Relevant bibliographies by topics / Lower order perturbation

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Lower order perturbation'

Author: Grafiati
Published: 22 February 2023
Last updated: 19 July 2025

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Journal articles on the topic "Lower order perturbation"

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Hu, Yu-Min, Bi-Chu Li, Yang Yu, Martin Krššák, Emmanuel N. Saridakis, and Yi-Fu Cai. "Lowering the strong coupling mode of modified teleparallel gravity theories." Journal of Cosmology and Astroparticle Physics 2025, no. 05 (2025): 088. https://doi.org/10.1088/1475-7516/2025/05/088.

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Abstract We investigate the strong coupling problem in modified teleparallel gravity theories using the effective field theory (EFT) approach, demonstrating that it is possible to shift the emergence of new degrees of freedom (DoFs) to lower orders in perturbation theory. We first focus on the case of f(T) gravity, and we show that in its conformally equivalent form the scalar perturbations are non-dynamical up to the cubic action. We then propose a simple modification of the theory, which lowers the appearance of new DoFs to cubic order, compared to the quartic order in standard f(T) gravity. Our work opens a new avenue to address the issue of strong coupling in modified teleparallel gravity, and suggests a new classification scheme of these theories based on the perturbative order at which new DoFs appear.
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AZHAR, Muhammad Raees Furquan, Umair ZULFIQAR, and Muwahida LIAQUAT. "Lower order controller design using weighted singular perturbation approximation." TURKISH JOURNAL OF ELECTRICAL ENGINEERING & COMPUTER SCIENCES 27, no. 5 (2019): 3935–50. http://dx.doi.org/10.3906/elk-1807-4.

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DASH, JAN W. "MULTIVARIATE INTEGRAL PERTURBATION TECHNIQUES I: THEORY." International Journal of Theoretical and Applied Finance 10, no. 08 (2007): 1287–304. http://dx.doi.org/10.1142/s0219024907004652.

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We present a quasi-analytic perturbation expansion for multivariate N-dimensional Gaussian integrals. The perturbation expansion is an infinite series of lower-dimensional integrals (one-dimensional in the simplest approximation). This perturbative idea can also be applied to multivariate Student-t integrals. We evaluate the perturbation expansion explicitly through 2nd order, and discuss the convergence, including enhancement using Padé approximants. Brief comments on potential applications in finance are given, including options, models for credit risk and derivatives, and correlation sensitivities.
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GUERRERO, J., and V. ALDAYA. "A PERTURBATIVE APPROACH TO THE RELATIVISTIC HARMONIC OSCILLATOR AND UNITARITY." Modern Physics Letters A 14, no. 25 (1999): 1689–99. http://dx.doi.org/10.1142/s0217732399001784.

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A quantum realization of the relativistic Harmonic oscillator is achieved in terms of the spatial variable x and [Formula: see text] (the minimal canonical representation). The Hamiltonian operator is found (at lower order) by using a perturbative expansion in the constant c-1. Unlike the Foldy–Wouthuysen version of the relativistic hydrogen atom, conventional perturbation theory cannot be applied and a perturbation of the scalar product itself is required to make the theory unitary.
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Grzywny, Tomasz, Tomasz Jakubowski, and Grzegorz Żurek. "Green function for gradient perturbation of unimodal Lévy processes." Probability and Mathematical Statistics 37, no. 1 (2018): 119–43. http://dx.doi.org/10.19195/0208-4147.37.1.5.

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GREEN FUNCTION FOR GRADIENT PERTURBATION OF UNIMODAL LÉVY PROCESSESWe prove that the Green function of a generator of isotropic unimodal Lévy processes with the weak lower scaling order greater thanone and the Green function of its gradient perturbations are comparable for bounded smooth open sets if the drift function is from an appropriate Kato class.
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Liu, J. K., and H. C. Chan. "Universal Matrix Perturbation Method for Structural Dynamic Reanalysis of General Damped Gyroscopic Systems." Journal of Vibration and Control 10, no. 4 (2004): 525–41. http://dx.doi.org/10.1177/1077546304036230.

