Narrow Range Of Scales Research Articles

Pressure anisotropy and viscous heating in weakly collisional plasma turbulence

Pressure anisotropy can strongly influence the dynamics of weakly collisional, high-beta plasmas, but its effects are missed by standard magnetohydrodynamics (MHD). Small changes to the magnetic-field strength generate large pressure-anisotropy forces, heating the plasma, driving instabilities and rearranging flows, even on scales far above the particles’ gyroscales where kinetic effects are traditionally considered most important. Here, we study the influence of pressure anisotropy on turbulent plasmas threaded by a mean magnetic field (Alfvénic turbulence). Extending previous results that were concerned with Braginskii MHD, we consider a wide range of regimes and parameters using a simplified fluid model based on drift kinetics with heat fluxes calculated using a Landau-fluid closure. We show that viscous (pressure-anisotropy) heating dissipates between a quarter (in collisionless regimes) and half (in collisional regimes) of the turbulent-cascade power injected at large scales; this does not depend strongly on either plasma beta or the ion-to-electron temperature ratio. This will in turn influence the plasma's thermodynamics by regulating energy partition between different dissipation channels (e.g. electron and ion heat). Due to the pressure anisotropy's rapid dynamic feedback onto the flows that create it – an effect we term ‘magneto-immutability’ – the viscous heating is confined to a narrow range of scales near the forcing scale, supporting a nearly conservative, MHD-like inertial-range cascade, via which the rest of the energy is transferred to small scales. Despite the simplified model, our results – including the viscous heating rate, distributions and turbulent spectra – compare favourably with recent hybrid-kinetic simulations. This is promising for the more general use of extended-fluid (or even MHD) approaches to model weakly collisional plasmas such as the intracluster medium, hot accretion flows and the solar wind.

Magnetic Field Spectral Evolution in the Inner Heliosphere

Parker Solar Probe and Solar Orbiter data are used to investigate the radial evolution of magnetic turbulence between 0.06 ≲ R ≲ 1 au. The spectrum is studied as a function of scale, normalized to the ion inertial scale d i . In the vicinity of the Sun, the inertial range is limited to a narrow range of scales and exhibits a power-law exponent of, α B = −3/2, independent of plasma parameters. The inertial range grows with distance, progressively extending to larger spatial scales, while steepening toward a α B = −5/3 scaling. It is observed that spectra for intervals with large magnetic energy excesses and low Alfvénic content steepen significantly with distance, in contrast to highly Alfvénic intervals that retain their near-Sun scaling. The occurrence of steeper spectra in slower wind streams may be attributed to the observed positive correlation between solar wind speed and Alfvénicity.

Effects of mesoscale turbulence on the wind-driven circulation in a closed basin with topography

This paper studies the effects of time-dependent, mesoscale turbulence on the wind-driven ocean circulation in a closed basin with variable topography. Numerical simulations of a single-layer fluid with finite topography at the sloping boundaries are performed. The flow is forced by a suitable combination of a steady, basin-scale wind that generates the classical western-intensified anticyclonic gyre, plus a shorter, time-dependent forcing that injects energy at a narrow range of scales. Two contrasting situations are considered. First, in the absence of the large-scale forcing, the turbulence generates a cyclonic flow that follows the geostrophic contours around the basin. Second, the resulting mean circulation is studied when the large and small-scale forcing terms are considered together. In particular, it is discussed that the alteration of the anticyclonic gyre may be due to the turbulent-induced cyclonic circulation.

Real-time Arabic scene text detection using fully convolutional neural networks

The aim of this research is to propose a fully convolutional approach to address the problem of real-time scene text detection for Arabic language. Text detection is performed using a two-steps multi-scale approach. The first step uses light-weighted fully convolutional network: TextBlockDetector FCN, an adaptation of VGG-16 to eliminate non-textual elements, localize wide scale text and give text scale estimation. The second step determines narrow scale range of text using fully convolutional network for maximum performance. To evaluate the system, we confront the results of the framework to the results obtained with single VGG-16 fully deployed for text detection in one-shot; in addition to previous results in the state-of-the-art. For training and testing, we initiate a dataset of 575 images manually processed along with data augmentation to enrich training process. The system scores a precision of 0.651 vs 0.64 in the state-of-the-art and a FPS of 24.3 vs 31.7 for a VGG-16 fully deployed.

