bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of nonlinear methods symbolic dynamics, detrended fluctuation, and Poincaré plot analysis in risk stratification in patients with dilated cardiomyopathy
Authors: Voss Andreas , Schroeder Rico , Truebner Sandra , Goernig Matthias , Figulla Hans Reiner , Schirdewan Alexander
Published: March 2007

Dilated cardiomyopathy (DCM) has an incidence of about 20∕100 000 new cases per annum and accounts for nearly 10 000 deaths per year in the United States. Approximately 36% of patients with dilated cardiomyopathy (DCM) suffer from cardiac death within five years after diagnosis. Currently applied methods for an early risk prediction in DCM patients are rather insufficient. The objective of this study was to investigate the suitability of short-term nonlinear methods symbolic dynamics (STSD), detrended fluctuation (DFA), and Poincaré plot analysis (PPA) for risk stratification in these patients. From 91 DCM patients and 30 healthy subjects (REF), heart rate and blood pressure variability (HRV, BPV), STSD, DFA, and PPA were analyzed. Measures from BPV analysis, DFA, and PPA revealed highly significant differences (p<0.0011) discriminating REF and DCM. For risk stratification in DCM patients, four parameters from BPV analysis, STSD, and PPA revealed significant differences between low and high risk (maximum sensitivity: 90%, specificity: 90%). These results suggest that STSD and PPA are useful nonlinear methods for enhanced risk stratification in DCM patients.
Virtual cell and tissue dynamics of ectopic activation of the ventricles
Authors: Benson Alan P. , Halley Graeme , Li Pan , Tong Wing C. , Holden Arun V.
Published: March 2007

Cardiac ventricular cells and tissues are normally excitable, and are activated by propagating waves of excitation that are initiated in the specialized pacemaking region of the heart. However, isolated or repetitive activity can be initiated at abnormal (ectopic) sites in the ventricles. To trigger an endogenous ectopic beat, there must be a compact focus of cells with changed membrane excitation parameters and kinetics, which initiate activity by after-depolarizations triggered by propagating activity, or that have bifurcated into autorhythmicity. This ectopic focus needs to be large enough, and adequately coupled, to drive the surrounding tissue. We investigate the initiation of ectopic excitation in computational models of human ventricular cells triggered by after-depolarizations and by up/down regulation of specific membrane conductance systems, and the propagation and evolution of ectopic activity in homogeneous or heterogeneous and isotropic, anisotropic, or orthotropic tissues.
Vascular coupling induces synchronization, quasiperiodicity, and chaos in a nephron tree
Authors: Marsh Donald J. , Sosnovtseva Olga V. , Mosekilde Erik , Holstein-Rathlou Niels-Henrik
Published: March 2007

The paper presents a study of synchronization phenomena in a system of 22 nephrons supplied with blood from a common cortical radial artery. The nephrons are assumed to interact via hemodynamic and vascularly propagated coupling, both mediated by vascular connections. Using anatomic and physiological criteria, the nephrons are divided into groups: cortical nephrons and medullary nephrons with short, intermediate and long Henle loops. Within each of these groups the delay parameters of the internal feedback regulation are given a random component to represent the internephron variability. For parameters that generate simple limit cycle dynamics in the pressure and flow regulation of single nephrons, the ensemble of coupled nephrons showed steady state, quasiperiodic or chaotic dynamics, depending on the interaction strengths and the arterial blood pressure. When the solutions were either quasiperiodic or chaotic, cortical nephrons synchronized to a single frequency, but the longer medullary nephrons formed two clusters with different frequencies. Under no physiologically realistic combination of parameters did all nephrons assume a common frequency. Our results suggest a greater variability in the nephron dynamics than is apparent from measurements performed on cortical nephrons only. This variability may explain the development of chaotic dynamics in tubular pressure records from hypertensive rats.
Nonlinear oscillator model reproducing various phenomena in the dynamics of the conduction system of the heart
Authors: Żebrowski J. J. , Grudziński K. , Buchner T. , Kuklik P. , Gac J. , Gielerak G. , Sanders P. , Baranowski R.
Published: March 2007

A dedicated nonlinear oscillator model able to reproduce the pulse shape, refractory time, and phase sensitivity of the action potential of a natural pacemaker of the heart is developed. The phase space of the oscillator contains a stable node, a hyperbolic saddle, and an unstable focus. The model reproduces several phenomena well known in cardiology, such as certain properties of the sinus rhythm and heart block. In particular, the model reproduces the decrease of heart rate variability with an increase in sympathetic activity. A sinus pause occurs in the model due to a single, well-timed, external pulse just as it occurs in the heart, for example due to a single supraventricular ectopy. Several ways by which the oscillations cease in the system are obtained (models of the asystole). The model simulates properly the way vagal activity modulates the heart rate and reproduces the vagal paradox. Two such oscillators, coupled unidirectionally and asymmetrically, allow us to reproduce the properties of heart rate variability obtained from patients with different kinds of heart block including sino-atrial blocks of different degree and a complete AV block (third degree). Finally, we demonstrate the possibility of introducing into the model a spatial dimension that creates exciting possibilities of simulating in the future the SA the AV nodes and the atrium including their true anatomical structure.
Phase-rectified signal averaging for the detection of quasi-periodicities and the prediction of cardiovascular risk
Authors: Kantelhardt Jan W. , Bauer Axel , Schumann Aicko Y. , Barthel Petra , Schneider Raphael , Malik Marek , Schmidt Georg
Published: March 2007

