Direct Resolution Research Articles

Analysis of acoustic direction finding methods for unmanned aerial vehicles

Currently, classical means of detecting objects do not provide the necessary efficiency for detecting small UAVs, and acoustic location among the known methods for their observation is the most cost-effective solution.
 The article analyzes the well-known methods of direction finding of acoustic signals in order to select algorithms for processing UAV signals. Obtaining qualitative indicators of the analyzed algorithms was carried out by the method of statistical computer modeling in the Matlab environment.
 Based on the simulation results, it is shown that classical methods are the most stable under conditions of low signal-to-noise ratios. The GCC-PHAT direction finding algorithm, based on determining the difference in the time of arrival of a signal at spaced points, is computationally economical and simple enough to determine the direction to the UAV, but it is not capable of distinguishing more than one radiation source within the diagram orientation. Beamforming methods are also relatively easy to implement and computationally efficient, and are more robust at low signal-to-noise ratios. The SRP-NAM algorithm has a greater accuracy in determining angles than SRP-PHAT, so it can be an adequate replacement for the SRP-PHAT algorithm.
 High-resolution methods provide better directional resolution than classical methods, which, in the case of a limited microphone array aperture, is a positive factor in the design of an UAV direction finding station. High resolution methods were considered: non-coherent MUSIC, non-coherent normalized MUSIC and TOPS method. It is shown that incoherent MUSIC gives poor results in distinguishing close UAV signals, since unequal estimates of the entire frequency range are concentrated during bearing formation. The incoherent normalized MUSIC algorithm is able to efficiently use the entire frequency range of the UAV acoustic signal. The TOPS algorithm is inferior to the incoherent normalized MUSIC algorithm, and on the other hand, it does not require a priori estimates of the number of radiation sources.

Elevational Synthetic Aperture Focusing for Three-Dimensional Photoacoustic Imaging Using a Clinical One-Dimensional Array Transducer.

Two-dimensional (2D) photoacoustic (PA) imaging based on array transducers provide high spatial resolution in the lateral direction by adopting receive dynamic focusing. However, the quality of PA image is often deteriorated by poor elevational resolution which is achieved by an acoustic lens. To overcome this limitation, we present a three-dimensional (3D) image reconstruction method using a commercial one-dimensional (1D) array transducer. In the method, the elevational resolution is improved by applying synthetic aperture focusing (SAF) technique along the elevational direction. For this, a commercially available 1D array transducer with an acoustic lens is modeled and appropriate synthetic focusing delay that can minimize the effect of the acoustic lens is derived by mathematical analysis. From the simulation and experiment results, it was demonstrated that the proposed method can enhance the image quality of PA imaging, i.e., elevational resolution and signal-to-noise ratio (SNR). 3D PA images with improved elevational resolution were achieved using a clinical 1D array transducer. The presented method may be useful for clinical application such as detecting microcalcification, imaging of tumor vasculature and guidance of biopsy in real time.

P-023: 2,3-DIPHOSPHOGLYCERATE DETECTION VIA DIRECT INFUSION HIGH RESOLUTION MASS SPECTROMETRY CORRELATES WITH QUANTITATIVE DETECTION IN BLOOD OF PATIENTS WITH SICKLE CELL DISEASE

