bluuebunny/crossref_metadata_2025 huggingface dataset:
POWER-LAW MASS DISTRIBUTION IN A FLOW-CATCHING MASS GROWTH MODEL
Authors: INAOKA HAJIME
Published: November 2004

We model cluster growth with scrambling dynamics. The model contains a one-dimensional flow-source region and a set of growing mass points. The mass points scramble the flow-source region so that the heavier mass points occupy the wider region and grow as the growth rate of the mass points is proportional to the width of their flow-source region. Given a uniform random mass distribution as an initial condition, the scrambling dynamics results in a power-law mass distribution.
SEDIMENTATION OF GLASS BEADS UNDER THE INFLUENCE OF GRAVITY
Authors: KURNAZ M.L. , McCLOUD K.V. , MAHER J.V.
Published: November 2004

The quasi-two-dimensional sedimentation of 0.06 cm diameter silica spheres in viscous oil (between glass plates separated by a 1 mm gap) results in quasi-one dimensional rough surfaces. These surfaces are rough on all length-scales between the particle size and the cell size, but different roughness exponents are observed in each of two well defined regimes (αs=0.81±0.03 for L≤2 cm and αl=0.92±0.05 for L≥2 cm). The dynamical exponent, β, is measured to be 0.48±0.16. The role and range of hydrodynamic forces must be considered before this system can be related to available rough interface theories. A first attempt at assessing the effect of hydrodynamics yields a noise spectrum whose probability distribution is close to Gaussian (with significant excess of large fluctuations) and whose correlation function resembles that measured for density-density correlations in the oil far above the growing interface.
STATISTICAL BEHAVIOR OF CHARACTERISTIC LENGTHS OF VIBRATIONS ON TWO-DIMENSIONAL RANDOM FRACTALS
Authors: PETRI ALBERTO , RUOCCO GIANCARLO
Published: November 2004

We analyze the behavior of some characteristic lengths of the normal modes of square percolating lattices at threshold. Generalized inverse participation ratios are taken as estimates of the localization lengths, while the wavenumber kM having the maximum weight in the Fourier transform of the autocorrelation function of each mode is supposed to be inversely proportional to the relevant wavelength. Both site and bond percolating lattices are considered. It is found that, on average, these quantities follow about the same supposed scaling law, therefore supporting the idea of a universal length. At the same time they all exhibit large deviations from the expected values with no apparent correlation among fluctuations in the localization lengths and in the relevant wavelengths, as it turns out from the computed correlation coefficient.
A STUDY OF THE SHORT WAVE COMPONENTS IN COMPUTATIONAL ACOUSTICS
Authors: TAM CHRISTOPHER K. W. , WEBB JAY C. , DONG ZHONG
Published: November 2004

It is shown by using a Dispersion-Relation-Preserving [Formula: see text] finite difference scheme that it is feasible to perform direct numerical simulation of acoustic wave propagation problems. The finite difference equations of the [Formula: see text] scheme have essentially the same Fourier-Laplace transforms and hence dispersion relations as the original linearized Euler equations over a broad range of wavenumbers (here referred to as long waves). Thus it is guaranteed that the acoustic waves, the entropy and the vorticity waves computed by the [Formula: see text] scheme are good approximations of those of the exact solutions of Euler equations as long as the wavenumbers are in the long wave range. Computed waves with higher wavenumber, or the short waves, generally have totally different propagation characteristics. There are no counterparts of such waves in the exact solutions. The short waves of a computation scheme are, therefore, contaminants of the numerical solutions. The characteristics of these short waves are analyzed here by group velocity consideration and standard dispersive wave theory. Numerical results of direct simulations of these waves are reported. These waves can be generated by discontinuous initial conditions. To purge the short waves so as to improve the quality of the numerical solution, it is suggested that artificial selective damping terms be added to the finite difference scheme. It is shown how the coefficients of such damping terms may be chosen so that damping is confined primarily to the high wavenumber range. This is important for then only the short waves are damped leaving the long waves basically unaffected. The effectiveness of the artificial selective damping terms is demonstrated by direct numerical simulations involving acoustic wave pulses with discontinuous wave fronts.
WAVELET SOLUTIONS FOR TIME HARMONIC ACOUSTIC WAVES IN A FINITE OCEAN
Authors: GILBERT R. P. , LIN WEI
Published: November 2004

In this paper, we show how wavelet analysis may be used to solve the parabolic approximate wave equation. The paper is naturally subdivided into three parts. The first entails a crash course in wavelet analysis with the aim of using it to solve partial differential equations. The second part develops the wavelet-Galerkin approximation for solving partial differential equations in variational form. Finally, the third section derives a range-depth adaptive wavelet approach, and, moreover, provides an algorithm for solving the propagation problem.
THE INFLUENCE OF THE REFERENCE WAVENUMBER IN COMPUTATIONAL OCEAN ACOUSTICS
Authors: PIERCE ALLAN D. , LEE DING
Published: November 2004

