bluuebunny/crossref_metadata_2025 huggingface dataset:
Photo-oxidation of SO2 and of SO2 trapped in amorphous water ice studied by IR spectroscopy. Implications for Jupiter's satellite Europa
Authors: Schriver-Mazzuoli L , Schriver A , Chaabouni H
Published: May 2003

Fourier Transform Infrared Spectroscopy (FTIR), is used to characterize thin films of sulfur dioxide trapped in excess of amorphous water ice and to study the photo-oxidation of pure solid SO2 or of SO2 diluted in water ice. These laboratory experiments were undertaken in an attempt to find information on the formation of hydrated sulfuric acid detected on Europa's surface. Vibrational spectra at 30 K of mixed films containing SO2 with an excess of water depend on the deposition conditions. A metastable (SO2)m(H2O)n phase and a solid solution of SO2 in water ice have been evidenced. Irradiation at 266 nm of mixed films SO2/O3/H2O produces sulfur trioxide and hydrogen peroxide without traces of sulfuric acid. Irradiation of films of pure SO2, under 200 nm, leads to sulfur trioxide and to ozone. When SO2 is diluted in amorphous water ice, new weak bands that appear after irradiation suggest the formation of sulfuric acid.

PACS No.: 82.50Hp
Neutron-scattering studies of the phase transitions in high-pressure ices during annealing
Authors: Wang Y. , Kolesnikov A I , Dong S L , Li J C
Published: May 2003

Inelastic incoherent neutron scattering was used to study the phase transition process of high-density amorphous (HDA) ice to low-density amorphous (LDA) ice by thermal treatment. The results show that when the annealing temperature is lower than 136 K no obvious phase-transition is observed, and transformation of the HDA ice to the LDA ice occurs between 136 and 144 K. From comparison of the measured inelastic neutron-scattering spectra for HDA ice and ice Ih, it is found that the internal interactions (covalent bond OH and three-body interaction HOH) are stronger in HDA ice, which correlates with the longer nearest OO distances in HDA ice compared to ice Ih (2.80 and 2.75 Å, respectively). The report also discusses the differences in vibrational spectra of LDA ices obtained by different methods (annealing HDA ice and depositing water vapour on a cold substrate).

PACS No.: 64.60-i
A neural network framework for mechanical behavior of unsaturated soils
Authors: Habibagahi Ghassem , Bamdad Alireza
Published: May 2003

In this paper, a neural network approach is used to describe the mechanical behavior of unsaturated soils. A sequential architecture was chosen for the network, that is, a multilayer perceptron network with feedback capability. The input layer consisted of nine neurons, where six of them represented the initial soil conditions and the remaining three neurons were continuously updated for each increment of axial strain based on outputs from the previous increment. The output layer consisted of three neurons representing values of deviatoric stress, volumetric strain, and change in suction at the end of each increment. Next, a database was developed from triaxial test results available in the literature. The database was used to train and test the network. Neural network simulations were compared with experimental results. The comparison indicates the good performance of the proposed network for predicting the mechanical behavior of unsaturated soils. Moreover, the trained network was employed to simulate other stress paths not present in the database to model the so-called "collapse phenomena." The results were promising.Key words: unsaturated soil, neural network, stressstrain, collapse, modeling, constitutive law.
Strain-induced anisotropy in fabric and hydraulic parameters of oil sand in triaxial compression
Authors: Wong Ron CK
Published: May 2003

Dense locked Athabasca oil sand specimens were tested in drained triaxial compression with lubricated ends at confining pressures of 5750 kPa. Computer tomography and scanning electron microscopy imaging techniques were used to examine the microstructural features (interlocked structure, grain fabric, and rearrangement inside and outside shear bands) of the intact and sheared specimens. The average hydraulic radii and tortuosity along three principal directions were also measured using thin section imaging and electrical resistivity measurement methods. It was found that changes in fabric and hydraulic parameters of oil sand in triaxial compression are highly inter-related. Intrinsic and induced anisotropies in permeability were observed.Key words: oil sand, fabric, strain induced anisotropy, permeability, tortuosity, dilatancy.
Genetic structure ofAcer platanoidesandBetula pendulain northern Europe
Authors: Rusanen M , Vakkari P , Blom A
Published: May 2003

Marker variation was measured in 12 Acer platanoides L. and 9 Betula pendula Roth populations using 11 and 18 allozyme loci, respectively. Both species grow in the borealtemperate zone. Insect-pollinated A. platanoides with limited seed dispersal has a scattered occurrence, while wind-pollinated B. pendula with light wind-dispersed seeds has a more continuous distribution. The average expected heterozygosity was 0.132 for A. platanoides and 0.141 for B. pendula. Genetic differentiation among A. platanoides populations (Fst= 0.099) was higher than that of B. pendula (Fst= 0.032). Expected heterozygosities in marginal and central populations of A. platanoides were at approximately the same level. Contrary to the expectation, differentiation was higher among central populations.
Variation among slash pine families in chlorophyll fluorescence traits
Authors: Koehn Anita C , Roberds James H , Doudrick Robert L
Published: May 2003

