Complex Transfer Function Research Articles

Pulse shaping with birefringent crystals: a tool for quantum metrology

A method for time differentiation based on a Babinet-Soleil-Bravais compensator is introduced. The complex transfer function of the device is measured using polarization spectral interferometry. Time differentiation of both the pulse field and pulse envelope are demonstrated over a spectral width of about 100 THz with a measured overlap with the objective mode greater than 99.8%. This pulse shaping technique is shown to be perfectly suited to time metrology at the quantum limit.

Stochastic modeling of signal propagation in power‐line communication networks

SUMMARYSignal propagation through power‐line networks has been studied by a number of researchers. Among a number of propagation models described in literature, deterministic models based on actual physical description of the network can be constructed as both very accurate and very efficient in computational terms. Yet they have an inherent drawback of being suitable for propagation analyses in static conditions and steady state only. Thus, our main research problem was how to extend a deterministic frequency‐domain‐based propagation model for a more practically useful modeling of channels of multi‐port power‐line communication networks. We have concentrated on a particular model that we presented in an earlier literature. Our main findings are as follows: Computationally efficient deterministic models can be utilized for stochastic simulations in multi‐port power‐line network environments by repeating the propagation simulation routine virtually as many times as needed, to model the network parameter variability by appropriate stochastic modeling of termination impedances connected to each of the multiple network ports. In this way, an extended set of physical properties of the channel can be simulated and statistically analyzed, such as the complex transfer function, impulse response, delay spread, and group delay. Copyright © 2013 John Wiley & Sons, Ltd.

Optical Modulation of Neurotransmission

The computational properties of an isolated neuron have been analyzed in detail by postsynaptic activation with caged compounds. However, new tools are needed to manipulate neurotransmission at individual synapses in order to understand how a neuron integrates physiological stimuli received from presynaptic neurons within a circuit. Here we describe a method to control neurotransmitter exocytosis at the presynaptic compartment by using a light-gated glutamate receptor (LiGluR). In chromaffin cells, LiGluR supports exocytosis by means of a calcium influx that is comparable to voltage-gated calcium channels. Presynaptic expression of LiGluR in hippocampal neurons enables direct and reversible control of neurotransmission with light, and allows modulating the firing rate of the postsynaptic neuron with the wavelength of illumination. This method constitutes an important step toward the determination of the complex transfer function of individual synapses.

Optical modulation of neurotransmission using calcium photocurrents through the ion channel LiGluR

A wide range of light-activated molecules (photoswitches and phototriggers) have been used to the study of computational properties of an isolated neuron by acting pre and postsynaptically. However, new tools are being pursued to elicit a presynaptic calcium influx that triggers the release of neurotransmitters, most of them based in calcium-permeable Channelrhodopsin-2 mutants. Here we describe a method to control exocytosis of synaptic vesicles through the use of a light-gated glutamate receptor (LiGluR), which has recently been demonstrated that supports secretion by means of calcium influx in chromaffin cells. Expression of LiGluR in hippocampal neurons enables reversible control of neurotransmission with light, and allows modulating the firing rate of the postsynaptic neuron with the wavelength of illumination. This method may be useful for the determination of the complex transfer function of individual synapses.

The calculation of impulse responses in concert halls below 80 Hz

Computer Simulation of room acoustics in large and medium-size venues has become a standard in the acoustic design process. But the Ray or Beam Tracing methods used in all such simulation programs cannot be applied at low frequencies. Here the rules of wave Acoustics must be considered. This work introduces a practical and accurate software-based approach for simulating the acoustic properties of concert and other large halls based on FEM. A detailed approach to obtain complex transfer functions is presented. By means of an inverse FFT impulse responses are obtained and compared with Ray Tracing results. It is shown that the results calculated with FEM extend the fine structure of Ray Tracing results at low frequencies. Also, it is understandable that the FEM simulation software can help to avoid modal phenomena and to place absorbers and diffusers in order to improve the acoustic quality of the hall.

Design of a Direct Sampling Mixer with a Complex Coefficient Transfer Function

The Direct Sampling Mixer (DSM) with a complex coefficient transfer function is demonstrated. The operation theory and the detail design methodology are discussed for the high order complex DSM, which can achieve large image rejection ratio by introducing the attenuation pole at the image frequency band. The proposed architecture was fabricated in a 65nm CMOS process. The measured results agree well with the theoretical calculation, which proves the validity of the proposed architecture and the design methodology. By using the proposed design method, it will be possible for circuit designers to design the DSM with large image rejection ratio without repeated lengthy simulations.

