Type Boundary Research Articles

Revealing and Controlling Energy Barriers and Valleys at Grain Boundaries in Ultrathin Organic Films.

In organic electronics, local crystalline order is of critical importance for the charge transport. Grain boundaries between molecularly ordered domains are generally known to hamper or completely suppress charge transfer and detailed knowledge of the local electronic nature is critical for future minimization of such malicious defects. However, grain boundaries are typically hidden within the bulk film and consequently escape observation or investigation. Here, a minimal model system in form of monolayer-thin films with sub-nm roughness of a prototypical n-type organic semiconductor is presented. Since these films consist of large crystalline areas, the detailed energy landscape at single grain boundaries can be studied using Kelvin probe force microscopy. By controlling the charge-carrier density in the films electrostatically, the impact of the grain boundaries on charge transport in organic devices is modeled. First, two distinct types of grain boundaries are identified, namely energetic barriers and valleys, which can coexist within the same thin film. Their absolute height is found to be especially pronounced at charge-carrier densities below 1012 cm- 2 -the regime at which organic solar cells and light emitting diodes typically operate. Finally, processing conditions by which the type or energetic height of grain boundaries can be controlled are identified.

Boundary element method with particle swarm optimization for solving potential problems

In this paper, the boundary element method (BEM) based on the particle swarm optimization (PSO) algorithm is proposed for solving potential problems. At present, the traditional Gaussian elimination method still needs to improve for computing results accuracy. The PSO algorithms with substantial accuracy used to improve the accuracy of potential problems. So it is introduced the PSO to solve the system of matrix equations derived from the boundary integral equation (BIE). For the presented method, unknown solutions to the system of matrix equations are considered particles, and the optimal solution is sought through group collaboration. Some parameters in this model play a vital role, so confirming them and initializing the positions and velocities of the particles are needed. Then, the positions of the particles are constantly updated with the iteration formula until obtained the optimum solutions. Furthermore, the optimum solution are arrived at in which the cycle is jumped when meeting the conditions (i. e. given the maximum number of iterations or the fitness value). There are examples with constant element and linear element and quadratic element types of boundary, in turn. The three numerical models of 2D potential problems are analyzed and discussed. They certified that the PSO algorithm has feasibility and good convergence. Most importantly, it is proved that the PSO applied in BEM has higher accuracy compared with the Gaussian elimination method for solving potential problems.

Sedimentary Architecture Analysis of Deltaic Sand Bodies Using Sequence Stratigraphy and Seismic Sedimentology: A Case Study of Jurassic Deposits in Zhetybay Oilfield, Mangeshrak Basin, Kazakhstan

Three-dimensional (3D) seismic data and well log data were used to investigate the sandstone architecture of the Middle Jurassic deltaic reservoirs of the Zhetybay Oilfield, Mangeshrak Basin, Kazakhstan. The base-level cycles of different scales were identified and divided using well log and 3D seismic data. Five types of sedimentary boundaries were identified in the mouth bar sandstones. The boundaries divide single mouth bars. Vertically, the spatial distribution of sand bodies can be divided into superposed, spliced, and isolation modes. Laterally, contact modes can be divided into superposition, lateral, and isolation modes. We found that the base-level cycle controls the evolution of the delta front sand body architecture. In the early decline or late rise of the base-level cycle, the superimposed or spliced modes dominate the sand body. By contrast, the lateral or isolation modes dominate the sand body in the late decline or early rise of the base-level cycle. This paper proposes an architecture model of the delta front sand bodies controlled by the base-level cycle. The spatial distribution and morphological variation of deltaic sand bodies could be linked to the base-level cycles.

A Perceiver-Centered Approach for Representing and Annotating Prosodic Functions in Performed Music.

