Edge Amplitudes Research Articles

Characteristic space-based algorithm for detecting abnormal monitoring data in underground engineering

Abnormal points in underground space monitoring data contain valuable information. An anomaly detection algorithm based on characteristic space is proposed in this document. First, based on a temporal edge operator, the edge amplitude of each point in time series data is calculated. The monitoring data curve is linearly segmented by selecting the points with larger edge amplitudes. Second, the data characteristics of each subsegment are extracted, and the original monitoring curve is mapped into the characteristic space. Finally, the abnormal features are identified by the local anomaly factor outlier algorithm, from which abnormal data points can be further obtained. The effectiveness of the proposed algorithm was first verified by identifying artificial abnormal data serials or discrete data point from a normal dataset. The feasibility and applicability of the algorithm was further verified by applying the developed algorithm to detect the anomaly of monitoring data for a real tunnel project.

Large-amplitude oscillations of foils for efficient propulsion

Large-amplitude oscillations of foils have been observed to yield greater propulsive efficiency than small-amplitude oscillations. Using scaling relations and experiments on foils with peak-to-peak trailing edge amplitudes of up to two chord lengths, we explain why this is so. In the process, we reveal the importance of drag, specifically how it can significantly reduce the efficiency, and how this effect depends on amplitude. The scaling relations and experimental data also reveal a fundamental tradeoff between high thrust and high efficiency, where the drag also plays a crucial role.

Effects of Flexible Propulsors on Hydrodynamic Forces

We present experimental measurements of forward forces and external torques generated during forced oscillations of a tail on a fish-like body. The experiments were performed in a towing basin. Three panels having different flexural rigidity were tested over a range of oscillatory frequencies and leading edge amplitudes at 0 m/s and 0.35 m/s. The results show that tail panel flexibility enhances thrust production and thrust-to-input power ratios, with propulsive efficiencies reaching up to 45%.

Undulatory Swimming Performance and Body Stiffness Modulation in a Soft Robotic Fish-Inspired Physical Model.

Undulatory motion of the body is the dominant mode of locomotion in fishes, and numerous studies of body kinematics and muscle activity patterns have provided insights into the mechanics of swimming. However, it has not been possible to investigate how key parameters such as the extent of bilateral muscle activation affect propulsive performance due to the inability to manipulate muscle activation in live, freely swimming fishes. In this article we extend previous work on passive flexible mechanical models of undulatory propulsion by using actively controlled pneumatic actuators attached to a flexible foil to gain insight into undulatory locomotion and mechanisms for body stiffness control. Two soft actuators were attached on each side of a flexible panel with stiffness comparable to that of a fish body. To study how bilateral contraction can be used to modify axial body stiffness during swimming, we ran a parameter sweep of actuator contraction phasing and frequency. Thrust production by the soft pneumatic actuators was tested at cyclic undulation frequencies ranging from 0.3 to 1.2 Hz in a recirculating flow tank at flow speeds up to 28 cm/s. Overall, this system generated more thrust at higher tail beat frequencies, with a plateau in thrust above 0.8 Hz. Self-propelled speed was found to be 0.8 foil lengths per second or ∼13 cm/s when actuated at 0.55 Hz. This active pneumatic model is capable of producing substantial trailing edge amplitudes with a maximum excursion equivalent to 1.4 foil lengths, and of generating considerable thrust. Altering the extent of bilateral co-contraction in a range from -22% to 17% of the cycle period showed that thrust was maximized with some amount of simultaneous left-right actuation of ∼3% to 6% of the cycle period. When the system is exposed to water flow, thrust was substantially reduced for conditions of greatest antagonistic overlap in left-right actuation, and also for the largest latencies introduced. This experimental platform provides a soft robotic testbed for studying aquatic propulsion with active control of undulatory kinematics.

Boosting Wigner’s nj-symbols

We study the SL(2,ℂ) Clebsch-Gordan coefficients appearing in the Lorentzian EPRL spin foam amplitudes for loop quantum gravity. We show how the amplitudes decompose into SU(2) nj− symbols at the vertices and integrals over boosts at the edges. The integrals define edge amplitudes that can be evaluated analytically using and adapting results in the literature, leading to a pure state sum model formulation. This procedure introduces virtual representations which, in a manner reminiscent of virtual momenta in Feynman amplitudes, are off-shell of the simplicity constraints present in the theory, but with the integrands that peak at the on-shell values. We point out some properties of the edge amplitudes which are helpful for numerical and analytical evaluations of spin foam amplitudes, and suggest among other things a simpler model useful for calculations of certain lowest order amplitudes. As an application, we estimate the large spin scaling behaviour of the simpler model, on a closed foam with all 4-valent edges and Euler characteristic χ, to be Nχ−5E+V/2. The paper contains a review and an extension of the results on SL(2,ℂ) Clebsch-Gordan coefficients among unitary representations of the principal series that can be useful beyond their application to quantum gravity considered here.