Photochemical quenching, nonphotochemical quenching, and yield of photosystem II were measured on seedlings of full-sibling, open-, and self-pollinated slash pine (Pinus elliottii Engelm. var. elliottii) families. Our results reveal that genetic variation in photochemical quenching and yield of photosystem II exists within this species. The pattern of variation found in these traits is consistent with the variance profile expected to occur as a result of segregation among nuclear genes. Variation among families accounted for 17% of the total variation observed in photochemical quenching, whereas the component for trees within families made up slightly more than 25% of the total. Less variation, both among families as well as among trees within families, was found for yield of photosystem II. A strikingly different pattern was observed for nonphotochemical quenching. Other than the error term, only pretreatment effects contributed significantly to the variation observed. This suggests that nonphotochemical quenching is largely influenced by environmental factors. With regard to associations between fluorescence and growth traits, both height and diameter growth were found to be positively correlated with photochemical quenching (0.36 and 0.33, respectively) when selfed and open-pollinated families were analyzed along with control-pollinated families.
Morphometric, allometric, and developmentally adaptive traits in red spruce and black spruce. I. Species and seed-source variation
Authors: Major John E , Mosseler Alex , Barsi Debby C , Campbell Moira , Rajora Om P
Published: May 2003

The study objective was to compare intraspecific seed source and interspecifc variation of red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) BSP) in a number of morphometric, allometric, and adaptive traits. Analyses of variance for cotyledon number, root dry weight, shoot to root ratio, and seedling water balance revealed significant species effects. Germination time, total height, diameter, needle and stem wood dry weight, and survival had significant species effects and species × region interactions. Potential inbreeding depression effects were reflected in a positive relationship between height growth and percent germination and a negative relationship between height growth and germination time; these effects may have partly contributed to the species × region interactions. On average, 66% of the height growth difference between the species may be attributable to earlier germination and the other 34% to faster growth. Covariate allometric analysis showed that black spruce had a 39% higher shoot to root ratio than red spruce. Red spruce allocated 25% more dry weight (per unit needle weight) towards roots than did black spruce. When the resource sinks (stem wood and roots) are summed, black spruce is 8.6% more efficient at converting resources into sink biomass than is red spruce.
BROWNIAN MOTORS BASED ON ELECTRIC DIPOLE INTERACTION
Authors: ZHANG HONGWEI , ZHI LIANHE , LI YUXIAO
Published: May 2003

Brownian motors based on electric dipoles interaction are studied. Directed motion is induced by the transitions of the electric dipoles potentials between two states. The stationary probability current of the Brownian motors is evaluated. The current is sensitive to temperature and the values of the transition rates between two states. There are optimal values of temperature and the transition rates for the current, and for a suitable choice of the transition rates the current can be reversed.
FIELD PURIFICATION OF A GENERAL THREE-LEVEL SYSTEM INTERACTING WITH RADIATION
Authors: ABDEL-ATY MAHMOUD
Published: May 2003

In this essay we introduce a new Hamiltonian which represents the interaction between a three-level atom and a single electromagnetic field including arbitrary forms of nonlinearities of both the field and the intensity-dependent coupling. We derive an exact solution for the density operator of the system by means of which we study the field purity for the entangled state of the system. Also, the influences of the nonlinearities on the field purity and mean photon number are examined. Under the condition of an initial coherent field, the field purity shows the collapse-revival phenomenon. It is found that features of these phenomenon are sensitive to the changes of different kinds of the nonlinearities.
DIELECTRIC LOSSES IN ISOTENAX N
Authors: MITROI MIHAI RAZVAN , IANCU VLADIMIR , GAVRILA DOINA ELENA
Published: May 2003

The limits of the Maxwell–Wagner model for interfacial losses in composite materials are discussed. The model is improved by taking into account the frequency dependence of the loss resistances. The improved model is applied to the statistical analysis of the experimental data obtained on Isotenax N. The results of the model are in very good agreement with the experiment.
ATOMIC ENVIRONMENT IN LEAD-BISMUTHATE GLASSES CONTAINING MANGANESE
Authors: SIMON V. , BAKO-SZILAGYI H. , NEUMANN M. , CHIUZBĂIAN S. G. , SIMON S.
Published: May 2003

The atomic environment of 20MnO · 80(x Bi 2 O 3 · y PbO ) glass samples having the ratio of bismuth to lead atoms of 8:1 and 3:1 was investigated with respect to the thermal induced structural changes, cationic field strength and electronic structure of the compound. The position and full width at half maximum of X-ray photoelectron peaks were estimated using spectra simulation based on the summation of Lorentzian and Gaussian functions. Data obtained from XPS core-level spectra Bi 4f, Pb 4f, Mn 2p, and O 1s indicate a reduction of glass disorder both by heat treatment and by increasing the PbO content in the samples. The cations behave essentially as network formers that could be correlated with an intermediate range structure.
MAGNETIC TUNNEL JUNCTIONS BASED ON PARTIALLY-OXIDIZED-IRON ELECTRODES
Authors: PAN LIQING , WU SHUXIN , QIU HONG , WANG FENGPING , WU PING , ZHANG GUOHUA , ZHANG GUOMIN
Published: May 2003

Partially-oxidized-iron(Fe-O)-based magnetic tunnel junctions with large magnetoresistance have been fabricated. The compositions, and the structural and transport properties of the two Fe-O electrodes are characterized. The top Fe-O layer containing 25%–28% oxygen shows a metallic characteristic with fine grain structure. No crystalline iron oxides are detected in the layer. The bottom Fe-O layer whose surface was oxidized during the oxidation process of the Al layer reveals the formation of α-Fe2O3 at the surface. The α-Fe2O3(104) is likely to be epitaxially grown on the Fe(110) plane. The layer shows a nonmetallic transport feature with negative temperature coefficient of resistance.
MAGNETIC PROPERTIES OF CaxLa1 - xMnO3 (x > 0.5) PEROVSKITES
Authors: HIMCINSCHI C. , BURZO E. , TETEAN R. , RISTOIU D. , POP V.
Published: May 2003