Purpose: Sickle cell disease (SCD) is a hereditary and chronic life-threatening disorder, characterized by haemolytic anaemia. Increased 2,3-diphosphoglycerate (2,3-DPG) concentrations, along with decreased oxygen affinity of hemoglobin, may be related to the variability of clinical outcomes in SCD. Furthermore, genomic health data holds promise to improve the prediction of disease severity in SCD. Based on the integration of genomics, metabolomics and clinical data from 1000 SCD patients, to be included in 2022, GenoMED4all aims to develop Artificial Intelligence (AI) based deep learning algorithms to improve the prediction of disease severity and phenotype in SCD. This study aims to correlate non-quantitative metabolomics data obtained from dried blood spots (DBS), one of the inputs for GenoMED4all, to quantitative measurement of 2,3-DPG. Aiming to improve the potential of non-quantitative metabolomics from DBS to asses 2,3-DPG. Materials and methods: In snap frozen blood samples from 37 SCD patients and 29 healthy controls, 2,3-DPG was quantified by liquid chromatography mass spectrometry. 2,3-DPG was also detected in DBS from the same subjects by direct infusion high resolution mass spectrometry (DIHRMS). The oxygen tension at 50% Hb saturation (p50) was determined using a Hemox Analyzer (TCS). Statistical analysis were performed by Spearman’s correlation coefficients (SPSS v26.0.0.1) and Mann Whitney testing (GraphPad Prism v9.3.0). Results: After correcting for Hb, 2,3-DPG concentrations were higher in SCD patients than in controls (p<0.001) and Z-scores for 2,3-DPG, as assessed by DIHRMS, were similar in patients and controls. The Z-scores positively correlated with 2,3-DPG concentrations (Fig1A, 0.353, p=0.004). Because of the anaemia in SCD, red blood cells (RBCs) and plasma make up lower and higher volumes in the blood, respectively, compared to healthy controls. This affects the ratio of RBC and plasma metabolites on the DBS. DIHRMS detects a wide range of RBC and plasma metabolites, whereas the quantitative measurement is restricted to measuring 2,3-DPG of RBCs. To correct for those differences between methods, we applied a correction factor to the DIHRMS data using (1/Ht)*(1-Ht/1), correcting for the RBC volume (1/Ht) and the plasma volume (1-Ht/1). This resulted in a trend towards higher Z-scores in patients than controls (p=0.0597). Moreover, the positive correlation with 2,3-DPG concentrations increased to 0.526 (Fig1B, p<0.001). As 2,3-DPG affects the oxygen affinity of Hb, all measurements were correlated to p50. Expectedly, 2,3-DPG concentrations positively correlated with p50 (0.842, p<0.001). After applying the correction factor to the DIHRMS data, p50 correlations increased from 0.361 (p=0.003) to 0.529 (p<0.001). Conclusion: Strongest correlation between quantitative and non-quantitative methods for 2,3-DPG detection were observed after correcting for both RBC and plasma volumes in non-quantitative metabolomics. After correction, DIHRMS can be used to assess 2,3-DPG concentrations in DBS. This translation of non-quantitative to quantitative metabolomics for 2,3-DPG and potentially other RBC metabolites adds significant value to the use of DIHRMS, as DIHRMS is far more efficient in obtaining extensive information about the total metabolome than quantitative methods. The large population size and the AI based deep learning algorithms of GenoMED4all will enable to evaluate the potential of non-quantitative metabolomics in SCD. Funding: Horizon2020, GenoMED4all(https://genomed4all.eu/), Agios Pharmaceuticals Inc., ERN-EuroBloodNetFig 1. correlations between non-quantitative (Z-score) and quantitative 2,3-DPG detection A) non-quantitative and quantitative 2,3-DPG detection B) non-quantitative detection corrected for RBC and plasma volume and quantitative 2,3-DPG detection The authors do not declare any conflict of interest

Accelerated Deconvolved Imaging Algorithm for 2D Multibeam Synthetic Aperture Sonar.

High-accuracy level underwater acoustical surveying plays an important role in ocean engineering applications, such as subaqueous tunnel construction, oil and gas exploration, and resources prospecting. This novel imaging method is eager to break through the existing theory to achieve a higher accuracy level of surveying. Multibeam Synthetic Aperture Sonar (MBSAS) is a kind of underwater acoustical imaging theory that can achieve 3D high-resolution detecting and overcome the disadvantages of traditional imaging methods, such as Multibeam Echo Sounder (MBES) and Synthetic Aperture Sonar (SAS). However, the resolution in the across-track direction inevitably decreases with increasing range, limited by the beamwidth of the transducer array of MBES. Furthermore, the sidelobe problem is also a significant interference of imaging sonar that introduces image noise and false peaks, which reduces the accuracy of the underwater images. Therefore, we proposed an accelerated deconvolved MBSAS beamforming method that introduces exponential acceleration and vector extrapolation to improve the convergence velocity of the classical Richardson-Lucy (R-L) iteration. The method proposed achieves a narrow beamwidth with a high sidelobe ratio in a few iterations. It can be applied to actual engineering applications, which breaks through the limitation of the actual transducer array scale. Simulations, tank, and field experiments also demonstrate the feasibility and advantages of the method proposed. 3D high-accuracy level underwater acoustical surveying can be achieved through this 2D MBES transducer array system, which can be widely promoted in the field of underwater acoustical remote sensing.

