bluuebunny/crossref_metadata_2025 huggingface dataset:
Methylation of Acridin-9-ylthioureas. Structure, Fluorescence and Biological Properties of Products
Authors: Bernát Juraj , Balentová Eva , Kristian Pavol , Imrich Ján , Sedlák Erik , Danihel Ivan , Böhm Stanislav , Prónayová Naďa , Pihlaja Kalevi , Klika Karel D.
Published: April 2004

The structure, fluorescence, biological properties and S(N)-methylation reactions of ten 1,1-alkyl/aryl-disubstituted 3-(acridin-9-yl)thioureas 4 have been studied. Various reaction conditions allowed to obtain corresponding S-methyl 5 and S,N-dimethyl derivatives 6 in good yields. Structure and stereochemistry of the synthesized products are demonstrated by ab initio quantum chemical calculations and NMR techniques including PDQF-COSY, selective INEPT and NOE-difference experiments. Remarkable upfield 13C shifts of resonance signals of carbons C-4a, C-10a adjacent to acridine N-10 are characteristic of hydroiodides in contrast to free bases. Z configuration in isothioureas 7 with secondary amino rest in relation to E configuration of isothioureas with primary amino rest is discussed. Of the obtained products, some isothiourea salts 6 exhibit more than 2 orders of magnitude higher intensity of fluorescence, using 9-isothiocyanatoacridine as a standard. The obtained isothiourea hydroiodides 5 and dimethylisothiourea iodides 6 show remarkable biological activity against Mycobacterium tuberculosis.
6-Amino-2,6-dideoxy- or -2,3,6-trideoxyhexono-1,6-lactams: Synthesis and Conformation
Authors: Hamerníková Michaela , Havlíček Jaroslav , Bláhová Romana , Pospíšilová Helena , Votavová Hana , Kefurt Karel
Published: April 2004

6-Amino-2,6-dideoxy-D-ribo-hexono-1,6-lactam (1a), 6-amino-2,6-dideoxy-D-arabino-hexono-1,6-lactam (2a), 6-amino-2,3,6-trideoxy-L-threo-hexono-1,6-lactam (3a) and per-O-acetyl derivatives 1b-3b were synthesized and their seven-membered lactam ring conformation was studied. 1H and 13C NMR spectra of the named lactams, measured at low temperature, always disclosed the presence of both 1,NC4 and 4C1,N conformations in ratios which were affected mainly by the stereochemistry of cyclohexane. There were no CD extremes over 200 nm found in water solutions of the lactams 1a and 2a, probably owing to the symmetry of the C2-C6 parts of their seven-membered rings. These results contrast with those previously found for the lactams having OH or OAc at C2, and support a concept of the directive role of the C2 substituent in conformation equilibrium.
Photophysical Characterisation, Metal Ion Binding and Enantiomeric Recognition of Chiral Ligands Containing Phenazine Fluorophore
Authors: Dolci Luisa Stella , Huszthy Péter , Samu Erika , Montalti Marco , Prodi Luca , Zaccheroni Nelsi
Published: April 2004

Enantiomerically pure dimethyl- and diisobutyl-substituted phenazino-18-crown-6 ligands bind metal and ammonium ions and also primary aralkylammonium perchlorates in acetonitrile with high affinity, causing pronounced changes in their luminescence properties. In addition, they show enantioselectivity towards chiral primary aralkylammonium perchlorates. The possibility to monitor the binding process by photoluminescence spectroscopy can gain ground for the design of very efficient enantioselective chemosensors for chiral species. The observed changes in the photophysical properties are also an important tool for understanding the interactions present in the adduct.
Facile Synthesis of Aryl-Substituted 1,2,5,6-Tetrahydropyrimidines and Their Stereochemical Investigation
Authors: Chebanov Valentin A. , Muravyova Elena A. , Sadchikova Yulia V. , Desenko Sergey M. , Chernenko Vitaly N. , Kobzar Kiril M. , Musatov Vladimir I.
Published: April 2004

The present work is devoted to the investigation of 2,4,6-triaryl-1,2,5,6-tetrahydropyrimidine derivatives. A new facile approach to their synthesis based on the reaction of α,β-unsaturated ketones, carbonyl compounds and ammonia was developed. Some stereochemical features of the compounds obtained were fixed on the base of NMR data (including COSY and NOESY experiments).
Synthesis of N4-Amino and N4-Hydroxy Derivatives of 5-Azacytidine. A Facile Rearrangement of the N4-Amino Derivative to 5-(3-β-D-Ribofuranosylureido)-1H-1,2,4-triazole
Authors: Pískala Alois , Hanna Naeem B. , Masojídková Milena , Fiedler Pavel , Votruba Ivan
Published: April 2004

