Multiple Resource Acquisitions Research Articles

Relationship multiplexity, multiple resource acquisition, and export performance of emerging-market firms

Relationship multiplexity, multiple resource acquisition, and export performance of emerging-market firms

Perennial grass root system specializes for multiple resource acquisitions with differential elongation and branching patterns.

Roots optimize the acquisition of limited soil resources, but relationships between root forms and functions have often been assumed rather than demonstrated. Furthermore, how root systems co-specialize for multiple resource acquisitions is unclear. Theory suggests that trade-offs exist for the acquisition of different resource types, such as water and certain nutrients. Measurements used to describe the acquisition of different resources should then account for differential root responses within a single system. To demonstrate this, we grew Panicum virgatum in split-root systems that vertically partitioned high water availability from nutrient availability so that root systems must absorb the resources separately to fully meet plant demands. We evaluated root elongation, surface area, and branching, and we characterized traits using an order-based classification scheme. Plants allocated approximately 3/4th of primary root length towards water acquisition, whereas lateral branches were progressively allocated towards nutrients. However, root elongation rates, specific root length, and mass fraction were similar. Our results support the existence of differential root functioning within perennial grasses. Similar responses have been recorded in many plant functional types suggesting a fundamental relationship. Root responses to resource availability can be incorporated into root growth models via maximum root length and branching interval parameters.

A multivariate perspective of resource acquisition behaviours in bighorn sheep

Quantifying variation in individual resource acquisition and allocation to costly life-history functions is critical to understand the evolution of life-histories. Individuals should adaptively respond to changes in resource requirements throughout their lifetime through flexibility in resource acquisition behaviours. Empirical investigation of behavioural adjustments in wild settings are scarce and rarely consider more than one behaviour. Resource acquisition, however, involves several behaviours and should be considered in a multivariate framework. We measured four resources acquisition behaviours – bite rate, rumination rate, chews per bolus and bolus processing time in bighorn sheep, Ovis canadensis . We then tested whether individuals adjust these behaviours as expected based on individual differences in resource allocation to lactation and annual mass gain. Using a multivariate mixed effects model, we also evaluated the prediction that bite rate and rumination behaviours are repeatable and show strong covariation among individuals. Both bite rate and rumination effort increased with allocation to lactation. Allocation to mass gain, however, was positively correlated with rumination effort but not with bite rate. Rumination behaviours also showed significant variation with sex and mass, suggesting potential morphological and/or physiological constraints. Although all four behaviours were significantly repeatable, contrary to our predictions, bite rate was not significantly correlated with rumination behaviours among individuals. This study highlights strong correlations between expected resource allocation to costly life-history functions and multiple resource acquisition behaviours. There was, however, no evidence that variance in multiple resource acquisition behaviours originates from a single axis of variation among individuals. • Bite rate and rumination effort increased with resource allocation to lactation. • Only rumination effort increased with mass gain. • Individual level repeatability of resource acquisition behaviours was significant. • Resource acquisition behaviours were not correlated among individuals.

Modeling Microbial Adaptations to Nutrient Limitation During Litter Decomposition

Microbial decomposers face large stoichiometric imbalances when feeding on nutrient-poor plant residues. To meet the challenges of nutrient limitation, microorganisms might: (i) allocate less carbon (C) to growth vs. respiration or excretion (i.e., flexible C-use efficiency, CUE), (ii) produce extracellular enzymes to target compounds that supply the most limiting element, (iii) modify their cellular composition according to the external nutrient availability, and (iv) preferentially retain nutrients at senescence. These four resource use modes can have different consequences on the litter C and nitrogen (N) dynamics–modes that selectively remove C from the system can reduce C storage in soil, whereas modes that delay C mineralization and increase internal N recycling could promote storage of C and N. Since we do not know which modes are dominant in litter decomposers, we cannot predict the fate of C and N released from plant residues, in particular under conditions of microbial nutrient limitation. To address this question, we developed a process-based model of litter decomposition in which these four resource use modes were implemented. We then parameterized the model using ∼80 litter decomposition datasets spanning a broad range of litter qualities. The calibrated model variants were able to capture most of the variability in litter C, N, and lignin fractions during decomposition regardless of which modes were included. This suggests that different modes can lead to similar litter decomposition trajectories (thanks to the multiple alternative resource acquisition pathways), and that identification of dominant modes is not possible using “standard” litter decomposition data (an equifinality problem). Our results thus point to the need of exploring microbial adaptations to nutrient limitation with empirical estimates of microbial traits and to develop models flexible enough to consider a range of hypothesized microbial responses.

