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Inflection Point (inflection + point)
Selected AbstractsEffects of unidirectional and mutual interactions between microstructures and azo dyes as "kinetic" probe molecules on cis,trans isomerization rate constants in aqueous P85 and F88 triblock copolymer solutionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2008Helmut Knoll Rate constants of the thermal cis , trans isomerization of azo dyes have been studied in aqueous P85 and F88 triblock copolymer solutions by means of microsecond flash photolysis. Inflection points or maxima of the nonlinear Arrhenius plots indicate microstructure changes around the "kinetic" probe molecules. Unidirectional interactions of micelle formation on reactivity are reflected by discontinuous change of rate constants at temperatures near the critical micellization temperatures (cmT) determined by means of probe-free methods. Mutual interactions have been identified by means of significant differences between cmT and temperatures, where rate constants change discontinuously. The type of interactions depends on the properties of probe molecules and amphiphiles. Systems as studied in this work might be models of more complex biological reaction systems with temperature-dependent microstructure changes. © 2007 Wiley Periodicals, Inc. 40: 59,65, 2007 [source] Characteristics of Subtractive Anodic Stripping Voltammetry of Lead, Cadmium and Thallium at Silver-Gold Alloy ElectrodesELECTROANALYSIS, Issue 17 2003Y. Bonfil Abstract Silver-gold alloy electrodes have been studied for the purpose of the quantitative determination of heavy metals by subtractive anodic stripping voltammetry, (SASV). The results have been compared with those obtained with the silver and gold electrodes. The 50/50 a/o Ag/Au alloy electrode is the most suitable for quantifying thallium in the presence of lead and cadmium. The separation of its peak from those of lead and cadmium is 200,mV, which is about twice the separation obtained on the pure metal electrodes and is also better than on mercury. The silver electrode is suitable for the simultaneous determination of thallium, lead and cadmium. The peaks of lead and cadmium overlap on the 50/50 alloy. Pure silver or pure gold can be used for simultaneous quantification of these two metals. The use of gold for quantifying lead and cadmium is more limited because the peak potential of cadmium is shifted in the negative direction as its concentration increases and at [Cd2+]>200,nM, the two peaks merge. SASV enables correction for background currents and is of utmost importance for obtaining well-defined peaks. The peaks of lead, cadmium and thallium appear over a relatively narrow potential range (ca. 200,mV) on all the electrodes presented in this work. For this reason, the quantifying of a peak is based on the derivative at the inflection point of only one of its branches (ascending or descending). All SASV measurements were carried out without removal of oxygen. [source] System peaks in micellar electrophoresis: I. Utilization of system peaks for determination of critical micelle concentrationELECTROPHORESIS, Issue 5 2008Jana Lokajová Abstract A new way to determine the critical micelle concentration (CMC) based on the mobilities of system peaks is presented. A general approach for the CMC determination is based on the change of the slope or on finding the inflection point in the plot of a physical property of solution as a function of surfactant concentration. The determination of CMC by system peaks in CE utilizes a "jump" instead of a continuous change in the measured quantity. This phenomenon was predicted by the program PeakMaster, which was modified for simulation of micellar systems. The simulation of the steep change in mobilities of the anionic system peaks showing the CMC value was verified experimentally in a set of measurements, where the concentration of the surfactant was varied while the ionic strength was kept constant. The experimental work fully proved our model. A comparative electric current measurement was carried out. The proposed method seems to offer easier CMC determination as compared to the standard methods. [source] New valley ridge inflection point associated to the bifurcation of a valley on potential energy surfacesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007R. Palmeiro Abstract There are currently two definitions of valley ridge inflection point on an adiabatic potential energy surface (PES), one introduced by Basilevsky and the other by Valtazanos and Ruedenberg. Here, we investigate the validity of both definitions on bidimensional surfaces without symmetry constraints, with neither producing completely satisfactory results. Hence, we propose new conditions which must obey a valley bifurcation point (VBP) locally and demonstrate that such conditions are necessary when a valley splits into two, finishing at two energy minima. Finally, we localize such VBPs on the bidimensional surfaces and check the certainty of our previous deductions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Hepatic effects of an open lung strategy and cardiac output restoration in an experimental lung injuryACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 5 2010M. KREDEL Background: Ventilation with high positive end-expiratory pressure (PEEP) can lead to liver dysfunction. We hypothesized that an open lung concept (OLC) using high PEEP impairs liver function and integrity dependent on the stabilization of cardiac output. Methods: Juvenile female Pietrain pigs instrumented with flow probes around the common hepatic artery and portal vein, pulmonary and hepatic vein catheters underwent a lavage-induced lung injury. Ventilation was continued with a conventional approach (CON) using pre-defined combinations of PEEP and inspiratory oxygen fraction