A class of ocean acoustic propagation problems can be solved efficiently by the Parabolic Equation (PE) approximation method. The application of the PE method for the prediction of wave propagation introduces a new parameter, the reference wavenumber k0. This requires selection of the most appropriate k0, which is related to the reference sound speed c0. The influence on the acoustic field by the choice of c0 is rarely visible under weak range-dependent environments. Even if it is visible, the difference is small and is usually negligible since the present judicious choice of the c0 seems to provide acceptable results. When the environment is not weakly range-dependent, the choice of c0 will likely affect the computation of acoustic results. This paper examines a few different choices of c0 and analyzes how these different choices can influence the acoustic results. An application is given where the farfield wave equation represents a realistic range-dependent environment. Different choices of c0 were made for the computation of the acoustic field; as a consequence, different choices of c0 produce different acoustic results. These numerical results are not in agreement with a known reference exact solution. The differences are not too small and may be considered non-negligible. So, there is a need to make an appropriate choice of c0 in order to produce reasonable results. For the purpose of achieving satisfactory and acceptable acoustic results dealing with a PE-type equation, the requirements of the reference wavenumber will be discussed both mathematically and physically. Then, a number of computational choices of c0 will be examined, especially the k0-formula. An analysis as well as an assessment of the k0-formula will be given.
SCATTERING OF TRANSIENT WAVES BY FINITE CRACKS IN AN ANTI-PLANE STRAIN ELASTIC SOLID
Authors: TENG YU-CHIUNG
Published: November 2004

The transient problem of finite cracks with vanishing thickness in an anti-plane strain solid is investigated by finite element method. The infinitesimally thin crack with traction free on both faces of the crack is simulated by the energy-sharing-node technique. The following cases are considered: (a) One finite line crack in a whole space subjected to (i) a concentrated line source and (ii) an inclined incident SH plane wave. (b) Two cracks in a whole space subjected to an inclined incident SH plane wave. Emphasis has been laid on the quantitative evaluation of the dynamic disturbances for the problem in the interference stage, which is generally difficult to be obtained by analytical approaches. The synthetic seismograms for displacements along the crack surfaces, which cover a period up to an instant of time during which the second order scattering from crack tips can be observed, are presented. Snapshots of the scattered displacement field for each case are also displayed so that the generations of the scatterings and the processes of the wave propagations can be clearly visualized. The two-dimensional wave propagation for transient acoustic problem and electromagnetic problem with the same nature of boundaries can be analogously obtained.
ANALYSIS OF TIME-DOMAIN ACOUSTIC WAVEFIELDS IN HORIZONTALLY CONTINUOUSLY LAYERED CONFIGURATIONS BASED ON THE MODIFIED CAGNIARD METHOD
Authors: VERWEIJ MARTIN D. , DE HOOP ADRIANUS T.
Published: November 2004

A combination of the Neumann series and the modified Cagniard method is used to derive a theoretically exact space-time domain solution for the 3-D acoustic wave propagation problem in horizontally continuously layered media. Firstly, integral transformations (among which is a one-sided temporal Laplace transformation) are applied to the space-time domain basic acoustic equations. Secondly, a system of transform domain integral equations is derived, which is solved using a convergent Neumann series. Finally, the individual terms of this series are transformed back to the space-time .domain using the modified Cagniard method. The space-time domain series turns out to be convergent for every continuously layered configuration and at any time instant. In contrast to the standard angular wave number-frequency domain analysis, in the present analysis, difficulties due to turning points, etc., are avoided.
ON THE CONDITIONS FOR UNIQUENESS AND EXISTENCE OF THE SOLUTION TO AN ACOUSTIC INVERSE PROBLEM I: THEORY
Authors: GILBERT R. P. , LIN ZHONGYAN
Published: November 2004

This paper which is Part I of a sequence deals with the problem of determining a radially dependent coefficient n (r) in the equation ∆ u − n2 (r) u = 0, in the unit disk Ω from the Dirichlet–Neumann data pair [Formula: see text]. We prove that the sufficiency condition for uniqueness established in Ref. 2 is, in some instances, also a necessity for uniqueness. We also discuss the solvability of this inverse problem. In Part II numerical experiments will be presented which illustrate the theory developed here.
ORTHOGONAL CUBIC SPLINE COLLOCATION SOLUTION OF UNDERWATER ACOUSTIC WAVE PROPAGATION PROBLEMS
Authors: ROBINSON MARK P. , FAIRWEATHER GRAEME
Published: November 2004

In this paper, a new method for the numerical solution of the two-dimensional parabolic equation of Tappert in horizontally-stratified media is presented. This method uses orthogonal cubic spline collocation for the semidiscretization with respect to depth, and the resulting system of differential-algebraic equations is solved using the NAG Library routine D02NNF. In the present application, orthogonal spline collocation, which has been exceedingly effective in the approximate solution of a broad class of problems, has the advantage that it systematically incorporates the requisite interface conditions. The state-of-the-art routine D02NNF, which implements backward differentiation formulas, has been used successfully in the solution of related problems.
A MODAL INVERSION SCHEME FOR OCEAN ACOUSTIC TOMOGRAPHY
Authors: TAROUDAKIS MICHAEL I. , PAPADAKIS JOHN S.
Published: November 2004

An inversion scheme based on normal-mode representation of the acoustic field is applied in ocean acoustic tomography for a range-dependent reconstruction of the sound speed variations at a vertical slice. The scheme is based on the assumption that modal phase can be measured by suitable mode filtering at some range from the sound source. Two cases have been considered. The first of them makes no use of oceanographic information on the variability to be recovered, while the second one makes use of empirical orthogonal functions (EOFs) that describe sound speed variations in the ocean. The data used in the applications presented in this paper are synthetic ones. It is shown that both modal inversion schemes can be used for the recovery of range-dependent sound speed variations of compact support in the ocean, provided that a range dependent background environment is used to describe an initial guess of the variations. The scheme is more powerful when EOFs are used.
FUZZY REASONING BY CASE FOR DECISION SUPPORT SYSTEMS
Authors: BALDWIN J. F. , RIBEIRO RITA A.
Published: November 2004