Treatment of methoxyribosyltriazinone 4 with hydrazine in methanol afforded crude 4-hydrazino-1-β-D-ribofuranosyl-1,3,5-triazin-2(1H)-one (N4-amino-5-azacytidine) (2), which rearranged rapidly to isomeric 5-ribosylureidotriazole 6. The rearrangement proceeds easily also in water solutions of 2. Alkaline hydrolysis of 6 gave a mixture of 5-ureidotriazole 7 and 5-aminotriazole 8. Acid hydrolysis of 6 afforded only 7. This compound was also prepared by thermal rearrangement of 5-amino-1-carbamoyltriazole 9 or on reaction of cyano(formyl)guanidine 10 with hydrazine hydrochloride. Treatment of benzoylated methoxyribosyltriazinone 4a with hydrazine in methanol gave only the rearranged product 6a. Reaction of tribenzoylribosyl isocyanate 12 with aminotriazole 8 gave 1-triazolecarboxamidotribenzoylribose 13, which afforded by methanolysis oxazoloribofuranose 14 and aminotriazole 8. Compound 14 was also obtained by methanolysis of blocked ribosylcarbamate 16. Reaction of methoxyribosyltriazinone 4 with hydroxylamine in methanol afforded 4-hydroxylamino-1-β-D-ribofuranosyl-1,3,5-triazin-2(1H)-one (N4-hydroxy-5-azacytidine) (3), which on the action of excess hydroxylamine yielded 1-cyano-1-hydroxy-5-β-D-ribofuranosylisobiuret (19). Treatment of methoxy-1,3,5-triazinone 18 with a solution of hydroxylamine in methanol gave 4-hydroxylamino-1-methyl-1,3,5-triazin-2(1H)-one (N4-hydroxy-1-methyl-5-azacytosine) (17). Heating of cyano(formyl)guanidine 10 with hydroxylamine hydrochloride in water lead to the formation of triuret (21). The mechanisms of the reactions of methoxyribosyltriazinone 4 with hydrazine and hydroxylamine are discussed. Compounds 2, 6 and 19 exhibited no significant antibacterial or cytostatic activity.
Synthesis of Racemic 2-Hydroxy-4- and 2-Hydroxy-5-(hydroxymethyl)cyclohexane Pyrimidine C-Nucleoside Analogues
Authors: Šála Michal , Hřebabecký Hubert , Masojídková Milena , Holý Antonín
Published: April 2004

The oxirane ring opening of 3-[(benzyloxy)methyl]-7-oxabicyclo[4.1.0]heptane with sodium salt of diethyl malonate followed by treatment with TsOH gave (3aR*,6R*,7aS*)-6-[(benzyloxy)methyl]hexahydro-1-benzofuran-2(3H)-one (3a) and (3aR*,5R*,7aS*)-5-[(benzyloxy)methyl]hexahydro-1-benzofuran-2(3H)-one (3b). Lactones 3a and 3b were formylated and then treated with thiourea or guanidine to give, after deprotection, racemic 5-[2-hydroxy-4- and 2-hydroxy-5-(hydroxymethyl)cyclohexyl]-2-thiouracil (5a and 5b) or -isocytosine (12a and 12b). Simple transformations of the 2-thiouracil derivative led to uracil (7a and 7b), 4-thiouracil (9a and 9b), and cytosine derivatives (10a and 10b).
Block Copolymers as Compatibilizers in Coarsening of Polymer Blends: Polystyrene-Poly(methyl methacrylate)-Poly(styrene-block-methyl methacrylate) System
Authors: Holoubek Jaroslav
Published: April 2004

The time-resolved light scattering experiments have been conducted to investigate the kinetics of coarsening of phase-separated immiscible polymer blends with or without added block copolymer. The blends studied were polystyrene-poly(methyl methacrylate) mixtures with a diblock copolymer composed of the corresponding homopolymer blocks. The time evolution of the peak position qm(t,T) and the scattered intensity maximum Im(t,T) at qm have been compared with the theoretically predicted values of exponents for various time scales of phase separation at various annealing temperatures.
THE TRAFFIC BOTTLENECK EFFECTS CAUSED BY THE LANE CLOSING IN THE CELLULAR AUTOMATA MODEL
Authors: JIA BIN , JIANG RUI , WU QING-SONG
Published: April 2004

As a kind of bottleneck, the lane closing has seldomly been investigated with cellular automata model. In this paper, we study this issue using the cellular automata traffic flow model. The capacity and the density distribution of this kind of bottleneck are discussed in details. We find that (i) the capacity of the bottleneck is a little smaller than the maximum flow rate of single-lane road; (ii) different regulations may lead to different density distributions of the vehicles upstream of the lane closing. Moreover, the density inversion phenomenon is reported under certain conditions. This enlightens us to propose that the phenomenon of density inversion reported in many publications may be caused by the bottlenecks on the highway.
FORCED FUSION IN THE EXCITED STATE OF dtμ MUONIC-MOLECULE AND ITS POSSIBLE DRIVERS
Authors: ESKANDARI M. R. , FAGHIHI F.
Published: April 2004

It is shown that the cycling rate in the optimum tritium concentration in μCF and in the n=2, J=1, ν=0 state is 2.35 times higher than in n=1, J=ν=0 state. The methods to explore forced μCF of the n=2 state is discussed. Although the n=2 state shows to be more efficient in terms of its cycling rate, all suggested drivers seems to be useless with respect to the input energy requirement and short life-time of resonance states. It is shown that even using x-ray sources as a driver, and designing hybrid system, the suggested forced hybrid system energy gain is 13 and very good gain enhancement but still is far away to be of interest for practical applications with respect to very short life-time of resonance states.
THE SIMULATION OF 2D SPIN-1 ISING MODEL WITH POSITIVE BIQUADRATIC INTERACTION ON A CELLULAR AUTOMATON
Authors: KUTLU BÜLENT
Published: April 2004

The two-dimensional antiferromagnetic spin-1 Ising model with positive biquadratic interaction is simulated on a cellular automaton which based on the Creutz cellular automaton for square lattice. Phase diagrams characterizing phase transition of the model are presented for a comparison with those obtained from other calculations. We confirm the existence of the intermediate phase observed in previous works for some values of J/K and D/K. The values of the static critical exponents (β, γ and ν) are estimated within the framework of the finite-size scaling theory for D/K<2J/K. Although the results are compatible with the universal Ising critical behavior in the region of D/K<2J/K-4, the model does not exhibit any universal behavior in the interval 2J/K-4<D/K<2J/K.
NEGATIVE PRESSURE TAIL OF A REFLECTED PRESSURE PULSE: COMPARISON OF A LATTICE BOLTZMANN STUDY TO THE EXPERIMENTAL RESULTS
Authors: IMRE ATTILA R. , HÁZI GÁBOR , BESOV ALEXEY
Published: April 2004

