External Boundary Research Articles

An efficient dense discs packing method in complex domains for DEM simulations

Efficiently assembling densely packed discs in complex domains remains an unresolved challenge for discrete element simulations. This study develops an efficient dense disc packing method based on the advancing front method (AFM) with closed form version. The new method enables a unified and efficient generation of intricate packings incorporating not just interior boundaries with multiple cavities, but also convex or non-convex external boundaries with complex geometric shapes. Furthermore, the new method can eliminate potential discontinuity encountered in certain DEM assemblies, such as the one-sided lifting problem that arises during discs packing using AFM with open form version. Several examples with complex geometries are presented to showcase the versatility, capability and performance of the proposed method. The proposed approach not only offers an efficient means of generating DEM packings, but also empowers DEM for enhanced simulations with complex geometric boundaries. Specifically, it takes only 70.92 s to generate 675.3 million discs on a 2 GHz laptop.

Mechanistic Modeling of Pollutant Mass Redistribution (Sorption/Desorption) in Heterogeneous Systems Explaining Unexpected Slow Kinetics.

Redistribution of pollutants between different solid phases occurs frequently in field and laboratory settings. Examples include the input of urban particles carrying pollutants into soils or rivers with suspended particles or passive sampling. Since multiple mass transfer mechanisms are involved and natural particles typically are very heterogeneous, modeling of sorption/desorption kinetics is challenging. Here, we present a semi-analytical model formulated in the Laplace domain to simulate pollutant redistribution kinetics in heterogeneous systems. The model accounts for a coupled process governed by intraparticle and external boundary layer diffusion, and it considers the heterogeneity of various sorbents (e.g., geometric shape, size, sorption capacity coefficient, and solid and porous particles). The model is validated against data of two batch experiments: (i) the redistribution of phenanthrene in spherical polyethylene particles of different sizes and (ii) redistribution of anthracene-d10 and phenanthrene in a heterogeneous sediment suspension with polyethylene passive samplers. It allows to explain the temporary overshooting of concentrations in the aqueous phase due to different kinetic controls of various particles involved (fast desorption vs. slow sorption) as well as initial fast kinetics followed by surprising long tailing in batch experiments. The approach is very flexible and can be used for many different scenarios.

Microfluidic Bubble-Templating Multinozzle 3D Printing for Preparations of Macroporous Hydrogels with Ordered Pores of Large Size Ranges.

A strategy for fabrication of macroporous hydrogels through 3D printing assisted by molding and multiple microfluidic bubble-templating nozzles is proposed here. This approach aims to address the challenges faced by methods for 3D printing macroporous hydrogels, such as difficulties in precisely controlling the spatial distribution of macropores, limited porosity, and low resolution of external boundaries due to the poor mechanical properties of hydrogel solutions as printing ink. In this method, fast-switching microfluidic bubble-templating nozzles of varying sizes allowed for precise control of target pore sizes over a wide range. Cavities of polydimethylsiloxane (PDMS) molds were used to define the overall external shape of the hydrogels and enhance the resolution of the boundaries. During the printing process, the laminar shear force generated by a coaxial microfluidic system generated microbubbles which were then injected into the PDMS mold cavities. The spatial distribution of the microbubble clusters within the cavities was controlled by a 3D motion module. Finally, macroporous hydrogels with a pore size range of 238-930 μm were fabricated while avoiding millimeter round corners on the boundaries. A control precision of pore sizes was about 60 μm. Most importantly, this strategy broke through the space occupancy limitations of pores in traditional 3D printing methods for macroporous hydrogels. The space occupancy of pores could reach a maximum of about 87% within a single layer.