or with an OLC using PEEP set above the lower inflection point of the lung. Volume replacement with colloids was guided to maintain cardiac output in the CON(V+) and OLC(V+) groups or acceptable blood pressure and heart rate in the OLC(V,) group. Indocyanine green plasma disappearance rate (ICG-PDR), blood gases, liver-specific serum enzymes, bilirubin, hyaluronic acid and lactate were tested. Finally, liver tissue was examined for neutrophil accumulation, TUNEL staining, caspase-3 activity and heat shock protein 70 mRNA expression. Results: Hepatic venous oxygen saturation was reduced to 18 ± 16% in the OLC(V,) group, while portal venous blood flow decreased by 45%. ICG-PDR was not reduced and serum enzymes, bilirubin and lactate were not elevated. Liver cell apoptosis was negligible. Liver sinusoids in the OLC(V+) and OLC(V,) groups showed about two- and fourfold more granulocytes than the CON(V+) group. Heat shock protein 70 tended to be higher in the OLC(V,) group. Conclusions: Open lung ventilation elicited neutrophil infiltration, but no liver dysfunction even without the stabilization of cardiac output. [source] Corporate Debt Financing and Earnings QualityJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 5-6 2010Aloke (Al) Ghosh Abstract:, Our study establishes linkages between two extensively researched areas, debt financing and the quality of earnings. Debt can have a ,positive influence'on earnings quality because managers are likely to use their accounting discretion to provide private information about the firms' future prospects to lower financing costs. For high debt, it can also have a ,negative influence' on earnings quality as managers use accruals aggressively to manage earnings to avoid covenant violations. Using accruals quality as a proxy for earnings quality, we document a non-monotonic (curvilinear) relation between debt and earnings quality. The relationship is positive at low levels of debt and negative at high debt levels with an inflection point around 41%. Our results suggest that firms that rely heavily on debt financing might be willing to bear higher costs of borrowing from lower earnings quality because the benefits from avoiding potential debt covenant violations exceed the higher borrowing costs. [source] Temporal patterns of growth in larval cohorts of the Japanese sardine Sardinops melanostictus in a coastal nursery areaJOURNAL OF FISH BIOLOGY, Issue 6 2008G. Plaza Growth patterns of larval sardine Sardinops melanostictus were studied in a coastal nursery area, in southern Japan for four monthly hatch cohorts of larvae (November, December, January and February) for the 2003,2004 and 2004,2005 seasons. Laird,Gompertz models were fitted to each cohort using both total length (LT)-at-age at capture and mean LT -at-age data derived from backcalculations. In both approaches, the absolute daily growth rates (GR) and absolute daily growth rates at the inflection point (GXO) were estimated. In parallel, individual growth rates (GI) were derived from backcalculated LT (LB). Growth showed the following general common patterns irrespective of hatch month, season and methods: (1) significant Laird,Gompertz fits, (2) asymptotic growth, (3) a decrease in GR after the inflexion point, except for February for the 2003,2004 season that showed an apparent constant growth pattern, (4) six in eight cohorts showed GXO ranging from 0·8 to 1·2 mm day,1 and (5) a decreasing tendency of GI from 1·75 to 0·24 mm day,1, from first feeding through the first month of larval life. The contrasting pattern between the 2003,2004 and the 2004,2005 seasons were: (1) allometric v. logarithmic (ln) LT and otolith radius relationships, (2) low GXOv. high GXO, (3) high GRv. low GR when growth turned asymptotic, (4) low GXOv. high GXO when monthly hatch cohorts were combined and (5) LB and GI not differing among monthly hatch cohorts. The differences in growth patterns and growth rates between seasons seemed to be linked to the influx of warmer and oligotrophic waters of the Kuroshio Current that triggered an increase of 3° C in the coastal area for the 2003,2004 seasons. In the overall context, however, the high GXO, within cohorts and seasons reported in the current study, suggests that either sea surface temperature (SST) or food availability, or both are in the optimal range of preferences for S. melanostictus larvae. Consequently, nearshore coastal areas seem to be playing an important role as a nursery area for the larval stage of this species. [source] Spectrophotometric determination of the transition system for interactions involving model hydrogen bonds in acetonitrileJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2002Józef Mago Abstract The bonds formed by interactions of picric acid (HA) with each of 12 (un)substituted pyridines (B) in acetonitrile (AN) were studied by UV,vis spectrophotometry to determine the corresponding to the transition system. The choice of both model system and experimental technique enabled the effect of heteroconjugation to be observed and the effects of formation of two theoretically possible homoconjugates (AHA, and BHB+) to be eliminated. The relationship between the wavelength at the absorbance maximum (,max) for 10,4,M solutions of complexes of picric acid with (un)substituted pyridines in acetonitrile and was found to have a sigmoidal shape with an inflection point at of ca ,0.3. On the basis of this relationship and UV,vis spectra, the picric acid,3-acetylpyridine system was recognized as that being the nearest to the transition system. The fact that the transition was lower than zero has been explained by the remarkable effect of species having the average structures A,···+HB on the established ,max values. The general results of this work and our previous results based on IR and 1H NMR studies, and also the lack of any