A numerical pressure wave reflection experiment in a two-dimensional liquid and its comparison with experimental results are presented. The liquid is simulated by the pseudo-potential extension of the lattice-Boltzmann method. In the simulation a pressure pulse is produced by a point source and the resulting pressure wave is reflected back by a wettable rigid wall. Negative pressure tail can be observed at the vicinity of the wall/liquid interface. The resulted shape of the positive and the negative pressure wave is compared with experimental results obtained in an electromagnetic shock-wave generator. Good agreement has been found between the experimental and simulation results.
ON SPATIAL CONSENSUS FORMATION: IS THE SZNAJD MODEL DIFFERENT FROM A VOTER MODEL?
Authors: BEHERA LAXMIDHAR , SCHWEITZER FRANK
Published: April 2004

In this paper, we investigate the so-called "Sznajd Model" (SM) in one dimension, which is a simple cellular automata approach to consensus formation among two opposite opinions (described by spin up or down). To elucidate the SM dynamics, we first provide results of computer simulations for the spatio-temporal evolution of the opinion distribution L(t), the evolution of magnetization m(t), the distribution of decision times P(τ) and relaxation times P(μ). In the main part of the paper, it is shown that the SM can be completely reformulated in terms of a linear voter model (VM), where the transition rates towards a given opinion are directly proportional to frequency of the respective opinion of the second-nearest neighbors (no matter what the nearest neighbors are). So, the SM dynamics can be reduced to one rule, "Just follow your second-nearest neighbor". The equivalence is demonstrated by extensive computer simulations that show the same behavior between SM and VM in terms of L(t), m(t), P(τ), P(μ), and the final attractor statistics. The reformulation of the SM in terms of a VM involves a new parameter σ, to bias between anti- and ferromagnetic decisions in the case of frustration. We show that σ plays a crucial role in explaining the phase transition observed in SM. We further explore the role of synchronous versus asynchronous update rules on the intermediate dynamics and the final attractors. As compared to the original SM, we find three additional attractors, two of them related to an asymmetric coexistence between the opposite opinions.
THE OLDEST OLD AND THE POPULATION HETEROGENEITY
Authors: ŁASZKIEWICZ A. , SZYMCZAK SZ. , CEBRAT S.
Published: April 2004

We have simulated the effect of the diversity of the late expressed genes in the genetic pool of population on the phenotypes of individuals in the late ages. Using Penna model based on the Monte Carlo method we have obtained for the oldest fractions of populations lower mortality rates than predicted by the exponential Gompertz function. Such deviations from the expected exponential increase of mortality are the characteristic for populations which are not in equilibrium with the environment, or if a relatively high probability of reversions was assumed, or if the population is heterogeneous. In such populations, the genes expressed in the late ages, are under the very weak selection pressure and thus, highly-polymorphic. As an effect, the probability of the genetically-determined death of the oldest organisms does not grow as fast as predicted by the Gompertz exponential curve describing mortality during earlier periods of life.
ON SITE PERCOLATION ON THE CORRELATED SIMPLE CUBIC LATTICE
Authors: TARASEVICH YURIY YU. , MANZHOSOVA ELENA N.
Published: April 2004

We consider site percolation on a correlated bi-colored simple cubic lattice. The correlated medium is constructed from a strongly alternating bi-colored simple cubic lattice due to anti-site disordering. The percolation threshold is estimated. The cluster size distribution is obtained. A possible application to the double 1:1 perovskites is discussed.
RAPID ALGORITHM FOR IDENTIFYING BACKBONES IN THE TWO-DIMENSIONAL PERCOLATION MODEL
Authors: YIN WEI-GUO , TAO RUIBAO
Published: April 2004

We present a rapid algorithm for identifying the current-carrying backbone in the two-dimensional percolation model. Taking advantage of the modified Hoshen–Kopelman cluster labeling algorithm, our algorithm identifies dangling parts using their local properties. For planar graphs, it finds the backbone almost four times as fast as the commonly-used Tarjan's depth-first-search algorithm. Comparison with other algorithms for backbone identification is also addressed.
DOES THE PRICE MULTIPLIER EFFECT ALSO HOLD FOR STOCKS?
Authors: MASLOV SERGEI , ROEHNER BERTRAND M.
Published: April 2004

The price multiplier effect provides precious insight into the behavior of investors during episodes of speculative trading. It tells us that the higher the price of an asset (within a set of similar assets), the more its price is likely to increase during the upgoing phase of a speculative price peak. In short, instead of being risk averse, as is often assumed, investors rather seem to be "risk prone". While this effect is known to hold for several sorts of assets, it has not yet been possible to test it for stocks because the price of one share has no intrinsic significance, which means that one cannot say that stock A is more expensive than stock B on the basis of its price. In this paper we show that the price-dividend ratio gives a good basis for assessing the price of stocks in an intrinsic way. When this alternative measure is used instead, it turns out that the price multiplier effect also holds for stocks, at least if one concentrates on samples of companies which are sufficiently homogeneous.
ON THE EVALUATION OF NOISE LEVELS FOR QUANTIZED DATA
Authors: SUZUKI TOMOYA , IKEGUCHI TOHRU , SUZUKI MASUO
Published: April 2004