Realtime multi-scale scene text detection with scale-based region proposal network

Multi-scale approaches have been widely used for achieving high accuracy for scene text detection, but they usually slow down the speed of the whole system. In this paper, we propose a two-stage framework for realtime multi-scale scene text detection. The first stage employs a novel Scale-based Region Proposal Network (SRPN) which can localize text of wide scale range and estimate text scale efficiently. Based on SRPN, non-text regions are filtered out, and text region proposals are generated. Moreover, based on text scale estimation by SRPN, small or big texts in region proposals are resized into a unified normal scale range. The second stage then adopts a Fully Convolutional Network based scene text detector to localize text words from proposals of the first stage. Text detector in the second stage detects texts of narrow scale range but accurately. Since most non-text regions are eliminated through SRPN efficiently, and texts in proposals are properly scaled to avoid multi-scale pyramid processing, the whole system is quite fast. We evaluate both performance and speed of the proposed method on datasets ICDAR2015, ICDAR2013, and MSRA-TD500. On ICDAR2015, our system can reach the state-of-the-art F-measure score of 85.40% at 16.5 fps (frame per second), and competitive performance of 79.66% at 35.1 fps, either of which is more than 5 times faster than previous best methods. On ICDAR2013 and MSRA-TD500, we also achieve remarkable speedup by keeping competitive performance. Ablation experiments are also provided to demonstrate the reasonableness of our method.

Interplay between intermittency and dissipation in collisionless plasma turbulence

We study the damping of collisionless Alfvénic turbulence in a strongly magnetised plasma by two mechanisms: stochastic heating (whose efficiency depends on the local turbulence amplitude $\unicode[STIX]{x1D6FF}z_{\unicode[STIX]{x1D706}}$ ) and linear Landau damping (whose efficiency is independent of $\unicode[STIX]{x1D6FF}z_{\unicode[STIX]{x1D706}}$ ), describing in detail how they affect and are affected by intermittency. The overall efficiency of linear Landau damping is not affected by intermittency in critically balanced turbulence, while stochastic heating is much more efficient in the presence of intermittent turbulence. Moreover, stochastic heating leads to a drop in the scale-dependent kurtosis over a narrow range of scales around the ion gyroscale.

Features in single field slow-roll inflation

We compare the effects of local features (LF) and branch features (BF) of the inflaton potential on the spectrum of primordial perturbations. We show that LF affect the spectrum in a narrow range of scales while BF produce a step between large and small scales with respect to the featureless spectrum. We comment on the possibility of distinguishing between these two types of feature models from the analysis of the Cosmic Microwave Background (CMB) radiation data.We also show that there exists a quantitative similarity between the primordial spectra predicted by two of the BF potentials considered. This could lead to a degeneracy of their predicted CMB temperature spectra which could make difficult to discriminate between the models from a CMB analysis. We comment on the possibility that the degeneracy can be broken when higher order terms in the perturbations are considered. In this sense non-Gaussianity may play an important role in discerning between different inflationary models which predict similar spectra.

NOBCChE cultivates young scientists

“I left college with the understanding that chemistry was on the scale of gold atoms and molecules like acetone and benzene,” says Ron W. Darbeau, dean of the College of Science, Technology, Engineering & Mathematics at the University of Arkansas, Fort Smith (UAFS). Darbeau is also a member of the American Chemical Society’s Committee on Professional Training (CPT). “There’s a wealth of chemistry outside that very narrow scale range.” CPT, which creates guidelines for undergraduate chemistry programs, is trying to ensure that students are exposed to that wealth of chemistry. Approved undergraduate programs must now include some instruction on the preparation, characterization, and physical properties of macromolecular, supramolecular, mesoscale, and nanoscale systems. The new requirement is part of the guidelines under which CPT approves undergraduate programs. Approved programs in turn grant ACS-certified bachelor’s degrees to students who complete coursework that satisfies the requirements. CPT periodic...

