Showing papers by "Romanian Academy published in 2004"

Modelling the spectral energy distribution of galaxies. III. Attenuation of stellar light in spiral galaxies

Abstract: We present new calculations of the attenuation of stellar light from spiral galaxies using geometries for stars and dust which can reproduce the entire spectral energy distribution from the ultraviolet (UV) to the Far-infrared (FIR)/submillimeter (submm) and can also account for the surface brightness distribution in both the optical/Near-infrared (NIR) and FIR/submm. The calculations are based on the model of Popescu et al. (2000), which incorporates a dustless stellar bulge, a disk of old stars with associated diffuse dust, a thin disk of young stars with associated diffuse dust, and a clumpy dust component associated with star-forming regions in the thin disk. The attenuations, which incorporate the effects of multiple anisotropic scattering, are derived separately for each stellar component, and presented in the form of easily accessible polynomial fits as a function of inclination, for a grid in optical depth and wavelength. The wavelength range considered is between 912A and 2.2 μm, sampled such that attenuation can be conveniently calculated both for the standard optical bands and for the bands covered by GALEX. The attenuation characteristics of the individual stellar components show marked differences between each other. A general formula is given for the calculation of composite attenuation, valid for any combination of the bulge-to-disk ratio and amount of clumpiness. As an example, we show how the optical depth derived from the variation of attenuation with inclination depends on the bulge-to-disk ratio. Finally, a recipe is given for a self-consistent determination of the optical depth from the Hα/Hβ line ratio.

Munc13-4 is an effector of rab27a and controls secretion of lysosomes in hematopoietic cells.

Abstract: Griscelli syndrome type 2 (GS2) is a genetic disorder in which patients exhibit life-threatening defects of cytotoxic T lymphocytes (CTLs) whose lytic granules fail to dock on the plasma membrane and therefore do not release their contents. The disease is caused by the absence of functional rab27a, but how rab27a controls secretion of lytic granule contents remains elusive. Mutations in Munc13-4 cause familial hemophagocytic lymphohistiocytosis subtype 3 (FHL3), a disease phenotypically related to GS2. We show that Munc13-4 is a direct partner of rab27a. The two proteins are highly expressed in CTLs and mast cells where they colocalize on secretory lysosomes. The region comprising the Munc13 homology domains is essential for the localization of Munc13-4 to secretory lysosomes. The GS2 mutant rab27aW73G strongly reduced binding to Munc13-4, whereas the FHL3 mutant Munc13-4Δ608-611 failed to bind rab27a. Overexpression of Munc13-4 enhanced degranulation of secretory lysosomes in mast cells, showing that it has a positive regulatory role in secretory lysosome fusion. We suggest that the secretion defects seen in GS2 and FHL3 have a common origin, and we propose that the rab27a/Munc13-4 complex is an essential regulator of secretory granule fusion with the plasma membrane in hematopoietic cells. Mutations in either of the two genes prevent formation of this complex and abolish secretion.

Statistical limit theorems for suspension flows

Abstract: In dynamical systems theory, a standard method for passing from discrete time to continuous time is to construct the suspension flow under a roof function. In this paper, we give conditions under which statistical laws, such as the central limit theorem and almost sure invariance principle, for the underlying discrete time system are inherited by the suspension flow. As a consequence, we give a simpler proof of the results of Ratner (1973) and recover the results of Denker and Philipp (1984) for Axiom A flows. Morcover, we obtain several new results for nonuniformly and partially hyperbolic flows, including frame flows on negatively curved manifolds satisfying a pinching condition.

Finite-difference lattice Boltzmann model with flux limiters for liquid-vapor systems.

Abstract: In this paper we apply a finite difference lattice Boltzmann model to study the phase separation in a two-dimensional liquid-vapor system. Spurious numerical effects in macroscopic equations are discussed and an appropriate numerical scheme involving flux limiter techniques is proposed to minimize them and guarantee a better numerical stability at very low viscosity. The phase separation kinetics is investigated and we find evidence of two different growth regimes depending on the value of the fluid viscosity as well as on the liquid-vapor ratio.

