bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolism of Carcinogenic Azo Dye Sudan I by Rat, Rabbit, Minipig and Human Hepatic Microsomes
Authors: Martínek Václav , Stiborová Marie
Published: December 2002

We investigated the ability of hepatic microsomal samples from different species including human to metabolize rodent carcinogen Sudan I (C.I. Solvent Yellow 14, 1-(phenylazo)-2-naphthol). A comparison between experimental animals and the human microsomal enzymatic system is essential for the extrapolation of animal carcinogenicity data to assess human health risk. Major metabolites produced from Sudan I by microsomes of all species were C-hydroxylated derivatives identified as 1-[(4-hydroxyphenyl)azo]-2-naphthol and 1-(phenylazo)naphthalene-2,6-diol. Additional minor C-hydroxylated products of Sudan I oxidation were 1-[(4-hydroxyphenyl)azo]naphthalene-2,6-diol and 1-[(3,4-dihydroxyphenyl)- azo]-2-naphthol. Human microsomes generated the pattern of Sudan I metabolites reproducing that formed by hepatic microsomes of rats. While microsomes of rabbit and minipig favored the production of the metabolite hydroxylated in position 6 of the naphthol ring of the Sudan I molecule, those of human and rat predominantly produced 1-[(4-hydroxyphenyl)azo]-2-naphthol. Therefore, rat microsomes are a suitablein vitrosystem mimicking the metabolism of Sudan I in humans. To define the role of specific cytochromes P450 in the Sudan I metabolism by rat microsomes, we investigated the modulation of Sudan I oxidation by specific inducers and selective inhibitors of these enzymes. The results suggest that cytochromes P450 1A1 and 3A are responsible for Sudan I metabolism by rat microsomes. Using purified enzymes, their ability to oxidize Sudan I was confirmed. The data clearly demonstrate the predominant role of cytochrome P450 1A1 in the Sudan I metabolism and suggest a carcinogenic potency of this rodent carcinogen for humans.
Grafting of Hydroxy-Terminated Polybutadiene with 2-Mercaptoethanol
Authors: Pleska Alexander , Klichová Iva , Pytela Jindřich
Published: December 2002

A method for functionalization of hydroxy-terminated polybutadiene with 2-sulfanylethan-1-ol (2-mercaptoethanol) leading to a controlled increase in the OH functionality of the polymer was developed. The polybutadiene used contained about 65% of unsaturation in the form of 1,2-vinyl groups. The reaction was carried out without using volatile solvents. The radical addition of 2-sulfanylethan-1-ol on the polymer proceeded quantitatively and the products were free of the mercaptan odour. A series of functionalized polybutadienes were synthesized and characterized by their physical and chemical properties. The differential scanning calorimetry and thermogravimetric analysis measurements revealed that the functionalization improves the stability of the polybutadiene to thermooxidation. The obtained polymers were used for the preparation of polyurethane elastomers. The effect of the increased functionality of the polybutadiene on mechanical properties, thermal behavior and hydrolytic resistance of the elastomers was assessed.
ESTABLISHING MUTUAL-BELIEF AMONG COOPERATIVE AGENTS
Authors: JIAO WENPIN
Published: December 2002

Mutual-belief is one important premise to ensure that cooperation among multiple agents goes smoothly. However, mutual-belief among agents is also always taken for granted. In this paper, we adapt a method based on the position-exchange principle (PEP) to reason about mutual-belief among agents. By reasoning about mutual-belief among agents, we can judge whether cooperation among agents can go on rationally or not.

However, if there are malicious agents involved in cooperation, the profit of honesty agents will be injured. To make cooperation useful, agents should be able to reason about cheating behaviors of malicious agents during cooperation. We extend the standard pi-calculus to specify the expectations of agents and define a group of criteria for anti-cheating that agents can use to establish true mutual-belief.
HANDLING SEMANTIC INCONSISTENCIES IN QUERY ANSWERING BASED ON DISTRIBUTED KNOWLEDGE MINING
Authors: RAŚ ZBIGNIEW W. , DARDZIŃSKA AGNIESZKA
Published: December 2002

Traditional query processing provides exact answers to queries. It usually requires that users fully understand the database structure and content to issue a query. Due to the complexity of the database applications, the so-called global queries can be posed which traditional query answering systems cannot handle. Query posed to a database D is global if a minimum of its attributes is missing in D while it occurs in other databases. In this paper a query answering system based on distributed data mining is presented to rectify these problems. Task ontologies are used as a tool to handle semantic inconsistencies between sites.
USING MARKET VALUE FUNCTIONS FOR TARGETED MARKETING DATA MINING
Authors: YAO Y. Y. , ZHONG NING , HUANG JIAJIN , OU CHUANGXIN , LIU CHUNNIAN
Published: December 2002

Targeted marketing typically involves the identification of customers or products having potential market values. We propose a linear model for solving this problem by drawing and extending results from information retrieval. It is assumed that each object is represented by values of a finite set of attributes. A market value function, which is a linear combination of utility functions on attribute values, is used to rank objects. Several methods are examined for mining market value functions. The main advantage of the model is that one can rank objects of interest according to their market values, instead of classifying the objects. Both the theoretical and experimental results are reported in this paper. It establishes a basis on which further studies and experimental evaluation can be carried out.
SOME SPATIO-TEMPORAL MODELS IN IMMUNOLOGY
Authors: SEGEL LEE A.
Published: December 2002