In recent years, quantitative methods for evaluating chaotic properties have been developed in the field of nonlinear time-series analysis. The embedding theorem, which is a mathematical background for the methods, assumes an ideal situation in which noiseless time series are observed with infinite resolution and an infinite amount of data points. However, under real situations we cannot ignore two classes of noises which are included in really observed data. The first one is observational and dynamical noises which depend on internal nonlinear systems and performance of observational instruments. The second one is quantization error included in the time series since we usually use digital computers for applying the methods. In the present paper, we derive formulae for evaluating the levels of observational and quantization noises in the case of embedding observed time series in reconstructed state spaces. By measuring a distance between noiseless and noisy attractors, we also confirm that the derived formulae are appropriate for quantifying the noise included in the reconstructed attractor.
NONLINEAR DEVELOPMENT OF BACTERIAL COLONY MODELED WITH CELLULAR AUTOMATA AND AGENT OBJECTS
Authors: KRAWCZYK KRZYSZTOF , DZWINEL WITOLD , YUEN DAVID A.
Published: April 2004

Despite a number of different numerical techniques existing for modeling the uptake of the nutrients, metabolism, maintenance, cell division and growth of bacteria population, none of them can be treated as a universally one. In this new model we have combined two techniques. The first one — agent-based — has been used for modeling the behavior of an individual bacterium. The agent objects (AOs) define generic features of the bacterium and the ways they interact with the environment and with the neighboring bacteria. The cellular automata are used for modeling the bacterial environment and represent communication layer for the agents, while a fixed two-dimensional grid defines the living space. The growth of the bacterial colony depends on the amount of free space in the closest neighborhood of individuals, which is required for reproduction, and on the availability of nutrients. We have matched the parameters of the model to demonstrate various growth structures developed by bacteria populations. We show that the patterns generated by the bacteria due to their collective behavior reflect the dynamical vitality of population and its fitness factor. We observe that the strongest populations self-organize in rod-like structures, which are reproduced in experimental microscopy images characteristic for bioflims and anthrax bacterial colonies.
BIASED DIFFUSION: TRAP ANALYSIS IN TWO DIMENSIONS
Authors: KIRSCH ALEXANDER
Published: April 2004

A method for analyzing clusters which block the random walk of particles in two-dimensional biased diffusion on percolation lattices above the percolation threshold pc is presented, focusing on the arising problems and explaining the phase transition. The difficulties in a precise trap definition are illustrated. Different trap definitions result in different trap statistics, more or less capable of capturing the trend of the phase diagram.
PHASE DIAGRAMS OF SYSTEMS WITH TWO COUPLED ORDER PARAMETERS
Authors: NICOLAIDES D. , LISYANSKY A. A.
Published: April 2004

Within the framework of an exactly solvable model, which takes into account only the interaction of fluctuating modes with equal and opposite momenta, we study phase diagrams in systems with coupled scalar order parameters. We show that, in agreement with renormalization group theory, the fluctuation interaction can split the continuous order–disorder transition locus into two phase transitions of first order, replacing a bicritical point by a triple point and two tricritical points. The effect disappears when the fluctuation interaction is reduced.
SIMULATION STUDIES OF ADSORPTION-INDUCED SURFACE SEGREGATION IN BIMETALLIC Pd–Cu NANOSTRUCTURES
Authors: KHANRA BADAL C. , MENON MAHESH
Published: April 2004

We use the Monte-Carlo (MC) simulation technique to study the role of various coverages of (CO) adsorption on the spatial distribution of atoms on the surface of fcc cubo-octahedral Pd–Cu nanoparticles. The coordination-dependent pair interaction energy, required for the MC simulation, has been computed by an empirical formula obtained from the experimental values of dimer energy, (100) surface energy and the energy for monovacancy creation for constituent metals. It has been found that for clean particles of all sizes the surface is enriched in Cu. However, with increase in (CO) adsorption the extent of Cu segregation gradually reduces and at higher (CO) coverage there is segregation reversal leading to Pd segregation. At low coverage, usually the six- and seven-coordinated sites are occupied by Cu atoms. But at higher coverage (θ>0.25) they are also gradually occupied by Pd atoms along with the fcc(100)- and fcc(111)-like face sites. For a full monolayer coverage surface sites of all coordinates are occupied by Pd atoms. The significance of these results in the context of catalytic activity of alloys is discussed.
POLARITON-ADDED MECHANISM FOR NONCLASSICAL EXCITON PRODUCTION
Authors: AN NGUYEN BA , TINH VO
Published: April 2004

We have shown that the coupling of a coherent exciton–photon system to an m-photon two-level atom may produce both quadrature-amplitude and number-phase squeezed excitons.
THE EFFECTS OF QUENCHED DISORDER ON THE CHAOTIC DIFFUSION FOR SIMPLE MAPS
Authors: TSENG HSEN-CHE , CHEN HUNG-JUNG
Published: April 2004

That both normal and anomalous chaotic diffusions are suppressed by the presence of quenched disorder for a large class of maps was established by G. Radons.1 In this paper, we consider simple maps (which exhibit normal diffusion) modified by discrete disorder. By decomposing the mean square displacement (MSD) σ2(t) of the system into three terms, namely, [Formula: see text], we find that the MSD of the random walk which corresponds to disorder, [Formula: see text], enhances that of the original unmodified map, [Formula: see text] and that the term 2σ01(t), which describes the correlation between the diffusion fronts of the previous two diffusive processes, just essentially cancels the sum of [Formula: see text] and [Formula: see text]. In consequence, the trajectories of the system are effectively localized. In this formalism, exact numerical calculations without any round-off error can be achieved, the numerical errors coming only from the limited sampling of the initial conditions.
ELECTRONIC STRUCTURE OF GaxIn1-xASyP1-y QUATERNARY ALLOY BY RECURSION METHOD
Authors: EL-HASAN MUSA
Published: April 2004

The electronic structure of Ga x In 1-x As y P 1-y quaternary alloy, calculated by recursion method is reported. A five orbitals sp3s* per atom model was used in the tight-binding representation of the Hamiltonian.