This paper presents a selection of alternative approaches to handle classification problems using the paradigm of case-based reasoning with fuzzy concepts. Our main concern is classification and pattern recognition queries in a fuzzy environment. An example was developed to explain the various methods and the results compared.
ON A MULTICRITERIA FUZZY CLUSTERING METHOD FOR 3-WAY DATA
Authors: SATO MIKA , SATO YOSHIHARU
Published: November 2004

In this paper, we discuss the fuzzy clustering for 3-way data which is composed of objects, attributes and situations. In the case of 2-way data, the clustering of objects are usually based on the values of attributes. However, for 3-way data, a clustering of objects is not always coincident for all situations, because the values of attributes vary with each situation. Therefore, the clustering problem for 3-way data can be regarded as a multicriteria optimization problem. It is known that the practical solutions for a multicriteria optimization problem are Pareto efficient solutions. In a multicriteria hard (non-fuzzy) clustering problem, it is difficult to find a Pareto efficient cluster since this is essentially combinatorial problem. But we show that a multicriteria fuzzy clustering, which is an extension of this hard clustering problem, has merit to obtain Pareto efficient clusters. We investigate the features for Pareto efficient clusters using an artificial 3-way data and we show a numerical example applied to the data of the growth of physical constitutions.
THE RISK MANAGEMENT OF THE ENTREPRENEUR: AN ECONOMIC-PSYCHOLOGICAL PERSPECTIVE
Authors: DELMAR FREDERIC
Published: November 2004

The risk management of the entrepreneur is an important factor that can explain the success or failure of a business venture. The problem of risk management is here approached from an economic-psychological perspective. In this study the risk management of entrepreneurs is compared. The entrepreneurs are divided into three subgroups; super-entrepreneurs, small business owner-managers, and failed entrepreneurs (who went bankrupt).

In this study, some interesting results are found. There seems to be some differences in how the categories of entrepreneurs manage risk. An entrepreneur’s acceptance of uncertainty, ability to manage risk and perception of the situation are discussed in this paper. In general, the results show the super-entrepreneur as risk aversive and highly motivated, and the success of the business as attributable to this combination. The small business owner-manager prefers control to growth. The failed entrepreneur does not use the social network and has no buffer for problems.
THE RELATION BETWEEN ABILITY AND POST START-UP SUCCESS FOR ENTREPRENEURS
Authors: OLSEN BJORN , JOHANNESSEN JON-ARILD
Published: November 2004

The literature widely argues that there is a strong and positive causal relationship between the entrepreneur’s abilities and post start-up success. Hence, implying that founders with limited abilities are likely to be at a greater disadvantage due to these very inabilities. However, even though the advantages of their abilities may appear as intuitively obvious, there exists a lack of well developed theoretical foundations to the causal link between the entrepreneurs ability and future venture performance. The paper is based on a literature review on the relationship between ability and future venture performance. The starting point stems from the notion of entrepreneurial learning, and we ask the question “What is entrepreneurial learning and how do abilities acquired through learning affect the future performance of a new firm? Using learning theory, we try to outline possible directions. We then review the entrepreneurial literature linking it with education, managerial experience, start-up experience, and industry experience. In conclusion we design a causal model which integrates the literature review on entrepreneurial ability and learning theory, with respect to future venture performance.
ENTERPRISE FAILURES AND THE RUNAWAY ENTREPRENEURIAL SPIRIT
Authors: GOH DAVID
Published: November 2004

One main thrust in entrepreneurial education and development is to create a ‘venturesome’ mindset that allows for a higher tolerance of risk, bearing in mind that most people are risk averse and as a result make “timid choices” (Kahneman & Lovallo, 1993). Coupled with this is the effort to teach/train entrepreneurs the skills necessary in evaluating risky opportunities. While technical skills are important, what is also required is an understanding of the cognitive biases of humans (particularly toward excessive optimism) as the failure to address these biases will lead to ineffective entrepreneurship training programmes where budding entrepreneurs swing to the other end of the spectrum and become foolhardy risk takers and speculators. This paper proposes that entrepreneurship development programmes include tools to help entrepreneurs identify their own cognitive biases and help them overcome these biases. The three thinking tools reviewed are 1) “outside view” taking, 2) “shared experience view” taking, and 3) “reflective view” taking.
AN INTERMITTENTLY USED SYSTEM WITH PREPARATION TIME FOR THE REPAIR FACILITY
Authors: YADAVALLI V. S. S. , CLAASEN S. J. , UDAYABASKARAN S. , GEETHA S.
Published: November 2004

Two models of an intermittently used system with preparation time for the repair facility are considered. Mean stationary rate of the disappointments, the joint probability that disappointments do not occur at specified intervals are obtained for both the models.
BEST TIME SCALE FOR AGE REPLACEMENT
Authors: KORDONSKY KH.B. , GERTSBAKH I.
Published: November 2004

