bluuebunny/crossref_metadata_2025 huggingface dataset:
Songbird response to seismic lines in the western boreal forest: a manipulative experiment
Authors: Machtans Craig S.
Published: December 2006

Millions of kilometres of seismic lines have been created for hydrocarbon exploration in the boreal forest and their impact on songbirds is unknown. I conducted a replicated before–after control–impact (BACI) field experiment in southern Northwest Territories to evaluate the impact of 6 m wide seismic lines on songbirds. Territories of all birds on six pairs of 12 ha control and treatment plots were mapped for one year before and one year after seismic lines were cut through the treatment plots. The songbird community was not dramatically affected by seismic lines. At the community level, birds did not decline in abundance or move their territories relative to the seismic lines, and they included the seismic lines in their territories. However, ground and shrub nesting species that had territories spanning the seismic lines increased the size of their territories. At the species level, only the Ovenbird ( Seiurus aurocapilla (L., 1766)) showed a consistent response to seismic lines. Ovenbirds declined in abundance, moved their territories away from seismic lines, and were not observed crossing the lines. Pressure on industry from land managers to reduce the width of seismic lines should continue to minimize the impact of these clearings on all species.
Contribution of catabolic tissue replacement to the turnover of stable isotopes in Danio rerio
Authors: Tarboush Rania A. , MacAvoy Stephen E. , Macko Stephen A. , Connaughton Victoria
Published: December 2006

Stable isotopes of carbon, nitrogen, and sulfur in organisms can trace nutrient sources and determine trophic interactions. However, time is required for an organism to reflect the isotopic composition of its diet. The rate at which an organism incorporates the isotopic signature of its food has a growth (k) component and a metabolic tissue replacement (m) component. This study shows that metabolic tissue replacement accounts for between 68% and 80% of the observed changes in isotopic signature in zebra danio ( Danio rerio (Hamilton, 1822)) muscle following a dietary shift, with the remainder owing to growth of new tissue. The half-lives of carbon, nitrogen, and sulfur were ~53, ~147 and ~58 days, respectively. This indicates that a significant period of isotopic disequilibria exists before zebra danio resemble dietary isotopic composition. These results show that catabolic replacement of tissue, as well as growth, must be taken into account when predicting the rate of isotope incorporation in warm-water fish. When using isotopic ratios to decipher food webs and trophic interactions, researchers should be aware that the often held assumption of isotopic equilibrium between diet and consumer may be violated.
Changes in sex ratio over time in the endangered iguana Cyclura cychlura inornata
Authors: Smith Geoffrey R. , Iverson John B.
Published: December 2006

Changes in sex ratio of a population over time can indicate possible conservation concerns. Using population estimates for males and females, we examined changes in the sex ratio of two populations of the endangered Allen’s Cay Rock Iguana ( Cyclura cychlura inornata Barbour and Noble, 1916) in the Bahamas over nearly 25 years. The sex ratios of both populations changed from strongly male-biased early in the study to nearly 1:1 in recent years. We hypothesize that this shift has occurred because of the recovery of these populations from intense harvesting (particularly of females) over the previous 100 years and, more recently, because of the removal of large males from the islands either by poachers or by tourists.
Agonistic behaviours and movement in the signal crayfish,Pacifastacus leniusculus: can dominance interactions influence crayfish size-class distributions in streams?
Authors: Harrison Megan L. , Hoover Trent M. , Richardson John S.
Published: December 2006

Size-structured population distributions can result from stage-specific differences in habitat preference or from intraspecific dominance interactions between large and small individuals. The relative importance of these two factors in structuring population distributions was examined in the signal crayfish ( Pacifastacus leniusculus (Dana, 1852)), an organism whose populations are distinctly spatially size-sorted in streams, with adults (A) occupying deeper pools and juveniles (J) inhabiting riffles. In the first of two experiments, groups of crayfish (2A, 2A+2J, or 4J) were released in a constructed riffle–pool–riffle sequence in an experimental channel and individual behaviours and rates of movement were recorded at 2 min intervals. There were differences in habitat preference between the two size classes: adults showed a distinct preference for pools, whereas juveniles did not. In the second experiment, pairs of individuals (A+A, A+J, J+J) were placed in experimental arenas. Analysis of recorded interactions between pairs showed that agonistic interactions and subsequent post-encounter movements were sufficient to produce the exclusion of subordinate individuals from habitats occupied by dominant individuals. These results show that adults have a greater preference for pool habitats than juveniles and that interactions between asymmetrically sized pairs are likely to displace smaller individuals from areas where adult–juvenile encounter rates are high.
The effect of artificial light on male breeding-season behaviour in green frogs, Rana clamitans melanota
Authors: Baker B.J. , Richardson J.M.L.
Published: December 2006