We present the phase-rectified signal averaging (PRSA) method as an efficient technique for the study of quasi-periodic oscillations in noisy, nonstationary signals. It allows the assessment of system dynamics despite phase resetting and noise and in relation with either increases or decreases of the considered signal. We employ the method to study the quasi-periodicities of the human heart rate based on long-term ECG recordings. The center deflection of the PRSA curve characterizes the average capacity of the heart to decelerate (or accelerate) the cardiac rhythm. It can be measured by a central wavelet coefficient which we denote as deceleration capacity (DC). We find that decreased DC is a more precise predictor of mortality in survivors of heart attack than left ventricular ejection fraction, the current “gold standard” risk predictor. In addition, we discuss the dependence of the DC parameter on age and on diabetes.
Arrhythmogenesis in the heart: Multiscale modeling of the effects of defibrillation shocks and the role of electrophysiological heterogeneity
Authors: Arevalo Hermenegild , Rodriguez Blanca , Trayanova Natalia
Published: March 2007

The mechanisms of initiation of ventricular arrhythmias as well as those behind the complex spatiotemporal wave dynamics and its filament organization during ventricular fibrillation (VF) are the topic of intense research and debate. Mechanistic inquiry into the various mechanisms that lead to arrhythmia initiation and VF maintenance is hampered by the inability of current experimental techniques to resolve, with sufficient accuracy, electrical behavior confined to the depth of the ventricles. The objective of this article is to demonstrate that realistic 3D simulations of electrical activity in the heart are capable of bringing a new level of understanding of the mechanisms that underlie arrhythmia initiation and subsequent organization. The article does this by presenting the results of two multiscale simulation studies of ventricular electrical behavior. The first study aims to uncover the mechanisms responsible for rendering the ventricles vulnerable to electric shocks during a specific interval of time, the vulnerable window. The second study focuses on elucidating the role of electrophysiological heterogeneity, and specifically, differences in action potential duration in various ventricular structures, in VF organization. Both studies share common multiscale modeling approaches and analysis, including characterization of scroll-wave filament dynamics.
Cardiac Resynchronization Therapy and phase resetting of the sinoatrial node: A conjecture
Authors: Cantini Federico , Varanini Maurizio , Macerata Alberto , Piacenti Marcello , Morales Maria-Aurora , Balocchi Rita
Published: March 2007

Congestive heart failure is a severe chronic disease often associated with disorders that alter the mechanisms of excitation-contraction coupling that may result in an asynchronous left ventricular motion which may further impair the ability of the failing heart to eject blood. In recent years a therapeutic approach to resynchronize the ventricles (cardiac resynchronization therapy, CRT) has been performed through the use of a pacemaker device able to provide atrial-based biventricular stimulation. Atrial lead senses the spontaneous occurrence of cells depolarization and sends the information to the generator which, in turn, after a settled delay [atrioventricular (AV) delay], sends electrical impulses to both ventricles to stimulate their synchronous contraction. Recent studies performed on heart rate behavior of chronically implanted patients at different epochs after implantation have shown that CRT can lead to sustained overall improvement of heart function with a reduction in morbidity and mortality. At this moment, however, there are no studies about CRT effects on spontaneous heart activity of chronically implanted patients. We performed an experimental study in which the electrocardiographic signal of five subjects under chronic CRT was recorded during the activity of the pacemaker programmed at different AV delays and under spontaneous cardiac activity after pacemaker deactivation. The different behavior of heart rate variability during pacemaker activity and after pacemaker deactivation suggested the hypothesis of a phase resetting mechanism induced by the pacemaker stimulus on the sinoatrial (SA) node, a phenomenon already known in literature for aggregate of cardiac cells, but still unexplored in vivo. The constraints imposed by the nature of our study (in vivo tests) made it impossible to plan an experiment to prove our hypothesis directly. We therefore considered the best attainable result would be to prove the accordance of our data to the conjecture through the use of models and physical considerations. We first used the data of literature on far-field effects of cardiac defibrillators to prove that the pacemaker impulses delivered to the two ventricles were able to induce modifications in membrane voltage at the level of the SA node. To simulate a phase resetting mechanism of the SA node, we used a Van der Pol modified model to allow the possibility of changing the refractory period and the firing frequency of the cells separately. With appropriate parameters of the model we reproduced phase response curves that can account for our experimental data. Furthermore, the simulated curves closely resemble the functional form proposed in literature for perturbed aggregate of cardiac cells. Despite the small sample of subjects investigated and the limited number of ECG recordings at different AV delays, we think we have proved the plausibility of the proposed conjecture.
Ion energy measurements near a dormant cathode in a multiple-cathode gridded ion thruster
Authors: Rovey Joshua L. , Gallimore Alec D.
Published: March 2007