Optimal chordwise stiffness profiles of self-propelled flapping fins

The versatility of fish to adapt to different swimming requirements is attributed to their complex muscular system. Fish modulate their fin stiffness and shape for maximized performance. In this paper, optimal chordwise stiffness profiles that maximize the propulsive performance have been predicted using theoretical studies. An experimental setup has been fabricated to measure the stiffness profiles of real fish caudal fins. Chordwise varying stiffness robotic fins fabricated using carbon fiber reinforced composites (CFRC) have been tested in the water tunnel to evaluate their performance over constant stiffness fins. It is observed that the varying stiffness fins produce larger thrusts and efficiencies compared to constant stiffness fins for all the operating conditions considered in this work. A comparison of the digital image correlation (DIC) measured deformations of the fins showed that the better performance of varying stiffness fins is due to their larger curvatures and trailing edge amplitudes. These theoretical and experimental studies provide a greater understanding of the role of stiffness in fish fins for locomotion.

Effect of head swing motion on hydrodynamic performance of fishlike robot propulsion

This paper studies the effect of the head swing motion on the fishlike robot swimming performance numerically. Two critical parameters are employed in describing the kinematics of the head swing: the leading edge amplitude of the head and the trailing edge amplitude of the head. Three-dimensional Navier-Stokes equations are used to compute the viscous flow over the robot. The user-defined functions and the dynamic mesh technology are used to simulate the fishlike swimming with the head swing motion. The results reveal that it is of great benefit for the fish to improve the thrust and also the propulsive efficiency by increasing the two amplitudes properly. Superior hydrodynamic performance can be achieved at the leading edge amplitudes of 0.05L (L is the fish length) and the trailing edge amplitudes of 0.08L. The unsteady flow fields clearly indicate the evolution process of the flow structures along the swimming fish. Thrust-indicative flow structures with two pairs of pressure cores in a uniform mode are generated in the superior performance case with an appropriate head swing, rather than with one pair of pressure cores in the case of no head swing. The findings suggest that the swimming biological device design may improve its hydrodynamic performance through the head swing motion.

Form factor approach to dynamical correlation functions in critical models

We develop a form factor approach to the study of dynamical correlation functions of quantum integrable models in the critical regime. As an example, we consider the quantum non-linear Schrödinger model. We derive the long-distance/long-time asymptotic behavior of various two-point functions of this model. We also compute edge exponents and amplitudes characterizing the power-law behavior of dynamical response functions on the particle–hole excitation thresholds. These last results confirm predictions based on the non-linear Luttinger liquid method. Our results rely on a first principles derivation, based on a microscopic analysis of the model, without invoking, at any stage, any correspondence with a continuous field theory. Furthermore, our approach only makes use of certain general properties of the model, so that it should be applicable, possibly with minor modifications, to a wide class of (not necessarily integrable) gapless one-dimensional Hamiltonians.

On knottings in the physical Hilbert space of LQG as given by the EPRL model

We consider the EPRL spin foam amplitude for arbitrary embedded two-complexes. Choosing a definition of the face- and edge amplitudes which lead to spin foam amplitudes invariant under trivial subdivisions, we investigate invariance properties of the amplitude under consistent deformations, which are deformations of the embedded two-complex where faces are allowed to pass through each other in a controlled way. Using this surprising invariance, we are able to show that the physical Hilbert space, as defined by the sum over all spin foams, contains no information about knotting classes of graphs anymore.

No-reference image-quality metric based on blur radius and visual blockiness

We propose new blur and blocking metrics and then present a no-reference image-quality assessment method using these blur and blocking metrics. To compute the blur metric, we first estimated a blur radius from a given image and its reblurred version by using edge differences and edge amplitudes. Because blurring in edge regions is generally more sensitive to human perception, the blur metric was estimated from the edge blocks. We also used kurtosis and structural similarity to better estimate the blur metric. To compute the blocking metric, the blocking artifact was modeled as a 2-D step function and the blockiness visibility was estimated by the brightness difference between adjacent blocks. After the blocky position was determined, the blocking metric was computed from the six differences between four adjacent blocks. Experimental results show that the objective quality scores correlated highly with the subjective quality scores.

