Remote Boundaries Research Articles

First and Second Conversations: Remote Learning and Interpretive Boundaries

AbstractThis article examines the nature of student‐to‐student text discussion in a dialogically organized remote classroom. Conducted as teacher research, I investigated student talk in a PreK‐1st grade biblical literature class. In the fall of 2020, I taught a biblical literature class to a fully remote PreK‐1st grade cohort in a Jewish independent school on the East Coast. Four undergraduate research assistants from the SCRoLL education lab helped with ongoing data analysis. Through self‐study of my teaching and classroom, I discovered the ways that the remote setting shaped intensive text discussion, facilitating students' comfort stepping into their own interpretive authority and moving past the classroom fixture of teacher as interpretive authority. In the remote classroom, the students comfortably moved between the first conversation, the meaning of the text, and the second conversation, competing conventions for determining the meaning of the text. I conclude with suggestions for how teachers interested in dialogically organized classrooms can carry the assets of the remote classroom forward.

A novel method for measuring AFO stiffness using motion capture

A mathematical strip-saturation model is proposed to analyze the influence of changing poling direction on two hairline electrically semi-permeable collinear cracks embedded in a piezoelectric strip. The remote boundaries of the piezoelectric strip are subjected to anti-plane mechanical and in-plane electrical loads. Fourier series method is applied to transform the model into triple series equations which are then reduced to singular integral equations using the integral equation technique. The closed-form analytical expressions are derived for saturation zones length, crack-sliding displacement (CSD), crack opening potential drop (COPD), intensity factors (IFs), and energy release rate (ERR). Influence of the poling angle on CSD, COPD, and ERR are shown graphically for various cracked piezoelectric ceramics. In addition, the numerical study is also presented for analyzing the effect of inter-crack distance and prescribed electrical and mechanical loadings on the fracture parameters. All graphical results are analyzed and compared.

Sleep quality and its impacts on quality of life among military personnel in remote frontier areas and extreme cold environments

BackgroundPoor sleep quality negatively affects the readiness of military operations and is also associated with the development of mental health disorders and decreased quality of life. The purpose of this study was to investigate the sleep quality of military personnel from remote boundaries of China and its relationship with coping strategies, anxiety, and health-related quality of life (HRQoL).MethodsA cross-sectional survey was performed among military officers and soldiers from a frontier defence department and an extreme cold environment. The participants were surveyed using the Pittsburgh Sleep Quality Index (PSQI), Trait Coping Style Questionnaire (TCSQ), Self-rating Anxiety Scale (SAS), and Short Form Health Survey (SF-36).ResultsA total of 489 military officers and soldiers were included. The participants had a mean age of 22.29 years. The median overall PSQI score was 7.0 (IQR, 4.0 ~ 9.0), with 40.9% (200/489) of the subjects reporting poor sleep quality. The difficulties with sleep were mainly related to daytime dysfunction due to disrupted sleep, sleep latency, and subjective sleep quality. The median score of the SF-36 physical component was 83.5 (IQR, 73.0 ~ 90.5), and the median score of the mental component was 74.1 (IQR, 60.4 ~ 85.1). Significant correlations were found between the PSQI and SF-36 (r = − 0.435, P < 0.01). Anxiety symptoms, marital status, educational background, and global PSQI score were demonstrated as predictors of a low SF-36 physical component by multiple regression analysis (F = 17.06, P < 0.001, R2 = 0.117).ConclusionsSleep difficulty is a prevalent and underestimated problem in the military that negatively influences HRQoL, especially in physical and social functioning. Evaluation of and education on pain were recommended because of body pain and its negative impacts on sleep quality, coping strategies, anxious emotions and HRQoL.

Poling angle effect on two mode-III semi-permeable collinear cracks in a piezoelectric strip: Strip-saturation model

A mathematical strip-saturation model is proposed to analyze the influence of changing poling direction on two hairline electrically semi-permeable collinear cracks embedded in a piezoelectric strip. The remote boundaries of the piezoelectric strip are subjected to anti-plane mechanical and in-plane electrical loads. Fourier series method is applied to transform the model into triple series equations which are then reduced to singular integral equations using the integral equation technique. The closed-form analytical expressions are derived for saturation zones length, crack-sliding displacement (CSD), crack opening potential drop (COPD), intensity factors (IFs), and energy release rate (ERR). Influence of the poling angle on CSD, COPD, and ERR are shown graphically for various cracked piezoelectric ceramics. In addition, the numerical study is also presented for analyzing the effect of inter-crack distance and prescribed electrical and mechanical loadings on the fracture parameters. All graphical results are analyzed and compared.

