Path Histories Research Articles

Creep Characteristics of Reconstituted Silty Clay under Different Pre-Loading Path Histories

Due to the long-term deformation settlement of foundations, issues such as damage and functional failure of buildings and structures have long been a concern in the engineering field. The creep of soil is one of the primary causes leading to long-term deformation of foundations. In this paper, the consolidation deformation, creep characteristics, and creep model of reconstituted saturated silty clay were studied using the isotropic consolidation creep test and triaxial compression creep test. The results show that for the isotropic consolidation creep test, although the applied load adopted different stages of loading, as long as the final applied confining pressure was the same, the number of stages applied by the confining pressure had little effect on the final isotropic consolidation deformation of the sample and the triaxial undrained shear strength after creep. However, for the triaxial shear creep test, it was found that under the same final deviatoric stress, the final deviatoric strain of the sample was closely related to the number of loading stages of deviatoric stress. The test showed that the more loading stages with the same deviatoric stress, the smaller the final deviatoric strain, and the triaxial undrained shear strength of the sample after creep increased. In addition, it was reasonable to set the pore pressure dissipation of the sample at 95% ((u0 − u)/u0 = 95%) as the time (t100) at which the primary consolidation of the soil sample was completed. The isotropic consolidation creep curves and the triaxial compression creep curves showed certain non-linearity. Then, the logarithmic model and the hyperbolic model were used to fit the creep curves of the samples. It was found that the hyperbolic model had a better fitting effect than the logarithmic model, but for the triaxial compression creep test, the creep parameters of the sample changed greatly. Therefore, studying the creep characteristics of soil under different pre-loading steps is of significant engineering importance for evaluating the long-term deformation of underground structures.

Spatial correlations and relative velocities of polydisperse droplets in homogeneous isotropic turbulence

We investigate the motions of polydisperse droplets in homogeneous and isotropic turbulence at Reynolds numbers Reλ=200–300. The emphasize is put on the parameter dependences of spatial velocity correlations (SVCs) and relative velocities (RVs) of droplets, which are relevant to particle transport and dispersion in turbulence and have been less studied in experiments. The Kolmogorov-scale Stokes number is Stp=10−1–101, and the settling parameter, i.e., the ratio of particle settling velocity to fluid velocity fluctuations, is SvL=0.5–2.0. Using high-resolution measurements, we can resolve the motions of turbulence and droplet over a wide range of scales (10−1η to 102η, η is Kolmogorov length). The parabolic behavior in droplet SVCs near the origin is observed, similar to turbulence. The droplet SVCs are smaller than turbulence for all scales and decrease with both Stp and SvL. At large scales, the droplet RVs, smaller than those of turbulence due to the inertial filtering effect, also decrease with Stp and SvL. At small scales, the path-history effect leads to larger droplet RVs than fluid RVs. Interestingly, we find RVs present a non-monotonic trend with Stp and reach a valley at Stp≈1.0. It may originate from particle clustering and preferential sweeping effects, which both prevail at Stp≈1.0. It is also found that droplet motions are less intermittent than turbulence. This is in contrast to the previous observations by simulations with the gravity effect being ignored. The intermittency of droplet RVs decreases with SvL due to the diminished droplet–turbulence interactions, and it presents opposite trends with Stp for small and large scales. Finally, the balance between the effects of path histories and turbulent structures makes the velocity statistics of droplets quasi-independent from the scale in the range of the dissipative scale (r≲5η).