Brief descriptions of spatio-temporal structures that arose in the author's explorations of theoretical immunology are provided. Topics range from singular perturbation theory for a biological assay and a model for skin rashes (reaction–diffusion patterns), through immunotherapy for allergy and selection of appropriate antibody types (compartment models), to a somewhat abstract "shape space".
DECAY OF COHERENCE OF A DILUTE BOSE–EINSTEIN CONDENSATE
Authors: POMEAU YVES
Published: December 2002

Over the years, Manuel Velarde and myself shared often a common interest in very varied topics. In this hommage to him, I go back to our very first foray in research, that is to a fundamental question of nonequilibrium thermodynamics. With our common mentor, Pierre Résibois, Manuel wrote one of his first papers on some quantum effects in kinetic theory [Résibois & Velarde, 1971; Velarde & Résibois, 1973]. Below I examine a question where quantum effects and thermal fluctuations are of fundamental importance too, that is the coherence time of a Bose–Einstein condensate at finite temperature. Surprisingly, although this question could have been looked at long ago, I have not found it treated in the literature, at least following the simple and straightforward approach developed below.
COHERENT MOTIONS AND CLUSTERS IN A DISSIPATIVE MORSE RING CHAIN
Authors: DUNKEL J. , EBELING W. , ERDMANN U. , MAKAROV V. A.
Published: December 2002

We study a one-dimensional ring chain of length L with N particles interacting via Morse potentials and influenced by dissipative forces (passive and active friction). We show that by negative friction the system can be driven far from the thermodynamic equilibrium states. For over-critical pumping with free energy several types of coherent motions including uniform rotations, optical oscillations and waves emerge in the ring. We also show the existence of a critical particle density nc= N/Lc, below that the particles spontaneously organize into clusters which can actively rotate. Additionally, the influence of white noise on the clustering is discussed.
INTERACTION OF A SOLITARY WAVE WITH AN EXTERNAL FORCE IN THE EXTENDED KORTEWEG–DE VRIES EQUATION
Authors: GRIMSHAW ROGER , PELINOVSKY EFIM
Published: December 2002

The interaction of a strongly nonlinear solitary wave with an external force is studied using the extended Korteweg–de Vries equation as a model. This equation has several different families of nonlinear wave solutions: solitons, the so-called "thick" solitons, algebraic solitons and breathers, depending upon the sign of the cubic nonlinear term. A simple nonlinear dynamical system of the second order for the amplitude and position of the solitary wave is derived, and used to study the interaction. Its solutions are investigated in the phase plane. The conditions for the capture or reflection of a solitary wave by a single localized external force are obtained, with an emphasis on the role of the cubic nonlinear term.
DISSIPATIVE QUASI-PARTICLES: THE GENERALIZED WAVE EQUATION APPROACH
Authors: CHRISTOV C. I.
Published: December 2002

Generalized Wave Equations containing dispersion, dissipation and energy-production (GDWE) are considered in lieu of dissipative NEE as more suitable models for two-way interaction of localized waves. The quasi-particle behavior and the long-time evolution of localized solutions upon take-over and head-on collisions are investigated numerically by means of an adequate difference scheme which represents faithfully the balance/conservation laws. It is shown that in most cases the balance between energy production/dissipation and nonlinearity plays a similar role to the classical Boussinesq balance between dispersion and nonlinearity, namely it can create and support localized solutions which behave as quasi-particles upon collisions and for a reasonably long time after that.
STATIONARY LOCALIZED SOLUTIONS IN THE SUBCRITICAL COMPLEX GINZBURG–LANDAU EQUATION
Authors: DESCALZI O. , ARGENTINA M. , TIRAPEGUI E.
Published: December 2002

It is shown that pulses in the complete quintic one-dimensional Ginzburg–Landau equation with complex coefficients appear through a saddle-node bifurcation which is determined analytically through a suitable approximation of the explicit form of the pulses. The results are in excellent agreement with direct numerical simulations.
TEMPORAL EVOLUTIONS AND STATIONARY WAVES FOR PERTURBED KDV EQUATION WITH NONLOCAL TERM
Authors: FENG BAO-FENG , KAWAHARA TAKUJI
Published: December 2002

Initial value problems as well as stationary solitary and periodic waves are investigated for a perturbed KdV equation including the Hilbert transform; ut + uux + βuxxx + η(ℋux - uxx) = 0 (η > 0). Multi-hump stationary solitary and periodic wave solutions are numerically identified. Furthermore, the close relation between the structure of the stationary waves and the behavior of the temporal evolutions is discussed in comparison with other perturbed KdV equations with different instability and dissipation terms. The results support some general features common to this type of nonlinear evolution equations.
NEW METHOD FOR THE ESTIMATION OF DOMAINS OF ATTRACTION OF FIXED POINTS FROM LYAPUNOV FUNCTIONS
Authors: DÍAZ-SIERRA R. , FAIRÉN V.
Published: December 2002

The estimation of the domain of stability of fixed points of nonlinear differential systems constitutes a practical problem of much interest in engineering. The procedures based on Lyapunov's second method configures an alternative worth consideration. It has the appeal of reducing calculation complexity and is time-saving with respect to the direct, computer crunching approach which requires a systematic numerical integration of the evolution equations from a gridlike pattern of initial conditions. However, it is not devoid of problems inasmuch as the Lyapunov function itself is problem-dependent and relies too much on presumptions. Additionally, the evaluation of its corresponding domain is produced in terms of a nonlinear programming problem with inequality constraints the resolution of which may sometimes require a large investment in computer time. These problems are in part avoided by restricting to quadratic Lyapunov functions, with the possible obvious consequence of limiting the estimation of the domain. In order to simplify the estimation of domains we exploit here a novel formulation of the issue of stability of invariant surfaces within Lyapunov's direct method [Díaz-Sierra et al., 2001]. The resulting method addresses directly the optimization problem associated to the evaluation of the stability domain. The problem is recast in a new, simpler form by playing both on the Lyapunov function itself and on the constraints. The gains from the procedure permit to conceive increased returns in the application of Lyapunov's direct method once it is realized that it is not prohibitive from a computational point of view to depart from the limited quadratic Lyapunov functions.
ANALYTICS OF HOMOCLINIC BIFURCATIONS IN THREE-DIMENSIONAL SYSTEMS
Authors: BELHAQ MOHAMED , LAKRAD FAOUZI
Published: December 2002