A Petri Net Based Deadlock Avoidance Policy for Flexible Manufacturing Systems With Assembly Operations and Multiple Resource Acquisition

Efficient deadlock control policies are very important in the operation of flexible manufacturing systems (FMS). This paper focuses on deadlock control problems for a general class of FMS. They have three interesting characteristics from the application point of view. First, flexible routes of parts and assembly operations are allowed. Second, the number of parts of the same type in a product may be more than one. Third, an operation may require multiple resources. To characterize such FMS, a Petri net model that can deal well with all FMS characteristics is developed. Based on it, this paper proposes a Banker's-algorithm-like deadlock avoidance policy. The proposed policy is proved to be polynomial in the model size. Moreover, experimental results indicate its effectiveness and superiority over the state-of-the-art policies.

Environmental filtering limits functional diversity during succession in a seasonally wet tropical secondary forest

AbstractAimsSuccessional shifts in biodiversity are key drivers of the recovery of ecosystem functioning following disturbances. Identifying mechanisms that enhance or limit the ecological processes that drive these successional patterns can strengthen efforts to manage biodiversity‐dependent ecosystem functions across human‐dominated landscapes. Here, we examine successional patterns of multiple aspects of functional diversity in a seasonally wet tropical secondary forest and changes in the strength of environmental filtering during secondary succession.LocationCentral Panama.MethodsWe calculate functional richness (FRic) and dispersion (FDis) across a secondary forest chronosequence (n = 51 0.1‐ha plots) using nine functional traits related to resource acquisition and conservation. Functional diversity indices are calculated using all traits and each trait individually. Using a null model approach, we test the effects of environmental filtering during secondary succession.ResultsFRic and FDis exhibit saturating relationships with time since abandonment, reaching their maxima after 7 and 10 years, respectively. Overall, we find evidence that environmental filtering reduces FDis to a greater extent than FRic and that the strength of environmental filtering on both FDis and FRic increases during succession. The impacts of environmental filtering on functional diversity of individual traits are consistent; the mean standardized effect sizes (SES) of FRic and FDis of at least six of the nine studied traits are lower than expected. Notably, environmental filtering on FRic and FDis of particular traits associated with light and nutrient acquisition increases significantly along the secondary forest chronosequence, suggesting that functional convergence of multiple resource acquisition strategies strengthens in parallel.ConclusionsWe find that successional shifts in environmental conditions limit trait variation in seasonally wet tropical secondary forests. Our results suggest that the increasing strength of environmental filtering shifts abundance of trait combinations towards a subset of functionally convergent species that compete for light and nutrients in similar ways.

On near-optimal deadlock control for a class of generalized Petri nets using reachability graph

PurposeDeadlock is a rather undesirable phenomenon and must be well solved in flexible manufacturing systems (FMS). This paper aims to propose a general iterative deadlock control method for a class of generalized Petri nets (GPN), namely, G-systems, which can model an FMS with assembly and disassembly operations of multiple resource acquisition. When given an uncontrolled G-system prone to deadlocks, the work focuses on the synthesis of a near-optimal, non-blocking supervisor based on reachability graph (RG) analysis.Design/methodology/approachThe concept of a global idle place (GIP) for an original uncontrolled G-system is presented. To simplify the RG computation of an uncontrolled G-system, a GIP is added temporarily to the net model during monitor computation steps. Starting with one token and then by gradually increasing the number of tokens in the GIP at each iteration step, the related net system is obtained. The minimal-covered-set of all bad markings of the related net system suffering from deadlock can be identified and then removed by additional monitors through an established place-invariant control method. Consequently, all related systems are live, and the GIP is finally removed when the non-blockingness of the controlled system is achieved. Meanwhile, the redundancy of monitors is also checked.FindingsA typical G-system example is provided to demonstrate the applicability and effectiveness of the proposed method. Experiments show that the proposed method is easy to use and provides very high behavioral permissiveness for G-system. Generally, it can achieve an optimal or a near-optimal solution of the non-blocking supervisor.Originality/valueIn this work, the concept of GIP for G-systems is presented for synthesis non-blocking supervisors based on RG analysis. By using GIP, an effective deadlock control method is proposed. Generally, the proposed method can achieve an optimal or a near-optimal, non-blocking supervisor for an uncontrolled G-system prone to deadlocks.