The lifetime of a system is measured in two principal time scales, L and H. We consider a family of time scales of type Ta=(1−a) · L+a · H, for which the lifetime is T=(1−a) L+aH, a∈[0, 1], where L and H are the lifetimes in the principal time scales. The optimal time scale, by the definition, provides the minimal value of the coefficient of variation of system lifetime. We consider the age replacement model in time scale Ta and develop a nonparametric numerical procedure for finding the optimal weighting parameter a* that provides the smallest value of the corresponding cost function. This procedure is applied to fatigue test data, and it is demonstrated that the best time scale with respect to the age replacement cost function is very close to the optimal time scale. The same is true for a modified age replacement scheme in which the replacement age equals the p-quantile of system lifetime.
ALGORITHMS TO REALIZE AN ARBITRARY BPC PERMUTATION IN CHORDAL RING NETWORKS WITH FAILURES
Authors: MASUYAMA HIROSHI , MASUYAMA ETSUKO
Published: November 2004

A family of regular graphs of degree 3, called chordal rings is presented as a possible candidate for the implementation of a distributed system and for fault-tolerant architectures. The symmetry of graphs makes it possible to determine message routing by using a simple distributed algorithm. Arbitrary data permutations are generally accomplished by sorting. For certain classes of permutations, however, there exist algorithms that are more efficient than the best sorting algorithm. One such class is the Bit Permute Complement (BPC) class of permutations.

In this paper, we first develop algorithms requiring two token storage registers in each node to realize an arbitrary BPC permutation. We next evaluate its ability to realize BPC permutations in networks of arbitrary size by estimating the number of required routing steps when a single fault is present and when not.
METRICS FOR MEASURING THE EFFECT OF MENTAL STRESS ON FAULT GENERATION DURING SOFTWARE DEVELOPMENT
Authors: FURUYAMA TSUNEO , ARAI YOSHIO , IIO KAZUHIKO
Published: November 2004

The effects of mental stress on fault-generation are quantitatively determined through a controlled experiment. Two teams develop the same software program under the same conditions, except for mental stress. One team is mentally stressed during the functional design phase, while the other one is not. The degree of stress is measured by two types of metrics: “inner metrics” and “outer metrics”. The inner metrics, which measure the degree of stress, show that the “stressed team” generates more faults than the “nonstressed team”. Among the inner metrics, the “schedule pressure” and “workload” metrics are the most effective for predicting fault generation. Among the outer metrics, the fatigue meter value is related to all inner metrics and is therefore useful for verifying the inner metric values.
A NEW APPROACH FOR RELIABILITY ESTIMATION OF SYSTEMS WITH COMPLEX COMMON CAUSE FAILURES
Authors: PAN ZHIJIE , NONAKA YASUO
Published: November 2004

This paper presents a new concept, complex common cause failure, for common cause failure analysis. A common stress model is developed, in which the common cause events are described as common stresses that will affect directly and simultaneously on the internal aging process of each system component and further change their failure probabilities, while the internal aging processes of components are still considered mutually independent. The common stress model can be used to estimate the reliability of systems with complex common cause failures.
PRODUCTION RATE OF A SPLIT PRODUCTION SYSTEM
Authors: GOPALAN M.N. , DINESH KUMAR U.
Published: November 2004

In this paper, a split production system which has two parallel stations in the second stage is analyzed to evaluate the production rate of the system. A mathematical model is developed using semi-regenerative phenomena and a system of convolution integral equations satisfied by various state probabilities is obtained. An iterative numerical technique is used to solve the system of integral equations obtained.
A NEW AND FAST ELECTRIC POWER GENERATING SYSTEM RELIABILITY EVALUATION MODEL USING PETRI NETS
Authors: SALEHFAR H. , RODICK R.
Published: November 2004

This paper presents a new power generating system reliability evaluation model which performs like a Monte Carlo based reliability model but without using random number generators or probability distribution of system components. The proposed method is based on a class of Petri Nets known as timed state machine Petri Nets (TSMPNs). The method is simple, flexible, accurate, and extremely fast. A comparison of results from the new model with those from conventional Monte Carlo based reliability techniques shows the fidelity of the model and its potential usefulness in power system reliability studies. The method can also be extended and utilized for other system reliability studies in a more general sense.
PREVENTIVE MAINTENANCE SCHEDULING FOR A SYSTEM WITH ASSURED RELIABILITY USING FUZZY SET THEORY
Authors: SURESH P.V. , CHAUDHURI DIPAK
Published: November 2004

Preventive maintenance of any system should depend on its starting, ending and operating conditions. Systems working with a minimum permissible reliability should be maintained at predetermined points to ensure its reliability do not fall below the permissible level. For any period, the starting condition of a system and the operating condition can be specified using fuzzy sets. Since the condition of the system at the end of a period depends on its starting condition and the operating condition during the period, linguistic variables are also required to specify it. This paper describes how to select periods of maintenance and the types of maintenance for such a system. The model utilizes the fuzzy set theory to determine the period length and the type of maintenance.
IL-7 exacerbates chronic colitis with expansion of memory IL-7RhighCD4+mucosal T cells in mice
Authors: Okada Eriko , Yamazaki Motomi , Tanabe Masanobu , Takeuchi Tsutomu , Nanno Masanobu , Oshima Shigeru , Okamoto Ryuichi , Tsuchiya Kiichiro , Nakamura Tetsuya , Kanai Takanori , Hibi Toshifumi , Watanabe Mamoru
Published: November 2004