Musical prosody is characterized by the acoustic variations that make music expressive. However, few systematic and scalable studies exist on the function it serves or on effective tools to carry out such studies. To address this gap, we introduce a novel approach to capturing information about prosodic functions through a citizen science paradigm. In typical bottom-up approaches to studying musical prosody, acoustic properties in performed music and basic musical structures such as accents and phrases are mapped to prosodic functions, namely segmentation and prominence. In contrast, our top-down, human-centered method puts listener annotations of musical prosodic functions first, to analyze the connection between these functions, the underlying musical structures, and acoustic properties. The method is applied primarily to the exploring of segmentation and prominence in performed solo piano music. These prosodic functions are marked by means of four annotation types—boundaries, regions, note groups, and comments—in the CosmoNote web-based citizen science platform, which presents the music signal or MIDI data and related acoustic features in information layers that can be toggled on and off. Various annotation strategies are discussed and appraised: intuitive vs. analytical; real-time vs. retrospective; and, audio-based vs. visual. The end-to-end process of the data collection is described, from the providing of prosodic examples to the structuring and formatting of the annotation data for analysis, to techniques for preventing precision errors. The aim is to obtain reliable and coherent annotations that can be applied to theoretical and data-driven models of musical prosody. The outcomes include a growing library of prosodic examples with the goal of achieving an annotation convention for studying musical prosody in performed music.

Eph/ephrin signaling controls cell contacts and formation of a structurally asymmetrical tissue boundary in the Xenopus gastrula

In the primitive vertebrate gastrula, the boundary between ectoderm and mesoderm is formed by Brachet's cleft. Here we examine Brachet's cleft and its control by Eph/ephrin signaling in Xenopus at the ultrastructural level and by visualizing cortical F-actin. We infer cortical tension ratios at tissue surfaces and their interface in normal gastrulae and after depletion of receptors EphB4 and EphA4 and ligands ephrinB2 and ephrinB3. We find that cortical tension downregulation at cell contacts, a normal process in adhesion, is asymmetrically blocked in the ectoderm by Eph/ephrin signals from the mesoderm. This generates high interfacial tension that can prevent cell mixing across the boundary. Moreover, it determines an asymmetric boundary structure that is suited for the respective roles of ectoderm and mesoderm, as substratum and as migratory layers. The Eph and ephrin isoforms also control different cell-cell contact types in ectoderm and mesoderm. Respective changes of adhesion upon isoform depletion affect adhesion at the boundary to different degrees but usually do not prohibit cleft formation. In an extreme case, a new type of cleft-like boundary is even generated where cortical tension is symmetrically increased on both sides of the boundary.

Boundary state feedback control for semilinear fractional-order reaction diffusion systems

This paper investigates the stabilization results for a semilinear time fractional-order reaction diffusion partial differential equations using backstepping method. The parabolic system is addressed with time fractional-order of (0, 1) in the Caputo sense. More general type of actuation setup which can be expressed as Dirichlet, Neumann and Robin type boundary actuation's is considered. The main aim is to achieve the stabilization of the considered system using an invertible transformation through the stability of target system which is verified by Mittag-Leffler stability based on (Q, S, R) dissipativity theory and linear matrix inequality (LMI) technique. The explicit solutions of kernel functions are found by method of successive approximation and to be design the boundary control law for the closed loop system. Finally, the proposed results are validated through numerical examples.

Deformation evolution depending on grain boundary type and hydrogen concentration in nickel investigated by molecular dynamics simulation

The impacts of hydrogen concentration on tensile deformation in the nickel bicrystals with different typical grain boundaries (GB) were investigated by molecular dynamics simulation. The deformation behavior was dependent on the GB type and hydrogen concentration. A critical hydrogen concentration was obtained from a drastic change of the theoretical yield strength. Below critical concentration, hydrogen increased the yield strength and the atomic rearrangement was effectively hindered due to uniform distribution of hydrogen. Above critical concentration, the nickel-hydride formed and caused a sharp decrease in yield strength, which was independent of the GB type.

3D In-situ Stop Action Study of Recrystallization in Additively Manufactured 316L Stainless Steel: Reconstruction Optimization and Observations

A volume of an additively manufactured 316L stainless steel sample has been tracked during its recrystallization using near- and far-field High Energy Diffraction Microscopy (HEDM) and absorption tomography at Advanced Photon Source beamline 1-ID. A near-field compatible in situ furnace allows monitoring of Bragg diffraction signals as they evolve out of a weak and diffuse background while the sample temperature is ≈ 1250° C. The sample is rapidly cooled to room temperature after observation of significant signal evolution and ∼ 0.035 mm3 is mapped by the near-field method. Four cycles of heat treatment follow the structure from a state of small, isolated grains through impingement of domains to near completion of recyrstallization. Here, the experiment and reconstructions are described, and recrystallized fractions, twin domains, and distributions of grain boundary types are discussed.