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We investigate an effective matrix perturbation method for structural dynamic reanalysis of general damped gyroscopic systems. By using the complex eigensubspace condensation and the or thogonal decomposition procedures, two greatly reduced generalized eigenvalue equations are obtained. The lower-order perturbations of eigensolutions (i.e. complex eigenvalues and the corresponding left and right eigenvectors) are then determined by solving the two reduced eigenvalue problems. The higher-order perturbations of eigensolutions are obtained by executing a singular value decomposition procedure for a complex matrix. The proposed method is a universal perturbation method, for it is universally applicable to the reanalysis of general damped gyroscopic systems with all three cases of complex eigenvalues: distinct, repeated, and closely spaced eigenvalues. Numerical examples corresponding to the three different cases of eigenvalues are presented. The perturbed eigensolutions are computed using the present method and compared with the exact solutions.
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Takeuchi, Akitsugu. "On the Convective Stability of Solar Photospheric Flux Tubes." Publications of the Astronomical Society of Japan 47, no. 3 (1995): 331–36. https://doi.org/10.1093/pasj/47.3.331.

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Abstract One-dimensional magnetohydrodynamic (MHD) numerical simulations were performed in order to investigate the convective stability of an intense photosheric flux tube, adopting the thin flux-tube approximation. The radiative heat exchange between the flux tube and its surroundings was also taken into account using Newton's law of cooling. To study the stability, we examined the temporal evolution of a small perturbation (downflow) added to an initial atmosphere. When a closed-boundary condition is adopted at the lower boundary, the perturbation evolves into a longitudinal overstable oscillation. However, an open (flow-through) condition at the lower boundary should be more suitable for representing the actual solar conditions, because a closed condition excludes the leakage of perturbations through the boundary. We thus repeated the simulation while adopting an open condition for the lower boundary. As a result, it was shown that the perturbation does not evolve into an overstable oscillation, but, rather, leaks out completely through the lower boundary. Our results imply that the actual photospheric flux tubes are in a convectively stable state, consistent with the recent observational results.
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Chabrowski, J. "On a critical Neumann problem with a perturbation of lower order." Acta Mathematicae Applicatae Sinica, English Series 24, no. 3 (2008): 441–52. http://dx.doi.org/10.1007/s10255-008-8038-5.

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Rubakov, V. A., and O. Yu Shvedov. "Sphalerons and large order behaviour of perturbation theory in lower dimension." Nuclear Physics B 434, no. 1-2 (1995): 245–63. http://dx.doi.org/10.1016/0550-3213(94)00447-m.

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Sawicki, Jerzy T., and T. V. V. L. N. Rao. "A Nonlinear Model for Prediction of Dynamic Coefficients in a Hydrodynamic Journal Bearing." International Journal of Rotating Machinery 10, no. 6 (2004): 507–13. http://dx.doi.org/10.1155/s1023621x04000508.

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This paper investigates the variation of nonlinear stiffness and damping coefficients in a journal orbit with respect to equilibrium position. The journal orbit is obtained by the combined solution of equations of motion and Reynolds equation. In the linearized dynamic analysis, dynamic pressure is written as a perturbation of static pressure and pressure gradients at equilibrium position. However, in order to obtain nonlinear dynamic coefficients about equilibrium position, the dynamic pressure gradients in the orbit are also written as the first order perturbation of static pressure gradients and higher order pressure gradients for displacement and velocity perturbations. The dynamic coefficients are functions of bearing displacement and velocity perturbations. The higher order pressure gradients at equilibrium position are evaluated at various eccentricity ratios and L/D ratios of 0.5 and 1.0. The variation of nonlinear dynamic coefficients is analyzed for three Sommerfeld numbers of a two-axial groove journal bearing under the action of an external synchronous load along and perpendicular to the radial journal load. Results indicate that the oil film nonlinearities affect the journal motion at lower eccentricity ratios (higher Sommerfeld numbers) with wide variation in stiffness and damping coefficients.
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Dissertations / Theses on the topic "Lower order perturbation"

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Lee, Haewon. "Nolinear Evolution Equations and Optimization Problems in Banach Spaces." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1127498683.