We have previously demonstrated that mucosal CD4+T cells expressing high levels of IL-7 receptor (IL-7Rhigh) are pathogenic cells responsible for chronic colitis. Here we investigate whether IL-7 is directly involved in the expansion of IL-7Rhighmemory CD4+mucosal T cells and the exacerbation of colitis. We first showed that CD4+lamina propria lymphocytes (LPLs) from wild-type, T cell receptor-α-deficient (TCR-α−/−), and recombinase-activating gene (RAG)-2−/−-transferred mice with or without colitis showed phenotypes of memory cells, but only CD4+LPLs from colitic mice showed IL-7Rhigh. In vitro stimulation by IL-7, but not by IL-15 and thymic stromal lymphopoietin, enhanced significant proliferative responses and survival of colitic CD4+, but not normal CD4+LPLs. Importantly, in vivo administration of IL-7 mice accelerated the expansion of IL-7Rhighmemory CD4+LPLs and thereby exacerbated chronic colitis in RAG-2−/−mice transferred with CD4+LPLs from colitic TCR-α−/−mice. Conversely, the administration of anti-IL-7R monoclonal antibody significantly inhibited the development of TCR-α−/−colitis with decreased expansion of CD4+LPLs. Collectively, the present data indicate that IL-7 is essential for the expansion of pathogenic memory CD4+T cells under pathological conditions. Therefore, therapeutic approaches targeting the IL-7R pathway may be feasible in the treatment of human inflammatory bowel disease.
Sinusoidal endothelial COX-1-derived prostanoids modulate the hepatic vascular tone of cirrhotic rat livers
Authors: Graupera Mariona , March Sandra , Engel Pablo , Rodés Juan , Bosch Jaume , García-Pagán Joan-Carles
Published: November 2004

CCl4cirrhotic rat liver exhibits a hyperresponse to the α1-adrenergic agonist methoxamine (Mtx) that is associated with enhanced thromboxane A2(TXA2) production and is abrogated by indomethacin. To further elucidate the molecular mechanisms involved in the hyperresponse to vasoconstrictors, portal perfusion pressure dose-response curves to Mtx were performed in CCl4cirrhotic rats livers after preincubation with vehicle, the cyclooxygenase (COX)-1 selective inhibitor SC-560, and the COX-2 selective inhibitor SC-236. TXA2production was determined in samples of the perfusate. COX-1 expression was analyzed and quantified in hepatocytes, Kupffer cells, sinusoidal endothelial cells (SEC), and hepatic stellate cells (HSC) isolated from control and cirrhotic rat livers by double-immunofluorescence staining, with specific markers for each population using flow cytometry or Western blot analysis. COX-1 protein levels were not significantly increased in cirrhotic livers, but COX-2 protein expression was increased. COX-1 inhibition, but not COX-2, significantly attenuated the response to Mtx and prevented the increased production of TXA2. Cirrhotic livers showed an increased expression of COX-1 in SEC and reduced expression in HSC compared with control livers, whereas COX-1 was similarly distributed in Kupffer cells. Despite abundant hepatic COX-2 expression, the increased response to Mtx of cirrhotic livers is mainly dependent of COX-1. Upregulation of COX-1 in cirrhotic SEC may be responsible for the hyperesponse to Mtx.
Adaptation to mechanical load determines shape and properties of heart and circulation: the CircAdapt model
Authors: Arts Theo , Delhaas Tammo , Bovendeerd Peter , Verbeek Xander , Prinzen Frits W.
Published: November 2004

With circulatory pathology, patient-specific simulation of hemodynamics is required to minimize invasiveness for diagnosis, treatment planning, and followup. We investigated the advantages of a smart combination of often already known hemodynamic principles. The CircAdapt model was designed to simulate beat-to-beat dynamics of the four-chamber heart with systemic and pulmonary circulation while incorporating a realistic relation between pressure-volume load and tissue mechanics and adaptation of tissues to mechanical load. Adaptation was modeled by rules, where a locally sensed signal results in a local action of the tissue. The applied rules were as follows: For blood vessel walls, 1) flow shear stress dilates the wall and 2) tensile stress thickens the wall; for myocardial tissue, 3) strain dilates the wall material, 4) larger maximum sarcomere length increases contractility, and 5) contractility increases wall mass. The circulation was composed of active and passive compliances and inertias. A realistic circulation developed by self-structuring through adaptation provided mean levels of systemic pressure and flow. Ability to simulate a wide variety of patient-specific circumstances was demonstrated by application of the same adaptation rules to the conditions of fetal circulation followed by a switch to the newborn circulation around birth. It was concluded that a few adaptation rules, directed to normalize mechanical load of the tissue, were sufficient to develop and maintain a realistic circulation automatically. Adaptation rules appear to be the key to reduce dramatically the number of input parameters for simulating circulation dynamics. The model may be used to simulate circulation pathology and to predict effects of treatment.
Normal distribution of ventricular pressure-volume area of arrhythmic beats under atrial fibrillation in canine heart
Authors: Mohri Satoshi , Shimizu Juichiro , Iribe Gentaro , Ito Haruo , Morita Terumasa , Yamaguchi Hiroki , Sano Shunji , Kajiya Fumihiko , Suga Hiroyuki
Published: November 2004