An analytical approach to determine critical parameter values of homoclinic bifurcations in three-dimensional systems is reported. The homoclinic orbit is supposed to be a limit of a unique periodic orbit. Hence, the multiple scales perturbation method is performed to construct an approximation of the periodic solution and its frequency. Then, two simple criteria are used. The first criterion is based on the collision between the periodic and the hyperbolic fixed point involved in the bifurcation. The second uses the infinity condition of the period of the periodic orbit. For illustration a specific system is investigated.
ROBUST HETEROCLINIC CYCLES IN TWO-DIMENSIONAL RAYLEIGH–BÉNARD CONVECTION WITHOUT BOUSSINESQ SYMMETRY
Authors: MERCADER ISABEL , PRAT JOANA , KNOBLOCH EDGAR
Published: December 2002

The onset of convection in systems that are heated via current dissipation in the lower boundary or that lose heat from the top boundary via Newton's law of cooling is formulated as a bifurcation problem. The Rayleigh number as usually defined is shown to be inappropriate as a bifurcation parameter since the temperature difference across the layer depends on the amplitude of convection and hence changes as convection evolves at fixed external parameter values. A modified Rayleigh number is introduced that does remain constant even when the system is evolving, and solutions obtained with the standard formulation are compared with those obtained via the new one. Near the 1 : 2 spatial resonance in low Prandtl number fluids these effects open up intervals of Rayleigh number with no stable solutions in the form of steady convection or steadily traveling waves. Direct numerical simulations in two dimensions show that in such intervals the dynamics typically take the form of a nearly heteroclinic modulated traveling wave. This wave may be quasiperiodic or chaotic.
THE PHYSICS OF CAVITY SOLITONS IN SEMICONDUCTOR MICROCAVITIES
Authors: LUGIATO LUIGI A. , SPINELLI LORENZO , TISSONI GIOVANNA , BRAMBILLA MASSIMO , MAGGIPINTO TOMMASO , PERRINI IDA M.
Published: December 2002

We start by reviewing the basic physical properties of cavity solitons, embedding this phenomenon in the general framework of optical instabilities and optical pattern formation. Next, we focus on the case of semiconductor microcavities and consider a first principle model. Its homogeneous stationary solutions and their stability are evaluated analytically. With the help of numerical simulations, we discuss two case studies, one in the passive and one in the active configuration.
"SPATIAL-TEMPORAL" PATTERNS IN PROKARYOTE GENOMES
Authors: HAO BAILIN
Published: December 2002

We have developed a simple scheme to visualize the string composition of long DNA sequences and applied it to all available prokaryote complete genomes. Each species has a specific "portrait" and most clearly seen patterns in these portraits are determined by short avoided and under-represented strings. The "spatial" patterns in the space of short strings might reflect some "temporal" events in the evolutionary history.
CLUSTERING AND SYNCHRONIZATION IN A ONE-DIMENSIONAL MODEL FOR THE CA3 REGION OF THE HIPPOCAMPUS
Authors: MONTEJO N. , LORENZO M. N. , PÉREZ-MUÑUZURI V. , PÉREZ-VILLAR V.
Published: December 2002

The behavior of a system of coupled ordinary differential equations is studied in order to characterize the CA3 region of the hippocampus. Clustering and synchronization behavior in a one-dimensional array of cells modeled by a modified Morris–Lecar model is analyzed in terms of a time delay included in the model. The random formation of phase dislocations whose number increases with the time delay seems to be responsible for complex spatiotemporal patterns that have been observed. Alterations to the transmission time between cells have been simulated by adding some noise to the system.
PHASE-LOCKING IN A GENERAL CLASS OF INTEGRATE AND FIRE MODELS
Authors: HAKEN HERMANN
Published: December 2002

This paper studies phase-locking in a network of N neurons. The dynamic variables are the phases of the axonal pulses as well as the dendritic currents. The coupling via synaptic strengths may be arbitrary, up to a specific constraint. Arbitrary time delays of pulses and dendritic currents are included. The class of integrate and fire models treated here is characterized by a great variety of dendritic response functions (Green's functions). We determine the phase-locked state, the pulse interval, and present the stability equation for the case in which the dendritic response function is Rall's α-function, but still arbitrary couplings and delays are admitted.
STOCHASTIC RESONANCE IN ALPHA OSCILLATORS IN THE HUMAN BRAIN
Authors: MORI TOSHIO , KAI SHOICHI
Published: December 2002