Low frequency approximation for a class of linear quantum systems using cascade cavity realization

This paper presents a method for approximating a class of complex transfer function matrices corresponding to physically realizable complex linear quantum systems. The class of linear quantum systems under consideration includes interconnections of passive optical components such as cavities, beam-splitters, phase-shifters and interferometers. This approximation method builds on a previous result for cascade realization and gives good approximations at low frequencies.

SOA Fiber Ring Lasers: Single- Versus Multiple-Mode Oscillation

Earlier investigations have demonstrated that a narrow bandwidth intracavity filter in a semiconductor optical amplifier (SOA) fiber ring laser results in an output spectrum comprising multiple longitudinal modes, whereas a large bandwidth filter generally leads to quasi-single-mode oscillation. In this paper, we report on a numerical model simulating the SOA fiber ring laser dynamics and compare its predictions with experimental results obtained with two different SOAs. We demonstrate that the observed experimental behavior results from the interplay between the complex transfer function of the intracavity optical filter, fast gain saturation and four-wave mixing (FWM) due to the linewidth enhancement factor. The dispersion introduced by the complex transfer function of the filter can lead to modulation instability, which plays a key role in the laser dynamics that can evolve into a single-longitudinal mode (SLM) operation. We also simulate the behavior of the laser emission when the wavelength of the optical filter is finely tuned.

Shape-enhanced maximum intensity projection

Maximum intensity projection (MIP) displays the voxel with the maximum intensity along the viewing ray, and this offers simplicity in usage, as it does not require a complex transfer function, the specification of which is a highly challenging and time-consuming process in direct volume rendering (DVR). However, MIP also has its inherent limitation, the loss of spatial context and shape information. This paper proposes a novel technique, shape-enhanced maximum intensity projection (SEMIP), to resolve this limitation. Inspired by lighting in DVR to emphasize surface structures, SEMIP searches a valid gradient for the maximum intensity of each viewing ray, and applies gradient-based shading to improve shape and depth perception of structures. As SEMIP may result in the pixel values over the maximum intensity of the display device, a tone reduction technique is introduced to compress the intensity range of the rendered image while preserving the original local contrast. In addition, depth-based color cues are employed to enhance the visual perception of internal structures, and a focus and context interaction is used to highlight structures of interest. We demonstrate the effectiveness of the proposed SEMIP with several volume data sets, especially from the medical field.

Comparison of room‐acoustical parameters predicted using different surface‐reaction models.

This paper presents the development of a beam‐tracing model for calculating the transient responses of rooms. The model is wave‐based (i.e., includes phase changes due to distance traveled and wall reflections), and can be applied to rooms with extended‐reaction surfaces. Room surfaces can be modeled as multiple layers of solid, fluid, and poroelastic materials; their acoustical properties are calculated using a transfer‐matrix approach. The beam‐tracing model calculates the complex transfer function of a room. Pressure impulse responses are then computed via Fourier transformation, and the room‐acoustical parameters derived. Since pressure impulse responses are calculated, the model can also be used for auralization. The model has been applied to different room configurations in order to study the effects of different surface‐reaction models on the predicted steady‐state characteristics and temporal variations of sound‐pressure fields in various room configurations. In particular, the audibility of using different boundary conditions (local versus extended reaction, wave‐based versus energy based modeling, and phase changes on reflection) on the room‐acoustical parameters has been investigated: In each configuration, room parameters have been calculated using different boundary conditions, and audible variations of the parameters have been studied and explained.

Cascade cavity realization for a class of complex transfer functions arising in coherent quantum feedback control

This paper presents a realization algorithm for a class of complex transfer function matrices corresponding to physically realizable linear quantum systems. The aim of the realization algorithm is to enable a coherent quantum feedback controller, which has been synthesized using methods such as quantum H ∞ control or quantum LQG control, to be constructed using optical components such as cavities and phase-shifters. The class of linear quantum systems under consideration are passive linear quantum systems which can be described purely in terms of annihilation operators. The proposed algorithm enables a complex transfer function matrix to be realized as a pure cascade connection involving only cavities and phase-shifters.