The magnetic properties of Ca x La 1 - x MnO 3 perovskites with x = 0.6 and x = 0.8 were studied in a large temperature range. A transition from mictomagnetic to antiferromagnetic state is evidenced at low temperatures for the samples with high lanthanum content. As the calcium content increases an essential antiferromagnetic behaviour is shown. The valences states of Mn ions were determined. The interactions inside the magnetic sublattices dominate those between the two sublattices as evidenced by the positive paramagnetic Curie temperature.
A LOW-POWER AND HIGH-SPEED D FLIP-FLOP USING A SINGLE LATCH
Authors: CHANG ROBERT C. , HSU L.-C. , SUN M.-C.
Published: May 2003

A novel low-power and high-speed D flip-flop is presented in this letter. The flip-flop consists of a single low-power latch, which is controlled by a positive narrow pulse. Hence, fewer transistors are used and lower power consumption is achieved. HSPICE simulation results show that power dissipation of the proposed D flip-flop has been reduced up to 76%. The operating frequency of the flip-flop is also greatly increased.
A SYSTEMATIC PROCEDURE FOR SYNCHRONIZING HYPERCHAOS VIA OBSERVER DESIGN
Authors: GRASSI GIUSEPPE , MASCOLO SAVERIO
Published: May 2003

In this Letter a systematic procedure for synchronizing different classes of hyperchaotic systems is illustrated. The approach can be applied to dynamic systems with one or more nonlinear elements as well as to time delay systems. The method is rigorous and systematic. Namely, if a structural property related to the drive system is satisfied, it is easy to design the synchronizing signal and the response system, which is chosen in the observer form. The technique is successfully applied to a recent example of 8th order circuit, to a cell equation in delayed Cellular Neural Networks and to an example of high dimensional system, which consists of five identical coupled Chua's circuits forming a ring. Simulation results are reported to show the performances of the technique.
1 V OTA USING CURRENT DRIVEN BULK CIRCUITS
Authors: LEHMANN TORSTEN , CASSIA MARCO
Published: May 2003

We show how the MOST threshold voltage can be reduced simply by forcing a constant current through the transistor bulk terminal. We characterize two versions of the resulting current driven bulk device by simulations, and conclude that this is a good method for improving circuit performance when the voltage supply is very low. Finally we show how the technique can be used to implement a 1 V folded cascode OTA with compatible input and output voltage ranges.
CORRELATIVE MESSAGE GROUP DIGITAL SIGNATURE AND ITS APPLICATION TO E-COMMERCE
Authors: TANG SHAOHUA
Published: May 2003

A new kind of digital signature scheme, correlative message group (CMG) signature, which concerning a group of correlative messages, is proposed in this paper. Each message mi in the correlative message group {m1,m2,…,mn} can only be delivered to the dedicated recipient Ui. The recipient Uj will not know mi(j ≠ i; 1 ≤ i, j ≤ n), but each Uj(j = 1,2,…,n) should be able to verify the CMG signature. The procedure of generating and verifying the CMG signature is described, and the security and performance of which are analyzed. A sample application of CMG signature to e-commerce is presented in this paper also.
ON MODIFIED COMPLEX RECURRENT NEURAL NETWORK ADAPTIVE EQUALIZER
Authors: JIANG HONG RUI , KWAK KYUNG SUP
Published: May 2003

A new modified version called decision feedback complex recurrent neural network equalizer (DFCRNNE) is proposed with the study of complex recurrent neural network equalizer (CRNNE). Based on DFCRNNE, a modified real time recurrent learning (CRTRL) algorithm is developed. Simulation results show that DFCRNNE has better performance than CRNNE based on traditional CRTRL algorithm2 in complex nonlinear channels with severe intersymbol interference (ISI) and nonlinear distortion.
ANALYSIS OF CLASS D–E RESONANT dc/dc CONVERTER USING THINNED-OUT METHOD
Authors: KOIZUMI HIROTAKA , SASASE IWAO , MORI SHINSAKU
Published: May 2003

Previous analytical descriptions of the Class D–E resonant dc/dc converter using thinned-out method have been based on some assumptions, which are assumed to make it simple the evaluation about effects of thinned-out control on the equivalent impedance variation. Therefore the difference between the calculated values and the measured values is significant in case when thinned-out ratio is high. This paper presents a new analysis for this circuit. The equivalent impedance variation by thinned-out control is taken into consideration. The measured performance shows good agreement with the analytical performance in wide range.
ANALOG-TO-DIGITAL INTERFACE FOR HETERODYNE RECEIVERS
Authors: PNEVMATIKAKIS ARISTODEMOS , DERMENTZOGLOU LAMPROS , ARAPOYANNI AGGELIKI
Published: May 2003

The analysis of the Intermediate Frequency (IF) section of a heterodyne receiver employing IF sampling, based on its Carrier-to-Interference ratio (C/I), yields various options on filtering, amplification, conversion to digital and interfacing to base-band. These options are considered using Bit Error Rate (BER) simulations, leading to an optimized design for the IF section and the interface to base-band of the heterodyne receiver.
OPTIMIZING SCALING FACTOR COMPUTATIONS IN FLAT CORDIC
Authors: SRIKANTHAN T. , GISUTHAN BIMAL
Published: May 2003