Artificial night lighting (or ecological light pollution) is only now gaining attention as a source of long-term effects on the ecology of both diurnal and nocturnal animals. The limited data available clearly indicate that artificial light can affect physiology and behaviour of animals, leading to ecological consequences at the population, community, and ecosystem levels. Aquatic ecosystems may be particularly vulnerable to such effects, and nocturnally breeding animals such as frogs may be especially affected. To address this potential, we quantify the effects of artificial light on calling and movement behaviour in a rural population of male green frogs ( Rana clamitans melanota (Rafinesque, 1820)) during the breeding season. When exposed to artificial light, frogs produced fewer advertisement calls and moved more frequently than under ambient light conditions. Results clearly demonstrate that male green frog behaviour is affected by the presence of artificial light in a manner that has the potential to reduce recruitment rates and thus affect population dynamics.
Sexual dimorphism in the second-to-fourth digit length ratio in green anoles,Anolis carolinensis(Squamata: Polychrotidae), from the southeastern United States
Authors: Chang Jennifer L. , Doughty Stephanie , Wade Juli , Lovern Matthew B.
Published: December 2006

Digit length ratios are organized during embryonic development and may show sexual dimorphism related to steroid exposure. The second-to-fourth digit length ratio (2D:4D) has received the most attention. In the present study, we measured 2D:4D of all four feet of adult male and female green anoles ( Anolis carolinensis Voigt, 1832) to determine whether it is sexually dimorphic and whether results are repeatable across laboratories. Lizards were housed at Michigan State University (MSU) and Oklahoma State University (OSU), and one investigator at each institution used digital calipers to measure the 2D:4D of each foot. At both MSU and OSU, we found that males had a significantly larger 2D:4D on the back right foot than females did, and that no sex difference existed in either the back left or the front right foot. Furthermore, although no sex difference in the front left foot was found at MSU, the 2D:4D on this foot was larger in females at OSU. Our results demonstrate both sexual dimorphism in 2D:4D and repeatability between laboratories, but they also suggest the importance of verifying such repeatability if 2D:4D or any other digit length ratio is used as a potential indicator of the early steroid environment.
PAINTING CHAOS: A GALLERY OF SENSITIVITY PLOTS OF CLASSICAL PROBLEMS
Authors: BARRIO ROBERTO
Published: December 2006

In this paper we study briefly several chaos indicators and we focus our attention on the recently developed [Formula: see text], presenting a numerical scheme for its calculation based on the Taylor method. Using this new indicator we present several sensitivity plots for several classical problems: the Hydrogen Atom in a magnetic field, an Extensible Pendulum, the Heavy-Top, the (N + 1)-body Ring problem and the Duffing-Oscillator. Most of these plots are new and they provide a global picture of the evolution of such a dynamical system. Besides, we show [Formula: see text] plots of variations in the parameters of the problem, giving a new perspective of the evolution of the problem.
A BRIEF SURVEY ON CONSTRUCTING HOMOCLINIC STRUCTURES OF SOLITON EQUATIONS
Authors: WU RANCHAO , SUN JIANHUA
Published: December 2006

To give rigorous mathematical proofs of chaotic behaviors in a given system, it is necessary to identify the homoclinic structures in the system. In this tutorial review, methods for constructing explicit solutions for nonlinear partial differential equations are presented, with more emphasis placed on those utilizing complete integrability associated with soliton equations. As an extended application, homoclinic orbits to spatial uniform plane waves of coupled modified nonlinear Schrödinger equations are obtained via the dressing method. During the procedure, it is necessary to introduce the Lax pair for these coupled equations, as well as its Floquet spectral analysis and corresponding Bloch functions.
A UNIFIED LORENZ-TYPE SYSTEM AND ITS CANONICAL FORM
Authors: YANG QIGUI , CHEN GUANGRONG , ZHOU TIANSHOU
Published: December 2006

Based on the generalized Lorenz system, a conjugate Lorenz-type system is introduced, and a new unified Lorenz-type system containing these two classes of systems is naturally constructed in the paper. Such a unified system is state-equivalent to a simple special form, which is parameterized by two parameters useful for chaos turning and system classification. More importantly, based on the parameterized form, three new chaotic attractors, called conjugate attractors, are found for the first time, which are conjugate to the Lorenz attractor, the Chen attractor, and the Lü attractor, respectively.
COUNTING LOW-PERIOD CYCLES FOR FLOWS
Authors: GALIAS ZBIGNIEW
Published: December 2006

In this paper we describe a rigorous method to find for a continuous system all low-period cycles enclosed in a certain region of the state space. As an example of the application of this technique we present the complete analysis of the Rössler attractor in terms of short periodic orbits. We construct the trapping region for the associated Poincaré map. The trapping region encloses the numerically observed attractor. We find all periodic orbits of the Poincaré map up to period 20. We prove that these periodic orbits correspond to all cycles of the flow with period shorter than 120. Using the number of short periodic orbits we compute estimates for topological entropy of the Poincaré map and the flow.
COMPLEX DYNAMICS IN PENDULUM EQUATION WITH PARAMETRIC AND EXTERNAL EXCITATIONS I
Authors: JING ZHUJUN , YANG JIANPING
Published: December 2006