Effects of local features of the inflaton potential on the spectrum and bispectrum of primordial perturbations

We study the effects of a class of features of the potential of slow-roll inflationary models corresponding to a step symmetrically dumped by an even power negative exponential factor, which we call local features. Local-type features differ from other branch-type features considered previously, because the potential is only affected in a limited range of the scalar field value, and are symmetric respect to the location of the feature. This type of features only affects the spectrum and bispectrum in a narrow range of scales which leave the horizon during the time interval corresponding to the modification of the potential. On the contrary branch-type features have effects on all the perturbation modes leaving the horizon when the field value is within the interval defining the branch, introducing for example differences in the power spectrum between large and small scale which are absent in the case of local-type features. The spectrum and bispectrum of primordial curvature perturbations are affected by oscillations around the scale $k_0$ exiting the horizon at the time $\tau_0$ corresponding to the feature. We also compute the effects of the features on the CMB temperature and polarization spectra, showing the effects or different choices of parameters.

Magnetized cosmological perturbations in the post-recombination era

We study inhomogeneous magnetised cosmologies through the post-recombination era in the framework of Newtonian gravity and the ideal-magnetohydrodynamic limit. The nonlinear kinematic and dynamic equations are derived and linearised around the Newtonian counterpart of the Einstein-de Sitter universe. This allows for a direct comparison with the earlier relativistic treatments of the issue. Focusing on the evolution of linear density perturbations, we provide new analytic solutions which include the effects of the magnetic pressure as well as those of the field's tension. We confirm that the pressure of field inhibits the growth of density distortions and can induce a purely magnetic Jeans length. On scales larger than the aforementioned characteristic length the inhomogeneities grow, though slower than in non-magnetised universes. Wavelengths smaller than the magnetic Jeans length typically oscillate with decreasing amplitude. We also identify a narrow range of scales, just below the Jeans length, where the perturbations exhibit a slower power-law decay. In all cases, the effect of the field is proportional to its strength and increases as we move to progressively smaller lengths.

Using local scale exponent to characterize heart rate variability in response to postural changes in people with spinal cord injury.

Heart rate variability (HRV) is a promising marker for evaluating the remaining autonomic function in people with spinal cord injury (SCI). HRV is commonly assessed by spectral analysis and detrended fluctuation analysis (DFA). This study aimed to investigate whether local scale exponent α(t) can reveal new features of HRV that cannot be reflected by spectral measures and DFA coefficients. We studied 12 participants with SCI and 15 healthy able-bodied controls. ECG signals were continually recorded during 10 min sitting and 10 min prone postures. α(t) was calculated for scales between 4 and 60 s. Because α(t) could be overestimated at small scales, we developed an approach for correcting α(t) based on previous studies. The simulation results on simulated monofractal time series with α between 0.5 and 1.3 showed that the proposed method can yield improved estimation of α(t). We applied the proposed method to raw RR interval series. The results showed that α(t) in healthy controls monotonically decreased with scale at scales between 4 and 12 s (0.083–0.25 Hz) in both the sitting and prone postures, whereas in participants with SCI, α(t) slowly decreased at almost all scales. The sharp decreasing trend in α(t) in controls suggests a more complex dynamics of HRV in controls. α(t) at scales between 4 (0.25 Hz) and around 7 s (0.143 Hz) was lower in subjects with SCI than in controls in the sitting posture; α(t) at a narrow range of scales around 12 s (0.083 Hz) was higher in participants with SCI than in controls in the prone posture. However, none of normalized low frequency (0.04–0.15 Hz) power, the ratio of low frequency power to high frequency (0.15–0.4 Hz) power and long-term (>11 beats) DFA coefficient showed significant difference between healthy controls and subjects with SCI in the prone posture. Our results suggest that α(t) can reveal more detailed information in comparison to spectral measures and the standard DFA parameters.

