113,891 research outputs found

    Irreversible thermodynamics of creep in crystalline solids

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    We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a non-hydrostatically stressed multi-component solid medium with non-conserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general expression for the entropy production rate and use it to identify of the relevant fluxes and driving forces and to formulate phenomenological relations among them taking into account symmetry properties of the material. As a simple application, we analyze a one-dimensional model of a bicrystal in which the grain boundary acts as a sink and source of vacancies. The kinetic equations of the model describe a creep deformation process accompanied by grain boundary migration and relative rigid translations of the grains. They also demonstrate the effect of grain boundary migration induced by a vacancy concentration gradient across the boundary

    The impact of cultural diversity on firm innovation: evidence from Dutch micro-data

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    An important question for firms and policy makers is whether the recruitment of foreign workers can boost innovation. Migration studies have demonstrated positive economic impacts of cultural diversity on productivity and innovation at the regional level, but the impacts at firm level are less well known. Merging data from four different sources, provided by Statistics Netherlands, we construct and analyze a unique linked employer-employee micro dataset of 4582 firms that includes qualitative information on firm innovation. We consider both the number of immigrants these firms employ and their cultural diversity. Potential endogeneity of migrant employment is addressed by an instrumental variables approach that accounts for the past geographic distribution of immigrants and the past culinary diversity of the municipality the firm is located in. We find robust evidence that firms employing relatively more migrants are less innovative. However, there is evidence of integration in that this effect is generally less strong or even absent for second generation immigrants. Moreover, firms employing a more diverse foreign workforce are more innovative, particularly in terms of product innovations. The benefits of diversity for innovation are more apparent in sectors employing relatively more skilled immigrants

    EU Enlargement, Migration and the New Constitution

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    The paper deals with the effects of migration resulting from EU Eastern enlargement on the welfare states of Western Europe. Although migration is good in principle, as it yields gains from trade and specialization for all countries involved, it does so only if it meets with flexible labour markets and if it is not artificially induced by gifts from the welfare state. This is not the present state of affairs in Western Europe. In addition to measures that make labour markets more flexible, the introduction of delayed integration of working migrants and the home country principle for non-working migrants is a rational reaction of the state. The proposed new EU constitution which contains far-reaching rules for a European social union should be amended accordingly.EU enlargement, migration, EU constitution, social union

    Refining self-propelled particle models for collective behaviour

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    Swarming, schooling, flocking and herding are all names given to the wide variety of collective behaviours exhibited by groups of animals, bacteria and even individual cells. More generally, the term swarming describes the behaviour of an aggregate of agents (not necessarily biological) of similar size and shape which exhibit some emergent property such as directed migration or group cohesion. In this paper we review various individual-based models of collective behaviour and discuss their merits and drawbacks. We further analyse some one-dimensional models in the context of locust swarming. In specific models, in both one and two dimensions, we demonstrate how varying the parameters relating to how much attention individuals pay to their neighbours can dramatically change the behaviour of the group. We also introduce leader individuals to these models with the ability to guide the swarm to a greater or lesser degree as we vary the parameters of the model. We consider evolutionary scenarios for models with leaders in which individuals are allowed to evolve the degree of influence neighbouring individuals have on their subsequent motion

    On the suitability and development of layout templates for analog layout reuse and layout-aware synthesis

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    Accelerating the synthesis of increasingly complex analog integrated circuits is key to bridge the widening gap between what we can integrate and what we can design while meeting ever-tightening time-to-market constraints. It is a well-known fact in the semiconductor industry that such goal can only be attained by means of adequate CAD methodologies, techniques, and accompanying tools. This is particularly important in analog physical synthesis (a.k.a. layout generation), where large sensitivities of the circuit performances to the many subtle details of layout implementation (device matching, loading and coupling effects, reliability, and area features are of utmost importance to analog designers), render complete automation a truly challenging task. To approach the problem, two directions have been traditionally considered, knowledge-based and optimization-based, both with their own pros and cons. Besides, recently reported solutions oriented to speed up the overall design flow by means of reuse-based practices or by cutting off time-consuming, error-prone spins between electrical and layout synthesis (a technique known as layout-aware synthesis), rely on a outstandingly rapid yet efficient layout generation method. This paper analyses the suitability of procedural layout generation based on templates (a knowledge-based approach) by examining the requirements that both layout reuse and layout-aware solutions impose, and how layout templates face them. The ability to capture the know-how of experienced layout designers and the turnaround times for layout instancing are considered main comparative aspects in relation to other layout generation approaches. A discussion on the benefit-cost trade-off of using layout templates is also included. In addition to this analysis, the paper delves deeper into systematic techniques to develop fully reusable layout templates for analog circuits, either for a change of the circuit sizing (i.e., layout retargeting) or a change of the fabrication process (i.e., layout migration). Several examples implemented with the Cadence's Virtuoso tool suite are provided as demonstration of the paper's contributions.Ministerio de Educación y Ciencia TEC2004-0175

    Market integration in China

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    Over the last three decades, China's product, labor, and capital markets have become gradually more integrated within its borders, although integration has been significantly slower for capital markets. There remains a significant urban-rural divide, and Chinese cities tend to be under-sized by international standards. China has also integrated globally, initially through the Special Economic Zones on the coast as launching grounds to connect with world markets, and subsequently through the accession to the World Trade Organization. For future policy considerations, this paper argues that its economic production needs to be spatially concentrated, and its social services need to be spread out to the interior to ensure harmonious development and domestic integration (through inclusive rural-urban transformations and effective territorial development).Economic Theory&Research,Banks&Banking Reform,Debt Markets,Emerging Markets,Access to Finance

    Return migration as channel of brain gain

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    Recent theoretical and empirical studies have emphasized the fact that the prospect of international migration increases the expected returns to skills in poor countries, linking the possibility of migrating (brain drain) with incentives to higher education (brain gain). If emigration is uncertain and some of the highly educated remain, such a channel may, at least in part, counterbalance the negative effects of brain drain. Moreover, recent empirical evidence seems to show that temporary migration is widespread among highly skilled migrants (such as Eastern Europeans in Western Europe and Asians in the U.S.). This paper develops a simple tractable overlapping generations model that provides an economic rationale for return migration and which predicts who will migrate and who will return among agents with heterogeneous abilities. We use parameter values from the literature and the data on return migration to calibrate our model and simulate and quantify the effects of increased openness on human capital and wages of the sending countries. We find that, for plausible values of the parameters, the return migration channel is very important and combined with the incentive channel reverses the brain drain into significant brain gain for the sending country
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