experimental counterexamples, indicate that the zero value of constitutes a fundamental basis for predicting which one, among the given family of protonic hetero systems, is the most likely to show transitional properties in acetonitrile. Finally, it is postulated that the protonic hetero systems which are the most likely to show transitional properties in a given solvent S are those for which is close to zero, the eventual shift arising from peculiarity of the technique applied. Copyright © 2002 John Wiley & Sons, Ltd. [source] SIMULTANEOUS INSTRUMENTAL MEASUREMENT OF FIRMNESS AND JUICINESS OF APPLE TISSUE DISCSJOURNAL OF TEXTURE STUDIES, Issue 3 2003F. ROGER HARKER Discs of apple tissue were compressed to 75% of their original height. Throughout compression, the force-distance curve was collected and the electrical impedance of the discs was measured at two frequencies of alternating current,1 kHz and 1 MHz. Electrical impedance was separated into its resistive and reactive components, and at these particular frequencies changes in resistance predominated. Measurements at 1 kHz indicate the resistance of extracellular regions of the discs (ruptured cells as well as those regions external to the plasma membrane), while measurements at 1 MHz indicate the resistance of the entire disc (combined intracellular and extracellular regions). Juice was released from the discs as a result of damage to cells and the extrusion of cellular fluid into intercellular air spaces. This resulted in a decline in electrical resistance at 1 kHz, but little change to the resistance at 1 MHz. Changes in juice release as determined by electrical measurement were related to the mechanical properties of the discs. Generally, the release of juice occurred after the inflection point on the force-distance curves, but much earlier than mechanical failure (indicated by maximum force). The extent of tissue damage was determined from the relative decrease in resistance at 1 kHz, and was found to vary among apple cultivars and in response to fruit ripening. [source] Major depression: emerging therapeuticsMOUNT SINAI JOURNAL OF MEDICINE: A JOURNAL OF PERSONALIZED AND TRANSLATIONAL MEDICINE, Issue 3 2008Srijan Sen MD Abstract The first effective antidepressants, monoamine oxidase inhibitors and tricyclic antidepressants, were identified 50 years ago, largely through serendipity. These medications were found to improve mood in a little more than half of depressed patients after a few weeks of chronic use. Almost all antidepressants prescribed today were developed through minor modifications of these original antidepressants and, like monoamine oxidase inhibitors and tricyclic antidepressants, act primarily through monoaminergic mechanisms. Although there have been improvements in side-effect profiles and overdose toxicity, these newer medications have not provided substantial advances in the efficacy and speed of the antidepressant effect for patients. Over the last 2 decades, our understanding of the neurobiology underlying depression has expanded exponentially. Given this expansion, we may be nearing an inflection point in antidepressant drug development, at which useful medicines will be designed through a rational understanding of the biological systems. In this review, we discuss the biological basis and preclinical and clinical evidence for a series of promising classes of antidepressants developed primarily out of a pathophysiologically informed approach. Mt Sinai J Med 75:203,224, 2008. © 2008 Mount Sinai School of Medicine [source] Programming Optimal Atrioventricular Delay in Dual Chamber Pacing Using Peak Endocardial Acceleration: Comparison with a Standard Echocardiographic ProcedurePACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1p2 2003JEAN-MARC DUPUIS DUPUIS, J.-M.,et al.: Programming Optimal Atrioventricular Delay in Dual Chamber Pacing Using Peak Endocardial Acceleration: Comparison with a Standard Echocardiographic Procedure.Optimization of programmed atrioventricular delay in dual chamber pacing is essential to the hemodynamic efficiency of the heart. Automatic AV delay optimization in an implanted pacemaker is highly desirable. Variations of peak endocardial acceleration (PEA) with AV delay at rest correlate well with echocardiography derived observations, particularly with end-diastolic filling and mitral valve closure timings. This suggests the possibility of devising a procedure for the automatic determination of the optimal AV delay. The aim of this study was to compare a proposed algorithm for optimal AV delay determination with an accepted echocardiographic method. Fifteen patients with high degree AV block received BEST-Living pacing systems. Automatic AV delay scans were performed at rest (60,300 ms in 20-ms steps with 60 beats per step) in DDD at 90 ppm, while simultaneously recording cycle-by-cycle PEA values, which were averaged for each AV delay to obtain a PEA versus AV delay curve. Nonlinear regression analysis based on a Boltzmann sigmoid curve was performed, and the optimal AV delay (OAVD) was chosen as the sigmoid inflection point of the regression curve. The OAVD was also evaluated for each patient using the Ritter echocardiographic method. Good sigmoid fit was obtained in 13 of 15 patients. The mean OAVD obtained by the PEA sigmoid algorithm was146.9 ± 32.1 ms, and the corresponding result obtained by echocardiography was156.4 ± 34.3 ms(range 31.8,39.7 ms). Correlation analysis yielded r = 0.79, P = 0.0012. In conclusion, OAVD estimates obtained by PEA analysis during automatic AV delay scanning are consistent with those obtained by echocardiography. The proposed algorithm can be used for automatic OAVD determination in an implanted pacemaker pulse generator. (PACE 2003; 26:[Pt. II]:210,213) [source] Relationship between bronchial hyperresponsiveness and development of