Choreographies in Practice

Choreographic Programming is a development methodology for concurrent software that guarantees correctness by construction. The key to this paradigm is to disallow mismatched I/O operations in programs, called choreographies, and then mechanically synthesise distributed implementations in terms of standard process models via a mechanism known as EndPoint Projection (EPP). Despite the promise of choreographic programming, there is still a lack of practical evaluations that illustrate the applicability of choreographies to concrete computational problems with standard concurrent solutions. In this work, we explore the potential of choreographies by using Procedural Choreographies (PC), a model that we recently proposed, to write distributed algorithms for sorting (Quicksort), solving linear equations (Gaussian elimination), and computing Fast Fourier Transform. We discuss the lessons learned from this experiment, giving possible directions for the usage and future improvements of choreography languages

Intraband Optical Spectral Weight in the presence of a van Hove singularity: application to Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

The Kubo single band sum rule is used to determine the optical spectral weight of a tight binding band with further than nearest neighbour hopping. We find for a wide range of parameters and doping concentrations that the change due to superconductivity at low temperature can be either negative or positive. In contrast, the kinetic energy change is always negative. We use an ARPES determined tight binding parametrization of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ to investigate whether this can account for recent observations of a positive change in the spectral weight due to the onset of superconductivity. With this band structure we find that in the relevant doping regime a straightforward BCS calculation of the optical spectral weight cannot account for the experimental observations.Comment: 10 page 9 figure

Model-Independent Sum Rule Analysis Based on Limited-Range Spectral Data

Partial sum rules are widely used in physics to separate low- and high-energy degrees of freedom of complex dynamical systems. Their application, though, is challenged in practice by the always finite spectrometer bandwidth and is often performed using risky model-dependent extrapolations. We show that, given spectra of the real and imaginary parts of any causal frequency-dependent response function (for example, optical conductivity, magnetic susceptibility, acoustical impedance etc.) in a limited range, the sum-rule integral from zero to a certain cutoff frequency inside this range can be safely derived using only the Kramers-Kronig dispersion relations without any extra model assumptions. This implies that experimental techniques providing both active and reactive response components independently, such as spectroscopic ellipsometry in optics, allow an extrapolation-independent determination of spectral weight 'hidden' below the lowest accessible frequency.Comment: 5 pages, 3 figure

Orchestrating Forest Policy in Italy: Mission Impossible?

In the Italian political and economic agenda the forest sector occupies a marginal role. The forest sector in Italy is characterized by a high institutional fragmentation and centralized decision-making processes dominated by Public Forest Administrations. Public participation in forest policy processes has been implemented since the 1990s at national, regional and local levels in several cases. However, today no significant changes have been observed in the overall governance of the forest sector and stakeholders' involvement in Italian forest policy decision-making is still rather limited. The aims of this paper are to describe the state of forest-related participatory processes in Italy at various levels (national, regional and local) and identify which factors and actors hinder or support the establishment and implementation of participatory forest-related processes in the country. The forest-related participatory processes are analyzed adopting a qualitative-based approach and interpreting interactive, complex and non-linear participatory processes through the lens of panarchy theory

On the probability distribution function of small scale interplanetary magnetic field fluctuations

In spite of a large number of papers dedicated to study MHD turbulence in the solar wind there are still some simple questions which have never been sufficiently addressed like: a)do we really know how the magnetic field vector orientation fluctuates in space? b) what is the statistics followed by the orientation of the vector itself? c) does the statistics change as the wind expands into the interplanetary space? A better understanding of these points can help us to better characterize the nature of interplanetary fluctuations and can provide useful hints to investigators who try to numerically simulate MHD turbulence. This work follows a recent paper presented by the same authors. This work follows a recent paper presented by some of the authors which shows that these fluctuations might resemble a sort of random walk governed by a Truncated Leevy Flight statistics. However, the limited statistics used in that paper did not allow final conclusions but only speculative hypotheses. In this work we aim to address the same problem using a more robust statistics which on one hand forces us not to consider velocity fluctuations but, on the other hand allows us to establish the nature of the governing statistics of magnetic fluctuations with more confidence. In addition, we show how features similar to those found in the present statistical analysis for the fast speed streams of solar wind, are qualitatively recovered in numerical simulations of the parametric instability. This might offer an alternative viewpoint for interpreting the questions raised above.Comment: 25pag, 20 jpg small size figures. In press on "ANnales Geophysicae" (September 2004

Hungarian International Development Cooperation: Context, Stakeholders and Performance

This paper explores the domestic and international context of Hungary's emerging international development policy. Specifically, it looks at three factors that may influence how this policy operates: membership in the European Union (EU) and potential ‘Europeanization’, Hungary's wider foreign policy strategy, and the influence of domestic stakeholders. In order to uncover how these factors affect the country's international development policy, semi-structured interviews were carried out with the main stakeholders. The main conclusions are: (1) While accession to the EU did play a crucial role in restarting Hungary's international development policy, the integration has had little effect since then; (2) international development policy seems to serve mainly Hungary's regional strategic foreign policy and economic interests, and not its global development goals; and (3) although all the domestic development stakeholders are rather weak, the Ministry of Foreign Affairs (MFA) still seems to play a dominating role. Convergence with European requirements and best practices is, therefore, clearly hindered by foreign policy interests and also by the weakness of non- governmental stakeholders

Precise and ultrafast molecular sieving through graphene oxide membranes

There has been intense interest in filtration and separation properties of graphene-based materials that can have well-defined nanometer pores and exhibit low frictional water flow inside them. Here we investigate molecular permeation through graphene oxide laminates. They are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves blocking all solutes with hydrated radii larger than 4.5A. Smaller ions permeate through the membranes with little impedance, many orders of magnitude faster than the diffusion mechanism can account for. We explain this behavior by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The ultrafast separation of small salts is attributed to an 'ion sponge' effect that results in highly concentrated salt solutions inside graphene capillaries

AIOCJ: A Choreographic Framework for Safe Adaptive Distributed Applications

We present AIOCJ, a framework for programming distributed adaptive applications. Applications are programmed using AIOC, a choreographic language suited for expressing patterns of interaction from a global point of view. AIOC allows the programmer to specify which parts of the application can be adapted. Adaptation takes place at runtime by means of rules, which can change during the execution to tackle possibly unforeseen adaptation needs. AIOCJ relies on a solid theory that ensures applications to be deadlock-free by construction also after adaptation. We describe the architecture of AIOCJ, the design of the AIOC language, and an empirical validation of the framework.Comment: Technical Repor

Deciphering solar turbulence from sunspots records

It is generally believed that sunspots are the emergent part of magnetic flux tubes in the solar interior. These tubes are created at the base of the convection zone and rise to the surface due to their magnetic buoyancy. The motion of plasma in the convection zone being highly turbulent, the surface manifestation of sunspots may retain the signature of this turbulence, including its intermittency. From direct observations of sunspots, and indirect observations of the concentration of cosmogenic isotopes $^{14}$C in tree rings or $^{10}$Be in polar ice, power spectral densities in frequency are plotted. Two different frequency scalings emerge, depending on whether the Sun is quiescent or active. %magnetic activity is maximum or minimum. From direct observations we can also calculate scaling exponents. These testify to a strong intermittency, comparable with that observed in the solar wind.Comment: 5 pages, 6 figures, accepted for publication in MNRAS Letter