Pendulum equation with parametric and external excitations is investigated in (I) and (II). In (I), by applying Melnikov's method, we prove the criterion of existence of chaos under periodic perturbation. The numerical simulations, including bifurcation diagram of fixed points, bifurcation diagram of system in three- and two-dimensional space, homoclinic and heteroclinic bifurcation surface, Maximum Lyapunov exponent, phase portraits, Poincaré map, are plotted to illustrate theoretical analysis, and to expose the complex dynamical behaviors including the period-n (n = 2 to 6, 10, 15 and 20) orbits in different chaotic regions, interlocking periodic orbits, symmetry-breaking of periodic orbit, cascade of period-doubling bifurcations from period-5 and -10 orbits, reverse period-doubling bifurcation, onset of chaos which occurs more than once for a given external frequency or parametric frequency and chaos suddenly converting to periodic orbits, sudden jump in the size of attractors which is associated with the transverse intersection of stable and unstable manifolds of perturbed saddle, hopping behavior of chaos, transient chaos with complex periodic windows and interior crisis, varied chaotic attractors including the more than three-band and eight-band chaotic attractors, chaotic attractor after strange nonchaotic attractor. In particular, we observe that the system can leave chaotic region to periodic motion by adjusting damping δ, spring constant α and frequency Ω of parametric excitation which can be considered as a control strategy. In (II), we will investigate the complex dynamics under quasi-periodic perturbation.
DYNAMICS OF A REACTION–DIFFUSION EQUATION WITH A DISCONTINUOUS NONLINEARITY
Authors: ARRIETA JOSÉ M. , RODRÍGUEZ-BERNAL ANÍBAL , VALERO JOSÉ
Published: December 2006

We study the nonlinear dynamics of a reaction–diffusion equation where the nonlinearity presents a discontinuity. We prove the upper semicontinuity of solutions and the global attractor with respect to smooth approximations of the nonlinear term. We also give a complete description of the set of fixed points and study their stability. Finally, we analyze the existence of heteroclinic connections between the fixed points, obtaining information on the fine structure of the global attractor.
DESIGNING CNN GENES FOR BINARY IMAGE EDGE SMOOTHING AND NOISE REMOVING
Authors: HE QINBIN , CHEN FANGYUE
Published: December 2006

Edge smoothing and noise removing for images are a common method of image processing. By designing CNN genes, edges can be smoothed and particles can be removed from a binary image. However, a satisfying result cannot be obtained by choosing only one CNN gene. In this paper, a group of edge smoothing and noise removing CNN genes is proposed as a synthetic disposal for a binary image. Disposed by the group of CNN genes, the characteristics of the original image can be preserved as much as possible. Two examples of edge smoothing and noise removing for a binary image are well illustrated by this method in this paper.
CHAOTIC EXPLORATION EFFECTS ON REINFORCEMENT LEARNING IN SHORTCUT MAZE TASK
Authors: MORIHIRO KOICHIRO , MATSUI NOBUYUKI , NISHIMURA HARUHIKO
Published: December 2006

Reinforcement learning is usually required in the process of trial and error called exploration, and the uniform pseudorandom number generator is considered effective in that process. As a generator for the exploration, chaotic sources are also useful in creating a random-like sequence such as in the case of stochastic sources. In this research, we investigate the efficiency of the deterministic chaotic generator for the exploration in learning a nonstationary shortcut maze problem. As a result, it is found that the deterministic chaotic generator based on the logistic map is better in the performance of the exploration than in the stochastic random generator. This has been made clear by analyzing the difference of the performances between the two generators in terms of the patterns of exploration occurrence. We also examine the tent map, which is homeomorphic to the logistic map, compared with other generators.
NULLCLINES AND NULLCLINE INTERSECTIONS
Authors: THOMAS RENÉ
Published: December 2006

One purpose of this paper is to document the fact that, in dynamical systems described by ordinary differential equations, the trajectories can be organized not only around fixed points (steady states), but also around lines. In 2D, these lines are the nullclines themselves, in 3D, the intersections of the nullclines two by two, etc.

We precise the concepts of "partial steady states" (i.e. steady states in a subsystem that consists of sections of phase space by planes normal to one of the axes) and of "partial multistationarity" (multistationarity in such a subsystem).

Steady states, nullclines or their intersections are revisited in terms of circuits, defined from nonzero elements of the Jacobian matrix. It is shown how the mere examination of the Jacobian matrix and the sign patterns of its circuits can help interpreting (and often predicting) aspects of the dynamics of systems.

The results reinforce the idea that chaotic dynamics requires both a positive circuit, to provide (if only partial) multistationarity, and a negative circuit, to provide sustained oscillations. As shown elsewhere, a single circuit may suffice if it is ambiguous (i.e. positive or negative depending on the location in phase space).

The description in terms of circuits is by no means exclusive of the classical description. In many cases, a fruitful approach involves repeated feedback between the two viewpoints.
ON HOMOCLINIC AND HETEROCLINIC ORBITS OF CHEN'S SYSTEM
Authors: LI TIECHENG , CHEN GUOTING , CHEN GUANRONG
Published: December 2006

We study the problem of existence of homoclinic and heteroclinic orbits of Chen's system. For the case of 2c > a > c > 0 and b ≥ 2a, we prove that the system has no homoclinic orbit but has two and only two heteroclinic orbits.
BIFURCATIONS OF A FORCED DUFFING OSCILLATOR IN THE PRESENCE OF FUZZY NOISE BY THE GENERALIZED CELL MAPPING METHOD
Authors: HONG LING , SUN JIAN-QIAO
Published: December 2006

