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Constant Frequency (constant + frequency)
Selected AbstractsA simple instant-estimation method for time-average quantities of single-phase power and application to single-phase power grid connection by inverterELECTRICAL ENGINEERING IN JAPAN, Issue 2 2007Shinji Shinnaka Abstract This paper presents and analyzes a new simple instant-estimation method for time-average quantities such as rms values of voltage and current, active and reactive powers, and power factor for single-phase power with the fundamental component of constant or nearly constant frequency by measuring instantaneous values of voltage and current. According to the analyses, the method can instantly estimate time-average values with accuracy of the fundamental frequency, and estimation accuracy of the power factor is about two times better than that of voltage, current, and powers. The instant-estimation method is simple and can be easily applied to single-phase power control systems that are expected to control instantly and continuously power factor on a single-phase grid by inverter. Based on the proposed instant-estimation method, two methods for such power control systems are also proposed and their usefulness is verified through simulations. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 34,43, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20236 [source] ADVERTISEMENT-CALL PREFERENCES IN DIPLOID-TETRAPLOID TREEFROGS (HYLA CHRYSOSCELIS AND HYLA VERSICOLOR): IMPLICATIONS FOR MATE CHOICE AND THE EVOLUTION OF COMMUNICATION SYSTEMSEVOLUTION, Issue 2 2005H. Carl Gerhardt Abstract Signals used for mate choice and receiver preferences are often assumed to coevolve in a lock-step fashion. However, sender-receiver coevolution can also be nonparallel: even if species differences in signals are mainly quantitative, females of some closely related species have qualitatively different preferences and underlying mechanisms. T o-alternative playback experiments using synthetic calls that differed in fine-scale temporal properties identified the receiver criteria in females of the treefrog Hyla chrysoscelis for comparison with female criteria in a cryptic tetraploid species (H. versicolor); detailed preference functions were also generated for both species based on natural patterns of variation in temporal properties. The species were similar in three respects: (1) pulses of constant frequency were as attractive as the frequency-modulated pulses typical of conspecific calls; (2) changes in preferences with temperature paralleled temperature-dependent changes in male calls; and (3) preference functions were unimodal, with weakly defined peaks estimated at values slightly higher than the estimated means in conspecific calls. There were also species differences: (1) preference function slopes were steeper in H. chrysoscelis than in H. versicolor; (2) preferences were more intensity independent in H. chrysoscelis than in H. versicolor; (3) a synergistic effect of differences in pulse rate and shape on preference strength occurred in H. versicolor but not in H. chrysoscelis; and (4) a preference for the pulse shape typical of conspecific calls was expressed at the species-typical pulse duration in H. versicolor but not in H. chrysoscelis. However, females of H. chrysoscelis did express a preference based on pulse shape when tested with longer-than-average pulses, suggesting a hypothesis that could account for some examples of nonparallel coevolution. Namely, preferences can be hidden or revealed depending on the direction of quantitative change in a signal property relative to the threshold for resolving differences in that property. The results of the experiments reported here also predict patterns of mate choice within and between contemporary populations. First, intraspecific mate choice in both species is expected to be strongly influenced by variation in temperature among calling males. Second, simultaneous differences in pulse rate and pulse shape are required for effective species discrimination by females of H. versicolor but not by females of H. chrysoscelis. Third, there is greater potential for sexual selection within populations and for discrimination against calls produced by males in other geographically remote populations in H. chrysoscelis than in H. versicolor. [source] Multiaxial fatigue criterion for a high-density polyethylene thermoplasticFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2010A. BERREHILI ABSTRACT The multiaxial fatigue behaviour of a high-density polyethylene was investigated at room temperature and constant frequency. As a consequence of the mode of failure, an end-of-life criterion for fatigue tests is discussed in the first part of the work, in order to define the number of cycles to failure. Based on force controlled fatigue tests under tension, compression and torsion at two stress ratio, a multiaxial fatigue criterion including the stress-ratio effect is proposed for the fatigue design of this polymer. This criterion is based on the maximum and mean values of the second invariant of the stress tensor. [source] Dynamics of human neocortex that optimizes its stability and flexibilityINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 9 2006Walter J. Freeman The electroencephalogram (EEG) in states of awake, sleep, and