Low-field NMR study of heat-induced gelation of pork myofibrillar proteins and its relationship with microstructural characteristics

The changes of water mobility and fractal dimension (Df) during pork myofibrillar proteins (PMP) heat-induced gelation were investigated using low-field nuclear magnetic resonance (NMR) and image analysis, respectively. The NMR data were related to the gel microstructure which was explained as fractal dimension and pore size using principal component analysis (PCA). Distributed exponential analysis of the T2 relaxation revealed that three water components corresponding to the three water molecule states exist during the heat-induced gelation. A significant change of T2 was occurred when the temperature increased, T21 relaxation times decreased significantly from 403.70ms to 231.01ms with the temperature increasing from 50 to 70°C. The fraction of T21 distributions declined from 99.27% to 77.01% as the temperature increased from 40 to 60°C. Pronounced different gel network structure was observed during the myofibrillar proteins heat-induced gelation and different Df which was determined by box count method was found between all treatments although evidencing a narrow scale range (from 2.835 to 2.860). Good correlations were detected between the NMR T2 parameters and microstructural data. Overall, combined low-field NMR, image analysis and PCA provide powerful tools for elucidating the pork myofibrillar protein heat-induced gelation.

Gourdron theory: revealing synthetically the masses for biological molecular particles of DNA and proteins and abiological particles of quarks and leptons

In the present report, we examine whether or not there are similar and different characteristics between biological molecular particles and non-living ones such as quark and leptons. While the Newton, Schrodinger, and Boltzmann equations and elementary particle theories describe only a narrow range of scales, the present statistic-fluid dynamic theory having only one arbitrary constant synthetically reveals masses as well as frequencies of various particles of quarks, leptons, W---Z bosons, Higgs boson, plank mass, hadrons, atoms, biological molecules, liquid droplets, living cells, biological organs, and stars. This is possible because each flexible particle is commonly generated by a mode in which a larger particle breaks up into two smaller ones through a gourd shape (gourdron) with two lumps rather than strings. These masses and frequencies dominated by the super-magic numbers, including the asymmetrically golden and symmetrically yamato ratios, can be derived by a quasi-stability principle weaker than neutral stability. The primordial mechanism underlying various types of symmetry breaking and the natural four forces including gravity is also revealed by this theory.

Fish foraging patterns, vulnerability to fishing, and implications for the management of ecosystem function across scales

The function of species has been recognized as critical for the maintenance of ecosystems within desired states. However, there are still considerable gaps in our knowledge of interspecific differences in the functional roles of organisms, particularly with regard to the spatial scales over which functional impact is exerted. This has implications for the delivery of function and the maintenance of ecosystem processes. In this study we assessed the allometric relationship between foraging movements and fish body length at three sites, for 20 species of herbivorous reef fishes within four different functional groups: browsers, farmers, grazer/ detritivores, and scraper/excavators. The relationship between vulnerability of species to fishing and their scale of foraging was also examined. We present empirical evidence of the strong, positive, log-linear relationship between the scale of foraging movement and fish body length. This relationship was consistent among sites and between the two different movement metrics used. Phylogeny did not affect these results. Functional groups foraged over contrasting ranges of spatial scales; for example, scraper/excavators performed their role over a wide range of scales, whereas browsers were represented by few species and operated over a narrow range of scales. Overfishing is likely not only to remove species operating at large scales, but also to remove the browser group as a whole. Large fishes typically have a significant role in removing algae on reefs, and browsers are key to controlling macroalgae and reversing shifts to macroalgal-dominated states. This vulnerability to exploitation has serious consequences for the ability of fish assemblages to deliver their functional role in the face of anthropogenic impacts. However, identification of the scales at which herbivorous fish assemblages are susceptible to fishing provides managers with critical knowledge to design management strategies to support coral-dominated reefs by maintaining function at the spatial scales at which vulnerable species operate.

