Invariant zeros of linear systems connected in series

In this paper, relationships are presented between the invariant zeros of two linear time-invariant systems to be connected in series, and those of the series connection of them.     

Electronic Structure Calculations Using Self-Adaptive Multiscale Voronoi Basis Functions

The multiscale self-adaptivity of Voronoi basis functions is currently proving to be useful for the simulation of complex fluid systems involving structures on a number of distinct lengthscales. In this paper, we explore the possibility of extending the use of such multiscale basis functions to the framework of density functional theoretic electronic structure computations.     

Towards a mesoscopic model of water-like fluids with hydrodynamic interactions

We present a mesoscopic lattice model for non-ideal fluid flows with directional interactions, mimicking the effects of hydrogen bonds in water. The model supports a rich and complex structural dynamics of the orientational order parameter, and exhibits the formation of disordered domains whose size and shape depend on the relative strength of directional order and thermal diffusivity. By letting the directional forces carry an inverse density dependence, the model is able to display a correlation between ordered domains and low density regions, reflecting the idea of water as a denser liquid in the disordered state than in the ordered one.     

Phase-field model of long-time glasslike relaxation in binary fluid mixtures

We present a new phase-field model for binary fluids, exhibiting typical signatures of soft-glassy behavior, such as long-time relaxation, aging, and long-term dynamical arrest. The present model allows the cost of building an interface to vanish locally within the interface, while preserving positivity of the overall surface tension. A crucial consequence of this property, which we prove analytically, is the emergence of free-energy minimizing density configurations, hereafter named "compactons," to denote their property of being localized to a finite-size region of space and strictly zero elsewhere (no tails). Thanks to compactness, any arbitrary superposition of compactons still is a free-energy minimizer, which provides a direct link between the complexity of the free-energy landscape and the morphological complexity of configurational space.     

Translocation of biomolecules through solid‐state nanopores: Theory meets experiments

The interest in polynucleotide translocation through nanopores has moved from purely biological to the need of realizing nanobiotechnological applications related to personalized genome sequencing. Polynucleotide translocation is a process in which biomolecules, like DNA or RNA, are electrophoretically driven through a narrow pore and their passage can be monitored by the change in the ionic current through the pore. Such a translocation process, which will be described here offers a very promising technology aiming at ultra‐fast low‐cost sequencing of DNA, though its realization is still confronted with challenges and drawbacks. In this review, we present the main aspects involved in the polynucleotide translocation through solid‐state nanopores by discussing the most relevant experimental, theoretical, and computational approaches and the way these can supplement each other. The discussion will expose the goals that have been reached so far, the open questions, and contains an outlook to the future of nanopore sequencing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 985–1011, 2011     

Heterogeneous diffuse interfaces: a new mechanism for arrested coarsening in binary mixtures. Heterogeneous diffuse interfaces

We discuss the dynamics of binary fluid mixtures in which surface tension density is allowed to become locally negative within the interface, while still preserving positivity of the overall surface tension (heterogeneous diffuse interface). Numerical simulations of two-dimensional Ginzburg-Landau phase field equations implementing such mechanism and including hydrodynamic motion, show evidence of dynamically arrested domain coarsening. Under specific conditions on the functional form of the surface tension density, dynamical arrest can be interpreted in terms of the collective dynamics of metastable, non-linear excitations of the density field, named compactons, as they are localized to finite-size regions of configuration space and strictly zero elsewhere. Aside from compactons, the heterogeneous diffuse interface scenario appears to provide a robust mechanism for the interpretation of many aspects of soft-glassy behaviour in binary fluid mixtures.     

A note on equilibrium boundary conditions in lattice Boltzmann fluid dynamic simulations

It is shown that Lattice Boltzmann (LB) simulations using simple equilibrium boundary conditions at solid walls, provide quantitatively accurate results for backward-facing step flows at moderate Reynolds numbers. The basic reason for such favorable behavior is that well-resolved LB simulations operate in the so-called weak non-equilibrium regime, in which shear effects at the scale of a single lattice spacing are weak, meaning by this that the cell-shear time scale is much longer than the molecular time scales, so that the LB collisional relaxation takes place in a quasi-homogeneous velocity field. Due to their simplicity, it is suggested that equilibrium boundary conditions may represent a viable option for the LB simulation of complex flows with solid boundaries at moderate Reynolds numbers.     

Alternative precursors for MOVPE growth of InN and GaN at low temperature

We report on the use of dimethylhydrazine (DMHy) and tertiarybuthylhydrazine (TBHy), as alternative nitrogen precursor for GaN low-temperature growth, as well as to improve the InN growth rate. Lowering the GaN growth temperature, would allow growing InN/GaN heterostructures by MOVPE, without damaging the InN layers. Increasing the low InN MOVPE growth rate is of major importance to grow reasonably thick InN layers. In this respect, triethylindium (TEIn) was also used as an alternative to trimethylindium (TMIn).     

InN excitonic deformation potentials determined experimentally

We report the experimental determination of the interband deformation potentials of indium nitride by combining both optical spectroscopy investigations and high-resolution X-ray measurements performed on a series of InN films grown by metal organic vapour-phase epitaxy. Our approach, which follows the one used for GaN by Shan et al. [Phys. Rev. B. 54 (1996) 13460], gives here for InN a₁=−7.66 eV, a₂=−2.59 eV, b₁=5.06 eV, and b₂=−2.53 eV.     

Flow through geometrically irregular media with lattice gas automata

Summary The determination of the permeability is an interesting problem of fluid dynamics of wide interdisciplinary concern. Many authors approached this subject by developing numerical models of flows through porous media at either macro-scale and micro-scale. According to the latter point of view, we present in this paper a verification of Darcy's law and a first determination of the permeability starting by the knowledge of the microstructure of a three-dimensional random medium. The flow is here reproduced by using a particular class of cellular automata with the Boltzmann approximation.

---

Sommario La determinazione del coefficiente di permeabilità rappresenta un interessante problema comune a molte discipline. Tale determinazione viene affrontata dai diversi autori o tramite la conoscenza di grandezze macroscopiche — come la resistività o la porositá — ovvero partendo dalla conoscenza della microstruttura del mezzo poroso e cercando di simulare il processo di moto fluido che si svolge lungo i canalicoli del mezzo stesso. Seguendo quest'ultimo punto di vista, viene qui di seguito presentata una tecnica alternativa per la verifica della legge di Darcy e, quindi, per una prima valutazione del coefficiente di permeabilità per un mezzo tridimensionale complesso. La simulazione dei moti fluidi viene effettuata tramite una particolare classe di gas reticolari che evolvono secondo le regole degli automi cellulari.