Showing papers by "Romanian Academy published in 2006"

Spiking Neural P Systems

Abstract: This paper proposes a way to incorporate the idea of spiking neurons into the area of membrane computing, and to this aim we introduce a class of neural-like P systems which we call spiking neural P systems (in short, SN P systems). In these devices, the time (when the neurons fire and/or spike) plays an essential role. For instance, the result of a computation is the time between the moments when a specified neuron spikes. Seen as number computing devices, SN P systems are shown to be computationally complete (both in the generating and accepting modes, in the latter case also when restricting to deterministic systems). If the number of spikes present in the system is bounded, then the power of SN P systems falls drastically, and we get a characterization of semilinear sets. A series of research topics and open problems are formulated.

Phosphorylation of polysaccharides: New results on synthesis and characterisation of phosphorylated cellulose

Abstract: New results regarding the synthesis and characterization of water-soluble phosphorylated cellulose by reaction of microcrystalline cellulose with phosphorous acid in molten urea are presented. The maximal value of DS attained by this method was about 1. By elemental analysis of phosphorous, titration of acidic groups and IR spectra the structure of monobasic cellulose phosphate was demonstrated. The results of elemental analysis are in agreement with those obtained by potentiometric or conductometric titration so that the potentiometric titration is proposed as a convenient and rapid method for the evaluation of the substitution degree. The thermal behavior and the ability to influence the separation of sparingly soluble salts were examined in view of the use of phosphorylated cellulose in the control of biomineralization processes or as additive in the preparation of hydroxyapatite or other inorganic salts by hydrothermal method.

Geochronology of Neogene magmatism in the Carpathian arc and intra-Carpathian area

Abstract: Neogene to Quaternary volcanism in the Carpathian-Pannonian Region was related to the youngest evolutionary stage of the Carpathian arc and the intra-Carpathian area, with subduction, extension and asthenospheric upwelling as the main driving mechanisms. Volcanism occurred between 21 and 0.1 Ma, and showed a distinct migration in time from West to East. Several groups of calc-alkaline magmatic rock-types (felsic, intermediate and mafic varieties) have been distinguished, and several minor alkalic types also occur, including shoshonitic, K-trachytic, ultrapotassic and alkali basaltic. On the basis of spatial distribution, relationship to tectonic processes and their chemical composition, the volcanic formations can be divided into: (1) areally distributed felsic calc-alkaline formations related to the initial stages of back-arc extension, (2) areally distributed intermediate calc-alkaline formations related to advanced stages of back-arc extension, (3) "arc-type" andesite volcanic formations with a complex relationship to subduction processes, and (4) alkali basaltic magmatism related to post-convergence extension. Petrological data and geotectonic reconstructions, which involve these magmatic groups, place significant con- straints on geodynamic models of the Carpathian-Pannonian area. Subduction and back-arc extension were not contempora- neous across the whole Carpathian arc and intra-Carpathian area. Instead, three major geographical segments can be defined (Western, Central, Eastern segments) with a progressively younger timing of subduction roll-back and back-arc extension: 21—11 Ma, 16—9 Ma, 14—0 Ma, respectively. Short-lived subduction-related volcanic activity can be interpreted as either an indication of a limited width of subducted crust (not greater than 200 km) or an indication of detachment of the sinking slab. Interpretation of the areally distributed felsic and intermediate calc-alkaline volcanic formations are considered as being initiated by back-arc extension induced by diapiric uprise of "fertile" asthenospheric material.

Analysis of the Swirling Flow Downstream a Francis Turbine Runner

Abstract: An experimental and theoretical investigation of the flow at the outlet of a Francis turbine runner is carried out in order to elucidate the causes of a sudden drop in the draft tube pressure recovery coefficient at a discharge near the best efficiency operating point. Laser Doppler anemometry velocity measurements were performed for both axial and circumferential velocity components at the runner outlet. A suitable analytical representation of the swirling flow has been developed taking the discharge coefficient as independent variable. It is found that the investigated mean swirling flow can be accurately represented as a superposition of three distinct vortices. An eigenvalue analysis of the linearized equation for steady, axisymmetric, and inviscid swirling flow reveals that the swirl reaches a critical state precisely (within 1.3%) at the discharge where the sudden variation in draft tube pressure recovery is observed. This is very useful for turbine design and optimization, where a suitable runner geometry should avoid such critical swirl configuration within the normal operating range.