A rectangular ion thruster discharge chamber was investigated for operation with multiple discharge cathode assemblies (DCAs). The multiple cathode approach attempts to increase thruster throughput and lifetime by operating three DCAs sequentially, possibly providing a threefold increase in discharge life. Previous multiple-cathode electric propulsion devices, such as the SPT-100, have shown dormant cathode erosion to be a life-limiting phenomenon. Similar results in a multiple-cathode discharge chamber may decrease the anticipated gain in discharge lifetime. In order to assess possible dormant cathode sputtering erosion, a diagnostic canister (DC) was designed and utilized to measure bombarding ion energy at the dormant cathode locations. The DC appeared similar to the active DCA, but was outfitted with a retarding potential analyzer. Most probable ion energy measurements show ions with energy of 27–35eV (±10%) with respect to cathode common and ion energy increases with increasing magnetic field strength. These results are consistent with an ion falling from the plasma potential to cathode common. A simple sputtering erosion model shows that, if doubly charged ions are present, these energies are enough to cause sputtering erosion of the dormant units.
Theory of microplasma fluctuations and noise in silicon diode in avalanche breakdown
Authors: Marinov Ognian , Deen M. Jamal , Jimenez Tejada Juan Antonio
Published: March 2007

A theory that explains physically the mechanism of microplasma switching from nonconducting to conducting state (turn-on process) and from conducting to nonconducting state (turn-off process) is presented. This theory describes the microplasma phenomenon in avalanche breakdown, and it provides relations between the microplasma properties (size, current density, and turn-on-off mechanism), noise properties (amplitude and wave form), and semiconductor properties (impurity concentration, lifetime constants, and diffusion coefficients). By use of this theory, the current-fluctuation [McIntyre, IEEE Trans. Electron Devices ED-13, 164 (1966)] and probability-dependent [Haitz, J. Appl. Phys. 35, 1370 (1964)] theories can be combined, and a very attractive characterization tool for investigation of semiconductor junctions in breakdown is developed.
Reshock and release response of aluminum single crystal
Authors: Huang H. , Asay J. R.
Published: March 2007

Reshock and release experiments were performed on single crystal aluminum along three orientations and on polycrystalline 1050 aluminum with 50μm grain size at shock stresses of 13 and 21GPa to investigate the mechanisms for previously observed quasielastic recompression behavior. Particle velocity profiles obtained during reshocking both single crystals and polycrystalline aluminum from initial shock stresses of 13–21GPa show similar quasielastic recompression behavior. Quasielastic release response is also observed in all single crystals, but the magnitude of the effect is crystal orientation dependent, with [111] and [110] exhibiting more ideal elastic-plastic release for unloading from the shocked state than for the [100] orientation and polycrystalline aluminum. The quasielastic response of 1050 aluminum is intermediate to that of the [100] and [111] orientations. Comparison of the wave profiles obtained for both unloading and reloading of single crystals and polycrystalline 1050 aluminum from shocked states suggests that the observed quasielastic response of polycrystalline aluminum results from the averaging response of single crystals for shock propagation along different orientations, and that the response of 1050 aluminum with large grain boundaries is not significantly different from the results obtained on single crystal aluminum. The yield strength of the single crystals and 1050 aluminum is found to increase with shock stress, which is consistent with previous results [H. Huang and I. R. Asay, J. Appl. Phys. 98, 033524 (2005)].
Seams near seams: The Jahn-Teller effect in the E″1 state of N3+
Authors: Dillon Joseph J. , Yarkony David R.
Published: March 2007

The E″1 electronic state of cyclic N3+ arising from the singly excited electron configuration e′3e″ is studied using multireference configuration interaction wave functions and a quadratic Jahn-Teller Hamiltonian determined from those calculations. It is shown that these two states have both a symmetry-required seam of conical intersections at D3h geometries and three proximal symmetry equivalent C2v seams, located on a circle with radius ρ0 from the D3h intersection. ρ0, a function of Qs, the breathing mode, is quite small but only attains a value of zero at Qscrit=1.252Å, resulting in a confluence or intersection node of the three C2v seams with the D3h seam. At this point only, g=∥g(Qs)∥, the norm of half the energy difference gradient, the linear Jahn-Teller term, vanishes and the intersection is of the Renner-Teller type. The close proximity of the previously unreported C2v seams to the D3h seam over the range of Qs considered is a consequence of the small values of g, compared to the quadratic Jahn-Teller term. The present analysis has important implications in the study of Jahn-Teller effects in ring systems and provides insight into a recent report that characterized this D3h seam as a Renner-Teller or glancing intersection.
Symmetry-adapted-cluster configuration interaction study of the doublet states of HCl+: Potential energy curves, dipole moments, and transition dipole moments
Authors: Gurin Valerij S. , Korolkov Mikhail V. , Matulis Vitaly E. , Rakhmanov Sergei K.
Published: March 2007