The Vacuum-Phonon (Sonon) Reinterpretation of QED

This paper provides a reference copy of one particular and highly informal comment in a multiweek Academia.edu discussion of the paper Randomness in Relational Quantum Mechanics by Gary Gordon. The other main participants in this particular thread of the discussion were Doug Marman, Conrad Dale Johnson, Ruth Kastner, and the author. In this comment, the author argues that the only self-consistent approach to reconciling Feynman path integrals with Maxwell’s experimentally well-proven theory of electromagnetic wave pressure is introducing a new spin-0 particle, the vacuum or space phonon (sonon), that conveys linear momentum. The path histories of QED become the always-expanding structure of the sonon field, which, like a bubble, becomes increasingly unstable as it expands. The collection of all sonon fields around well-defined bundles of conserved quantum properties creates xyz space by defining the complete set of relational information for those entities. Spacetime in the sonon model is granular, multi-scale, and entirely mass-energy dependent. Implications of the sonon model are discussed, including the need for a drastic update to general relativity to take the multi-scale granularity of spacetime directly into account, rather than explaining it obliquely via models such as dark matter, dark energy, or MOND.

Polycrystalline modeling of the behavior of neutron-irradiated recrystallized zirconium alloys during strain path change tests

During normal operating conditions, zirconium alloy nuclear fuel cladding tubes experience various biaxial loadings with complex strain path histories. Experiments have been conducted on neutron-irradiated thin cladding tubes in order to study the response to changes in the loading path. These tests consist of alternate internal pressure tests and axial tensile tests. During the internal pressure test steps, the flow stress exhibits significant cyclic strain softening, while axial tensile tests exhibit a smaller degree of cyclic strain softening. TEM analyses of the tested samples have revealed that the observed mechanical behavior can be attributed to clearing of irradiation-induced defect by gliding dislocations. The cyclic strain softening observed for internal pressure tests is due to clearing of defects by dislocations gliding in the basal planes. The smaller degree of cyclic strain softening in tensile tests is due to clearing of defects by dislocations gliding in the prismatic and pyramidal planes. A polycrystalline model has been developed to simulate these tests. This model is able to reproduce many features of the complex behavior of the material and provides a better understanding of the role of the clearing of defects and the contribution of kinematic hardening on the behavior of neutron-irradiated recrystallized zirconium alloys.

Ghost radiance suppression using backward ray path analysis for a Risley prism scanner of an active laser ranging system.

The LAser raDAR (LADAR) system designed in this study shows a ghost pattern around the object image when operated. The system contains 4 wedge prisms, each with different rotational directions and speeds. Therefore, an efficient and thorough analysis method was established. Ray path analysis was performed, and categorized, for every instantaneous case sampled using a backward ray tracing method. The rays' flux and directions were accumulated according to their path histories. This backward ray tracing was performed repeatedly with different neutral density (ND) filter orientations, until no measurable ghost radiance remained in the field of regard (FOR): a tilt angle of 5°. The ND filter was replaced with a mechanical vignette. Subsequently, the ghost flux was 21% of the total accumulated point cloud, coinciding with the actual measurement of 19%. The final image has significantly improved resolution and shows no ghost reflections where they were previously.

Dynamic crack arrest analysis by ordinary state-based peridynamics

Dynamic fracture analysis for the crack arrest phenomenon is performed by ordinary state-based peridynamics formulation and discretization employing transition bond concept. Double cantilever beam specimen is chosen for our numerical evidence purpose. The analysis consists of two main phases namely, generation and application (prediction) phases. In the generation phase, the dynamic stress intensity factors of propagating and arrested cracks are estimated by the present formulation for given crack path histories, and a good agreement is achieved. As for the application phase, dynamic stress intensity factors as well as total crack lengths after crack arrests are in good agreement with the experiments. Moreover, the influence of transition bond concept on the crack arrest behavior is investigated and it is found that the transition bond is very efficient in the simulation of the crack arrest problem such that premature arrests of cracks are observed without transition bond cases.