In CORDIC algorithm, where each micro-rotation (iteration) is realized by a shift and an add/subtract operation, a scaling operation on the resultant vector becomes necessary. In FLAT CORDIC, the CORDIC iterations are combined to form a single equation, which is expressed in terms of the initial vector.3 In this paper, a constructive method to attain a good scaling factor for FLAT CORDIC, by manipulating the basic FLAT CORDIC iterations, is proposed. The proposed method does not lead to an increase in the number of terms of the generalized FLAT CORDIC equation to an unacceptable level. Since the scaling factor computation is one of the major bottlenecks in the entire CORDIC procedure, the proposed method can be effectively used to speed up the FLAT CORDIC operation. The method employed to achieve a good scaling factor is explained in detail with the help of a suitable example.
AN IMPLEMENTATION OF LATTICE FILTERS USING FOUR OPERANDS REAL MULTIPLY ACCUMULATION
Authors: NEGISHI YOSHIMASA , WATANABE EIJI , NISHIHARA AKINORI
Published: May 2003

Four operands Real Multiply Accumulation (4op-RMA) is a method to implement transversal circuits, direct form circuits and 2D type circuits with real coefficients by using a complex multiplier. Digital Signal Processors (DSPs) with 4op-RMA implement these circuits twice as fast as the conventional ones. Besides, we can simplify the programs on such DSPs. However 4op-RMA have not been applied to the lattice circuits yet because of their circuit structures. In this paper, we propose an implementation method for the lattice circuits by using 4op-RMA. The lattice part can be calculated by a 4op-RMA operation, which corresponds to a complex multiplication.
LOW POWER 16 × 16 BIT MULTIPLIER DESIGN USING PAL-2N LOGIC FAMILY
Authors: WONG H. H. , LAU K. T.
Published: May 2003

Multiplication plays an important role in digital signal processing. Reducing the power consumption in multipliers will bring significant power reduction to the overall digital system. (7,3) counters are one of the components that are used in parallel multipliers though it is not so popular as the (4:2) compressor. Several (7,3) counters have been reported but most of them are implemented in conventional CMOS style. In this paper, a low power (7,3) counter based on adiabatic switching principles is proposed. HSPICE simulations show that it achieves huge power savings than the static CMOS counterpart.
SHORT-STEP BUTTERWORTH IMPEDANCE TRANSFORMERS
Authors: ZHU YI-SHENG , CHEN WAI-KAI
Published: May 2003

Based on a relationship among the order n (= 2m) of the impedance transformer, the impedance transformation ratio r and the 3-dB frequencies ωa and ωb, a 2m-order Butterworth semi-lumped-element impedance transformer is designed by using a coaxial structure, consisting of a cascade of line sections having various line impedances zi with the same effective length l. The performance of the resulting transformer is comparable to that of a smaller size quarter-wavelength transformer.
AN OPTIMAL DESIGN CONSIDERATION FOR HIGHER-ORDER DELTA–SIGMA AD CONVERTER
Authors: ZHANG YIKUI , HAYAHARA ETSURO , HIRANO SATOSHI , SAKAKIBARA NAOHITO
Published: May 2003

In this paper we proposed an approach for obtaining optimal stable modulator coefficients, which satisfy both SNR and stable input limit requirements. The empirical (3rd to 5th order) stable input limit formula is presented. Modulator examples are presented to demonstrate the usage of proposed method. The simulation results show that nearly 1-bit (6 dB) resolution is improved with the proposed method. The op-amp dc-offset influence on modulator performance is also discussed.
A KIND OF 2D ISOTROPIC WAVELET AND ITS APPLICATION IN IMAGE PRIMITIVE DETECTION
Authors: HOU ZHENGXIN , WANG WENQUAN , CHU JINGHUI
Published: May 2003

A custom-design of 2m-order nonorthogonal dyadic wavelet is proposed. The scaling function is 2m-order centered cardinal B-spline and the wavelet function dilated by factor 2 is proportional to the second difference of it. Taking them as 1D prototypes, the 2D minimum isotropic wavelet (MIW) along with a set of MIW filters and a bank of MIW packets are presented. The MIW filters are suitable for detecting edges and lines and the MIW packets can distinguish between multi-scale textures of an image. Some experimental results are given in this paper.
A COMPLETE MODEL FOR GLITCH ANALYSIS IN LOGIC CIRCUITS
Authors: CHUNG KI-SEOK , KIM TAEWHAN , LIU C. L.
Published: May 2003

One of the major factors, which contribute to the power consumption in CMOS combinational logic circuits, is the switching activities in the circuits. Many of such switching activities are due to spurious pulses, called glitches. Recently, a new model of glitch analysis, called G-vector has been proposed. The power of the model is that, unlike the existing ones, which model only the propagation of glitches to count the number of glitches in the circuits, it allows to model the generation, propagation and elimination of glitches to be able to not only count the number of glitches but also locate the glitches. In this paper, we complete the concept of G-vector by providing a set of efficient solutions to the three important practical issues: (1) extending to signals over multiple clock cycles, which exactly accounts for a sequence of input signals over multiple clock cycles. (2) extending to a nonzero delay model, which accounts for both nonzero and nonuniform delay of each gate in the circuit and (3) extending to a logic decomposition utilizing the model, which reveals a possibility of utilizing the model in synthesizing logic circuit with less glitches. Integrating the solutions all together enables G-vector to be practically very efficient. A set of experimental results is provided to show the effectiveness of the proposed solutions.
OVERSAMPLED CHAOTIC BINARY SEQUENCES WITH GOOD SECURITY
Authors: ZHANG HONGTAO , WANG HUIYUN , CHEN WAI-KAI
Published: May 2003

