bluuebunny/crossref_metadata_2025 huggingface dataset:
PhET: Interactive Simulations for Teaching and Learning Physics
Authors: Perkins Katherine , Adams Wendy , Dubson Michael , Finkelstein Noah , Reid Sam , Wieman Carl , LeMaster Ron
Published: December 2005

The Physics Education Technology (PhET) project creates useful simulations for teaching and learning physics and makes them freely available from the PhET website (http://phet.colorado.edu). The simulations (sims) are animated, interactive, and game-like environments in which students learn through exploration. In these sims, we emphasize the connections between real-life phenomena and the underlying science, and seek to make the visual and conceptual models of expert physicists accessible to students. We use a research-based approach in our design—incorporating findings from prior research and our own testing to create sims that support student engagement with and understanding of physics concepts.
Avatars of Hollywood in Physical Science
Authors: Efthimiou Costas J. , Llewellyn Ralph A.
Published: December 2005

This paper reports the results of the initial phase of an ambitious project known as Physics in Films, designed to help improve public understanding of the basic principles of physical science that the authors have embarked upon. The project began with several large groups of nonscience majors enrolled in the general education physical science course at the University of Central Florida (UCF), a course with a counterpart in nearly every college and university (and many high schools) in the nation.
There Is No Really Good Definition of Mass
Authors: Hecht Eugene
Published: December 2005

There seems to be a fairly prevalent belief in the physics community that the basic concepts of our discipline (mass, force, energy, and so forth) are well understood and easily defined.1 After all, there are dozens of textbooks on every level that supposedly define all the terms they introduce. Apparently, we teachers can pass this wisdom on to our students without any cautionary notes and without any concern for subtleties. Remarkably, this is most certainly not the case, and anyone who has studied the foundational literature in physics over the last several centuries knows that none of the fundamental ideas is satisfactorily defined.
A Quick Thermoelectricity Demonstration
Authors: Greenslade Thomas B.
Published: December 2005

The modern introductory student is unlikely to have observed a source of thermal emf in action. Once the parts have been made, this little demonstration of the effects of thermoelectricity can be assembled in a minute or two in front of a class.
A Developmental Timing MicroRNA and Its Target Regulate Life Span in
C. elegans
Authors: Boehm Michelle , Slack Frank
Published: December 2005

The microRNA
lin-4
and its target, the putative transcription factor
lin-14
, control the timing of larval development in
Caenorhabditis elegans
. Here, we report that
lin-4
and
lin-14
also regulate life span in the adult. Reducing the activity of
lin-4
shortened life span and accelerated tissue aging, whereas overexpressing
lin-4
or reducing the activity of
lin-14
extended life span. Lifespan extension conferred by a reduction in
lin-14
was dependent on the DAF-16 and HSF-1 transcription factors, suggesting that the
lin-4
–
lin-14
pair affects life span through the insulin/insulin-like growth factor–1 pathway. This work reveals a role for microRNAs and developmental timing genes in life-span regulation.
Trading Water for Carbon with Biological Carbon Sequestration
Authors: Jackson Robert B. , Jobbágy Esteban G. , Avissar Roni , Roy Somnath Baidya , Barrett Damian J. , Cook Charles W. , Farley Kathleen A. , le Maitre David C. , McCarl Bruce A. , Murray Brian C.
Published: December 2005

Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.
Inducible Nitric Oxide Synthase Binds, S-Nitrosylates, and Activates Cyclooxygenase-2
Authors: Kim Sangwon F. , Huri Daniel A. , Snyder Solomon H.
Published: December 2005

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) are two major inflammatory mediators. Here we show that iNOS specifically binds to COX-2 and S-nitrosylates it, enhancing COX-2 catalytic activity. Selectively disrupting iNOS–COX-2 binding prevented NO-mediated activation of COX-2. This synergistic molecular interaction between two inflammatory systems may inform the development of anti-inflammatory drugs.
Torus-Margo Pits Help Conifers Compete with Angiosperms
Authors: Pittermann Jarmila , Sperry John S. , Hacke Uwe G. , Wheeler James K. , Sikkema Elzard H.
Published: December 2005

The unicellular conifer tracheid should have greater flow resistance per length (resistivity) than the multicellular angiosperm vessel, because its high-resistance end-walls are closer together. However, tracheids and vessels had comparable resistivities for the same diameter, despite tracheids being over 10 times shorter. End-wall pits of tracheids averaged 59 times lower flow resistance on an area basis than vessel pits, owing to the unique torus-margo structure of the conifer pit membrane. The evolution of this membrane was as hydraulically important as that of vessels. Without their specialized pits, conifers would have 38 times the flow resistance, making conifer-dominated ecosystems improbable in an angiosperm world.
Protein Synthesis upon Acute Nutrient Restriction Relies on Proteasome Function
Authors: Vabulas Ramunas M. , Hartl F. Ulrich
Published: December 2005

The mechanisms that protect mammalian cells against amino acid deprivation are only partially understood. We found that during an acute decrease in external amino acid supply, before up-regulation of the autophagosomal-lysosomal pathway, efficient translation was ensured by proteasomal protein degradation. Amino acids for the synthesis of new proteins were supplied by the degradation of preexisting proteins, whereas nascent and newly formed polypeptides remained largely protected from proteolysis. Proteasome inhibition during nutrient deprivation caused rapid amino acid depletion and marked impairment of translation. Thus, the proteasome plays a crucial role in cell survival after acute disruption of amino acid supply.
Informing research participants of research results: analysis of Canadian university based research ethics board policies
Authors: MacNeil S D , Fernandez C V
Published: December 2005

Background:Despite potential benefits of the return of research results to research participants, the TriCouncil Policy Statement (TCPS), which reflects Canadian regulatory ethical requirements, does not require this. The policies of Canadian research ethics boards (REBs) are unknown.