Thoracoscopic anatomical lesion resection by fluorescence imaging on congenital lung malformation

TechniqueThoracoscopic anatomical lesion resection (TALR) is characteristic of removal of the lesion and preservation of all normal lung in treating congenital lung malformation(CLM). However, to conduct TALR is technically demanding for a beginner. To make the procedure easier to understand, the details for TALR are demonstrated in this report. TALR technique for CLM consisted of eight steps: step 0, ICG inhalation; step 1, mark the external lesion border; step 2, dissociate of the trunk of pulmonary vain; step 3, dissociate the pulmonary vain plane; step 4, split the parenchyma; step 5, dissect the tubular structures running into the lesion; step 6, remove the lesion; step 7, seal the wound, flush the thoracic cavity with normal saline, reinflate the lung to make sure there is no large air leak, then place 16 F chest tube. ResultsThe external lesion boundary is delineated via flurorescence imaging with inhaled indocyanine green (the normal lung displays flurorescent green while the lesion hardly shows green). TALR procedure are able to split the lung along the external border combined with the internal lesion border (pulmonary vain plane), during the process, all the tubular structure including vessels and bronchi running into the lesion can be separately sealed and divided. Thereafter, complete resection of the lesion and preservation of all normal lung can be achieved. ConclusionsTALR procedure is characteristic of dissection of the lesion along its borders, sealing and dividing the aberrant tubular structures, then the lesion can be exclusively removed and all the normal lung preserved, which may be considered as a preferable method in treating congenital lung malformation.

An experimental investigation of boundary layer over permeable interfaces in Hele-Shaw micromodels

This study experimentally investigates boundary layer development over permeable interfaces using Hele-Shaw micromodels and high-resolution micro-particle image velocimetry (micro-PIV). Velocity vectors, captured at a 5 μm scale, reveal the flow behavior at the interface between free-flow and porous media with ordered structures and porosities ranging from 50% to 85%. The results show that the boundary layer streamline alignment decreases with increasing porosity, while lower permeability fosters more uniform and parallel flow near the interface. Flow channeling occurs along paths of the least resistance, with more flow directed through the Hele-Shaw free-flow region as the solid fraction of the porous material increases. The Reynolds number (0.14–0.94), based on the Hele-Shaw hydraulic diameter, has a minimal effect on the normalized velocity distribution. Furthermore, an analytical solution for the external boundary layer thickness exhibited good agreement with experimental data, confirming a thickness of 2–4 times the square root of the free-flow Hele-Shaw permeability. Additionally, a Q-criterion analysis identified, for the first time, distinct zones within the external boundary layer, capturing the balance between rotational and deformation components as a function of permeability. These findings offer insight into flow dynamics in porous media systems, with implications for both natural and industrial applications, and contribute to the improved modeling of fluid dynamics and momentum transport in coupled free-flow and porous media environments.

The logic of monsters: development and morphological diversity in stem-cell-based embryo models.

Organoids and stem-cell-based embryo models (SEMs) are imperfect organ or embryo representations that explore a much larger space of possible forms, or morphospace, compared to their in vivo counterparts. Here, we discuss SEM biology in light of seminal work by Pere Alberch, a leading figure in early evo-devo, interpreting SEMs as developmental 'monstrosities' in the Alberchian sense. Alberch suggested that ordered patterns in aberrant development-i.e. 'the logic of monsters'-reveal developmental constraints on possible morphologies. In the same vein, we detail how SEMs have begun to shed light on structural features of normal development, such as developmental variability, the relative importance of internal versus external constraints, boundary conditions and design principles governing robustness and canalization. We argue that SEMs represent a powerful experimental tool to explore and expand developmental morphospace and propose that the 'monstrosity' of SEMs can be leveraged to uncover the 'hidden' rules and developmental constraints that robustly shape and pattern the embryo.

SPFDNet: Water Extraction Method Based on Spatial Partition and Feature Decoupling

Extracting water information from remote-sensing images is of great research significance for applications such as water resource protection and flood monitoring. Current water extraction methods aggregated richer multi-level features to enhance the output results. In fact, there is a difference in the requirements for the water body and the water boundary. Indiscriminate multi-feature fusion can lead to perturbation and competition of information between these two types of features during the optimization. Consequently, models cannot accurately locate the internal vacancies within the water body with the external boundary. Therefore, this paper proposes a water feature extraction network with spatial partitioning and feature decoupling. To ensure that the water features are extracted with deep semantic features and stable spatial information before decoupling, we first design a chunked multi-scale feature aggregation module (CMFAM) to construct a context path for obtaining deep semantic information. Then, an information interaction module (IIM) is designed to exchange information between two spatial paths with two fixed resolution intervals and the two paths through. During decoding, a feature decoupling module (FDM) is developed to utilize internal flow prediction to acquire the main body features, and erasing techniques are employed to obtain boundary features. Therefore, the deep features of the water body and the detailed boundary information are supplemented, strengthening the decoupled body and boundary features. Furthermore, the integrated expansion recoupling module (IERM) module is designed for the recoupling stage. The IERM expands the water body and boundary features using expansion and adaptively compensates the transition region between the water body and boundary through information guidance. Finally, multi-level constraints are combined to realize the supervision of the decoupled features. Thus, the water body and boundaries can be extracted more accurately. A comparative validation analysis is conducted on the public datasets, including the gaofen image dataset (GID) and the gaofen2020 challenge dataset (GF2020). By comparing with seven SOTAs, the results show that the proposed method achieves the best results, with IOUs of 91.22 and 78.93, especially in the localization of water bodies and boundaries. By applying the proposed method in different scenarios, the results show the stable capability of the proposed method for extracting water with various shapes and areas.