Trading polarizations for labels in P systems with active membranes

Abstract: This paper addresses the problem of removing the polarization of membranes from P systems with active membranes - and this is achieved by allowing the change of membrane labels by means of communication rules or by membrane dividing rules. As consequences of these results, we obtain the universality of P systems with active membranes which are allowed to change the labels of membranes, but do not use polarizations. Universality results are easily obtained also by direct proofs. By direct constructions, we also prove that SAT can be solved in linear time by systems without polarizations and with label changing possibilities. If non-elementary membranes can be divided, then SAT can be solved in linear time without using polarizations and label changing. Several open problems are also formulated.

Bio-steps beyond Turing.

Abstract: Are there 'biologically computing agents' capable to compute Turing uncomputable functions? It is perhaps tempting to dismiss this question with a negative answer. Quite the opposite, for the first time in the literature on molecular computing we contend that the answer is not theoretically negative. Our results will be formulated in the language of membrane computing (P systems). Some mathematical results presented here are interesting in themselves. In contrast with most speed-up methods which are based on non-determinism, our results rest upon some universality results proved for deterministic P systems. These results will be used for building "accelerated P systems". In contrast with the case of Turing machines, acceleration is a part of the hardware (not a quality of the environment) and it is realised either by decreasing the size of "reactors" or by speeding-up the communication channels. Consequently, two acceleration postulates of biological inspiration are introduced; each of them poses specific questions to biology. Finally, in a more speculative part of the paper, we will deal with Turing non-computability activity of the brain and possible forms of (extraterrestrial) intelligence.

Atoms and regularity for measures in a partially defined free convolution semigroup

Abstract: Consider a Borel probability measure μ on the real line, and denote by {μ t : t≥1} the free additive convolution semigroup defined by Nica and Speicher. We show that the singular part of μ t is purely atomic and the density of μ t is locally analytic, provided that t > 1. The main ingredient is a global inversion theorem for analytic functions on a half plane.

Magnetic changes observed in the formation of two filaments in a complex active region: Trace and MSDP observations

Abstract: This paper is focused on the formation of two filaments in a complex center of decaying active regions (AR 8329 and AR 8326), located in the northern hemisphere. The observations were obtained in Hα by the Multi-channel Subtractive Double Pass spectrograph (MSDP mounted on the German telescope VTT in Tenerife) and EUV lines with TRACE (Transition Region And Corona Explorer). High Doppler shifts are found to be related to the ends of filament segments where canceling magnetic fields are also located (as seen on magnetograms from Big Bear Solar Observatory). At these locations, velocities along the line of sight, derived by using a cloud model method reach −20 km s−1, the segments of filaments merge and frequently a time-related sub-flare is observed by TRACE. The chirality of the filament segments has been determined by different methods: the segments of dextral chirality join together and form a long dextral filament, and a single filament of sinistral chirality forms end to end with the dextral filament but does not merge with it. Assuming a model of twisted flux tube for filament material, we suggest that the dextral filament has negative helicity and a relationship between its formation and the close by sunspot with the same sign of helicity.

The linear quadratic optimization problems for a class of linear stochastic systems with multiplicative white noise and Markovian jumping

Abstract: In this paper, the linear quadratic optimization problem for a class of linear stochastic systems subject both to multiplicative white noise and Markovian jumping is investigated. Two classes of admissible controls are considered. One of these classes contains controls with additional property that corresponding trajectories tend to zero (in mean square) when tends to /spl infin/, while concerning the controls contained in the second class of admissible controls there is not any stability assumption. In the optimization problem over the first class of admissible controls, the cost functional could have indefinite sign of weights matrices. An iterative procedure to compute the maximal solution of the systems of generalized Riccati equations is provided. A numerical example to illustrate the applicability of the iterative procedure is given.

Artificial Inoculation—Perspectives in Tailings Phytostabilization

Abstract: Intensive mining and processing activities worldwide resulted in the generation of huge amounts of waste (tailings), generally characterized as toxic, radioactive, and/or hazardous. The exposure po...