Detection performance and inversion processing of logging-while-drilling extra-deep azimuthal resistivity measurements

We present systematic investigations on the physics, detection performance and inversion of logging-while-drilling extra-deep azimuthal resistivity measurements (EDARM). First, the definitions of EDRAM measurements are discussed, followed by the derivation of the attenuation and phase-shift geometrical factors to illustrate the relative contributions of formation units to the observed signals. Then, a new definition of detection depth, which considers the uncertainty of inversion results caused by the data noise, is proposed to quantify the detection capability of EDARM. Finally, the Bayesian theory associated with Markov chain Monte Carlo sampling is introduced for fast processing of EDARM data. Numerical results show that EDARM is capable of detecting the azimuth and distance of remote bed boundaries, and the detection capability increases with increasing spacing and resistivity contrast. The EDARM tool can accommodate a large range of formation resistivity and is able to provide the resistivity anisotropy at arbitrary relative dipping angles. In addition, multiple bed boundaries and reservoir images near the borehole are readily obtained by using the Bayesian inversion.

Effects of permeability conditions on time-dependent fracture of poroelastic media

The time-dependent fracture of fluid-infiltrated porous materials is known to be affected by fluid diffusion, which is strongly influenced by the initial pore pressure field attributed to loading and the permeability conditions on the boundaries. In this research, the concurrent solid deformation and fluid migration for a traction-free crack of finite length 2a in a poroelastic medium are analyzed. The remote boundaries of the medium are subjected to constant stress or constant stain in the direction perpendicular to crack faces. Without confining the range of the fluid diffusion to the neighborhood of the crack, four types of permeability conditions are considered on the boundaries: (I) the remote boundaries and the crack faces are both impermeable, (II) the remote boundaries are permeable to constant pore pressure, but the crack faces are impermeable, (III) the remote boundaries are impermeable, but the crack faces are permeable to constant pore pressure, and (IV) the remote boundaries and the crack faces are both permeable to constant pore pressure. The singularities of the stress and the pore pressure gradient at small flow times are obtained from finite element simulations and compared to asymptotic predictions. The instantaneous fracture energy J is evaluated using a method that uses the J-integral around the cohesive zone embedded ahead of the crack tip in the simulations. The numerical results of J are validated with the asymptotes predicted from stress intensities at small flow times. When there is a difference between the imposed pore pressure and the initial pore pressure caused by applying loading on the boundaries, the variation in J(t) is affected by short and long ranges of fluid flow, and J(t) reaches its drained limit at a time on the order of W2/c, where W is the dimensional size and c is the consolidation coefficient of porous materials. The drained limit may not be the maximum value of J, especially when the difference on the remote boundaries is positive under strain control. For stress-control cases, whether the maximum J occurs before the drained state depends not only on the difference in pore pressure but also on the location of the permeable boundaries.

Investigation of the influence of boundary conditions in the numerical solution of a vortex tube model

The applicability of various boundary conditions in the computational simulation of a Ranque–Hilsch vortex tube is investigated. A review of existing works on the effect of geometry and various thermodynamic parameters on the efficiency of the pipe is made. The substantiation of the possibility of introducing additional computational domains when moving the boundaries to study the influence of boundary conditions when modeling gas dynamics problems is given. To simulate the dynamics of a gas in a vortex tube, a mathematical model is written that includes the Navier–Stokes system of equations describing a compressible viscous fluid, which is closed by the equation of state of an ideal gas. Existing methods for calculating turbulent flows are considered. The applicability of various semi-empirical models of turbulence for modeling a vortex tube is described. The possibility of using the selected k−ε model and its description is argued. The boundary conditions characteristic of the vortex tube model are described, and the boundary conditions most combined in the simulation of gas dynamics problems are also shown. Presents a grid that takes into account the area formed by the removal of boundaries. The solution is based on the sonicFoam algorithm in the OpenFOAM package. Utilities of the postprocessor are used when preparing the model for calculations on a high-performance cluster and utilities for averaging the obtained physical quantities. The simulation results for different combinations of boundary conditions and models with remote boundaries are given. Comparison of the results obtained. It is shown that the geometrical dimensions have a strong influence on the operation of the pipe; the correct choice of boundary conditions makes it possible to obtain the values of physical quantities that are closest to the known experimental ones. Moving the boundaries away from direct exits provides an opportunity to more accurately estimate the effects that arise near the real boundaries of the vortex tube, especially affecting the magnitude of the Ranque–Hilsch effect.