Numerical Solution of External Boundary Conditions Inverse Multilayer Diffusion Problems

The present study is concerned with the numerical solution of external boundary conditions in inverse problems for one-dimensional multilayer diffusion, using the difference method. First, we formulate multispecies parabolic problems with three types of Dirichlet–Neumann–Robin internal boundary conditions that apply at the interfaces between adjacent layers. Then, using the symmetry of the diffusion operator, we prove the well-posedness of the direct (forward) problem in which the coefficients, the right-hand side, and the initial and boundary conditions are given. In inverse problems, instead of external boundary conditions of the first and the last layers, point observations of the solution within the entire domain are posed. Rothe’s semi-discretization of differential problems combined with a symmetric exponential finite difference solution for elliptic problems on each time layer is proposed to develop an efficient semi-analytical approach. Next, using special solution decomposition techniques, we numerically solve the inverse problems for the identification of external boundary conditions. Numerical test examples are discussed.

The longer arc of channel recovery post-dam removal

Dam removals are opportunistic experiments to address fundamental questions about river recovery to disturbance. Previous studies have shown that gravel-bedded rivers are resilient with covariate adjustments to channel dimensions occurring rapidly in the wake of disturbance. Yet, beyond the cross section, at the reach or watershed-scale, adjustment appears to take much longer. Understanding of the longer arc of reach and watershed recovery is limited by the relatively few dam removals studies that include long-term monitoring. Here, we present results from a five-year dam removal study punctuated by an extreme flood and show that the initial, rapid response of a channel is driven by the prevailing hydrology whereas longer-term adjustments to morphology at the reach scale are driven by external forces imposed on the channel. We summarize these results by classifying various channel features as either ‘intrinsic channel properties’ that are rapidly adjustable by the prevailing hydrology or ‘extrinsic channel properties’ that respond over various time scales to external boundary conditions imposed on the channel by climate, vegetation, geology, and valley dimensions (extrinsic controls). We show that this framework applies to channel recovery beyond the former reservoir and thus may prove applicable to channel disturbances beyond dam removal, such as extreme floods.

Strategic Change and Firms’ Optimal Distinctiveness: The Moderating Effect of Analyst Coverage

AbstractDrawing from optimal distinctiveness research, we explore the effect of strategic change on corporate social responsibility (CSR) activities in the context of CSR conformity and CSR differentiation. Additionally, we examine whether analyst coverage as a key external boundary condition can influence the magnitude of such an effect. Analysing an unbalanced panel of 2145 firm‐year observations with 422 firms over the period 2004–2013, we found support for our predictions that while strategic change negatively and significantly affects CSR conformity, it positively and significantly impacts CSR differentiation. Additionally, our results show that analyst coverage strengthens the relationship between strategic change CSR conformity and CSR differentiation. Our findings expand the optimal distinctiveness, strategic change, and analyst coverage literature and provide insights into the complex and multifaceted aspects of CSR activities. Finally, this study's findings can equip strategic leaders and investors with knowledge as they face complex decision‐making in their firms and investments.