Introduction to Membrane Computing

Abstract: This is a comprehensive (and friendly) introduction to membrane computing (MC), meant to offer both computer scientists and non-computer scientists an up-to-date overview of the field. That is why the set of notions introduced here is rather large, but the presentation is informal, without proofs and with rigorous definitions given only for the basic types of P systems — symbol object P systems with multiset rewriting rules, systems with symport/antiport rules, systems with string objects, tissue-like P systems, and neural-like P systems. Besides a list of (biologically inspired or mathematically motivated) ingredients/features which can be used in systems of these types, we also mention a series of results, as well as a series of research trends and topics.

Spike trains in spiking neural p systems

Abstract: We continue here the study of the recently introduced spiking neural P systems, which mimic the way that neurons communicate with each other by means of short electrical impulses, identical in shape (voltage), but emitted at precise moments of time. The sequence of moments when a neuron emits a spike is called the spike train (of this neuron); by designating one neuron as the output neuron of a spiking neural P system II, one obtains a spike train of II. Given a specific way of assigning sets of numbers to spike trains of II, we obtain sets of numbers computed by II. In this way, spiking neural P systems become number computing devices. We consider a number of ways to assign (code) sets of numbers to (by) spike trains, and prove then computational completeness: the computed sets of numbers are exactly Turing computable sets. When the number of spikes present in the system is bounded, a characterization of semilinear sets of numbers is obtained. A number of research problems is also formulated.

Membrane Computing and Economics: Numerical P Systems

Abstract: With inspiration from the economic reality, where numbers are basic entities to work with, we propose a genuinely new kind of P systems, where numerical variables evolve, starting from initial values, by means of production functions and repartition protocols. We prove that non-deterministic systems of this type, using polynomial production functions, characterize the Turing computable sets of natural numbers, while deterministic systems, with polynomial production functions having non-negative coefficients, compute strictly more than semilinear sets of natural numbers. A series of research topics to be addressed in this framework are mentioned.

New polypyrrole-multiwall carbon nanotubes hybrid materials

Abstract: We report the synthesis and characterization of new hybrid materials based on conducting polypyrrole (PPY) and multi wall carbon nanotubes (MWCNTs). MWCNTs were prepared by spray-pyrolysis of liquid hydrocarbon-ferrocene solution in an Ar atmosphere. The composites (PPY-CNT) were obtained by in-situ chemical oxidative polymerization of pyrrole in aqueous solution containing MWCNTs. The addition of a water based Fe 3 O 4 nanofluid to the polymerization solution results in the formation of a new hybrid nanostructure of MWCNTs coated with PPY containing magnetic nanoparticles. The properties of PPY composites were investigated by TEM, SEM, FTIR spectroscopy and X-ray diffraction (XRD) measurements. MWCNTs covered with PPY have a rough surface, containing some globular forms typical for the polymer. Significant differences between IR spectra for PPY and PPY-CNT nanocomposites appear for the bands ascribed to pyrrole ring vibrations, suggesting that an interaction between the polymer and CNT occurs and this could change the polymer conformation. XRD analysis shows that the crystalline structure of MWCNTs doesn't change significantly by the association with conducting PPY.

Membrane computing: Brief introduction, recent results and applications

Abstract: The internal organization and functioning of living cells, as well as their cooperation in tissues and higher order structures, can be a rich source of inspiration for computer science, not fully exploited at the present date. Membrane computing is an answer to this challenge, well developed at the theoretical (mathematical and computability theory) level, already having several applications (via usual computers), but without having yet a bio-lab implementation. After briefly discussing some general issues related to natural computing, this paper provides an informal introduction to membrane computing, focused on the main ideas, the main classes of results and of applications. Then, three recent achievements, of three different types, are briefly presented, with emphasis on the usefulness of membrane computing as a framework for devising models of interest for biological and medical research.

Critical Analysis of the Isoconversional Methods for Evaluating the Activation Energy. I. Theoretical background

Abstract: It is demonstrated that, if the activation energy depends on the degree of conversion, its values obtained by isoconversional differential and integral methods are different.

Tertiary-Quaternary subduction processes and related magmatism in the Alpine-Mediterranean region