We previously found the frequency distribution of the left ventricular (LV) effective afterload elastance (Ea) of arrhythmic beats to be nonnormal or non-Gaussian in contrast to the normal distribution of the LV end-systolic elastance (Emax) in canine in situ LVs during electrically induced atrial fibrillation (AF). These two mechanical variables determine the total mechanical energy [systolic pressure-volume area (PVA)] generated by LV contraction when the LV end-diastolic volume is given on a per-beat basis. PVA and Emaxare the two key determinants of the LV O2consumption per beat. In the present study, we analyzed the frequency distribution of PVA during AF by its χ2, significance level, skewness, and kurtosis and compared them with those of other major cardiodynamic variables including Eaand Emax. We assumed the volume intercept (V0) of the end-systolic pressure-volume relation needed for Emaxdetermination to be stable during arrhythmia. We found that PVA distributed much more normally than Eaand slightly more so than Emaxduring AF. We compared the χ2, significance level, skewness, and kurtosis of all the complex terms of the PVA formula. We found that the complexity of the PVA formula attenuated the effect of the considerably nonnormal distribution of Eaon the distribution of PVA along the central limit theorem. We conclude that mean (SD) of PVA can reliably characterize the distribution of PVA of arrhythmic beats during AF, at least in canine hearts.
Engineering skeletal myoblasts: roles of three-dimensional culture and electrical stimulation
Authors: Pedrotty Dawn M. , Koh Jennifer , Davis Bryce H. , Taylor Doris A. , Wolf Patrick , Niklason Laura E.
Published: November 2004

Immature skeletal muscle cells, or myoblasts, have been used in cellular cardiomyoplasty in attempts to regenerate cardiac muscle tissue by injection of cells into damaged myocardium. In some studies, muscle tissue within myoblast implant sites may be morphologically similar to cardiac muscle. We hypothesized that identifiable aspects of the cardiac milieu may contribute to growth and development of implanted myoblasts in vivo. To test this hypothesis, we designed a novel in vitro system to mimic some aspects of the electrical and biochemical environment of native myocardium. This system enabled us to separate the three-dimensional (3-D) electrical and biochemical signals that may be involved in myoblast proliferation and plasticity. Myoblasts were grown on 3-D polyglycolic acid mesh scaffolds under control conditions, in the presence of cardiac-like electrical current fluxes, or in the presence of culture medium that had been conditioned by mature cardiomyocytes. Cardiac-like electrical current fluxes caused increased myoblast number in 3-D culture, as determined by DNA assay. The increase in cell number was due to increased cellular proliferation and not differences in apoptosis, as determined by proliferating cell nuclear antigen and TdT-mediated dUTP nick-end labeling. Cardiomyocyte-conditioned medium also significantly increased myoblast proliferation. Expression of transcription factors governing differentiation along skeletal or cardiac lineages was evaluated by immunoblotting. Although these assays are qualitative, no changes in differentiation state along skeletal or cardiac lineages were observed in response to electrical current fluxes. Furthermore, from these experiments, conditioned medium did not appear to alter the differentiation state of skeletal myoblasts. Hence, cardiac milieu appears to stimulate proliferation but does not affect differentiation of skeletal myoblasts.
Fatty acid oxidation and its impact on response of spontaneously hypertensive rat hearts to an adrenergic stress: benefits of a medium-chain fatty acid
Authors: Labarthe François , Khairallah Maya , Bouchard Bertrand , Stanley William C. , Des Rosiers Christine
Published: November 2004

The spontaneously hypertensive rat (SHR) is a model of cardiomyopathy characterized by a restricted use of exogenous long-chain fatty acid (LCFA) for energy production. The aims of the present study were to document the functional and metabolic response of the SHR heart under conditions of increased energy demand and the effects of a medium-chain fatty acid (MCFA; octanoate) supplementation in this situation. Hearts were perfused ex vivo in a working mode with physiological concentrations of substrates and hormones and subjected to an adrenergic stimulation (epinephrine, 10 μM).13C-labeled substrates were used to assess substrate selection for energy production. Compared with control Wistar rat hearts, SHR hearts showed an impaired response to the adrenergic stimulation as reflected by 1) a smaller increase in contractility and developed pressure, 2) a faster decline in the aortic flow, and 3) greater cardiac tissue damage (lactate dehydrogenase release: 1,577 ± 118 vs. 825 ± 44 mU/min, P < 0.01). At the metabolic level, SHR hearts presented 1) a reduced exogenous LCFA contribution to the citric acid cycle flux (16 ± 1 vs. 44 ± 4%, P < 0.001) and an enhanced contribution of endogenous substrates (20 ± 4 vs. 1 ± 4%, P < 0.01); and 2) an increased lactate production from glycolysis, with a greater lactate-to-pyruvate production ratio. Addition of 0.2 mM octanoate reduced lactate dehydrogenase release (1,145 ± 155 vs. 1,890 ± 89 mU/min, P < 0.001) and increased exogenous fatty acid contribution to energy metabolism (23.7 ± 1.3 vs. 15.8 ± 0.8%, P < 0.01), which was accompanied by an equivalent decrease in unlabeled endogenous substrate contribution, possibly triglycerides (11.6 ± 1.5 vs. 19.0 ± 1.2%, P < 0.01). Taken altogether, these results demonstrate that the SHR heart shows an impaired capacity to withstand an acute adrenergic stress, which can be improved by increasing the contribution of exogenous fatty acid oxidation to energy production by MCFA supplementation.
Haptoglobin expression and activity during coronary collateralization
Authors: Lohr Nicole L. , Warltier David C. , Chilian William M. , Weihrauch Dorothee
Published: November 2004

