Circular Correlations Research Articles

Triantaspirols A-C and Paraphaeolactone Cs from Paraphaeosphaeria sp. KT4192: Sensitivity of CP3 in Distinguishing Close NMR Signals.

Hybridized spirobisnaphthalene derivatives, triantaspirols A-C (1-3) and paraphaeolactones C1 and C2 (4 and 5), were identified from the culture broth of the fungus Paraphaeosphaeria sp. KT4192. The NMR spectra of 2 and 3, as well as 4 and 5, closely resembled each other, indicating that these were pairs of diastereomers. Although this NMR spectral resemblance made it challenging to distinguish their relative configurations, detailed analysis of the electronic circular dichroism (ECD) spectra and NOE correlations allowed us to deduce them. The CP3 metric with the DFT-based NMR chemical shifts was found to distinguish configurations of diastereomers in a highly sensitive and accurate manner that DP4 could not account for because of the very close chemical shift differences in the experimental NMR spectra. The reliability of this method was assessed using 23 published examples which could not be distinguished by DP4 protocol.

Gas-liquid two-phase flow pressure drop in flattened tubes: an experimental and numerical study

Experimental, numerical and empirical research is carried out on pressure drop features of air-water two-phase flow in horizontal flattened tubes. Circular tubes of 10.5 mm I.D. made of copper were successively flattened into inner heights of 9, 8, and 6 mm (AR=1.27, 1.5, and 2.2, respectively). The experiment operation conditions were 200, 500, and 1000 kg/m2s for mass velocity, 6, 8, 10 LPM for flow rate, and 0 to 0.005 for gas quality. Also, the pressure drop for R134a and R410A was estimated numerically using ANSYS Fluent. The simulation test condi-tions were for vapor quality of 0.1 to 0.9 and saturation temperature of 40°C, while the condi-tions for mass velocity and flowrate are taken as that of the experiment test. The experimental data were examined to see how different factors affect on the pressure gradient. According to the outcomes and as compared to the circular tube, the pressure gradient was raised up to 27%, 95%, and 218% for tubes flattened with aspect ratio of 1.27, 1.5, and 2.2, respectively. More-over, the pressure drop for either air-water or refrigerant fluids is increased dramatically with increasing flow rate, but it decreases with increasing vapor quality. When compared to known circular tube correlations, a good agreement was achieved. Finally, the minimum difference between the experimental, numerical, and correlated results was less than 3% for gas quality of 0.0048 and aspect ratio of 2.2.

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

We perform a high-resolution cosmological zoom-in simulation of a Milky Way (MW)–like system, which includes a realistic Large Magellanic Cloud analog, using a large differential elastic dark matter self-interaction cross section that reaches ≈100 cm2 g−1 at relative velocities of ≈10 km s−1, motivated by the diverse and orbitally dependent central densities of dwarf galaxies within and surrounding the MW. We explore the effects of dark matter self-interactions on satellite, splashback, and isolated halos through their abundance, central densities, maximum circular velocities, orbital parameters, and correlations between these variables. We use an effective constant cross section model to analytically predict the stages of our simulated halos’ gravothermal evolution, demonstrating that deviations from the collisionless – relation can be used to select deeply core-collapsed halos, where is a halo’s maximum circular velocity, and is the radius at which it occurs. We predict that a sizable fraction (≈20%) of subhalos with masses down to ≈108 M ⊙ is deeply core collapsed in our SIDM model. Core-collapsed systems form ≈10% of the isolated halo population down to the same mass; these isolated, core-collapsed halos would host faint dwarf field galaxies with extremely steep central density profiles. Finally, most halos with masses above ≈109 M ⊙ are core-forming in our simulation. Our study thus demonstrates how self-interactions diversify halo populations in an environmentally dependent fashion within and surrounding MW-mass hosts, providing a compelling avenue to address the diverse dark matter distributions of observed dwarf galaxies.