We experimentally study stochastic resonance (SR) in the human brain through a noise effect for entrainment dynamics of the alpha (α) wave. The measurement has been carried out under the following conditions in order to obtain clear evidence of the SR phenomenon in the central nervous system. The periodic and noisy stimuli are respectively applied to the right and the left eyes of the subject independently. When only periodic and constant (but weak enough) stimulus is applied to the right eye, it does not induce any global entrainment of α-oscillators to the stimulus frequency. In this situation increasing the amplitude of the noise stimulus (frequency bandwidth from 15 to 60 Hz), harmonic entrainment occurs for a certain range of the noise amplitude and shows a sharp peak in the power spectrum of brain waves. Plotting the amplitude of the peak against the noise amplitude, a bell-type shape is seen, i.e. the maximum signal amplitude at an optimum noise. It clearly indicates the SR phenomenon. Taking account of our experimental conditions and set-up, the present SR phenomenon occurs not on the retina but on the visual processing area in the central nervous systems beyond the optic chiasma.
BUCKLING AND VIBRATION OF ORTHOTROPIC PLATES WITH AN INTERNAL LINE HINGE
Authors: GUPTA P. R. , REDDY J. N.
Published: December 2002

This paper presents the exact buckling loads and vibration frequencies of orthotropic rectangular plates with internal line hinge and having two opposite edges simply supported while the other two edges may have any combination of free, simply supported, and clamped conditions. An analytical method that uses the Lévy solution method and the domain decomposition technique is employed to determine the buckling loads and natural frequencies of rectangular plates with internal line hinge.
NOVEL METHODS FOR CALCULATING NATURAL FREQUENCIES AND BUCKLING LOADS OF COLUMNS WITH INTERMEDIATE MULTIPLE ELASTIC SPRINGS
Authors: LEE BYOUNG KOO , OH SANG JIN , LEE TAE EUN
Published: December 2002

Numerical methods for calculating both the natural frequencies and buckling loads of columns with intermediate multiple elastic springs are developed. In formulating the governing equations of the column, each elastic spring is modeled as a discrete Winkler foundation of the finite longitudinal length. By using this model, the differential equations governing both the free vibration and buckled shapes of the column are derived, which are solved numerically. The Runge–Kutta method is used to integrate the differential equations, and the determinant search method combined with Regula–Falsi method is used to determine the eingenvalues, namely, the natural frequencies and buckling loads. In the numerical examples, fixed–fixed, fixed-hinged, hinged-fixed and hinged–hinged end constraints are considered. The numerical results including the frequency parameters, mode shapes of free vibrations and buckling loads are presented in non-dimensional forms.
THE ELEMENT-FREE kp-RITZ METHOD FOR VIBRATION OF LAMINATED ROTATING CYLINDRICAL PANELS
Authors: LIEW K. M. , ZHAO X. , NG T. Y.
Published: December 2002

In this paper, the element-free kernel particle Ritz method or in short the kp-Ritz method, is developed and implemented for the free vibration analysis of rotating cylindrical panels. Over the years, researchers have employed various trial or admissible functions, such as harmonic and hyperbolic functions as well as polynomials, in the Ritz approximate approach for structural vibration analyses. The present work represents a significant development whereby 2-D reproducing kernel functions are employed to approximate the displacement field. The resulting kp-Ritz method represents the methodology development aspect of this paper. Further the rotating panel problem selected for demonstrating the accuracy and efficiency of this new methodology is also an important contribution of this paper. Although there is a moderate amount of published information on the vibration of rotating cylindrical shells, corresponding studies on rotating panels are conspicuously lacking. This is the first instance in which results have been obtained for rotating cylindrical panels whereby the essential boundary conditions have been fully enforced.
A COMPARATIVE STUDY OF PERFORMANCE OF VARIOUS ISOLATION SYSTEMS FOR LIQUID STORAGE TANKS
Authors: SHRIMALI M. K. , JANGID R. S.
Published: December 2002

A comparative study of performance of various isolation systems for liquid storage tanks is investigated under real earthquake ground motions. The various base isolation systems considered are the laminated rubber bearings (with and without lead core) and sliding isolation systems (with and without restoring force). The isolated liquid storage tank is idealized with three-degrees-of-freedom associated with convective, impulsive and rigid mass under uni-directional earthquake excitation. Since the force-deformation behaviour of the isolation systems is non-linear, as a result, the equations of motion are solved numerically by step-by-step method. In order to measure the effectiveness of the isolation systems, the seismic response of the isolated liquid storage tanks is compared with the corresponding response of non-isolated tanks. Further, the effectiveness of the isolation is also explored for wide range of practical liquid storage tanks considering the influence of tank aspect ratio. It is observed that the isolation systems are quite effective in attenuating the earthquake acceleration transmitted to the tank, which reduces the design seismic forces significantly. Further, it is also found that the sliding type isolation systems are more effective in controlling the response of liquid storage tanks in comparison to the elastomeric bearings. Among the various sliding systems, the resilient-friction base isolator is found to be most effective for seismic isolation of the tanks.
SOME ULTRAMATRICIAL ALGEBRAS WHICH ARISE AS INTERSECTIONS OF LEAVITT ALGEBRAS
Authors: ABRAMS GENE , ÁNH P. N.
Published: December 2002

Two known constructions of rings R, each having the property that different sized matrix rings Mn(R) and Mm(R) are isomorphic but the free left R-modules RRn and RRm are not, are shown to be isomorphic. The first construction utilizes a direct limit, while the second involves an intersection process.
ON RADICAL FIELD EXTENSIONS OF PRIME EXPONENT
Authors: ALBU TOMA
Published: December 2002

In this paper we investigate finite separable radical extensions K ⊆ L of prime exponent via the concept of G-Cogalois extension. As particular cases we retrieve some older results in I. Kaplansky [9] and A. Baker and H. M. Stark [7] concerning such radical extensions.
A CLASSIFICATION OF ℤ-GRADED LIE SUPERALGEBRAS OF INFINITE DEPTH
Authors: CANTARINI NICOLETTA
Published: December 2002

