Quantum Monte Carlo Study of electrons in low dimensions

We report on a diffusion Monte Carlo investigation of model electron systems in low dimensions, which should be relevant to the physics of systems obtainable nowadays in semiconductor heterostructures. In particular, we present results for a one dimensional electron gas, at selected values of the coupling strength and confinement parameter, briefly analyzing the pair correlations and relating them to predictions by Schulz for a Luttinger liquid with long-range interactions. We find no evidence of the the Bloch instability yielded by approximate treatments such as the STLS and DFT schemes.Comment: 6 pages, 3 figures. To appear in the proceedings of the 1999 International Conference on Strongly Coupled Coulomb Systems, Saint-Malo, Franc

A geographical issue: the contribution of Citizenship Education to the building of a European citizenship. The case of the VOICEs Comenius network

Citizenship Education is currently a consolidated issue within several European curricula. It has been integrated in national educational laws in different ways: as cross-curricular education (UK, Italy), as a subject (France, Spain) or as a skill (Ireland). Despite these differences, there is a common agreement on the ethical value of Citizenship Education and on its main aim: to foster students’ sense of local, national and European citizenship. In some ways this goal has been inspired by Morin’s path to a “plural” education and a planetary citizenship (Morin, 2000). Social sciences, and in particular Geography and History, keep the function of giving tools able to show how a dialogue among the different scales is possible. Nevertheless European citizenship is undergoing a constant redefinition due to the European enlargement process, the role of Europe inside national jurisdictions and to the changes in national curricula. This evolution directly affects the guiding function conferred to school in terms of skills, aims and themes; therefore competences and methods adopted by teachers may have to be reconsidered. This essay presents the first results of the updating of the state of the art of this issue that has been carried out by the Citizenship Education Research Group of the VOICEs Comenius network (The Voice of European Teachers). The main aim of this international research group is to face the challenge of building a European citizenship by developing a comparative analysis of teachers’ practices and strategies in different local, regional and national contexts, aiming to contribute, with renewed ideas, to the debate on this promising field of research

Two-Loop Corrections to Large Order Behavior of φ4\varphi^4 Theory

We consider the large order behavior of the perturbative expansion of the scalar $\varphi^4$ field theory in terms of a perturbative expansion around an instanton solution. We have computed the series of the free energy up to two-loop order in two and three dimension. Topologically there is only an additional Feynman diagram with respect to the previously known one dimensional case, but a careful treatment of renormalization is needed. The propagator and Feynman diagrams were expressed in a form suitable for numerical evaluation. We then obtained explicit expressions summing over $O(10^3)$ distinct eigenvalues determined numerically with the corresponding eigenfunctions.Comment: 12 pages, 2 figure

Plastic number and possible optimal solutions for an Euclidean 2-matching in one dimension

In this work we consider the problem of finding the minimum-weight loop cover of an undirected graph. This combinatorial optimization problem is called 2-matching and can be seen as a relaxation of the traveling salesman problem since one does not have the unique loop condition. We consider this problem both on the complete bipartite and complete graph embedded in a one dimensional interval, the weights being chosen as a convex function of the Euclidean distance between each couple of points. Randomness is introduced throwing independently and uniformly the points in space. We derive the average optimal cost in the limit of large number of points. We prove that the possible solutions are characterized by the presence of "shoelace" loops containing 2 or 3 points of each type in the complete bipartite case, and 3, 4 or 5 points in the complete one. This gives rise to an exponential number of possible solutions scaling as p^N , where p is the plastic constant. This is at variance to what happens in the previously studied one-dimensional models such as the matching and the traveling salesman problem, where for every instance of the disorder there is only one possible solution.Comment: 19 pages, 5 figure

Investigation of refractory composites for liquid rocket engines Final report, 1 Oct. 1969 - 31 Oct. 1970

Oxidation resistance and high temperature tests of rhenium, tungsten, hafnium, and tantalum matrix composites with iridium in oxygen, fluorine, and boron atmospheres for liquid propellant engine

Exact value for the average optimal cost of bipartite traveling-salesman and 2-factor problems in two dimensions

We show that the average cost for the traveling-salesman problem in two dimensions, which is the archetypal problem in combinatorial optimization, in the bipartite case, is simply related to the average cost of the assignment problem with the same Euclidean, increasing, convex weights. In this way we extend a result already known in one dimension where exact solutions are avalaible. The recently determined average cost for the assignment when the cost function is the square of the distance between the points provides therefore an exact prediction $$\overline{E_N} = \frac{1}{\pi}\, \log N$$ for large number of points $2N$. As a byproduct of our analysis also the loop covering problem has the same optimal average cost. We also explain why this result cannot be extended at higher dimensions. We numerically check the exact predictions.Comment: 5 pages, 3 figure

Reversa

1 archivo PDF (5 páginas). tyvlxxi

International actors as policymakers? Discussing the influence of international actors on the environmental policies of small island states

The environmental discourse on small island states is structured around a set of geographical categories. Among these, the category of smallness reflects the assumption that such spaces are vulnerable on account of their reduced size, reinforcing an image of islands as ‘prone’ to environmental threats and in need of ‘external support’. Such support is often provided by international actors, specifically international agencies, NGOs and sponsors, who consequently influence domestic policymaking processes. This paper offers a theoretical discussion of this influence in relation to environmental policies, drawing on concepts from the fields of international studies, development studies and island studies. I argue that the influence of international actors may be viewed as a form of leadership that is legitimised by the narrative of island vulnerability, the development paradigm, the authority attributed to reports and rankings, the symbolic functioning of global environmental threats and the overuse of geographical categories such as ‘small’ or ‘developing’. In the second part of the paper, I propose four research questions for future studies on the political outputs of this influence in the Republic of Maldives: an icon of the environmental challenges threatening small island states.peer-reviewe

Molecular imaging in nanomedical research

For years, nanomedical research has represented a challenge and an opportunity in terms of imaging techniques [...]