Absolute Proper Motion of the Fornax Dwarf Spheroidal Galaxy from Photographic and Hubble Space Telescope WFPC2 Data

Abstract: We have measured the absolute proper motion of the Fornax dwarf spheroidal galaxy from a combination of photographic plate material and Hubble Space Telescope Wide Field Planetary Camera 2 data that provide a time baseline of up to 50 yr. The extragalactic reference frame consists of eight QSO images and 48 galaxies. The absolute proper motion is μα cos δ = 0.59 ± 0.16 mas yr-1 and μδ = -0.15 ± 0.16 mas yr-1. The corresponding orbit of Fornax is polar, with an eccentricity of 0.27 and a radial period of 4.5 Gyr. Fornax's current location is near pericenter. The direction of the motion of Fornax supports the notion that Fornax belongs to the Fornax–Leo I–Leo II–Sculptor–Sextans stream as hypothesized by both Lynden-Bell and Majewski. According to our orbit determination, Fornax crossed the Magellanic plane ~190 Myr ago, a time that coincides with the termination of the star formation process in Fornax. We propose that ram pressure stripping due to the passage of Fornax through a gaseous medium denser than the typical intragalactic medium left behind from the LMC may have caused the end of star formation in Fornax. The excess, anomalous clouds within the south Galactic pole region of the Magellanic Stream, whose origin has long been debated in the literature as constituents of either the Magellanic Stream or of the extragalactic Sculptor group, are found to lie along the orbit of Fornax. We speculate that these clouds are stripped material from Fornax as the dwarf crossed the orbit of the Magellanic Clouds.

Electrochemical oxidation of aniline at boron-doped diamond electrodes

Abstract: The electrochemical oxidation of aniline at boron-doped diamond (BDD) electrodes was investigated by cyclic voltammetry, steady-state polarization measurements and bulk electrolysis under potentiostatic control. It was found that acidic media is suitable for efficient electrochemical oxidation of aniline, because at low pH, the potential required for avoiding electrode fouling is lower than in neutral and alkaline media. The results of the longtime polarization measurements suggested that more anodic potentials ensure slightly higher efficiency for the conversion of aniline to CO2, while the direct oxidation process does not play a prominent part in the overall electrochemical incineration of aniline. The current efficiencies (∼44%) and the efficiency of aniline conversion to CO2 (∼80%) favourably compare with those reported for other electrochemical methods for aniline destruction. The results demonstrate the possibility of using BDD as an electrode material for electrochemical wastewater treatment, mainly when very high anodic potentials are required.

Phases investigation in the antimony doped Bi2O3 system

Abstract: The present study investigates the influence of Sb ions, introduced as dopants in α-Bi 2 O 3 , on the structure of the oxide polymorph forms obtained at high temperature. The structural changes of α-Bi 2 O 3 for compositions in the system Bi 2-x Sb x O 3 (x=0, 0.05, 0,1, 0.15, 0.2), at different thermal treatment temperatures were analyzed by thermal analysis, powder X-ray diffraction and infrared transmission spectroscopy. A tendency of the structure to change to a higher symmetry (monoclinic → tetragonal → cubic) was observed, as the content in antimony increased and the temperature reached 850 °C. The presence of Sb 2 O 3 in the Bi 2 O 3 oxide system promotes an oxygen release from the oxide and enlarges the stabilization domain of the δ-phase.

δ Sct-type pulsations in eclipsing binary systems: Y Cam

Abstract: We present the results of a three-continent multisite photometric campaign carried out on the Algol-type eclipsing binary system RZ Cas, in which the primary component has recently been discovered to be a δ Sct-type pulsator. The present observations include, for the first time, complete simultaneous Stromgren uvby light curves together with a few Crawford Hβ data collected around the orbital phase of the first quadrature. The new observations confirm the pulsational behaviour of the primary component. A detailed photometric analysis, based on these observations, is presented for both binarity and pulsation. The results indicate a semidetached system where the secondary fills its Roche lobe. The appearance of the light curves reveals the presence of the mass stream from the secondary component and a hotspot where this stream impacts on the surface of the primary star. There are also some indications of chromospheric activity in the secondary. On the other hand, the pulsational behaviour out-of-primary eclipse can be well described with only one frequency at 64.1935 cd -1 similar to the main peak found by Ohshima et al. The existence of multiperiodicity is not confirmed in our data. Concerning the mode identification, our results indicate non-radial pulsation in a high radial order (n = 6), with l = 2, |m| = 1, 2 as the most suitable. However, additional effects must be taken into account in the predictions. Moreover, the pulsation amplitude in the u band is larger than in b and v, which is unusual among the δ Sct-type variables. This can be explained as due to pulsation in a high n value and close to the blue edge of the δ Sct region. On the other hand, the early data of Ohshima et al. have also been analysed and similar results are found concerning the frequency content and pulsational amplitude. Finally, a revision of all the photometric out-of-primary-eclipse data sets available in the literature is made together with some additional unpublished data leading to interesting findings relative to changes taking place in the pulsation amplitudes and frequencies from season to season. Furthermore, multiperiodicity is probably present in some epochs.