Measuring Pattern Separation in Hippocampus by in Situ Hybridization.

Distinguishing different contexts is thought to involve a form of pattern separation that minimizes overlap between neural ensembles representing similar experiences. Theoretical models suggest that the dentate gyrus (DG) segregates cortical input patterns before relaying its discriminated output patterns to the CA3 hippocampal field. This suggests that the evaluation of neural ensembles in DG and CA3 could be an important means to investigate the process of pattern separation. In the past, measurement of entorhinal cortex (EC), DG, and CA3 ensembles was largely dependent upon in vivo electrophysiological recording, which is technically difficult. This protocol provides a method to instead measure pattern separation by a molecular method that provides direct spatial resolution at the cellular level. © 2022 Wiley Periodicals LLC. Basic Protocol: Measuring pattern separation by molecular methods.

A Novel Method for Diagnosis of Broken Bars Based on Optimum Resolution of Prescient Direction Algorithm

Fourier transformation (FT) and Multiple Signal Classification (MUSIC) method suffer the insufficient ability in diagnosing broken rotor bar (BRB) fault using short-time data. Theoretical and simulation analyses show that the Optimum Resolution of Prescient Direction (ORPD) algorithm has the best frequency resolution performance due to a priori knowledge. The main objective of this paper is to detect BRB faults in induction machines using a condition monitoring architecture based on ORPD algorithm. In the proposed application, the ORPD algorithm with the best frequency resolution performance is used to estimate the fault-sensitive frequencies in the stator current signature. The prior information of BRB fault characteristic distribution is used to construct a weighting matrix in the ORPD algorithm, for acquiring the lowest signal-to-noise ratio resolution threshold. Once frequencies are estimated, their corresponding amplitudes are obtained by using the least squares estimator. The proposed methods were tested using experimental induction motors with different fault severity under the effect of several load levels or supply frequencies. Two types of power supply modes are considered: main and inverter. The results show that compared with traditional method which uses FT and MUSIC algorithm for fault diagnosing, the method based on ORPD algorithm has a higher frequency resolution and identification ability with short-time data, and still has good diagnostic performance even under light loading and lower supply frequencies.

On-chip beam rotators, adiabatic mode converters, and waveplates through low-loss waveguides with variable cross-sections

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report a new method for femtosecond laser writing of optical-fiber-compatible glass waveguides, namely spherical phase-induced multicore waveguide (SPIM-WG), which addresses this challenging task with three-dimensional on-chip light control. Fabricating in the heating regime with high scanning speed, precise deformation of cross-sections is still achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single-mode fiber. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate the polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric nonuniform modes; examples include circular, elliptical modes, and asymmetric modes from ppKTP (periodically poled potassium titanyl phosphate) waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fiber also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fiber connections.

Characterization of a 30 µm pixel size CLIP-based 3D printer and its enhancement through dynamic printing optimization.

Resolving microscopic and complex 3D polymeric structures while maintaining high print speeds in additive manufacturing has been challenging. To achieve print precision at micrometer length scales for polymeric materials, most 3D printing technologies utilize the serial voxel printing approach that has a relatively slow print speed. Here, a 30-µm-resolution continuous liquid interface production (CLIP)-based 3D printing system for printing polymeric microstructures is described. This technology combines the high-resolution from projection microstereolithography and the fast print speed from CLIP, thereby achieving micrometer print resolution at x103 times faster than other high-resolution 3D printing technologies. Print resolutions in both lateral and vertical directions were characterized, and the printability of minimum 30 µm features in 2D and 3D has been demonstrated. Through dynamic printing optimization, a method that varies the print parameters (e.g. exposure time, UV intensity, and dark time) for each print layer, overhanging struts at various thicknesses spanning 1 order of magnitude (25 µm - 200 µm) in a single print are resolvable. Taken together, this work illustrates that the micro-CLIP 3D printing technology, in combination with dynamic printing optimization, has the high resolution needed to enable manufacturing of exquisitely detailed and gradient 3D structures, such as terraced microneedle arrays and micro-lattice structures, while maintaining high print speeds.

