860 resultados para collective excitations in multilayers


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In the Andean highlands, indigenous environmental knowledge is currently undergoing major changes as a result of various external and internal factors. As in other parts of the world, an overall process of erosion of local knowledge can be observed. In response to this trend, some initiatives that adopt a biocultural approach aim at actively strengthening local identities and revalorizing indigenous environmental knowledge and practices, assuming that such practices can contribute to more sustainable management of biodiversity. However, these initiatives usually lack a sound research basis, as few studies have focused on the dynamics of indigenous environmental knowledge in the Andes and on its links with biodiversity management. Against this background, the general objective of this research project was to contribute to the understanding of the dynamics of indigenous environmental knowledge in the Andean highlands of Peru and Bolivia by investigating how local medicinal knowledge is socially differentiated within rural communities, how it is transformed, and which external and internal factors influence these transformation processes. The project adopted an actor-oriented perspective and emphasized the concept of knowledge dialogue by analyzing the integration of traditional and formal medicinal systems within family therapeutic strategies. It also aimed at grasping some of the links between the dynamics of medicinal knowledge and the types of land use systems and biodiversity management. Research was conducted in two case study areas of the Andes, both Quechua-speaking and situated in comparable agro-ecological production belts - Pitumarca District, Department of Cusco (Southern Peruvian Highlands) and the Tunari National Park, Department of Cochabamba (Bolivian inner-Andean valleys). In each case study area, the land use systems and strategies of 18 families from two rural communities, their environmental knowledge related to medicine and to the local therapeutic flora, and an appreciation of the dynamics of this knowledge were assessed. Data were collected through a combination of disciplinary and participatory action-research methods. It was mostly analyzed using qualitative methods, though some quantitative ethnobotanical methods were also used. In both case studies, traditional medicine still constitutes the preferred option for the families interviewed, independently of their age, education level, economic status, religion, or migration status. Surprisingly and contrary to general assertions among local NGOs and researchers, results show that there is a revival of Andean medicine within the younger generation, who have greater knowledge of medicinal plants than the previous one, value this knowledge as an important element of their way of life and relationship with “Mother Earth” (Pachamama), and, at least in the Bolivian case, prefer to consult the traditional healer rather than go to the health post. Migration to the urban centres and the Amazon lowlands, commonly thought to be an important factor of local medicinal knowledge loss, only affects people’s knowledge in the case of families who migrate over half of the year or permanently. Migration does not influence the knowledge of medicinal plants or the therapeutic strategies of families who migrate temporarily for shorter periods of time. Finally, economic status influences neither the status of people’s medicinal knowledge, nor families’ therapeutic strategies, even though the financial factor is often mentioned by practitioners and local people as the main reason for not using the formal health system. The influence of the formal health system on traditional medicinal knowledge varies in each case study area. In the Bolivian case, where it was only introduced in the 1990s and access to it is still very limited, the main impact was to give local communities access to contraceptive methods and to vaccination. In the Peruvian case, the formal system had a much greater impact on families’ health practices, due to local and national policies that, for instance, practically prohibit some traditional practices such as home birth. But in both cases, biomedicine is not considered capable of responding to cultural illnesses such as “fear” (susto), “bad air” (malviento), or “anger” (colerina). As a consequence, Andean farmers integrate the traditional medicinal system and the formal one within their multiple therapeutic strategies, reflecting an inter-ontological dialogue between different conceptions of health and illness. These findings reflect a more general trend in the Andes, where indigenous communities are currently actively revalorizing their knowledge and taking up traditional practices, thus strengthening their indigenous collective identities in a process of cultural resistance.