Hyper-gourd theory: solving simultaneously the mysteries in particle physics, biology, oncology, neurology, economics, and cosmology

The inevitability of various particle masses for hadrons, quarks, leptons, atoms, biological molecules, liquid droplets of fossil fuel and water, living cells including microorganisms and cancers, multi-cellar systems such as organs, neural systems, and the brain, stars, galaxies, and the cosmos is synthetically revealed. This is possible because each flexible particle is commonly generated by a mode in which a larger particle breaks up into two smaller ones through a gourd shape with two lumps. These masses, sizes, frequencies, and diversity dominated by super-magic numbers including the silver ratio, in fractal nature can be derived by the fusion of the quasi-stability principle defined between absolute instability and neutral stability, the indeterminacy principle extended for quantum, statistical, and continuum mechanics, and the spherical Lie group theory. The analyses also result in a new mathematical definition of living beings and non-living systems and further explain the standard network patterns of various particles and also the relation between information, structure, and function, because the proposed theory based on gourds posits a new hyper-interdisciplinary physics that explains a very wide range of scales, while the Newton, Schrodinger, and Boltzmann equations describe only a narrow range of scales.

Discovery of universal outflow structures above and below the accretion disc plane in radio-quiet quasars

59 quasars in the background of the Magellanic Clouds had brightness records monitored by the MACHO project during the years 1992–99. Because the circumpolar fields of these quasars had no seasonal sampling defects, their observation produced data sets well suited to further careful analysis. Following a preliminary report wherein we showed the existence of reverberation in the data for one of the radio-quiet quasars in this group, we now show that similar reverberations have been seen in all of the 55 radio-quiet quasars with adequate data, making possible the determination of the quasar inclination to the observer’s line of sight. The reverberation signatures indicate the presence of large-scale elliptical outflow structures similar to that predicted by the Elvis and ‘dusty torus’ models of quasars, whose characteristic sizes vary within a surprisingly narrow range of scales. More importantly, the observed opening angle relative to the polar axis of the universal elliptical outflow structure present was consistently found to be on the order of 78°.

Multiscale SPC using wavelets: Theoretical analysis and properties

AbstractMost practical process data contain contributions at multiple scales in time and frequency, but most existing SPC methods are best for detecting events at only one scale. For example, Shewhart charts are best for detecting large, localized changes, while EWMA and CUSUM charts are best for detecting small changes at coarse scales. A multiscale approach for SPC, adaptable to the scale of relevant signal features and developed based on wavelet analysis, detects abnormal events at multiple scales as relatively large wavelet coefficients. Univariate and multivariate multiscale SPC (MSSPC) for detecting abnormal operation are theoretically analyzed, and their properties are compared with existing SPC methods based on their average run lengths. SPC methods are best for detecting features over a narrow range of scales. Their performance can deteriorate rapidly if abnormal features lie outside this limited range. Since in most industrial processes, the nature of abnormal features is not known a priori, MSSPC performs better on average due to its adaptability to the scale of the features and for monitoring autocorrelated measurements since dyadic wavelets decorrelate most stochastic processes. MSSPC with dyadic discretization is appropriate for SPC of highly autocorrelated or nonstationary stochastic processes. If normal measurements are uncorrelated or contain only mild autocorrelation, it is better to use MSSPC with integer or uniformly discretized wavelets. Many existing methods such as MA, EWMA, CUSUM, Shewhart, batch means charts, and their multivariate extensions are special cases of MSSPC.