Objectives:To examine the policies of Canadian university based REBs regarding returning results to research participants, and to ascertain if the presence/absence of a policy may be influenced by REB member composition.

Design:Email survey of the coordinators of Canadian university based REBs to determine the presence/absence of a policy on return of research results to research participants both during an ongoing study and at conclusion. REB coordinators were asked to return a copy of the policy or guidelines and to describe the member composition of their REB.

Findings:Of 50 REBs that were contacted 34 (68%) responded and 22 (64.7%) met the inclusion criteria. Two (9.1%) had a policy that governed the return of research results while on a study, and seven (31.8%) following the completion of a study. Presence of an ethicist or a lawyer on the REB did not influence the presence/absence of such policies. No REBs had specific guidelines describing how participants should be informed of results.

Conclusions:Most REBs did not require researchers to disclose study results to research participants either during or following a study. Thus this study identifies an ethical shortcoming in the conduct of human research in Canada. It has also demonstrated that there are no clear recommendations by REBs to facilitate the return of results to participants following research projects.
Choosing Healthand the inner citadel
Authors: Allmark P
Published: December 2005

It is argued in this paper that the latest UK government white paper on public health,Choosing Health, is vulnerable to a charge of paternalism. For some years libertarians have levelled this charge at public health policies. The white paper tries to avoid it by constant reference to informed choice and choice related terms. The implication is that the government aims only to inform the public of health issues; how they respond is up to them. It is argued here, however, that underlying the notion of informed choice is a Kantian, “inner citadel” view of autonomy. According to this view, each of us acts autonomously only when we act in accord with reason. On such a view it is possible to justify coercing, cajoling, and conning people on the basis that their current behaviour is not autonomous because it is subject to forces that cause irrational choice, such as addiction. “Informed choice” in this sense is compatible with paternalism. This paternalism can be seen in public health policies such as deceptive advertising and the treatment of “bad habits” as addictions. Libertarians are bound to object to this. In the concluding section, however, it is suggested that public health can, nonetheless, find ethical succour from alternative approaches.
What should we say?
Authors: Savulescu J , Foddy B , Rogers J
Published: December 2005

Abstract ethics mostly focuses on what we do. One form of action is a speech act. What we say can have profound effects. We can and should choose our words and how we speak wisely. When someone close to us suffers an injury or serious illness, a duty of beneficence requires that we support that person through beneficial words or actions. Though our intentions are most often benign, by what we say we often make the unfortunate person feel worse. Beginning with two personal accounts, this article explains what can go wrong in the compassionate speech of wellwishers, and uncovers some of the reasons why people say things that are hurtful or harmful. Despite a large body of clinical evidence, there is no perfect strategy for comforting a friend or relative who is ill, and sometimes even the best thing to say can still be perceived as insensitive and hurtful. In some cases, we may have good reason to knowingly say a hurtful or insensitive thing. Saying these ‘wrong’ things can sometimes be the best way to help a person in the long term. To complicate matters, there can be moral reasons for overriding what is good for the patient. What kind of admonishments should we make to a badly behaved patient? What is the value of authenticity in our communication with the people we love? These questions demand an ethical defence of those speech acts which are painful to hear but which need to be said, and of those which go wrong despite the best efforts of the wellwisher. We offer an ethical account, identifying permissible and impermissible justifications for the things we say to a person with a serious injury or illness.
THE DYNAMICS OF CRIME AND PUNISHMENT
Authors: HAUSKEN KJELL , MOXNES JOHN F.
Published: December 2005

This article analyzes crime development which is one of the largest threats in today's world, frequently referred to as the war on crime. The criminal commits crimes in his free time (when not in jail) according to a non-stationary Poisson process which accounts for fluctuations. Expected values and variances for crime development are determined. The deterrent effect of imprisonment follows from the amount of time in imprisonment. Each criminal maximizes expected utility defined as expected benefit (from crime) minus expected cost (imprisonment). A first-order differential equation of the criminal's utility-maximizing response to the given punishment policy is then developed. The analysis shows that if imprisonment is absent, criminal activity grows substantially. All else being equal, any equilibrium is unstable (labile), implying growth of criminal activity, unless imprisonment increases sufficiently as a function of criminal activity. This dynamic approach or perspective is quite interesting and has to our knowledge not been presented earlier. The empirical data material for crime intensity and imprisonment for Norway, England and Wales, and the US supports the model. Future crime development is shown to depend strongly on the societally chosen imprisonment policy. The model is intended as a valuable tool for policy makers who can envision arbitrarily sophisticated imprisonment functions and foresee the impact they have on crime development.
FINANCIAL AND OTHER SPATIO-TEMPORAL TIME SERIES: LONG-RANGE CORRELATIONS AND SPECTRAL PROPERTIES
Authors: CHAKRABORTI A. , SANTHANAM M. S.
Published: December 2005