asthma in children with chronic coughPEDIATRIC PULMONOLOGY, Issue 6 2001Hideko Nishimura MD Abstract To evaluate the relationship between bronchial hyperresponsiveness (BHR) and the development of asthma in children with chronic cough, we performed methacholine inhalation challenges and transcutaneous oxygen pressure (tcPO2) measurements in 92 children with chronic cough aged from 1,13 years (55 boys and 37 girls; mean, 5.3 years) and followed them for ,,,10 years. Forty-four age-matched children with asthma (24 males and 20 females; mean, 6.5 years) and 44 age-matched children without cough or asthma served as controls (18 males and 26 females; mean, 4.6 years). Consecutive doubling doses of methacholine were inhaled until a 10% decrease in tcPO2 from baseline was observed. The cumulative dose of methacholine at the inflection point of the tcPO2 record (Dmin-PO2) was considered to represent hyperresponsiveness to inhaled methacholine. After 10 years or more of follow-up, 60 of the 92 subjects with cough answered our questionnaire, and 27/60 had been diagnosed with asthma. There was a statistical difference in Dmin-PO2 between the children who presented with chronic cough originally and who developed asthma (asthma-developed group) and those who did not develop asthma (asthma-free group). There was no difference in the value of Dmin-PO2 between the asthma-developed group and the asthma group, or between the asthma-free group and the age-matched control group. Among the children with chronic cough, there was no difference in Dmin-PO2 between girls and boys, either in the asthma-developed group or in the asthma-group. We conclude that 45% of the children with a chronic cough in early life developed asthma, and that BHR in children with chronic cough during the childhood period is a strong risk factor for the development of asthma. Pediatr Pulmonol. 2001; 31:412,418. © 2001 Wiley-Liss, Inc. [source] Measurement and Correlation of Critical Gas and Liquid Velocities for Complete Circulation of Solid Particles in External Loop Airlift Bubble ColumnsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003Katsumi Nakao Abstract The external loop airlift bubble column provides an easy way of good contacting among gas, liquid and solid phases due to a relatively high recirculating liquid velocity UL. The critical gas and liquid velocities for complete circulation of solid particles, UG,C and UL,C, were measured in two different scales of columns with air, tap water and aqueous CMC solutions, and ion exchange resin and glass beads (155,3834 µm) were employed. The UG,C was determined as the inflection point on the plot of the pressure drop due to the suspended solid particles in the downcomer as a function of the gas velocity UG. The critical liquid velocity UL,C corresponding to the UG,C was obtained from the measured relationship between UL and UG. As a result, a unified dimensionless empirical correlation of UL,C was obtained within an error of ±20% and a dimensionless empirical relationship between UL and UG was developed within an error of ±15%. La colonne à bulles de type airlift à boucle externe offre un moyen facile pour le contact entre les phases gazeuse, liquide et solide grâce à la vitesse de liquide en recirculation UL relativement élevée. Les vitesses de gaz et de liquide critiques pour la circulation complète des particules solides, UG,C et UL,C, ont été mesurées dans deux colonnes d'échelle différente avec de l'air, de l'eau du robinet et des solutions aqueuses de CMC, et des billes de verre et de résine échandeuse d'ions (155,3834 µm) ont été employées. La vitesse UG,C est déterminée comme étant le point d'inflexion sur la courbe de la perte de chgarge causée par les particules solides suspendues dans le déversoir en fonction de la vitesse de gaz UG. La vitesse de liquide critique UL.C correspondant à la vitesse UG.C est obtenue à partir de la relation mesurée entre UL et UG. Ainsi, on obtient une corrélation empirique adimensionnelle unifiée de UL.C avec une erreur de ± 20% et une relation empirique adimensionnelle entre UL et UG est établie avec une erreur de ±15%. [source] Philips QT Interval Measurement Algorithms for Diagnostic, Ambulatory, and Patient Monitoring ECG ApplicationsANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2009F.A.C.C., Sophia H. Zhou Ph.D. Background: Commonly used techniques for QT measurement that identify T wave end using amplitude thresholds or the tangent method are sensitive to baseline drift and to variations of terminal T wave shape. Such QT measurement techniques commonly underestimate or overestimate the "true" QT interval. Methods: To find the end of the T wave, the new Philips QT interval measurement algorithms use the distance from an ancillary line drawn from the peak of the T wave to a point beyond the expected inflection point at the end of the T wave. We have adapted and optimized modifications of this basic approach for use in three different ECG application areas: resting diagnostic, ambulatory Holter, and in-hospital patient monitoring. The Philips DXL resting diagnostic algorithm uses an alpha-trimming technique and a measure of central tendency to determine the median QT value of eight most reliable leads. In ambulatory Holter ECG analysis, generally only two or three channels are available. QT is measured on a root-mean-square vector magnitude signal. Finally, QT measurement in the real time in-hospital application is among the most challenging areas of QT measurement. The Philips real time QT interval measurement algorithm employs features from both Philips DXL 12-lead and ambulatory Holter QT algorithms with further enhancements. Results: The diagnostic 12-lead algorithm has been tested against the gold standard measurement database established by the CSE group with results surpassing the industrial ECG measurement