The electronic structure of the HCl+ molecular ion has been calculated using the general-R symmetry-adapted-cluster configuration interaction (SAC-CI) method. The authors present the potential energy curves, dipole moments, and transition dipole moments for a series of doublet states. The data are compared with the previous CASSCF and MCSCF calculations. The SAC-CI results reproduce quite well the data available in literature and extend the knowledge on the HCl+ electronic structure for several higher states. The calculated R-dependent behavior of both dipole moments and transition dipole moments for a series of bound and unbound states reveals an intricate dissociation process at intermediate distances (R>Re). The pronounced maxima in transition dipole moment (TDM) describing transitions into high electronic states (XΠ2→3Π2, XΠ2→3Σ2, 2Π2→3Π2, 3Π2→4Π2) occur at different interatomic separations. Such TDM features are promising for selection of excitation pathways and, consequently, for an optimal control of the dissociation products.
Density scaling and relaxation of the Pauli principle
Authors: Morrison Robert C. , Ayers Paul W. , Nagy Á
Published: March 2007

The relaxation of the Pauli principle associated with density scaling is examined. Scaling the density has been investigated in the development of density functional computational methods with higher accuracy. Scaling the density by ρ(r)ζ=ρ(r)∕ζ reduces the number of electrons to M=N∕ζ when ζ>1. The minimum kinetic energy of the scaled density, Ts[ρ∕ζ], can be scaled back to the N-electron system by multiplying the M-electron Kohn-Sham-type occupation numbers by ζ to produce Tζ[ρ]. This relaxes the Pauli principle when the orbital occupation numbers are greater than 1 in the N-electron system. The effects of antisymmetry on solutions to the Kohn-Sham equations are examined for Ne and the Be isoelectronic series. The changes in Tζ[ρ] and the exchange energy Exζ[ρ] when ζ is varied show that these two quantities are inextricably linked.
Polarization energy gradients in combined quantum mechanics, effective fragment potential, and polarizable continuum model calculations
Authors: Li Hui , Gordon Mark S.
Published: March 2007

A method that combines quantum mechanics (QM), typically a solute, the effective fragment potential (EFP) discrete solvent model, and the polarizable continuum model is described. The EFP induced dipoles and polarizable continuum model (PCM) induced surface charges are determined in a self-consistent fashion. The gradients of these two energies with respect to molecular coordinate changes are derived and implemented. In general, the gradients can be formulated as simple electrostatic forces and torques among the QM nuclei, electrons, EFP static multipoles, induced dipoles, and PCM induced charges. Molecular geometry optimizations can be performed efficiently with these gradients. The formulas derived for EFP∕PCM can be generally applied to other combined molecular mechanics and continuum methods that employ induced dipoles and charges.
Cardiovascular and respiratory dynamics during normal and pathological sleep
Authors: Penzel Thomas , Wessel Niels , Riedl Maik , Kantelhardt Jan W. , Rostig Sven , Glos Martin , Suhrbier Alexander , Malberg Hagen , Fietze Ingo
Published: March 2007

Sleep is an active and regulated process with restorative functions for physical and mental conditions. Based on recordings of brain waves and the analysis of characteristic patterns and waveforms it is possible to distinguish wakefulness and five sleep stages. Sleep and the sleep stages modulate autonomous nervous system functions such as body temperature, respiration, blood pressure, and heart rate. These functions consist of a sympathetic tone usually related to activation and to parasympathetic (or vagal) tone usually related to inhibition. Methods of statistical physics are used to analyze heart rate and respiration to detect changes of the autonomous nervous system during sleep. Detrended fluctuation analysis and synchronization analysis and their applications to heart rate and respiration during sleep in healthy subjects and patients with sleep disorders are presented. The observed changes can be used to distinguish sleep stages in healthy subjects as well as to differentiate normal and disturbed sleep on the basis of heart rate and respiration recordings without direct recording of brain waves. Of special interest are the cardiovascular consequences of disturbed sleep because they present a risk factor for cardiovascular disorders such as arterial hypertension, cardiac ischemia, sudden cardiac death, and stroke. New derived variables can help to find indicators for these health risks.
Pull-in voltage of microswitch rough plates in the presence of electromagnetic and acoustic Casimir forces
Authors: Palasantzas George
Published: March 2007

In this work, we investigate the combined influence of electromagnetic and acoustic Casimir forces on the pull-in voltage of microswitches with self-affine rough plates. It is shown that for plate separations within the micron range the acoustic term arising from pressure fluctuations can influence significantly the pull-in potential in a manner that depends on the particular roughness characteristics. Indeed, the acoustic term contribution can be comparable to that of surface roughness. Moreover, the temperature influence from the acoustic term appears to play a significant role besides that arising from the temperature dependence of the electromagnetic force due to quantum vacuum fluctuations.
Analysis of cardiovascular oscillations: A new approach to the early prediction of pre-eclampsia
Authors: Malberg H. , Bauernschmitt R. , Voss A. , Walther T. , Faber R. , Stepan H. , Wessel N.
Published: March 2007