Robust Edge Flows in Swarming Bacterial Colonies

Understanding if and how the chirality of biomolecules is transferred across scales into larger components and active processes remains elusive. For instance, flagellated bacteria swim in helical trajectories but chirality seems absent from the active turbulence dynamics they display in dense suspensions. We address this question by examining multiscale dynamics in colonies. We find active turbulence without manifest chirality in the bulk, but wide, clockwise (viewed from the air side) circulation all along the tortuous centimeter-scale external boundary, while similar but counterclockwise flows follow internal boundaries. We trace the origin of these robust edge flows to an unexpected asymmetry at the individual level that is amplified by local interactions. We rationalize our findings with a model of noisy self-propelled particles immersed in a Stokes fluid that accounts faithfully for our observations. Our modeling and experimental efforts reveal that local nematic alignment and hydrodynamic interactions amplify the weak chiral bias in individual motion, promoting the formation of strong edge flows. The likely topological protection of these flows provides robust transport mechanism over large scales. Such robust boundary phenomena in weakly chiral active fluids may inspire new control strategies for active and biological matter. Published by the American Physical Society 2024

Analysis of Production Decline Type Curves Considering Water Influx in Naturally Fractured Gas Reservoirs

Abstract In the development of fractured gas reservoirs with edge and bottom water, water invasion is a pervasive issue. However, most production decline analysis models focus on primary depletion with closed boundaries rather than secondary depletion with water influx. Therefore, this paper aims to develop decline type curves for analyzing and interpreting production data from existing natural water influx in fractured gas reservoirs. Firstly, a transient dual porosity flow model is developed considering water influx in naturally fractured gas reservoirs, the functions of Blasingame decline type curves are derived and obtained. Subsequently, the Blasingame production decline type curves of a vertical well in naturally fractured reservoirs experiencing natural water influx are plotted. These new type curves can estimate water invasion and dual medium parameters, offering valuable insights for production decline analysis in fractured reservoirs with water influx. The Blasingame production decline curves are divided into six regimes based on characteristics. Then, the effects of various formation parameters and water invasion cases on the type curves are discussed and analyzed. Compared with Blasingame type curves without water influx at the external boundary, the behaviors of those presented in this paper are quite different at the boundary responses. Finally, through the analysis of a case well, it is found that theoretical type curves considering dual-medium and water invasion are more consistent with actual production data. This suggests that these new type curves provide more accurate estimation for understanding and managing issues related to water invasion in fractured gas reservoirs.

Topological slow light and rainbow trapping of surface wave in valley photonic crystal bounded by air

Abstract Topological slow light and rainbow trapping tend to rely on large-scale interface structure in previous research work, which have restricted further miniaturization. In this work, we propose a method to realize slow light and rainbow trapping at the zigzag edge of a single valley photonic crystals (VPCs) bounded by air, which is very different from previous studies where rainbow trapping is supported at the interface separating two VPCs with inversion symmetry. By constructing the VPC–air boundaries and VPC–VPC interfaces experimentally, we have observed the topologically protected rainbow trapping simultaneously at the external and internal boundary. This work provides a feasible platform for the miniaturized optical communication devices such as optical buffers, optical storage and optical routing.

Струйный эффект при возникновении присоединенной каверны от системы импульсивных давлений

We consider the plane problem of the emergence of an attached cavity caused by the sudden action of impulsive pressures at some initial time. It is assumed that these pressures are distributed on the upper part of the boundary of a stationary circular cylinder immersed in liquid. A problem with unilateral constraints is formulated, on the basis of which the flow of liquid at the initial moment of time and the initial zone of separation of liquid particles are determined. At the next moments of time, an attached cavity is formed, the shape of which is determined based on the solution of the dynamic initial-boundary value problem of the theory of potential flows of an ideal incompressible fluid with free boundaries. The main unknowns in it are the velocity potential, the shape of the cavity, the dynamics of the separation points, and the perturbation of the external free boundary of the liquid. It is required to study the posed problem at short times, focusing on the behavior of the internal free boundary of the liquid near the separation points. When studying this problem, pressure in the cavern, which is created artificially, plays an important role. At low pressures, the internal free boundary of the liquid near the separation point is located on opposite sides of this point. In this case, the end part of the cavity resembles a stream of gas directed along the boundary of the cylinder towards the liquid.