In 1998 Victor Kac classified infinite-dimensional, transitive, irreducible ℤ-graded Lie superalgebras of finite depth. Here we classify bitransitive, irreducible ℤ-graded Lie superalgebras of infinite depth and finite growth which are not contragredient. In particular we show that the growth of every such superalgebra is equal to one.
FAILURE OF CANCELLATION FOR QUARTIC AND HIGHER-DEGREE ORDERS
Authors: KARR RYAN
Published: December 2002

Let D be a principal ideal domain with quotient field F and suppose every residue field of D is finite. Let K be a finite separable field extension of F of degree at least 4 and let [Formula: see text] denote the integral closure of D in K. Let [Formula: see text] where f ∈ D is a nonzero nonunit. In this paper we show, assuming a mild condition on f, that cancellation of finitely generated modules fails for R, that is, there exist finitely generated R-modules L, M, and N such that L ⊕ M ≅ L ⊕ N and yet M ≇ N. In case the unit group of D is finite, we show that cancellation fails for almost all rings of the form [Formula: see text], where p ∈ D is prime.
ELEMENTARY PARABOLIC TWIST
Authors: LYAKHOVSKY V. D. , SAMSONOV M. E.
Published: December 2002

The twist deformations for simple Lie algebras [Formula: see text] whose twisting elements ℱ are known explicitly are usually defined on the carrier subspace injected in the Borel subalgebra [Formula: see text]. We consider the case where the carrier of the twist intersects nontrivially with both [Formula: see text] and [Formula: see text]. The main element of the new deformation is the parabolic twist ℱ℘ whose carrier is the minimal parabolic subalgebra of simple Lie algebra [Formula: see text]. It has the structure of the algebra of two-dimensional motions, contains [Formula: see text] and intersects nontrivially with [Formula: see text]. The twist ℱ℘ is constructed as a composition of the extended jordanian twist [Formula: see text] and the factor [Formula: see text]. The latter can be considered as a special deformed version of the jordanian twist. The twisted costructure is found for [Formula: see text] and the corresponding universal ℛ-matrix is presented. The parabolic twist can be composed with certain types of chains of extended jordanian twists for algebras A2(n-1). The chains enlarged by the parabolic factor ℱ℘ perform the explicit quantization of the new set of classical r-matrices.
CATALYTIC OXIDATION OF p-TOLUIDINE AT MULTIWALLED FUNCTIONALIZED CARBON NANOTUBES
Authors: CROSTON M. , LANGSTON J. , SANGOI R. , SANTHANAM K. S. V.
Published: December 2002

The oxidation of p-toluidine in acetonitrile by hydrogen peroxide is a very slow reaction which produces 4,4'-dimethylazoxybenzene as the product. The presence of functionalized multiwalled carbon nanotubes (CNT) in the above reaction produces 4,4'-dimethylazobenzene. The reactions have been followed by GC/MS, which show the following mass nos.: 226,92 (without CNT) and 210,120,92,28 (with CNT). UV-VIS absorption spectroscopy shows maximum corresponding to 4,4'-dimethylazobenzene at 444 nm. The rate of formation of 4,4'-dimethylazobenzene has been determined as 0.0093 s -1.
CONVERSION OF ANILINE TO AZOBENZENE AT FUNCTIONALIZED CARBON NANOTUBES: A POSSIBLE CASE OF A NANODIMENSIONAL REACTION
Authors: CROSTON M. , LANGSTON J. , TAKACS G. , MORRILL T. C. , MIRI M. , SANTHANAM K. S. V. , AJAYAN P.
Published: December 2002

Aniline is oxidized to nitrosobenzene as the initial product, which undergoes further oxidation to nitrobenzene. The nitrosobenzene formation is catalyzed by functionalized multiwalled carbon nanotubes (CNT) followed by a coupling reaction between nitrosobenzene and aniline to produce azobenzene. This coupling requires close proximity of the reactants. It proceeds rapidly resulting in the UV-VIS absorption spectrum showing maxima at 327 nm and 425 nm. The nitrosobenzene yield in the presence of CNTs is controlled by the amount present in the medium. As the reaction is not catalyzed by unfunctionalized CNTs or graphitic particles, the uniqueness of the functionalized multiwalled CNTs in this catalysis suggests a nanodimensional reaction pathway.
REVERSIBLE HYDROGEN AND LITHIUM STORAGE OF MoS2 NANOTUBES
Authors: CHEN J. , LI S. L. , TAO Z. L. , ZHANG L. Z.
Published: December 2002

Inorganic fullerene-like MoS 2 nanotubes synthesized by a gas–solid reaction were used as the electrode materials of hydrogen and lithium storage in aqueous and nonaqueous electrolytes, respectively. Very interesting results such as reversible hydrogen reduction/oxidation and lithium insertion have been obtained.
NANOTUBE LIGHT-CONTROLLED ELECTRONIC SWITCH
Authors: ROTKIN SLAVA V. , ZHAROV ILYA
Published: December 2002

A novel carbon nanotube electronic device is proposed: a light-controlled electronic switch. A charged molecule has been designed for a noncovalent modification of the nanotube. Photon absorption by the molecule results in nanomechanical switching of the charge position which controls the electron/hole transport through the nanotube.
GROWTH OF CARBON NANOTUBES (CNTs) IN ELECTRIC-ARC DISCHARGE IN ARGON
Authors: BORISENKO D. N. , KOLESNIKOV N. N. , KULAKOV M. P. , KVEDER V. V.
Published: December 2002