Limiting oxygen concentration evaluation in flammable gaseous mixtures by means of calculated adiabatic flame temperatures

Abstract: The limiting oxygen concentration (LOC) of fuel–air–inert premixed gaseous systems are usually determined from measurements of explosion limits at progressive dilution with inert gas of fuel–air mixtures, which is a long and cumbersome procedure. An alternative procedure to evaluate LOC would be of great interest for all fields of activity involving the use of flammable mixtures, especially when less characterized fuels are used. The paper describes a new procedure (algorithm) meant to estimate the LOC of fuel–air–inert premixed systems, using the values of lower explosion limit (LEL) of the fuel–air mixture and the calculated adiabatic flame temperature (CAFT) both at LOC and LEL when nitrogen is used as an inert gas. It is based on an empirical correlation established between the CAFT computed for fuel–air–nitrogen mixtures at LOC and CAFT at LEL, for a large number of flammable gases and vapors. This requires only the measurement of LEL. The correlation was derived from flammability data taken from literature sources (German and American recommended values). The method is based upon the assumption that mixtures at LOC have an equivalence ratio ϕ =1.250, which is close to the equivalence ratio of the most reactive fuel–air systems. Inverse calculations made with this new algorithm for nine fuel–air–nitrogen mixtures allowed the determination of LOC with a relative deviation of 2–22%.

An Institution-independent Proof of Craig Interpolation Theorem

Abstract: We formulate a general institution-independent (i.e. independent of the details of the actual logic formalised as institution) version of the Craig Interpolation Theorem and prove it in dependence of Birkhoff-style axiomatizability properties of the actual logic. We formalise Birkhoff-style axiomatizability within the general abstract model theoretic framework of institution theory by the novel concept of Birkhoff institution. Our proof destills a set of conditons behind the Craig Interpolation Property, which are easy to establish in the applications. Together with the generality of our approach, this leads to a wide range of applications for our result, including conventional and non-conventional logics (many of them from algebraic specification theory), such as general algebra, classical model theory, partial algebra, rewriting logic, membership algebra, etc. all of them in various versions and with various types of sentences (including infinitary ones). In dependence of axiomatizability properties many other applications are expected for various institutions or logics.

The inexact, inexact perturbed, and quasi-Newton methods are equivalent models

Abstract: A classical model of Newton iterations which takes into account some error terms is given by the quasi-Newton method, which assumes perturbed Jacobians at each step. Its high convergence orders were characterized by Dennis and More [Math. Comp. 28 (1974), 549-560]. The inexact Newton method constitutes another such model, since it assumes that at each step the linear systems are only approximately solved; the high convergence orders of these iterations were characterized by Dembo, Eisenstat and Steihaug [SIAM J. Numer. Anal. 19 (1982), 400-408]. We have recently considered the inexact perturbed Newton method [J. Optim. Theory Appl. 108 (2001), 543 570] which assumes that at each step the linear systems are perturbed and then they are only approximately solved; we have characterized the high convergence orders of these iterates in terms of the perturbations and residuals. In the present paper we show that these three models are in fact equivalent, in the sense that each one may be used to characterize the high convergence orders of the other two. We also study the relationship in the case of linear convergence and we deduce a new convergence result.

Mechanical field fluctuations in polycrystals estimated by homogenization techniques

Abstract: The fluctuation of mechanical fields arising in polycrystals is investigated. These materials are viewed as composites of the HashinShtrikman type with a large number of anisotropic phases and a gr...

Symport/Antiport P Systems with Three Objects Are Universal

Abstract: The operations of symport and antiport, directly inspired frombiology, are already known to be rather powerful when used in the framework of P systems. In this paper we confirm this observation with a quite surprising result: P systems with symport/antiport rules using only three objects can simulate any counter machine, while systems with only two objects can simulate any blind counter machine. In the first case, the universality (of generating sets of numbers) is obtained also for a small number of membranes, four.

