An exact approach for the maximum concurrent k-splittable flow problem

We consider the maximization of a multicommodity flow throughput in presence of constraints on the maximum number of paths to be used. Such an optimization problem is strongly NP-hard, and is known in the literature as the maximum routable demand fraction variant of the k-splittable flow problem. Here we propose an exact approach based on branch and bound rules and on an arc-flow mixed integer programming formulation of the problem. Computational results are provided, and a comparison with a standard commercial solver is proposed.     

Multiscale self-organization of the organic semiconductor alpha-quinquethiophene

We show that thin films grown by vacuum sublimation, or formed by melted powders, of semiconductor alpha-quinquethiophene (T5) exhibit a hierarchical self-affinity organization that spans scales from tens of nanometers to hundreds of micrometers. T5 organization was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical microscopy. XRD showed that vacuum-evaporated T5 films were characterized by a preferred orientation of the h00 planes parallel to the glass substrate. Melting of the films followed by rapid quenching to room temperature led to the formation of micrometer-sized, single-crystal-like structures, characterized by uniaxially aligned stripes. XRD proved that the melting-quenching process enhanced molecular ordering and increased the size of domains with the molecule's long axes tilted by about 65 degrees with respect to the substrate plane and piled up side-by-side along parallel columns. AFM measurements on the melt-quenched structures showed that a hierarchical architecture was built by reiteration across multiple length scales of the same recurring motif. Because of the tendency of T5 to form highly crystalline vacuum-evaporated thin films, a field-effect hole mobility comparable to state-of-the-art FET mobility of alpha-sexithiophene films was reached, without any attempt to optimize deposition conditions.     

A new device for reducing diesel engine emissions: a preliminary investigation

A new catalytic converter is compose by a alloy noble metal supported on inert wool and located downstream to combustion chamber appears able to markedly reduce the content of toxic organics, fine particulates and CO emitted by a diesel engine equipped truck. By contrast, emissions of NOx and particulate n-alkanes remain unaltered or increase, according to the driving and operating conditions of the vehicle. Although this tesrs are preliminary the results obtained, however, suggest that the adoption of this device significantly reduce the health risk associated to fine aerosols and carcinogenic PAH. Exhaust concentrations of some unregulated species, e.g. volatile aldehydes, were lowered by the oxidising catalyzer.     

Effect of electron-phonon scattering on shot noise in nanoscale junctions

We investigate the effect of electron-phonon inelastic scattering on shot noise in nanoscale junctions in the regime of quasiballistic transport. We predict that when the local thermal energy of the junction is larger than its lowest vibrational mode energy eV(c), the inelastic contribution to shot noise (conductance) increases (decreases) with bias as V (sqrt[V]). The corresponding Fano factor thus increases as sqrt[V]. We also show that the inelastic contribution to the Fano factor saturates with increasing thermal current exchanged between the junction and the bulk electrodes to a value which, for V > V(c), is independent of bias. These predictions can be readily tested experimentally.     

Rappresentazione ottimale dei numeri reali in un elaboratore

Riassunto Viene studiata una rappresentazione di macchina dei numeri reali che minimizza l'errore relativo di arrotondamento, confrontandola con le rappresentazioni standard in virgola mobile.

---

Summary A computer representation of the real numbers which minimizes the relative rounding error is investigated. Comparison are made with the standard floating point representations.

     

Anti-thyroid drug methimazole: X-ray characterization of two novel ionic disulfides obtained from its chemical oxidation by I(2)

Interaction of methimazole (MMI, 1-methyl-imidazole-2-thione) with I2 in solvents having different polarity gives two new stable compounds containing a dication disulfide and a monocation disulfide arranged in dimers, respectively. These two species could represent effective intermediates in the reaction of MMI with an active iodine species in the thyroid gland and therefore shed more light on the mechanism of action of MMI as an antithyroid drug.     

Novel Thiophenic Copolymer as a Multi-Purpose Macromolecular Intermediate

The preparation of a new thiophenic dimer partially derivatized with a bromohexylic chain is described. Its polymerization under mild oxidative conditions leads to a polythiophene with a degree of functionalization of 50% and highly soluble in organic solvents. The product has been fully characterized by FT-IR, ¹H and ¹³C NMR using one and two-dimensional techniques as well as by SEC and thermal analysis. Solvatochromic effects of the new polymer have been investigated in different mixtures, underlining its self-assembling capability even in solvated states.     

On the design of low-thrust transfers through L1 for the ESMO mission

The following paper summarises the mission analysis studies performed for the phase A of the solar electric propulsion option of the European Student Moon Orbiter (ESMO) mission. ESMO is scheduled to be launched in 2011, as an auxiliary payload on board an Ariane 5. Hence the lack of influence on the launch date. Two methods were devised to assess efficiently wide launch windows for the Earth-Moon transfer, they are presented below. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulating structural transitions by direct transition current sampling: the example of LJ38

Reaction paths and probabilities are inferred, in a usual Monte Carlo or molecular dynamic simulation, directly from the evolution of the positions of the particles. The process becomes time-consuming in many interesting cases in which the transition probabilities are small. A radically different approach consists of setting up a computation scheme where the object whose time evolution is simulated is the transition current itself. The relevant timescale for such a computation is the one needed for the transition probability rate to reach a stationary level, and this is usually substantially shorter than the passage time of an individual system. As an example, we show, in the context of the "benchmark" case of 38 particles interacting via the Lennard-Jones potential ("LJ(38)" cluster), how this method may be used to explore the reactions that take place between different phases, recovering efficiently known results, and uncovering new ones with small computational effort.