Polynomial-complexity supervisory control for flexible assembly systems based on Petri nets

ABSTRACTFlexible assembly systems (FASs) are a class of resource allocation systems with assembly processes as their inevitable components. Deadlock resolution and liveness enforcement play important roles in the supervisory control of FASs. Design of deadlock avoidance policies (DAPs) for FASs has received significant attention recently. The computational feasibility of real-time DAPs is of great importance for the policies’ online implementation in practical applications. However, there are difficulties brought by the existence of assembly processes. So far, nearly all known DAPs with polynomial-time complexity apply only to systems without assembly operations. This study focuses on the deadlock-avoidance control problem of a broader class of FASs as compared to those discussed in the existing work. Specifically, for an FAS addressed in this paper, each resource can be shared by any two operations, and it also allows multiple resource acquisition at each processing step. This work develops a novel DAP for such FASs, which is based on their Petri-net models and actually an improved Banker’s algorithm that consists of three executable algorithms. Moreover, the computational time complexity of the DAP is polynomial in the size of the system model. The application of the proposed method to some examples illustrates its effectiveness and efficiency.

An integrated control method for designing non-blocking supervisors using Petri nets

This article presents an efficient integrated approach on designing a non-blocking supervisor for the most general classes of Petri nets, called G-systems that allow multiple resource acquisitions. This work mainly focuses on developing a deadlock prevention policy with a polynomial computational complexity. First, an extraction algorithm of liveness requirement constraints is presented according to the concept of resource partial orders. By considering the different resource requirements of various processes, monitors are added for the uncontrolled G-system on the basis of those precise linear inequality constraints. Afterward, we explore an iterative control policy by utilizing the traditional mathematical programming method, which can ensure the liveness of the resultant controlled system. Comparing with the existing deadlock control policies reported in the literature, the proposed method can achieve a non-blocking controlled G-system with simple structure and high computational efficiency. Finally, a...

A suboptimal deadlock control policy for designing non-blocking supervisors in flexible manufacturing systems

This work aims to resolve deadlock problems in flexible manufacturing systems. A novel deadlock control policy in the frame of Petri nets formalism is presented for a class of generalized Petri nets, namely G-systems, which can usually model assembly and disassembly operations of multiple resource acquisition. Based on the concept of elementary siphons, all strict minimal siphons (SMS) in an uncontrolled net system are first divided into elementary siphons and dependent ones. After that, a set of linear inequality constraints expressed by state vectors can be formalized for elementary siphons. After being modified by utilizing the conjunctive/disjunctive resources upstream neighborhood policy, a set of generalized mutual exclusion constraints expressed by marking vectors can be obtained. Then, the additional monitors are only designed for elementary siphons, whose control depth variables can be obtained by solving a linear programming problem. As a result, the controllability of dependent ones can be ensured by properly supervising its elementary siphons. Finally, all strict minimal siphons are max′-controlled and no insufficiently marked siphon is generated, which indicates that the sequential resources are allocated reasonably to guarantee the absence of deadlock states. The proposed method can usually lead to a near-optimal non-blocking supervisor with simple structure. A G-system example prone to deadlocks is used to illustrate the applicability and the effectiveness of the proposed method.

On the “Counter-Example” in the Article “Max $^{\prime}$-Controlled Siphons for Liveness of $S^{3}PGR^{2}$” Regarding the Results in “Deadlock Avoidance in Sequential Resource Allocation Systems With Multiple Resource Acquisitions and Flexible Routings”

The main purpose of this correspondence is to establish that, contrary to the claims that are made in the paper by D. Y. Chao in it, the results of the paper by Park and S. A. Reveliotis concerning the liveness characterization of the $S^{3}PGR^{2}$ nets by means of the structural object of deadly marked siphon, are correct and complete.