Single-Particle Cryo-EM Data Collection with Stage Tilt using Leginon.

Single-particle analysis (SPA) by cryo-electron microscopy (cryo-EM) is now a mainstream technique for high-resolution structural biology. Structure determination by SPA relies upon obtaining multiple distinct views of a macromolecular object vitrified within a thin layer of ice. Ideally, a collection of uniformly distributed random projection orientations would amount to all possible views of the object, giving rise to reconstructions characterized by isotropic directional resolution. However, in reality, many samples suffer from preferentially oriented particles adhering to the air-water interface. This leads to non-uniform angular orientation distributions in the dataset and inhomogeneous Fourier-space sampling in the reconstruction, translating into maps characterized by anisotropic resolution. Tilting the specimen stage provides a generalizable solution to overcoming resolution anisotropy by virtue of improving the uniformity of orientation distributions, and thus the isotropy of Fourier space sampling. The present protocol describes a tilted-stage automated data collection strategy using Leginon, a software for automated image acquisition. The procedure is simple to implement, does not require any additional equipment or software, and is compatible with most standard transmission electron microscopes (TEMs) used for imaging biological macromolecules.

Iterative method for partial discharges location in power transformers

In this paper an efficient and fast iterative method has been successfully used for detection and localization of partial discharges in a power transformer. It is mainly based on finite elements method solving in an isotropic medium. Current methods for localizing mechanical waves emitted by partial discharges are subject to the use of at least three acoustic sensors. A new numerical localization method based on the Newton-Raphson iterative method is presented. It reduces the number of sensors to only two. The propagation of an acoustic wave (AW), initiated by a Gaussian-type partial discharge inside a power transformer is analyzed. The wave equation was solved numerically by finite element using Comsol Multiphysics software. Two sensors made possible to follow the spatio-temporal distribution of the acoustic pressure of five partial discharges distributed in different positions of the transformer. The performance of the proposed method is demonstrated through a comparison with a direct resolution method.

P1500: 2,3-DIPHOSPHOGLYCERATE DETECTION VIA DIRECT INFUSION HIGH RESOLUTION MASS SPECTROMETRY CORRELATES WITH QUANTITATIVE DETECTION IN BLOOD OF PATIENTS WITH SICKLE CELL DISEASE

Background: Sickle cell disease (SCD) is a hereditary and chronic life-threatening disorder, characterized by haemolytic anaemia. Increased 2,3-diphosphoglycerate (2,3-DPG) concentrations, along with decreased oxygen affinity of hemoglobin, may be related to the variability of clinical outcomes in SCD. Furthermore, genomic health data holds promise to improve the prediction of disease severity in SCD. Based on the integration of genomics, metabolomics and clinical data from 1000 SCD patients, to be included in 2022, GenoMED4all aims to develop Artificial Intelligence (AI) based deep learning algorithms to improve the prediction of disease severity and phenotype in SCD. Aims: To correlate non-quantitative metabolomics data obtained from dried blood spots (DBS), one of the inputs for GenoMED4all, to quantitative measurement of 2,3-DPG. Aiming to improve the potential of non-quantitative metabolomics from DBS to asses 2,3-DPG. Methods: In snap frozen blood samples from 37 SCD patients and 29 healthy controls, 2,3-DPG was quantified by liquid chromatography mass spectrometry. 2,3-DPG was also detected in DBS from the same subjects by direct infusion high resolution mass spectrometry (DIHRMS). The oxygen tension at 50% Hb saturation (p50)was determined using a Hemox Analyzer (TCS). Statistical analysis were performed by Spearman’s correlation coefficients (SPSS v26.0.0.1) and Mann Whitney testing (GraphPad Prism v9.3.0). Results: After correcting for Hb, 2,3-DPG concentrations were higher in SCD patients than in controls (p<0.001) and Z-scores for 2,3-DPG, as assessed by DIHRMS, were similar in patients and controls. The Z-scores positively correlated with 2,3-DPG concentrations (Fig.1A, 0.353, p=0.004). Because of the anaemia in SCD, RBCs and plasma make up lower and higher volumes in the DBS, respectively, compared to healthy controls. DIHRMS detects a wide range of RBC and plasma metabolites, whereas the quantitative measurement is restricted to measuring 2,3-DPG of RBCs. To correct for those differences between methods, we applied a correction factor to the DIHRMS data using the formula (1/Ht)*(1-Ht/1), correcting for the RBC volume (1/Ht) and the plasma volume (1-Ht/1). This resulted in a trend towards higher Z-scores in patients than controls (p=0.0597). Moreover, the positive correlation with 2,3-DPG concentrations increased to 0.526 (Fig 1B, p<0.001). As 2,3-DPG affects the oxygen affinity of Hb, all measurements were correlated to p50. Expectedly, 2,3-DPG concentrations positively correlated with p50 (0.842, p<0.001). After applying the correction factor to the DIHRMS data, p50 correlations increased from 0.361 (p=0.003) to 0.529 (p<0.001). Image:Summary/Conclusion: Strongest correlation between quantitative and non-quantitative methods for 2,3-DPG detection were observed after correcting for both the RBC and plasma volume in non-quantitative metabolomics. After correction, DIHRMS can be used to assess 2,3-DPG concentrations in DBS. This translation of non-quantitative to quantitative metabolomics for 2,3-DPG and potentially other RBC metabolites adds significant value to the use of DIHRMS, as DIHRMS is far more efficient in obtaining extensive information about the total metabolome than quantitative methods. The large population size and the AI based deep learning algorithms of GenoMED4all will enable to evaluate the potential of non-quantitative metabolomics in SCD. Funding: Horizon2020, GenoMED4all (https://genomed4all.eu/), Agios Pharmaceuticals Inc., ERN-EuroBloodNet