accuracy standards. Holter and monitoring algorithm performance data on the PhysioNet QT database were shown to be similar to the manual measurements by two cardiologists. Conclusion: The three variations of the QT measurement algorithm we developed are suitable for diagnostic 12-lead, Holter, and patient monitoring applications. [source] Catalytic decomposition of methane over supported Ni catalysts with different particle sizesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Sun Yunfei Abstract Methane decomposition on ,-Al2O3 -supported Ni catalysts, as a method for the production of carbon nanofibers (CNFs) and CO-free hydrogen, has been investigated to show the effect of catalyst particle size on the rate and yield of CNFs formation. The catalysts were prepared by deposition,precipitation with different calcination temperature ranging from 725 to 1025 K so as to have different initial particle sizes. The results show that catalysts with smaller initial particle sizes had higher initial growth rate but experienced fast deactivation. The lifetime of the catalyst, ending at the inflection point on the rate curve of CNFs growth, could well represent the yield of CNFs of the catalyst, and the maximal yield of CNFs was achieved on the Ni catalysts calcinated at 823 K and with a particle size of around 56 nm. However, the diameters of the grown CNFs were not directly related to the initial size of the catalysts, because of particle sintering and breaking during catalyst reduction or CNFs formation. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of species richness and relative abundance on the shape of the species accumulation curveAUSTRAL ECOLOGY, Issue 4 2003Graham G. Thompson Abstract We explain how species accumulation curves are influenced by species richness (total number of species), relative abundance and diversity using computer-generated simulations. Species richness defines the boundary of the horizontal asymptote value for a species accumulation curve, and the shape of the curve is influenced by both relative abundance and diversity. Simulations with a high proportion of rare species and a few abundant species have a species accumulation curve with a low ,shoulder' (inflection point on the ordinate axis) and a long upward slope to the asymptote. Simulations with a high proportion of relatively abundant species have a steeply rising initial slope to the species accumulation curve and plateau early. Diversity (as measured by Simpson's and Shannon,Weaver indices) for simulations is positively correlated with the initial slope of the species accumulation curve. Species accumulation curves cross when one simulation has a high proportion of both rare and abundant species compared with another that has a more even distribution of abundance among species. [source] Ectoparasite load is linked to ontogeny and cell-mediated immunity in an avian host system with pronounced hatching asynchronyBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008RADOVAN VÁCLAV Several contrasting hypotheses have been proposed to account for host age-biased parasite distribution, with some of them suggesting a key role of ectoparasites in the evolution and maintenance of weight hierarchies within broods. We examined parasite distribution among individual hosts across the whole period of host exposure to the parasite in a host system that shows distinct within-brood differences in age and age-related mortality. By contrast to previous hypotheses, we found that the abundance of a haematophagous, mobile ectoparasite Carnus haemapterus on nestling European rollers (Coracias garrulus) was highest approximately during the mid-nestling stage of their host, coinciding with the inflection point of the host growth phase. Parasite load increased neither with absolute resource availability (i.e. body size), nor body condition index. By contrast to previous evidence, higher parasite load under natural conditions was associated with a stronger cell-mediated immune response. However, this association was moderated by low parasite densities, as well as a better brood body condition index. Overall, although we revealed remarkable host ontogenetic effects on parasite distribution, the present study suggests that a highly mobile ectoparasite generally prefers healthier hosts. We propose that, in host systems with a marked asynchrony of hatching and background mortality within the brood, parasites favour persistence rather than nutritional attractiveness of the host. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 463,473. [source] Moderate deviations for longest increasing subsequences: The upper tailCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 12 2001Matthias Löwe We derive the upper-tail moderate deviations for the length of a longest increasing subsequence in a random permutation. This concerns the regime between the upper-tail large-deviation regime and the central limit regime. Our proof uses a formula to describe the relevant probabilities in terms of the solution of the rank 2 Riemann-Hilbert problem (RHP); this formula was invented by Baik, Deift, and Johansson [3] to find the central limit asymptotics of the same quantities. In contrast to the work of these authors, who apply a third-order (nonstandard) steepest-descent approximation at an inflection point of the transition matrix elements of the RHP, our approach is based on a (more classical) second-order (Gaussian) saddle point approximation at the stationary points of the transition function matrix elements. © 2001 John Wiley & Sons, Inc. [source] Testing Parameters in GMM Without Assuming that They Are IdentifiedECONOMETRICA, Issue 4 2005Frank Kleibergen We propose a generalized method of moments (GMM) Lagrange multiplier statistic, i.e., the K statistic, that uses a Jacobian estimator based on the continuous updating estimator