribution of remaining oil is highly scattered, and the oil control area becomes smaller. It is necessary to carry out fine identification and description of small geological interfaces, so as to improve the accuracy of reservoir description. Therefore, low-level fault identification has become an extremely important link. However, due to the influence of seismic data resolution, it is often difficult to directly interpret small faults on conventional seismic profiles. In conventional seismic data, fault interpretation is often based on seismic attribute analysis. At present, there are many kinds of seismic attributes used for fault interpretation, such as coherence class, curvature body attribute, ant attribute body and so on. By comprehensively utilizing the time slices and seismic profiles of these seismic attributes, small faults can be identified more effectively. In the process of studying the three-dimensional work area of Putaohua oil layer of X block in Songliao Basin, the above methods are used in combination with various information such as seismic profiles to identify small faults that are difficult to identify on conventional seismic data volume and coherence volume, and good application results have been achieved.

Grain structure influence on synchronized two-dimensional spin-Hall nano-oscillators

Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 × 2 and 4 × 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.

Study on microstructure and properties of AA7075 coated by micro arc oxidation

Effect of ageing temperature on the properties of 7075 aluminum alloy coated by micro arc oxidation (MAO) technology has been investigated. The precipitates formed at various ageing temperatures are observed by transmission electron microscope (TEM), which would significantly influence the properties of the MAO coating. Coherent distortion, size and volume fraction of precipitates are related to the changing of electrical conductivity during ageing treatment. Full coherent and dense Guinier Preston zones (GP zones) formed at 90 °C can act as scattering centers to impede electron mobility, so decrease the electrical conductivity. η and η′ phases produced at 120 °C and 150 °C are semi-coherent and incoherent, respectively, meanwhile, the precipitate size increases and the volume fraction decreases with increasing the ageing temperature, therefore, the electrical conductivity increases. Higher electrical conductivity contributes to thicker coating with better surface morphology. Double cantilever beam (DCB) tests show that the thicker and less porous coatings prepared at 150 °C aged specimens own the best stress corrosion cracking (SCC) resistance. After pores are broke and coatings are ruptured, high Cu and low Mg segregation at the grain boundary of 150 °C aged specimens founded from high-angle annular dark field scanning transmission electron microscopy (HADDF-STEM) are beneficial to anodic dissolution and hydrogen assisted crack.

Q-Balls in the Pseudogap Phase of Superconducting HgBa2CuO4+y

Fast and local probes, such as X-ray spectroscopy, X-ray diffraction (XRD), and X-ray microscopy, have provided direct evidence for nanoscale phase separation in high temperature perovskite superconductors composed of (i) free particles coexisting with (ii) Jahn Teller polarons (i.e., charges associated with local lattice distortions) not detected by slow experimental methods probing only delocalized states. Moreover, these experimental probes have shown the formation of a superstripes phase in the pseudogap regime below T* in cuprates. Here, we focus on the anomalous temperature dependence of short range X-ray diffraction CDW reflection satellites with high momentum transfer, probing both charge and lattice fluctuations in superconducting HgBa2CuO4+y (Hg1201) in the pseudogap regime below T* and above Tc. We report compelling evidence of the anomalous anticorrelation of the coherence volume with the peak maximum amplitude of the CDW XRD satellite by cooling below T*. This anomalous temperature trend of the short-range striped Jahn Teller polaronic CDW puddles is in agreement with predictions of the Q-ball theory of the quark gluon plasma extended to cuprates, providing compelling evidence for non topological soliton puddles of striped condensate of pairs in the pseudogap phase.

Influence of Caribbean eddies on the Loop current system evolution

The Loop Current (LC) system dynamics are an essential component of the processes influencing circulation and transport in the Gulf of Mexico (GoM). The LC evolution is influenced by various factors, including the rich eddy field of the region and the flow exchange through the Yucatan Strait with the neighboring Caribbean Sea. These factors contribute to the complexity of the LC and, as a result, to the limitations in the predictability of the system. The focus of this study is to further elucidate the evolution of the LC, by quantifying the influence of coherent eddy fluxes originating in the Caribbean Sea. This is achieved by employing the Lagrangian-Averaged Vorticity Deviation (LAVD) method, an objective metric to evaluate eddy coherence in the Caribbean Sea that allows, for the first time, to quantify at different depths the evolution of coherent Caribbean eddies through the Yucatan Channel towards the GoM. The physical connectivity between the Caribbean Sea and the GoM is addressed using Lagrangian techniques to analyze processes that take place south of the Yucatan Channel and help quantify their strong relationship with the GoM eddy field. Coherent anticyclonic vorticity fluxes, as well as the net coherent anticyclonic volume transport between the Caribbean Sea and the GoM are associated with Loop Current Eddy (LCE) detachments through direct connectivity between the coherent Caribbean anticyclones and the forming LCE. The findings have important implications for understanding and predicting the LC system and the physical connectivity processes between the GoM and the Caribbean Sea.