Direct Crystallization Resolution of Racemates Enhanced by Chiral Nanorods: Experimental, Statistical, and Quantum Mechanics/Molecular Dynamics Simulation Studies.

Three chiral nanorods of C14-l-Thea, C14-l-Phe, and C14-d-Phe were first synthesized and utilized as heterogeneous nucleants to enhance the resolution of racemic Asp via direct crystallization. Through the statistical analysis from 320 batches of nucleation experiments, we found that the apparent appearance diversity of two enantiomeric crystals of Asp existed in 80 homogeneous experiments without chiral nanorods. However, in 240 heterogeneous experiments with 4.0 wt % chiral nanorods of solute mass added, the appearance of those nuclei with the same chirality as the nanorods was apparently promoted, and that with the opposite chirality was totally inhibited. Under a supersaturation level of 1.08, the maximum ee of the initial nuclei was as high as 23.51%. When the cooling rate was 0.025 K/min, the ee of the product was up to 76.85% with a yield of 14.41%. Furthermore, the simulation results from quantum mechanics (QM) and molecular dynamics (MD) revealed that the higher chiral recognition ability of C14-l-Thea compared to C14-l-Phe that originated from the interaction difference between C14-l-Thea and Asp enantiomers was larger than that between C14-l-Phe and Asp enantiomers. Moreover, the constructed nanorods exhibited good stability and recyclability.

Feasibility of two-dimensional die-level plasma process monitoring using spatially resolvable optical emission spectrometers

We demonstrated the feasibility of die-level process monitoring using spatially resolvable optical emission spectrometers (SROESs) in a low-pressure plasma reactor. The spatially resolved Ar emission line intensities and their intensity ratios were obtained from uniformly generated and intentionally perturbed plasma by inserting conductors of known sizes at known locations. The sheath and perturbed plasma distributions were identified from the Ar emission line intensity and their intensity ratio in the lateral direction to the SROES installment orientation. However, the resolution in the axial direction was insufficient to identify the sheath and perturbed the plasma distribution. We propose the superimposition of measured plasma emission intensities from two perpendicularly aligned SROESs for die-level process monitoring. The insufficient axial resolution can be compensated for by the lateral resolution of another SROES, and die-level process monitoring using SROES can thus be realized.

Transverse relaxation in fixed tissue: Influence of temperature and resolution on image contrast in magnetic resonance microscopy.