The local density of states and its orbital decomposition (LDOS), integrated density of states (IDOS) and structural energy (STE) were calculated for Ga, In, As and P sites in Ga 0.5 In 0.5 As 0.5 P 0.5, GaInAsP lattice matched to InP and lattice matched to GaAs as well. There are 216 atoms arranged in a zinc-blend structure. The calculated quantities are as expected for such systems.
QUALITATIVE RESONANCE OF SHIL'NIKOV-LIKE STRANGE ATTRACTORS, PART I: EXPERIMENTAL EVIDENCE
Authors: DE FEO OSCAR
Published: April 2004

This is the first of two papers introducing a new dynamical phenomenon, strongly related to the problems of synchronization and control of chaotic dynamical systems, and presenting the corresponding mathematical analysis, conducted both experimentally and theoretically. In particular, it is shown that different dynamical models (ordinary differential equations) admitting chaotic behavior organized by a homoclinic bifurcation to a saddle-focus (Shil'nikov-like chaos) tend to have a particular selective property when externally perturbed. Namely, these systems settle on a very narrow chaotic behavior, which is strongly correlated to the forcing signal, when they are slightly perturbed with an external signal which is similar to their corresponding generating cycle. Here, the "generating cycle" is understood to be the saddle cycle colliding with the equilibrium at the homoclinic bifurcation. On the other hand, when they are slightly perturbed with a generic signal, which has no particular correlation with their generating cycle, their chaotic behavior is reinforced. This peculiar behavior has been called qualitative resonance underlining the fact that such chaotic systems tend to resonate with signals that are qualitatively similar to an observable of their corresponding generating cycle. Here, the results of an experimental analysis are presented together with an intuitive geometrical qualitative model of the phenomenon.
STOCHASTIC SIMULATION OF CHEMICAL CHUA SYSTEM
Authors: LI QIAN SHU , ZHU RUI
Published: April 2004

A master equation for a scheme of chemical Chua system has been simulated stochastically. Two pairs of reaction simulations, one pair corresponding to deterministic chaos and the other pair to limit cycle, are carried out. The initial conditions differ with only one molecule for the former, while one hundred molecules for the latter. The rapid separation of time traces is shown only in the former case. This marked difference of dynamic behavior between the two cases might reveal the intrinsic random nature of deterministic chemical chaos, i.e. initial-condition sensitivity based on random collision events.
CONTROL OF THE CHUA'S SYSTEM BASED ON A DIFFERENTIAL FLATNESS APPROACH
Authors: AGUILAR-IBÁÑEZ CARLOS , SUÁREZ-CASTAÑÓN MIGUEL , SIRA-RAMÍREZ HEBERTT
Published: April 2004

In this paper, we present a flatness based control approach for the stabilization and tracking problem, for the well-known Chua chaotic circuit, that includes an additional input. We introduce two feedback controller design options for the set-point stabilization and the trajectory tracking problem: a direct pole placement approach, and Generalized Proportional Integral (GPI) approach based only on measured inputs and outputs.
CHAOS SYNCHRONIZATION IN SC-CNN-BASED CIRCUIT AND AN INTERESTING INVESTIGATION: CAN A SC-CNN-BASED CIRCUIT BEHAVE SYNCHRONOUSLY WITH THE ORIGINAL CHUA'S CIRCUIT?
Authors: KILIÇ RECAI
Published: April 2004

In this work, after giving a complete verification of the continuous synchronization between two identical SC-CNN-based circuits depending on the driving variable, we have investigated the continuous synchronization phenomenon between SC-CNN-based circuit and Chua's circuit. PSpice simulation results confirm that SC-CNN-based circuit can behave synchronously with Chua's circuit in the case when very accurate parameter equalities are provided.
TIME-DELAYED IMPULSIVE CONTROL OF CHAOTIC HYBRID SYSTEMS
Authors: TIAN YU-PING , YU XINGHUO , CHUA LEON O.
Published: April 2004

This paper presents a time-delayed impulsive feedback approach to the problem of stabilization of periodic orbits in chaotic hybrid systems. The rigorous stability analysis of the proposed method is given. Using the time-delayed impulsive feedback method, we analyze the problem of detecting various periodic orbits in a special class of hybrid system, a switched arrival system, which is a prototype model of many manufacturing systems and computer systems where a large amount of work is processed in a unit time. We also consider the problem of stabilization of periodic orbits of chaotic piecewise affine systems, especially Chua's circuit, which is another important special class of hybrid systems.
QUANTUM-CNN TO GENERATE NANOSCALE CHAOTIC OSCILLATORS
Authors: FORTUNA LUIGI , PORTO DOMENICO
Published: April 2004

In this letter we consider coupled quantum-dot cells, which are usually used for Quantum-dots Cellular Automata (QCA), to build Cellular Nonlinear Networks. In particular, it is shown how simple connection of few quantum-dot cells (even two of them) can cause the onset of chaotic oscillation only with small differences of polarizations and template between cells. An example of polarizations evolution in two adjacent cells is reported where hyperchaotic behavior has been observed. The richness of dynamics of Quantum CNN with only few dots is also emphasized.
MULTISTABILITY, BASIN BOUNDARY STRUCTURE, AND CHAOTIC BEHAVIOR IN A SUSPENSION BRIDGE MODEL
Authors: DE FREITAS MÁRIO S. T. , VIANA RICARDO L. , GREBOGI CELSO
Published: April 2004