Chaos of the 2D linear hyperbolic equation with general van der Pol type boundary condition

This paper is concerned with the complex dynamics of the initial-boundary value problem of a 2D linear hyperbolic partial differential equation (PDE), where the parameter α that appeared in the general van der Pol type boundary condition is given by α∈R. The whole real line is divided into three intervals of the parameter to discuss the dynamics. The existence of chaos is first established in the sense of the exponential growth of total variation when the parameter locates in the central interval, which allows it to be positive, negative, or zero. By analyzing the chaotic dynamics of the piecewise continuous map induced by the hyperbolic PDE, such a PDE is further rigorously proved to be chaos in the interval of the positive parameter that is to the right of the central interval. Finally, the asymptotic behaviors of the hyperbolic PDE are systematically presented in the rest of the whole real line; more precisely, the hyperbolic PDE is either globally stable or unbounded.

Complexity and evolution of knowledge boundaries in an interdisciplinary research project

AbstractThis paper aims to understand how and why knowledge boundaries occur, change, and evolve throughout the life‐cycle of interdisciplinary research projects, how they are experienced by different actors, and what strategies they deploy to overcome these boundaries. The study took a case study approach focusing on an interdisciplinary research project for the development of computerised tomography and digital X‐ray scanners in a governmental research organisation in Thailand. A multi‐method qualitative approach, involving semi‐structured interviews, participative observation, and artefact and document analysis, was adopted. Data was analysed through thematic analysis. The findings suggest that knowledge management is more complex and difficult than portrayed in previous studies because of the following: (1) knowledge boundaries evolve and exhibit different emphases at distinct stages of the project; (2) boundaries do not stem only from differences in knowledge across different organisational actors, but, equally importantly, due to the lack of awareness that these differences exist; (3) different organisational actors experience diverse types of knowledge boundary types when faced within the same situation; and (4) context, in terms of external pressures driving the project and influencing its direction, plays an important role in boundary construction and boundary‐spanning mechanisms. This paper presents a novel framework for conceptualising how and why knowledge boundaries evolve throughout an interdisciplinary research project, how these changes are experienced by different participating actors, and what boundary‐spanning mechanisms for bridging them are developed by them. It demonstrates that these changes are often shaped by external drivers that shape the development of the project.

Non‐local effects of human activity on the spatial distribution of migratory wildlife in Serengeti National Park, Tanzania

Abstract Human activities are transforming landscapes and altering the structure and functioning of ecosystems worldwide and often result in sharp contrasts between human‐dominated landscapes and adjacent natural habitats that lead to the creation of hard edges and artificial boundaries. The configuration of these boundaries could influence local biotic interactions and animal behaviours. Here, we investigate whether boundaries of different degrees of ‘hardness’ affect space utilization by migratory species in Serengeti National Park, Tanzania. We deployed camera traps along transects perpendicular to the national park boundary at three different locales. The transects were located in areas that consisted of two types of human–wildlife interface: a sudden transition from the national park into agro‐pastoral land use (termed a ‘hard’ boundary) and a more gradual transition mediated by a shared usage area (termed a ‘soft’ boundary). Camera traps were placed at 2 km intervals along each 10 km transect from the edge towards the core of the park and were programmed to collect images hourly between dawn and dusk between June 2016 and March 2019. We used a deep neural network to detect the presence of wildlife within images and then used a Bayesian model with diffuse priors to estimate parameters of a generalized linear model with a Bernoulli likelihood. We explored the binomial probability of either wildebeest or zebra presence as a function of distance to the boundary, the rate of grass greening or drying (dNDVI) and the concentration of grass protein. There was a strong negative effect of distance to boundary on the probability of detecting wildebeest or zebra; however, this was only observed where the transition from human‐dominated landscape to protected areas was sudden. Conversely, soft boundaries had little to no effect on the probability of detecting wildebeest or zebra. The results suggest that boundary type affects migratory species occurrence. The implications of these findings suggest that hard boundaries reduce the effective size of conservation areas; for many species, the area used by wildlife is likely less than the gazetted area under protection. The impacts may be severe especially for narrow protected areas or dispersal corridors.