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CLEMENTE, FRANCESCO. "On some nonlinear elliptic Dirichlet problems with lower order terms." Doctoral thesis, 2020. http://hdl.handle.net/11573/1360409.

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This Ph.D. Thesis is devoted to boundary value problems associated to some classes of second order nonlinear elliptic PDEs in bounded open subsets of R^N. More precisely, we consider, first, two classes of noncoercive Dirichlet problems and we study the regularizing effect of a lower order term of power type on the summability properties of solutions. Then, for one class, we investigate the asymptotic behaviour of solutions as the power goes to infinity, while, for the other, we analyse local properties of solutions depending on local properties of data (with and without the lower order term of power type). Finally, the last topic is also studied for a class of nonlinear elliptic Dirichlet problems with a singular nonlinearity.
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Book chapters on the topic "Lower order perturbation"

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Cruz-Uribe, David, Alberto Fiorenza, Michael Ruzhansky, and Jens Wirth. "Effective lower order perturbations." In Variable Lebesgue Spaces and Hyperbolic Systems. Springer Basel, 2014. http://dx.doi.org/10.1007/978-3-0348-0840-8_9.

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Gazzola, Filippo, Hans-Christoph Grunau, and Guido Sweers. "Positivity and Lower Order Perturbations." In Lecture Notes in Mathematics. Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12245-3_5.

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Xie, Jiaqiang, and Wei Kuang. "Simulation of the Mixing Performance of an Optimized Air Injector." In Lecture Notes in Mechanical Engineering. Springer Nature Singapore, 2025. https://doi.org/10.1007/978-981-97-7887-4_99.

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Abstract The trim air system is an important system for realizing the temperature control of the flight deck and passenger cabin of commercial aircraft. The trim air duct is designed to bleed the high-temperature air to mix the cold air from the upstream of the refrigeration components in order to satisfy the independent temperature requirements of each area of the flight deck and passenger cabin. If the cold air and hot air mixing situation was poor, downstream temperature sensor layout location there is still a more serious hot and cold air stratification, the measured value is more difficult to reflect the average temperature of the mixed air, thus affecting the accuracy of the air conditioning system temperature regulation. In order to improve the mixing efficiency of the trim hot bleed air and ventilation air, this paper proposes an optimized trim air injector based on typical configuration, then models and calculates two configurations of the trim injector using three-dimensional simulation to obtain the fluid flow and temperature distribution characteristics under different conditions. In this paper, the MAX temperature difference, the Surface standard deviation of temperature, the Surface uniformity of temperature and other parameters are also utilized to model and calculate the air flow and temperature distribution characteristics of the two configurations of the trim injector. The mixing effects of the two trim injectors were analyzed and evaluated. The results show that, after optimization, the radial high-speed thermal jet can effectively improve the perturbation and mixing between the hot and cold fluids after the hot bleed air passes through the inflow nozzle; compared with the typical configuration, the optimized configuration has a lower maximum temperature difference of about 67% and a lower standard deviation of temperature of 71% in each cross-section. The surface temperature uniformity coefficient of the optimized configuration is closer to 1 in each cross-section, and the temperature stratification effect and mixing effect are better than that of the typical configuration.
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Kenny, S. D., G. Rajagopal, r. J. Needs, et al. "Quantum Monte Carlo calculations of the energy of the relativistic homogeneous electron gas." In Quantum Monte Carlo. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00105.

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Abstract Several earlier QMC calculations0,b had been successful in predicting the energy of the homogeneous electron gas. This paper extended the earlier work to include relativistic effects with use of first-order perturbation theory for a wide range of densities. The required perturbation expression was derived in the 1950s. It consists of four terms known as the mass-velocity, Darwin, contact, and retardation terms. The small perturbative correction to the nonrelativistic energy is given by the sum of the expectation values of the individual terms The wavefunctions were obtained from variational and fixed-node diffusion calculations. The system was treated as a face-centered cubic simulation cell with periodic boundary conditions, containing up to 338 electrons for the variational and 178 electrons for the diffusion calculations. The trial functions 1/JT were composed of Slater determinants of plane waves, along with Jastrow factors. The required integrals based on ff were accumulated with Metropolis sampling, and those based on J1/}T were accumulated with importance-sampling diffusion simulations. Values based on lp2 were obtained by extrapolation The mass-velocity term was found to dominate at high densities and to agree with Hartree-Fock results. At lower densities the mass-velocity term from QMC was a factor of three larger than for HF, but the retardation term was dominant and much larger than predicted by HF. Overall, the results show clearly the importance of correlation, even for relativistic effects.
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Ross, John, Igor Schreiber, and Marcel O. Vlad. "Experimental Test of the Pulse Perturbation Method for Determining Causal Connectivities of Chemical Species in a Reaction Network." In Determination of Complex Reaction Mechanisms. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780195178685.003.0008.

