Incremental Forms Research Articles

Trajectories of agricultural modernization and rural resilience: some first insights derived from case studies in 14 countries

In this paper, alternative trajectories of agricultural modernization and rural resilience are explored based on case studies in 14 countries. The analysis is to support discussions about the further development of agriculture at a time when the agricultural sector must respond to an increasing scarcity of natural resources, challenges like climate change, urbanization, demographic change, food security, consumer demands, distributional issues in food value chains and changing urban-rural relations. The discussion relates different trajectories of agricultural modernization to the multiple mechanisms underlying rural prosperity and resilience. The mainstream capital-intensive and technology-driven model of agricultural modernization is contrasted with more incremental, socially embedded and localised forms of development. Potential synergies between different modes of farm ‘modernization’, resilience and sustainable rural development are highlighted and a different future-oriented understanding of the term ‘modernization’ explored. The basis for the analysis are case studies in 14 countries (including Turkey and Israel). The key question asked is how actors are connecting economic, social and natural systems in the different cases and how the connections made (or not) point to different ideas about modernization. The conclusions focus on some current information needs of policy-makers: the links between different forms of farm modernization, rural development and resilience, and the implications for agricultural knowledge systems and the new European Innovation Partnerships. It is emphasized that local capacities for transdisciplinary research need to be strengthened and that more attention should be paid to addressing modernization potentials that are less mainstream. The paper seeks to foster discussions that help overcome simplistic viewpoints of what ‘modernization’ entails. It is based on an earlier review paper by Knickel, Zemeckis and Tisenkopfs (2014).

Nonexistence and non-decoupling of the dissipative potential for geo-materials

Two fundamental issues exist in the damage theory of geo-material based on the concept of thermodynamics: existence or nonexistence of the dissipation potential, and whether the dissipation potential could be decoupled into a damage potential and a plastic one or not. Thermodynamics theory of elastoplastic damage assumes the existence of dissipation potential, but the presence of dissipation potential is conditional. Based on the dissipation inequality in accord with the second law of thermodynamics, the sufficient and necessary conditions are given for the existence of the dissipation potential separately in total and incremental forms firstly, and proved strictly in theory. With taking advantage of the basic mechanical properties of geo-materials, the nonexistence of the dissipative potential is verified. The sufficient and necessary conditions are also given and proved for the decoupling of the dissipation potential of geo-materials in total and incremental forms. Similarly, the non-decoupling of the dissipation potential has also been proved, which indicates the dissipation potential of geo-materials in total or incremental forms could not be decoupled into a dissipative potential for plasticity and that for damage respectively. The research results for the fundamental issues in the thermodynamics theory of damage will help establish and improve the theoretic basis of elastoplastic damage constitutive model for geo-materials.

Nonexistence and non-decoupling of the dissipative potential for geo-materials

Two fundamental issues exist in the damage theory of geo-material based on the concept of thermodynamics: existence or nonexistence of the dissipation potential, and whether the dissipation potential could be decoupled into a damage potential and a plastic one or not. Thermodynamics theory of elastoplastic damage assumes the existence of dissipation potential, but the presence of dissipation potential is conditional. Based on the dissipation inequality in accord with the second law of thermodynamics, the sufficient and necessary conditions are given for the existence of the dissipation potential separately in total and incremental forms firstly, and proved strictly in theory. With taking advantage of the basic mechanical properties of geo-materials, the nonexistence of the dissipative potential is verified. The sufficient and necessary conditions are also given and proved for the decoupling of the dissipation potential of geo-materials in total and incremental forms. Similarly, the non-decoupling of the dissipation potential has also been proved, which indicates the dissipation potential of geo-materials in total or incremental forms could not be decoupled into a dissipative potential for plasticity and that for damage respectively. The research results for the fundamental issues in the thermodynamics theory of damage will help establish and improve the theoretic basis of elastoplastic damage constitutive model for geo-materials.

Relative performance of two unsaturated soil models using different constitutive variables

Mechanical and water retention behaviour of unsaturated soils is investigated in the context of two well established coupled constitutive models, each of which is formulated in terms of a different set of stress state variables or constitutive variables. Incremental relationships describing the volume change and variation of the degree of saturation are derived for each model. These incremental relationships are used to simulate a set of experimental tests on compacted Speswhite kaolin previously reported in the literature. Six individual tests, involving isotropic compression and various forms of shearing, are analyzed in the context of the incremental forms developed, and the model predictions are then compared against experimental results. The results show that, although each constitutive model uses a different set of constitutive variables and a different scheme for coupling mechanical and water retention behaviour, the two sets of model predictions are similar and both sets provide a reasonable match to the experimental results, suggesting that both models are able to capture the relevant features of unsaturated soil behaviour, despite expressing the constitutive laws in different ways.