An iterative method for synthesizing non-blocking supervisors for a class of generalized Petri nets using mathematical programming

This paper presents a novel and computational deadlock prevention policy for a class of generalized Petri nets, namely G-systems, which allows multiple resource acquisitions and flexible routings with machining, assembly and disassembly operations. In this research, a mixed integer programming (MIP)-based deadlock detection technique is used to find an insufficiently marked minimal siphon from a maximal deadly marked siphon for generalized Petri nets. In addition, two-stage control method is employed for deadlock prevention in Petri net model. Such proposed method is an iterative approach consisting of two stages. The first one is called siphons control, which adds a control place to the original net for each insufficiently marked minimal siphon. The objective is to prevent minimal siphons from being insufficiently marked. The second one, called control-induced siphons control, is to add a control place to the augmented net with its output arcs connecting to source transitions, which assures that there is no new insufficiently marked siphon generated due to the addition of the monitors. Compared with the existing approaches, the proposed deadlock prevention policy can usually lead to a non-blocking supervisor with more permissive behavior and high computational efficiency for a sizeable plant model due to avoiding complete siphon enumeration. Finally, a practical flexible manufacturing system (FMS) example is utilized to illustrate the proposed method.

Local and global deadlock prevention policies for resource allocation systems using partially generated reachability graphs

This paper considers the deadlock prevention problem for a class of conjunctive/disjunctive resource allocation systems (C/D-RAS) which cover relatively general cases in which the multiple resource acquisitions and flexible routings are allowed. First, an improved siphon-based liveness characterization for the Petri nets modeling C/D-RAS is proposed. Subsequently, this characterization facilitates the utilization of a mixed integer programming (MIP) based deadlock prevention policy that can well avoid the explicit enumeration of both siphons and the reachable states. The resulting policy is implemented by an iterative algorithm each step of which is characterized as an MIP formulation in conjunction with both a bad marking detection and a feedback control operation. Finally, the deadlock prevention policy developed in this paper is, respectively, characterized by the local and global ones so as to realize a trade-off between the behavior permissiveness and the structural simplicity of the supervisor. Both the theoretical and experimental results validate the effectiveness and efficiency of such an approach.

On Controllability of Dependent Siphons for Deadlock Prevention in Generalized Petri Nets

A fair amount of research has shown the importance of siphons in the analysis and control of deadlocks in a variety of resource allocation systems by using a Petri net formalism. In this paper, siphons in a generalized Petri net are classified into elementary and dependent ones, as done for ordinary nets in our previous work. Conditions are derived under which a dependent siphon is controlled by properly supervising its elementary siphons, which indicates that the controllability of dependent siphons in an ordinary Petri net is a special case of that in a generalized one. The application of the controllability of dependent siphons is shown by considering the deadlock prevention problem for a class of resource allocation systems, namely, G-system that allows multiple resource acquisitions and flexible routings in a flexible manufacturing system with machining, assembly, and disassembly operations. We develop a monitor-based deadlock prevention policy that first adds monitors for elementary siphons only to a G-system plant model such that the resultant net system satisfies the maximal controlled-siphon property (maximal cs-property). Then, by linear programming, initial tokens in the additional monitors are decided such that liveness is enforced to the supervised system. Also, a simplified live marking relationship for a G-system between the initial tokens of the source places and those of the resource places is derived. Finally, the proposed deadlock prevention methods are illustrated by using an example.

Root architectural tradeoffs for water and phosphorus acquisition.

Root architectural traits that increase topsoil foraging are advantageous for phosphorus acquisition but may incur tradeoffs for the acquisition of deep soil resources such as water. To examine this relationship, common bean genotypes contrasting for rooting depth were grown in the field and in the greenhouse with phosphorus stress, water stress and combined phosphorus and water stress. In the greenhouse, water and phosphorus availability were vertically stratified to approximate field conditions, with higher phosphorus in the upper layer and more moisture in the bottom layer. Under phosphorus stress, shallow-rooted genotypes grew best, whereas under drought stress, deep-rooted genotypes grew best. In the combined stress treatment, the best genotype in the greenhouse had a dimorphic root system that permitted vigorous rooting throughout the soil profile. In the field, shallow-rooted genotypes surpassed deep-rooted genotypes under combined stress. This may reflect the importance of early vegetative growth in terminal drought environments. Our results support the hypothesis that root architectural tradeoffs exist for multiple resource acquisition, particularly when resources are differentially localised in the soil profile. Architectural plasticity and root dimorphism achieved through complementary growth of distinct root classes may be important means to optimise acquisition of multiple soil resources.