Abstract: During Tertiary to Quaternary times, convergence between Eurasia and Africa resulted in a variety of collisional orogens and different styles of subduction in the Alpine-Mediterranean region. Characteristic features of this area include arcuate orogenic belts and extensional basins, both of which can be explained by roll-back of subducted slabs and retreating subduction zones. After cessation of active subduction, slab detachment and post-collisional gravitational collapse of the overthickened lithosphere took place. This complex tectonic history was accompanied by the generation of a wide variety of magmas. Most of these magmas (e.g. low-K tholeiitic, calc-alkaline, shoshonitic and ultrapotassic types) have trace element and isotopic fingerprints that are commonly interpreted to reflect enrichment of their source regions by subduction-related fluids. Thus, they can be considered as 9subduction-related9 magmas irrespective of their geodynamic relationships. Intraplate alkali basalts are also found in the region and generally postdated the 9subduction-related9 volcanism. These mantle-derived magmas have not (or only slightly) been influenced by subduction-related enrichment. This paper summarizes the geodynamic setting of the Tertiary-Quaternary 9subduction-related9 magmatism in the various segments of the Alpine-Mediterranean region (Betic-Alboran-Rif province, Central Mediterranean, the Alps, Carpathian-Pannonian region, Dinarides and Hellenides, Aegean and Western Anatolia), and discusses the main characteristics and compositional variation of the magmatic rocks. Radiogenic and stable isotope data indicate the importance of continental crustal material in the genesis of these magmas. Interaction with crustal material probably occurred both in the upper mantle during subduction (9source contamination9) and in the continental crust during ascent of mantle-derived magmas (either by mixing with crustal melts or by crustal contamination). The 87 Sr/ 86 Sr and 206 Pb/ 204 Pb isotope ratios indicate that an enriched mantle component, akin to the source of intraplate alkali mafic magmas along the Alpine foreland, played a key role in the petrogenesis of the 9subduction-related9 magmas of the Alpine-Mediterranean region. This enriched mantle component could be related to mantle plumes or to long-term pollution (deflection of the central Atlantic plume and recycling of crustal material during subduction) of the shallow mantle beneath Europe since the late Mesozoic. In the first case, subduction processes could have had an influence in generating asthenospheric flow by deflecting nearby mantle plumes as a result of slab roll-back or slab break-off. In the second case, the variation in the chemical composition of the volcanic rocks in the Mediterranean region can be explained by 9statistical sampling9 of the strongly inhomogeneous mantle followed by variable degrees of crustal contamination.

Synthesis, structure and properties of doped Bi2O3

Abstract: Oxide ion conductors have been increasingly studied for many years because of their application in devices with high economical interest such as solid oxide fuel cells (SOFC), oxygen sensors, dense ceramic membranes for oxygen separation, and membrane reactors for oxidative catalysis. Bismuth oxides present polymorph forms, such as δ-, β- or γ-Bi 2 O 3 , with great potential for such applications, alone or in combination with other oxides. The present study investigates the influence of selected ions (Fe 3+ , Sb 3+ /Sb 5+ , and Ta 5+ ), introduced as dopant in α-Bi 2 O 3 and their effect on the structure and properties of the oxide polymorph forms obtained at high temperature. The molar ratio was Bi 2 O 3 :M x O y 0.95:0.05 where M = Fe 2 O 3 , Sb 2 O 3 or Ta 2 O 5 , respectively. The structural changes of α-Bi 2 O 3 were analysed by powder X-ray diffraction, SEM/EDX analysis and infrared spectroscopy. The structural changes are correlated with bulk ceramic characteristics (density, porosity) and their electrical behaviour versus temperature. The presence of some dopants (antimony and tantalum) on bismuth sites enlarges and enhances the stability of the polymorph forms, which is relevant to potential application.

The Distribution of the Free Path Lengths in the Periodic Two-Dimensional Lorentz Gas in the Small-Scatterer Limit

Abstract: We study the free path length and the geometric free path length in the model of the periodic two-dimensional Lorentz gas (Sinai billiard). We give a complete and rigorous proof for the existence of their distributions in the small-scatterer limit and explicitly compute them. As a corollary one gets a complete proof for the existence of the constant term \(c=2-3\ln 2+\frac{27\zeta(3)}{2\pi^2}\) in the asymptotic formula \(h(T)=-2 \ln \epsilon +c+o(1)\) of the KS entropy of the billiard map in this model, as conjectured by P. Dahlqvist.

Velocity Shear of the Thick Disk from SPM3 Proper Motions at the South Galactic Pole

Abstract: The kinematical properties of the Galactic thick disk are studied using absolute proper motions from the Third Yale/San Juan Southern Proper Motion Catalog and Two Micron All Sky Survey near-infrared photometry for a sample of ~1200 red giants in the direction of the south Galactic pole. The photometrically selected sample is dominated by thick-disk stars, as indicated by the number-density distribution that varies with distance from the Galactic plane as a single-valued exponential over the range 1 kpc < z < 4 kpc. The inferred scale height of the thick disk is 0.783 ± 0.048 kpc. The kinematics of the sample are also consistent with disklike motion. The U-velocity component is roughly constant, reflecting the Sun's peculiar motion, while a considerable shear is seen in the mean rotational velocity, V. The V-velocity profile's dependence on z is linear, with a gradient of dV/dz = -30 ± 3 km s-1 kpc-1. The velocity dispersions in both U and V show a lesser gradient of about 9 ± 3 km s-1 kpc-1. We demonstrate that the derived velocity and velocity-dispersion profiles are consistent with the assumptions of dynamical equilibrium and reasonable models of the overall Galactic potential.