The barriers and consequences of radical innovations: Introduction to the issue

This article introduces the special issue on barriers and consequences of radical innovation (RI). Radical innovation, as distinct from more incremental forms of innovation, is increasingly important for organizations and national economies. However, firms face many challenges and barriers (both internal and external) which hinder their RI efforts, and result in significantly higher failure rates for RIs as compared with other forms of innovation. Individually and collectively, the twelve cross-disciplinary articles in this special issue provide a number of important contributions to the extant knowledge base. While most of the contributions focus on barriers, with a concomitant emphasis on enablers, some insights are also offered into the lesser examined area of consequences, particularly the unintended consequences of RI. The editorial concludes by summarizing key issues and presenting provocations for further research.

Optimization of Incremental Sheet Metal Forming Parameters by Design of Experiments

The purpose of the paper is to investigate the dependency of various parameters on metal forming process using mathematical models. The incremental sheet metal forming process was studied using Box–Behnken design of experiments along with response from surface methodology analysis. In the study process factors namely feed rate, speed and coolant were analysed to understand the effect on the surface roughness, percentage (%) of thickness reduction, grain size and hardness of the Aluminium (Al) sheet metal, were examined after forming. The surface model analysis predicts that all four responses of the incremental forms show very strong correlation with the experimental results. The optimized process of incremental forming that runs on maintained levels of predicted factors, yield responses very close to that predicted from the model.

CTDAE & CTODE models and their applications to power system stability analysis with time delays

In this paper, two new models suitable for power system stability analysis with considering time delays are derived. They are constraint time-delayed ordinary differential equation model (CTODE model) and constraint time-delayed differential algebraic equation model (CTDAE model). In these two models, dimension of the time-delayed equation is significantly reduced so as to speed up the calculation efficiency. Detail derivations to their nonlinear and incremental linear forms are given. And, some of their good features are discussed. Finally, a typical time-delayed system and single-machine-infinite-bus system are selected to validate the new models through Lyapunov-Krasovskii criterion and eigenvalue locus tracing procedure. It reveals that some unnecessary calculations in the algorithm can be avoided to achieve higher efficiency based on new models. The new models and new criterion given in this paper are helpful to design wide area protectors for bulk power systems.

A Drying Cake Method for Measuring Suction-Stress Characteristic Curve, Soil–Water-Retention Curve, and Hydraulic Conductivity Function

Abstract A drying cake (DC) method is invented for measurement of the suction-stress characteristic curve (SSCC), the soil–water-retention curve (SWRC), and the hydraulic conductivity function (HCF) of soils under drying conditions. The DC method employs particle image velocimetry (PIV) technique to acquire digital still images of the radial displacement field of a disk-shaped soil specimen during drying, while the moisture content of the specimen is recorded using an electronic balance. A linear elasticity theory employing the suction-stress-based effective stress in both total and incremental forms is developed to calculate suction stress, suction, and hydraulic conductivity from the moisture-content-dependent displacement fields; thus permitting definition of the SSCC, SWRC, and HCF of a soil. Five different soils, representing a wide spectrum of soil variety from pure sand, to silt and organic silt, to non-swelling and swelling clays are used to illustrate and test the principle and theory, the validity, and applicability of the DC method. Established measurement techniques for the constitutive relationships of unsaturated soils, such as the Tempe cell, constant flow, transient water release and imbibition, and shear-strength relationships were used to validate the DC method. The results from the DC method were found to compare well with those techniques. Repeated DC tests confirm that the results from the test are unique. It is shown that the DC method is superior to other existing methods in: (1) providing simple and accurate data acquisition (involving taking sequential digital still images and monitoring specimen’s moisture content by an electronic balance without use of suction or moisture probe), (2) facilitating fast testing time (in less than one week for the primary drying path of the SSCC, SWRC, and HCF), (3) permitting concurrent measurement of the SSCC, SWRC, and HCF by using one soil sample, and (4) its applicability to all types of soils under wide suction and moisture-content conditions.