In this paper, we review some of the properties of financial and other spatio-temporal time series generated from coupled map lattices, GARCH(1,1) processes and random processes (for which analytical results are known). We use the Hurst exponent (R/S analysis) and detrended fluctuation analysis as the tools to study the long-time correlations in the time series. We also compare the eigenvalue properties of the empirical correlation matrices, especially in relation to random matrices.
NONEQUILIBRIUM PHASE TRANSITIONS IN MODEL FERROMAGNETS: A REVIEW
Authors: ACHARYYA MUKTISH
Published: December 2005

The thermodynamical behaviors of ferromagnetic systems in equilibrium are well studied. However, the ferromagnetic systems far from equilibrium became an interesting field of research in last few decades. Recent exploration of ferromagnetic systems in the presence of a steady magnetic field are also studied by using standard tools of equilibrium statistical physics. The ferromagnet in the presence of time-dependent magnetic field, shows various interesting phenomena. An usual response of a ferromagnet in the presence of a sinusoidally oscillating magnetic field is the hysteresis. Apart from this hysteretic response, the nonequilibrium dynamic phase transition is also a very interesting phenomenon. In this chapter, the nonequilibrium dynamic phase transitions of the model ferromagnetic systems in presence of time-dependent magnetic field are discussed. For this kind of nonequilibrium phase transition, one cannot employ the standard techniques of equilibrium statistical mechanics. The recent developments in this direction are mainly based on numerical simulation (Monte Carlo). The Monte Carlo simulation of kinetic Ising model, in presence of sinusoidally oscillating (in time but uniform over space) magnetic field, is extensively performed to study the nonequilibrium dynamic phase transition. The temperature variations of dynamic order parameter, dynamic specific heat, dynamic relaxation time etc. near the transition point are discussed. The appearance and behaviors of a dynamic length scale and a dynamic time scale near the transition point are also discussed. All these studies indicate that this proposed dynamic transition is a nonequilibrium thermodynamic phase transition. The disorder (quenched) induced zero temperature (athermal) dynamic transition is studied in random field Ising ferromagnet. The dynamic transition in the Heisenberg ferromagnet is also studied. The nature of this transition in the Heisenberg ferromagnet depends on the anisotropy and the polarisation of the applied time varying magnetic field. The anisotropic Heisenberg ferromagnet in the presence of elliptically polarised magnetic field shows multiple dynamic transitions. This multiple dynamic transitions in anisotropic Heisenberg ferromagnet are discussed here. Recent experimental evidences of dynamic transitions are also discussed very briefly.
SIMULATIONS OF LIQUID BREAK UP WITH AN AXISYMMETRIC, MULTIPLE RELAXATION TIME, INDEX-FUNCTION LATTICE BOLTZMANN MODEL
Authors: MCCRACKEN MICHAEL E. , ABRAHAM JOHN
Published: December 2005

Liquid break up is an important phenomenon in many practical applications including combustion engines and paint sprays. The fundamental mechanisms which lead to this break up are not well understood. In this paper, the lattice Boltzmann method is employed to assess its potential for investigating these mechanisms. To do this, an axisymmetric, multiple relaxation time (MRT) lattice Boltzmann method, which allows for higher Reynolds numbers to be achieved than with the standard Bhatnagar-Gross-Krook (BGK) lattice Boltzmann model, is employed to simulate liquid break up. To assess the accuracy of the model, it is employed to simulate Rayleigh break up. The computational results for Rayleigh break up are compared to experimental and theoretical predictions and shown to have agreement within several percent. Then, the model is employed to carry out initial studies of transient liquid jets to investigate the influence of surface tension, injection velocity, and liquid viscosity.
PRICE FORMATION BASED ON PARTICLE-CLUSTER AGGREGATION
Authors: WANG SHIJUN , ZHANG CHANGSHUI
Published: December 2005

In the present work, we propose a microscopic model of financial markets based on particle-cluster aggregation on a two-dimensional small-world information network in order to simulate the dynamics of the stock markets. "Stylized facts" of the financial market time series, such as fat-tail distribution of returns, volatility clustering and multifractality, are observed in the model. The results of the model agree with empirical data taken from historical records of the daily closures of the NYSE composite index.
LORENTZ INVARIANT AND SUPERSYMMETRIC INTERPRETATION OF NONCOMMUTATIVE QUANTUM FIELD THEORY
Authors: KOBAYASHI YOSHISHIGE , SASAKI SHIN
Published: December 2005

In this paper, using a Hopf-algebraic method, we construct deformed Poincaré SUSY algebra in terms of twisted (Hopf) algebra. By adapting this twist deformed super-Poincaré algebra as our fundamental symmetry, we can see the consistency between the algebra and non(anti)commutative relation among (super)coordinates and interpret that symmetry of non(anti)commutative QFT is in fact twisted one. The key point is validity of our new twist element that guarantees non(anti)commutativity of space. It is checked in this paper for [Formula: see text] case. We also comment on the possibility of noncommutative central charge coordinate. Finally, because our twist operation does not break the original algebra, we can claim that (twisted) SUSY is not broken in contrast to the string inspired [Formula: see text] SUSY in [Formula: see text] non(anti)commutative superspace.
UPPER AND LOWER LIMITS ON THE EIGENVALUES OF THE SPINLESS SALPETER EQUATION
Authors: BRAU FABIAN
Published: December 2005