To describe transverse relaxation of water in fixed tissue, we propose a model of transverse relaxation accelerated by diffusion and exchange (TRADE) that assumes exchange between free (visible) and bound (invisible) water, which relax by the dipole-dipole interaction, chemical exchange, and translation in the field gradient. Depending on the prevailing mechanism, transverse relaxation time (T2 ) of water in fixed tissue could increase (when dipole-dipole interaction prevails) or decrease with temperature (when diffusion in the field gradient prevails). Chemical exchange can make T2 even temperature independent. Also, variation of resolution from 100 to 15 μm/pxl (or less) affects effective transverse relaxation. T2 steadily decreases with increased resolution ( , is the read direction resolution). TRADE can describe all of these observations (semi)quantitatively. The model has been experimentally verified on water phantoms and on formalin-fixed zebrafish, mouse brain, and rabbit larynx tissues. TRADE could help predict optimal scanning parameters for high-resolution MRM from much faster measurements at lower resolution.

Laser induced fluorescence spectra of the [formula omitted][formula omitted] – [formula omitted][formula omitted] transition of jet cooled [formula omitted]NO3 and [formula omitted]NO3 I: [formula omitted] progressions in the ground [formula omitted][formula omitted] state

14NO3 and 15NO3 were generated in a supersonic free jet, and their laser excitation spectra and dispersed laser induced fluorescence (LIF) spectra of the B∼2E′ – X∼2A2′ transitions from the vibrationless B∼2E′ state were observed. Because of the cooling of the gas in the supersonic jet, the observed spectra are with resolution an order of magnitude higher than those previously reported and allowed us to resolve, for example, the splitting between the a1′ and e′ components of the 2ν4 state. The spectra of 14NO3 and 15NO3 are similar but small isotope shift in the latter allowed us to separate the ν1 band from the 3ν4 (a1′) band which were overlapped in the former.The high resolution dispersed LIF spectra revealed panoramic views of the vibrational level structures in the X∼2A2′ ground electronic states of the two isotopomers. Although the accuracies of the measurement of energy levels are much less than those obtained from the direct high resolution infrared spectroscopy, the obtained patterns are more complete because totally symmetric (a1′) vibrations such as ν1,2ν2,2ν1,ν1 + 2ν2 etc. are also observed. Such clear and complete spectra have revealed remarkable ν4 progressions with detailed vibrational structures in the ground X∼2A2′ state. Near complete progressions of nν4 overtone bands, nν4 with n = 1 ∼ 5, ν1 + nν4 bands with n = 1 ∼ 4, some 2ν2 + nν4 and ν3 + nν4 have been assigned leaving few lines unassigned. There is no evidence of anomaly in the degenerate ν4 bending progression of the B∼2E′ – X∼2A2′ electronic transition of NO3.

Numerical study of heat transfer, flow fields, turbulent length scales, and anisotropy in corrugated heat exchanger channels

In this study, we report on large eddy simulation (LES) of convectively dominated heat transfer in a corrugated heat exchanger channel using the computational fluid dynamics toolbox, OpenFOAM. A chevron pattern domain with 63 contact points is used to represent the conditions in a real plate heat exchanger (PHE). The unsteady nature of the flow is elucidated using visualization techniques based on volume rendering of temperature and iso surfaces of vorticity defined using the λ2-criterion and contours of wall shear stress and wall heat flux to illustrate the heat transfer process. Global surface averaged temperature and pressure drop are extracted from the LES on successively finer grids, approaching direct numerical simulation resolution, to increase the understanding of grid resolution requirements for LES in PHEs. Industry standard Reynolds-averaged Navier–Stokes simulations are compared to the LES results along selected profiles to demonstrate similarities and differences between the two techniques. The differences detected are further investigated using anisotropy invariant mapping, energy spectra, and turbulence length scale distributions. Significant differences between the model classes are detected and detailed. Moreover, the LES resolution requirements for the flow and the heat transfer processes are found to be different with the latter being more severe.

Resolution Limit of Correlation Plenoptic Imaging between Arbitrary Planes

Correlation plenoptic imaging (CPI) is an optical imaging technique based on intensity correlation measurement, which enables detecting, within fundamental physical limits, both the spatial distribution and the direction of light in a scene. This provides the possibility to perform tasks such as three-dimensional reconstruction and refocusing of different planes. Compared with standard plenoptic imaging devices, based on direct intensity measurement, CPI overcomes the problem of the strong trade-off between spatial and directional resolution. Here, we study the resolution limit in a recent development of the technique, called correlation plenoptic imaging between arbitrary planes (CPI-AP). The analysis, based on Gaussian test objects, highlights the main properties of the technique, as compared with standard imaging, and provides an analytical guideline to identify the limits at which an object can be considered resolved.