Electric-arc discharge deposition (EADD) is used to produce CNT products. The design and electric scheme are discussed in details, as well as all technological features. The results of the outputs of all technological schemes are discussed on the basis of thermal analysis (TGA and DTA), supported by TEM and fullerene-dissolving tests. It is established that CNTs mainly form as compact cathode deposits ("stubs"). Conditions of stub preferential growth are experimentally defined. These conditions have narrow range of parameters that may cause some difficulties in scaling of CNT production.
MECHANICAL AND ELECTRONIC PROPERTIES OF STRAINED LAYER SUPERLATTICES STUDIED BY DENSITY FUNCTIONAL TB AND PATH PROBABILITY METHODS
Authors: MASUDA-JINDO K. , KIKUCHI R.
Published: December 2002

The atomic and electronic structures of semiconductor heterostructures, including steps, misfit dislocations and interface disorder, are studied by using the density-functional tight-binding (TB) method. Atomic structures of misfit dislocations both edge type 1/2 <110> (001) and 60° dislocations in the semiconductor heterostructures, like Si-Ge superlattices and GaAs/Si, InAs/GaAs(001), InP/GaAs(001) systems, are studied by using order of N [O(N)] calculational method. The path probability method (PPM) in the statistical physics is used to study the influence of the interface disorder on the electronic properties of the semiconductor heterostructures. It is shown that the junction relaxation influences quite significantly the electronic and mechanical properties of semiconductor heterostructures. The critical layer thickness hc for the generation of misfit dislocations depends significantly on the interface disorder (increase of hc) at the semiconductor heterostructures.
Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability
Authors: Loram Ian D. , Lakie Martin
Published: December 2002

During quiet standing the human ‘inverted pendulum’ sways irregularly. In previous work where subjects balanced a real inverted pendulum, we investigated what contribution the intrinsic mechanical ankle stiffness makes to achieve stability. Using the results of a plausible model, we suggested that intrinsic ankle stiffness is inadequate for providing stability. Here, using a piezo‐electric translator we applied small, unobtrusive mechanical perturbations to the foot while the subject was standing freely. These short duration perturbations had a similar size and velocity to movements which occur naturally during quiet standing, and they produced no evidence of any stretch reflex response in soleus, or gastrocnemius. Direct measurement confirms our earlier conclusion; intrinsic ankle stiffness is not quite sufficient to stabilise the body or pendulum. On average the directly determined intrinsic stiffness is 91 ± 23 % (mean ±s.d.) of that necessary to provide minimal stabilisation. The stiffness was substantially constant, increasing only slightly with ankle torque. This stiffness cannot be neurally regulated in quiet standing. Thus we attribute this stiffness to the foot, Achilles’ tendon and aponeurosis rather than the activated calf muscle fibres. Our measurements suggest that the triceps surae muscles maintain balance via a spring‐like element which is itself too compliant to guarantee stability. The implication is that the brain cannot set ankle stiffness and then ignore the control task because additional modulation of torque is required to maintain balance. We suggest that the triceps surae muscles maintain balance by predictively controlling the proximal offset of the spring‐like element in a ballistic‐like manner.
Phase‐disparity coding in extrastriate area 19 of the cat
Authors: Mimeault Daniel , Paquet Valérie , Lepore Franco , Guillemot Jean‐Paul
Published: December 2002

Binocular interactions were investigated in area 19 of the anaesthetized cat using dichoptically presented phase‐shifted static spatial frequency gratings that flickered at a fixed temporal rate. More than two‐thirds of the binocular cells showed phase specificity to static phase disparities leading to either summation or facilitation interactions. This proportion of spatial disparity selectivity was higher than that shown for the same area (one‐third of the units) when drifting light bars or drifting spatial frequencies were used to create disparities. The range of phase disparities encoded by binocular cells in area 19 is inversely related to the optimal spatial frequency of the dominant eye. Thus, cells in this area are tuned to coarse spatial disparities which, as supported by behavioural studies, could reflect its involvement in the analysis of stereoscopic pattern having gross disparities but devoid of motion cues. Because of the nature of its interconnections with numerous visual cortical areas, area 19 could serve as a way station where stereoscopic information could be first analysed and sent to other higher order areas for a complete representation of three‐dimensional objects.
Stretch reflex gain in cat triceps surae muscles with compliant loads
Authors: Serres Sophie J. De , Bennett David J. , Stein Richard B.
Published: December 2002

The triceps surae (TS) stretch reflex was measured in decerebrate cats during crossed extensor stimulation (tonic contractions) and after spinalization during rhythmic locomotor activity. The TS reflex force in response to a short pulse stretch measured during tonic contractions at low level of background activity was greater than when more background activity was present at the time of application of stretch. In contrast, the reflex force measured during rhythmic contractions was very small at low level of background force (flexion phase) and increased at moderate and high levels of background activity (extension phase). Thus, even in reduced preparations, a task modulation of the stretch reflex occurs. Throughout the experimental procedure, the torque motor used to stretch the muscles behaved like a spring of a preset compliance (from isometric to very compliant). A reflex model was used to simulate the responses obtained experimentally. The gain of the stretch reflex loop was estimated for each load condition and both behavioural tasks. The reflex loop gain was significantly larger as the compliance of the external load increased for both tonic and rhythmic contractions, although to a lesser extent in the phasically activated muscles. During rhythmic locomotor contractions the gain was less than 1, assuring stability of the system. In contrast, during tonic contractions against a compliant load the gain exceeded 1, consistent with the instability (oscillations, clonus) seen at times under these load conditions. However, the high gain and instability was only transient, since repeated stretch reduced the gain. Thus, non‐linearities in the system assured vigorous responses at the onset of perturbations, but then weaker responses to ongoing perturbations to reduce the chance of feedback instability (clonus).
Regulation of Cl−−Hco3− exchangers by cAMP‐dependent protein kinase in adult rat hippocampal CA1 neurons
Authors: Brett Christopher L. , Kelly Tony , Sheldon Claire , Church John
Published: December 2002