that is asymptotically uncorrelated with the sample average of the moments. Its asymptotic ,2 distribution therefore holds under a wider set of circumstances, like weak instruments, than the standard full rank case for the expected Jacobian under which the asymptotic ,2 distributions of the traditional statistics are valid. The behavior of the K statistic can be spurious around inflection points and maxima of the objective function. This inadequacy is overcome by combining the K statistic with a statistic that tests the validity of the moment equations and by an extension of Moreira's (2003) conditional likelihood ratio statistic toward GMM. We conduct a power comparison to test for the risk aversion parameter in a stochastic discount factor model and construct its confidence set for observed consumption growth and asset return series. [source] A perturbation analysis of harmonic generation from saturated elements in power systemsELECTRICAL ENGINEERING IN JAPAN, Issue 4 2010Teruhisa Kumano Abstract Nonlinear phenomena such as saturation of magnetic flux have considerable effects in power systems analysis. It is reported that a failure in a real 500-kV system triggered islanding operation, where resultant even harmonics caused malfunctions in protective relays. It is also reported that the major origin of this wave distortion is nothing but unidirectional magnetization of the transformer iron core. Time simulation is widely used today to analyze phenomena of this type, but it has basically two shortcomings. One is that the time simulation takes too much computing time in the vicinity of inflection points in the saturation characteristic curve because certain iterative procedures such as N-R (Newton,Raphson) must be used and such methods tend to be caught in an ill-conditioned numerical hunting. The other is that such simulation methods sometimes do not aid an intuitive understanding of the studied phenomenon because all of the nonlinear equations are treated in matrix form and are not properly divided into understandable parts, as is done in linear systems. This paper proposes a new computation scheme that is based on the so-called perturbation method. Magnetic saturation of iron cores in a generator and a transformer are taken into account. The proposed method has a special feature to deal with the first shortcoming of the N-R-based time simulation method stated above. The proposed method does not use an iterative process to reduce the equation residue, but uses perturbation series, so that it is free of the ill-conditioning problem. The user need only calculate the perturbation terms one by one until the necessary accuracy is attained. In a numerical example treated in the present paper, first-order perturbation can achieve reasonably high accuracy, which means very fast computing time. In a numerical study, three nonlinear elements are considered. The calculation results are almost identical to the conventional N-R-based time simulation, which shows the validity of the method. The proposed method can be effectively used in screening where many case studies are needed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 35,42, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20895 [source] Hedging Affecting Firm Value via Financing and Investment: Evidence from Property Insurance UseFINANCIAL MANAGEMENT, Issue 3 2010Hong Zou I provide evidence about the value effects of alternative risk management by examining corporate purchase of property insurance, a commonly used pure hedge of asset-loss risks. Using an insurance data set from China, I find that there is an inverted U-shape effect of the extent of property insurance use on firm value measured by several versions of Tobin's Q. Therefore, the use of property insurance, to a certain degree, has a positive effect on firm value; however, over insurance appears detrimental to firm value. Given that the inflection points occur at relatively high levels of the observed insurance spending, insurance use appears beneficial to the majority of my sample firms. The estimated average hedging premium is about 1.5%. I demonstrate that an avenue for insurance to create value in China is that it helps firms secure valuable new debt financing and enhance investment. [source] Growth of the Yellow River delta over the past 800 years, as influenced by human activitiesGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2003Xu Jiongxin Abstract Based on measurements made over the past 50 years and data extracted from historical documents, a study has been made of the effect of human activities on the growth of the Yellow River delta over a time scale of 102 -103 years. During the period studied, the Yellow River emptied into the Yellow Sea and Bohai Sea, successively, and the deltas it created are known as the Abandoned and Modern Yellow River deltas. The growth of the Abandoned Yellow River delta can be divided into two stages. The first extended from AD 1194 to 1578, during which the growth was rather slow. The second extended from AD 1579 to 1855, when the growth was greatly accelerated. The curve showing the temporal variation of the growth of the Modern Yellow River mouth can be fitted by three straight lines with different slopes. Accordingly, its growth from 1855 to present can be divided into three stages, and the inflection points associated with three straight lines may be regarded as threshold points, reflecting marked changes in the nature and extent of human activities. On this basis, a three-stage descriptive model has been proposed to describe the process of river mouth extension in response to changing human activities. [source] Analysis of a Vertical Dipole Tracer Test in Highly Fractured RockGROUND WATER, Issue 5 2002William E. Sanford The results of a vertical dipole tracer experiment performed in highly fractured rocks