Completing Explorer Games with a Deep Reinforcement Learning Framework Based on Behavior Angle Navigation

In cognitive electronic warfare, when a typical combat vehicle, such as an unmanned combat air vehicle (UCAV), uses radar sensors to explore an unknown space, the target-searching fails due to an inefficient servoing/tracking system. Thus, to solve this problem, we developed an autonomous reasoning search method that can generate efficient decision-making actions and guide the UCAV as early as possible to the target area. For high-dimensional continuous action space, the UCAV’s maneuvering strategies are subject to certain physical constraints. We first record the path histories of the UCAV as a sample set of supervised experiments and then construct a grid cell network using long short-term memory (LSTM) to generate a new displacement prediction to replace the target location estimation. Finally, we enable a variety of continuous-control-based deep reinforcement learning algorithms to output optimal/sub-optimal decision-making actions. All these tasks are performed in a three-dimensional target-searching simulator, i.e., the Explorer game. Please note that we use the behavior angle (BHA) for the first time as the main factor of the reward-shaping of the deep reinforcement learning framework and successfully make the trained UCAV achieve a 99.96% target destruction rate, i.e., the game win rate, in a 0.1 s operating cycle.

Modeling Tube Clearance and Bounding the Effect of Friction in Concentric Tube Robot Kinematics.

The shape of a concentric tube robot depends not only on the relative rotations and translations of its constituent tubes, but also on the history of relative tube displacements. Existing mechanics-based models neglect all history-dependent phenomena with the result that when calibrated on experimental data collected over a robot's workspace, the maximum tip position error can exceed 8 mm for a 200-mm-long robot. In this paper, we develop a model that computes the bounding kinematic solutions in which Coulomb friction is acting either to maximize or minimize the relative twisting between each pair of contacting tubes. The path histories associated with these limiting cases correspond to first performing all tube translations and then performing relative tube rotations of sufficient angle so that the maximum Coulomb friction force is obtained along the interface of each contacting tube pair. The robot tip configurations produced by these path histories are shown experimentally to bound position error with respect to the estimated frictionless model compared to path histories comprised of translation or mixed translation and rotation. Intertube friction forces and torques are computed as proportional to the intertube contact forces. To compute these contact forces, the standard zero-clearance assumption that constrains the concentrically combined tubes to possess the same centerline is relaxed. The effects of clearance and friction are explored through numerical and physical experiments and it is shown that friction can explain much of the prediction error observed in existing models. This model is not intended for real-time control, but rather for path planning-to provide error bounds and to inform how the ordering of tube rotations and translations can be used to reduce the effect of friction.

Foliation intersection/inflection axes within porphyroblasts (FIAs): a review of advanced applications and significance

Foliation Intersection/Inflection Axes within porphyroblasts (FIAs) provide a quantitative approach to microstructural and metamorphic analysis that can be used to integrate multiple deformation and metamorphic events and develop lengthy PT path histories during orogenesis. This paper reviews applications of FIAs for determining (1) porphyroblast rotation vs. nonrotation; (2) inclusion trail orientations and orogenic processes involving changes in the direction of bulk horizontal shortening; (3) in situ age determinations for multiple deformation episodes; (4) P-T-t-d paths of poly-metamorphism in an orogenic belt; and (5) constraining relative plate movement paths within ancient orogens. Quantitative structural and metamorphic data correlated directly to relative plate motions, are currently allowing the tectonic reconstruction of multiply deformed and metamorphosed terrains in orogens around the world.

A Study on Infrared Local Heat Treatment for AA5083 to Improve Formability and Automotive Part Forming

Automotive industries are increasingly employing aluminum alloys for auto parts to reduce vehicle weight. However, the low formability of aluminum alloys has been an obstacle to their application. To resolve the formability problem, some studies involving heat treatments under laboratory conditions have been reported. However, for industrial applications, the heat treatment sequence, heating energy efficiency, and a commercial part test should be studied. This work shows an infrared (IR) local heat treatment, heating only small areas where the heat treatment is required, for an aluminum alloy to improve the formability with a reduction of heating energy. The experiment shows that the formability drastically increases when the aluminum alloy is heat treated between two forming stages, referred to as intermediate heat treatment. The microstructures of the test pieces are evaluated to identify the cause of the increase in the formability. For an industrial application, an aluminum tailgate, which cannot be manufactured without heat treatment, was successfully manufactured by the IR local heat treatment with a reduction of energy. A simulation was also conducted with a stress-based forming limit diagram, which is not affected by the strain path and heat treatment histories. The simulation gives a good prediction of the formability improvement.