Based on chaotic maps, a simple method is given for obtaining the novel oversampled chaotic map (OSCM) binary sequences. Such sequences are a priori to chaotic map sequences in terms of the security. Furthermore, their balance property is optimal, the correlation properties of the two families are not clearly different, and the generation is easy. In this paper we also discuss the topological conjugation properties of the chaotic maps, analyze in details the reconstruction process of the chaotic sequences and the security of the OSCM binary sequences. The result demonstrates that OSCM binary sequences cannot be reconstructed, meaning that they are secure. Hence, the OSCM sequences are good spreading sequences for personal communications, especially for the secure communications.
QUEUE CONTROL UNDER TIME-VARIANT DELAYS: A DISCRETE TIME SYSTEM APPROACH
Authors: BAUER PETER H. , SICHITIU MIHAIL L. , PREMARATNE KAMAL
Published: May 2003

This paper introduces a discrete time model for time-variant delays and investigates the very nature of such delays. It is shown that a linear system-delay interface is a system theoretic necessity for the construction of composite linear systems with time-variant delays. Based on this analysis, two interfaces of particular importance are presented and used to obtain new, simple to check stability results for queue control systems. The relevance of the presented modeling and stability results on queue control systems to QoS control in modern communication networks is illustrated via several examples.
HIERARCHIC MODELS OF HELMHOLTZ PROBLEMS ON THIN DOMAINS
Authors: GERDES KLAUS , SCHWAB CHRISTOPH
Published: May 2003

The Helmholtz equation in a three-dimensional plate is approximated by a hierarchy of two-dimensional models. Computable a posteriori error estimators of the modeling error in exponentially weighted norms are derived, and sharp, computable estimates for their effectivity indices are also obtained. The necessity of including, besides polynomials, a certain number of trigonometric director functions into the Ansatz, in order to prevent pollution effects at high wave numbers is demonstrated both theoretically and computationally.
THE PEKERIS WAVEGUIDE: A CASE STUDY IN CLASSICAL APPLIED MATHEMATICS
Authors: ADAM JOHN A.
Published: May 2003

In this paper various mathematical models for underwater acoustic wave propagation are reviewed and summarized. The primary model is the Pekeris waveguide, and this is used as a case study by incorporating many related mathematical methods in a single context. Often such methods are perceived by graduates in a compartmentalized fashion, and rarely, without artificiality, is it possible to utilize more than a few such techniques to gain deeper insight into a physical problem. In addition, (i) a continuously-stratified problem, (ii) a related inverse problem and (iii) a non-self-adjoint problem associated with a lossy waveguide are discussed in the light of results from the basic two-layer model. Three appendices briefly address more technical aspects of the associated governing differential equations.
ASYMPTOTIC BEHAVIOR FOR TWO REGULARIZATIONS OF THE CAUCHY PROBLEM FOR THE BACKWARD HEAT EQUATION
Authors: AMES K. A. , PAYNE L. E.
Published: May 2003

One method of regularizing the initial value problem for the backward heat equation involves replacing the equation by a singularly perturbed hyperbolic equation which is equivalent to a damped wave equation with negative damping. Another regularization of this problem is obtained by perturbing the initial condition rather than the differential equation. For both of these problems, we investigate the asymptotic behavior of the solutions as the distance from the finite end of a semi-infinite cylinder tends to infinity and thus establish spatial decay results of the Saint-Venant type.
NONLINEAR EFFECTS FOR FLOW IN PERIODICALLY CONSTRICTED CHANNEL CAUSED BY HIGH INJECTION RATE
Authors: BOURGEAT ALAIN , MARUSIC-PALOKA EDUARD
Published: May 2003

We consider a stationary viscous incompressible flow through a periodically constricted channel with the period and thickness ∊, governed by a strong injection of order ∊-1. We prove the well-posedness of the homogenized problem and the convergence of the homogenization process. We obtain a nonlinear filtration law and we give the Taylor expansion of the filtration velocity as a function of the pressure gradient.
QUALITATIVE ANALYSIS OF SEMILINEAR CATTANEO EQUATIONS
Authors: HILLEN T.
Published: May 2003

The linear Cattaneo equation appears in heat transport theory to describe heat wave propagation with finite speed. It can also be seen as a generalization of a correlated random walk. If the system admits nonconservative forces (or reactions), then a nonlinear Cattaneo system is obtained. Here we consider asymptotic behavior of solutions of the nonlinear Cattaneo system. Following Brayton and Miranker we define a Lyapunov function to show global existence of solutions and to show that each ω-limit set is contained in the set of all stationary solutions.
A SINGULAR PERTURBATION PROBLEM IN FRACTURED MEDIA WITH PARALLEL DIFFUSION
Authors: LOGAN J. DAVID , LEDDER GLENN , HOMP MICHELLE REEB
Published: May 2003

We study differential equations that model contaminant flow in a semi-infinite, fractured, porous medium consisting of a single fracture channel bounded by a porous matrix. Models in the literature usually do not incorporate diffusion in the porous matrix in the direction parallel to the fracture, and therefore they must omit a no-flux boundary condition at the edge, which, in some problems, may be unphysical. Herein we show that the problem usually treated in the literature is the outer problem for a correctly posed singular perturbation problem which includes diffusion in both directions as well as the no-flux boundary condition.
ON MODELLING REFLECTION–TRANSMISSION PROBLEMS
Authors: CAVIGLIA GIACOMO , MORRO ANGELO
Published: May 2003

The analytical and algebraic aspects associated with the modelling of reflection–transmission processes for acoustic and electromagnetic waves are investigated. The standard approaches are shown to reduce to selecting m/2 elementary (plane homogeneous or inhomogeneous) waves, among the m available ones, as the generators of the outgoing waves in each half-space. The selection of the generators is performed through the direction of the wave as indicated by the corresponding energy flux. Yet two alternative nonequivalent sets of generators occur for reflected and transmitted waves. This results in two alternative models for the reflection–transmission problem. A detailed comparison of the two schemes indicates that the generators associated with the elementary waves are the only ones which are admissible on a physical ground.
A REMARK ON "THE PARAMETER DEPENDENCE OF THE COEFFICIENT IN A MODEL FOR CONSTANT PRESSURE STEAM INJECTION IN SOIL"
Authors: RUSSO G.
Published: May 2003