Disruption of a dwarf galaxy under strong shocking: the origin of ω Centauri

Abstract: We perform N-body simulations of the dynamical evolution of a dwarf galaxy falling into the Milky Way galaxy in order to understand the formation scenario of the peculiar globular cluster ω Centauri. We use self-consistent models of the bulge and the disc of the Milky Way, as well as of the dwarf galaxy, and explore a range of dwarf models with different density distributions. Namely, we use King and Hemquist density profiles to model the density distribution in the dwarf. The central region of our King model has a density profile approximately oc r -2 , while that of the Hernquist model is r -1 . The difference in the dwarfs density distributions leads to distinct evolutionary scenarios. The King model dwarf loses its mass exponentially as a function of apocentric distance, with the mass loss rate depending on the initial mass and size of the dwarf. Regardless of the initial mass and size, the King model dwarf remains more massive than 10 8 M ○. after a few gigayears of evolution. The Hemquist model dwarf experiences an accelerated mass loss, and the mass of the remnant falls below 10 8 M ○. within a few gigayears. By exploring an appropriate set of parameters, we find a Hernquist model that can attain the mass and orbital characteristics of co Cen after a few gigayears.

Model parameter identification for vehicle vibration control with magnetorheological dampers using computational intelligence methods

Abstract: The parameter identification of magnetorheological dampers by an inverse method is proposed. A modified Bouc-Wen modified dynamic model is considered and its parameters are obtained by using genetic algorithms. The experimental data consist of time histories of current, displacement, velocity, and force measured for both constant and variable current. The model parameters are determined using a set of experimental measurements corresponding to different constant current values and the resulting model is validated on the data measured for variable current. Based on this model a semi-active control of vehicle suspension is studied and a fuzzy controller is developed to reduce the chattering effect.

Oxalato‐Bridged [CuIICrIII] and [MnIICrIII] Binuclear Complexes: Synthesis, Crystal Structures, Magnetic and EPR Investigations

Abstract: Two new heterobinuclear complexes, [(bipy)(C2O4)Cr(μ-C2O4)Cu(Hfsaaep)(H2O)]·2H2O (1) and [(phen)(C2O4)Cr(μ-C2O4)Mn(phen)2(N3)]·H2O (2) have been obtained by using bis(oxalato)chromium(III) anions, [Cr(AA)(C2O4)2]−, as building blocks [AA = 2,2′-bipyridine (bipy); 1,10-phenanthroline (phen)]. The crystal structures of the two complexes have been solved. These complexes comprise neutral oxalato-bridged CrIII−CuII and CrIII−MnII units. The [Cr(AA)(C2O4)2]− anion acts as a bidentate ligand toward CuII in compound 1 and as a monodentate ligand toward MnII in compound 2. The copper(II) ion in 1 exhibits a slightly distorted square bipyramidal stereochemistry, with the aqua ligand and one of the bridging oxalato oxygen atoms disposed in the apical positions [Cu(1)−O(1w) = 2.360(3) A and Cu(1)−O(4) = 2.504(2) A]. The second bridging oxalato oxygen atom [Cu(1)−O(2) = 2.0747(18) A] and the N,N,O-type Hfsaaep ligand are located in the basal plane. The distance between the CrIII and CuII ions across the bridging oxalate unit is 5.506 A. The MnII ion in compound 2 is hexacoordinate (two chelating phen ligands, one oxalato bridging oxygen, and one terminal azido group). The intermolecular CrIII···MnII distance is 5.257 A. The magnetic properties of the two complexes have been investigated. The magnetic coupling between CrIII and CuII in 1 was found to be ferromagnetic (J = +1.4 cm−1). The nature of the ground state (S = 2) has been further confirmed by plotting the magnetization-versus-field curve. An antiferromagnetic interaction was found between CrIII and MnII in compound 2 (J = −1.9 cm−1). The magnetization-versus-field curve indicates the occurrence of a crossover between the Zeeman components: MS = −1 (ground state S = 1), MS = −2, from the first excited state (S = 2), and MS = −3, from the second excited state. The EPR spectra of the two compounds are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)