On the relationship between the non-local clustering mechanism and preferential concentration

‘Preferential concentration’ (Squires & Eaton,Phys. Fluids, vol. A3, 1991, pp. 1169–1178) refers to the clustering of inertial particles in the high strain, low-rotation regions of turbulence. The ‘centrifuge mechanism’ of Maxey (J. Fluid Mech., vol. 174, 1987, pp. 441–465) appears to explain this phenomenon. In a recent paper, Bragg & Collins (New J. Phys., vol. 16, 2014, 055013) showed that the centrifuge mechanism is dominant only in the regime$St\ll 1$, where$St$is the Stokes number based on the Kolmogorov time scale. Outside this regime, the centrifuge mechanism gives way to a non-local, path history symmetry breaking mechanism. However, despite the change in the clustering mechanism, the instantaneous particle positions continue to correlate with high strain, low-rotation regions of the turbulence. In this paper, we analyse the exact equation governing the radial distribution function and show how the non-local clustering mechanism is influenced by, but not dependent upon, the preferential sampling of the fluid velocity gradient tensor along the particle path histories in such a way as to generate a bias for clustering in high strain regions of the turbulence. We also show how the non-local mechanism still generates clustering, but without preferential concentration, in the limit where the time scales of the fluid velocity gradient tensor measured along the inertial particle trajectories approaches zero (such as white noise flows or for particles in turbulence settling under strong gravity). Finally, we use data from a direct numerical simulation of inertial particles suspended in Navier–Stokes turbulence to validate the arguments presented in this study.

Decoupled fluorescence Monte Carlo model for direct computation of fluorescence in turbid media.

We present a decoupled fluorescence Monte Carlo (dfMC) model for the direct computation of the fluorescence in turbid media. By decoupling the excitation-to-emission conversion and transport process of the fluorescence from the path probability density function and associating the corresponding parameters involving the fluorescence process with the weight function, the dfMC model employs the path histories of the excitation photons and the corresponding new weight function to directly calculate the fluorescence. We verify the model’s accuracy using phantom experiments and compare it with that of the perturbation fluorescence Monte Carlo model. The results indicate that the model is accurate for the direct fluorescence calculation and, thus, has great potential for application in fluorescence-based in vivo tomography.

Efficient computation of population distribution of microdefects at any location in growing Czochralski silicon single crystals

A computationally efficient model to quantify the distribution of microdefect population at any given location in Czochralski grown silicon crystals is proposed and numerically solved. For this purpose, all microdefects are approximated as spherical clusters and the concentration fields of intrinsic point defects and other intermediate species are evolved using a lumped model which eliminates the requirement to store formation and path histories of the clusters. The formation of all clusters is modeled by the classical nucleation theory, while they grow by diffusion-limited kinetics. The model is validated by comparing its predictions against that of a rigorous model, where actual cluster population distribution is captured on the basis of formation and path histories of the clusters.

Direct Monte Carlo computation of time-resolved fluorescence in heterogeneous turbid media

We show that a multiexponential model for time-resolved fluorescence allows the use of an absorption-perturbation Monte Carlo (MC) approach based on stored photon path histories. This enables the rapid fitting of fluorescence yield, lifetimes, and background tissue absorptions in complex heterogeneous media within a few seconds, without the need for temporal convolutions or MC recalculation of photon path lengths. We validate this method using simulations with both a slab and a heterogeneous model of the mouse head.