Using modified state surface approach to select parameter values in the Barcelona basic model

SUMMARYThe Barcelona basic model (BBM) successfully explained many key features of unsaturated soils and received extensive acceptance. It is also one of the few elastoplastic constitutive models for unsaturated soils that have been implemented within finite element codes and applied to the analysis of real boundary value problems. The BBM was proposed in incremental forms according to theories of soil plasticity in which individual aspects of the isotropic virgin behavior are controlled by multiple parameters, whereas at the same time, a single parameter controls more than one aspect of soil behavior. Although a variety of methods have been recently developed for calibrating model parameters for elastoplastic soil models, at present, there are no well‐established, simple, and objective methods for selecting parameter values in the BBM from laboratory tests. This has been one of the major obstacles to the dissemination of this constitutive model beyond the research context.This article presents an optimization approach especially developed for simple and objective identification of material parameters in the BBM. This is achieved by combining a modified state surface approach, recently proposed to model the elastoplastic behavior of unsaturated soils under isotropic stress conditions, with the Newton or quasi‐Newton method to simultaneously determine the five parameters governing isotropic virgin behavior in the BBM. The comparison between results using the proposed method and an existing method for the same laboratory tests was discussed from which the simplicity and objectivity of the proposed method were evaluated. Copyright © 2012 John Wiley & Sons, Ltd.

Electroelastic waves in a finitely deformed electroactive material

In this paper, the coupling between a finite deformation and an electric field is examined with particular reference to the propagation of small amplitude waves in a non-linear electroelastic material based on the quasi-electrostatic approximation. The general equations governing the linearized response of electroelastic solids superimposed on a state of finite deformation in the presence of an electric field are derived along with incremental forms of the electroelastic constitutive laws and boundary conditions. Both unconstrained and incompressible materials are considered. Without restriction on the electroelastic constitutive law, the theory is first applied to the analysis of plane waves propagating in a homogeneously deformed material with an underlying uniform electric field and illustrated in the case of an isotropic material. The general equations governing 2D incremental motions are then derived and applied to the study of surface waves in a homogeneously deformed half-space of incompressible isotropic material with the electric field normal to the surface of the half-space. The dependence of the wave speed on the deformation, the electric field and the electromechanical coupling parameters is illustrated for a prototype electroelastic constitutive law.

Efficient numerical implementation of pressure, time, and temperature superposition for elasto‐visco‐plastic material model by using a symbolic approach

AbstractThis article is concerned with the finite element implementation of an elasto‐visco‐plastic constitutive model using a symbolic approach. The model combines the Knauss–Emri (KE) pressure, temperature, and time superposition principle in the implicit finite element scheme. The equation development and code generation was performed using the symbolic tool AceGen. The same symbolic system was applied to derive analytical sensitivities of the numerical model with respect to the material and shape parameters. To enable efficient numerical implementation of the KE model the convolution integrals were transformed into their respective incremental forms, so that radical improvements of code efficiency and computer storage requirements were achieved. The numerical examples derived for polyethylene terephthalate (PET) polymers demonstrate that symbolic systems can be applied to develop complex constitutive models capable of simulating material responses that are in good agreement with experimental measurements over a wide range of strain rates, temperatures, and loading conditions. Copyright © 2010 John Wiley & Sons, Ltd.

Developer Collaboration in Urban Land Development: Partnership Working in Paddington, London

Urban development companies are described as ‘profit maximisers' and ‘risk minimisers' in their approach to development. This frequently manifests into a discrete or site-focused mindset where outcomes such as high plot-coverage ratios, inward-looking developments, and homogenous land uses are prioritised. Incremental forms of development often result which overlook the potential for higher profits through cooperation and the opportunity to redevelop urban areas more creatively on a greater scale. Although large-scale development projects have attracted critical interest during recent decades, research has tended to assess the achievements of single landowning organisations or consortiums. This downplays the tendency for development sites to be clustered and the importance of investigating the factors which encourage and/or discourage nearby developers from collaborating. Drawing on empirical research, the author focuses on the case of Paddington on the western fringe of central London. Interview material reveals how a multisite developer partnership was established, strengthened over time, and adopted various regeneration initiatives. Critical insights describe how area collaboration was shaped by the complexities facing individual development sites and contradictory local authority attitudes. Conclusions are drawn about area master planning and future urban development research.