In the context of relativistic quantum mechanics, we obtain a nonlinear first order differential equation for the energy as a function of the coupling constant of a central potential. This differential equation is only exact for power law and logarithmic potentials in the massless limit. For other potentials, we discuss under which conditions the differential equation yields rigorous upper and lower limits on the value of energy levels. These results are applied to the Cornell potential used in meson spectroscopy. We also show that the method applies to noncentral potentials.
${\mathcal{CPT}}$-CONSERVING HAMILTONIANS AND THEIR NONLINEAR SUPERSYMMETRIZATION USING DIFFERENTIAL CHARGE-OPERATORS ${\mathcal C}$
Authors: BAGCHI BIJAN , BANERJEE A. , CALICETI EMANUELA , CANNATA FRANCESCO , GEYER HENDRIK B. , QUESNE CHRISTIANE , ZNOJIL MILOSLAV
Published: December 2005

A brief overview is given of recent developments and fresh ideas at the intersection of [Formula: see text]- and/or [Formula: see text]-symmetric quantum mechanics with supersymmetric quantum mechanics (SUSY QM). Within the framework of the resulting supersymmetric version of [Formula: see text]-symmetric quantum mechanics we study the consequences of the assumption that the "charge" operator [Formula: see text] is represented in a differential-operator form of the second or higher order. Besides the freedom allowed by the Hermiticity constraint for the operator [Formula: see text], encouraging results are obtained in the second-order case. In particular, the integrability of intertwining relations proves to match the closure of our nonlinear (viz., polynomial) SUSY algebra. In a particular illustration, our form of [Formula: see text]-symmetric SUSY QM leads to a new class of non-Hermitian polynomial oscillators with real spectrum which turn out to be [Formula: see text]-asymmetric.
MULTISCALE MODELING OF SOLIDIFICATION: PHASE-FIELD METHODS TO ADAPTIVE MESH REFINEMENT
Authors: PROVATAS NIKOLAS , GREENWOOD MICHAEL , ATHREYA BADRINARAYAN , GOLDENFELD NIGEL , DANTZIG JONATHAN
Published: December 2005

We review the use of phase field methods in solidification modeling, describing their fundamental connection to the physics of phase transformations. The inherent challenges associated with simulating phase field models across multiple length and time scales are discussed, as well as how these challenges have been addressed in recent years. Specifically, we discuss new asymptotic analysis methods that enable phase field equations to emulate the sharp interface limit even in the case of quite diffuse phase-field interfaces, an aspect that greatly reduces computation times. We then review recent dynamic adaptive mesh refinement algorithms that have enabled a dramatic increase in the scale of microstructures that can be simulated using phase-field models, at significantly reduced simulation times. Combined with new methods of asymptotic analysis, the adaptive mesh approach provides a truly multi-scale capability for simulating solidification microstructures from nanometers up to centimeters. Finally, we present recent results on 2D and 3D dendritic growth and dendritic spacing selection, which have been made using phase-field models solved with adaptive mesh refinement.
R.F. SPUTTERING DEPOSITION OF BUFFER LAYERS FOR Si/YBCO INTEGRATED MICROELECTRONICS
Authors: ROMBOLÀ G. , BALLARINI V. , CHIODONI A. , GOZZELINO L. , MEZZETTI E. , MINETTI B. , PIRRI C. F. , TRESSO E. , CAMERLINGO C.
Published: December 2005

The aim of the present work is the optimization of the Si /buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO 2 system, obtained by RF magnetron sputtering of CeO 2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N 2 and O 2 atmospheres. The presence of an unwanted amorphous SiO 2 layer at the Si/CeO 2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition.

A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO 2, respectively. Results on YSZ/Si and CeO 2/ YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO 2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO 2/ Si configuration, is c-axis oriented.
STUDY OF THE ELECTRONIC STRUCTURE AND PHYSICAL PROPERTIES OF THE IRIDIUM BASED INTERMETALLIC COMPOUNDS UNDER PRESSURE
Authors: SUNDARESWARI M. , RAJAGOPALAN M.
Published: December 2005

The electronic structure of the Iridium based L12 intermetallic compounds ( A 3 B ) such as Ir 3 Ti , Ir 3 Zr , Ir 3 Hf , Ir 3 V , Ir 3 Nb and Ir 3 Ta , which have wide applications as high temperature structural materials are studied by means of Self-Consistent Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method. These compounds are found to crystallize in the Cu 3 Au type structure. The total energies are calculated as a function of volume and fitted to Birch equation of state to find the equilibrium lattice parameter and the bulk modulus. They are tabulated and compared with the available experimental and other theoretical data. The partial number of electrons at A and B sites of these compounds are calculated as a function of volume. We find that there is a continuous transfer of d-electrons from A-site to B-site. The band structure and density of states histograms are plotted. From the DOS histograms, we find that the plots are similar for all the compounds except for Ir 3 V . In the case of Ir 3 V , we find that there are hybridization between Ir -d like and V -d like states at the Fermi level. Hence, it is predicted that under compression there may be a Lifshitz type of transition in Ir 3 V . The cohesive energy, heat of formation and the electronic specific heat coefficient of the compounds are also computed.
SILICON IMPLEMENTATION OF A CHEMICAL REACTION–DIFFUSION PROCESSOR FOR COMPUTATION OF VORONOI DIAGRAM
Authors: ASAI TETSUYA , COSTELLO BEN DE LACY , ADAMATZKY ANDREW
Published: December 2005