Coronary collateral development relies on the coordinated secretion of growth factors. However, alone they are insufficient for permanent collateral growth. We utilized proteomics to identify other important proteins in the extracellular environment that could facilitate collateralization. Chronically instrumented dogs developed coronary collaterals by the repetitive occlusion method. Subendocardial (0.19 ± 0.04, 0.27 ± 0.06, 0.48 ± 0.10, and 0.81 ± 0.11 ml·min−1·g−1 on days 1, 7, 14, and 21, respectively) and subepicardial (0.14 ± 0.01, 0.36 ± 0.06, 0.51 ± 0.07, and 0.71 ± 0.08 ml·min−1·g−1 on days 1, 7, 14, and 21, respectively) blood flow increased in animals subjected to repetitive occlusion. Sham animals exhibited no changes in blood flow. Myocardial interstitial fluid (MIF) from both groups was analyzed by two-dimensional electrophoresis with matrix-assisted laser desorption/ionization time-of-flight identification. The acute-phase protein haptoglobin was identified in the group subjected to repetitive occlusion. ELISA of MIF showed haptoglobin to be elevated at all time points of collateral development compared with sham, with maximal production on day 7. Purified haptoglobin dose dependently stimulated endothelial cells to form tubes and vascular smooth muscle cells to migrate. Purified haptoglobin did not stimulate proliferation of either cell type. The relative contribution of haptoglobin to the chemotactic properties of MIF was tested using a neutralizing antibody. Neutralized MIF could not stimulate smooth muscle cells to migrate at any time during collateral development. Endothelial cell tube formation was inhibited after the midpoint of collateralization. Therefore, the acute-phase protein haptoglobin plays a critical role during coronary collateralization.
Estrogen receptor-α mediates estrogen facilitation of baroreflex heart rate responses in conscious mice
Authors: Pamidimukkala Jaya , Xue Baojian , Newton Leslie G. , Lubahn Dennis B. , Hay Meredith
Published: November 2004

Estrogen facilitates baroreflex heart rate responses evoked by intravenous infusion of ANG II and phenylephrine (PE) in ovariectomized female mice. The present study aims to identify the estrogen receptor subtype involved in mediating these effects of estrogen. Baroreflex responses to PE, ANG II, and sodium nitroprusside (SNP) were tested in intact and ovariectomized estrogen receptor-α knockout (ERαKO) with (OvxE+) or without (OvxE−) estrogen replacement. Wild-type (WT) females homozygous for the ERα+/+were used as controls. Basal mean arterial pressures (MAP) and heart rates were comparable in all the groups except the ERαKO-OvxE+ mice. This group had significantly smaller resting MAP, suggesting an effect of estrogen on resting vascular tone possibly mediated by the ERβ subtype. Unlike the WT females, estrogen did not facilitate baroreflex heart rate responses to either PE or ANG II in the ERαKO-OvxE+ mice. The slope of the line relating baroreflex heart rate decreases with increases in MAP evoked by PE was comparable in ERαKO-OvxE− (−6.97 ± 1.4 beats·min−1·mmHg−1) and ERαKO-OvxE+ (−6.18 ± 1.3) mice. Likewise, the slope of the baroreflex bradycardic responses to ANG II was similar in ERαKO-OvxE− (−3.87 ± 0.5) and ERαKO-OvxE+(−2.60 ± 0.5) females. Data suggest that estrogen facilitation of baroreflex responses to PE and ANG II is predominantly mediated by ERα subtype. A second important observation in the present study is that the slope of ANG II-induced baroreflex bradycardia is significantly blunted compared with PE in the intact as well as the ERαKO-OvxE+ females. We have previously reported that this ANG II-mediated blunting of cardiac baroreflexes is observed only in WT males and not in ovariectomized WT females independent of their estrogen replacement status. The present data suggest that in females lacking ERα, ANG II causes blunting of cardiac baroreflexes similar to males and may be indicative of a direct modulatory effect of the ERα on those central mechanisms involved in ANG II-induced resetting of cardiac baroreflexes. These observations suggest an important role for ERα subtype in the central modulation of baroreflex responses. Lastly, estrogen did not significantly affect reflex tachycardic responses to SNP in both WT and ERαKO mice.
Blood pressure maintenance in NHE3-deficient mice with transgenic expression of NHE3 in small intestine
Authors: Noonan William T. , Woo Alison L. , Nieman Michelle L. , Prasad Vikram , Schultheis Patrick J. , Shull Gary E. , Lorenz John N.
Published: November 2004