Convergence properties of the primal and dual forms of variational data assimilation

AbstractThe variational data assimilation problem can be solved in either its primal (3D/4D‐Var) or dual (3D/4D‐PSAS) form. The methods are equivalent at convergence but the dual method exhibits a spurious behaviour at the beginning of the minimization which leads to less probable states than the background state. This is a serious concern when using the dual method in operational implementations when only a finite number of iterations can be afforded. Two classes of minimization algorithms are examined in this article: the conjugate gradient (CG) and the minimum residual (MINRES) methods. While the CG algorithms ensure a monotonic reduction of the cost function, those based on the MINRES enforce instead a monotonic decrease of the norm of the gradient. In this article, it is shown that when applied to the minimization of the dual problem, the MINRES algorithms also lead to iterates for which their ‘image’ in physical space leads to a monotonic decrease of the primal cost function. A relationship is established showing that the primal objective function is related to the value of the dual cost function and the norm of its gradient. This holds for the incremental forms of both the three‐ and four‐dimensional cases. A new convergence criterion is introduced based on the error norm in model space to make sure that, for the dual problem, the same accuracy is obtained in the analysis when only a finite number of iterations is completed. Copyright © 2010 Royal Meteorological Society

Nonlinear micromechanical formulation of the high fidelity generalized method of cells

The recent High Fidelity Generalized Method of Cells (HFGMC) micromechnical modeling framework of multiphase composites is formulated in a new form which facilitates its computational efficiency that allows an effective multiscale material–structural analysis. Towards this goal, incremental and total formulations of the governing equations are derived. A new stress update computational method is established to solve for the nonlinear material constituents along with the micromechanical equations. The method is well-suited for multiaxial finite increments of applied average stress or strain fields. Explicit matrix form of the HFGMC model is presented which allows an immediate and convenient computer implementation of the offered method. In particular, the offered derivations provide for the residual field vector (error) in its incremental and total forms along with an explicit expression for the Jacobian matrix. This enables the efficient iterative computational implementation of the HFGMC as a stand alone. Furthermore, the new formulation of the HFGMC is used to generate a nested local-global nonlinear finite element analysis of composite materials and structures. Applications are presented to demonstrate the efficiency of the proposed approach. These include the behavior of multiphase composites with nonlinearly elastic, elastoplastic and viscoplastic constituents.

TreeHuggerTV: Re-Visualizing Environmental Activism in the Post-Network Era

As a collection of online videos that explores how to create, consume, and live in environmentally responsible ways, TreeHuggerTV offers a productive site for examining environmental activism at the intersection of nature and culture. This paper looks at TreeHuggerTV as a form of environmental activism that emerges on post-network television. This analysis traces how TreeHuggerTV productively re-visualizes the environment, environmentalists, and environmentalism. In the online videos, the environment appears in the urban landscapes where people live, environmentalists are shown as “hip, not hippie,” and environmentalism is manifested in the form of green consumerism. Despite the limitations of consumer-driven forms of environmentalism, the author examines the potential of this environmental activism that embraces human culture in relation to the environment. While promoting green consumption may fail to push viewers beyond individual and incremental forms of activism, TreeHuggerTV creates an accessible entrance into environmentalism for viewers in a commercial medium. The fragmented viewing audience of this post-network form of television further indicates that this consumer environmentalism operates as a productive supplement to, rather than replacement of, other forms of environmental activism. The interplay between the form and content of TreeHuggerTV represents an important site to begin studying the future of environmental activism and its intersections with new media developments such as post-network television.

Determination of the Kinetics for Dynamic and Static Recrystallization by Using the Flow Curves

Improved methods to estimate the kinetics of dynamic and static recrystallization are proposed in this paper. The kinetics for dynamic and static recrystallization can be evaluated by inverse analysis of the flow curves obtained using the single-hit and double-hit hot compression tests carried out on Gleeble 3500. The dynamic and static recrystallization volume fractions can be seen as functions of plastic strain and time, respectively. The mathematical formulations between the recrystallization volume fractions and the dislocation density related to the flow stress are used in incremental forms in the study. The methods are applied to the hot compression tests of plain carbon steel and the kinetics of dynamic and static recrystallization are gained successfully for some conditions at elevated temperature. The results are clarified by comparing them with those reported in previous investigations. It is confirmed that the present methods can provide accurate kinetics for dynamic and static recrystallization with shorter time for experiment and computation.