The detection of structure in glass patterns: Psychophysics and computational models

Experiments are reported which examine the judgement of the mean orientation of textures composed either of short lines or dipoles ( Glass patterns). The effects of element length, density, and orientation varaition are described. Psychophysical data are compared with predictions from four schemes for extracting features from Glass patterns: token matching, isotropic filtering, oriented filtering, and “adaptive” filtering (selection of local peak output from multiply oriented filters). Glass patterns are spatially broadband but only contain orientation structure at a narrow range of scales making them suitable for examining how filter size is selected for texture processing. A criterion for scale selection is proposed: that local variation of feature orientation should be minimized. Simulations indicate that neither models using isotropic filtering nor token matching achieve human levels of performance on certain tasks. Adaptive filtering, operating at a scale selected using the criterion described, provides good agreement with the psychophysical data reported and is a practical scheme for deriving features using oriented filters.

Transfer of power in non-linear gravitational clustering

We investigate the transfer of power between different scales and coupling of modes during non-linear evolution of gravitational clustering in an expanding universe. We start with a power spectrum of density fluctuations that is exponentially damped outside a narrow range of scales and use numerical simulations to study evolution of this power spectrum. Non-Linear effects generate power at other scales with most power flowing from larger to smaller scales. The ``cascade'' of power leads to equipartition of energy at smaller scales, implying a power spectrum with index $n\approx -1$. We find that such a spectrum is produced in the range $1 < \delta < 200$ for density contrast $\delta$. This result continues to hold even when small scale power is added to the initial power spectrum. Semi-analytic models for gravitational clustering suggest a tendency for the effective index to move towards a critical index $n_c\approx -1$ in this range. For n<n_c, power in this range grows faster than linear rate, while if n>n_c, it grows at a slower rate - thereby changing the index closer to n_c. At scales larger than the narrow range of scales with initial power, a k^4 tail is produced. We demonstrate that non-linear small scales do not effect the growth of perturbations at larger scales.

Wake resonance mechanisms in bluff body interactions

When inhomogeneous upstream turbulence impinges on a dowstream bluff body many complicated interactions occur including: modification of the properties of the upstream turbulence; buffeting of the body; and modification of the bluff body flow regime near the body. Some features of the interactions are similar to the effects obtained with homogeneous upstream turbulence (eg grid turbulence) however the presence of coherent structures can lead to a wake resonance condition in which the quasi-periodic coherent structures force a quasi-resonant response of the wake of the downstream body. This resonance can have significant effects on the flow near the body and the bluff body loading. The buffeting and wake resonance components of the interaction of inhomogeneous turbulence with downstream bluff bodies have been studied using analytical, numerical and experimental techniques (Ramsay 1988a). This paper discusses the wake resonance mechanisms in the context of the interaction of turbulent shear flows (eg wake) with downstream bluff bodies. For weak inhomogeneous upstream turbulence it is possible to extend the methods of Rapid Distortion Theory (RDT) (Hunt 1973) to obtain a linear approximation to the vorticity dynamics of the inhomogeneous interaction. The extended RDT analysis; representation of the coherent and incoherent parts of the upstream inhomogeneous turbulent fields in an appropriate mathematical form; and other details of the analysis have been discussed previously (Ramsay 1988b, 1988c). This analysis can be used to investigate the interaction when the wake resonance is weak. For conditions of strong wake resonance experimental methods must be used. Some progress has also been made with investigations using numerical models of the wake resonance interaction. The results of the analytical and experimental studies show that the interaction of the inhomogeneous upstream turbulence is well described by linear theory using equivalent homogeneous turbulence parameters (integral scale and intensity) when the scale of the upstream coherent structures is well removed from the wake resonance range. Near the wake resonance condition nonlinear behaviour becomes dominant and the linear approximation breaks down. The range of strong wake resonance interactions has been experimentally delineated and occurs for a narrow range of scales of upstream coherent structures approximately equal to the scale of the structures in the wake of the downstream bluff body wake. Over this range of scales the character and magnitude of the response varies considerably from the predictions of the equivalent linear homogeneous theory.