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For an experimental test of the pulse perturbation method we choose a part of glycolysis shown in fig. 6.1. There are similarities and some differences between the model in fig. 5.12 and the reaction system in fig. 6.1. The reaction system has reactants, enzymes, and some effectors. One point of interest in choosing this system is the test of detecting and identifying the split of the reaction chain, from glucose to F1,6BP, at the aldolase reaction into two chains, one terminating at G3P and the other at 3PG. The experiments were run in a continuous-flow stirred tank reactor (CSTR) with the reaction system at a nonequilibrium stationary state, such that the reactions run spontaneously from glucose to G3P and 3PG. The concentrations of the species at this state are close to those of physiological conditions. The metabolites G6P, F6P, F1,6BP, DHAP, G3P, and 3PG were detected and analyzed by capillary electrophoresis. Typical relative errors were 4% for G6P, 11% for F6P, 15% for F1,6BP, 9% for DHAP, 6% for 3PG, and 3% for G3P. Figure 6.3 shows the responses of the species to a pulse of G6P, in a plot of relative concentrations versus. time during the relaxation, after the pulse, back to the stationary state. Complete relaxation took about half an hour. As seen from the amplitudes of the responses in the plot, the temporal order of propagation of the pulse is: G6P, F6P, DHAP, G3P, and 3PG. The time ordering of the maximum deviations agrees with this ordering except perhaps for G3P and 3PG. In some experiments, as in this one, the species F1,6BP could not be measured adequately and is not shown. It is possible to extract qualitative information on rates but difficult to derive quantitative information. Following a pulse of F1,6BP, the temporal order of propagation in the maximum relative concentrations is F1,6BP, DHAP, and with similar amplitudes G6P (slightly higher), G3P, 3PG, and F6P (slightly lower). These small differences were within errors of measurement and are therefore not significant. In this experiment the measurements of F1,6BP are reliable.
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Chan, Benny K. K., Kingsley J. H. Wong, and Yu-Rong Cheng. "Biogeography and Host Usage of Coral-Associated Crustaceans: Barnacles, Copepods, and Gall Crabs as Model Organisms." In Evolution and Biogeography. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190637842.003.0008.

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Most of the diverse groups of crustaceans associated with scleractinian and fire corals form symbiotic relationship with their coral hosts. Coral-associated barnacles include species from the orders Acrothoracica and Thoracica. Most of the coral-associated barnacles belong to the family Pyrgomatidae in Thoracica. Within Pyrgomatidae, the subfamily Ceratoconchinae contains mostly extant species and is present from Florida through the Caribbean to Brazilian waters. The subfamily Megatrematinae has lower species diversity and has a cosmopolitan distribution (except the Eastern Pacific). The Pyrgomatinae are the most species-rich subfamily and distributed only in Indo-West Pacific waters. Host usage of pyrgomatinid barnacles varies spatially, probably related to coral host diversity. Copepods are the most common and most abundant coral-associated crustaceans, often associated with scleractinian, gorgonian, and alcyonacean corals. More than 90% of coral-associated copepods are endemic to the Indo-West Pacific. In contrast, only a few species (<10%) have been discovered from the Atlantic due to several historical perturbations reducing the diversity of their coral hosts. The communities of coral-associated copepods thus show dramatic differences between geographic regions, notably between the Indian, Pacific, and Atlantic Oceans. Brachyurans of the family Cryptochiridae (gall crabs) are obligate associates or parasites, of scleractinian coral hosts in tropical and subtropical seas, being a monophyletic group of only 52 species, from the intertidal to the deep sea (to 512 m) habitats with most (46) recorded in the seas of the tropical Indo-West Pacific and none being cosmopolitan. Atlantic species of Cryptochiridae, apparently not phylogenetically related, display less strict host specificity than their Indo-West Pacific counterparts. Current phylogenetic understandings of the group remain preliminary, while one consistent Indo-West Pacific clade reflects rapid species diversification during the last ~15 million years.
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Conference papers on the topic "Lower order perturbation"