of the Clare Valley, South Australia, are presented. The injection and withdrawal piezometers were both screened over 3 m and were separated by 6 m (midpoint to midpoint). Due to the long screen length, several fracture sets were intersected, some of which do not connect the two piezometers. Dissolved helium and bromide were injected into the dipole flow field for 75 minutes, followed by an additional 510 minutes of flushing. The breakthrough of helium was retarded relative to bromide, as was expected due to the greater aqueous diffusion coefficient of helium. Also, only 25% of the total mass injected of both tracers was recovered. Modeling of the tracer transport was accomplished using an analytical one-dimensional flow and transport model for flow through a fracture with diffusion into the matrix. The assumptions made include: streamlines connecting the injection and withdrawal point can be modeled as a dipole of equal strength, flow along each streamline is one dimensional, and there is a constant Peclet number for each streamline. In contrast to many other field tracer studies performed in fractured rock, the actual travel length between piezometers was not known. Modeling was accomplished by fitting the characteristics of the tracer breakthrough curves (BTCs), such as arrival times of the peak concentration and the center of mass. The important steps were to determine the fracture aperture (240 ,m) based on the parameters that influence the rate of matrix diffusion (this controls the arrival time of the peak concentration); estimating the travel distance (11 m) by fitting the time of arrival of the centers of mass of the tracers; and estimating fracture dispersivity (0.5 m) by fitting the times that the inflection points occurred on the front and back limbs of the BTCs. This method works even though there was dilution in the withdrawal well, the amount of which can be estimated by determining the value that the modeled concentrations need to be reduced to fit the data (,50%). The use of two tracers with different diffusion coefficients was not necessary, but it provides important checks in the modeling process because the apparent retardation between the two tracers is evidence of matrix diffusion and the BTCs of both tracers need to be accurately modeled by the best fit parameters. [source] Automatic characterization of ignition processes with machine learning clustering techniquesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2006Edward S. Blurock Machine learning clustering techniques are used to characterize and, after the training phase, to identify phases within an ignition process. For the ethanol mechanism used in this paper, four physically identifiable phases were found and characterized: the initiation phase, preignition phase, ignition phase, and the postignition phase. The clustering is done with respect to fuzzy logic predicates identifying the maxima, minima, and inflection points of the species profiles. The cluster descriptions characterize the phases found and are in human interpretable form. In addition, these descriptions are powerful enough to be used to predict the phase structure under new conditions. Cluster phases were calculated for the ethanol mechanism at an equivalence ratio of 0.5, a pressure of 3.3 bar, and the temperatures 1200, 1300, 1400, and 1500 K. The resulting cluster phase descriptions were then successfully used to predict the phase structure and ignition delay times for other temperatures in the range from 1200 to 1500 K. The effect of different fuzzy logic predicate profile descriptions is studied to emphasize that the boundaries of some phases, specifically that between the preignition and the ignition phase, are a matter of what the modeler considers important. The end of the ignition phase corresponds to the ignition delay time and was relatively independent of the predicate descriptions used to determine the phases. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 621,633, 2006 [source] Are parametric models suitable for estimating avian growth rates?JOURNAL OF AVIAN BIOLOGY, Issue 4 2007William P. Brown For many bird species, growth is negative or equivocal during development. Traditional, parametric growth curves assume growth follows a sigmoidal form with prescribed inflection points and is positive until asymptotic size. Accordingly, these curves will not accurately capture the variable, sometimes considerable, fluctuations in avian growth over the course of the trajectory. We evaluated the fit of three traditional growth curves (logistic, Gompertz, and von Bertalanffy) and a nonparametric spline estimator to simulated growth data of six different specified forms over a range of sample sizes. For all sample sizes, the spline best fit the simulated model that exhibited negative growth during a portion of the trajectory. The Gompertz curve was the most flexible for fitting simulated models that were strictly sigmoidal in form, yet the fit of the spline was comparable to that of the Gompertz curve as sample size increased. Importantly, confidence intervals for all of the fitted, traditional growth curves were wholly inaccurate, negating the apparent robustness of the Gompertz curve, while confidence intervals of the spline were acceptable. We further evaluated the fit of traditional growth curves and the spline to a large data set of wood thrush Hylocichla mustelina mass and wing chord observations. The spline fit the wood thrush data better than the traditional growth curves, produced estimates that did not differ from known observations, and described negative growth rates at relevant life history stages that were not detected by the growth curves. The common rationale for using parametric growth curves, which compress growth information into a few parameters, is to predict an expected size or growth rate at some