Theta dependence, sign problems, and topological interference

In a Euclidean path integral formulation of gauge theory and quantum mechanics, the theta-term induces a sign problem, and relatedly, a complex phase for the fugacity of topological defects; whereas in Minkowskian formulation, it induces a topological (geometric) phase multiplying ordinary path-amplitudes. In an SU(2) Yang-Mills theory which admits a semi-classical limit, we show that the complex fugacity generates interference between Euclidean path histories, i.e., monopole-instanton events, and radically alters the vacuum structure. At theta=0, a mass gap is due to the monopole-instanton plasma, and the theory has a unique vacuum. At theta=pi, the monopole induced mass gap vanishes, despite the fact that monopole density is independent of theta, due to destructive topological interference. The theory has two options: to remain gapless or to be gapped with a two-fold degenerate vacua. We show the latter is realized by the magnetic bion mechanism, and the two-vacua are realization of spontaneous CP-breaking. The effect of the theta-term in the circle-compactified gauge theory is a generalization of Aharonov-Bohm effect, and the geometric (Berry) phase. As theta varies from 0 to pi, the gauge theory interpolates between even- and odd-integer spin quantum anti-ferromagnets on two spatial dimensional bi-partite lattices, which have ground state degeneracies one and two, respectively, as it is in gauge theory at theta=0 and theta=pi.

Coordination in Large Numbers: An Agent-Based Model of International Negotiations

How do states solve n- choice cooperation problems? Although classical game theory offers useful insights into how states achieve cooperation, its focus on equilibria means that it is largely silent on the processes of negotiation, particularly when multiple solutions to a cooperation problem exist. To explore the path histories of international cooperation, this article uses an agent-based model to explore how states solve a coordination game with three equilibria. To further enrich the analysis, the model explores how domestic constraints may affect coordination games. Such state-level constraints may present negotiators with considerable informational costs and high barriers to understanding each other's preferences. The model finds that the process of communicating preferences can greatly affect the prospects for cooperation, independent of distributional consequences and concerns about cheating. It also finds that, contrary to collective goods theory, a large number of states coordinate a solution to the problem easier than small groups. This is because larger groups create denser networks that communicate preferences more efficiently. The agent-based model thus illustrates how simulation as a method can challenge our extant thinking about cooperation among nation-states. These findings have implications for research on interstate coordination, since it suggests transnational linkages may help states overcome information barriers that frustrate agreements.

An Analysis of Strain Path Effects on Static Recrystallisation in Hot Worked Aluminium Alloy AA5052 Using Forward and Reverse Torsion

The effects of strain path reversal, using forward and reverse torsion, on the microstructure evolution in the aluminium alloy AA5052 have been studied using high resolution electron backscatter diffraction. Deformation was carried using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300°C and strain rate of 1s-1 to a total equivalent tensile strain of 0.5. Sections of the as-deformed gauge lengths of both test specimens were then annealed at 400°C for 1 hour in a salt bath in order to investigate their subsequent recrystallisation response. In both strain path histories the deformation substructure in the grains analysed consisted of microband arrays within an equiaxed dislocation cell structure. The material subjected to forward/forward deformation did, however, have a slightly greater number of low angle boundaries, i.e. boundaries < 15° misorientation, whilst the forward/reverse material had some grains containing little evidence of substructure. On annealing both materials had significantly reduced levels of low angle boundaries but only the forward/forward material had an increased number of high angle boundaries and a reduced grain size, indicating recrystallisation had only occurred in this material. This would suggest that the deformation microstructure within the forward/forward condition was sufficient to initiate and maintain recrystallisation whilst the microstructure produced by the forward/reverse test contained insufficient nuclei or internal energy to produce a recrystallised material within 1 hour. Further work is now required at different annealing times in order to determine if the major effect of strain path is on retarding nucleation, growth or both.