A simple and accurate approximation is obtained to the numerical solution of the integral equation presented in Ref. 1 by using nonlinear optimization.
HYDROMAGNETIC FLOW OF A SECOND-GRADE FLUID IN A CHANNEL — SOME APPLICATIONS TO PHYSIOLOGICAL SYSTEMS
Authors: MISRA J. C. , PAL B. , GUPTA A. S.
Published: May 2003

An asymptotic series solution for steady flow of an incompressible, second-grade electrically conducting fluid in a channel permeated by a uniform transverse magnetic field is presented. The depth of the channel is assumed to vary slowly in the axial direction. Analytical expressions are derived for the vorticity and pressure drop along the channel as well as the wall shear stress. It is found that for fixed values of the Reynolds number R and the non-Newtonian parameter K1, the wall shear stress increases with increasing value of magnetic parameter M. Numerical computations carried out for a specific slowly varying channel show that flow separation occurs for both second-grade (K1<0) and second-order (K1>0) fluids when |K1|<0.15. The analysis also reveals the interesting result that while flow separation takes place for a second-order fluid for K1≥0.15, no separation occurs at all for |K1|≥0.15 for a second-grade fluid.
SECOND-ORDER ASYMPTOTIC APPROXIMATION OF FLEXURAL VIBRATIONS IN ELASTIC RODS
Authors: IRAGO H. , VIAÑO J. M.
Published: May 2003

We address the approximation of the eigenvalues and eigenfunctions of the spectral problem derived from the linearized elastic system for a rod. The geometric properties of domain (area of cross-section is very small with respect to its length) allow us to use an asymptotic method as principal tool using the diameter of cross-section as a small parameter ∊. We characterize zeroth- and second-order terms. Convergence results to the zeroth-order term have already been studied elsewhere. Here we analyze several questions related to the second-order term as an improvement on the zeroth-order approximation that includes Timoshenko and torsion effects.
STRATEGIES OF APPLIED MATHEMATICS TOWARDS AN IMMUNO-MATHEMATICAL THEORY ON TUMORS AND IMMUNE SYSTEM INTERACTIONS
Authors: BELLOMO N. , DE ANGELIS E.
Published: May 2003

This paper deals with the analysis of the cellular dynamics of tumors interacting with the immune system in the presence of cytokine signals. The aim is to develop an immuno-mathematical theory suitable to describe the cellular and macroscopic behavior of the system. The paper presented here develops ideas towards this objective and towards the analysis of several open problems.
THE MOST REFINED VASSILIEV INVARIANT OF DEGREE ONE OF KNOTS AND LINKS IN ℝ1-FIBRATIONS OVER A SURFACE
Authors: Tchernov Vladimir
Published: May 2003

As it is well-known, all Vassiliev invariants of degree one of a knot K ⊂ ℝ3 are trivial. There are nontrivial Vassiliev invariants of degree one, when the ambient space is not ℝ3. Recently, T. Fiedler introduced such invariants of a knot in an ℝ1-fibration over a surface F. They take values in the free ℤ-module generated by all the free homotopy classes of loops in F. Here, we generalize them to the most refined Vassiliev invariant of degree one. The ranges of values of all these invariants are explicitly described.

We also construct a similar invariant of a two-component link in an ℝ1-fibration. It generalizes the linking number.
A COMBINATORIAL HALF-INTEGRATION FROM WEIGHT SYSTEM TO VASSILIEV KNOT INVARIANT
Authors: WILLERTON SIMON
Published: May 2003

Generalizing a result of Domergue and Donato, it is shown that if the transition from degree n weight system to type n Vassiliev knot invariant is thought of as n steps of integration, then at least half of these steps can be performed canonically following symmetry considerations and a combinatorial formula is given for each of these steps.
SYMMETRIES OF MINIMUM GRAPHS IN THE 3-SPHERE
Authors: SOMA TERUHIKO
Published: May 2003

In this paper, a new equivalence relation, weak isotopy, on spatial graphs will be introduced. By using a rearrangement theorem (Theorem 1), it is shown that, for any spatial embedding Γ of a connected graph, the weak isotopy class [Γ] w.i. contains a unique minimum element Γ min up to ambient isotopy. We will see that this minimum element plays an important role in investigating symmetries of embeddings in [Γ] w.i. .
BÄCKLUND TRANSFORMATIONS AND KNOTS OF CONSTANT TORSION
Authors: CALINI ANNALISA , IVEY THOMAS
Published: May 2003

The Bäcklund transformation for pseudospherical surfaces, which is equivalent to that of the sine-Gordon equation, can be restricted to give a transformation on space curves that preserves constant torsion. We study its effects on closed curves (in particular, elastic rods) that generate multiphase solutions for the vortex filament flow (also known as the Localized Induction Equation). In doing so, we obtain analytic constant-torsion representatives for a large number of knot types.
BRAIDS, ORDERINGS AND ZERO DIVISORS
Authors: ROLFSEN DALE , ZHU JUN
Published: May 2003

