Analysis Of Synergies Research Articles

Adaptation and mitigation strategies in agriculture: an analysis of potential synergies

As climate changes due to rising concentrations of greenhouse gases in the atmosphere, agriculture will be one of the key human activities affected. Projections show that while overall global food production in the coming decades may keep pace with the food requirements of a growing world population, climate change might worsen existing regional disparities because it will reduce crop yields mostly in lands located at lower latitudes where many developing countries are situated. Strategies to enhance local adaptation capacity are therefore needed to minimize climatic impacts and to maintain regional stability of food production. At the same time, agriculture as a sector offers several opportunities to mitigate the portion of global greenhouse gas emissions that are directly dependent upon land use, land-use change, and land-management techniques. This paper reviews issues of agriculture and climate change, with special attention to adaptation and mitigation. Specifically, as adaptation and mitigation strategies in agriculture are implemented to alleviate the potential negative effects of climate change, key synergies need to be identified, as mitigation practices may compete with modifications to local agricultural practices aimed at maintaining production and income. Under future climate and socio-economic pressures, land managers and farmers will be faced with challenges in regard to selecting those mitigation and adaptation strategies that together meet food, fiber and climate policy requirements.

Participatory integrated watershed management: Evolution of concepts and methods in an ecoregional program of the eastern African highlands

This paper focuses on the conceptual evolution of watershed management within the context of an action research program operating in the highlands of eastern Africa, as informed by both theory and practice. Following a review of the watershed management literature, and brief program and methodological overviews, the paper explores in detail the concepts of “participation” and “integration” in watershed management. Conceptual and methodological dimensions of the terms are discussed in the context of a watershed implementation process, clarifying how “watershed issues” are defined by local users, how “stakeholders” are defined with respect to those issues, and how participation and integration may be operationalized in practice. Data are selectively chosen from different pilot sites to illustrate how concepts underlying watershed management have been refined, and methods improved. It is clear that “participation” in problem diagnosis and program implementation must move beyond community-level fora to socially-disaggregated processes and explicit management of trade-offs to diverse groups. Secondly, integration does not come about through implementation of parallel interventions, but rather through an explicit analysis of potential trade-offs and synergies of interventions to diverse system components, and strategies to define and reach systems-level goals. Each approach requires attention to ways to optimize returns to diverse social groups and system components while minimizing negative spin-offs. The paper concludes with a discussion of implications for agricultural research and development in the eastern African region.

Muscle synergies during voluntary body sway: combining across-trials and within-a-trial analyses

We investigated co-varied changes in muscle activity during voluntary sway tasks that required a quick shift of the center of pressure (COP). We hypothesized that multi-muscle synergies (defined as task-specific covariation of elemental variables, muscle modes) stabilize a COP location in the anterior-posterior direction prior to a voluntary COP shift and that during the shift the synergies would weaken. Standing subjects performed two tasks, a cyclic COP shift over a range corresponding to 80% of the maximal amplitude of voluntary COP shift at 1 Hz and a unidirectional quick COP shift over the same nominal amplitude. The cyclic sway task was used to define muscle modes (M-modes, leg and trunk muscle groups with parallel scaling of muscle activation level within a group) and the relations between small changes in the magnitudes of M-modes [in the principal component analysis (PCA), the M-mode magnitudes are equivalent to PC scores] and COP shifts. A novel approach was used involving PCA applied to indices of muscle integrated activity measured both within a trial and across trials. The unidirectional sway task was performed in a self-paced (SP) manner and under a typical simple reaction time (RT) instruction. M-modes were also defined along trials at those tasks; they have been shown to be similar across tasks. Integrated indices of muscle activity in the SP-sway and RT-sway tasks were transformed into the M-modes. Variance in the M-mode space was partitioned into two components, one that did not affect the average value of COP shift (V (UCM)) and the other that did (V (ORT)). An index (DeltaV) corresponding to the normalized difference between V (UCM) and V (ORT) was computed. During steady-state posture, DeltaV was positive corresponding to most M-mode variance lying in a sub-space corresponding to a stable COP location across trials. Positive DeltaV values have been interpreted as reflecting a multi-M-mode synergy stabilizing the COP location. The magnitude of DeltaV was larger in SP trials than in RT trials. During voluntary COP shifts, the DeltaV magnitude dropped to zero or even became negative. We conclude that M-mode synergies stabilize COP location during quiet standing, while these synergies weaken or disappear during fast voluntary COP shifts. Under RT conditions, the COP stabilizing synergies were weaker supposedly to facilitate a quick COP shift without time for preparation. The suggested method of M-mode identification may potentially be applied to analysis of postural synergies in persons with impaired postural control such as elderly persons, persons with atypical development, or in the course of rehabilitation after an injury.