Bifurcations of a forced Duffing oscillator in the presence of fuzzy noise are studied by means of the fuzzy generalized cell mapping (FGCM) method. The FGCM method is first introduced. Two categories of bifurcations are investigated, namely catastrophic and explosive bifurcations. Fuzzy bifurcations are characterized by topological changes of the attractors of the system, represented by the persistent groups of cells in the context of the FGCM method, and by changes of the steady state membership distribution. The fuzzy noise-induced bifurcations studied herein are not commonly seen in the deterministic systems, and can be well described by the FGCM method. Furthermore, two conjectures are proposed regarding the condition under which the steady state membership distribution of a fuzzy attractor is invariant or not.
DELAY-DEPENDENT SYNCHRONIZATION CRITERION FOR LUR'E SYSTEMS WITH DELAY FEEDBACK CONTROL
Authors: HE YONG , WEN GUILIN , WANG QING-GUO
Published: December 2006

A master-slave synchronization scheme for Lur'e systems is studied for a known delay existing between master and slave systems. Based on the latest development of stability studies for time-delay systems, a new delay-dependent synchronization criterion is derived by the free-weighting matrix approach. The criterion shown by example is less conservative than the existing synchronization criteria.
VIBRATION-INDUCED CONDUCTIVITY FLUCTUATION (VICOF) TESTING OF SOILS
Authors: KISH L. B. , MORGAN C. L. S. , KISHNÉ A. SZ.
Published: December 2006

In this Letter, we propose and experimentally demonstrate a simple method to provide additional information on the electro-mechanical properties of soils by electrical conductivity measurements. The AC electrical conductance of the soil is measured while it is exposed to a periodic vibration. The vibration-induced density fluctuation implies a corresponding conductivity fluctuation that can be seen as combination frequency components, the sum and the difference of the mean AC frequency and the double of vibration frequency, in the current response. The method is demonstrated by measurements on clayey and sandy soils.
TOWARDS A UNIFIED RATE THEORY OF STOCHASTIC RESONANCE
Authors: BENNETT MATTHEW R. , WIESENFELD KURT
Published: December 2006

We present a theory which connects two-state and excitable versions of stochastic resonance. The latter appears as an extreme asymmetric limit of traditional two-state rate theory. To achieve this unified view we are led to a simple generalization of excitable stochastic resonance.
QUANTA, CIPHERS AND COMPUTERS
Authors: EKERT ARTUR , KWEK L. C. , LINARES ANTIA LAMAS
Published: December 2006

On the atomic scale, matter obeys the rules of quantum mechanics which are quite different from the classical rules that determine the properties of conventional computers. Today's advanced lithographic techniques can etch logic gates and wires less than a micron across onto the surfaces of silicon chips. Soon they will yield even smaller parts and inevitably reach a point where logic gates are so small that they are made out of only a handful of atoms. So, if computers are to become smaller in the future, new, quantum technology must replace or supplement what we have now. This article provides a grand overview of quantum information theory from the concept of quantum bits (qubits) to entanglement to quantum computation to quantum cryptography.
QUANTUM INFORMATION, ENTANGLEMENT AND RELATIONSHIPS
Authors: DURT THOMAS
Published: December 2006

We present several physical applications that were generated in the framework of quantum information science. We emphasize the crucial role played, in this approach, by a group of unitary transformations, the generalized Pauli or Heisenberg–Weyl group, and by a non-classical property, called entanglement, which appears to be a basic ingredient in Quantum Information Theory. We sketch the links between entanglement and non-locality, and discuss an analogy between entanglement and (human) relationships.
QUANTUM COMPUTING, GROVER'S SEARCH ALGORITHM AND ITS APPLICATIONS IN BIOINFORMATICS
Authors: CHOO K. W.
Published: December 2006

This article reviews quantum computing and quantum algorithms. Some insights into its potential in speeding up computations are covered, with emphasis on the use of Grover's Search. In the last section, we discuss applications of quantum algorithm to bioinformatics. In particular, the extension of quantum counting algorithm to protein mass spectra counting is proposed.
GEOMETRIC PHASES OF PURE AND MIXED STATES
Authors: RAVISHANKAR R. , DU J. F.
Published: December 2006

The purpose of this article is to review the literature for pure and mixed state geometric phase and also the experimental measurement of the phase using NMR.
BLIND QUANTUM COMPUTATION
Authors: ARRIGHI PABLO , SALVAIL LOUIS
Published: December 2006

We investigate the possibility of having someone carry out the work of executing a function for you, but without letting him learn anything about your input. Say Alice wants Bob to compute some known function f upon her input x, but wants to prevent Bob from learning anything about x. The situation arises for instance if client Alice has limited computational resources in comparison with mistrusted server Bob, or if x is an inherently mobile piece of data. Could there be a protocol whereby Bob is forced to compute ,f(x)blindly, i.e. without observing x? We provide such a blind computation protocol for the class of functions which admit an efficient procedure to generate random input–output pairs, e.g. factorization. The cheat-sensitive security achieved relies only upon quantum theory being true. The security analysis carried out assumes the eavesdropper performs individual attacks.
ENTANGLEMENT AND QUANTUM PHASE TRANSITION IN A ONE-DIMENSIONAL SYSTEM OF QUANTUM DOTS WITH DISORDER
Authors: WANG HEFENG , KAIS SABRE
Published: December 2006