We consider the dynamics of the first vibrational mode of a suspension bridge, resulting from the coupling between its roadbed (elastic beam) and the hangers, supposed to be one-sided springs which respond only to stretching. The external forcing is due to time-periodic vortices produced by impinging wind on the bridge structure. We have studied some relevant dynamical phenomena in such a system, like periodic and quasiperiodic responses, chaotic motion, and boundary crises. In the weak dissipative limit the dynamics is mainly multistable, presenting a variety of coexisting attractors, both periodic and chaotic, with a highly involved basin of attraction structure.
COUPLED BISTABLE MAPS: A TOOL TO STUDY CONVECTION PARAMETERIZATION IN OCEAN MODELS
Authors: LIND PEDRO G. , TITZ SVEN , KUHLBRODT TILL , CORTE-REAL JOÃO A. M. , KURTHS JÜRGEN , GALLAS JASON A. C. , FEUDEL ULRIKE
Published: April 2004

We present a study of ocean convection parameterization based on a novel approach which includes both eddy diffusion and advection and consists of a two-dimensional lattice of bistable maps. This approach retains important features of usual grid models and allows to assess the relative roles of diffusion and advection in the spreading of convective cells. For large diffusion our model exhibits a phase transition from convective patterns to a homogeneous state over the entire lattice. In hysteresis experiments we find staircase behavior depending on stability thresholds of local convection patterns. This nonphysical behavior is suspected to induce spurious abrupt changes in the spreading of convection in ocean models. The final steady state of convective cells depends not only on the magnitude of the advective velocity but also on its direction, implying a possible bias in the development of convective patterns. Such bias points to the need for an appropriate choice of grid geometry in ocean modeling.
A SMOOTHING ALGORITHM FOR NONLINEAR TIME SERIES
Authors: BILLINGS S. A. , LEE K. L.
Published: April 2004

A new NARMA based smoothing algorithm is introduced for chaotic and nonchaotic time series. The new algorithm employs a cross-validation method to determine the smoother structure, requires very little user interaction, and can be combined with wavelet thresholding to further enhance the noise reduction. Numerical examples are included to illustrate the application of the new algorithm.
SECURE COMMUNICATIONS USING CASCADED CHAOTIC OPTICAL RINGS
Authors: YOSHIMURA K.
Published: April 2004

We show that transmitter and receiver systems consisting of cascaded chaotic optical rings can synchronize when they are coupled by using direct light injection from the transmitter into the receiver. Binary messages can be transmitted by the chaotic switching scheme. The proposed chaos secure communication system can satisfy some requirements to enhance security.
FITZHUGH–NAGUMO REVISITED: TYPES OF BIFURCATIONS, PERIODICAL FORCING AND STABILITY REGIONS BY A LYAPUNOV FUNCTIONAL
Authors: KOSTOVA TANYA , RAVINDRAN RENUKA , SCHONBEK MARIA
Published: April 2004

We study several aspects of FitzHugh–Nagumo's (FH–N) equations without diffusion. Some global stability results as well as the boundedness of solutions are derived by using a suitably defined Lyapunov functional. We show the existence of both supercritical and subcritical Hopf bifurcations. We demonstrate that the number of all bifurcation diagrams is 8 but that the possible sequential occurrences of bifurcation events is much richer. We present a numerical study of an example exhibiting a series of various bifurcations, including subcritical Hopf bifurcations, homoclinic bifurcations and saddle-node bifurcations of equilibria and of periodic solutions. Finally, we study periodically forced FH–N equations. We prove that phase-locking occurs independently of the magnitude of the periodic forcing.
SN-EQUIVARIANT SYMMETRY-BREAKING BIFURCATIONS
Authors: ELMHIRST TOBY
Published: April 2004

I analyze generic symmetry-breaking bifurcations of S N-equivariant vector fields (where genericity is in the restricted space of S N-equivariant systems). The normal form for the Liapunov–Schmidt reduced bifurcation problem is derived, and its codimension 1 symmetry-breaking bifurcations are investigated. Branch equations are given along with the conditions for stability, and the parameter space is partitioned accordingly. Applications in complex systems theory are suggested in which the dynamics of S N-equivariant systems are used to model the emergent behavior of systems of multiple interacting agents.
ON SEMI-ANALYTICAL PROCEDURE FOR DETECTING LIMIT CYCLE BIFURCATIONS
Authors: ROBBIO FEDERICO I. , ALONSO DIEGO M. , MOIOLA JORGE L.
Published: April 2004

This paper reports some computation of periodic solutions arising from Hopf bifurcations in order to build up a more accurate procedure for semi-analytical approximations to detect limit cycle bifurcations. The approximation formulas are derived using nonlinear feedback systems theory and the harmonic balance method. The monodromy matrix is computed for several simple nonlinear flows to detect the first bifurcation of the cycles in the neighborhood of the original Hopf bifurcation.
DYNAMICAL ANALYSIS OF A CHAOTIC SYSTEM WITH TWO DOUBLE-SCROLL CHAOTIC ATTRACTORS
Authors: LIU WENBO , CHEN GUANRONG
Published: April 2004

Dynamical behaviors of a three-dimensional autonomous chaotic system with two double-scroll attractors are studied. Some basic properties such as bifurcation, routes to chaos, periodic windows and compound structure are demonstrated with various numerical examples. System equilibria and their stabilities are discussed, and chaotic features of the attractors are justified numerically.
SYMMETRY INDUCED HETEROCLINIC CYCLES IN A CO2 LASER
Authors: LÓPEZ-RUIZ R. , BOCCALETTI S.
Published: April 2004

The conditions for the existence of heteroclinic connections between the transverse modes of a CO 2 laser whose setup has a perfect cylindrical symmetry are discussed by symmetry arguments for the cases of three, four and five interacting modes. Explicit conditions for the parameters are derived, which can guide observation of such phenomena.
QUALITATIVE RESONANCE OF SHIL'NIKOV-LIKE STRANGE ATTRACTORS, PART II: MATHEMATICAL ANALYSIS
Authors: DE FEO OSCAR
Published: April 2004