An Experimental Derivation of Transient Nonuniform External Boundary Conditions for the Solidification Process Modeling of Equiaxed Investment Castings

An Experimental Derivation of Transient Nonuniform External Boundary Conditions for the Solidification Process Modeling of Equiaxed Investment Castings

Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco) derived from mineralogical and geochemical analysis of mudrocks

A model of the Cenozoic tectono-sedimentary evolution of the External Rif Chain (Morocco) is provided by means of the study of the mineralogical and geochemical composition of mudrocks. To date there was a lack of homogeneous data and of a complete and extensive study of the whole External Rif Zone (ERZ). Therefore, this work shows the study of the whole ERZ where the most representative stratigraphic sections have been selected. This work provides important information about the geodynamic evolution and the variations in source-area provenance related to the growing of the Rif orogenic belt. Although there is still much work to be done, this study aims to improve the knowledge of the Cenozoic tectono-sedimentary evolution of the entire western ERZ with a homogeneous method, with a focus on the paleogeographic and paleotectonic evolution, the paleoweathering and the source areas deduced from mineralogical and geochemical data of the Cenozoic mudrocks. The bulk mineralogy is mainly characterized by the presence of calcite, quartz and dolomite plus ankerite. Feldspars have few percentages. The clay minerals are principally represented by mixed-layer illite/smectite (I/S). Illite and kaolinite are in little amount. Femic minerals, mixed-layer chlorite/smectite (C/S) and chlorite are the most abundant. The I/S features suggest a different thermal condition for the three domains. The chemical composition indicates that the mudrocks can be described as mixtures of carbonates with aluminosilicate components. The Al/Ti, Th/Cr, Th/Sc, La/Th and La/Sc ratios, the Cr/V vs. Y/Ni plot, the V-Ni-Th∗10 and La-Th-Sc ternary diagrams indicate a predominantly felsic source with a minor mafic input more evident in the Paleocene-Eocene samples of the External Intrarif and Mesorif. The External Rif Zones changed in the Cenozoic from a passive margin to a complex foreland system with the incoming of the Alpine tectonic phases. In general, the felsic contribution should be linked to the foreland area consisting in the Middle Atlas and Mesetas massifs made of a crystalline domain. This margin probably presented an intermediate narrow oceanic branch in the External Intrarif-Mesorif boundary that surprisingly should start to close during Paleogene times providing the mafic contribution. This Paleogene tectonic activity in these domains is corroborated by the thermal maturity indicating late diagenesis. The chemical weathering indices, such as the CIA (Chemical index of Alteration) and its modifications, show medium-high values and thus suggest generally moderate paleoweathering conditions in agreement with the predominant amount of I/S.

Neoclassical realism(s) vis-à-vis other theories of foreign policy: taking the indistinguishability problem seriously

Neoclassical realism (NCR)’s opponents have considered it an incoherent and indistinctive approach because of its interest in addressing ideational and institutional factors. Specifically, they have denounced NCR’s fuzzily established internal and external conceptual boundaries, corresponding to central dimensions of this approach’s ‘indistinguishability’ problem. Even though NCR has responded in a sophisticated manner to its critics, such a response still falls short of advancing some subtle strategies to forge NCR’s theoretical identity and research design. To fill this gap, I distinguish several neoclassical realist theories (Types I, II, IIA, IIB and III) to clarify NCR works’ common ground and the several options available to the analyst to cope with the indistinguishability problem’s internal dimension. Furthermore, I compare neoclassical realist theories with organizational, bureaucratic, realist, liberal and constructivist approaches to foreign policy to discuss the indistinguishability problem’s external dimension. Dealing with this dimension entails acknowledging that neoclassical realist theories provide a top-down, as compared to a bottom-up approach to explain foreign policy as a policy rather than a process. It also provides a thorough explanation rather than a parsimonious account aimed at distinguishing independent and intervening variables. With different intensities, neoclassical realist theories embrace specific, refined logics of consequentialism rather than appropriateness to explain distinct state preferences rather than assuming power maximization or security seeking as pre-fixed state goals.