Pre-eclampsia (PE) is a serious disorder with high morbidity and mortality occurring during pregnancy; 3%–5% of all pregnant women are affected. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients show pathological uterine perfusion in the second trimester, this parameter has a positive predictive accuracy of only 30%, which makes it unsuitable for early, reliable prediction. The study is based on the hypothesis that alterations in cardiovascular regulatory behavior can be used to predict PE. Ninety-six pregnant women in whom Doppler investigation detected perfusion disorders of the uterine arteries were included in the study. Twenty-four of these pregnant women developed PE after the 30th week of gestation. During pregnancy, additional several noninvasive continuous blood pressure recordings were made over 30 min under resting conditions by means of a finger cuff. The time series extracted of systolic as well as diastolic beat-to-beat pressures and the heart rate were studied by variability and coupling analysis to find predictive factors preceding genesis of the disease. In the period between the 18th and 26th weeks of pregnancy, three special variability and baroreflex parameters were able to predict PE several weeks before clinical manifestation. Discriminant function analysis of these parameters was able to predict PE with a sensitivity and specificity of 87.5% and a positive predictive value of 70%. The combined clinical assessment of uterine perfusion and cardiovascular variability demonstrates the best current prediction several weeks before clinical manifestation of PE.
Interaction of intrinsic defects with impurities in Al doped ZnSe single crystals
Authors: Ivanova G. N. , Nedeoglo D. D. , Negeoglo N. D. , Sirkeli V. P. , Tiginyanu I. M. , Ursaki V. V.
Published: March 2007

We report on the results of a complex study of electrical (77−300 K) and luminescence (10−300 K) properties of n-ZnSe single crystals annealed in a Zn melt containing Al impurity at concentrations ranging from 0.1 to 80 at. %. It was established that Al atoms form donor centers only at a low impurity concentration (≤0.5 at. %). The increase of the amount of Al atoms in the crystal results in the formation of (VZnAlZn) associative acceptor centers leading to the self-compensation of the shallow Al donor impurity. This process is accompanied by the emergence and development of a self-activated luminescence band associated with the (VZnAlZn) acceptor centers. We show that further increase of the Al content in the melt (≥10 at. %) leads to the dissociation of the acceptor complexes and to a recurrent donor doping effect. The photoluminescence spectra of such crystals are dominated by activated luminescence via the (CuZnVSeCui) and (CuZnAlZn) associative centers.
Dynamic comparisons of piezoelectric ejecta diagnostics
Authors: Buttler W. T. , Zellner M. B. , Olson R. T. , Rigg P. A. , Hixson R. S. , Hammerberg J. E. , Obst A. W. , Payton J. R. , Iverson A. , Young J.
Published: March 2007

We investigate the quantitative reliability and precision of three different piezoelectric technologies for measuring ejected areal mass from shocked surfaces. Specifically we performed ejecta measurements on Sn shocked at two pressures, P≈215 and 235 kbar. The shock in the Sn was created by launching a impactor with a powder gun. We self-compare and cross-compare these measurements to assess the ability of these probes to precisely determine the areal mass ejected from a shocked surface. We demonstrate the precision of each technology to be good, with variabilities on the order of ±10%. We also discuss their relative accuracy.
Bosonic helium droplets with cationic impurities: Onset of electrostriction and snowball effects from quantum calculations
Authors: Coccia E. , Bodo E. , Marinetti F. , Gianturco F. A. , Yildrim E. , Yurtsever M. , Yurtsever E.
Published: March 2007

Variational Monte Carlo and diffusion Monte Carlo calculations have been carried out for cations such as Li+, Na+, and K+ as dopants of small helium clusters over a range of cluster sizes up to about 12 solvent atoms. The interaction has been modeled through a sum-of-potential picture that disregards higher order effects beyond atom-atom and atom-ion contributions. The latter were obtained from highly correlated ab initio calculations over a broad range of interatomic distances. This study focuses on two of the most striking features of the microsolvation in a quantum solvent of a cationic dopant: electrostriction and snowball effects. They are discussed here in detail and in relation with the nanoscopic properties of the interaction forces at play within a fully quantum picture of the cluster features.
Feedback system for improving the performance of extended x-ray absorption fine structure measurements
Authors: Kudo Togo , Tanida Hajime
Published: March 2007

A rapid fine energy tuning method for a double-crystal monochromator (DCM) is developed by combining a feedback control system with a phase sensitive detector. This method maintains both a parallel angle between the first and second crystals of the DCM and the peak of the rocking curve. The method is used to perform a continuous energy scan of the DCM without readjustment of the angle between the two crystals. The time taken by this method to measure the extended x-ray absorption fine structure is 60% of that taken by a conventional procedure.
Multipole shimming of permanent magnets using harmonic corrector rings
Authors: Jachmann R. C. , Trease D. R. , Bouchard L.-S. , Sakellariou D. , Martin R. W. , Schlueter R. D. , Budinger T. F. , Pines A.
Published: March 2007

Shimming systems are required to provide sufficient field homogeneity for high resolution nuclear magnetic resonance (NMR). In certain specialized applications, such as rotating-field NMR and mobile ex situ NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in principle achievable by utilizing this shimming method for z-gradient correction and higher order xy gradients.
Turbulence control with local pacing and its implication in cardiac defibrillation
Authors: Cao Zhoujian , Li Pengfei , Zhang Hong , Xie Fagen , Hu Gang
Published: March 2007