We begin with the observation that the group algebras [Formula: see text] of Artin's braid groups have no zero divisors or nontrivial units. This follows from the recent discovery of Dehornoy that braids can be totally ordered by a relation < which is invariant under left multiplication. We then show that there is no ordering of Bn, n ≥ 3 which is simultaneously left and right invariant. Nevertheless, we argue that the subgroup of pure braids does possess a total ordering which is invariant on both sides. This follows from a general theorem regarding orderability of certain residually nilpotent groups. As an application, we show that the pure braid groups have no generalized torsion elements, although full braid groups do have such elements.
ON THE COMPUTATION OF THE TURAEV-VIRO MODULE OF A KNOT
Authors: ABCHIR H. , BLANCHET C.
Published: May 2003

Let M be the manifold obtained by 0-framed surgery along a knot K in the 3-sphere. A Topological Quantum Field Theory assigns to a fundamental domain of the universal abelian cover of M an operator, whose non-nilpotent part is the Turaev-Viro module of K. In this paper, using surgery formulas, we give a matrix presentation for the Turaev-Viro module of any knot K, in the case of the (Vp, Zp) TQFT of Blanchet, Habegger, Masbaum and Vogel. We do the computation for a family of knots in the special case p = 8, and note the relation with the fibering question.
NONTRIVIAL EMBEDDINGS OF POLYGONAL INTERVALS AND UNKNOTS IN 3-SPACE
Authors: CANTARELLA JASON , JOHNSTON HEATHER
Published: May 2003

We consider embedding classes of polygonal intervals and circles with fixed edge lengths. We classify all embeddings of polygonal lines of five segments, finding that this space has three connected components for suitable edge lengths. We then construct a class of "stuck" unknotted hexagons, which cannot be deformed to the standard unknotted hexagon. The edge lengths of our examples are not equal.
THE PREDICTABILITY OF LETTERS IN WRITTEN ENGLISH
Authors: SCHÜRMANN THOMAS , GRASSBERGER PETER
Published: May 2003

We show that the predictability of letters in written English texts depends strongly on their position in the word. The first letters are usually the least easy to predict. This agrees with the intuitive notion that words are well defined subunits in written languages, with much weaker correlations across these units than within them. It implies that the average entropy of a letter deep inside a word is roughly 4–5 times smaller than the entropy of the first letter.
FROM A COMPACT TO A RUGGED BORDER IN RAMIFIED COPPER ELECTRODEPOSITS
Authors: OTERO D. , MARSHALL G. , TAGTACHIAN S.
Published: May 2003

We study the origin of the rugged border of thin-layer ramified copper electrodeposits influenced by chemical perturbations. Our main interest is to look for the smallest growth building blocks toward the understanding of the transition from a compact to a rugged structure. Using electron microscopy, we found two building blocks, well differentiated in shape and size, consisting of: (a) Spikes or rods of a diameter between 100 and 500 nm and a maximum observed length of up to 10 μm; and (b) crystalline grains with a diameter between 200 nm and 2 μm. Through X-rays Bragg diffraction, we tentatively assessed a Cu2O and metallic Cu chemical composition to the crystals and rods, respectively. The relative concentration of metallic Cu to Cu2O changes as we move from the base to the front of the aggregation and this result could be associated with the Hecker effect.
A MULTIFRACTAL ANALYSIS OF IFSP INVARIANT MEASURES WITH APPLICATION TO FRACTAL IMAGE GENERATION
Authors: GUTIÉRREZ J. M. , IGLESIAS A. , RODRÍGUEZ M. A.
Published: May 2003

In this paper, we focus on invariant measures arising from Iterated Function System with Probabilities (IFSP). We show the equivalence between an IFSP and a linear dynamical system driven by a white noise. Then, we use a multifractal analysis to obtain scaling properties of the resulting invariant measures, working within the framework of dynamical systems. Finally, as an application to fractal image generation, we show how this analysis can be used to obtain the most efficient choice for the probabilities to render the attractor of an IFS by applying the probabilistic algorithm known as “chaos game”.
A FRACTAL APPROACH TO CLUSTERING OF THE 1983–1984 SEISMICITY IN THE CAMPI FLEGREI CALDERA, SOUTHERN ITALY
Authors: LUONGO G. , MAZZARELLA A. , PALUMBO A.
Published: May 2003

The volcanic seismicity occurring in Campi Flegrei during the 1983–1984 volcanic crisis is quantitatively analyzed by means of fractal (scale invariant) geometry in all its five dimensional set (magnitude, time and space). The significant power laws, relating the number of earthquakes to magnitude, time and space, within a limited range of scales, show that the Campi Flegrei region is in a critical state during the whole crisis.
MULTIFRACTAL DESCRIPTION OF NATURAL SCENES
Authors: ANH V. V. , GRAS F. , TSUI H. T.
Published: May 2003

In this paper, a general class of fractional random fields, ℬα, 0≤α<2, is defined. The members of ℬα can be used to model natural scenes and textures. It is shown that the fractal dimension of random fields in ℬα is a linear nonincreasing function of a for 0≤α<α0 and a linear nondecreasing function of α for α0<α<2. The number α0 corresponds to the Hausdorff-Besicovitch dimension of the random field. These linear relationships are significant for texture comparison and classification.
SCALE EXPONENTS OF ATMOSPHERIC TURBULENCE UNDER DIFFERENT STRATIFICATIONS
Authors: MINWEI QIAN , SHIDA LIU
Published: May 2003