Positivity in Lorentzian Barrett–Crane models of quantum gravity

The Barrett–Crane models of Lorentzian quantum gravity are a family of spin foam models based on the Lorentz group. We show that for various choices of edge and face amplitudes, including the Perez–Rovelli normalization, the amplitude for every triangulated closed 4-manifold is a non-negative real number. Roughly speaking, this means that if one sums over triangulations, there is no interference between the different triangulations. We prove non-negativity by transforming the model into a ‘dual variables’ formulation in which the amplitude for a given triangulation is expressed as an integral over three copies of hyperbolic space for each tetrahedron. Then we prove that, expressed in this way, the integrand is non-negative. In addition to implying that the amplitude is non-negative, the non-negativity of the integrand is highly significant from the point of view of numerical computations, as it allows statistical methods such as the Metropolis algorithm to be used for efficient computation of expectation values of observables.

Spin foam models of Riemannian quantum gravity

Using numerical calculations, we compare three versions of the Barrett–Crane model of four-dimensional Riemannian quantum gravity. In the version with face and edge amplitudes as described by De Pietri, Freidel, Krasnov and Rovelli, we show the partition function diverges very rapidly for many triangulated 4-manifolds. In the version with modified face and edge amplitudes given by Perez and Rovelli, we show the partition function converges so rapidly that the sum is dominated by spin foams where all the spins labelling faces are zero except for small, widely separated islands of higher spin. We also describe a new version which appears to have a convergent partition function without drastic spin-zero dominance. Finally, after a general discussion of how to extract physics from spin foam models, we discuss the implications of convergence or divergence of the partition function for other aspects of a spin foam model.

A single-ended blockiness measure for JPEG-coded images

In three subjective experiments, dissimilarity data and numerical category scaling data were obtained to determine the underlying attributes of image quality in sequential baseline-coded JPEG images. Although several distortions were perceived, namely blockiness, ringing and blur, the subjective data for all attributes were highly correlated, so that image quality could approximately be described in one dimension. We therefore proceeded by developing an instrumental measure for one of the distortions, namely, blockiness. In this paper a single-ended blockiness measure is proposed, i.e., one that uses only the coded image. Our approach is therefore fundamentally different from most (double-ended) image quality models that need both the original and the degraded image. The proposed measure is based on detecting the low-amplitude edges that result from blocking and estimating the edge amplitudes. Because of the approximate one-dimensionality of the underlying psychological space, the proposed blockiness measure also predicts the image quality of sequential baseline coded JPEG images.

Relativistic effects in the x-ray-absorption fine structure.

A relativistic model for the extended x-ray-absorption fine structure, in which the energy loss of the emitted photoelectron is accounted for by using a complex energy-dependent exchange-correlation potential, has been developed. Relativistic curved-wave single-, double-, and triple-scattering formulas for excitation from any core hole have been found. The dominant single-scattering signal has been computed for the first shell at the ${\mathit{L}}_{2}$ and ${\mathit{L}}_{3}$ edges of Th (Z=90), Pt (Z=78), and Eu (Z=63) and at the K edge of Sr (Z=38) using this model. Comparisons of the relativistic scattering amplitudes of the Dirac model with the current standard Schr\odinger curved-wave model reveal that the latter deviates from the more exact Dirac model by 20% above 240 eV for Th, by 15% above 240 eV for Pt, and by 10% above 140 eV for Eu. For lower energies, the deviations are as much as two times larger. Differences between the Dirac model ${\mathit{L}}_{2}$- and ${\mathit{L}}_{3}$-edge amplitudes occur below 240 eV for Th and Pt with values of 2% and 6%, respectively. For Eu, this difference diminishes to 4% and occurs only below 140 eV. In the case of the K edge of Sr, the Schr\odinger single-scattering amplitude differs from the Dirac amplitude by 5% for energies above 95 eV. The spin dependence of the generalized Ramsauer-Townsend effect is also exhibited.

Modeling of the influence of coil winding pattern on tooth forces in brushless DC motors

The use of neodymium and other rare earth magnets in brushless DC motors increases their torque, but also magnetically induced vibration due to rotating stator tooth force. This paper investigates the influence of the stator coil winding pattern on stator tooth force and torque from three common winding patterns, e.g., center-tapped-wye (CTY), wye (Y) and delta (/spl Delta/), with equivalent torque output. Stator tooth forces and torque in a 6-pole, 9-tooth, 3-phase motor were calculated from the flux density using finite element analysis and the Maxwell stress tensor. Their frequency spectra were analyzed through multi-dimensional spectral analysis. The analyses show that the driving frequencies of tooth forces appear at the integer multiple of rotor speed multiplied by the number of pole. The driving frequencies of forces have larger amplitudes at the leading edge than at the trailing edge of the tooth. At low frequencies, CTY and /spl Delta/ windings produce larger amplitudes at the leading edge and smaller amplitudes at the trailing edge than those of Y winding. Y windings may produce higher torque ripple than the other winding patterns. >