seizure in a patient with intractable partial complex seizures was recorded through a 1- × 1-cm microgrid of 64 electrodes on the right inferior temporal gyrus during a week-long neurosurgical evaluation. Comparisons with a normal intracranial EEG were perforce from animals. Analytic phase and amplitude from the Hilbert transform gave the temporal resolution needed to resolve EEG spatiotemporal structure. The rest state revealed multiple overlapping patterns of high-frequency coherent oscillations resembling bubbles in boiling water. Bubble diameters gave estimates of the distances across the cortex over which the cortical oscillations were synchronized. Superimposed on these bubbles were large-sized epochs of phase locking with briefly constant frequency and high amplitude. These coordinated analytic phase differences occurred between short periods of high phase variance. The variance gave evidence for state transitions between transiently stable states with constant phase gradients. In sleep these phase patterns persisted with reduced amplitude, occasionally interrupted by long-lasting (,1 s) epochs with no spatial textures in phase and amplitude despite a large increase in amplitude. Seizures had high amplitude 3/s spikes with steep spatial gradients. Onset occurred after pre-ictal reduction in bubble diameters as evidence for large-scale cortical disintegration preceding loss of stability. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 881,901, 2006. [source] Polymer dynamics in rubbery epoxy networks/polyhedral oligomeric silsesquioxanes nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Th. Kourkoutsaki Abstract Dielectric techniques, including thermally stimulated depolarization currents (TSDC, ,150 to 30°C) and, mainly, broadband dielectric relaxation spectroscopy (DRS, 10,2 , 106 Hz, ,150 to 150°C) were employed, next to differential scanning calorimetry (DSC), to investigate molecular dynamics in rubbery epoxy networks prepared from diglycidyl ether of Bisphenol A (DGEBA) and poly(oxypropylene)diamine (Jeffamine D2000, molecular mass 2000) and modified with polyhedral oligomeric silsesquioxanes (POSS) units covalently bound to the chains as dangling blocks. Four relaxations were detected and analyzed: in the order of increasing temperature at constant frequency, two local, secondary , and , relaxations in the glassy state, the segmental , relaxation associated with the glass transition and the normal mode relaxation, related with the presence of a dipole moment component along the Jeffamine chain contour. Measurements on pure Jeffamine D2000 helped to clarify the molecular origin of the relaxations observed. A significant reduction of the magnitude and a slight acceleration of the , and of the normal mode relaxations were observed in the modified networks. These results suggest that a fraction of polymer is immobilized, probably at interfaces with POSS, due to constraints imposed by the covalently bound rigid nanoparticles, whereas the rest exhibits a slightly faster dynamics due to increaseof free volume resulting from loosened molecular packing of the chains (plasticization by the bulky POSS units). The increase of free volume is rationalized by density measurements. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Structure,property relationships for film-forming copoly(amide imide)sPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2003Valery P. Privalko Abstract Thin films of copoly(amide imide)s (coPAIs) from dichloro-dianhydride of trimellitimide- N -acetic acid and mixtures of diphenylmethane diamine (DPA) and cardo 9,9,-bis-phenylfluorene diamine (CDA) cast from solutions in dimethylacetamide (DMAA) were characterized by wide-angle and small-angle X-ray scattering (WAXS and SAXS), dynamic mechanical thermal analysis (DMTA) (temperature interval: 293,703,K, frequency range: 1,100,Hz), and thermogravimetric analysis (TGA) (nitrogen flux, temperature interval: 303,973 K). The mean interchain spacings (WAXS) smoothly increased with the CDA/DPA molar ratio from 0.55,nm for CDA/DPA,=,0/1 up to 0.60,nm for CDA/DPA,=,1/0. The smooth patterns of the SAXS curves for all coPAIs were explained by the smearing-out of electron density differences between densely-packed and loosely-packed microregions of coPAIs due to the wide dispersion of their sizes. The step-like patterns of the TGA traces in the temperature intervals below and above 600,K were associated with successive weight losses due to the evaporation of residual water and of DMAA, and to the thermal degradation of diamine and dianhydride chain fragments, respectively. As could be inferred from the TGA data, the loosely-packed regions comprise about 25,35% of the total volume of studied coPAIs. The mechanical relaxations observed in all coPAIs at T,,<,T,,,<,T, (DMA) were attributed to the onset of non-cooperative segment motion in loosely-packed regions, of cooperative segment motion in loosely-packed regions, and of cooperative segment motion in densely-packed regions, respectively. At constant frequency, the sub-glass relaxations were roughly composition-independent, while chain-stiffening effect was assumed to be responsible for the smooth increase of T,, and T,, as well as of the corresponding apparent activation energies with the CDA/DPA ratio. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||