Diffusive Atomistic Dynamics of Edge Dislocations in Two Dimensions

The fundamental dislocation processes of glide, climb, and annihilation are studied on diffusive time scales within the framework of a continuum field theory, the Phase Field Crystals (PFC) model. Glide and climb are examined for single edge dislocations subjected to shear and compressive strain, respectively, in a two dimensional hexagonal lattice. It is shown that the natural features of these processes are reproduced without any explicit consideration of elasticity theory or ad hoc construction of microscopic Peierls potentials. Particular attention is paid to the Peierls barrier for dislocation glide/climb and the ensuing dynamic behavior as functions of strain rate, temperature, and dislocation density. It is shown that the dynamics are accurately described by simple viscous motion equations for an overdamped point mass, where the dislocation mobility is the only adjustable parameter. The critical distance for the annihilation of two edge dislocations as a function of separation angle is also presented.Comment: 13 pages with 17 figures, submitted to Physical Review

Generic Model and Architecture for Cooperating Objects in Sensor Network Environments

The complexity and heterogeneity of cooperating object applications in ubiquitous environments or of applications in the sensor network domain require the use of generic models and architectures. These architectures should provide support for the following three key issues: flexible installation, management and reconfiguration of components in the system; optimization strategies whose implementation usually involves the proper management of cross-layer information; and proper adaptation techniques that allow for the self-configuration of nodes and components in the system with minimal human intervention. In this paper, we present one possible instance of such a generic model and architecture and show its applicability using Sustainable Bridges, a sensor network application that requires the analysis of complex sensor data to achieve its goal of effectively monitoring bridges for the detection of structural defects

Vortex dynamics in disordered Josephson junction arrays: from plastic flow to flux flow

We study the dynamics of Josephson junction arrays with positional disorder and driven by an external current. We consider weak magnetic fields, corresponding to a frustration $f=n+1/25$ with $n$ integer. We find that above the critical current $i_c$ there is a plastic flow of vortices, where most of the vortices are pinned and only a few vortices flow through channels. This dynamical regime is characterized by strong fluctuations of the total vorticity. The number of the flow channels grow with increasing bias current. At larger currents there is a dynamical regime characterized by the homogeneous motion of all the vortices, i.e. a flux flow regime. We find a dynamical phase transition between the plastic flow and the flux flow regimes when analyzing voltage-voltage correlation functions.Comment: 9 pages. 3 Figures available upon request. Presented in the Workshop on Josephson Junction Arrays, ICTP (August 1995). To appear in Physica B (1996

Current-induced vortex dynamics in Josephson-junction arrays: Imaging experiments and model simulations

We study the dynamics of current-biased Josephson-junction arrays with a magnetic penetration depth smaller than the lattice spacing. We compare the dynamics imaged by low-temperature scanning electron microscopy to the vortex dynamics obtained from model calculations based on the resistively-shunted junction model, in combination with Maxwell's equations. We find three bias current regions with fundamentally different array dynamics. The first region is the subcritical region, i.e. below the array critical current I_c. The second, for currents I above I_c, is a "vortex region", in which the response is determined by the vortex degrees of freedom. In this region, the dynamics is characterized by spatial domains where vortices and antivortices move across the array in opposite directions in adjacent rows and by transverse voltage fluctuations. In the third, for still higher currents, the dynamics is dominated by coherent-phase motion, and the current-voltage characteristics are linear.Comment: 10 pages, with eps figures. To appear in Phys. Rev.

Magnetic Field Effect in a Two-dimensional Array of Short Josephson Junctions

We study analytically the effect of a constant magnetic field on the dynamics of a two dimensional Josephson array. The magnetic field induces spatially dependent states and coupling between rows, even in the absence of an external load. Numerical simulations support these conclusions

Renegotiating and Overcoming Frontiers and Constituting Crosscutting and Overlapping Social Spaces and Institutions: Conceptual and Methodological Issues in Development

Die Autorin erörtert konzeptionelle und methodologische Aspekte der geschlechtsspezifischen Strukturierung von Entwicklungspolitiken im Hinblick auf die Handlungsmacht sowie die Wissensproduktion und Konstitution von sozialen Räumen. Sie beleuchtet hierzu die Alltagspraxis der Beziehungen zwischen Staat und Zivilgesellschaft in verschiedenen Ländern Westafrikas im Sinne der Herstellung von Translokalität. Dabei geht es zum einen um die Interaktion und die Dynamiken an den Schnittstellen zwischen Behörden und staatlichen Dienstleistungen mit Gemeinderäten, Klienten und zivilgesellschaftlichen Organisationen, die partizipative Räume der Aushandlung von Konzepten darstellen. Zum anderen werden die Machtstrukturen und die Konstruktion von Systemen des Nichtwissens hinsichtlich der Produktion von entwicklungsrelevantem und lokalem Wissen sowie der staatlich gesteuerten Einführung neuer Formen der lokalen Demokratie in den Blick genommen. Im Mittelpunkt steht die Frage, ob eine Restrukturierung der Öffentlichkeit im Sinne von multiplen, sich überlappenden sozialen Räumen und der kritischen Aushandlung von Wissen aus den verschiedenen Arenen hinsichtlich eines Feedbacks zu lokaler Selbstverwaltung, staatlichen Behörden und Diensten stattfindet. (ICI