This is the second of two papers introducing a new dynamical phenomenon, strongly related to the problems of synchronization and control of chaotic dynamical systems, and presenting the corresponding mathematical analysis, conducted both experimentally and theoretically. In particular, it is shown that different dynamical models (ordinary differential equations) admitting chaotic behavior organized by a homoclinic bifurcation to a saddle-focus (Shil'nikov-like chaos) tend to have a particular selective property when externally perturbed. Namely, these systems settle on a very narrow chaotic behavior, which is strongly correlated to the forcing signal, when they are slightly perturbed with an external signal which is similar to their corresponding generating cycle. Here, the "generating cycle" is understood to be the saddle cycle colliding with the equilibrium at the homoclinic bifurcation. On the other hand, when they are slightly perturbed with a generic signal, which has no particular correlation with their generating cycle, their chaotic behavior is reinforced. This peculiar behavior has been called qualitative resonance underlining the fact that such chaotic systems tend to resonate with signals that are qualitatively similar to an observable of their corresponding generating cycle. Here, a detailed mathematical analysis of the qualitative resonance phenomenon is presented, confirming the intuitions given by the geometrical model discussed in Part I.
CHAOS AND CONTROL OF TRANSIENT CHAOS IN TURBO-DECODING ALGORITHMS
Authors: KOCAREV LJUPCO , TASEV ZARKO
Published: April 2004

We suggest a link between coding theory (iterative algorithms) and chaos theory. A whole range of phenomena known to occur in nonlinear systems, like the existence of multiple fixed points, oscillatory behavior, bifurcations, chaos and transient chaos are found in turbo-decoding algorithms. We develop a simple technique to control transient chaos in turbo-decoding algorithms and improve the performance of the classical turbo codes.
ALLOY FORMATION OF ULTRATHIN Ni FILMS ON Al(111) SURFACE AT ROOM TEMPERATURE
Authors: KIM Y. W. , WHITE G. A. , REIBEL R. , SMITH R. J.
Published: April 2004

The growth characteristics of ultrathin Ni films deposited on Al(111) surfaces at room temperature have been studied using high energy ion scattering/channeling (HEIS), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Ion channeling results show that Ni atoms deposited on the Al(111) surface react with Al substrate atoms to form two different Ni–Al alloys between 0 and 5.5 ML of Ni coverage. Alloy phases of Ni 2 Al 3 up to 1.5 ML and NiAl up to 5.5 ML were determined by XPS peak analysis. At higher Ni coverage, LEIS and XPS spectra suggest that islands of Ni metal were formed on the surface. Diffusion of Ni into the Al substrate or segregation of Al to the surface was observed during the alloy formation. The Ni 2 Al 3 phase was apparently transformed into the NiAl phase by the additional Ni deposition, and the islands of Ni metal formed on the Al-rich surface of the NiAl alloy.
THE INTERACTION OF CARBON DIOXIDE WITH SINGLE CRYSTAL CaO(100) SURFACES
Authors: DOYLE C. S. , KENDELEWICZ T. , CARRIER X. , BROWN G. E.
Published: April 2004

We have carried out synchrotron-based photoemission spectroscopy ( O 1s, C 1s, Ca 2p, Ca 3p/ O 2s/ VB ) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy (C K-edge) study of the interaction of CO 2 with UHV-cleaved synthetic single crystal CaO(100) surfaces. Our data are compared with data collected from a high quality natural sample of [Formula: see text] (calcite). The CaO (100) surface readily undergoes hydroxylation with the ambient p H2O associated with most UHV systems. Carbon coverages were observed to be lower for the most hydroxylated sample. Comparison of our C K-edge data for CO 2/ CaO(100) and calcite indicates that there is formation of a surface carbonate species at CO 2 pressures above 10-6 Torr. The reaction of CaO(100) with CO 2 occurs at far lower CO 2 pressures than for MgO(100), which is consistent with equilibrium thermodynamic predictions.
A new species of Phyllodytes (Anura: Hylidae) from the State of Sergipe, Northeastern Brazil
Authors: Caramaschi Ulisses , Peixoto Oswaldo Luiz
Published: April 2004

A new species of the genus Phyllodytes is described from Fazenda Gravatá (10° 47'S, 36° 54'W), Municipality of Santo Amaro das Brotas, State of Sergipe, Brazil. Phyllodytes punctatus sp. nov. is distinguished from all other species of the genus by the small size (SVL 18.2-22.8 mm; x 20.6, s 1.49), dorsum of body pale brown with distinctive brown dots and smaller brown dots on dorsal surfaces of hindlimbs, dorsal surfaces of body and hindlimbs with small rounded tubercles, and presence of a distinctive tubercle on the tip of snout and one to three small tubercles on upper eyelid.
Diet divergence, jaw size and scale counts in two neighbouring populations of tiger snakes (Notechis scutatus)
Authors: Bradshaw Don , Fabien Aubret , Maumelat Stéphanie , Schwaner Terry , Bonnet Xavier
Published: April 2004