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Motahari, Nicholas, Nandeesh Hiremath, and Narayanan Komerath. "Towards Generalized Certification of Slung Load Flight Envelopes." In Vertical Flight Society 72nd Annual Forum & Technology Display. The Vertical Flight Society, 2016. http://dx.doi.org/10.4050/f-0072-2016-11501.

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An alternative is sought to individual full-scale flight testing in order to certify the safe flight envelope for every combination of helicopter and slung load. The major uncertainty has been the difficulty in obtaining reliable aerodynamic load maps for use in dynamic simulation. The possibility of reliable certification based on an iterative process is discussed. Knowledge bases with parametric variation of canonical shapes are now feasible using the Continuous Rotation method. The test case of an empty engine canister is considered. An initial estimate of dynamics based on interpolation from a canonical knowledge base shows surprising accuracy, when the initial level of perturbation is adjusted. This is followed with scale model experimental data at different levels of detail, compared to estimates from knowledge of the geometry and inertia. It is shown that initial perturbation level changes the amplification path, but the eventual divergence speed is uncertain to less than 10 percent. Higher perturbation levels cause lower divergence speed as expected. Intermediate amplification behavior is also captured.
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Severnyak, Alexei, Edward Smith, and Christopher Rahn. "Multi-Axis Active Vibration Damping Using Electric Rotor Torque with Pitch-Lag Coupling in eVTOL Aircraft: Demonstration of Concept." In Vertical Flight Society 81st Annual Forum and Technology Display. The Vertical Flight Society, 2025. https://doi.org/10.4050/f-0081-2025-399.

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Active vibration damping by rotor torque modulation has been demonstrated for vibratory modes in the rotor disk plane. In this study, we introduce a simple, first-principles model, which includes kinematic coupling between lag movement and blade pitch, in order to extend damping authority to strut vibratory modes normal to the rotor disk plane. Using a medium-sized (12kg) quadcopter drone model, we demonstrate the capability to excite strut vibrations normal to the rotor disk plane, indicating control authority for vibration damping. For this vehicle model, a steady state strut deflection of over 12% is obtained using a 15% voltage perturbation, with under 2% rotor speed change. Redesign of the vehicle to have lower and/or co-located lag and structural frequencies increases the control authority of rotor torque actuation with pitch-lag coupling.
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Flores-G�mez, Luis R., Fernando I. G�mez-Castro, Francisco L�pez-Villarreal, and Vicente Rico-Ram�rez. "Implementation and assessment of fractional controllers for an extractive distillation system." In The 35th European Symposium on Computer Aided Process Engineering. PSE Press, 2025. https://doi.org/10.69997/sct.181543.

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This work presents an approach to implement and assess fractional controllers in an extractive distillation system. The experimental dynamic data for an extractive distillation column is used as a case study. A strategy is developed to fit the operation data to fractional-order transfer functions. Then, the fractional controllers are designed in the Simulink environment in Matlab, tuning the controllers through a hybrid optimization approach. First, the approach uses a genetic algorithm to find an initial point, and then the solution is improved through the fmincon algorithm. According to the results of the design of fractional controllers, the sum of the square of errors is below 2.9x10-6 for perturbations in heat duty, and 1.2x10-5 for perturbations in the reflux ratio. Moreover, after controller tuning, a minimal value for ISE of 1,278.12 is obtained, which is approximately 8% lower than the value obtained for an integer-order controller.
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Fennelly, A. J. "Generalized gauge-invariant perturbations of optical fibers." In OSA Annual Meeting. Optica Publishing Group, 1987. http://dx.doi.org/10.1364/oam.1987.wy3.