age or to compare estimated growth with other published estimates. The suitability of these traditional growth curves may be compromised by several factors, however, including variability in the true growth trajectory. Nonparametric methods, such as the spline, provide a precise description of empirical growth yet do not produce such parameter estimates. Selection of a growth descriptor is best determined by the question being asked but may be constrained by inherent patterns in the growth data. [source] Regional pulmonary pressure volume curves in mechanically ventilated patients with acute respiratory failure measured by electrical impedance tomographyACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 3 2006J. Hinz Background:, We hypothized, that in mechanically ventilated patients with acute respiratory failure, regional pressure volume curves differ markedly from conventional global pressure volume curves of the whole lung. Methods:, In nine mechanically ventilated patients with acute respiratory failure during an inspiratory low-flow manoeuvre, conventional global pressure volume curves were registered by spirometry and regional pressure volume curves in up to 912 regions were assessed simultaneously using electrical impedance tomography. We compared the lower (LIP) and upper (UIP) inflection points obtained from the conventional global pressure volume curve and regional pressure volume curves. Results:, We identified from the conventional global pressure volume curves LIP [3,11 (8) cmH2O] in eight patients and UIP [31,39 (33) cmH2O] in three patients. Using electrical impedance tomography (EIT), LIP [3,18 (8) cmH2O] in 54,264 (180) regions and UIP [23,42 (36) cmH2O] in 149,324 (193) regions (range and median) were identified. Lung mechanics measured by conventional global pressure volume curves are similar to the median of regional pressure volume curves obtained by EIT within the tomographic plane. However, single regional pressure volume curves differ markedly with a broad heterogeneity of lower and upper inflection points. Conclusion:, Lower and upper inflection points obtained from conventional global pressure volume curves are not representative of all regions of the lungs. [source] pH-Dependent Spectral Properties of HpIX, TPPS2a, mTHPP and mTHPC,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2001Beata, underlíková ABSTRACT Lower extracellular pH in tumors as compared to normal tissues has been proposed to be a factor contributing to the tumor selective uptake of several photosensitizers. Therefore, the pH dependence of absorption and fluorescence spectral properties of four different drugs relevant for photodynamic therapy (hematoporphyrin IX [HpIX], disulfonated meso -tetraphenylporphine [TPPS2a], meso -tetra(3-hydroxyphenyl)porphine [mTHPP] and meso -tetra(3-hydroxyphenyl)chlorin [mTHPC]) has been examined. Spectral analysis of the dyes dissolved in phosphate buffered saline (PBS) indicates pH-dependent modification in the physiologically important region (6.0,8.0) only in the case of HpIX. This modification is probably related to the protonation of carboxylic groups. Spectral changes of HpIX in PBS observed at acidic pH values <5, as well as those of the rest of the drugs (inflection points of titration curves occurred at about 5.1, 3.8 and 2.4 for TPPS2a, mTHPP and mTHPC, respectively), are likely to be due to the protonation of imino nitrogens. The tumor localizing properties of mTHPP and mTHPC reported in the literature appear to be due to factors other than pH-dependent changes in the lipophilicity of the drugs. [source] Core loss depending on magnetizing angle from easy axis in grain-oriented 3% silicon-ironPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004K. S. Ryu Abstract The profiles of ac hysteresis loops have been measured as function of the angle , between H -field and [001] axis in (110)[001] grain oriented 3% silicon-iron. As , increases, for , , 30° the loop changes into a wasp-waisted shape with inflection points. The observed ac hysteresis loop profiles have been analyzed in terms of domain reorientation under field. The core losses in silicon-iron are measured for various magnetizing angles with respect to the easy axis at magnetizing frequency 50 Hz and 60 Hz and at magnetic induction 1.3 T and 1.0 T. At magnetic induction 1.3 T, the core loss increased to near 70° and decreased at magnetizing frequency 60 Hz, but at 50 Hz this trend was different from 60 Hz and the core loss was monotonously increased. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ontogeny of the shi drum Umbrina cirrosa (Linnaeus 1758), a candidate new species for aquacultureAQUACULTURE RESEARCH, Issue 13 2005Giorgos Koumoundouros Abstract The ontogeny of shi drum Umbrina cirrosa (Linnaeus 1758), a candidate new species for aquaculture, was studied throughout the entire larval phase. Geometric morphometric analysis revealed two clear inflection points (7.0 and 12.7 mm total length, TL) in the shape ontogeny of this species, separating the studied period into three phases of different allometric priorities. Spline graphs demonstrated that the major non-uniform shape ontogeny correlated with the development of the fins, the anterior dorsal area of the body, the caudal peduncle, the eye and the mouth. Concerning the morphological features, shi drum larvae are characterized by an upward anterior bending of the notochord. The ontogeny of the fins began with the formation of the pectoral buds (2.9 mm TL), continued with the notochord flexion (4.3 mm TL, associated with the caudal fin development), the appearance of the pelvic buds, the first anal rays (4.5 mm TL) and the first dorsal rays (4.8 mm TL). Shi drum juveniles presented 25 vertebrae and the following dominant fin types: D XI,23, AII,6, VI,5, P17 and C17. [source] | ||||||||||||||||||||||||||||