Calcic amphibole growth and compositions in calc-alkaline magmas: Evidence from the Motru Dike Swarm (Southern Carpathians, Romania)

Abstract: A Late Pan-African calc-alkaline dike swarm (basalt-andesite-dacite-rhyolite) has been investigated in a region of over 2000 km 2 in the Alpine Danubian window, South Carpathians (Romania). Amphibole phenocrysts and microphenocrysts have been investigated by wavelength-dispersive microprobe analysis and BSE imaging. The Ca-amphibole population, represented in all the lithologies, displays a large compositional range, interpreted as the result of two processes: (1) magmatic evolution (kaersutite → Ti-pargasite → pargasite → Ti-magnesiohastingsite → magnesiohastingsite → edenite → tschermakite → magnesiohornblende) linked to magmatic differentiation from andesitic basalt to rhyolite; and (2) deuteritic alteration of the primary amphibole related to late-emplacement hydrothermal activity (yielding numerous varieties comprising those cited above). In all rock types, amphibole phenocrysts equilibrated at a nearly constant pressure of about 0.6 ± 0.1 GPa, but their temperatures of crystallization ranged from 1000–900 °C for basaltic andesites to 700–600 °C for dacites. In rhyolites, edenite to magnesiohornblende crystals res ect a continuous range of P-T conditions from 700 °C/0.6 GPa to 600 °C/0.1 GPa, in agreement with their change of habit from euhedral to subhedral. Complex zonations in pargasite-magnesiohastingsite (including resorption) are interpreted in term of self-organization of

Singular phenomena in nonlinear elliptic problems. From blow-up boundary solutions to equations with singular nonlinearities

Abstract: In this survey we report on some recent results related to various singular phenomena arising in the study of some classes of nonlinear elliptic equations. We establish qualitative results on the existence, nonexistence or the uniqueness of solutions and we focus on the following types of problems: (i) blow-up boundary solutions of logistic equations; (ii) Lane-Emden-Fowler equations with singular nonlinearities and subquadratic convection term. We study the combined effects of various terms involved in these problems: sublinear or superlinear nonlinearities, singular nonlinear terms, convection nonlinearities, as well as sign-changing potentials. We also take into account bifurcation nonlinear problems and we establish the precise rate decay of the solution in some concrete situations. Our approach combines standard techniques based on the maximum principle with non-standard arguments, such as the Karamata regular variation theory.

Generalized Diagonal Crossed Products and Smash Products for Quasi-Hopf Algebras. Applications

Abstract: In this paper we introduce generalizations of diagonal crossed products, two-sided crossed products and two-sided smash products, for a quasi-Hopf algebra H. The results we obtain may then be applied to H *-Hopf bimodules and generalized Yetter-Drinfeld modules. The generality of our situation entails that the “generating matrix” formalism cannot be used, forcing us to use a different approach. This pays off because as an application we obtain an easy conceptual proof of an important but very technical result of Hausser and Nill concerning iterated two-sided crossed products.

Seismic Emission from A M9.5-Class Solar Flare

Abstract: Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29, 2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves emitted from the β γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated with the flare some 30 Mm across in the East – West direction and 15 Mm in the North – South direction nestled in the southern penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum emission observed.

Repetitive occurrence of explosive events at a coronal hole boundary

Abstract: SUMER/SoHO data taken at a coronal hole boundary show a repetitive explosive event occurrence rate of around 3 min increasing to over 5 min towards the end of the activity. We suggest that the neighbouring oppositely directed closed and open field lines at the coronal hole boundary undergo repetitive reconnection seen as a sequence of explosive events. The repetitive reconnection may be triggered by transverse oscillations of the flux tubes in the closed field line region. These oscillations periodically separate and bring together the closed and open field lines on the two sides of the coronal hole boundary. An important indicator favouring the interpretation in terms of a kink mode is the observed increase in the oscillation period.

A note on regularity for free convolutions

Abstract: Let μ ⊞ ν and μ ⊠ ν denote the free additive convolution and the free multiplicative convolution, respectively, of the Borel probability measures μ and ν. We analyze the boundary behavior of the functions G μ ⊞ ν ( z ) = ∫ 1 z − t d ( μ ⊞ ν ) ( t ) and ψ μ ⊠ ν ( z ) = ∫ z t 1 − z t d ( μ ⊠ ν ) ( t ) . We prove that, under certain conditions, these functions extend continuously to the boundary of their natural domains as functions with values in the extended complex plane C ∪ { ∞ } . As a consequence, we obtain that μ ⊞ ν (respectively μ ⊠ ν ) can never be purely singular, unless μ or ν is concentrated in one point.