Constant-head test at a partially penetrating well in an aquifer-aquitard system

An analytical model for describing pumping induced drawdown by constant-head test at a partially penetrating well in a leaky confined aquifer is developed by treating the leakage of aquitard storage as an interface phenomenon rather than an volumetric effect, which is the novel and never developed so far. Three different cases of remote lateral boundaries are considered in the model. The new drawdown solution in Laplace space is obtained and inverted into time-domain solution utilizing the Stehfest method. The (semi-)analytical solutions for well discharge are then obtained under three different cases. Analytical solutions in Laplace and time domains are developed for calculating the (total) leakage rate and volume across the aquitard-aquifer interface due to constant-head test at a partially penetrating well in a leaky confined aquifer, and such solutions are of great use for groundwater resource management. Based on the newly developed solutions, the distribution of wellbore flowrate and aquitard leakage are explored and the sensitivity analysis is conducted to identify the most important controlling factor. The sensitivity analysis shows that the wellbore flowrate and the drawdown in infinite (Case 1), finite (Case 2), and closed (Case 3) leaky confined aquifer systems are both sensitive to the variation of well partial penetration, well radius, and aquifer anisotropic ratio during the whole pumping period and they are most sensitive to the change of outer boundary distance at late time for Case 3. The effect of the outer boundary on the drawdown or wellbore flowrate is more significant for a shorter outer boundary distance.

Boundary enhanced effects on the existence of quadratic solitons

We investigate, both analytically and numerically, the boundary enhanced effects exerted on the quadratic solitons consisting of fundamental waves and oscillatory second harmonics in the presence of boundary conditions. The nonlocal analogy predicts that the soliton for fundamental wave is supported by the balance between equivalent nonlinear confinement and diffraction (or dispersion). Under Snyder and Mitchell’s strongly nonlocal approximation, we obtain the analytical soliton solutions both with and without the boundary conditions to show the impact of boundary conditions. We can distinguish explicitly the nonlinear confinement between the second harmonic mutual interaction and the enhanced effects caused by remote boundaries. Those boundary enhanced effects on the existence of solitons can be positive or negative, which depend on both sample size and nonlocal parameter. The piecewise existence regime of solitons can be explained analytically. The analytical soliton solutions are verified by the numerical ones and the discrepancy between them is also discussed.

A finite difference method for off-fault plasticity throughout the earthquake cycle

We have developed an efficient computational framework for simulating multiple earthquake cycles with off-fault plasticity. The method is developed for the classical antiplane problem of a vertical strike-slip fault governed by rate-and-state friction, with inertial effects captured through the radiation-damping approximation. Both rate-independent plasticity and viscoplasticity are considered, where stresses are constrained by a Drucker–Prager yield condition. The off-fault volume is discretized using finite differences and tectonic loading is imposed by displacing the remote side boundaries at a constant rate. Time-stepping combines an adaptive Runge–Kutta method with an incremental solution process which makes use of an elastoplastic tangent stiffness tensor and the return-mapping algorithm. Solutions are verified by convergence tests and comparison to a finite element solution. We quantify how viscosity, isotropic hardening, and cohesion affect the magnitude and off-fault extent of plastic strain that develops over many ruptures. If hardening is included, plastic strain saturates after the first event and the response during subsequent ruptures is effectively elastic. For viscoplasticity without hardening, however, successive ruptures continue to generate additional plastic strain. In all cases, coseismic slip in the shallow sub-surface is diminished compared to slip accumulated at depth during interseismic loading. The evolution of this slip deficit with each subsequent event, however, is dictated by the plasticity model. Integration of the off-fault plastic strain from the viscoplastic model reveals that a significant amount of tectonic offset is accommodated by inelastic deformation ( ∼ 0.1 m per rupture, or ∼ 10% of the tectonic deformation budget).