We study the entanglement of formation and quantum phase transition in a one-dimensional quantum dot system with disorder modeled by the Hubbard Hamiltonian. The entanglement for three different cases is studied: the homogeneous case, the impurity case of symmetric electron hopping, and asymmetric electron hopping. We find that the local entanglement of the system can be tuned by introducing different impurities characterized by the physical parameters of the system. In particular, for certain parameters, the entanglement is negligible up to a critical point Uc, where a quantum phase transition occurs, and is different from zero above Uc.
QUANTUM WALKS ON GENERAL GRAPHS
Authors: KENDON VIV
Published: December 2006

Quantum walks, both discrete (coined) and continuous time, on a general graph of N vertices with undirected edges are reviewed in some detail. The resource requirements for implementing a quantum walk as a program on a quantum computer are compared and found to be very similar for both discrete and continuous time walks. The role of the oracle, and how it changes if more prior information about the graph is available, is also discussed.
OPTIMAL DATABASE SEARCH: WAVES AND CATALYSIS
Authors: PATEL APOORVA
Published: December 2006

Grover's database search algorithm, although discovered in the context of quantum computation, can be implemented using any system that allows superposition of states. A physical realization of this algorithm is described using coupled simple harmonic oscillators, which can be exactly solved in both classical and quantum domains. Classical wave algorithms are far more stable against decoherence compared to their quantum counterparts. In addition to providing convenient demonstration models, they may have a role in practical situations, such as catalysis.
QUANTUM KEY DISTRIBUTION BASED ON ENTANGLEMENT SWAPPING BETWEEN TWO BELL STATES
Authors: GUO FENZHUO , LIU TAILIN , WEN QIAOYAN , ZHU FUCHEN
Published: December 2006

Based on entanglement swapping between two Bell states, two novel quantum key distribution protocols are proposed. One is for two-level systems, where there is no need for classical communication before each entanglement swapping. This feature is essential to its practical realization. Furthermore, to establish an arbitrarily long key, the protocol needs only two Bell states. The other is for d-level (d > 2) systems, in which higher security and higher source capacity are achieved. Using the theory of quadratic residue, we prove that in the two-qudit systems, each Bell state is a uniform superposition of all basis states in the dual basis, which is different to the situation in two-qubit systems. This difference means our two-level protocol cannot be generalized to the d-level situation directly. On the other hand, it results in higher security of our d-level protocol and is instructive to design quantum cryptography protocols.
CONCENTRATION FOR ATOMIC ENTANGLEMENT STATES VIA CAVITY DECAY
Authors: ZHANG GANG , YANG MING , XUE ZHENG-YUAN , CAO ZHUO-LIANG
Published: December 2006

We present a physical scheme for entanglement concentration of atomic entangled states via cavity QED. In our scheme cavity decay and atomic spontaneous emission are taken into consideration, and the atomic qubit is used as stationary qubit and photonic qubit as flying qubit, thus it is more practical to discuss entanglement concentration.
SCHEME TO IMPLEMENT GENERAL PHASE-COVARIANT QUANTUM CLONING
Authors: ZHANG WEN–HAI , YE LIU , DAI JIE-LIN
Published: December 2006

We propose an experimentally feasible scheme to implement the optimal general 1→2 phase-covariant quantum cloning machine based on cavity QED. In the scheme, the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay.
Cardiac dilatation and pump dysfunction without intrinsic myocardial systolic failure following chronic β-adrenoreceptor activation
Authors: Osadchii Oleg E. , Norton Gavin R. , McKechnie Richard , Deftereos Dawn , Woodiwiss Angela J.
Published: December 2006

There is no direct evidence to indicate that pump dysfunction in a dilated chamber reflects the impact of chamber dilatation rather than the degree of intrinsic systolic failure resulting from myocardial damage. In the present study, we explored the relative roles of intrinsic myocardial systolic dysfunction and chamber dilatation as mediators of left ventricular (LV) pump dysfunction. Administration of isoproterenol, a β-adrenoreceptor agonist, for 3 mo to rats (0.1 mg·kg−1·day−1) resulted in LV pump dysfunction as evidenced by a reduced LV endocardial fractional shortening (echocardiography) and a decrease in the slope of the LV systolic pressure-volume relation (isolated heart preparations). Although chronic β-adrenoreceptor activation induced cardiomyocyte damage (deoxynucleotidyl transferase-mediated dUTP nick-end labeling) as well as β1- and β2-adrenoreceptor inotropic downregulation (attenuated contractile responses to dobutamine and salbutamol), these changes failed to translate into alterations in intrinsic myocardial contractility. Indeed, LV midwall fractional shortening (echocardiography) and the slope of the LV systolic stress-strain relation (isolated heart preparations) were unchanged. A normal intrinsic myocardial systolic function, despite the presence of cardiomyocyte damage and β-adrenoreceptor inotropic downregulation, was ascribed to marked increases in myocardial norepinephrine release, to upregulation of α-adrenoreceptor-mediated contractile effects as determined by phenylephrine responsiveness, and to compensatory LV hypertrophy. LV pump failure was attributed to LV dilatation, as evidenced by increased LV internal dimensions (echocardiography), and a right shift and increased volume intercept of the LV diastolic pressure-volume relation. In conclusion, chronic sympathetic stimulation, despite reducing β-adrenoreceptor-mediated inotropic responses and promoting myocyte apoptosis, may nevertheless induce pump dysfunction primarily through LV dilatation, rather than intrinsic myocardial systolic failure.
Bradykinin activates calcium-dependent potassium channels in cultured human airway smooth muscle cells
Authors: Liu Bo , Freyer Anette M. , Hall Ian P.
Published: December 2006

