Terms Of Transfer Function Research Articles

Critical dynamics of Hopf bifurcations in the corticothalamic system: Transitions from normal arousal states to epileptic seizures

A physiologically based corticothalamic model of large-scale brain activity is used to analyze critical dynamics of transitions from normal arousal states to epileptic seizures, which correspond to Hopf bifurcations. This relates an abstract normal form quantitatively to underlying physiology that includes neural dynamics, axonal propagation, and time delays. Thus, a bridge is constructed that enables normal forms to be used to interpret quantitative data. The normal form of the Hopf bifurcations with delays is derived using Hale's theory, the center manifold theorem, and normal form analysis, and it is found to be explicitly expressed in terms of transfer functions and the sensitivity matrix of a reduced open-loop system. It can be applied to understand the effect of each physiological parameter on the critical dynamics and determine whether the Hopf bifurcation is supercritical or subcritical in instabilities that lead to absence and tonic-clonic seizures. Furthermore, the effects of thalamic and cortical nonlinearities on the bifurcation type are investigated, with implications for the roles of underlying physiology. The theoretical predictions about the bifurcation type and the onset dynamics are confirmed by numerical simulations and provide physiologically based criteria for determining bifurcation types from first principles. The results are consistent with experimental data from previous studies, imply that new regimes of seizure transitions may exist in clinical settings, and provide a simplified basis for control-systems interventions. Using the normal form, and the full equations from which it is derived, more complex dynamics, such as quasiperiodic cycles and saddle cycles, are discovered near the critical points of the subcritical Hopf bifurcations.

A history of cepstrum analysis and its application to mechanical problems

It is not widely realised that the first paper on cepstrum analysis was published two years before the FFT algorithm, despite having Tukey as a common author, and its definition was such that it was not reversible even to the log spectrum. After publication of the FFT in 1965, the cepstrum was redefined so as to be reversible to the log spectrum, and shortly afterwards Oppenheim and Schafer defined the “complex cepstrum”, which was reversible to the time domain. They also derived the analytical form of the complex cepstrum of a transfer function in terms of its poles and zeros. The cepstrum had been used in speech analysis for determining voice pitch (by accurately measuring the harmonic spacing), but also for separating the formants (transfer function of the vocal tract) from voiced and unvoiced sources, and this led quite early to similar applications in mechanics. The first was to gear diagnostics (Randall), where the cepstrum greatly simplified the interpretation of the sideband families associated with local faults in gears, and the second was to extraction of diesel engine cylinder pressure signals from acoustic response measurements (Lyon and Ordubadi). Later Polydoros defined the differential cepstrum, which had an analytical form similar to the impulse response function, and Gao and Randall used this and the complex cepstrum in the application of cepstrum analysis to modal analysis of mechanical structures. Antoni proposed the mean differential cepstrum, which gave a smoothed result. The cepstrum can be applied to MIMO systems if at least one SIMO response can be separated, and a number of blind source separation techniques have been proposed for this. Most recently it has been shown that even though it is not possible to apply the complex cepstrum to stationary signals, it is possible to use the real cepstrum to edit their (log) amplitude spectrum, and combine this with the original phase to obtain edited time signals. This has already been used for a wide range of mechanical applications. A very powerful processing tool is an exponential “lifter” (window) applied to the cepstrum, which is shown to extract the modal part of the response (with a small extra damping of each mode corresponding to the window). This can then be used to repress or enhance the modal information in the response according to the application.

Investigating the Consistency of Models for Water Splitting Systems by Light and Voltage Modulated Techniques.

The optimization of solar energy conversion devices relies on their accurate and nondestructive characterization. The small voltage perturbation techniques of impedance spectroscopy (IS) have proven to be very powerful to identify the main charge storage modes and charge transfer processes that control device operation. Here we establish the general connection between IS and light modulated techniques such as intensity modulated photocurrent (IMPS) and photovoltage spectroscopies (IMVS) for a general system that converts light to energy. We subsequently show how these techniques are related to the steady-state photocurrent and photovoltage and the external quantum efficiency. Finally, we express the IMPS and IMVS transfer functions in terms of the capacitive and resistive features of a general equivalent circuit of IS for the case of a photoanode used for solar fuel production. We critically discuss how much knowledge can be extracted from the combined use of those three techniques.