Microscopy image resolution improvement by deconvolution of complex fields

Based on truncated inverse filtering, a theory for deconvolution of complex fields is studied. The validity of the theory is verified by comparing with experimental data from digital holographic microscopy (DHM) using a high-NA system (NA=0.95). Comparison with standard intensity deconvolution reveals that only complex deconvolution deals correctly with coherent cross-talk. With improved image resolution, complex deconvolution is demonstrated to exceed the Rayleigh limit. Gain in resolution arises by accessing the objects complex field - containing the information encoded in the phase - and deconvolving it with the reconstructed complex transfer function (CTF). Synthetic (based on Debye theory modeled with experimental parameters of MO) and experimental amplitude point spread functions (APSF) are used for the CTF reconstruction and compared. Thus, the optical system used for microscopy is characterized quantitatively by its APSF. The role of noise is discussed in the context of complex field deconvolution. As further results, we demonstrate that complex deconvolution does not require any additional optics in the DHM setup while extending the limit of resolution with coherent illumination by a factor of at least 1.64.

A Single-Input Space Vector for Control of AC–DC Converters Under Generalized Unbalanced Operating Conditions

This paper introduces a new technique to generate a space vector from a single real-valued signal via complex transfer functions. The single-input space vector concept may be readily integrated within conventional feedback control loops to introduce new controller functionality. In this paper, the single-input space vector is used to regulate a grid-connected ac-dc converter under generalized unbalanced conditions (i.e., grid unbalance and/or reactor unbalance). The proposed controller, based upon the single-input space vector, regulates real and reactive power while mitigating low-order harmonic voltages and currents that plague ac-dc converters under generalized unbalanced conditions. The negative feedback structure of the proposed single-input space vector controller offers high robustness, high controller bandwidth, and low controller complexity. The combination of high bandwidth and low-order harmonic ripple elimination allows significant reduction in the size and cost of the dc storage capacitor. The efficacy of the controller is proven by experimental results.

Efficient loop antenna modeling for zero-offset, off-ground electromagnetic induction in multilayered media

Retrieval of the subsurface electrical properties from electromagnetic induction (EMI) data using inverse modeling relies in particular on the accuracy of the considered EMI model. We have developed a new EMI approach whereby a zero-offset, off-ground loop antenna is efficiently modeled using frequency-dependent, complex linear transfer functions and the air subsurface is described by a Green’s function for wave propagation in 3D multilayered media. To ensure proper calibration of the system, vector network analyzer (VNA) technology is used as the transmitter and receiver. An optimal integration path is proposed for fast evaluation of the spatial Green’s function from its spectral counterpart. We validated the antenna model in laboratory conditions with measurements performed with a loop antenna in free space and at different heights above a perfect electrical conductor. Provided that the loop antenna is high enough above the reflector (off-ground condition), the measured and modeled Green’s functions agreed remarkably well. In addition, inversion of the EMI data resulted in accurate estimates of the antenna heights. Yet, as expected, signal-to-noise-ratio issues occurred for the higher antenna heights and frequencies away from the loop resonant frequency. The method appears to be promising for accurate and robust soil characterization, but needs high VNA dynamic range and antenna gain.

Combining predicate and numeric abstraction for software model checking

Predicate (PA) and numeric (NA) abstractions are the two principal techniques for software analysis. In this paper, we develop an approach to couple the two techniques tightly into a unified framework via a single abstract domain called NumPredDom. In particular, we develop and evaluate four data structures that implement NumPredDom but differ in their expressivity and internal representation and algorithms. All our data structures combine BDDs (for efficient propositional reasoning) with data structures for representing numerical constraints. Our technique is distinguished by its support for complex transfer functions that allow two-way interaction between predicate and numeric information during state transformation. We have implemented a general framework for reachability analysis of C programs on top of our four data structures. Our experiments on non-trivial examples show that our proposed combination of PA and NA is more powerful and more efficient than either technique alone.