Reaction–diffusion (RD) chemical systems are known to realize sensible computation when both data and results of the computation are encoded in concentration profiles of chemical species; the computation is implemented via spreading and interaction of either diffusive or phase waves, while a silicon RD chip is an electronic analog of the chemical RD systems where the concentration profiles of chemicals are represented by voltage distributions on the chip's surface. In this paper, we present a prototype RD chip implementing a chemical RD processor for a well-known NP-complete problem of computational geometry — computation of a Voronoi diagram. We offer experimental results for fabricated RD chips and compare the accuracy of information processing in silicon analogs of RD processors and their experimental "wetware" prototypes.
ROTATING CONVECTION IN A BINARY VISCOELASTIC LIQUID MIXTURE
Authors: LAROZE D. , MARTÍNEZ-MARDONES J. , PÉREZ-GARCIA C.
Published: December 2005

In this work we report theoretical and numerical results on convection in a viscoelastic binary mixture under rotation. Instability thresholds for stationary convection are calculated. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system for oscillatory convection. Finally, we analyze the stabilizing effect of rotation on instability thresholds for aqueous DNA suspensions.
CHAOS IN CROSS-COUPLED BVP OSCILLATORS
Authors: UETA TETSUSHI , KAWAKAMI HIROSHI
Published: December 2005

In this letter, we investigate the cross-coupled BVP oscillators. A single BVP oscillator has two terminals which can extract an independent state variable, so in the preceding works, several coupling systems have been studied. Synchronization modes and chaos in these systems are classified as results of bifurcation problems. We revisit a coupled oscillator, and clarify new results which have not been reported before, i.e. stable tori and its breakdown, and chaotic motions. Also classification of synchronized periodic solutions is done by a bifurcation diagram.
OCCURRENCE OF ELLIPTICAL FRACTAL PATTERNS IN MULTI-BIT BANDPASS SIGMA DELTA MODULATORS
Authors: HO CHARLOTTE YUK-FAN , LING BINGO WING-KUEN , REISS JOSHUA D. , YU XINGHUO
Published: December 2005

It has been established that the class of bandpass sigma delta modulators (SDMs) with single bit quantizers could exhibit state space dynamics represented by elliptic or fractal patterns confined within trapezoidal regions. In this letter, we find that elliptical fractal patterns may also occur in bandpass SDMs with multibit quantizers, even for the case when the saturation regions of the multibit quantizers are not activated and a large number of bits are used for the implementation of the quantizers. Moreover, the fractal pattern may occur for low bit quantizers, and the visual appearance of the phase portraits between the infinite state machine and the finite state machine with high bit quantizers is different. These phenomena are different from those previously reported for the digital filter with two's complement arithmetic. Furthermore, some interesting phenomena are found. A bit change of the quantizer can result in a dramatic change in the fractal patterns. When the trajectories of the corresponding linear systems converge to a fixed point, the regions of the elliptical fractal patterns diminish in size as the number of bits of the quantizers increases.
TRANSITION FROM PERIODICITY TO CHAOS IN A PWM-CONTROLLED BUCK CONVERTER WITH ZAD STRATEGY
Authors: ANGULO FABIOLA , FOSSAS ENRIC , OLIVAR GERARD
Published: December 2005

The transition from periodicity to chaos in a DC-DC Buck power converter is studied in this paper. The converter is controlled through a direct Pulse Width Modulation (PWM) in order to regulate the error dynamics at zero. Results show robustness with low output error and a fixed switching frequency. Furthermore, some rich dynamics appear as the constant associated with the first-order error dynamics decreases. Finally, a transition from periodicity to chaos is observed. This paper describes this transition and the bifurcations in the converter. Chaos appears in the system with a stretching and folding mechanism. It can be observed in the one-dimensional Poincaré map of the inductor current. This Poincaré map converges to a tent map with the variation of the system parameter ks.
NETWORKED CONTROL SYSTEMS: A PERSPECTIVE FROM CHAOS
Authors: ZHANG GUOFENG , CHEN TONGWEN
Published: December 2005

In this paper, a nonlinear system aiming at reducing the signal transmission rate in a networked control system is constructed by adding nonlinear constraints to a linear feedback control system. Its stability is investigated in detail. It turns out that this nonlinear system exhibits very interesting dynamical behaviors: in addition to local stability, its trajectories may converge to a nonorigin equilibrium or be periodic or just be random. Furthermore it exhibits sensitive dependence on initial conditions — a sign of chaos. Complicated bifurcation phenomena are exhibited by this system. After that, control of the chaotic system is discussed. All these are studied under scalar cases in detail. Some difficulties involved in the study of this type of systems are analyzed. Finally an example is employed to reveal the effectiveness of the scheme in the framework of networked control systems.
ON THE ONSET OF QUASI-PERIODIC SOLUTIONS IN THIRD-ORDER NONLINEAR DYNAMICAL SYSTEMS
Authors: GENESIO R. , GHILARDI C.
Published: December 2005