Elastic fields of straight wedge disclinations axially piercing bodies with spherical free surfaces

Linear elasticity problem for a straight wedge disclination, which axially pierces a hollow sphere (a spherical layer), is solved analytically. The disclination displacements, stresses and dilatation are given in the form of series with Legendre polynomials. The related elasticity problems for a wedge disclination in a bulk elastic sphere and those one treading a spherical cavity are addressed, as well. It is demonstrated that the found solutions satisfy the boundary conditions on spherical free surfaces including the disclination emerging points. The distribution and the magnitude of the disclination elastic fields in spherical bodies strongly depend on the presence and the size of the inner cavity. For the correct treatment of elasticity for a disclination penetrating through a spherical pore, it is necessary to take into account strictly the boundary conditions on the remote external boundaries of the elastic body.

Large deviation principles in boundary problems for compound renewal processes

We find explicit logarithmic asymptotics for the probability of events related to the intersection (or nonintersection) of arbitrary remote boundaries by the trajectory of a compound renewal process.

Prolog to, "Leaky-wave theory, techniques, and applications: From microwaves to visible frequencies"

The theory of electromagnetic leaky waves can explain a variety of electromagnetic phenomena and scenarios, from microwave to visible frequencies. In the field of wave physics, the damping of harmonic oscillations in time and/or space is associated with losses in a dissipative system. Moreover, in open systems, oscillation energy gradually gets lost in the form of radiation toward the remote boundaries of an open region, reducing the amplitude of oscillations, even in a nondissipative system. This effect occurs with radioactive states in quantum mechanics, with damped resonances in open acoustic or electromagnetic cavities, and with leaky-waves in open waveguiding structures. The theory of electromagnetic leaky waves can explain a variety of electromagnetic phenomena and scenarios, from microwave to visible frequencies.

The nature of stress state: numerical and laboratory experiments and some field observations

Abstract Simulations of the stress state in a region of discontinuously fractured rock revealed a strongly heterogeneous, self-organized stress distribution displaying internally balanced strains and corresponding energy storage. The explicit simulations follow a sequence which may be inferred to be irreversible and strongly dependent on interaction between fractures, implying a time-dependency. The state of the simulated reservoir displays a sensitivity characteristic of marginal stability. These numerical observations are compared with new and previous laboratory and field experiments spanning a wide range of size, stress magnitude and stress difference. The characteristics of the state of the simulated reservoir, laboratory samples and field behaviour are found to be consistent with the numerical predictions. A stress memory is evident. This supports previous conclusions that the concept of stress state as uniform, constant and resulting from averaged values of stresses or displacements, presently applied at remote and artificial boundaries, is grossly oversimplified and flawed.

Behavioural studies of faecal continence in the rat

A behavioural animal model of faecal continence and/or incontinence would be of value in experimental studies of the mechanisms by which sacral neuromodulation can effect continence mechanisms in humans. The aim of this behavioural study was to establish whether the rat, an obligate coprophagic species, exhibits patterns of faecal continence. Standard rat cages were modified to consist of a food and drink area, a nesting area and an empty latrine area. Three floor pressure pads were connected to hour meters to record the time spent in each area over the course of 4 days. The door to the latrine was open for 2 days and closed for another 2 days to create a physical barrier that could only be surmounted by climbing over a partition. In the first 2 days, most faecal pellets (74 ± 20 %; p < 0.0001) were deposited in the latrine and this was not changed by door closure (81 ± 13 %). Door closure had no effect per se on pellet output (p = 0.99), nor did it alter the place preference for defaecation (p = 0.17, two factor ANOVA). Rats spent less time in the latrine area accounting for 23 and 13 % of total time before and after the door was closed, respectively. Normal and infrared videography showed that the place preference for pellets was not due to pellet collection for coprophagic purposes. The rat demonstrates place preference for defaecation and may drop pellets to mark remote boundaries. This simple method may prove useful in future animal studies of neuropathic faecal incontinence and refinement of neuromodulation interventions that lack placebo effects.