The contributions of HCO3−‐dependent, DIDS‐sensitive mechanisms to the maintenance of steady‐state pHi, and the regulation of their activities by cAMP‐dependent protein kinase (PKA), were investigated in CA1 neurons with the H+‐sensitive fluorophore, BCECF. The addition of HCO3−/CO2 to neurons with ‘low’ (pHi≤ 7.20) and ‘high’ (pHi > 7.20) initial pHi values under Hepes‐buffered conditions, increased and decreased steady‐state pHi, respectively. Conversely, under HCO3−/CO2‐buffered conditions, DIDS caused pHi to decrease and increase in neurons with low and high initial pHi values, respectively. In the presence, but not the absence, of HCO3−, the PKA inhibitor Rp‐adenosine‐3′,5′‐cyclic monophosphorothioate (Rp‐cAMPS; 50 μm) evoked DIDS‐sensitive increases and decreases in pHi in neurons with low and high initial pHi values, respectively. In contrast, in neurons with low initial pHi values, activation of PKA with the Sp isomer of cAMPS (Sp‐cAMPS; 25 μm) elicited increases in pHi that were smaller in the presence than in the absence of HCO3−, whereas in neurons with high initial pHi values, Sp‐cAMPS‐evoked rises in pHi were larger in the presence than in the absence of HCO3−; the differences between the effects of Sp‐cAMPS on pHi under the different buffering conditions were attenuated by DIDS. Consistent with the possibility that changes in the activities of HCO3−‐dependent, DIDS‐sensitive mechanisms contribute to the steady‐state pHi changes evoked by the PKA modulators, in neurons with initial pHi values ≤ 7.20, Rp‐cAMPS concurrently inhibited Na+‐independent Cl−‐HCO3− exchange and stimulated Na+‐dependent Cl−‐HCO3− exchange; in contrast, Sp‐cAMPS concurrently stimulated Na+‐independent Cl−‐HCO3− exchange and inhibited Na+‐dependent Cl−‐HCO3− exchange. Data from a limited number of neurons with initial pHi values > 7.20 suggested that the directions of the reciprocal changes in anion exchange activities (inhibition or stimulation) evoked by Rp‐ and Sp‐cAMPS may be opposite in cells with low vs. high resting pHi values. Taken together, the results indicate that the effects of modulating PKA activity on steady‐state pHi in rat CA1 neurons under HCO3−/CO2‐buffered conditions reflect not only changes in Na+‐H+ exchange activity but also changes in Na+‐dependent and Na+‐independent Cl−‐HCO3− exchange activity that, in turn, may be dependent upon the initial pHi.
Quantitative responses of spinothalamic lamina I neurones to graded mechanical stimulation in the cat
Authors: Andrew David , Craig A. D. (Bud)
Published: December 2002

Nociceptive spinothalamic tract (STT) neurones in lamina I of the lumbosacral spinal cord of anaesthetized cats were characterized by recording their responses to graded mechanical stimulation with controlled forces of 10‐120 g and probes of 5.0, 0.5 and 0.1 mm2 contact area. Neurones were identified by antidromic activation from the contralateral thalamus, and cells that responded to noxious stimulation were categorized as either nociceptive specific (NS, n= 20) or as polymodal nociceptive (HPC, responsive to heat, pinch and cold, n= 19) based on their responses to quantitative thermal stimuli. The mean responses of the 39 units increased linearly as stimulus intensity increased, and the population stimulus‐response curves evoked by each of the three probes were all significantly different from each other. Thresholds were 45 g for the 5.0 mm2 probe, 30 g for the 0.5 mm2 probe and 20 g for the 0.1 mm2 probe. Further analysis showed that the NS neurones encoded both stimulus intensity and area (probe size) significantly better than HPC neurones in terms of their thresholds to individual probes, their peak discharge rates, their suprathreshold responsiveness and their ability to discriminate the three different probe sizes. These differences are consistent with the known differences between the mechanical encoding properties of A‐fibre nociceptors, which provide the dominant inputs to NS neurones, and C‐fibre nociceptors, which are the dominant inputs to HPC cells. Comparison of the stimulus‐response curves of NS and HPC neurones indicated that the discharge of NS neurones better match the psychophysics of mechanical pain sensations in humans than the discharge of the HPC neurones do. Our findings support the view that NS neurones have a prominent role in mechanical pain and sharpness, and they corroborate the concept that the lamina I STT projection comprises several discrete channels that are integrated in the forebrain to generate qualitatively distinct sensations.
Modulation of homomeric and heteromeric kcnq1 channels by external acidification
Authors: Peretz Asher , Schottelndreier Hella , Aharon‐Shamgar Liora Ben , Attali Bernard
Published: December 2002