Single and Multiband Acoustic-Wave-Lumped- Element-Resonator (AWLR) Bandpass Filters With Reconfigurable Transfer Function

New types of single- and multiband acoustic-wave resonator-based bandpass filters (BPFs) with continuously variable transfer function in terms of bandwidth (BW), selectivity, and out-of-band isolation (IS) are presented. They are based on single-/multiband resonant branches that are shaped by high-quality-factor ( $Q$ ) acoustic-wave-lumped-element resonators (AWLRs) and are connected in parallel to an all-pass network through variable impedance inverters. With the proposed configuration, quasi-elliptic-type passbands with wide fractional BWs (FBWs)—i.e., larger than the electromechanical coupling coefficient $k_{t}^{\mathrm {2}}$ of its constituent acoustic-wave resonator—can be realized and continuously tuned while preserving the high- $Q$ characteristics of its acoustic-wave resonators. Furthermore, by reconfiguring the location of the transmission zeros (TZs) of the AWLRs, tunable out-of-band IS profiles and asymmetrical passband BWs can be created. The operating principles of the devised spectrally agile filter concept are demonstrated through coupling-matrix-based synthesis and linear-circuit simulations. They are experimentally validated at the UHF band through the realization of: 1) a three-pole/six-TZ single-band prototype at 418 MHz with tunable BW between 0.16 and 0.49 MHz (FBW: 0.5– $1.5k_{t}^{\mathrm {2}})$ for an insertion loss (IL) between 3.3 and 1.2 dB (i.e., effective $Q >10$ 000), reconfigurable order (first-to-third-order states), out-of-band IS controllability in terms of BW (18–26.5 MHz at the upper stopband) and magnitude (23–46 dB at 426 MHz), and an intrinsically selectable all-pass mode and 2) a six-pole/nine-TZ dual-band BPF with two transmission bands located at 418 and 433.9 MHz. They, respectively, feature symmetrical and asymmetrical BW tuning between 0.3–0.54 and 0.6–1.23 MHz with in-band IL <1.7 dB for all tunable states.

Analysis of thermoacoustic instability with corresponding eigenfrequencies in a large scale industrial oil furnace

It has been a serious concern to cope with noise and vibration problems due to thermoacoustic instability in design and operation of large industrial furnaces. In this work Reynolds-averaged Navier-Stokes (RANS) simulation was performed with resulting mean scalar fields provided as an input for acoustic analysis at the Maximum continuous rating (MCR) and 50 % MCR loads. Large Eddy simulation (LES) was performed for a single burner to investigate shear layer oscillations leading to vortex shedding which was suspected to be an excitation source. The Rayleigh parameter was estimated to check mutual correlation and any positive feedback of fluctuating pressure and heat release throughout the single burner domain. The flame transfer function in terms of n and τ was obtained for simplified network analysis from LES results. The peak frequency in turbulence energy spectrum was in good agreement with the measured resonant frequency with positive Rayleigh parameters around the region of shear layer oscillation at the MCR load. No instability was predicted at 50 % MCR load to be consistent with test results, with negative Rayleigh parameters throughout the domain. And the energy spectrum analysis confirms that there is mismatch between the peak frequency and the eigenfrequencies of the furnace at 50 % MCR load.

Modelling and control of double-cone dielectric elastomer actuator

Among various dielectric elastomer devices, cone actuators are of large interest for their multi-degree-of-freedom design. These objects combine the common advantages of dielectric elastomers (i.e. solid-state actuation, self-sensing capability, high conversion efficiency, light weight and low cost) with the possibility to actuate more than one degree of freedom in a single device. The potential applications of this feature in robotics are huge, making cone actuators very attractive. This work focuses on rotational degrees of freedom to complete existing literature and improve the understanding of such aspect. Simple tools are presented for the performance prediction of the device: finite element method simulations and interpolating relations have been used to assess the actuator steady-state behaviour in terms of torque and rotation as a function of geometric parameters. Results are interpolated by fit relations accounting for all the relevant parameters. The obtained data are validated through comparison with experimental results: steady-state torque and rotation are determined at a given high voltage actuation. In addition, the transient response to step input has been measured and, as a result, the voltage-to-torque and the voltage-to-rotation transfer functions are obtained. Experimental data are collected and used to validate the prediction capability of the transfer function in terms of time response to step input and frequency response. The developed static and dynamic models have been employed to implement a feedback compensator that controls the device motion; the simulated behaviour is compared to experimental data, resulting in a maximum prediction error of 7.5%.