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In order to fully describe the construct of empowerment and to determine possible measures for this construct in racially and ethnically diverse neighborhoods, a qualitative study based on Grounded Theory was conducted at both the individual and collective levels. Participants for the study included 49 grassroots experts on community empowerment who were interviewed through semi-structured interviews and focus groups. The researcher also conducted field observations as part of the research protocol.^ The results of the study identified benchmarks of individual and collective empowerment and hundreds of possible markers of collective empowerment applicable in diverse communities. Results also indicated that community involvement is essential in the selection and implementation of proper measures. Additional findings were that the construct of empowerment involves specific principles of empowering relationships and particular motivational factors. All of these findings lead to a two dimensional model of empowerment based on the concepts of relationships among members of a collective body and the collective body's desire for socio-political change.^ These results suggest that the design, implementation, and evaluation of programs that foster empowerment must be based on collaborative ventures between the population being served and program staff because of the interactive, synergistic nature of the construct. In addition, empowering programs should embrace specific principles and processes of individual and collective empowerment in order to maximize their effectiveness and efficiency. And finally, the results suggest that collaboratively choosing markers to measure the processes and outcomes of empowerment in the main systems and populations living in today's multifaceted communities is a useful mechanism to determine change. ^

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The French sociologist Maurice Halbwachs (1877–1945) conceived re- membrance as a product of ›collective memory‹ and explained this idea in his book on ›La Topographie légendaire des Évangiles en Terre sainte‹ (1941) showing that the topography of the Holy Land was predominantly an imaginary landscape construed by Christian communities. Following this concept, this article studies the ›Palästinalied‹, a text describing the arrival of a pilgrim in the Holy Land in the time of the crusades, abundantly transmitted under the name of Walther von der Vogelweide. The high degree of textual variance in the diverse manuscripts testifies the acting of ›collective memory‹ in the medieval poetic tradition. Of special interest in this context are the strophic arrangements, the variation of deictic markers, the reworking of melodic models documented in the manuscript transmission and the diatopic opposition existing between the emphasis of ›distant love‹ expressed in Jaufré Rudel’s Occitan song ›Lanqand li jorn son lonc en mai‹ (one of the named models) and the attitude of proximity prevailing in the ›Palästinalied‹.

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We investigate the transition from unitary to dissipative dynamics in the relativistic O(N) vector model with the λ(φ2)2 interaction using the nonperturbative functional renormalization group in the real-time formalism. In thermal equilibrium, the theory is characterized by two scales, the interaction range for coherent scattering of particles and the mean free path determined by the rate of incoherent collisions with excitations in the thermal medium. Their competition determines the renormalization group flow and the effective dynamics of the model. Here we quantify the dynamic properties of the model in terms of the scale-dependent dynamic critical exponent z in the limit of large temperatures and in 2≤d≤4 spatial dimensions. We contrast our results to the behavior expected at vanishing temperature and address the question of the appropriate dynamic universality class for the given microscopic theory.