Two-stage re-estimation adaptive design: a simulation study


 
 
 Background: adaptive clinical trial design has been proposed as a promising new approach to improve the drug discovery process. Among the many options available, adaptive sample size re-estimation is of great interest mainly because of its ability to avoid a large ‘up-front’ commitment of resources. In this simulation study, we investigate the statistical properties of two-stage sample size re-estimation designs in terms of type I error control, study power and sample size, in comparison with the fixed-sample study.
 Methods: we simulated a balanced two-arm trial aimed at comparing two means of normally distributed data, using the inverse normal method to combine the results of each stage, and considering scenarios jointly defined by the following factors: the sample size re-estimation method, the information fraction, the type of group sequential boundaries and the use of futility stopping. Calculations were performed using the statistical software SAS™ (version 9.2).
 Results: under the null hypothesis, any type of adaptive design considered maintained the prefixed type I error rate, but futility stopping was required to avoid the unwanted increase in sample size. When deviating from the null hypothesis, the gain in power usually achieved with the adaptive design and its performance in terms of sample size were influenced by the specific design options considered.
 Conclusions: we show that adaptive designs incorporating futility stopping, a sufficiently high information fraction (50-70%) and the conditional power method for sample size re-estimation have good statistical properties, which include a gain in power when trial results are less favourable than anticipated. 
 

Thermal Response of a Thick Circular Plate With Internal Heat Sources in Time Fractional Frame

Present paper investigated the thermoelastic response of an axisymmetric two-dimensional time fractional thermoelastic problem. The order of the problem is 0   2 which occupy the space D{(x, y,z)R3 : 0r b, h z h}. Further, convection type boundaries with heating ( ) ( ) 1 0 Q t  r  r and ( ) ( ) 2 0 Q  t  r  r are applied on the both surfaces respectively, whereas plate is subjected to the action of internal heat is the linear function of temperature. Next, integral transformation techniques are used to calculate temperature, displacement and thermal stresses. The graphical method is used to analyze the properties of Aluminum.

Grain Structure Engineering of NiTi Shape Memory Alloys by Intensive Plastic Deformation.

To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary Ni55Ti45 (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. In situ synchrotron X-ray Laue microdiffraction and in situ synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro- and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the Ni4Ti3 and NiTi2 precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19′ martensite is not strongly dependent on the grain structure.

Influence of Long-Term Mine Activity on Hydraulic Relations between Separate Hydrogeological Units—New Aspects of Regional Water Circulation Assessment

In the course of the documentation works aimed at updating exploitable resources of the groundwater intake, an unexpected change in hydrodynamic field arrangement was observed in a fragment of the area. In relation to the observations made so far, lasting several decades, the groundwater table switched its slope, indicating the flow in the opposite direction than originally. Initially, in the range of the surveyed hydrogeological structure, no object was identified whose draining character could cause such an effect. No significant groundwater extraction or drainage points were documented within a radius of several kilometers. It was only the extended scope of spatial analysis that made it possible to identify the probable cause of a local change in the water table position as a mining pit located in the neighboring hydrogeological structure. The two adjacent hydrogeological structures treated separately so far revealed an experimentally confirmed hydraulic connection. An in-depth analysis of the problem showed the necessity of modifying the existing model of the structure in order to map the observed interactions. An additional simulation module of General-Head Boundary type was applied. The quantity of lateral groundwater exchange between two hydrogeological structures was estimated using mathematical modeling at 3.4 thousand m3/d (reconstructed current state, after model calibration). Further work should aim at treating reservoirs as hydraulically connected after exceeding limiting parameters.

Beta critical of Schrödinger operator with delta potential in one and two dimension

We consider 1D and 2D Schrödinger equation with delta potential on the positive half-axis with Dirichlet, Neumann, and Robin type boundary conditions. We presented and estimated the exact values of the beta critical.