Active Control of Automotive Intake Noise under Rapid Acceleration using the Co-FXLMS Algorithm

The method of reducing automotive intake noise can be classified by passive and active control techniques. However, passive control has a limited effect of noise reduction at low frequency range (below 500 Hz) and is limited by the space of the engine room. However, active control can overcome these passive control limitations. The active control technique mostly uses the Least-Mean-Square (LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time, particularly when the Filtered-X LMS (FXLMS) algorithm is applied to an active noise control (ANC) system. However, the convergence performance of the LMS algorithm decreases significantly when the FXLMS algorithm is applied to the active control of intake noise under rapidly accelerating driving conditions. Therefore, in this study, the Co-FXLMS algorithm was proposed to improve the control performance of the FXLMS algorithm during rapid acceleration. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. The performance of the Co-FXLMS algorithm is presented in comparison with that of the FXLMS algorithm. Experimental results show that active noise control using Co-FXLMS is effective in reducing automotive intake noise during rapid acceleration.

Frequency dependence of average phase shift from human calcaneusin vitro

If dispersion in a medium is weak and approximately linear with frequency (over the experimental band of frequencies), then it can be shown that the constant term in a polynomial representation of phase shift as a function of frequency can produce errors in measurements of phase-velocity differences in through-transmission, substitution experiments. A method for suppressing the effects of the constant phase shift in the context of the single-wave-model was tested on measurements from 30 cancellous human calcaneus samples in vitro. Without adjustment for constant phase shifts, the estimated phase velocity at 500 kHz was 1516+/-6 m/s (mean+/-standard error), and the estimated dispersion was -24+/-4 m/s MHz (mean+/-standard error). With adjustment for constant phase shifts, the estimated mean velocity decreased by 4-9 m/s, and the estimated magnitude of mean dispersion decreased by 50%-100%. The average correlation coefficient between the measured attenuation coefficient and frequency was 0.997+/-0.0026 (mean+/-standard deviation), suggesting that the signal for each sample was dominated by one wave. A single-wave, linearly dispersive model conformed to measured complex transfer functions from the 30 cancellous-bone samples with an average root-mean-square error of 1.9%+/-1.0%.

Dynamic Analysis of a Boost Converter With Ripple Cancellation Network by Model-Reduction Techniques

The boost topology with ripple cancellation network allows input and output current ripples attenuation, which means the suppression of the input filter and a high reduction of the output filter. However, to achieve the ripple cancellation, the complexity and the number of components of the converter need to be increased as compared with the conventional boost. A detailed analysis is developed to specify the advantages and disadvantages of this topology. This paper presents the averaged model that derives the complex transfer function of the topology. The theoretical transfer function is obtained. Due to the complexity of the seventh-order transfer function that is obtained, a simplified second-order transfer function is calculated to simplify control design calculations. A comparison between the analyzed topology and a conventional boost in terms of weight and losses is carried out. To estimate the current ripple calculation, it is proposed to use the ripple theorem, which allows an estimation of the efficiency of the cancellation network using the averaged model. A prototype to validate ripple cancellation and the dynamic analysis is developed. Measured waveforms and Bode plots are enclosed. Current ripple cancellation at the input and output in both conduction modes of the converter is also validated.

Electrochemical Behavior of Vanadium in Azide Electrolyte in Comparison with the Behavior in Halogen Ions-Containing Electrolytes

The influence of azide ion concentration and temperature on the electrochemical behavior of vanadium was studied using open-circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The steady state potential (Ess) is a linear function of azide ion concentration. Polarization measurements have shown that the rate of corrosion icorr increases with increasing the azide ion concentration as well as increasing solution temperature. EIS investigations under open-circuit conditions confirm these results as can be identified by the decrease of the polarization resistance (Rox) and oxide thickness (1/Cox) with increasing the azide ion concentration. The measured impedance responses were analyzed using a constant phase element (CPE) model with its complex transfer function. The behavior of vanadium in the azide medium is also compared to that in other halide salt solutions, it was found that the tendency for spontaneously grown thicker oxide film increases in the order: Br - > Cl - > I - > N 3 > F - .

The Complex Controller Applied To The Induction Motor Control

This paper presents a design and tuning method of the complex gain controller, based on the three-phase induction motormathematicalmodel complex transfer function to be used in induction motor control when the machine operates at low speed which is a problem so far. The complex gain controller was applied in the direct rotor field orientation controlmethod and also on the direct torque control method. It was designed and tuned using the frequency-response function of the closed loop system. The complex gain controller presents low complexity in the inductionmotor control implementation. Experimental results were carried out for the controller validation.