Bradykinin (BK) is an inflammatory mediator that can cause bronchoconstriction. In this study, we investigated the membrane currents induced by BK in cultured human airway smooth muscle (ASM) cells. Depolarization of the cells induced outward currents, which were inhibited by tetraethylammonium (TEA) in a concentration-dependent manner with an IC50 of 0.33 μM. The currents were increased by elevating intracellular free Ca2+ concentration, suggesting they are calcium-activated potassium channels [ IK(Ca)]. Preexposure to inhibitor of IK(Ca) of large conductance (BKCa), iberiotoxin, and small conductance (SKCa), apamin, inhibited the increase of outward current induced by BK. The relative contribution of BKCa was greatest in early passage cells. Both nickel and SKF-96365 (10 μM) inhibited the increase of the IK(Ca) induced by BK; however, the l-type Ca2+ channel blocker, nifedipine, had no effect. Activation of the BK-induced current was inhibited by heparin, indicating dependence on intact inositol 1,4,5-triphosphate (IP3)-sensitive intracellular Ca2+ stores. BK also increased inositol phosphate accumulation and induced a transient Ca2+-activated chloride current (CACC) and a sustained nonselective cation current ( ICAT). In summary, BK activates BKCa, SKCa, CACC, and ICAT via IP3-sensitive stores in human ASM.
Ketamine inhibits fetal ACTH responses to cerebral hypoperfusion
Authors: Powers Melanie J. , Wood Charles E.
Published: December 2006

The present study tested the effect of ketamine on the fetal reflex responses of late-gestation sheep to brachiocephalic occlusion (BCO), a stimulus that mimics the reduction in cerebral blood flow that results from severe fetal hypotension. Ketamine, a dissociative anesthetic and known noncompetitive antagonist of N-methyl d-aspartate (NMDA) receptors, has previously been shown to impair chemoreceptor responsiveness. Studies from this laboratory suggest that fetal reflex ACTH responses to hypotension are largely mediated by chemoreceptors; therefore, we hypothesized that ketamine would inhibit the reflex hormonal response to BCO. Chronically catheterized fetal sheep were subjected to acute cerebral hypoperfusion through occlusion of the brachiocephalic artery. Fetal blood pressure and heart rate were continuously recorded, and fetal blood samples drawn during the experiment were analyzed with specific hormone assays. Our results demonstrate that ketamine attenuates hemodynamic responses to cerebral hypoperfusion and is a potent inhibitor of ACTH and proopiomelanocortin (POMC)/pro-ACTH release. These data support the hypothesis that fetal reflex responses hypotension are chemoreceptor mediated. Given the potency with which ketamine inhibits ACTH response to fetal hypotension, we suggest that the use of ketamine or other anesthetic or analgesic drugs that block or otherwise interact with the NMDA-glutamate pathways, in late pregnancy or in preterm newborns be reconsidered.
Vitamin E supplementation reverses renal altered vascular reactivity in chronic bile duct-ligated rats
Authors: Alcaraz A. , Iyú D. , Atucha N. M. , García-Estañ J. , Ortiz M. C.
Published: December 2006

An altered vascular reactivity is an important manifestation of the hemodynamic and renal dysfunction during liver cirrhosis. Oxidative stress-derived substances and nitric oxide (NO) have been shown to be involved in those alterations. In fact, both can affect vascular contractile function, directly or by influencing intracellular signaling pathways. Nevertheless, it is unknown whether oxidative stress contributes to the impaired systemic and renal vascular reactivity observed in cirrhosis. To test this, we evaluated the effect of vitamin E supplementation (5,000 IU/kg diet) on the vasoconstrictor and vasodilator responses of isolated perfused kidneys and aortic rings of rats with cirrhosis induced by bile duct ligation (BDL), and on the expression of renal and aortic phospho-extracellular regulated kinase 1/2 (p-ERK1/2). BDL induced a blunted renal vascular response to phenylephrine and ACh, while BDL aortic rings responded less to phenylephrine but normally to ACh. Cirrhotic rats had higher levels of oxidative stress-derived substances [measured as thiobarbituric acid-reactive substances (TBARS)] and NO (measured as urinary nitrite excretion) than controls. Vitamin E supplementation normalized the renal hyporesponse to phenylephrine and ACh in BDL, although failed to modify it in aortic rings. Furthermore, vitamin E decreased levels of TBARS, increased levels of NO, and normalized the increased kidney expression of p-ERK1/2 of the BDL rats. In conclusion, BDL rats showed a blunted vascular reactivity to phenylephrine and ACh, more pronounced in the kidney and reversed by vitamin E pretreatment, suggesting a role for oxidative stress in those abnormalities.
Myosin light chain phosphorylation inhibits muscle fiber shortening velocity in the presence of vanadate
Authors: Franks-Skiba Kathleen , Lardelli Rea , Goh Germaine , Cooke Roger
Published: December 2006