Influence of wind disturbance on smart stiffness identification of building structure using limited micro-tremor observation

While most of researches on system identification of building structures are aimed at finding modal parameters first and identifying the corresponding physical parameters by using the transformation in terms of transfer functions and cross spectra, etc., direct physical parameter system identification methods have been proposed recently. Due to the problem of signal/noise (SN) ratios, the previous methods are restricted mostly to earthquake records or forced vibration data. In this paper, a theoretical investigation is performed on the influence of wind disturbances on stiffness identification of building structures using micro-tremor at limited floors. It is concluded that the influence of wind disturbances on stiffness identification of building structures using micro-tremor at limited floors is restricted in case of using time-series data for low-rise buildings and does not cause serious problems.

Determining which quantum measurement performs better for state estimation

We introduce an operational and statistically meaningful measure, the quantum tomographic transfer function, that possesses important physical invariance properties for judging whether a given informationally complete quantum measurement performs better tomographically in quantum-state estimation relative to other informationally complete measurements. This function is independent of the unknown true state of the quantum source, and is directly related to the average optimal tomographic accuracy of an unbiased state estimator for the measurement in the limit of many sampling events. For the experimentally-appealing minimally complete measurements, the transfer function is an extremely simple formula. We also give an explicit expression for this transfer function in terms of an ordered expansion that is readily computable and illustrate its usage with numerical simulations, and its consistency with some known results.

Symbolic representation for analog realization of a family of fractional order controller structures via continued fraction expansion

This paper uses the Continued Fraction Expansion (CFE) method for analog realization of fractional order differ-integrator and few special classes of fractional order (FO) controllers viz. Fractional Order Proportional-Integral-Derivative (FOPID) controller, FO[PD] controller and FO lead–lag compensator. Contemporary researchers have given several formulations for rational approximation of fractional order elements. However, approximation of the controllers studied in this paper, due to having fractional power of a rational transfer function, is not available in analog domain; although its digital realization already exists. This motivates us for applying CFE based analog realization technique for complicated FO controller structures to get equivalent rational transfer functions in terms of the controller tuning parameters. The symbolic expressions for rationalized transfer function in terms of the controller tuning parameters are especially important as ready references, without the need of running CFE algorithm every time and also helps in the synthesis of analog circuits for such FO controllers.

How important is a transfer function in discrete heuristic algorithms

Transfer functions are considered the simplest and cheapest operators in designing discrete heuristic algorithms. The main advantage of such operators is the maintenance of the structure and other continuous operators of a continuous algorithm. However, a transfer function may show different behaviour in various heuristic algorithms. This paper investigates the behaviour and importance of transfer functions in improving performance of heuristic algorithms. As case studies, two algorithms with different mechanisms of optimisation were chosen: Gravitational Search Algorithm and Particle Swarm Optimisation. Eight transfer functions were integrated in these two algorithms and compared on a set of test functions. The results show that transfer functions may show diverse behaviours and have different impacts on the performance of algorithms, which should be considered when designing a discrete algorithm. The results also demonstrate the significant role of the transfer function in terms of improved exploration and exploitation of a heuristic algorithm.

English

There are two most important and advantageous systems are merge one is Fuzzy inference system and PID controller are come together. This paper propose improved fuzzy PID controller with methodology and mathematical model. Controller is to be constructing to control DC motor, we consider DC motor in terms of transfer function. The modelling control and simulation have been done using software package MATLAB/SIMULINK and also the control rules are established with the fuzzy logic.