On-axis polarization of beams radiated by electromagnetic circularly coherent sources.

On-axis spectral density and degree of polarization of beams radiated by electromagnetic (EM) sources with circular correlations are shown to be finely controlled by changing the source parameters. We reveal, in particular, that in this beam class, unlike for all previously known stationary beams, it is possible to control independently the dynamics of the on-axis spectral density and the degree of polarization. This was enabled by the obtained analytical expression for the on-axis polarization matrix, derived for general EM sources with circular coherence and Gaussian spectral density across the source plane. A simple experimental scheme for generating a broad class of EM circularly coherent sources is devised involving only a line source, a lens, and a transparency, possibly anisotropic.

On the circular correlation coefficients for bivariate von Mises distributions on a torus

This paper studies circular correlations for the bivariate von Mises sine and cosine distributions. These are two simple and appealing models for bivariate angular data with five parameters each that have interpretations connected to those in the ordinary bivariate normal model. However, the variability and association of the angle pairs cannot be easily deduced from the model parameters unlike the bivariate normal. Thus to compute such summary measures, tools from circular statistics are needed. We derive analytic expressions and study the properties of the Jammalamadaka–Sarma and Fisher–Lee circular correlation coefficients for the von Mises sine and cosine models. Likelihood-based inference of these coefficients from sample data is then presented. The correlation coefficients are illustrated with numerical and visual examples, and the maximum likelihood estimators are assessed on simulated and real data, with comparisons to their non-parametric counterparts. Implementations of these computations for practical use are provided in our R package BAMBI.

Functional Magnetic Resonance Imaging Studies in Sexual Medicine: A Primer

Over the past 30 years, functional magnetic resonance imaging (fMRI) has emerged as a powerful tool to non-invasively study the activity and function of the human brain. But along with the potential of fMRI to shed light on neurological, psychiatric, and psychological processes, there are methodological challenges and criticisms. We herein provide an fMRI primer designed for a diverse audience, from the neuroimaging novice to the experienced user. This primer is structured as follows: Part 1: Overview: "What is fMRI and what can it tell us?." Part 2: Basic fMRI principles: MR physics, the BOLD signal, and components of a typical scan session. Part 3: Basic fMRI experimental design: why timing is critical, and common sources of noise in the signal. Part 4: Basic fMRI analysis methods: software, the 3 stages of data analysis (preprocessing, individual, and group level), and a survey of advanced topics and methods including connectivity, machine learning, and assessing statistical significance. Part 5: Criticism, crises, and opportunities related to power of studies, computing requirements, logistical, and interpretational challenges, and methodological debate (assessing causality, circular correlations, and open science best practices). OUTCOMES N/A CLINICAL TRANSLATION: fMRI has primarily been used in clinical research to elucidate the brain correlates of sexual behavior. The translational potential of the method into clinical practice has not yet been realizedfMRI has primarily been used in clinical research to elucidate the brain correlates of sexual behavior. The translational potential of the method into clinical practice has not yet been realized STRENGTHS AND LIMITATIONS: fMRI is a useful and powerful tool for understanding the brain basis of human sexuality. However, it is also expensive, requires extensive methods expertise, and lacks the precision needed to be immediately translatable to clinical practice. The recency of the method, need for basic research, technical limitations, as well as inherent variability in individuals brain activity also impact the pace at which fMRI for sexual medicine can move from the scanner to the clinic. This primer provides the novice an understanding of the appropriate uses and limitations of fMRI, and for the experienced user, a concise update on current issues and methodological advances. Mills-Finnerty C, Frangos E, Allen K, et al. Functional Magnetic Resonance Imaging Studies in Sexual Medicine: A Primer. J Sex Med 2022;19:1073-1089.