We have shown that myosin light chain phosphorylation inhibits fiber shortening velocity at high temperatures, 30°C, in the presence of the phosphate analog vanadate. Vanadate inhibits tension by reversing the transition to force-generating states, thus mimicking a prepower stroke state. We have previously shown that at low temperatures vanadate also inhibits velocity, but at high temperatures it does not, with an abrupt transition in inhibition occurring near 25°C (E. Pate, G. Wilson, M. Bhimani, and R. Cooke. Biophys J 66: 1554–1562, 1994). Here we show that for fibers activated in the presence of 0.5 mM vanadate, at 30°C, shortening velocity is not inhibited in dephosphorylated fibers but is inhibited by 37 ± 10% in fibers with phosphorylated myosin light chains. There is no effect of phosphorylation on fiber velocity in the presence of vanadate at 10°C. The Kmfor ATP, defined by the maximum velocity of fibers partially inhibited by vanadate at 30°C, is 20 ± 4 μM for phosphorylated fibers and 192 ± 40 μM for dephosphorylated fibers, showing that phosphorylation also affects the binding of ATP. Fiber stiffness is not affected by phosphorylation. Inhibition of velocity by phosphorylation at 30°C depends on the phosphate analog, with ∼12% inhibition in fibers activated in the presence of 5 mM BeF3and no inhibition in the presence of 0.25 mM AlF4. Our results show that myosin phosphorylation can inhibit shortening velocity in fibers with large populations of myosin heads trapped in prepower stroke states, such as occurs during muscle fatigue.
Increase in matrix metalloproteinases from endothelial cells exposed to umbilical cord plasma from high birth weight newborns
Authors: Johannsson Erlingur , Henriksen Tore , Iversen Per Ole
Published: December 2006

Large for gestational age infants have increased risk of developing the metabolic syndrome and cardiovascular disease in child- and adulthood. The vascular endothelium is a target site in the pathogenesis of many cardiovascular disorders. The matrix metalloproteinases (MMP) are important modulators of the extracellular matrix and serve as markers of these disorders. Here, we asked whether umbilical cord plasma of high birth weight (HBW; >4 kg) infants could modulate functional properties of human umbilical vein endothelial cells (HUVEC) compared with plasma from normal birth weight (NBW; 3.1–3.6 kg) infants. To test this, HUVECs were exposed for 48 h to 20% venous cord plasma from HBW or NBW infants. The MMP activity in supernatants of HUVECs exposed to HBW plasma was nearly three times higher ( P < 0.05) than that obtained with NBW plasma. MMP-9, but not MMP-2, protein concentration and mRNA expression were enhanced in HBW ( P < 0.05). With specific blockers, MMP activity and mRNA-MMP-9 were inhibited by ∼60–70%. Cord lipid and insulin concentrations were similar ( P > 0.05) among the two groups. We could not detect any significant differences between the two groups in the concentrations of proinflammatory cytokines or specific tissue inhibitors of MMP in plasma or HUVEC supernatants. In conclusion, cord plasma from HBW infants induced more MMP-9 in HUVECs compared with cord plasma from NBW infants. Although not identified, cord plasma of HBW infants may contain factors that increase endothelial cell MMP. These findings may indicate an association between fetal nutritional conditions and endothelial cell functions.
Advances in magnetic resonance imaging of lung physiology
Authors: Hopkins Susan R. , Levin David L. , Emami Kiarash , Kadlecek Stephen , Yu Jiangsheng , Ishii Masaru , Rizi Rahim R.
Published: December 2006

This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrast-enhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.
Spike frequency adaptation of rat hindlimb motoneurons
Authors: Button Duane C. , Kalmar Jayne M. , Gardiner Kalan , Cahill Farrell , Gardiner Phillip F.
Published: December 2006

The objective of our study was to resolve two issues pertaining to motoneuron (MN) spike frequency adaptation (SFA): 1) to develop an index of SFA that is sensitive to a wide range of adaptation patterns and would correlate well with MN excitability and 2) to determine whether SFA pattern is stimulus current dependent. Sprague-Dawley rats (250–350 g) were anesthetized (ketamine-xylazine) before electrophysiological properties from sciatic nerve MNs located in the lumbar spinal cord were recorded. SFA was measured by 30-s square-wave current injections at 1.5, 3.0, and 5.0 nA above estimated rhythmic firing threshold. Discharges per second were significantly ( P < 0.001) higher for 5-nA than for 1.5- and 3-nA currents > rhythmic firing threshold in the first 2 s. SFA was quantified by using ratios of the final to initial number of discharges with 1-, 2-, and 5-s bins. The best index of SFA was the percent decline in the number of spikes fired in the fifth 5-s bin relative to the first 5-s bin [1 − ( bin 5/ bin 1)]. With the use of this index, we found that SFA was significantly correlated with several measures of MN excitability, including estimated persistent inward current amplitude ( r = −0.76) and rheobase current ( r = 0.71), and tended to correlate with input resistance ( r = −0.43) and frequency-current slope ( r = −0.57). This index also showed the widest range of SFA among MNs. In conclusion, an SFA pattern can be ascertained for each MN and becomes more pronounced as MN excitability decreases. Finally, for the first time, we report evidence of a relationship between persistent inward current and SFA.
Aging, exercise, and endothelial progenitor cell clonogenic and migratory capacity in men
Authors: Hoetzer Greta L. , Van Guilder Gary P. , Irmiger Heather M. , Keith Rebecca S. , Stauffer Brian L. , DeSouza Christopher A.
Published: December 2006