A numerical analysis of sheet metal formability for automotive stamping applications

A theoretical failure model is presented for the numerical prediction of the forming limit strains of automotive sheets. The model uses the Swift’s diffuse necking and Hill’s localized necking concepts in describing tearing-type sheet metal failures and a computational scheme is proposed in which the failure conditions are expressed in incremental forms. The Bauschinger effect is included properly in the deformation modeling using an additive backstress form of the nonlinear-kinematic hardening rule. The necking conditions and plasticity model are transformed into a set of algebraic equations that may be applied both for proportional and non-proportional strain-controlled loadings. An iterative approach is employed in the incremental solution of algebraic equations. The formability analyses are conducted using the proposed theoretical model and the forming limit strains of two new generation auto sheets (Trip600 1.4mm, DP980 1.15mm) are estimated. The numerically generated FLC are compared with the experimental data and the FLC calculated with the Keeler–Brazier equation. For both steels, the model produced conservative plain–strain intercept values, FLC0, when compared with the predictions of Keeler–Brazier equation. Also the negative minor strain part of the experimental FLD’s is estimated with sufficient accuracy. For the positive minor strain side, however, the predictions are lower than both the experimental fit and the standard curve.

Dynamic Response Analysis of Bird Strike on Aircraft Windshield Based on Damage-modified Nonlinear Viscoelastic Constitutive Relation

Damage-modified nonlinear viscoelastic constitutive equation and failure criterion are introduced and the three-dimensional incremental forms are deduced based on the updated Lagrangian approach. A simple tensile test model and a split Hopkinson pressure bar model are built to verify the accuracy of the subroutine implemented within the non-linear finite element program LS-DYNA. A numerical model of bird strike on windshield is established to study the responses of windshield under three different bird velocities at three sites. The bird is represented by a cylinder with a hemisphere at each end and the contact-impact coupling algorithm is used in this study. It is found that the implemented subroutine can properly describe the mechanical behavior of polymethyl methacrylate under low and high strain rates and large deformation, and can be used validly.

Nonlinear constitutive law for ferroelectric/ferroelastic material and its finite element realization

The hysteresis phenomena of ferroelectric/ferroelastic material in polarization procedure are investigated. Some assumptions are presented based on the published experimental data. The electrical yielding criterion, mechanical yielding criterion and isotropic hardening model are established. The flow theory in incremental forms in polarization procedure is presented. The nonlinear constitutive law for electrical-mechanical coupling is proposed phenomenologically. Finally, the nonlinear constitutive law expressed in a form of matrices and vectors, which is immediately associated with finite element analysis, is formulated. In the example problem of a rectangular specimen subjected to a uniaxial electric field, the procedure from virgin state to fully polarized state is simulated. Afterward, a uniaxial compressive loading is applied to depolarizing the specimen. Results are in agreement with the experimental data.

Target-Specific Regulation of Synaptic Efficacy in the Feeding Central Pattern Generator ofAplysia:Potential Substrates for Behavioral Plasticity?

The contributions to this symposium are unified by their focus on the role of synaptic plasticity in sensorimotor learning. Synaptic plasticities are also known to operate within the central pattern generator (CPG) circuits that produce repetitive motor programs, where their relation to adaptive behavior is less well understood. This study examined divergent synaptic plasticity in the signaling of an influential interneuron, B20, located within the CPG that controls consummatory feeding-related behaviors in Aplysia. Previously, B20 was shown to contain markers for catecholamines and GABA (Díaz-Ríos et al., 2002), and its rapid synaptic signaling to two follower motor neurons, B16 and B8, was found to be mediated by dopamine (Díaz-Ríos and Miller, 2005). In this investigation, two incremental forms of increased synaptic efficacy, facilitation and summation, were both greater in the signaling from B20 to B8 than in the signaling from B20 to B16. Manipulation of the membrane potentials of the two postsynaptic motor neurons did not affect facilitation of excitatory postsynaptic potentials (EPSPs) to either follower cell. Striking levels of summation in B8, however, were eliminated at hyperpolarized membrane potentials and could be attributed to distinctive membrane properties of this postsynaptic cell. GABA and the GABAB agonist baclofen increased facilitation and summation of EPSPs from B20 to B8, but not to B16. The enhanced facilitation was not affected when the membrane potential of B8 was pre-set to hyperpolarized levels, but GABAergic effects on summation were eliminated by this manipulation. These observations demonstrate a target-specific amplification of synaptic efficacy that can contribute to channeling the flow of divergent information from an intrinsic interneuron within the buccal CPG. They further suggest that GABA, acting as a cotransmitter in B20, could induce coordinated and target-specific pre- and postsynaptic modulation of these signals. Finally, we speculate that target-specific plasticity and its modulation could be efficient, specific, and flexible substrates for learning-related modifications of CPG function.