Comparison of SCATSAT-1 swath data with global in situ buoy winds

Indian Space Research Organisation (ISRO) launched SCATSAT-1 scatterometer, on 26 September 2016 as a continuation and enhancement of OSCAT onboard OceanSat-2. The present work carries out a detailed inter-comparison of swath-wise level 2B data from SCATSAT-1 with in situ winds from three moored buoy arrays: Global Tropical Moored Buoy Array (GTMBA), National Data Buoy Center (NDBC) and Ocean Moored Buoy Network for northern Indian Ocean (OMNI). To assess the agreement between the satellite and in situ observations in different regions, the comparison was split between tropical, extra-tropical and coastal regions for each of the global ocean basins. Furthermore, the agreement between the two wind vector datasets was also estimated at each buoy location separately. Poor circular correlations in wind direction (WD) were observed in regions of shallow bathymetry and low mean wind speed, while some WD errors were found to be associated with the failure to resolve directional ambiguity.

Comparison of Correlation-Based OFDM Radar Receivers

Various correlation-based receivers have been proposed in passive bistatic and active monostatic radar exploiting orthogonal frequency-division multiplexing communications signals, but too little has been dedicated to establishing their relations and advantages over each other. Accordingly, this article provides an analytical comparison of the common filters in such waveform sharing scenarios, along with a performance analysis regarding three criteria: computational complexity, signal-to-interference-plus-noise-ratio, and resilience to ground clutter. The last two especially assess the possible detrimental effects of the random sidelobes (or pedestal) induced by the data symbols in the range-Doppler map. Although simulations show that none of the filters performs unanimously better, the ones employing circular correlations globally evidence attractive results.

Systolic array multiplier for augmenting data center networks communication link

The paper will present a heuristic architecture that is used for the systolic array multiplier for the delay and power—the delay product minimization using various input bit sizes. Systolic architecture maps high-level computation into hardware structures. As these have regularity and can be easily reckoned, the systolic systems are easy to implement. This architecture results in cost effective, better performance and special purpose systems that can solve a wide variety of problems. An effective method for designing Very Large Scale Integration (VLSI) architecture that is based on the proper decomposition technique that uses circular correlations has been presented. Here the multiplication is a commonly used operation in both Mathematics and also in Digital Signal Processing applications. The Systolic algorithm will be an efficient algorithm that performs binary multiplication and the Systolic architectures will provide better performance in design like that of the multiplier, matrix multiplication, the Finite Impulse Response based filter and also the Distributed Array Arithmetic. This work proposed a VLSI architecture based on systolic multiplier that can be implemented on Network links to reduce energy consumption. The proposed work concentrate on the development of a novel architecture having decomposition cells used for the systolic multiplier. There are two different architectures that are proposed and among them the Architecture-I has been designed having the decomposition cells along with registers in case of the feed forward path delay for the delay minimization. This proposed work has resulted in the delay reduction of about 32% that is compared to the existing work. In the architecture-II and their Processing Elements that have been designed along with the tristate buffers and also the multiplexer that is based on the full adder in power minimization. Their results in a lower power delay based product of about 6% compared to the current work and the Field Programmable Gate Array tested proved the delay and the improvement of power-delay product compared to other conventional architectures.

Pressure drop and heat transfer characteristics of a high-temperature printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is one of the leading intermediate heat exchanger (IHX) candidates to be employed in the very-high-temperature gas-cooled reactors (VHTRs) due to its capability for high-temperature, high-pressure applications. In the current study, a reduced-scale zigzag-channel PCHE was fabricated using Alloy 617 plates for the heat exchanger core and Alloy 800H pipes for the headers. The pressure drop and heat transfer characteristics of the PCHE were investigated experimentally in a high-temperature helium test facility (HTHF) at The Ohio State University. The PCHE helium inlet temperatures and pressures were varied up to 464°C/2.7MPa for the cold side and 802°C/2.7MPa for the hot side, respectively, while the maximum helium mass flow rates on both sides of the PCHE reached 39kg/h. The corresponding maximum channel Reynolds number was approximately 3558, covering the laminar flow and laminar-to-turbulent flow transition regimes. New pressure drop and heat transfer correlations for the current zigzag channels with rounded bends were developed based on the experimental data. Comparisons between the experimental data and the results obtained from the available PCHE and straight circular pipe correlations were conducted. Compared to the heat transfer performance in straight circular pipes, the zigzag channels provided little advantage in the laminar flow regime but significant advantage near the transition flow regime.