Numerical investigation of the effect of spanwise length and mesh density on flow around cylinder at Re = 3900 using LES model.

Flow around circular cylinder has been extensively studied by researchers for several decades due to its wide range of engineering applications such as in heat exchangers, marine cables, high rise building, chimneys, and offshore structures. The lack of clear understanding of the unsteady flow dynamics in the wake of circular cylinder and high computational cost are still an area of high interest amongst the researchers. The aim of the current study is to investigate the effect of variation in spanwise length and grid resolution in the spanwise direction on the recirculation length, separation angle of wake flow by performing large eddy simulations (LES). This study is an extension to previous work by Khan, NB et al, 2019 in which the spanwise length is restricted to 4D only. In current study, the spanwise length is changed from 0.5D to 8D where D is diameter of cylinder and mesh resolution in the spanwise direction is changed from 1 to 80 elements in the present study. The recirculation length, separation angle and wake characteristics are analyzed in detail. It is concluded that after getting optimize spanwise length, mesh resolution in the spanwise direction is the only parameter contributing toward better result.

Quantitative comparison of the DRESOR and Monte Carlo methods for calculating radiative heat flux

The Monte Carlo method (MCM) can be used to calculate the radiative heat flux and divergence with high accuracy, and the Distribution of Ratios of Energy Scattered by the medium Or Reflected by the boundary surface (DRESOR) method based on the MCM provides the radiation intensity with high directional resolution. However, the accuracy and efficiency of the DRESOR method for calculating the radiative heat flux and divergence have not been verified. Therefore, in this article, the DRESOR method is reformed to make it more suitable for calculating the radiative heat flux and divergence, and the DRESOR method and MCM are compared quantitatively. In the comparison, the influences of the Mean Optical Thickness per Element (MOTE), the surface and medium parameters, anisotropic scattering, and a nonuniform medium are considered. The results show that the figure of merit (FoM) of the reformed DRESOR method is 81.18 and 6.04 times that of the MCM for the surface element and space element, respectively when the MOTE is 0.17 for calculating the radiative heat flux and divergence. The larger the surface emissivity, and the smaller the scattering albedo, the better the performance of the DRESOR method than the MCM is. Meanwhile, the MOTE (mesh density), anisotropic scattering, and the nonuniform medium have similar influences on the DRESOR method and the MCM.

In vivo irreversible and reversible transverse relaxation rates in human cerebral cortex via line scans at 7 T with 250 micron resolution perpendicular to the cortical surface

Understanding how and why MR signals and their associated relaxation rates vary with cortical depth could ultimately enable the noninvasive investigation of the laminar architecture of cerebral cortex in the living human brain. However, cortical gray matter is typically only a few millimeters thick, making it challenging to sample many cortical depths with the voxel sizes commonly used in MRI studies. Line-scan techniques provide a way to overcome this challenge and here we implemented a novel line-scan GESSE pulse sequence that allowed us to measure irreversible and reversible transverse relaxation rates—R2 and R2´, respectively—with extremely high resolution (250 μm) in the radial direction, perpendicular to the cortical surface. Eight healthy human subjects were scanned at 7 T using this sequence, with primary visual cortex (V1) targeted in three subjects and primary motor (M1) and somatosensory cortex (S1) targeted in the other five. In all three cortical areas, a peak in R2 values near the central depths was seen consistently across subjects—an observation that has not been made before, to our knowledge. On the other hand, no consistent pattern was apparent for R2´ values as a function of cortical depth. The intracortical R2 peak reported here is unlikely to be explained by myelin content or by deoxyhemoglobin in the microvasculature; however, this peak is in accord with the laminar distribution of non-heme iron in these cortical areas, known from prior histology studies. Obtaining information about tissue microstructure via measurements of transverse relaxation (and other quantitative MR contrast mechanisms) at the extremely high radial resolutions achievable through the use of line-scan techniques could therefore bring us closer to being able to perform “in vivo histology” of the cerebral cortex.