Numerical and functional impairment of circulating endothelial progenitor cells (EPCs) is thought to contribute to vascular aging and the associated increase in cardiovascular risk. We tested the following hypotheses: 1) EPC clonogenic and migratory capacity decrease progressively with age in healthy, sedentary adult men; and 2) regular aerobic exercise will improve EPC clonogenic and migratory capacity in previously sedentary middle-aged and older men. Peripheral blood samples were collected from 46 healthy sedentary men: 10 young (26 ± 1 yr), 15 middle-aged (47 ± 1 yr), and 21 older (63 ± 1 yr). Mononuclear cells were isolated and preplated for 2 days, and nonadherent cells were further cultured for 7 days to determine EPC colony-forming units. Migratory activity of EPCs was determined using a modified Boyden chamber. Ten sedentary middle-aged and older men (59 ± 3 yr) were studied before and after a 3-mo aerobic exercise intervention. The number of EPC colony-forming units was ∼75% lower ( P < 0.01) in middle-aged (12 ± 3) and older (8 ± 2) compared with young (40 ± 7) men. There was no difference in colony count between middle-aged and older men. EPC migration (fluorescent units) was significantly reduced in older (453 ± 72) compared with young (813 ± 114) and middle-aged (760 ± 114) men. The exercise intervention increased ( P < 0.05) both EPC colony-forming units (10 ± 3 to 22 ± 5) and migratory activity (683 ± 96 to 1,022 ± 123) in previously sedentary middle-aged and older men. These results provide further evidence that aging adversely affects EPC function. Regular aerobic-endurance exercise, however, is an effective lifestyle intervention strategy for improving EPC clonogenic and migratory capacity in middle-aged and older healthy men.
Effects of p-Nonylphenol and 4-tert-Octylphenol on the Anterior Pituitary Functions in Adult Ovariectomized Rats
Authors: Furuta Miyako , Funabashi Toshiya , Kawaguchi Maiko , Nakamura Takahiro J. , Mitsushima Dai , Kimura Fukuko
Published: December 2006

p-Nonylphenol (NP) and 4-tert-octylphenol (OP) are known to mimic the action of estrogens as endocrine disruptors. However, their acute effects on the pituitary and the hypothalamus functions in vivo have been uncertain. We therefore determined their effects on the anterior pituitary, in particular, gonadotropin secretion. Two weeks after ovariectomy, the rats were given a subcutaneous injection of 10 mg NP, 10 mg OP, 10 mg bisphenol A, 1 µg 17β-estradiol, or sesame oil alone as control. Twenty-four hours after the treatment, the expression of progesterone receptor mRNA in the anterior pituitary and the level of luteinizing hormone (LH), follicle-stimulating hormone, and prolactin were determined. The expression of progesterone receptor mRNA in the anterior pituitary was significantly increased by either NP, OP, bisphenol A, or estradiol, but bisphenol A was less effective. The level of LH was significantly decreased by either NP or OP, but not by bisphenol A and estradiol. Only estradiol significantly increased the level of prolactin. The level of follicle-stimulating hormone was unchanged by any of the treatments. To check the effects of NP and OP on pulsatile LH secretion, blood samplings were done at 6-min intervals for 3 h. Twenty-four hours after treatment in ovariectomized adult rats, we found that the injection of NP significantly decreased the amplitude of LH pulses and the mean LH concentrations, but not the frequency of LH pulses. The injection of OP significantly decreased the mean LH concentrations without affecting the frequency and amplitude of the LH pulses. Finally, the rats given an injection of NP or sesame oil were intravenously injected with 50 ng of gonadotropin-releasing hormone (GnRH) to check whether NP affected the LH secretory responsiveness of the anterior pituitary to GnRH. We found that the responsiveness to GnRH in NP-injected rats was significantly attenuated compared to the sesame oil-injected rats. The present study suggests that NP, even with a single injection, suppresses the pulsatile LH secretion in adult ovariectomized rats, probably by affecting the anterior pituitary level.
Diversity of Lactobacilli in the Oral Cavities of Young Women with Dental Caries
Authors: Caufield P.W. , Li Y. , Dasanayake A. , Saxena D.
Published: December 2006

For nearly a century, lactobacilli (LB) in the oral cavity have been generally associated with dental caries. Here, we characterized the LB isolated from the saliva of 6 women with active caries using genetic-based taxonomical identification methods. From each subject, 30 isolates growing on Rogosa medium and presumed to be LB were analyzed. Of the 180 isolates, 176 were further characterized by biotyping, DNA melting points, DNA chromosomal fingerprinting, genotyping, and phylogenetic cluster assessment. We found a total of 30 unique genotypes of LB in the saliva of caries-active women, with each woman harboring between 2 and 8 distinct genotypes. Although Lactobacillus vaginalis, L. fermentum, and L. salivarius were found in 4 of 6 of the subjects, results from other studies using comparable methods show an entirely different array of LB associated with caries. These collective observations lead us to surmise that LB associated with dental caries are likely exogenous and opportunistic colonizers, arising from food or other reservoirs outside the oral cavity.