Mergers and Acquisitions: An Experimental Analysis of Synergies, Externalities and Dynamics

Mergers and acquisitions improve market efficiency by capturing synergies between firms. But takeovers also impose externalities (both positive and negative) on the remaining firms in the industry. This paper describes a new equilibrium concept designed to explain and predict takeovers in this setting. We experimentally compare the new equilibrium concept to that of competing con- cepts in situations without and with externalities. Moreover, we examine the predicted dynamics of takeovers and outcome implications of those dynamics. Our experimental results support the predictions of the new equilibrium concept and provide implications for further empirical tests.

Mergers and Acquisitions: An Experimental Analysis of Synergies, Externalities and Dynamics*

Mergers and Acquisitions: An Experimental Analysis of Synergies, Externalities and Dynamics*

Muscle synergies during shifts of the center of pressure by standing persons: identification of muscle modes

When a standing person performs a movement such that the center of gravity shifts, the activity of postural muscles adjusts to keep the balance. We assume that such adjustments are controlled using a small set of central variables, while each variable induces changes in the activity of a subgroup of postural muscles. The purpose of this study has been to identify such muscle groups (muscle modes or M-modes) and compare them across tasks and subjects. Four tasks required the subjects to release a load from extended arms leading to a center of pressure (COP) shift prior to the load release. The fifth task required an explicit COP shift by voluntary sway. Electromyographic activity of 11 postural muscles on one side of the body was integrated over a 100-ms interval corresponding to the early stage of the COP shift, and this integrated EMG activity was subjected to a principal component (PC) analysis across multiple repetitions of each task. Three PCs were identified and associated with a "push-back M-mode," a "push-forward M-mode," and a "mixed M-mode." Cluster analysis of the PC vectors across tasks and across subjects confirmed the existence of distinctive push-forward and push-back muscle groups. PC vectors were also compared across tasks and across subjects using cosines as a measure of colinearity between pairs of vectors. In general, M-modes were similar across both tasks and subjects. We conclude that shifts of the COP, whether implicit or explicit, are controlled using a small set of central variables associated with changes in the activity of robust subsets of postural muscles. These results can be used for future analysis of muscle synergies associated with postural tasks.

Analysis of postural control synergies during quiet standing in healthy children and children with cerebral palsy

Objective. To estimate the contribution of body transverse rotation using weighted differential center of pressure signals during quiet standing in healthy children and in children with cerebral palsy. Design. Body sway was indirectly measured through center of pressure data, which was calculated using dual force platforms. Background. Assessment of postural control synergies using center of pressure data provides a unique method for center of mass data analysis in characterizing complex balance sway. Methods. Using dual force platforms, linear expressions for the coordinates of right and left center of pressure signals were developed to identify and characterize balance control synergies during quiet standing. Subjects were also tested during eyes open and eyes closed trials to determine the significance of visual input on these control synergies. Results. The limb protraction/retraction control was found to be dominant during medial–lateral sway, whereas the estimated body transverse rotation contribution was found to be more significant than the previously reported measures of anterior–posterior balance. These findings were consistent in healthy children and in children with cerebral palsy during both eyes open and eyes closed trials. Conclusion. The weighted differential center of pressure signals show that the estimated body transverse rotation contribution is significant in healthy children and critical for postural stability in children with cerebral palsy. Relevance This study identifies the significance of body transverse rotation control contribution in upright posture. Children with cerebral palsy with relatively poor ankle control demonstrate the importance of body transverse rotation for postural stability.

Quantitative Analysis of Human Movement Synergies: Constructive Pattern Analysis for Gait

To record three-dimensional coordinates of the joints from normal human subjects during locomotion, we used a digital motion analysis system (ELITE). Recordings were obtained under several different conditions, which included normal walking and stepping over obstacles. Principal component analysis was used to analyze coordinate data after conversion of the data to segmental angles. This technique gave a stable summary of the redundancy in gait kinematic data in the form of reduced variables (principal components). By modeling the shapes of the phase plots of reduced variables (distortion analysis) and using a limited number of model parameters, good resolution was obtained between subtly different conditions. Hence, it was possible to accurately resolve small distributed changes in gait patterns within subjects. These methods seem particularly suited to longitudinal studies in which relevant movement features are not known a priori. Assumptions and neurophysiological applications are discussed.

Development of coordinated movement in chicks: II. Temporal analysis of hindlimb muscle synergies at embryonic day 10 in embryos with spinal gap transections.