Wavelet analysis is used to measure directly the scale exponents of atmospheric turbulence at inertial range under different stratifications. It is found that the average values of the scale exponents under different stratifications are clearly different and are all lower than the Kolmogorov 1941 value of 1/3. The difference shows that, according to the intermittent turbulence model, turbulence under stable stratification behaves more intermittently than under unstable stratification. The reason may be that the gravity wave, which could exist only under stable stratification, modulates the state of nocturnal surface layer and causes this kind of intermittence.
UNIVERSAL MULTIFRACTAL SINGULARITY SPECTRUM OF GENERALIZED PURITY MEASURES
Authors: LYRA MARCELO L.
Published: May 2003

The set of generalized purity functions, appearing in the problem of electromagnetic fields copropagating through a nonlinear Kerr medium, is characterized as a family of multifractal measures. The singularity spectra of these multifractal measures are obtained, and it is shown that they can be grouped into three distinct sets according to a characteristic moment m. The measures with m<3/2 and m>3 have a universal singularity spectrum, once the singularity strengths are properly scaled. For the set of intermediate moments the singularity spectrum exhibits a non-universal crossover.
FRACTAL TIME, LONG-RANGE CORRELATIONS AND STRETCHED OR COMPRESSED EXPONENTIAL SURVIVAL STATISTICS
Authors: VLAD MARCEL OVIDIU , SCHÖNFISCH BIRGITT , MACKEY MICHAEL C.
Published: May 2003

A stochastic model for stretched or compressed exponential survival statistics is suggested based on the following assumptions. (1) The state of an individual is characterized by a finite set of random variables z=(y1, y2,…); the time evolution of these variables is described by a non-Markovian stochastic process with long memory. (2) In the state space of an individual there are some critical regions for which the death of an individual can occur; for a state vector z belonging to a critical region, there is a probability 0<p(z)≤1 different from zero that the individual dies. (3) Two characteristic fractal time laws are introduced, for the random behavior of an individual at a given moment and for the long range time correlations of the fluctuations in the state space of the individual, respectively. A systematic procedure for the evaluation of the average survival function of an individual is suggested, based on a cumulant expansion in terms of the bit number b= −ln(1−p(z)) of the probability of survival corresponding to a state vector z belonging to a critical region. Explicit computations are performed both for discrete and continuous time in the case of a non-Markovian and Gaussian process with long memory describing the time evolution of the bit number b. It is shown that the main cause for the occurrence of the stretched or compressed exponential statistics is the fractal time behavior for one-time fluctuations. The second fractal time law, which describes the long range correlations of state fluctuations leads only to a correction which increases the value of the survival function, i.e., the long memory fluctuations of the state variables increase the chances of survival of the individuals. Some implications of the model for the interpretation of the survival data in population biology and health statistics are investigated.
CHAOTIC INDICATORS AND GAUSSIAN RANDOM PROCESSES: SOME SURPRISING RESULTS
Authors: BERGAMASCO L. , SERIO M.
Published: May 2003

The search for low-dimensional chaos in ocean surface waves is nowadays a very active field. The interpretation of the results, however, is not always straightforward. The issue addressed in this paper is how time series analysis tools from dynamical systems theory behave for a class of Gaussian processes often used in the study of ocean surface waves. The study includes the largest Lyapunov exponent, the Grassberger and Procaccia correlation dimension and the self-similarity properties. Surprisingly, for certain parameter ranges, the correlation dimension is found to be finite, the largest Lyapunov exponent is found to be positive and structure appears on all time scales. These results suggest that improved techniques and data analysis procedures may be required in order to study chaos properties of ocean surface waves or of other Gaussian processes with similar power spectra.
BOX DIMENSION OF COLORED NOISE AND DETERMINISTIC TIME SERIES IN HIGH DIMENSIONAL EUCLIDEAN SPACES
Authors: ZHANG WEN , WEST BRUCE J.
Published: May 2003

We investigate the box dimension of a time series having an inverse power-law spectra in a high dimensional Euclidean space. The time series can be random (colored noise) or deterministic. Both isotropic and anisotropic cases are included in our investigation. We study both the graph dimension and trail dimension of the time series. We show that with the same inverse power-law spectra, the deterministic series has a lower graph dimension than that of the colored noise, though they both can have fractal dimensions. We also derive a sharp upper bound on the trial dimension of the time series.
FRACTAL PARAMETERS OF SOIL PORE SURFACE AREA UNDER A DEVELOPING CROP
Authors: PACHEPSKY YA. A. , KORSUNSKAIA L. P. , HAJNOS M.
Published: May 2003

Fractal parameters of soils has become increasingly important in understanding and quantifying transport and adsorption phenomena in soils. It is not known how soil plant development may affect fractal characteristics of soil pores. We estimated pore surface area fractal parameters from mercury porosimetry data on gray forest soil before and during crop development, in samples both containing and not containing soil carbohydrates known to be important structure-forming agents. Two distinct intervals with different fractal dimensions were found in the range of pore radii from 4 nm to 1 μm. This could be attributed to differences in mineral composition of soil particles of different sizes. The interval of the smallest radii had the highest average fractal dimension close to 3. Smaller surface area fractal dimensions corresponding to low surface irregularity were found in the next interval of radii. The plant development affected neither fractal dimensions nor the cutoff values of soil samples. The carbohydrate oxidation caused a significant increase in the fractal dimension in the interval of larger radii, but did not affect fractal dimension in the interval of small radii. The cutoff values decreased after carbohydrate oxidation.
DISTRIBUTION OF HEIGHTS IN THE ABELIAN SANDPILE MODEL ON THE HUSIMI LATTICE
Authors: PAPOYAN Vl. V. , SHCHERBAKOV R. R.
Published: May 2003

An Abelian sandpile model is considered on the Husimi lattice of triangles with an arbitrary coordination number q. Exact expressions for the distribution of height probabilities in the Self-Organized Critical state are derived.