18,321 research outputs found
Modal Analysis of Grid Connected Doubly-Fed Induction Generators
This paper presents the modal analysis of a gridconnected doubly fed induction generator (DFIG). The change in modal properties for different system parameters, operating points, and grid strengths are computed and observed. The results offer a better understanding of theDFIG intrinsic dynamics,which can also be useful for control design and model justification. Index Terms—Doubly fed induction generator, eigenvalue analysis, nonlinear dynamic model, small-signal stability.Published versio
Influence of large deflection and transverse shear on random response of rectangular symmetric composite laminates to acoustic loads
Nonlinear equations of motion of symmetrically laminated anisotropic plates are derived accounting for von Karman strains. The effect of transverse shear is included in the formulation and the rotatory inertia effect is ignored. Using a single-mode Galerkin procedure the nonlinear modal equation is obtained. Direct equivalent linearization is employed. The response of acoustic excitation on moderately thick composite panels is studied. Further, the effects of transverse shear on large deflection vibration of laminates under random excitation are studied. Mean-square deflection and mean-square inplane stresses are obtained for some symmetric graphite-epoxy laminates. Using equilibrium equations and the continuity requirements, the mean-square transverse shear stresses are calculated. The results obtained will be useful in the sonic fatigue design of composite aircraft panels. The analysis is presented in detail for simply supported plate. The analogous equations for a clamped case are given in the appendix
A cluster expansion approach to renormalization group transformations
The renormalization group (RG) approach is largely responsible for the
considerable success which has been achieved in developing a quantitative
theory of phase transitions. This work treats the rigorous definition of the RG
map for classical Ising-type lattice systems in the infinite volume limit at
high temperature. A cluster expansion is used to justify the existence of the
partial derivatives of the renormalized interaction with respect to the
original interaction. This expansion is derived from the formal expressions,
but it is itself well-defined and convergent. Suppose in addition that the
original interaction is finite-range and translation-invariant. We will show
that the matrix of partial derivatives in this case displays an approximate
band property. This in turn gives an upper bound for the RG linearization.Comment: 13 page
Intensities of backscatter Mössbauer spectra
The intensities of γ‐ray and x‐ray backscatter Mössbauer spectra of ^(57)Fe nuclei in different matrix materials were studied theoretically and experimentally. A previous analysis by J. J. Bara [Phys. Status Solidi A 58, 349 (1980] showed that negative peak intensities occur in backscatter γ‐ray spectra when the ^(57)Fe nuclei are in a matrix of light elements. We report a confirmation of this work and offer a simple explanation of the phenomenon. The present paper extends Bara’s analysis to the case of conversion x‐ray spectra; expressions for the intensity of conversion x‐ray spectra as a function of absorber thickness and absorber material parameters are presented. We show that negative peak intensities are expected in conversion x‐ray spectra when the ^(57)Fe nuclei are in a matrix of heavy elements
Pseudoscalar-photon Interactions, Axions, Non-Minimal Extensions, and Their Empirical Constraints from Observations
Pseudoscalar-photon interactions were proposed in the study of the relations
among equivalence principles. The interaction of pseudoscalar axion with gluons
was proposed as a way to solve the strong CP problem. Subsequent proposal of
axion as a dark matter candidate has been a focus of search. Motivation from
superstring theories add to its importance. After a brief introduction and
historical review, we present (i) the current status of our optical experiment
using high-finesse Fabry-Perot resonant cavity - Q & A experiment - to detect
pseudoscalar-photon interactions, (ii) the constraints on pseudoscalar-photon
interactions from astrophysical and cosmological observations on cosmic
polarization rotation, and (iii) theoretical models of non-minimal interactions
of gravitational, electromagnetic and pseudoscalar (axion) fields, and their
relevance to cosmology.Comment: 8 page
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Supporting proactive management in the context of climate change: Prioritizaing range-shifting invasive plants based on impact
Non-native, invasive plants are projected to shift their ranges with climate change, creating hotspots of risk where a multitude of novel species may soon establish and spread. The Northeast U.S. is one such hotspot. However, because monitoring for novel species is costly, these range-shifting invasive plants need to be prioritized. Preventing negative impacts is a key goal of management, thus, comparing the potential impacts of range-shifting invasive species could inform this prioritization. Here, we adapted the Environmental Impacts Classification for Alien Taxa (EICAT) protocol to evaluate potential impacts of 100 invasive plants that could establish either currently or by 2050 in the states of New York, Massachusetts, Connecticut, or Rhode Island. We searched Web of Science for each species and identified papers reporting ecological, economic, human health, or agricultural impacts. We scored ecological impacts from 1 (‘minimal concern’) to 4 (‘major’) and socio-ecological impacts as present or absent. We evaluated 865 impact studies and categorized 20 species as high-impact, 36 as medium-impact, and 26 as low-impact. We further refined high-impact invasive species based on whether major impacts affect ecosystems found in Northeast U.S. and identified five high-priority species: Anthriscus caucalis, Arundo donax, Avena barbata, Ludwigia grandiflora, and Rubus ulmifolius. Additional research is needed for 18 data-deficient species, which had no studies reporting impacts. Identifying and prioritizing range-shifting invasive plants provides a unique opportunity for early detection and rapid response that targets future problem species before they can establish and spread. This research illustrates the feasibility of using impacts assessments on range-shifting invasive species in order to inform proactive policy and management
Interfacial chemical oxidative synthesis of multifunctional polyfluoranthene.
A novel polyfluoranthene (PFA) exhibiting strong visual fluorescence emission, a highly amplified quenching effect, and widely controllable electrical conductivity is synthesized by the direct cationic oxidative polymerization of fluoranthene in a dynamic interface between n-hexane and nitromethane containing fluoranthene and FeCl3, respectively. A full characterization of the molecular structure signifies that the PFAs have a degree of polymerization from 22-50 depending on the polymerization conditions. A polymerization mechanism at the interface of the hexane/nitromethane biphasic system is proposed. The conductivity of the PFA is tunable from 6.4 × 10-6 to 0.074 S cm-1 by doping with HCl or iodine. The conductivity can be significantly enhanced to 150 S cm-1 by heat treatment at 1100 °C in argon. A PFA-based chemosensor shows a highly selective sensitivity for Fe3+ detection which is unaffected by other common metal ions. The detection of Fe3+ likely involves the synergistic effect of well-distributed π-conjugated electrons throughout the PFA helical chains that function as both the fluorophore and the receptor units
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