A New Neolignan from Panicum turgidum

A new neolignan, paniculignan (1), and a known lignan, tetracentronside B (2), were isolated from Panicum turgidum. The structure of 1 was elucidated by extensive spectroscopic methods including ID and 2D NMR and HR-ESI-MS. The relative configuration of 1 was determined on the basis of circular dichroism spetroscopy, optical rotation, and NOESY correlations.

Experimental study of burning rate in large-scale rectangular pool fire

Rectangular pool fires are common in the liquid fuel storage and transportation industries, but the existing burning rate correlations are largely focused on circular pool fires. Through experimental means, this work measured the steady mass burning rates of both n-heptane and gasoline fires in large-scale rectangular pools with aspect ratios ranging from 0.5 to 4.0. The effects of pool width and aspect ratio on the mass burning rate were investigated. A modified model was developed to estimate the mass burning rate in a rectangular pool fire as a function of the pool width and the aspect ratio. Correlations for n-heptane and gasoline burning rates were proposed based on the experimental results. The comparisons between the presented correlations and the existed circular burning rate correlations were analyzed accordingly.

Relativistic theory for the elementary process of bremsstrahlung induced by heavy spin-zero nuclei

Doubly and triply differential cross sections for the bremsstrahlung emission by high-energy spin-polarized electrons in the field of heavy bare nuclei are calculated within a fully relativistic partial-wave approach at collision energies between 1 and 30 MeV. Investigating $^{208}\mathrm{Pb}$ as a test case, it is shown that if the photons are emitted at backward angles, nuclear size effects may play an important role even below 10 MeV. Comparison is made with experimental data on the circular polarization correlations between incoming electron and emitted photon at a collision energy of 3.5 MeV. It is demonstrated that, independent of energy, the plane-wave Born approximation severely underestimates the cross section for heavy targets. Moreover, it gives at most a qualitative prescription of the polarization correlations, except possibly in the forward hemisphere.

An Alternative Complexity Reduction Method for Partitioned-Block Frequency-Domain Adaptive Filters

Partitioned-block frequency-domain adaptive filters provide lower algorithmic complexity than their time-domain counterparts. However, for certain applications, it is desirable to reduce complexity even further. This can be achieved by reducing the complexity of the constraint, or linearization, of the circular correlations. Existing methods are either suboptimal or are not sufficiently flexible in terms of the design parameters. Therefore, an alternative complexity reduction method is proposed, which achieves near-optimal performance and which, in addition, is flexible in terms of the design parameters, as these can be arbitrarily chosen.

Convective Heat Transfer in a High Aspect Ratio Minichannel Heated on One Side

Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusselt numbers in the transition regime being reasonably predicted by Gnielinski's correlation. The dependence of the heat transfer coefficient on the Prandtl number is larger than that predicted by circular tube correlations, and is likely a result of the asymmetric heating. The problem of asymmetric heating condition is approached theoretically using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl. The analysis clarifies the influence of asymmetric heating on the Nusselt number and correctly predicts the experimentally observed trend with Prandtl number. A semi-analytic correlation is derived from the analysis that accounts for the effect of aspect ratio and asymmetric heating, and is shown to predict the experimental results of this study with a mean absolute error (MAE) of less than 5% for 4000 < Re < 70,000.