Large snakes usually possess a higher number of scales to cover their larger bodies and their larger heads. It has been suggested that a diet based on large prey items also favours the development of scale number because the skin would be more extensible and would enable easier swallowing of voluminous prey. A recent study, however, suggested that although body size positively influences scale count in snakes, diet is probably unimportant (Shine, 2002). We took advantage of a natural experiment that separated two neighbouring and genetically indistinguishable populations of tiger snakes in the vicinity of Perth, Western Australia. In one population, situated on a small coastal Island (Carnac Island), snakes feed primarily on seagull chicks (large prey). In the second population, located on the mainland (Herdsman Lake), snakes feed mostly on frogs (small prey). Carnac Island snakes possess more scales (labial and mid-body rows) and larger relative jaw lengths compared with Herdsman Lake snakes. Although preliminary, these data suggest that tiger snakes, whose many populations show contrasted feeding habits, are suitable models to test the "dietary habits / scale count" hypothesis.
Integumental water movement and rate of water ingestion during rain harvesting in the Texas horned lizard, Phrynosoma cornutum
Authors: Sherbrooke Wade
Published: April 2004

Capture of rainfall on skin surfaces and its transport via capillary channels between scales to the mouth for drinking has been documented in a few agamid (Moloch and Phrynocephalus) and iguanid (Phrynosoma spp.) lizards. Associated behaviors include a postural stance and jaw motions. This experimental study documents that rate of jaw opening and closing cycles is positively correlated with rate of water delivery to lizards' backs and to gain in mass of lizards attributable to drinking. The mean mass of water that can be held by the interscalar, capillary-flow system is correlated with body size, smaller lizards holding a larger percentage of their body mass in the rain-harvesting system. Ingestion mechanisms for water flow from the integumental channels to the mouth surfaces for drinking are discussed, with note being made of the possible roles of a fold of skin at the jaw angle (at the postlabial scales) and tongue actions. Recent hatchlings exhibit rain-harvesting behavior, suggesting its innate nature.
The effect of supplemental feeding on the territorial behavior of the green frog (Rana clamitans)
Authors: Gordon Noah
Published: April 2004

The green frog, Rana clamitans, exhibits a resource defense mating strategy whereby males advertise for mates and defend territories along the shoreline of breeding ponds for periods up to several weeks. Because male green frogs may be energy-limited during the breeding season, I tested the predictions that males provided with extra food would 1) have longer tenures on territories, 2) show reduced movement between territories (due to greater site specificity), and 3) expend more energy in calling and territory defense. I tested these predictions by supplementally feeding frogs and by conducting regular surveys of frog location and behavior over the course of the breeding season in a fenced-in pond. My results support the second prediction but do not support the first and third predictions. Supplementally-fed male green frogs moved less than half the distance of sham-fed males. Green frog males reduce foraging but do not increase activities associated with aggression and territorial defense when food resources are more abundant.
Spatial patterns in species richness and priority areas for conservation of anurans in the Cerrado region, Central Brazil
Authors: Brandão Divino , Bastos Rogério , De Souza Márcia , Vieira Cleiber , Bini Luis , Oliveira Leandro , Diniz-Filho José Alexandre
Published: April 2004

Declines in anuran populations worldwide are increasingly creating demands for quick and urgent strategies to maximize efforts to conserve amphibian populations, especially in areas in which few detailed data on diversity, abundance and distribution are available, such as the Cerrado of Central Brazil. We used extent of occurrence of 105 species of Anura (Amphibia) in the Cerrado region to establish a regional system of potential areas that preserves all anuran species in the region, at a macroecological scale. The final network, obtained using a simple "greedy" algorithm based on complementarity, has a total of 10 regions, widely distributed in the biome. These areas were also evaluated in terms of their human demographic parameters (human population size and growth rate). Strong spatial autocorrelation in species richness indicates that alternative systems based on pre-existing conservation units will also be efficient in terms of biodiversity conservation. Although macro-scale approaches are usually coarse, they can provide overall guidelines for conservation and define the focus for more local and effective conservation efforts, which is particularly important when dealing with a taxonomic group such as anurans for which quick and drastic population declines have been reported in many regions of the world.
Reproductive biology of the southern Brazilian pitviper Bothrops neuwiedi pubescens (Serpentes, Viperidae)
Authors: Marques Otavio , Almeida-Santos Selma , Hartmann Marília
Published: April 2004

Dissection of 286 specimens of the Bothrops neuwiedi pubescens, combined with data on captive individuals, provided information on the reproductive biology of this viperid snake from southern Brazil. Females attained larger body sizes than males, and reproduction was seasonal with mating taking place in autumn when males were more frequently encountered. Vitellogenesis occurred from summer to spring (January-September), sperm storage during autumn and winter (May-September), ovulation and fertilization in early spring (September), embryonic development during middle spring and summer (October-March), and parturition in the summer (January-March). Embryonic development was estimated to last from three to five months, a shorter time than was previously reported. The number of offspring of Bothrops neuwiedi pubescens born in one litter can vary from four to 25 (x = 11). Fecundity is correlated with maternal body size. Neonates measure 17-25 cm SVL. Inferred growth rate of juveniles was low (10 mm/month in first year), with males attaining sexual maturity at about 16 months, but maturity is delayed in females for at least two additional years.
On the taxonomy of ichthyophiid caecilians from southern Thailand: A reevaluation of the holotype of Ichthyophis supachaii Taylor 1960 (Amphibia: Gymnophiona: Ichthyophiidae)
Authors: Müller Hendrik , Kupfer Alexander
Published: April 2004

The taxonomy of South-East Asian ichthyophiid caecilians is largely in a woeful state. We give a new diagnosis for Ichthyophis supachaii from Thailand, based on a reexamination of the complete type series and recently collected material. The holotype is redescribed. The higher number of splenial than dentary teeth, a previously reported main diagnostic character of the taxon, is rejected. Ichthyophis supachaii follows the usual pattern of ichthyophiid caecilians in having more dentary than splenial teeth. Nevertheless, Ichthyophis supachaii is regarded as a valid taxon based on several morphometric and meristic characters. We provide a detailed description of the male phallodeum.