The IKS K+ channel plays a major role in repolarizing the cardiac action potential. It consists of an assembly of two structurally distinct α and β subunits called KCNQ1 and KCNE1, respectively. Using two different expression systems, Xenopus oocytes and Chinese hamster ovary cells, we investigated the effects of external protons on homomeric and heteromeric KCNQ1 channels. External acidification (from pH 7.4 to pH 5.5) markedly decreased the homomeric KCNQ1 current amplitude and caused a positive shift (+25 mV) in the voltage dependence of activation. Low external pH (pHo) also slowed down the activation and deactivation kinetics and strongly reduced the KCNQ1 inactivation process. In contrast, external acidification reduced the maximum conductance and the macroscopic inactivation of the KCNQ1 mutant L273F by only a small amount. The heteromeric IKS channel complex was weakly affected by low pHo, with minor effects on IKS current amplitude. However, substantial current inhibition was produced by protons with the N‐terminal KCNE1 deletion mutant Δ11‐38. Low pHo increased the current amplitude of the pore mutant V319C when co‐expressed with KCNE1. The slowing of IKS deactivation produced by low pHo was absent in the KCNE1 mutant Δ39‐43, suggesting that the residues lying at the N‐terminal boundary of the transmembrane segment are involved in this process. In all, our results suggest that external acidification acts on homomeric and heteromeric KCNQ1 channels via multiple mechanisms to affect gating and maximum conductance. The external pH effects on IKrversus IKS may be important determinants of arrhythmogenicity under conditions of cardiac ischaemia and reperfusion.
O2−sensitive K+ channels in immortalised rat chromaffin‐cell‐derived MAH cells
Authors: Fearon Ian M. , Thompson Roger J. , Samjoo Imtiaz , Vollmer Cathy , Doering Laurie C. , Nurse Colin A.
Published: December 2002

The regulation of K+ channels by O2 levels is a key link between hypoxia and neurotransmitter release in neuroendocrine cells. Here, we examined the effects of hypoxia on K+ channels in the immortalised v‐myc, adrenal‐derived HNK1+ (MAH) cell line. MAH cells possess a K+ conductance that is sensitive to Cd2+, iberiotoxin and apamin, and which is inhibited by ≈24 % when exposed to a hypoxic perfusate (O2 tension 20 mmHg). This conductance was attributed to high‐conductance Ca2+‐activated K+ (BK) and small‐conductance Ca2+‐activated K+ (SK) channels, which are major contributors to the O2‐sensitive K+ conductance in adrenomedullary chromaffin cells. Under low [Ca2+]i conditions that prevented activation of Ca2+‐dependent K+ conductances, a rapidly activating and slowly inactivating K+ conductance, sensitive to both TEA and 4‐aminopyridine (4‐AP), but insensitive to 100 nm charybdotoxin (CTX), was identified. This current was also reduced (by ≈25 %) when exposed to hypoxia. The hypoxia‐sensitive component of this current was greatly attenuated by 10 mm 4‐AP, but was only slightly reduced by 10 mm TEA. This suggests the presence of delayed‐rectifier O2‐sensitive channels comprising homomultimeric Kv1.5 or heteromultimeric Kv1.5/Kv1.2 channel subunits. The presence of both Kv1.5 and Kv1.2 α‐subunits was confirmed using immunocytochemical techniques. We also demonstrated that these K+ channel subunits are present in neonatal rat adrenomedullary chromaffin cells in situ. These data indicate that MAH cells possess O2‐sensitive K+ channels with characteristics similar to those observed previously in isolated chromaffin cells, and therefore provide an excellent model for examining the cellular mechanisms of O2 sensing in adrenomedullary chromaffin cells.
Cessation of activity in red nucleus neurons during stimulation of the medial medulla in decerebrate rats
Authors: Mileykovskiy Boris Y. , Kiyashchenko Lyudmila I. , Siegel Jerome M.
Published: December 2002

The pontine oral reticular nucleus, gigantocellular reticular nucleus (Gi) and dorsal paragigantocellular nucleus (DPGi) of the medulla are key elements of a brainstem‐reticulospinal inhibitory system that participates in rapid eye movement (REM) sleep atonia. Our recent study has shown that excitation of these brainstem nuclei in decerebrate rats inhibits locus coeruleus cells and the midbrain locomotor region neurons related to muscle tone facilitation. In the present study we have examined the influences of electrical and chemical stimulation of Gi and DPGi inhibitory sites on the activity of neurons located in the magnocellular part of the red nucleus (RMC), a cell group that participates in both the tonic and phasic regulation of motor output. A total of 192 RMC neurons were recorded in precollicular‐premammillary decerebrate rats with muscle rigidity and induced locomotion. Thirty‐three RMC neurons were identified antidromically as rubrospinal (RMC‐spinal) cells by stimulation of the contralateral dorsolateral funiculus at the L2 level. A total of 141 RMC neurons (88.7 %) and all RMC‐spinal neurons were inhibited during electrical stimulation of Gi and DPGi inhibitory sites. This cessation of activity was correlated with bilateral muscle atonia or blockage of locomotion. Six RMC cells (3.8 %) were excited (224 ± 50 %, n= 6, minimum = 98, maximum = 410, P < 0.05) and 11 cells (7 %) gave no response to Gi and DPGi stimulation. Microinjections of kainic acid (100 μm, 0.2 μl) into Gi and DPGi inhibitory sites, previously identified by electrical stimulation, produced a short‐latency (35 ± 3.5 s, n= 11) decrease of rigid hindlimb muscle tone and inhibition of all tested RMC (n= 7) and RMC‐spinal (n= 5) neurons. These results, combined with our recent published data, suggest that inhibition of motor function during activation of the brainstem inhibitory system is related to both the descending inhibition of spinal motoneurons and suppression of activity in supraspinal motor facilitatory systems. These two mechanisms acting synergistically may cause generalized motor inhibition during REM sleep and cataplexy.