Broken symmetry of row switching in 2D Josephson junction arrays

We present an experimental and theoretical study of row switching in two-dimensional Josephson junction arrays. We have observed novel dynamic states with peculiar percolative patterns of the voltage drop inside the arrays. These states were directly visualized using laser scanning microscopy and manifested by fine branching in the current-voltage characteristics of the arrays. Numerical simulations show that such percolative patterns have an intrinsic origin and occur independently of positional disorder. We argue that the appearance of these dynamic states is due to the presence of various metastable superconducting states in arrays.Comment: 4 Pages, 6 Figure

Transnationalisation and development - methodological issues

Am 31. Mai und 1. Juni 2007 fand im Bielefelder Zentrum für interdisziplinäre Forschung (ZIF) die Konferenz "Transnationalisation and Development(s): Towards a North-South Perspective" statt. Die Tagung brachte deutsche und internationale Wissenschaftlerinnen und Wissenschaftler aus verschiedenen Fachrichtungen (Soziologie, Politikwissenschaft, Wirtschaftswissenschaften, Ethnologie) zusammen. Ziel war es, auf dem Ansatz der Transnationalen Sozialen Räume aufzubauen, um Akkomodation im Rahmen von diskursiven, sozialräumlichen und institutionellen Grenzveränderungen zu analysieren. Der vorliegende Beitrag stellt die Beiträge zum Panel I (Concepts and Methodology: The Transnational Turn) vor und diskutiert sie kritisch. Im Zentrum der Beiträge standen folgende Fragen: Welche Hauptelemente der sozialen, wirtschaftlichen und politischen Entwicklungen jenseits des "methodologischen Nationalismus" lassen sich ausmachen? Welches Verständnis von Raum liegt dem Konzept des Transnationalismus zu Grunde? Was sind die Gemeinsamkeiten und Unterschiede zwischen einer transnationalen Perspektive und den Globalisierungstheorien? Sind transnationale soziale Räume Konglomerate wirtschaftlicher, kultureller und politischer Strukturen, die anderen Formen der Integration widersprechen oder diese ergänzen? Wie nützlich sind transnationale Ansätze für die Analyse des Verhältnisses von Migration und Entwicklung? (ICD

Engendering embeddedness of economy in society and culture

Die Autorin setzt sich für eine Einbeziehung der Kategorie Geschlecht in die Entwicklungstheorie und Entwicklungspolitik ein. Die grundlegenden Veränderungen in Wirtschaft, Kultur und Gesellschaft in den Entwicklungsländern während der letzten Dekade sollten aus einer geschlechtsspezifischen Perspektive betrachtet werden, insbesondere für die Bereiche Partizipation, 'Good Governance', Strukturanpassung, 'Capacity Building' und Zivilgesellschaft. Durch den Gender-Ansatz bei der Erforschung der wichtigen Prozesse von Dezentralisierung und Demokratisierung kann der Gegensatz zwischen Gleichheit und Effizienz überwunden werden. Die Autorin verdeutlicht ihre Ausführungen durch empirische Beispiele aus ihrer eigenen Forschungstätigkeit in Kamerun und Senegal. Um die geschlechtsbezogene Verankerung der Ökonomie aufzuzeigen, nimmt sie eine analytische Annäherung an die Strukturierung von Märkten und die Beziehung zwischen dem reproduktiven, informellen Sektor und der formalen Ökonomie vor. (ICI

Decentralisation and civil society: negotiating local development in West Africa

"The paper, referring to fieldwork i.a. in Senegal, challenges the concept of decentralisation by regarding the interface of knowledge systems at the local rural arena. It is asked whether there is a process of marginalisation of knowledge which had been acquired and generated these last years by peasant organisations and women's movements after the breakdown of the authoritarian development State. Applying an agency and gender perspective, it is asked how decentralisation is conceived of by various types of local and especially female actors - including the elected rural councillors - as access to development information from which they are again excluded and therefore obliged to renegotiate. On the other side, their conceptions and experiences of sustainable development including social and food security are devaluated and not made use of in newly designed blueprints of local development plans which are said to be elaborated by participatory procedures, thereby challenging good governance through interaction with other levels." (author's abstract