Reported impact and protective factors of the care partner role during persistent critical illness: a content analysis

BackgroundPatients with persistent critical illness experience prolonged multi-system morbidity, functional impairments, and chronic conditions. As a result, these patients have prolonged intensive care unit admissions. If discharged, they return home with long-term medical dependencies. Care partners take on a variety of physical, mental health, cognitive, and social roles to support the provision of care for these patients. There is limited evidence, however, of the impact of being a care partner for this patient population during hospitalization.MethodsA qualitative descriptive study was conducted to explore the impact care provision on care partners for patients experiencing persistent critical illness. Patients who have or have had persistent critical illness and care partners were recruited from two inpatient units in a single community academic hospital in Toronto, Canada to participate in semi-structured interviews. Data was analyzed using a team-based inductive content analysis.ResultsSeven (43.8%) participants were patient survivors, and nine (56.3%) were care partners. Patients and care partners reported physical, socio-emotional, and social stress as impacts of care provision during persistent critical illness hospitalization. Care partners identified several protective strategies that they used to mitigate the impacts of care provision on them such as seeking external mental health support and boundary setting. Features of formalized and care partner programs were also identified and suggest that these programs can be protective of care partner values, mitigate feelings of helplessness and stress, and may improve relationships between the family members who are in the care partner role and the healthcare team.ConclusionsThis study identified physical, socio-emotional, and social stress related impacts of care provision on care partners of patients with persistent critical illness during hospitalization. Additionally, this study identified protective factors initiated by care partners to mitigate the reported stresses of the role, as well as protective features of a care partner program. The results provide a better understanding supportive features of care partner programs that are specific to the experiences and needs of persistent critical illness and add to the growing body of evidence about how to provide equitable access to care during and post hospitalization.

An analytical solution model of oil–water dynamic imbibition considering dynamic contact angle effect and osmotic pressure at micro-nano scale

Spontaneous imbibition is one of the important mechanisms to enhance oil recovery during hydraulic fracturing process of shale reservoirs. The dynamic contact angle effect in imbibition kinetics of liquid–liquid system is complicated due to the large number of micro-nano pores in shale reservoir. Moreover, the content of clay minerals is high, the chemical osmosis effect is significant, and the impact of osmotic pressure on imbibition is not clear. In order to clarify the dynamic contact angle effect in imbibition kinetics and correctly understand the role of osmotic pressure in imbibition process. In this paper, based on the molecular kinetic theory (MKT), the dynamic contact angle effect is successfully coupled with imbibition kinetic equation, and a capillary pressure equation is developed. On the basis, considering the effects of osmotic pressure, external displacement pressure and boundary layer effect on imbibition, An analytical solution model of oil–water dynamic imbibition model is developed. The results shows that under the respective effects of capillary pressure and osmotic pressure, the imbibition velocity initially stabilizes before increasing over time; under the action of displacement pressure, the imbibition velocity increases with time. Imbibition velocity is directly proportional to interfacial tension and capillary radius, but inversely proportional to contact angle and oil viscosity. With the salt concentration difference increasing from 80 mol/m3 to 4710 mol/m3, the imbibition velocity increased by about 54 times. Compared with the membrane efficiency of 30 % and 5 %, the imbibition velocity is increased by 4.95 times. In this work, the dynamic contact angle effect in the imbibition kinetics of liquid–liquid system was accurately characterized, clarified the action mechanism of osmotic pressure, and provided theoretical support for enhancing oil recovery of shale reservoirs.

Tacit knowledge sharing in a Lebanese family business: the influence of organizational structure and tie strength

PurposeThis study explores the influence of organizational structure on relationship formation and tacit knowledge sharing within a family business context.Design/methodology/approachUtilizing a single case study approach, data were collected through interviews and questionnaires from 12 participants at a family-owned advertising and communication firm in Beirut, Lebanon.FindingsThe research highlights the critical role of organizational structure in enhancing organizational effectiveness through knowledge transfer. It underscores how both intraorganizational and interorganizational ties influence knowledge sharing processes and demonstrates the varying impacts of tie strength on tacit knowledge distribution.Originality/valueThis paper contributes to the literature by examining the interdependence between organizational structure, tacit knowledge transfer and tie strength in family businesses. By analyzing these elements across internal and external boundaries, the study offers a fresh perspective on network dynamics. The research highlights that traditional definitions of network ties may not fully capture the unique environment of family firms, where structural nuances impact knowledge sharing and performance. Practically, the findings provide actionable insights for managers to design organizational structures that optimize tacit knowledge flow, fostering innovation and competitiveness. This work challenges existing frameworks and offers guidance for improving knowledge management in family businesses, supporting sustainable growth and success.