The paper considers the existence of quasi-periodic solutions in three-dimensional systems. Since these solutions commonly arise as a consequence of a Neimark–Sacker bifurcation of a limit cycle, a fairly general relation connected to this phenomenon is pointed out as the main result of the paper. Then, the application of harmonic balance techniques makes possible to exploit such a relation. In particular, a simplified condition denoting the quasi-periodicity onset can be derived, in making evident the main elements for this transition in terms of structure and parameters, and hence some remarks on the features of the interested systems. Several examples show the application of the above condition to detect "tori" in the state space in a qualitative (not simply numerical) way. They consider classical systems — Rössler, where such behavior seems to be unknown, Chua, forced Van der Pol — and new quadratic systems.
ESTIMATING ERROR GROWTH AND SHADOW BEHAVIOR IN NONLINEAR DYNAMICAL SYSTEMS
Authors: ORRELL D.
Published: December 2005

In modeling nonlinear dynamical systems, error growth can arise both because of dynamical error in the model, and observational error in measurements of the underlying system. Errors thus introduced can be further amplified by the system dynamics. This paper develops a method to approximate error growth, based on the model drift, for the general case when the model is given by a (possibly large) set of ordinary differential equations. The ability of the model to shadow (stay close to) the true system is analyzed, and a criterion for model quality based on the error dynamics is proposed. Examples are given with a range of models, which are chosen to be representative of different types of model error.
Cytoplasmic targeting signals mediate delivery of phospholemman to the plasma membrane
Authors: Lansbery Kristan L. , Burcea Lauren C. , Mendenhall Margaretta L. , Mercer Robert W.
Published: December 2005

The FXYD protein family consists of several small, single-span membrane proteins that exhibit a high degree of homology. The best-known members of the family include the γ-subunit of the Na+-K+-ATPase and phospholemman (PLM), a phosphoprotein of cardiac sarcolemma. Other members of the family include corticosteroid hormone-induced factor (CHIF), mammary tumor protein of 8 kDa (Mat-8), and related to ion channels (RIC). The exact physiological roles of the FXYD proteins remain unknown. To better characterize the function of the members of the FXYD protein family, we expressed several members of the family in Madin-Darby canine kidney (MDCK) cells. All of the FXYD proteins, with the exception of PLM, were primarily found in the basolateral plasma membrane. Surprisingly, PLM, a previously characterized plasma membrane protein, was found to colocalize with the endoplasmic reticulum marker protein disulfide isomerase. Treatment of MDCK cells expressing PLM with an agonist of PKC caused some of the PLM to be redistributed to the plasma membrane. Site-directed mutagenesis of residues within the cytoplasmic domain of PLM indicated that a negative charge at Ser69 is necessary to shift the localization of PLM to the plasma membrane. In addition, other regions of PLM necessary for either its endoplasmic reticulum or plasma membrane localization have been elucidated. In contrast to PLM, the plasma membrane localization of CHIF and RIC was not altered by mutation of potential cytoplasmic phosphorylation sites. Overall, these results suggest that phosphorylation of specific residues of PLM may direct PLM from an intracellular compartment to the plasma membrane.
Glutamate induces oxidative stress and apoptosis in cerebral vascular endothelial cells: contributions of HO-1 and HO-2 to cytoprotection
Authors: Parfenova Helena , Basuroy Shyamali , Bhattacharya Sujoy , Tcheranova Dilyara , Qu Yan , Regan Raymond F. , Leffler Charles W.
Published: December 2005

In cerebral circulation, epileptic seizures associated with excessive release of the excitatory neurotransmitter glutamate cause endothelial injury. Heme oxygenase (HO), which metabolizes heme to a vasodilator, carbon monoxide (CO), and antioxidants, biliverdin/bilirubin, is highly expressed in cerebral microvessels as a constitutive isoform, HO-2, whereas the inducible form, HO-1, is not detectable. Using cerebral vascular endothelial cells from newborn pigs and HO-2-knockout mice, we addressed the hypotheses that 1) glutamate induces oxidative stress-related endothelial death by apoptosis, and 2) HO-1 and HO-2 are protective against glutamate cytotoxicity. In cerebral endothelial cells, glutamate (0.1–2.0 mM) increased formation of reactive oxygen species, including superoxide radicals, and induced major keystone events of apoptosis, such as NF-κB nuclear translocation, caspase-3 activation, DNA fragmentation, and cell detachment. Glutamate-induced apoptosis was greatly exacerbated in HO-2 gene-deleted murine cerebrovascular endothelial cells and in porcine cells with pharmacologically inhibited HO-2 activity. Glutamate toxicity was prevented by superoxide dismutase, suggesting apoptotic changes are oxidative stress related. When HO-1 was pharmacologically upregulated by cobalt protoporphyrin, apoptotic effects of glutamate in cerebral endothelial cells were completely prevented. Glutamate-induced reactive oxygen species production and apoptosis were blocked by a CO-releasing compound, CORM-A1 (50 μM), and by bilirubin (1 μM), consistent with the antioxidant and cytoprotective roles of the end products of HO activity. We conclude that both HO-1 and HO-2 have anti-apoptotic effects against oxidative stress-related glutamate toxicity in cerebral vascular endothelium. Although HO-1, when induced, provides powerful protection, HO-2 is an essential endogenous anti-apoptotic factor against glutamate toxicity in the cerebral vascular endothelium.
Changes in plasma protein extravasation in rat skin during inflammatory challenges evaluated by microdialysis
Authors: Borge B. Å. , Iversen V. V. , Reed R. K.
Published: December 2005