NHE3 Na+/H+ exchanger knockout ( Nhe3−/−) mice have severe absorptive deficits in the kidney proximal tubule and intestinal tract. The resulting hypovolemia has confounded efforts to carefully evaluate the specific effects of NHE3 deficiency on kidney function. Development of mice with transgenic expression of NHE3 in the small intestine (tg Nhe3−/−) has allowed us to analyze the role of renal NHE3 in overall maintenance of blood pressure, pressure natriuresis, and autoregulation of both glomerular filtration rate (GFR) and renal blood flow (RBF). Ambulatory blood pressure, measured by telemetry, was lower in tg Nhe3−/− mice than in wild-type controls (tg Nhe3+/+) when the mice were maintained on a normal NaCl diet but was normalized when they were provided with a high NaCl intake. Furthermore, administration of the AT1-receptor blocker losartan showed that circulating ANG II plays a major role in maintaining blood pressure in tg Nhe3−/− mice fed normal NaCl but not in those receiving high NaCl. Clearance studies revealed a blunted pressure-natriuresis response in tg Nhe3−/− mice at lower blood pressures but a robust response at higher blood pressures. Autoregulation of GFR and RBF was normal in tg Nhe3−/− mice. These results show that dietary NaCl loading normalizes blood pressure in awake tg Nhe3−/− mice and that alterations in NHE3 activity are not essential for normal autoregulation of GFR and RBF. Furthermore, the data strongly support the hypothesis that NHE3 plays an important role in the diuretic and natriuretic responses to increases in blood pressure but also show that mechanisms not involving NHE3 mediate pressure natriuresis in the higher range of blood pressures studied.
New Concepts in Lacunar Stroke Etiology: The Constellation of Small-Vessel Arterial Disease
Authors: Arboix Adrià , Martí-Vilalta J.L.
Published: November 2004

Objective: To update the less frequent etiologies causing lacunar infarcts (LIs). To highlight recent advances in risk factors, clinical syndromes, topography, complementary tests and long-term prognosis in this subtype of ischemic stroke. Patients and Methods: The most important studies are analyzed, from CM Fisher works, selecting those referring to LIs of unusual etiology, and recent advances and controversies in the clinical management of LI are discussed. Results: LIs are found in approximately 11% of patients admitted with stroke. The pure motor hemiparesis (55%) constitutes the most usual lacunar syndrome. However, lacunar syndromes may not be caused by LIs in 10–20% of cases. LIs caused by microembolism and cholesterol embolism from the aortic arch are reviewed. Hematological diseases can also cause LI, such as polycythemia rubra vera, essential thrombocythemia and primary antiphospholipidic antibody syndrome. Other etiologies are carotid plaque embolism, severe stenosis of a perforated arteriole and amyloid angiopathy. Infectious arteritis by neurolues, neurocysticercosis, neuroborreliosis, by AIDS or Helicobacter pylori infection have also been associated with the presence of LIs. Likewise, inflammatory arteritis in systemic lupus erythematosus or granulomatous angiitis, cocaine abuse and panarteritis nodosa have been related to LI, although in the latter LI would be caused by a thrombotic microangiopathy and not by vasculitis. Conclusions: LI is an ischemic stroke subtype with a characteristic clinical presentation and a short-term favorable prognosis. Although high blood pressure constitutes the main risk factor and the main etiology, LIs may be caused, in less than 5% of cases, by various etiologies, mainly hematological diseases and infectious or inflammatory arteritis. It is essential to make a correct etiological diagnosis for LI as treatment will be different according to its etiology.
The Cost of Stroke
Authors: Martínez-Vila Eduardo , Irimia Pablo
Published: November 2004

The control of health expenditure has become one of the main axes of health policy. Cost studies are an indispensable tool for determining the economic impact of disease and for assigning the material and human resources required for the prevention, diagnosis, treatment, and follow-up of patients with different diseases. Cost studies in stroke are necessary due to the increasing incidence of this disease which represents a significant cause of death and invalidity in adults and produces important hospital and social spending, and for which patients must be treated in specialized units (stroke units). The principal cost-determining factors in most studies are those generated by hospital admission (principally hospital stay). Other cost-determining factors include severity, stroke subtype or the fate of patients on discharge. Future health policies aimed at optimizing economic resources must be directed towards reducing hospital stay and minimizing patient disability.
Acute Care in Stroke: The Importance of Early Intervention to Achieve Better Brain Protection
Authors: Díez-Tejedor E. , Fuentes B.
Published: November 2004

It is known that ‘time is brain’, and only early therapies in acute stroke have been effective, like thrombolysis within the first 3 h, and useful neuroprotective drugs are searched for that probably would be effective only with their very early administration. General care (respiratory and cardiac care, fluid and metabolic management, especially blood glucose and blood pressure control, early treatment of hyperthermia, and prevention and treatment of neurological and systemic complications) in acute stroke patients is essential and must already start in the prehospital setting and continue at the patient’s arrival to hospital in the emergency room and in the stroke unit. A review of published studies analyzing the influence of general care on stroke outcome and the personal experience from observational studies was performed. Glucose levels >8 mmol/l have been found to be predictive of a poor prognosis after correcting for age, stroke severity, and stroke subtype. Although a clinical trial of glucose-insulin-potasium infusions is ongoing, increased plasma glucose levels should be treated. Moreover, insulin therapy in critically ill patients, including stroke patients, is safe and determines lower mortality and complication rates. Both high and low blood pressure levels have been related to a poor prognosis in acute stroke, although the target levels have not been defined yet in clinical trials. The body temperature has been shown to have a negative effect on stroke outcome, and its control and early treatment of hyperthermia are important. Hypoxemia also worsens the stroke prognosis, and oxygen therapy in case of <92% O2 saturation is recommended. Besides, blood pressure stabilization avoiding falls of the diastolic pressure and the lowering of glycemia and temperature have been related to a better prognosis in stroke units patients, and homeostasis maintenance is associated with a better outcome. General care has become an emergent and first-line brain-protectant treatment that must be started at the prehospital level from the very beginning. This could help to save more brain tissue to get the best conditions for further specific stroke therapies such as the use of neuroprotective or thrombolytic drugs in the hospital.