Half-space stationary Kardar–Parisi–Zhang equation beyond the Brownian case

We study the Kardar–Parisi–Zhang (KPZ) equation on the half-line x ⩾ 0 with Neumann type boundary condition. Stationary measures of the KPZ dynamics were characterized in recent work: they depend on two parameters, the boundary parameter u of the dynamics, and the drift −v of the initial condition at infinity. We consider the fluctuations of the height field when the initial condition is given by one of these stationary processes. At large time t, it is natural to rescale parameters as (u, v) = t −1/3(a, b) to study the critical region. In the special case a + b = 0, treated in previous works, the stationary process is simply Brownian. However, these Brownian stationary measures are particularly relevant in the bound phase (a < 0) but not in the unbound phase. For instance, starting from the flat or droplet initial condition, the height field near the boundary converges to the stationary process with a > 0 and b = 0, which is not Brownian. For a + b ⩾ 0, we determine exactly the large time distribution of the height function h(0, t). As an application, we obtain the exact covariance of the height field in a half-line at two times 1 ≪ t 1 ≪ t 2 starting from stationary initial condition, as well as estimates, when starting from droplet initial condition, in the limit t 1/t 2 → 1.

Exact Augmented Perpetual Manifolds Define Specifications for the Steady States of Similar Rigid Body Modes, a Corollary for Nonautonomous Systems

Recently, the perpetual points in mathematics have been defined. In mechanical systems, the perpetual points for linear and some nonlinear systems are associated with rigid body motions and they form the perpetual manifolds. The mechanical systems that admit perpetual manifolds of rigid body motions are called perpetual mechanical systems, and these systems are not limited to linear (with a zero natural frequency) only but also nonlinear systems are considered. The concept of perpetual manifold is extended to the augmented perpetual manifold that is defined in externally forced mechanical systems when all the accelerations are equal but not necessarily zero. A proved theorem defines the external forcing conditions that a mechanical, and also a structural system can have solutions described by the exact augmented perpetual manifolds, which are the rigid body motions. Herein a corollary is proved defining the conditions that the steady states of a mechanical and also a structural system are associated with rigid body motions. The internal forces corresponding to the structural elements of the original system are separated to these forces that are associated with a perpetual mechanical (structural) system and the rest forces, which are associated with boundary structural elements, as external forces are considered. The developed theory is applied in a nonlinear perpetual structural system for the design of four types of boundaries, linear, nonlinear smooth, nonsmooth, and nonlinear generalized forces boundaries, and the numerical results verified the developed theory. This design can be considered as a passive control method for vibration mitigation of mechanical and structural systems, since in the exact augmented perpetual manifolds all the inertia elements move without oscillations and the sum of their internal forces is zero. This work is rather significant in engineering since it can be used for the structural design of systems.

On the nature of planar defects in transition metal diboride line compounds

Planar defect structures appearing in transition metal diboride (TMB2) thin films, grown by different magnetron sputtering-deposition approaches over a wide compositional and elemental range, were systematically investigated. Atomically resolved scanning transmission electron microscopy (STEM) imaging, electron energy loss spectroscopy (EELS) elemental mapping, and first principles calculations have been applied to elucidate the atomic structures of the observed defects. Two distinct types of antiphase boundary (APB) defects reside on the {11¯00} planes. These defects are without (named APB-1) or with (APB-2) local deviation from stoichiometry. APB-2 defects, in turn, appear in different variants. It is found that APB-2 defects are governed by the film's composition, while APB-1 defects are endemic. The characteristic structures, interconnections, and circumstances leading to the formation of these APB-defects, together with their formation energies, are presented.

Boundaries Reduce Disorientation in Virtual Reality

Virtual reality users are susceptible to disorientation, particularly when using locomotion interfaces that lack self-motion cues. Environmental cues, such as boundaries defined by walls or a fence, provide information to help the user remain oriented. This experiment evaluated whether the type of boundary impacts its usefulness for staying oriented. Participants wore a head-mounted display and performed a triangle completion task in virtual reality by traveling two outbound path segments before attempting to point to the path origin. The task was completed with two teleporting interfaces differing in the availability of rotational self-motion cues, and within five virtual environments differing in the availability and type of boundaries. Pointing errors were highest in an open field without environmental cues, and lowest in a classroom with walls and landmarks. Environments with a single square boundary defined by a fence, drop-off, or floor texture discontinuity led to errors in between the open field and the classroom. Performance with the floor texture discontinuity was similar to that with navigational barriers (i.e., fence and drop-off), indicating that an effective barrier need not be a navigational impediment. These results inform spatial cognitive theory about boundary-based navigation and inform application by specifying the types of environmental and self-motion cues that designers of virtual environments should include to reduce disorientation in virtual reality.