Review: Religion at the Edge: Nature, Spirituality, and Secularity in the Pacific Northwest, edited by Paul Bramadat, Patricia O’Connell Killen, and Sarah Wilkins-Laflamme

Religion at the Edge presents a collection of essays that analyze the most irreligious regions of the United States and Canada, namely the Pacific Northwest. Also called Cascadia, the area encompasses British Columbia, Washington, Oregon, and even parts of Idaho, Wyoming, Montana, and northern California, although the book focuses on the first three provinces/states.The book is an exemplary model of how a diverse group of scholars can create a coherent volume. Working through the Centre for Studies in Religion and Society at the University of Victoria, the authors met in person two times, read and discussed each others’ articles multiple times, and made revisions as a result of those encounters. They also drew from a common pool of resources, such as interview transcripts, focus group data, archival materials, and perhaps most important, results of the Pacific Northwest Social Survey (PNSS). The result is a cohesive volume that examines Cascadia’s unique, or “peculiar,” configuration of religion, spirituality, and secularity.The PNSS, conducted in 2017 (Wilkins-Laflamme), found that 49 percent of residents of British Columbia claimed no religion, while 44 percent of Washingtonians and Oregonians reported no religion. The essays in the book explain the historical and contemporary reasons for Cascadia being the “None Zone,” and speculate as to its anticipation of a post-Christian America in the future (Silk). They consider the influence of indigenous traditions and settler colonialism (Horton, O’Brien), the environmental beauty of the region and a concomitant “reverential naturalism” (Bramadat, Morrill), the tradition of irreligion across generations (Block and Marks, O’Connell Killen), and the effect of secularism upon Evangelical and Liberal Protestants (Wellman and Corcoran, Wilkinson) as well as upon minority religions (Brown).Readers seeking information about secularism, the spiritual-but-not-religious cohort, environmentalism and religion, and the future of religion across Canada and the United States will want to read Religion at the Edge. As Mark Silk points out, “Cascadia has proven to be not an outlier but the advance guard of religion in the public life of the two countries of which it is a part” (128). Highly recommended.

Prediction and research of fracture distribution characteristics of the Chang 8 reservoir in Zhenjing area, Ordos Basin

The Zhenjing area is on the southwestern margin of the Ordos Basin where the tectonic activity is strong, and natural fractures are widely developed. As the main seepage channels of the reservoir, fractures significantly affect the accumulation of oil and gas. Therefore, it is crucial to study the distribution of fractures in this area. This study comprehensively used cores, image logging, field outcrops, and geophysical data to study the genesis and distribution characteristics of these fractures. The results indicate that the Chang 8 reservoirs in the study area primarily developed high-angle structural fracture-oriented northwest-west and northeast-east. We used five methods to identify and predict the fractures of the Chang 8 reservoir in the Zhenjing area: coherent volume fracture detection, a high-precision curvature method, a maximum likelihood method, a structural restoration method, and ant-tracking technology. After comparing and analyzing the prediction results of the five methods, it was concluded that the structural restoration method performed relatively poorly, whereas the maximum likelihood method was more accurate and better at fracture detection. It was found that the distribution direction of the fractures of the Chang 8 reservoir was primarily northeast-east and northwest-west, showing a strip shape. Oil and gas enrichment is obviously dependent on faults and fractures. The degree of oil and gas enrichment in the northeast-east-oriented tension-torsional fractures was significantly higher than that of northwest-west directional compression-torsional fractures, and oil and gas were more likely to accumulate at the intersections and tails of these fractures.

Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening

Metamorphism of dry, lower crust within orogens is often localized in shear zones composed of mechanically weaker rocks1–4. Several field-based studies suggest shear zone development is preceded by brittle faults which provide the fluid pathways required for metamorphism and weakening4–12. However, a unifying model which couples long-term geological deformation to fluid migration and metamorphic reactions does not exist. Here, we present a visco-elasto-plastic model where the most pertinent features observed in transformed lower crust emerge from basic mechanical principles during the deformation of a coherent rock volume with associated fluid introduction. These include a strikingly dynamic and heterogeneous pressure distribution in the reacting and deforming rock volumes. Lower crustal pressure variations may reach 1 GPa at the same depth. This will have first order effects on the pattern of fluid migration in the lower crust, and may explain the apparent discrepancies between the relevant tectonic settings and petrologically-inferred burial depths.

Towards practical physical-optics rendering

Physical light transport (PLT) algorithms can represent the wave nature of light globally in a scene, and are consistent with Maxwell's theory of electromagnetism. As such, they are able to reproduce the wave-interference and diffraction effects of real physical optics. However, the recent works that have proposed PLT are too expensive to apply to real-world scenes with complex geometry and materials. To address this problem, we propose a novel framework for physical light transport based on several key ideas that actually makes PLT practical for complex scenes. First, we restrict the spatial coherence shape of light to an anisotropic Gaussian and justify this restriction with general arguments based on entropy. This restriction serves to simplify the rest of the derivations, without practical loss of generality. To describe partially-coherent light, we present new rendering primitives that generalize the radiometric radiance and irradiance, and are based on the well-known Stokes parameters. We are able to represent light of arbitrary spectral content and states of polarization, and with any coherence volume and anisotropy. We also present the wave BSDF to accurately render diffractions and wave-interference effects. Furthermore, we present an approach to importance sample this wave BSDF to facilitate bi-directional path tracing, which has been previously impossible. We show good agreement with state-of-the-art methods, but unlike them we are able to render complex scenes where all the materials are new, coherence-aware physical optics materials, and with performance approaching that of "classical" rendering methods.

Degree-of-spatial-coherence laser scanning confocal fluorescence microscope

The modulation of degree of spatial coherence (DOSC) plays an optical gating which highly correlates with the coherence volume (CV) in the proposed DOSC laser scanning confocal fluorescence microscope (DOSC-LSCFM). The axial resolution at sub-diffraction-limit performance was demonstrated and discussed.

The Swahili World

The Swahili World