In this review article, we describe turbulence control in excitable systems by using a local periodic pacing method. The controllability conditions of turbulence suppression and the mechanisms underlying these conditions are analyzed. The local pacing method is applied to control Winfree turbulence (WT) and defect turbulence (DT) induced by spiral-wave breakup. It is shown that WT can always be suppressed by local pacing if the pacing amplitude and frequency are properly chosen. On the other hand, the pacing method can achieve suppression of DT induced by instabilities associated with the motions of spiral tips while failing to suppress DT induced by the instabilities of wave propagation far from tips. In the latter case, an auxiliary method of applying gradient field is suggested to improve the control effects. The implication of this local pacing method to realistic cardiac defibrillation is addressed.
Heterodyne Z-scan measurements of slow absorbers
Authors: Guedes I. , Misoguti L. , de Boni L. , Zilio S. C.
Published: March 2007

We report a single-beam heterodyne Z-scan method capable of measuring slow response nonlinear refraction of absorbers with excellent sensitivity. By imposing a small sinusoidal modulation on the incoming continuous wave laser beam and recording both the magnitude and phase of the intensity transmitted through a small aperture, we are able to eliminate parasitic linear effects and achieve a sensitivity good enough to determine the absorption coefficient of a 2 mm-thick water sample at 532 nm with moderate power.
Polarizable atomic multipole solutes in a Poisson-Boltzmann continuum
Authors: Schnieders Michael J. , Baker Nathan A. , Ren Pengyu , Ponder Jay W.
Published: March 2007

Modeling the change in the electrostatics of organic molecules upon moving from vacuum into solvent, due to polarization, has long been an interesting problem. In vacuum, experimental values for the dipole moments and polarizabilities of small, rigid molecules are known to high accuracy; however, it has generally been difficult to determine these quantities for a polar molecule in water. A theoretical approach introduced by Onsager [J. Am. Chem. Soc. 58, 1486 (1936)] used vacuum properties of small molecules, including polarizability, dipole moment, and size, to predict experimentally known permittivities of neat liquids via the Poisson equation. Since this important advance in understanding the condensed phase, a large number of computational methods have been developed to study solutes embedded in a continuum via numerical solutions to the Poisson-Boltzmann equation. Only recently have the classical force fields used for studying biomolecules begun to include explicit polarization in their functional forms. Here the authors describe the theory underlying a newly developed polarizable multipole Poisson-Boltzmann (PMPB) continuum electrostatics model, which builds on the atomic multipole optimized energetics for biomolecular applications (AMOEBA) force field. As an application of the PMPB methodology, results are presented for several small folded proteins studied by molecular dynamics in explicit water as well as embedded in the PMPB continuum. The dipole moment of each protein increased on average by a factor of 1.27 in explicit AMOEBA water and 1.26 in continuum solvent. The essentially identical electrostatic response in both models suggests that PMPB electrostatics offers an efficient alternative to sampling explicit solvent molecules for a variety of interesting applications, including binding energies, conformational analysis, and pKa prediction. Introduction of 150mM salt lowered the electrostatic solvation energy between 2 and 13kcal∕mole, depending on the formal charge of the protein, but had only a small influence on dipole moments.
Deformation of glass forming metallic liquids: Configurational changes and their relation to elastic softening
Authors: Harmon John S. , Demetriou Marios D. , Johnson William L. , Tao Min
Published: March 2007

The change in the configurational enthalpy of metallic glass forming liquids induced by mechanical deformation and its effect on elastic softening is assessed. The acoustically measured shear modulus is found to decrease with increasing configurational enthalpy by a dependence similar to one obtained by softening via thermal annealing. This establishes that elastic softening is governed by a unique functional relationship between shear modulus and configurational enthalpy.
Existence of tetrahedral site symmetry about Ge atoms in a single-crystal film of Ge2Sb2Te5 found by x-ray fluorescence holography
Authors: Hosokawa S. , Ozaki T. , Hayashi K. , Happo N. , Fujiwara M. , Horii K. , Fons P. , Kolobov A. V. , Tominaga J.
Published: March 2007

The authors discuss x-ray fluorescence holography (XFH) measurements taken from an epitaxial layer of the digital versatile disk random access memory (DVD-RAM) material Ge2Sb2Te5 grown on a single-crystal GaSb(100) substrate. By using fluorescent photons from the Ge atoms in the matrix, a three-dimensional atomic image was obtained around the Ge atoms in a Ge2Sb2Te5 film; details of the three-dimensional atomic arrangement will aim at clarification of the high-speed writing and erasing mechanism of the laser-induced crystal-amorphous phase transition in this DVD-RAM material. Analysis of the XFH images revealed that the epitaxial layer did not possess a hexagonal structure as in the equilibrium phase of Ge2Sb2Te5, but a cubic structure with tetrahedral site symmetry about Ge atoms, different from the previous powder diffraction result. The present structure may support the umbrella-flip model of the Ge atoms between the octahedral site in the distorted rocksalt crystal and the tetrahedral site in the amorphous phase on the laser-induced phase transition.
Temperature dependence of Hall effects in organic thin-film transistors on plastic films
Authors: Takamatsu Yasushi , Sekitani Tsuyoshi , Someya Takao
Published: March 2007