시공간 이동 시퀀스 패턴 마이닝 기법

최근 모바일 컴퓨팅 시스템에서 위치 기반 서비스(Location Based System: LBS)에 대한 연구가 활발히 진행되고 있다. 시공간 이동 시퀀스 마이닝은 이동 경로 데이터로부터 사용자 이동 패턴을 추출하는 새로운 마이닝 기법이다. 시공간 이동 시퀀스 패턴 마이닝은 기존의 빈발 패턴 마이닝 기법과 유사하나 몇 가지 차이점이 있다. 빈발 패턴 마이닝은 장바구니 분석에서와 같이 고객이 구입한 아이템과 관련된 것이나 시공간 이동 시퀀스 패턴 마이닝은 사용자 이동 시퀀스 경로를 대상으로 한다. 또한 사용자의 관심도를 반영하기 위해 해당 위치에서의 소요시간을 고려한다. 본 연구는 대표적인 빈발 패턴 마이닝 기법의 하나인 Apriori 알고리즘에 이동 시퀀스 데이터를 적용하여 Apriori_msp 알고리즘을 제안하였으며 성능 평가를 수행한 결과를 제시하였다. Recently many LBS(Location Based Service) systems are issued in mobile computing systems. Spatial-Temporal Moving Sequence Pattern Mining is a new mining method that mines user moving patterns from user moving path histories in a sensor network environment. The frequent pattern mining is related to the items which customers buy. But on the other hand, our mining method concerns users' moving sequence paths. In this paper, we consider the sequence of moving paths so we handle the repetition of moving paths. Also, we consider the duration that user spends on the location. We proposed new Apriori_msp based on the Apriori algorithm and evaluated its performance results.

Mixed-Mode Dynamic Crack Growth in Functionally Graded Glass-Filled Epoxy

Compositionally graded glass-filled epoxy sheets with edge cracks initially along the gradient are studied under dynamic loading conditions. Specimens with monotonically varying volume fraction of reinforcement are subjected to mixed-mode loading by eccentric impact relative to the crack plane. The optical method of Coherent Gradient Sensing and high-speed photography are used to map transient crack tip deformations before and after crack initiation. Two configurations, one with a crack on the stiffer side of a graded sheet and the second with a crack on the compliant side, are examined experimentally. To elucidate the differences in fracture behavior due to functional grading, a homogeneous sample is also tested. The differences in both pre- and post-crack initiation behaviors are observed interms of crack initiation time, crack path, crack speed and stress intensity factor histories. When a crack is situated on the compliant side of the sample, it kinks significantly less compared to when it is on the stiffer side. Crack tip mode mixity histories show small but positive values during crack growth from the stiffer side of the sample towards the compliant side whereas a small but negative mode mixity prevails for the opposite configuration.

The Influence of Meteorological Conditions on the Wet Deposition of Mercury in Southern Florida

Abstract Source–receptor relationships for mercury (Hg) and other trace elements wet deposited in southeastern Florida were investigated using daily event precipitation samples collected over a 1-yr period in 1995–96. Data collected in Davie, Florida, showed significantly higher (2.2 times) volume-weighted mean (VWM) Hg concentrations during the spring and summer seasons relative to winter. A meteorological tracer analysis, utilizing the ratio of trace elements lanthanum (La) to cerium (Ce), determined that “feed” air to precipitation cells arriving at the site incorporated local urban emissions more frequently during the spring and summer seasons. Using Weather Surveillance Radar-1988 Doppler (WSR-88D) data, analysis of precipitation-cell path histories for events collected at 17 sites in southeastern Florida over 1 month in the summer of 1995 showed significantly higher (2.0 times) VWM Hg concentrations in events with easterly cell paths than in those with westerly paths for storms arriving at Everglades sites. Significantly higher VWM concentrations for known anthropogenic elements vanadium (V) and nickel (Ni) (oil combustion) and lead (Pb) and antimony (Sb) (waste incineration) were also observed in events with easterly paths. In addition, events arriving from the east (offshore) that impacted the coastal sites were significantly lower in Hg (a factor of 2.6) than were events from the east that impacted the urban sites (after events moved inland over emission sources). This study demonstrates that source–receptor relationships can be established by analyzing the meteorological conditions corresponding to each precipitation event, and it supports the previous finding that local anthropogenic sources played the dominant role in the wet deposition of Hg to southern Florida and the Everglades during the study period.