Spinal neural circuits can recruit muscles to produce organized patterns of activity early in embryonic development. In a previous study, using multichannel electromyographic (EMG) recordings, we characterized burst parameters for these patterns in the legs of chick embryos during spontaneous motility in ovo at embryonic days (E) 9 and E10 (Bradley and Bekoff, 1990). Results of the study suggested both neural and biomechanical factors play an important role in the development of coordinated limb movements. In this study, to explore the contribution of descending neural inputs to the control of leg movements during motility, we applied similar methods to characterize motor patterns produced by the spinal cord in the absence of descending inputs. Thoracic spinal gap transections were performed at E2 and EMG patterns were recorded at E10. Several EMG features for chronic spinal embryos were similar to those for normal embryos and demonstrate that lumbar spinal circuits can be correctly assembled to control limb movements in the absence of connectivity with more rostral neural structures during early differentiation processes. However, certain aspects of the EMG patterns in chronic spinal embryos were different from patterns in normal embryos and provide support for conclusions drawn earlier by Oppenheim (1975). Specifically, our data support the view that propriospinal and/or supraspinal inputs function to regulate the timing of cyclic limb movements controlled by spinal neural circuits. Finally, we consider the possible long-term effects of chronic spinal gap transections as compared to acute spinal transections on the development of motility.

Development of coordinated movement in chicks: I. Temporal analysis of hindlimb muscle synergies at embryonic days 9 and 10

In this study, we examined electromyographic activity for an ensemble of hindlimb muscles during spontaneous activity in chick embryos to advance understanding of early motor coordination and its relationship to later emerging behaviors. Four-channel recordings were obtained from 6 muscles in ovo at embryonic Days 9 and 10. Analyses indicated that when muscles are repetitively active, patterns during embryonic motility are distinct from those for other behaviors. For example, unlike the muscle patterns for locomotion, extensor muscles and flexor muscles are synchronously activated at 50% of the extensor cycle period. Furthermore, flexor and extensor bursts are similar in duration and show little correlation with extensor cycle period. Finally, our data suggest that the ensemble of muscles active can vary from cycle to cycle. This study provides the basis for future studies that will examine neural and biomechanical interactions underlying the development of coordinated movement.

On the Nucleolus of a Characteristic Function Game

Introduction. The nucleolus is a solution concept for games in characteristic function form. It was introduced by D. Schmeidler in [1]. This paper is concerned with some of the properties of the nucleolus. Some of the results are new (Theorems 2, 4, 5) whereas others are known (Theorems l and 3), but the proofs given here are, in a sense, simpler than those in [1]. A characteristic function game is a pair (N, v) consisting of a set N = {1, 2, , n} of n players, and a characteristic function v, which maps each subset S of N, called a coalition, to a number v(S). In addition, it is assumed that v(N) _ 0, and that v(S) = 0 for all one-person coalitions, as well as for the empty coalition. A payoff vector is an n-tuple x = (x1, , xn) such that xi > 0 for all i = 1, , n, and x(N) = v(N), where for each coalition S, x(S) denotes Zi,eS Xi. X is the set of all payoff vectors. Of course, X depends on the particular game v. For any x in X, let q(x) be a vector in E2n, the components of which are the numbers v(S) x(S), arranged in order of decreasing magnitude, where S runs over all the coalitions of N. We shall say that x is at least as acceptable as y (with respect to v), and write x > y, if q(x) is not greater than q(y), in the lexicographical order on E2n. If q(x) is smaller than q(y), we shall say that x is more acceptable than y and write x >y. The nucleolus of the game is the set of those points in X which are "most acceptable," that is, {x E X :x > y for all y E X}. In [1], Schmeidler proved the basic result that every game possesses a nonempty nucleolus. He further showed that the nucleolus actually consists of just one point, and that-viewed as a point function of the game-it is continuous. Our aim is to give new proofs of the uniqueness and of the continuity of the nucleolus. To this end, we will have to introduce a few definitions and to prove an auxiliary theorem (Theorem 2), which may have some interest in its own right. DEFINITION. Let bo, b1, ... , bp be a sequence of sets whose elements are coalitions of N. This sequence is a coalition array whenever: (i) every coalition of N is contained in exactly one of the sets b1, bp, (ii) bo contains only one-element coalitions. For every game v and payoff vector x, let b1(x, v) be the set of those S c N for which max {v(S) x(S): S c N} is attained. Similarly, b2(x, v) is the set of those S c N where max {v(S) x(S) :S ? b1(x, v)} is attained, and so on. Finally, let bo(x) = {{i} : xi = 0}. It is obvious that bo(x), b1(x, v), . . , bp(x, v) is a coalition array. We shall say that it is the array that belongs to (v, x). DEFINITION 2. A coalition array bo, , bp has property I if for all k= 1,2,...,pandanyyinE n, (1) y(S) _ 0forall Sebo, (2) y(S) ? O for all Se b1 U U bk, and (3) y(N) = 0