Deadlock Resolution Strategy for Automated Manufacturing Systems Including Conjunctive Resource Service

Automated manufacturing systems (AMSs) can process different parts according to operation sequences sharing a finite number of resources. In these systems, deadlock situations can occur so that the flow of parts is permanently inhibited, and the processing of jobs is partially or completely blocked. Hence, one of the tasks of the control system is ruling resource allocation to prevent such situations from occurring. A large part of the existing literature focused on systems in which every operation is performed by only one resource. This paper proposes a deadlock strategy to avoid deadlock conditions in more complex systems where multiple resource acquisitions are allowed to complete a working operation conjunctive resource service system (CRSS). The AMS structure and dynamics is described by a colored timed Petri net model, suitable for following resource changes and working procedure updating. Moreover, digraphs characterize the complex interactions between resources and jobs so that the conditions for the deadlock occurrence are derived. Finally, an event-based controller is defined to avoid deadlock in CRSSs on the basis of the system state knowledge and of the given priority law ruling the concurrent job selection.

Optimization modeling of plant root architecture for water and phosphorus acquisition

An optimization model is presented that examines the relationship between root architecture and multiple resource acquisition, specifically water and phosphorus in spatially heterogeneous environments. The basal root growth angle of an individual common bean plant, which determines the orientation and localization of the bulk of the root system, was modeled as the decision variable. The total payoff to the plant, the benefit obtained from water and phosphorus acquisition, minus the costs of spatial competition between roots, is given as a function of the ( x, y) coordinates of the basal root in two-dimensional Cartesian space. We obtained a general solution and applied it to four unique environmental cases which are as follows: (1) the case of uniformly distributed water and phosphorus; (2) the case of localized shallow phosphorus; (3) the case of localized deep water; and (4) the case of shallow phosphorus and deep water. The general solution states that the optimal basal root growth angle will occur at the point where the total rate of change in the value of the resources acquired equals the total rate of change in cost that results from locating the root deeper in the soil. An optimizing plant locates its roots deeper in the soil profile until the marginal benefit exactly equals the marginal cost. The model predicts that the basal root angle of an optimizing plant will be shallower for Case 2 and deeper for Case 3, relative to the basal root angle obtained in the case of uniformly distributed water and phosphorus. The optimal basal root angle for Case 4 will depend on the marginal rate of substitution of water availability for phosphorus availability that occurs with depth. Empirical observations of bean root architecture in the greenhouse and in the field confirm model results and are discussed. In addition, the potential importance of phenotypic plasticity and phenotypic variation are discussed in relation to optimization of traits and adaptation to spatially heterogeneous environments.

Deadlock avoidance in sequential resource allocation systems with multiple resource acquisitions and flexible routings

Considers the deadlock avoidance problem for the class of conjunctive/disjunctive (sequential) resource allocation systems (C/D-RAS), which allows for multiple resource acquisitions and flexible routings. First, a siphon-based characterization for the liveness of Petri nets (PNs) modeling C/D-RAS is developed, and subsequently, this characterization facilitates the development of a polynomial-complexity deadlock avoidance policy (DAP) that is appropriate for the considered RAS class. The resulting policy is characterized as C/D-RUN. The last part of the paper exploits the aforementioned siphon-based characterization of C/D-RAS liveness, in order to develop a sufficiency condition for C/D-RAS liveness that takes the convenient form of a mixed integer programming (MIP) formulation. The availability of this MIP formulation subsequently allows the automatic correctness verification of any tentative C/D-RAS DAP for which the controlled system behavior remains in the class of PNs modeling C/D-RAS, and the effective flexibility enhancement of the aforementioned C/D-RUN DAP implementations. Finally, we notice that, in addition to extending and complementing the current theory on deadlock-free sequential resource allocation to the most powerful class of C/D-RAS, the presented results also (i) nontrivially generalize important concepts and techniques of ordinary PN structural analysis to the broader class of nonordinary PNs, while (ii) from a practical standpoint, they can find direct application in the (work-) flow management of modern production, service and/or transportation environments.