Multi-sinc Schell-model beams and the interaction with a linear random medium

Two stochastic beams with circular and Cartesian symmetry correlations, generated by a recently introduced novel class of multi-sinc Schell-model (MSSM) source, in a linear isotropic random medium is investigated and comparatively analysed with that in free space. It is demonstrated that the spectral density distributions of such beams on propagation in free space and weaker turbulence medium exhibit unique features and produce multi-rings and lattice patterns of being shape-invariant in the far field. They are destroyed when such beams pass in the stronger turbulence medium at sufficiently large distances. The influence of the fractal constant of the atmospheric power spectrum and refractive-index structure constant on the spectral density of beams is analysed in depth. The unique characteristics in the spectral density are shown to occur on random medium propagation, which was not previously known for any other beams.

Polarization correlations for electron-impact excitation of neon at 50 eV

We present measurements and calculations of linear and circular polarization correlations for angle-differential electron-impact excitation of the neon resonance transition at an impact energy of 50 eV, most importantly extended to large scattering angles up to 105°. The measured linear polarization parameters of the vacuum ultra-violet transition are in very good agreement with a number of theoretical predictions at all angles. At intermediate scattering angles, however, the circular polarization parameter measurements are only found to be in excellent agreement with theoretical results obtained with the B-spline R-matrix theory, but not with those from other models.

Partial-Aliasing Correlation Filters

Correlation filters (CFs) are useful tools for detecting and locating signals or objects within a larger signal or scene of interest. Typically, these filters are designed during the training stage without worrying about how the cross-correlation between a test signal and the designed CF template will be carried out during the testing or use stage. Because of its computational benefits, the Fast Fourier Transform (FFT) algorithm is usually used for performing cross-correlations, leading to circular correlations and aliasing in the resulting correlation outputs. The aliasing effects can be suppressed by zero-padding, but at the expense of using longer FFTs and thus incurring more computational complexity. In this paper, we present a new approach where CFs are designed to explicitly allow partial aliasing at test time (thus allowing the use of shorter FFTs). This approach of allowing aliasing in the cross-correlation output and explicitly taking such partial aliasing into account when designing the CF is diametrically opposite to the conventional CF approaches which try to avoid aliasing effects. We demonstrate through numerical results that these new partial-aliasing correlation filters (PACFs) achieve better recognition performance than conventional CFs when used in block filtering architectures that allow aliasing.

A New Heat Transfer Correlation for Turbulent Flow of Air With Variable Properties in Noncircular Ducts

Turbulent flow and heat transfer of air with variable properties in a set of regular polygonal ducts and circular tube have been numerically simulated. All the ducts have the same hydraulic diameter as their characteristic lengths in the Reynolds number. The flow is modeled as three-dimensional (3D) and fully elliptic by using the finite volume method and the standard k-ε turbulence model. The results showed that the relatively strong secondary flow could be observed with variable properties fluid. For the regular polygonal ducts, the local heat transfer coefficient along circumferential direction is not uniform; there is an appreciable reduction in the corner region and the smaller the angle of the corner region, the more appreciable deterioration the corner region causes. The use of hydraulic diameter for regular polygonal ducts leads to unacceptably large errors in turbulent heat transfer determined from the circular tube correlations. Based on the simulation results, a correction factor is proposed to predict turbulent heat transfer in regular polygonal ducts.

Polarization correlations for electron-impact excitation of the resonant transitions of Ne and Ar at low incident energies

The electron--polarized-photon coincidence method is used to determine linear and circular polarization correlations in vacuum ultraviolet (VUV) for the differential electron-impact excitation of neon and argon resonance transitions at impact energies of 25 and 30 eV at small scattering angles up to 40\ifmmode^\circ\else\textdegree\fi{}. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present $B$-spline $R$-matrix theory concerning the violation of a long-established propensity rule regarding angular momentum transfer in electron-impact excitation of $S\ensuremath{\rightarrow}P$ transitions. Comparisons with the results from the present relativistic distorted-wave approximation and an earlier semirelativistic distorted-wave Born model are also made. For the case of Ar, at 25 and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence as to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by S. H. Zheng and K. Becker [Z. Phys. D 23, 137 (1992); J. Phys. B 26, 517 (1993)].