Detection thresholds in structural health monitoring

Most health-monitoring methods for analysis of full-scale structures detect changes in the soil-system response by comparison of the identified response parameters “before” and “after” large excitations. However, because the deformations of the foundation soil, which are almost always present, are nonlinear, and because permanent deformations and changes in the soil depend differently on the excitation histories of different sites, it is difficult at best to (1) make use of classical concepts, which are based on signal-to-noise ratio, and (2) the vibrational description of the response in terms of transfer functions. This situation then necessitates a selection of methods and metrics that detect changes in the system parameters that (1) can be evaluated in almost real-time conditions, and (2) are as insensitive as possible to the contributions to the response of the soil–structure interaction. This, in turn, requires case-by-case, specific, and complex methods of analysis, which can only occasionally be generalized to other buildings and which can also be quite different from one event to the next. In this paper, we present examples of what has been done thus far to avoid the associated complexities for a group of full-scale structures, two of which experienced damaging response during earthquake shaking. In the examples presented, we emphasize those features of the analyses that are related to detection thresholds and to the time- and case-dependent amplitudes of the detection “noise”.

Minimum dynamic response of cantilever beams supported by optimal elastic springs

In this study, optimal distribution of springs which supports a cantilever beam is investigated to minimize two objective functions defined. The optimal size and location of the springs are ascertained to minimize the tip deflection of the cantilever beam. Afterwards, the optimization problem of springs is set up to minimize the tip absolute acceleration of the beam. The Fourier Transform is applied on the equation of motion and the response of the structure is defined in terms of transfer functions. By using any structural mode, the proposed method is applied to find optimal stiffness and location of springs which supports a cantilever beam. The stiffness coefficients of springs are chosen as the design variables. There is an active constraint on the sum of the stiffness coefficients and there are passive constraints on the upper and lower bounds of the stiffness coefficients. Optimality criteria are derived by using the Lagrange Multipliers. Gradient information required for solution of the optimization problem is analytically derived. Optimal designs obtained are compared with the uniform design in terms of frequency responses and time response. Numerical results show that the proposed method is considerably effective to determine optimal stiffness coefficients and locations of the springs.

Safety monitoring of exothermic reactions using time derivatives of temperature sensors

We propose a new method of safety monitoring for overheating in exothermic reactions that is applicable to detection of thermal runaway in Li-ion batteries. The proposed method is based on the solutions of a one-dimensional heat conduction problem across the wall thickness of a cylinder. The problem is known as an Inverse Heat Conduction Problem (IHCP) since heat is conducted outwards while monitoring sensors only have access to the outside surface. We first obtain the transfer functions relating the inner and outer boundaries through Laplace transform. We then use Hadamard factorization theorem to express the transfer functions in terms of infinite product of polynomials. Truncations of the polynomial transfer functions represent time domain relationships between physically accessible measurements and the heating inside a cylindrical wall. These relationships lead us to propose time derivatives of temperature as better indicators for safety monitoring in exothermic processes.

Analysis of the operation of gradient echo memories using a quantum input–output model

The gradient echo memory (GEM) technique is a promising candidate for real devices due to its demonstrated performance, but to date high performance experiments can only be described numerically. In this paper we derive a model for GEM as a cascade of infinite interconnected harmonic oscillators. We take a quantum input–output approach to analyse this system, describing the read and write processes of GEM each as a linear-time-invariant process. We provide an analytical solution to the problem in terms of transfer functions which describe the memory behaviour for arbitrary inputs and operating regimes. This allows us to go beyond previous works and analyse the storage quality in the regimes of high optical depth and memory-bandwidth comparable to input bandwidth, exactly the regime of high-efficiency experiments.

Neurodynamics of somatosensory cortices studied by magnetoencephelography

From the viewpoint of statistical inverse problems, identification of transfer functions in feedback models is applied for neurodynamics of somatosensory cortices, and brain communication among active regions can be expressed in terms of transfer functions. However, brain activities have been investigated mainly by averaged waveforms in the conventional magnetoencephalography analysis, and thus brain communication among active regions has not yet been identified. It is shown that brain communication among two more than three brain regions is determined, when fluctuations related to concatenate averaged waveforms can be obtained by using a suitable blind source separation method. In blind identification of feedback model, some transfer functions or their impulse responses between output variables of current dipoles corresponding to active regions are identified from reconstructed time series data of fluctuations by the method of inverse problem. Neurodynamics of somatosensory cortices in 5 Hz median nerve stimuli can be shown by cerebral communication among active regions of somatosensory cortices in terms of impulse responses of feedback model.