Docetaxel and prostaglandin E1 (PGE1) increase transcapillary albumin extravasation and reduce interstitial fluid pressure in the skin. In this study the microdialysate concentration (Cm) of 125I-labeled human serum albumin (125I-HSA) and different-sized endogenous plasma proteins (EPP) was compared to evaluate changes in transcapillary extravasation of plasma proteins. 125I-HSA was also used to estimate changes in the specific activity of albumin. Extravasation of 125I-HSA and EPP from plasma to interstitium in the rat skin was compared during continuous administration of docetaxel and PGE1 by using microdialysis in anesthetized rats. Also, 20 ml of Ringer solution (RS) were injected intravenously during 10 min in a separate group. Two hollow plasmapheresis fibers (3 cm, cut off 3,000 kDa), one acting as control, were placed subcutaneously on the back skin and perfused with RS (5 μl/min, 140 min, collected every 10 min). The size of the different EPP was estimated to be 73, 65, 56, 47, and 39 Å, separated by a size-exclusion high-performance liquid chromatography column and quantified by UV detection (280 nm). Docetaxel (0.5 mg/ml, n = 5) increased Cm of 125I-HSA and EPP of sizes 73, 65, 56, and 39 Å significantly ( P < 0.05) compared with control. PGE1 (20 μg/ml, n = 6) increased Cm of 125I-HSA significantly ( P < 0.05) but none of the different-sized EPP was increased compared with control. Intravenous RS (20 ml, n = 6) increased Cm of 125I-HSA and increased all the different-sized EPP significantly ( P < 0.05) compared with control. Although the microdialysis method is able to monitor qualitative changes in capillary permeability, a quantitative determination of the capillary reflection coefficient or permeability-surface area product was not possible, because steady state between plasma and dialysate was not achieved during the measurement period. The different pattern of extravasation of EPP and 125I-HSA after docetaxel, PGE1, and RS indicates increased interstitial transport rate and/or increased capillary permeability after docetaxel and RS, whereas PGE1 seems to increase transcapillary fluid flux without altering the permeability.
Effect of phosphodiesterase 5 inhibitor on alteration in vascular smooth muscle sensitivity and renal function in rats with liver cirrhosis
Authors: Tahseldar-Roumieh Rima , Ghali-Ghoul Rana , Lugnier Claire , Sabra Ramzi
Published: December 2005

Previous studies suggested that increased activity of phosphodiesterase (PDE)5 in the kidneys of cirrhotic rats contributes to sodium retention. This study examined the role of PDE5 in the changes in vascular reactivity, hemodynamics, and sodium excretion in rats with liver cirrhosis. Four weeks after bile duct ligation (BDL) or sham operation (SO), in vitro reactivity of aortic rings to various agents and in vivo effects of a PDE5-selective inhibitor [1,3-dimethyl-6-(2-propoxy-5-methanesulfonylamidophenyl)pyrazolo[3,4 d]-pyrimidin-4-(5 H)-one, DMPPO] were studied. The vasodilator responses to nitroglycerin and S-nitroso- N-acetyl-penicillamine (SNAP) in phenylephrine-precontracted rings without endothelium were attenuated in BDL compared with SO rats. Pretreatment with DMPPO (0.1 μM) enhanced these responses and eliminated the differences between the two groups. Vasodilation to DMPPO itself was also less in BDL rats. The responses to phenylephrine were attenuated in endothelium-rich aorta from BDL relative to SO rats, but they were similar in endothelium-denuded aorta and remained similar despite preincubation with SNAP (0.1 μM) alone or with SNAP and DMPPO. In vivo, BDL rats were vasodilated relative to SO rats; DMPPO (5 mg/kg iv) decreased arterial pressure and vascular resistance in both groups equally and caused significant increase in sodium excretion in BDL rats only. In conclusion, the results are in accordance with a possible increase in PDE5 activity in aorta and kidney of cirrhotic rats that results in reduced responses to NO donors and contributes to the increase in sodium retention. PDE5 inhibitors may ameliorate sodium retention in cirrhosis but may worsen vasodilation. Examining the effect of PDE5 inhibitors after chronic administration will be more revealing.
Calcium paradox of aldosteronism and the role of the parathyroid glands
Authors: Vidal Alex , Sun Yao , Bhattacharya Syamal K. , Ahokas Robert A. , Gerling Ivan C. , Weber Karl T.
Published: December 2005