Semi-automated analysis of infarct heterogeneity on DE-MRI using graph cuts

Background Two popular methods for determining the threshold values for the infarct core and gray zone on delayed enhancement MR images (DE-MRI) have been proposed previously: full width and half maximum (FWHM) and standard deviation (SD) methods [1]. Major limitations of these methods are:1) three manually drawn contours are needed for endocardial, epicardial and remote myocardium boundaries, which is time consuming and suffers from inter-observer and intra-observer variability; 2) the difficulty in reproducible manual delineation of remote myocardium, is an important contributor to variability in results; and 3) the dependence on the remote region statistics is problematic due to the low SNR of this region [2]. The purpose of this research was to develop a novel algorithm for segmentation of infarct core and gray zone from conventional IR-GRE shortaxis MR images with highly robust and reproducible results comparable to the FWHM analysis while eliminating the requirement for drawing a remote myocardial region.

Shakedown Fatigue Limits for Materials With Minute Porosity

The intention of this study is to predict the fatigue-safe long life behavior of elastoplastic porous materials subjected to zero-tension fluctuating load. It is assumed that the materials contain a dilute amount of voids (less than 5%) and obey Gurson’s model of plastic yielding. The question to be answered is what would be the highest allowable stress amplitude that a porous material can endure (the “endurance limit”) when undergoing an infinite number of loading/unloading cycles. To reach the answer we employ the two shakedown theorems: (a) Melan’s static shakedown theorem (“elastic shakedown”) for establishing the lower bound to fatigue limit and (b) Koiter’s kinematic shakedown theorem (“plastic shakedown”) for establishing its upper bound. The two bounds are formulated rigorously but solved with some numerical assistance, mainly due to the nonlinear pressure dependency of the material behavior and the complex description of the plastic flow near stress-free voids. Both bounds (“dual bounds”) are adjusted to capture Gurson-like porous materials with noninteractive voids. General residual stresses (either real or virtual) are presented in the analysis. They are assumed to be time-independent as generated, say, by permanent temperature gradient between void surfaces and remote material boundaries. Such a situation is common, for instance, in ordinary porous sleeves (used in space industry and alike). A few experiments agree satisfactorily with the shakedown bounding concept.

Boundary force effects exerted on solitons in highly nonlocal nonlinear media

We study the effects caused by remote boundaries on soliton dynamics in nonlinear media with a large range of nonlocality, and demonstrate theoretically and experimentally how asymmetric boundary forces can lead to soliton steering and oscillation in predetermined trajectories.

Automated diagnostics for resonance signature recognition on IMAGE/RPI plasmagrams

The Radio Plasma Imager (RPI) aboard the IMAGE spacecraft probes plasma at both far and near ranges by means of radio sounding. The RPI plasmagrams, similar in their concept to the ground‐based and topside ionograms, contain not only a variety of signatures pertaining to the remote plasma structures and boundaries, but also a suite of the local plasma resonances stimulated by the RPI radio transmissions. Detection and interpretation of the resonance signatures is a valuable diagnostic tool providing the actual electron density and magnetic field strength at the spacecraft location, which are needed for the accurate processing of the remote sensing information on the plasmagrams. The high volume of the RPI sounding data demanded the development of automated techniques for routine interpretation of the plasmagrams. This paper discusses a new method for the detection and interpretation of the resonance signatures in the RPI plasmagrams that employs pattern recognition techniques to localize the signatures and identifies them in relation to model‐based resonances.

Finite element simulation of straight plunge grinding for advanced ceramics

The objective of this work is to model the grinding forces and the associated stress and deformation fields generated in a ceramic workpiece during plunge surface grinding. A two-dimensional finite element model is constructed with the grinding parameters and the mechanical properties of the workpiece as input variables. The size of the geometric model is several times larger than the size of the cutting zone, using approximately 5200 rectangular solid elements with a finer mesh in the cutting zone and with fixed remote boundaries. The loading in the cutting zone is imposed by displacement vectors proportional to the local undeformed chip thickness, which is a function of grinding parameters. For a given set of inputs, the model predicts the normal and tangential forces generated by the grinding wheel, as well as the deformation and the stress fields within the workpiece. As an example, the simulation is applied to a silicon nitride workpiece. Analysis of the stress fields developed in this material suggests that shear failure within the cutting zone is the dominant mode of subsurface failure, which could lead to the formation of shear micro- cracks at the grain interfaces. The depth of the subsurface shear failure zone increases with an increase in maximum undeformed chip thickness or the wheel depth of cut. The resulting local grinding force vectors, maximum stresses and damage zone sizes are predicted as a function of maximum undeformed chip thickness (or the wheel depth of cut).