가변 안내익을 이용한 터보팬 엔진 압축기의 서지 제어

Surge phenomenon can be occurred in a compressor when compressor performance of turbofan engine for an aircraft is changed considerably in a short time on the cases like take-off phase and changing of RPM from idle to maximum, because performance of aircraft engine is changed suddenly. This study is aimed to avoid surge in a compressor. Dynamic simulation in a compressor is modeled by simulink in specific condition. Fuel flow is control input, rpm and air mass flow are expressed in terms of transfer function. Surge margin is obtained by using compressor performance map from NPSS. VIGV(Variable Inlet Guide Vane) is controlled by PD controller with difference between surge margin and reference. Finally this paper verifies IGV can prevent surge phenomenon in a compressor.

Some new results in the theory of negative imaginary systems with symmetric transfer matrix function

This note represents a first attempt to provide a definition and characterisation of negative imaginary systems for not necessarily rational transfer functions via a sign condition expressed in the entire domain of analyticity, along the same lines of the classic definition of positive real systems. Under the standing assumption of symmetric transfer functions, we then derive a necessary and sufficient condition that characterises negative imaginary transfer functions in terms of a matrix sign condition restricted to the imaginary axis, once again following the same line of argument of the standard positive real case. Using this definition, even transfer functions with a pole at the origin with double multiplicity, as well as with a possibly negative relative degree, can be negative imaginary.

Analytical models for a small LFR core dynamics studies

Analytical models for the study of a small Lead-cooled Fast Reactor (LFR) demonstrator (DEMO) core dynamics, in a control-oriented perspective, have been developed aimed at providing a useful, very flexible and straightforward tool allowing relatively quick transient design-basis and stability analyses. A simplified approach has been developed consisting in a lumped-parameter modeling of the coupled neutronics and thermal-hydraulics. The reactor transient responses following both postulated accident initiators such as Unprotected Transient of OverPower (UTOP), Loss of Heat Sink (ULOHS) and Loss of Flow (ULOF), and an emergency SCRAM event have been studied in MATLAB/SIMULINK® environment. A benchmark analysis has been then performed by means of the SAS4A/SASSYS-1 Liquid Metal Reactor Code System with the purpose of providing verification for the analytical outcomes of the nonlinear model and indicating how the latter relate to more realistic one-dimensional calculations. As a general result, responses concerning the main core characteristics (namely, power, reactivity, etc.) have turned out to be mutually consistent in terms of both steady-state absolute figures and transient developments, showing discrepancies of the order of only few per cents. DEMO dynamic behavior has been studied through a linear approach as well, so as to enable the use of linear analysis tools allowing to verify the system stability, thanks to the possibility of expressing a physical model in terms of transfer functions or state–space representation. The impact of linearization and point-kinetics one-precursor-group approximation has been further evaluated by examining the respective transient predictions, which have been compared to the nonlinear reference ones for increasing perturbations. An asymptotic stability analysis, according to Lyapunov's definition, is finally presented.

Optimal damper placement based on base moment in steel building frames

A new damper optimization method for finding optimal size and location of the added viscous dampers is proposed based on the elastic base moment in planar steel building frames. A Fourier Transform is applied to the equation of the motion and the transfer function in terms of the fundamental natural frequency of the structures is defined. The transfer function amplitude of the elastic base moment evaluated at the first natural circular frequency of the structure is chosen as a new objective function in the minimization problem. The damper coefficients of the added viscous dampers are taken into consideration as design variables in a steel planar building frame. The transfer function amplitude of the elastic base moment is minimized under an active constraint on the sum of the damper coefficients of the added dampers and the passive constraints on the upper and lower bounds of the added dampers. The optimal damper design presented in this paper is compared with other optimal damper methods based on top displacement, top absolute acceleration and base shear. A ten-storey steel planar building frame is chosen to be rehabilitated with the optimal dampers. The optimal damper allocation is obtained for the transfer function amplitude of the elastic base moment then compared with the other damper optimization methods in terms of the transfer function response. The results of the proposed method show that the method can also be beneficial to decrease both the base moment and the interstorey drift ratios in some frequency regions.