The authors investigated the temperature dependence of Hall effects on polycrystalline pentacene thin-film transistors manufactured on plastic base films. The temperature dependence of the charge amounts evaluated from the Hall effect measurements is systematically compared with that evaluated from capacitance-voltage (CV) measurements. Our result indicates that the conduction carriers are dominated by hopping between polycrystalline grain boundaries below 260K and tend to be delocalized above 260K.
Coupling interaction in 1-3-type multiferroic composite thin films
Authors: Lu XiaoYan , Wang Biao , Zheng Yue , Ryba Earle
Published: March 2007

Using the time-dependent Ginzburg-Landau equation, the coupling interaction of the ferroelectric (FE) and ferromagnetic (FM) phases in epitaxial 1-3-type multiferroic thin films was investigated considering the effect of elastic stress arising from the FE/FM and film/substrate interfaces. The result of the authors shows that the maximum polarization and magnetization appear with the FM fractions of 70% and 30%, respectively. The significant changes of the FE and FM properties are caused by the special structure in which the induced misfit strain greatly affects the anisotropy of the crystals and the properties of the materials.
Nonlinear regime of the filamentation of a microwave produced plasma
Authors: Shokri B. , Niknam A. R.
Published: March 2007

The nonlinear dynamics of the magnetic field and anisotropic instability due to interaction of a plasma with microwave radiation, by making use of magnetohydrodynamic equations and Ampere-Maxwell law, are investigated. Also, it is shown that the Lienard nonlinear differential equation describes the evolution of the magnetic field in the plasma. We investigate the profiles of magnetic field and electron density variation in plasma and show that these profiles have a nonsinusoidal shape in the nonlinear regime. Furthermore, it is shown that the electron density becomes highly peaked in this regime. Also, due to the nonlinear effect, the cross section and shape of transverse filamentation can vary in the static limit.
Surface-induced large side-gating phenomenon in GaAs quantum wire transistors and its removal by surface passivation using Si interface control layer
Authors: Jia Rui , Kasai Seiya , Wang Qing , Long Shi Bing , Niu Jie Bin , Li Zhi Gang , Liu Ming
Published: March 2007

Side-gating behaviors of GaAs-based quantum wire transistors (QWRTr’s) were investigated. Using AlGaAs∕GaAs high electron mobility transistor wafer, the QWRTr was fabricated with a nanosized side gate beside the nanowire. Anomalous large side-gating effect was found for the QWRTr. Experiments showed that the large side-gating effect was owing to the strong surface Fermi level pinning around the nanowire, which is caused by a thin layer of deep traps located at the surface. Then, Si interface control layer passivation technology was performed to remove the large side gating.
Fabrication and characterization of femtosecond laser written waveguides in chalcogenide glass
Authors: Hughes M. , Yang W. , Hewak D.
Published: March 2007

The authors describe the fabrication of buried waveguides in a highly nonlinear chalcogenide glass, gallium lanthanum sulfide, using focused femtosecond laser pulses. Through optical characterization of the waveguides, they have proposed a formation mechanism and provide comparisons to previous work. Tunneling has been identified as the dominant nonlinear absorption mechanism in the formation of the waveguides. Single mode guidance at 633nm has been demonstrated. The writing parameters for the minimum propagation loss of 1.47dB∕cm are 0.36μJ pulse energy and 50μm∕s scanning speed.
Subsurface probing of terahertz particle plasmons
Authors: Chau K. J. , Rieckmann K. M. , Elezzabi A. Y.
Published: March 2007

Here, the authors exploit the potential barrier at the interface between dissimilar metals to probe frequency dependent subsurface charge induction on metallic microparticles excited with terahertz radiation. The authors’ experimental data and model show that terahertz electromagnetic charge induction on the microparticles occurs over a distance comparable to the skin depth. This work provides a technique to probe subsurface terahertz charge induction in subwavelength metallic structures and may open research avenues of low-frequency plasmonic behavior.
Precise control of phase transformation process in lead zirconate titanate thin films by focused line-beam scanning
Authors: Lee Jang-Sik , Lee Jung-Kun , Joo Seung-Ki
Published: March 2007

Phase transformation and grain growth processes of lead zirconate titanate (PZT) thin films have been precisely controlled by using focused line-beam scanning. The authors promoted the lateral crystallization of PZT grains by controlling a nucleation process and increasing the size of single grains to be as large as 40μm in length. Focused line-beam scanning allows for the selective growth and crystallization of large PZT grains on predetermined nucleation sites. The high growth rate of the selected PZT grains was attributed to successive suppression of undesirable nucleation except at predetermined positions when pretreated PZT films were exposed to the focused line beam.
Spatial Clustering and Organizational Dynamics of Transborder Production Networks: A Case Study of Taiwanese Information-Technology Companies in the Greater Suzhou Area, China
Authors: Yang You-Ren , Hsia Chu-Joe
Published: March 2007