The hypercalciuria and hypermagnesuria that accompany aldosteronism contribute to a fall in plasma ionized extracellular Ca2+ and Mg2+ concentrations ([Ca2+]o and [Mg2+]o). Despite these losses and the decline in extracellular levels of these cations, total intracellular and cytosolic free Ca2+ concentration ([Ca2+]i) is increased and oxidative stress is induced. This involves diverse tissues, including peripheral blood mononuclear cells (PBMC) and plasma. The accompanying elevation in plasma parathyroid hormone (PTH) and reduction in bone mineral density caused by aldosterone (Aldo)-1% NaCl treatment (AldoST) led us to hypothesize that Ca2+ loading and altered redox state are due to secondary hyperparathyroidism (SHPT). Therefore, we studied the effects of total parathyroidectomy (PTx). In rats receiving AldoST, without or with a Ca2+-supplemented diet and/or PTx, we monitored urinary Ca2+ and Mg2+ excretion; plasma [Ca2+]o, [Mg2+]o, and PTH; PBMC [Ca2+]i and H2O2 production; plasma α1-antiproteinase activity; total Ca2+ and Mg2+ in bone, myocardium, and rectus femoris; and gp91phox labeling in the heart. We found that 1) the hypercalciuria and hypermagnesuria and decline ( P < 0.05) in plasma [Ca2+]o and [Mg2+]o that occur with AldoST were not altered by the Ca2+-supplemented diet alone or with PTx; 2) the rise ( P < 0.05) in plasma PTH with AldoST, with or without the Ca2+-supplemented diet, was prevented by PTx; 3) increased ( P < 0.05) PBMC [Ca2+]i and H2O2 production, increased total Ca2+ in heart and skeletal muscle, and fall in bone Ca2+ and Mg2+ and plasma α1-antiproteinase activity with AldoST were abrogated ( P < 0.05) by PTx; and 4) gp91phox activation in right and left ventricles at 4 wk of AldoST was attenuated by PTx. AldoST is accompanied by SHPT, with parathyroid gland-derived calcitropic hormones being responsible for Ca2+ overload in diverse tissues and induction of oxidative stress. SHPT plays a permissive role in the proinflammatory vascular phenotype.
Shift of Intracellular Chloride Concentration in Ganglion and Amacrine Cells of Developing Mouse Retina
Authors: Zhang Ling-Li , Pathak Hemal R. , Coulter Douglas A. , Freed Michael A. , Vardi Noga
Published: December 2005

GABA and glycine provide excitatory action during early development: they depolarize neurons and increase intracellular calcium concentration. As neurons mature, GABA and glycine become inhibitory. This switch from excitation to inhibition is thought to result from a shift of intracellular chloride concentration ([Cl−]i) from high to low, but in retina, measurements of [Cl−]ior chloride equilibrium potential ( ECl) during development have not been made. Using the developing mouse retina, we systematically measured [Cl−]iin parallel with GABA's actions on calcium and chloride. In ganglion and amacrine cells, fura-2 imaging showed that before postnatal day (P) 6, exogenous GABA, acting via ionotropic GABA receptors, evoked calcium rise, which persisted in HCO3−- free buffer but was blocked with 0 extracellular calcium. After P6, GABA switched to inhibiting spontaneous calcium transients. Concomitant with this switch we observed the following: 6-methoxy- N-ethylquinolinium iodide (MEQ) chloride imaging showed that GABA caused an efflux of chloride before P6 and an influx afterward; gramicidin-perforated-patch recordings showed that the reversal potential for GABA decreased from −45 mV, near threshold for voltage-activated calcium channel, to −60 mV, near resting potential; MEQ imaging showed that [Cl−]ishifted steeply around P6 from 29 to 14 mM, corresponding to a decline of EClfrom −39 to −58 mV. We also show that GABAergic amacrine cells became stratified by P4, potentially allowing GABA's excitatory action to shape circuit connectivity. Our results support the hypothesis that a shift from high [Cl−]ito low causes GABA to switch from excitatory to inhibitory.
Dynamic Ensemble Coding of Saccades in the Monkey Superior Colliculus
Authors: Goossens H.H.L.M. , Van Opstal A. J.
Published: December 2005

The deeper layers of the midbrain superior colliculus (SC) contain a topographic motor map in which a localized population of cells is recruited for each saccade, but how the brain stem decodes the dynamic SC output is unclear. Here we analyze saccade-related responses in the monkey SC to test a new dynamic ensemble-coding model, which proposes that each spike from each saccade-related SC neuron adds a fixed, site-specific contribution to the intended eye movement command. As predicted by this simple theory, we found that the cumulative number of spikes in the cell bursts is tightly related to the displacement of the eye along the ideal straight trajectory, both for normal saccades and for strongly curved, blink-perturbed saccades toward a single visual target. This dynamic relation depends systematically on the metrics of the saccade displacement vector, and can be fully predicted from a quantitative description of the cell’s classical movement field. Furthermore, we show that a linear feedback model of the brain stem, which is driven by dynamic linear vector summation of measured SC firing patterns, produces realistic two-dimensional (2D) saccade trajectories and kinematics. We conclude that the SC may act as a nonlinear, vectorial saccade generator that programs an optimal straight eye-movement trajectory.
Feedback Effects of Horizontal Cell Membrane Potential on Cone Calcium Currents Studied With Simultaneous Recordings
Authors: Cadetti Lucia , Thoreson Wallace B.
Published: December 2005

Horizontal cell (HC) to cone feedback helps establish the center-surround arrangement of visual receptive fields. It has been shown that HC activity influences cone synaptic output by altering the amplitude and voltage dependence of the calcium current ( ICa) in cones. In this study, we obtained voltage-clamp recordings simultaneously from cones and HCs to directly control the membrane potential of HCs and thereby measure the influence of HC membrane potential changes on ICa in adjacent cones. Directly hyperpolarizing voltage clamped HCs produced a negative activation shift and increased the amplitude of ICa in cones. Both of these effects were abolished by enhancing extracellular pH buffering capacity with HEPES. In contrast, addition of the gap junction blocker, carbenoxolone, did not significantly alter the shifts or amplitude changes in cone ICa produced by changes in HC membrane potential. These results support the hypothesis that changes in the HC membrane potential alter the voltage dependence and amplitude of cone ICa by altering extracellular pH levels at the synapse.