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Review of the effects of different perturbations of optical fibers shows that their physical effects are generally identical: that usually is the transfer of the lower-order modes (as measured in the far field) to the higher-order modes of the fiber. This is so for the general classes of microbends, macrobends, pressure variations, temperature variations, and chemical changes. This means that rather than being truly different perturbations, they are physically really the same thing. Each represents a true gauge-invariant perturbation plus a piece that is merely a gauge transformation. Each perturbation is then transformable, and their apparent differences are physically trivial. We take as our points of departure the perturbed fiber discussions of Snyder and Love1 and Hill’s2 analysis of differential equations from their group invariance properties. We analyze the modal structure of unperturbed fiber in terms of the invariance group of the wave equation for the appropriate fiber geometries and boundary conditions and then show how their perturbations consist of a true physical piece and insignificant parts that are just gauge transformations of each other.
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Sawyer, W. Gregory, and John A. Tichy. "Non-Newtonian Lubrication With the Second Order Fluid." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0468.

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Abstract In certain applications where the lubricant is subjected to rapidly changing conditions along its flowing path (such as an elastohydrodynamic contact), the inherently time dependent nature of the lubricant may be significant. The simplest type of model to correctly account for such time dependence is the second order fluid, which is a systematic small departure from Newtonian behavior, involving higher order rate-of-rate-of strain tensors. Using a regular perturbation in the Deborah number, with the conventional lubrication case as the leading term, a solution can be obtained. Viscoelasticity may raise or lower pressure depending on the nature of edge boundary conditions.
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Rajagopal, K. R. "On the Development of Boundary Layers in Non-Newtonian Fluids." In ASME 1997 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/imece1997-0467.

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Abstract Boundary layers, regions of concentration of vorticity, appear adjacent to boundaries in the flow of a linearly viscous fluid at high Reynolds numbers. When the equations governing the flow of the linearly viscous fluid are appropriately non-dimensionalized, we find that the inertial term is multiplied by the Reynolds number, and this term while it is the only non-linear term in the equation is of lower order than the highest order term in the equation usually leading to a singular perturbation problem at high Reynolds numbers. The study of boundary layers in such fluids has led to significant developments in singular perturbation theory.
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Idahosa, Uyi, Abhishek Saha, Navid Khatami, Chengying Xu, and Saptarshi Basu. "Acoustic Perturbation Effects on the Fluid Dynamics and Swirling Flame Response in a Non-Premixed Co-Flow Burner." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23735.

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An investigation into the response of non-premixed swirling flames to acoustic perturbations at various frequencies (fp = 0–315 Hz) and swirl intensities (S = 0.09 and 0.34) is carried out. Perturbations are generated using a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes |u′/Uavg| in the 0.03–0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. Flame heat release is quantitatively measured and simultaneously imaged using a photomultiplier (PMT) and a phase-locked CCD camera. Both of which are fitted with 430nm bandpass filters for observing CH*chemiluminescence. The flame response is observed to exhibit a low-pass filter characteristic with minimal flame response beyond pulsing frequencies of 200Hz. Flames at lower fuel flow rates are observed to remain attached to the central fuel pipe at all acoustic pulsing frequencies. PIV imaging of the associated isothermal fields show the amplification in flame aspect ratio is caused by the narrowing of the inner recirculation zone (IRZ). The Rayleigh criterion (R) is used to assess the potential for instability of specific perturbation configurations and is found to be a good predictor of unstable modes. Phase conditioned analysis of the flame dynamics yield additional criteria in highly responsive modes to include the effective amplitude of velocity oscillations induced by the acoustic pulsing. Highly amplified responses were observed in pulsed flame configurations with Strouhal numbers (St = fpUavg/dm) in the 1–3.5 range. Heat release to velocity perturbation time delays on the order of the acoustic pulsing period also characterized the highly responsive flames. Finally, wavelet analyses of heat release perturbations indicate sustained low frequency oscillations that become more prominent for low acoustic pulsing frequencies in lean flame configurations.
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Caruntu, Dumitru I., Israel Martinez, and Martin W. Knecht. "Reduced Order Model of Electrostatically Actuated MEMS Resonators Resonance Near Half Natural Frequency." In ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-70326.