Feedstock recycling from plastic and thermoset fractions of used computers (I): pyrolysis

Abstract: The increasing production of computers, the progress in their performance, and the shorter time between innovation and production has led to increasing numbers of obsolete products. It has thus become necessary to recover some materials from old computers and to protect the environment from a new type of pollution. Such recycling is difficult because of the diversity of polymeric materials used, e.g., thermoplastics (polystyrene or acrylonitrile-butadiene-styrene) and thermosets (epoxy resins), and the relatively high levels of flame retardants (halogen- and nitrogen-containing compounds) added during production. Pyrolysis seems to be a suitable way to recover materials and energy from such waste without component separation if an efficient method for reducing toxic compounds can be applied. In this study, the pyrolysis of plastic and thermoset fractions (keyboards, casings, printed circuit boards, and mixtures thereof) of used computers was studied by thermogravimetry and batch reactor pyrolysis. The degradation products were separated into three fractions, solid, liquid, and gaseous, each of them being characterized by suitable methods such as gas chromatography (GC-MSD, gas chromatography-mass spectrometry detection; GC-AED, gas chromatography-atomic emission detection), infrared (FT-IR) and 1H-NMR (nuclear magnetic resonanace) spectroscopy, and elemental analysis. It has been established that most of the halogens, nitrogen, and sulfur is concentrated in the residue. However, the elimination of hazardous toxic compounds, mainly those containing bromine, is necessary before being able to safely use the pyrolysis oils as fuels or in refinery or petrochemical industry flows.

An universality result for a (mem)brane calculus based on mate/drip operations

Abstract: Operations with membranes are essential both in brane calculi and in membrane computing. In this paper we take four basic operations from brane calculi, pino, exo, mate, drip, we express them in terms of the membrane computing formalism, and then we investigate the computing power of the P systems using the mate, drip operations as unique evolution rules. All operations are controlled by – and make evolve – multisets of protein-objects embedded in the membranes themselves (not contained in the compartments of the cell, as standard in membrane computing; all compartments delimited by membranes are here empty). Somewhat surprisingly, for systems which use the mate, drip operations we obtain the Turing completeness. The power of P systems based on other operations remains to be investigated.

The large-scale jet-powered radio nebula of Circinus X-1

Abstract: We present multi-epoch observations of the radio nebula around the neutron star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia Telescope Compact Array between 2000 October and 2004 September. The nebula can be seen as a result of the interaction between the jet from the system and the interstellar medium and it is likely that we are actually looking toward the central X-ray binary system through the jet-powered radio lobe. The study of the nebula thus offers a unique opportunity to estimate for the first time using calorimetry the energetics of a jet from an object clearly identified as a neutron star. An extensive discussion on the energetics of the complex is presented: a first approach is based on the minimum energy estimation, while a second one employs a self-similar model of the interaction between the jets and the surrounding medium. The results suggest an age for the nebula of ≤ 10 5 yr and a corresponding time-averaged jet power ≥ 10 35 erg s -1 . During periodic flaring episodes, the instantaneous jet power may reach values of similar magnitude to the X-ray luminosity.

Markov processes associated with Lp-resolvents and applications to stochastic differential equations on Hilbert space

Abstract: We give general conditions on a generator of a C0-semigroup (resp. of a C0-resolvent) on Lp(E,μ), p ≥ 1, where E is an arbitrary (Lusin) topological space and μ a σ-finite measure on its Borel σ-algebra, so that it generates a sufficiently regular Markov process on E. We present a general method how these conditions can be checked in many situations. Applications to solve stochastic differential equations on Hilbert space in the sense of a martingale problem are given.

Influence of the polymer pre-treatment before its electroless metallization

Abstract: In order to activate polyvinylidene fluoride (PVDF) surfaces, a mixed Pd-Sn colloidal solution is used for further copper deposition. The plasma pre-treatment is performed using N 2 or N 2 /H 2 reactive gases. The conditions to prepare the colloidal solution like reaction temperature and growth time of colloids as well as the plasma processing conditions are studied in order to establish the elaboration and treatment parameters that allow obtaining the highest concentration of metallic palladium and also the good adhesion of copper onto the PVDF surface. This study is essentially supported by X-ray photoelectron spectroscopy (XPS) analysis.