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Cuando una colectividad de sistemas dinámicos acoplados mediante una estructura irregular de interacciones evoluciona, se observan dinámicas de gran complejidad y fenómenos emergentes imposibles de predecir a partir de las propiedades de los sistemas individuales. El objetivo principal de esta tesis es precisamente avanzar en nuestra comprensión de la relación existente entre la topología de interacciones y las dinámicas colectivas que una red compleja es capaz de mantener. Siendo este un tema amplio que se puede abordar desde distintos puntos de vista, en esta tesis se han estudiado tres problemas importantes dentro del mismo que están relacionados entre sí. Por un lado, en numerosos sistemas naturales y artificiales que se pueden describir mediante una red compleja la topología no es estática, sino que depende de la dinámica que se desarrolla en la red: un ejemplo son las redes de neuronas del cerebro. En estas redes adaptativas la propia topología emerge como consecuencia de una autoorganización del sistema. Para conocer mejor cómo pueden emerger espontáneamente las propiedades comúnmente observadas en redes reales, hemos estudiado el comportamiento de sistemas que evolucionan según reglas adaptativas locales con base empírica. Nuestros resultados numéricos y analíticos muestran que la autoorganización del sistema da lugar a dos de las propiedades más universales de las redes complejas: a escala mesoscópica, la aparición de una estructura de comunidades, y, a escala macroscópica, la existencia de una ley de potencias en la distribución de las interacciones en la red. El hecho de que estas propiedades aparecen en dos modelos con leyes de evolución cuantitativamente distintas que siguen unos mismos principios adaptativos sugiere que estamos ante un fenómeno que puede ser muy general, y estar en el origen de estas propiedades en sistemas reales. En segundo lugar, proponemos una medida que permite clasificar los elementos de una red compleja en función de su relevancia para el mantenimiento de dinámicas colectivas. En concreto, estudiamos la vulnerabilidad de los distintos elementos de una red frente a perturbaciones o grandes fluctuaciones, entendida como una medida del impacto que estos acontecimientos externos tienen en la interrupción de una dinámica colectiva. Los resultados que se obtienen indican que la vulnerabilidad dinámica es sobre todo dependiente de propiedades locales, por tanto nuestras conclusiones abarcan diferentes topologías, y muestran la existencia de una dependencia no trivial entre la vulnerabilidad y la conectividad de los elementos de una red. Finalmente, proponemos una estrategia de imposición de una dinámica objetivo genérica en una red dada e investigamos su validez en redes con diversas topologías que mantienen regímenes dinámicos turbulentos. Se obtiene como resultado que las redes heterogéneas (y la amplia mayora de las redes reales estudiadas lo son) son las más adecuadas para nuestra estrategia de targeting de dinámicas deseadas, siendo la estrategia muy efectiva incluso en caso de disponer de un conocimiento muy imperfecto de la topología de la red. Aparte de la relevancia teórica para la comprensión de fenómenos colectivos en sistemas complejos, los métodos y resultados propuestos podrán dar lugar a aplicaciones en sistemas experimentales y tecnológicos, como por ejemplo los sistemas neuronales in vitro, el sistema nervioso central (en el estudio de actividades síncronas de carácter patológico), las redes eléctricas o los sistemas de comunicaciones. ABSTRACT The time evolution of an ensemble of dynamical systems coupled through an irregular interaction scheme gives rise to dynamics of great of complexity and emergent phenomena that cannot be predicted from the properties of the individual systems. The main objective of this thesis is precisely to increase our understanding of the interplay between the interaction topology and the collective dynamics that a complex network can support. This is a very broad subject, so in this thesis we will limit ourselves to the study of three relevant problems that have strong connections among them. First, it is a well-known fact that in many natural and manmade systems that can be represented as complex networks the topology is not static; rather, it depends on the dynamics taking place on the network (as it happens, for instance, in the neuronal networks in the brain). In these adaptive networks the topology itself emerges from the self-organization in the system. To better understand how the properties that are commonly observed in real networks spontaneously emerge, we have studied the behavior of systems that evolve according to local adaptive rules that are empirically motivated. Our numerical and analytical results show that self-organization brings about two of the most universally found properties in complex networks: at the mesoscopic scale, the appearance of a community structure, and, at the macroscopic scale, the existence of a power law in the weight distribution of the network interactions. The fact that these properties show up in two models with quantitatively different mechanisms that follow the same general adaptive principles suggests that our results may be generalized to other systems as well, and they may be behind the origin of these properties in some real systems. We also propose a new measure that provides a ranking of the elements in a network in terms of their relevance for the maintenance of collective dynamics. Specifically, we study the vulnerability of the elements under perturbations or large fluctuations, interpreted as a measure of the impact these external events have on the disruption of collective motion. Our results suggest that the dynamic vulnerability measure depends largely on local properties (our conclusions thus being valid for different topologies) and they show a non-trivial dependence of the vulnerability on the connectivity of the network elements. Finally, we propose a strategy for the imposition of generic goal dynamics on a given network, and we explore its performance in networks with different topologies that support turbulent dynamical regimes. It turns out that heterogeneous networks (and most real networks that have been studied belong in this category) are the most suitable for our strategy for the targeting of desired dynamics, the strategy being very effective even when the knowledge on the network topology is far from accurate. Aside from their theoretical relevance for the understanding of collective phenomena in complex systems, the methods and results here discussed might lead to applications in experimental and technological systems, such as in vitro neuronal systems, the central nervous system (where pathological synchronous activity sometimes occurs), communication systems or power grids.