Transborder investment by Taiwanese information-technology (IT) companies has driven the development of a new industrial space in the Greater Suzhou Area (GSA) of China over the last ten years. In this paper we aim to explore some characteristics of this expansion from the perspective of the organizational dynamics of global production networks. We found that foreign brand-name companies have played a key role in propelling this wave of investment in the GSA by Taiwanese IT companies. At the same time, their business strategies have influenced the mechanisms governing these Taiwanese companies' supply chains and have forged the dynamics of spatial agglomeration. We argue that the transborder extension of the production networks is interwoven with the exercise of power between enterprise organizations. Our findings suggest that interdependence among firms in close geographical proximity is inseparable from the asymmetrical power relations embodied in global commodity chains; a point emphasized by economic geographers as the main reason for transborder production shifts that result in the formation of new industrial spaces in developing countries. However, if these production networks can respond collectively to such a strict environment through instituting suitable organizational governance, then their competitive advantage will be enhanced, while also benefiting the host region's development through localization.
The City and the Bottom Line: Urban Megaprojects and the Privatization of Planning in Southeast Asia
Authors: Shatkin Gavin
Published: March 2007

Prevailing perspectives on the impacts of globalization on urban form in large, globalizing cities in Asia hold that these cities are experiencing an inexorable process of ‘Westernization’ or ‘Americanization’. Yet this focus on convergence distracts us from the task of analyzing urban change and its causes, leading to analytical muddiness and awkward planning and policy implications. The author presents an alternative framework that focuses on actor-centered analysis, and the importance of understanding historical context. This framework is employed in a case study of recent trends in urban development in Metro Manila, based on interviews, government, private sector, and nonprofit sector documents, and newspapers. It is concluded that, in Metro Manila, a defining characteristic of contemporary urban development is the unprecedented privatization of urban and regional planning. Large developers have conceived of urban development plans on a metrowide scale, and begun to implement these with the assistance of government. This phenomenon has its roots in the historical development of social groups in the Philippines and their shifting interests with the globalization of the Philippine economy. The author concludes that the privatization of planning raises distinct issues for urban planning theory and practice.
Retrieving the Baby from the Bathwater: Slum Upgrading in Sub-Saharan Africa
Authors: Gulyani Sumila , Bassett Ellen M
Published: March 2007

Drawing on project experiences over a thirty-year period and academic literature, this paper focuses on the question: what has worked in slum upgrading in Africa? We find that efforts to regularize land titles to confer de jure security of tenure have not been encouraging. By contrast, infrastructure investment efforts have performed better—they have conferred de facto security of tenure and also ameliorated living conditions. Over time project-based learning and microlevel innovations have helped improve upgrading performance. To create broader and sustainable benefits, however, upgrading needs to go to scale. We propose an upgrading strategy with the following elements—a programmatic approach that links slums to citywide systems, is channelled through government, and combines a community-demand and participation approach with supply-side constraints and rules of access.
What Does Not Kill You: Historical Materialism and the Body
Authors: Orzeck Reecia
Published: March 2007

In recent decades the body has become an important object of inquiry within the discipline of geography, as it has within the humanities and social sciences more generally. Though often critical of the tenets of poststructuralism, Marxist geographers have responded with enthusiasm to the imperative that we denaturalize the body, and have demonstrated a capacious store of resources available to this task. Building on recent efforts by geographers to conceptualize a Marxist theory of the body, this paper moves in two directions. Aligning myself with those interested in demonstrating the constructedness of the body, I begin by arguing both that the notion of bodies-as-produced is latent in historical materialism and that we can employ our insights about the production of space in order to think about the production of bodies. I then turn away from this discussion of the production of bodies and consider whether there is, in the bloodline of theoretical Marxism, any notion of the natural body with which we must contend. I argue that evidence of such a body can be found both in deliberate treatises on the subject and in the work of at least one scholar for whom the body was not an explicit object of study. These investigations, moreover, suggest that historical materialism implies not only the production of bodies but also what presupposes and enables this production. I conclude by considering some of the implications of subscribing to a historical materialist theory of the body.
Insertion of a homing endonuclease creates a genes-in-pieces ribonucleotide reductase that retains function
Authors: Friedrich Nancy C. , Torrents Eduard , Gibb Ewan A. , Sahlin Margareta , Sjöberg Britt-Marie , Edgell David R.
Published: March 2007

In bacterial and phage genomes, coding regions are sometimes interrupted by self-splicing introns or inteins, which can encode mobility-promoting homing endonucleases. Homing endonuclease genes are also found free-standing (not intron- or intein-encoded) in phage genomes where they are inserted in intergenic regions. One example is the HNH family endonuclease,
mobE
, inserted between the large (
nrdA
) and small (
nrdB
) subunit genes of aerobic ribonucleotide reductase (RNR) of T-even phages T4, RB2, RB3, RB15, and LZ7. Here, we describe an insertion of
mobE
into the
nrdA
gene of
Aeromonas hydrophila
phage Aeh1. The insertion creates a unique genes-in-pieces arrangement, where
nrdA
is split into two independent genes,
nrdA-a
and
nrdA-b
, each encoding cysteine residues that correspond to the active-site residues of uninterrupted NrdA proteins. Remarkably, the
mobE
insertion does not inactivate NrdA function, although the insertion is not a self-splicing intron or intein. We copurified the NrdA-a, NrdA-b, and NrdB proteins as complex from Aeh1-infected cells and also showed that a reconstituted complex has RNR activity. Class I RNR activity in phage Aeh1 is thus assembled from separate proteins that interact to form a composite active site, demonstrating that the
mobE
insertion is phenotypically neutral in that its presence as an intervening sequence does not disrupt the function of the surrounding gene.