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This paper uses the Reduced Order Model (ROM) method to investigate the influence of nonlinearities from parametric electrostatic excitation due to soft AC voltage of frequency near half natural frequency of the MEMS cantilever resonator on its frequency response. Most of the analysis in literature investigates pull-in phenomenon, stability, amplitude–frequency relations, or finds time responses of such systems. In this work it is showed that the bifurcation points in the amplitude-frequency response occur at lower frequencies and amplitudes than predicted by the Method of Multiple Scales (MMS), a perturbation method. This result is extremely important for predicting pull-in phenomena. Also the ROM predicts pull-in instability for large initial amplitudes and AC frequencies less than half natural frequency of the resonator. MMS fails to predict this behavior. Increasing the damping and/or decreasing the voltage increases the frequency at which the system undergoes into a pull-in phenomenon.
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Kolarski, Aleksandra, Aleksandra Nina, Vladimir A. Srećković, and Filip Arnaut. "MONITORING SOLAR FLARES AND GAMMA RAY BURSTS: MULTI-INSTRUMENTAL APPROACH INVESTIGATION." In VI Conference on Active Galactic Nuclei and ravitational Lensing. Astronomical Observatory Belgrade, Volgina 7, 11060 Belgrade 38, Serbia, 2024. http://dx.doi.org/10.69646/aob24010.

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In this paper ionospheric phenomena were studied by utilization of VLF (Very Low Frequency radio signals, 3-30 kHz) technology for monitoring of lower ionospheric plasma response to driving agents originating both within our solar system, e.g. on Sun like solar flare (SF) events, and beyond our solar system, e.g. like gamma ray bursts (GRBs), with time span that encompasses period of several years. The data on X-ray fluxes measured by Geostationary Operational Environmental Satellites (GOES) were taken from NOAA National Centers for Environmental Information database, while data on GRBs were taken from Swift satellite database. VLF signal amplitude and phase data were monitored along multiple radio signal paths using network of VLF transmitters globally positioned worldwide and received in Belgrade, Serbia by BEL receiving system, covering mainly European subcontinent. Short-termed ionospheric perturbation associated with GRBs and relatively longer-lasting ionospheric perturbations associated with SFs were compared in order to study similarities and differences in ionospheric plasma responses to these fundamentally different driving mechanisms. Acknowledgments , , , The authors acknowledge the support from the Institute of Physics Belgrade which was made possible by grants from the Ministry of Science, Technological Development and Innovation of the Republic of Serbia.
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Macquisten, M. A., M. Whiteman, and J. A. Moran. "Application of Low Order Thermo-Acoustic Network to DLE Staged Combustor." In ASME Turbo Expo 2004: Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-54161.

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Lean premixed combustors have been developed to meet stringent NOx emission legislation. Operating close to the lean limit introduces a susceptibility to combustion oscillations, which have a damaging impact on hardware and affect combustor performance. The RB211 DLE aero derivative gas turbine has to be CO and NOx compliant from 60% power. Therefore the required turndown must be incorporated into the design. This is achieved by the addition of a second combustion stage, which provides the required CO burn out. Combustion instabilities can occur at different primary and secondary combustion temperatures in the form of noise islands. A 1/2 wave mode has been identified at high primary zonal temperatures and occurs over a certain range of secondary zonal temperatures. This observation suggests that the secondary flame can excite or dampen the instability depending on the phase relationship between the associated dynamic pressure and the fluctuating heat release rate. The mechanism is though to be fluctuations in temperature originating from the primary flame and convecting to the secondary flame. A second mode is observed at lower primary combustion temperatures, involving the axial combustor length and the circumference of the whole combustion system. A low order thermoacoustic network has been created by Stow et al [1] for the purpose of analysing eigen modes within aero annular combustors. This low order network is used to model the RB211 DLE combustion system. It uses linear perturbation theory to predict the eigen frequencies in the combustion system. Coupling between the unsteady flow and the fluctuating heat release rate is represented by a simple transfer function in both combustion zones. Results and discussion are given for both acoustic modes encountered on the RB211 DLE combustion system.
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