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Purpose – The purpose of this paper is to analyze how team management affects team-learning activities. Design/methodology/approach – The authors empirically study 68 teams as they operate in the natural business context of a major Spanish bank. Quantitative research utilizing multiple regression analyses is used to test hypotheses. Findings – The leadership behaviour (consideration, initiation of structure) displayed by the team leader plays a key role in facilitating team learning. Team leader behaviour characterised by consideration and in particular by initiation of structure are both positively related to team-learning activities. Cross-training of team members also contributes to team-learning behaviour. Research limitations/implications – A specific setting may limit the generalizability of findings. Further research may accordingly investigate to what extent these results can be generalized to other settings or other aspects of team learning. Practical implications – The leadership style adopted by the team leader, as well as cross-training of members, affect team-learning activities. These results link leadership theory to collective learning in teams and organizations, and suggest ways leaders can contribute to improved learning. Originality/value – The study provides new insight into how management of teams facilitates team-learning activities. While consideration is somewhat related to team learning, initiation of structure as well as cross-training appear as key variables.

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The spatial processes deployed by the 15-M movement in Spain include elements of social change that exceed the limits of conventional politics. Located at a liminal level, these processes operate in the often unnoticed realm of the micro-politics of urban everyday life and the regimes of place that regulate it, providing new criteria for understanding sociospatial and urban phenomena. This article shows how public space, its representations and the spatialities associated with them have served as a support for, have determined and, ultimately, have been reshaped and transformed by the Spanish “indignados” (outraged), in particular in the city and the metropolitan area of Madrid. Drawing on a series of theoretical approaches to the articulation of recent revolts, the deployment of a prefigurative politics and the occupation of public space, I will give an experience-based account of the spatial constitution and effects of these connections in and around Madrid’s Puerta del Sol. As a whole, the indignados’ occupations and actions provide urban theory with conceptual and practical tools to imagine alternative forms of collective commitment in the production of spaces of hope for social progress and generalized self-management.

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We report studies of energy transfer from the 800-nm absorbing pigment (B800) to the 850-nm absorbing pigment (B850) of the LH2 peripheral antenna complex and from LH2 to the core antenna complex (LH1) in Rhodobacter (Rb.) sphaeroides. The B800 to B850 process was studied in membranes from a LH2-reaction center (no LH1) mutant of Rb. sphaeroides and the LH2 to LH1 transfer was studied in both the wild-type species and in LH2 mutants with blue-shifted B850. The measurements were performed by using approximately 100-fs pulses to probe the formation of acceptor excitations in a two-color pump-probe measurement. Our experiments reveal a B800 to B850 transfer time of approximately 0.7 ps at 296 K and energy transfer from LH2 to LH1 is characterized by a time constant of approximately 3 ps at 296 K and approximately 5 ps at 77 K. In the blue-shifted B850 mutants, the transfer time from B850 to LH1 becomes gradually longer with increasing blue-shift of the B850 band as a result of the decreasing spectral overlap between the antennae. The results have been used to produce a model for the association between the ring-like structures that are characteristic of both the LH2 and LH1 antennae.

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Traditionally, literature estimates the equity of a brand or its extension but it pays little attention to collective brand equity even though collective branding is increasingly used to differentiate the homogenous products of different firms or organizations. We propose an approach that estimates the incremental effect of individual brands (or the contribution of individual brands) on collective brand equity through the various stages of a consumer hierarchical buying choice process in which decisions are nested: “whether to buy”, “what collective brand to buy” and “what individual brand to buy”. This proposal follows the approach of the Random Utility Theory, and it is theoretically argued through the Associative Networks Theory and the cybernetic model of decision making. The empirical analysis carried out in the area of collective brands in Spanish tourism finds a three-stage hierarchical sequence, and estimates the contribution of individual brands to the equity of the collective brands of “Sun, Sea and Sand” and of “World Heritage Cities”.

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We discuss Fermi-edge singularity effects on the linear and nonlinear transient response of an electron gas in a doped semiconductor. We use a bosonization scheme to describe the low-energy excitations, which allows us to compute the time and temperature dependence of the response functions. Coherent control of the energy absorption at resonance is analyzed in the linear regime. It is shown that a phase shift appears in the coherent control oscillations, which is not present in the excitonic case. The nonlinear response is calculated analytically and used to predict that four wave-mixing experiments would present a Fermi-edge singularity when the exciting energy is varied. A new dephasing mechanism is predicted in doped samples that depends linearly on temperature and is produced by the low-energy bosonic excitations in the conduction band.