Frequency Domain Techniques Research Articles

Classification of breast lesions using quantitative ultrasound biomarkers

Quantitative ultrasound (QUS) parameters are gaining attention recently as non-invasive biomarkers for soft tissue characterization. In this work, we use two QUS parameters, namely effective scatterer diameter (ESD) and mean scatterer spacing (MSS), for binary classification of breast lesions. To produce improved classification results, we propose a modified frequency-domain technique for ESD estimation of breast tissues from the diffuse component of backscattered radio-frequency (RF) data. Ensemble empirical mode decomposition (EEMD) is performed to separate the diffuse component from the coherent component of the backscattered RF data. A non-parametric Kolmogorov–Smirnov (K-S) test is employed for automatic selection of the intrinsic mode functions (IMFs). A novel multi-step system effect minimization process is also used. The ESD is estimated using a novel nearest neighborhood average regression line fitting (NNARLF) algorithm. Furthermore, we use an ameliorated EEMD domain autoregressive (AR) spectral estimation technique for MSS estimation. On using the ESD for binary classification of 139 lesions, we obtain high sensitivity, specificity, accuracy values of 95.45%, 95.79%, and 95.68%, respectively. The area under the receiver operating characteristics (ROC) curve is 0.95. On combining ESD with MSS we obtain even more improved sensitivity, specificity, and accuracy values of 97.73%, 95.79%, and 96.40%, respectively. The area under the ROC also increases to 0.97. This high classification performance demonstrates the potential of the use of these QUS parameters as non-invasive biomarkers for breast cancer detection.

Efficient CFO Estimation and Compensation Approach in OFDMA for Uplink Mobile WiMax

Synchronization is a complex task in uplink Orthogonal Frequency Division Multiple Access (OFDMA) for Mobile WiMax as each user presents different Carrier Frequency Offsets (CFO). Synchronization begins with the CFO estimation and followed by the compensation of residual CFO present in the received signal. This paper deals with various techniques in time and frequency domains to compensate the effect of CFO on the received signal for different estimation techniques. SImple time domain MultiUser Interference Cancellation (SIMUIC) performs in time domain. It employs delays in the compensation of CFO while synchronizing the last user. Decorrelation Successive Interference Cancellation (DC-SC) and Integrated Estimation and Compensation (IEC) perform in frequency domain for the compensation of CFO. These approaches are more complex for Inter-Carrier Interference (ICI) cancellation. In this paper, we propose a new efficient CFO compensation technique in frequency domain for different estimation methods. This technique is a modified version of IEC for reducing the CFO effect on the received signal with lesser computations. Simulation results show that the modified IEC performs better than SIMUIC, DC-SC and IEC for different estimation methods.

Quartz Crystal Resonator Sensor With Printed-on-Crystal Coil for Dual-Harmonic Electromagnetic Contactless Interrogation.

A novel quartz crystal resonator (QCR) sensor with a printed-on-crystal conductive coil, named sensor coil, is presented. The sensor coil electromagnetically coupled to an external readout coil allow to perform contactless interrogation of the QCR working as a stand-alone sensor unit. A frequency-domain readout technique is adopted that allows dual-harmonic operation by detecting the QCR frequencies of the fundamental and third harmonic, and offers first-order independence from the stand-off distance between the sensor and the readout unit. The QCR electrodes and sensor coil have been printed on a 330- [Formula: see text]-thick bare AT-cut quartz crystal exploiting the aerosol jet printing technology. The fabricated QCR sensor has reference values of the fundamental and third harmonic frequencies at 4.77 and 14.22 MHz, respectively. Distance-independent contactless operation has been demonstrated for distances up to 12 mm. The readout frequencies deviate from reference values less than 10 and 90 ppm for the fundamental and third harmonic, respectively, thus validating the proposed principle.

Reference Waveform Generation Techniques for Series Compensators

Series compensators are implemented in power system to overcome the power quality issues like voltage dip (sag) and voltage swell. Series compensators such as Dynamic Voltage Restorer have demonstrated their effectiveness in enhancement of power quality. The control techniques for these devices underwent the progressive changes as per industry needs. Control techniques can be majorly classified as frequency domain (s-domain) and time-domain techniques. In the time-domain algorithm reference signal generation is important step for successful implementation of algorithm. In this paper the two reference generation methods namely Synchronous Reference Frame (SRF) method and Unit Vector template (UVT) method are analyzed and compared for their suitability considerations.

Health status, resilience and quality of life of first and fourth year nursing students

Objective: To compare the health status (stress, depressive symptoms and sleep quality), the resilience and quality of life in first and fourth year nursing students.Methods: This is a cross-sectional research conducted in 2016 with 86 students enrolled in first and fourth years of the nursing degree. We applied the instrument for Assessment of Stress in Nursing Students, the Center for Epidemiologic Studies Depression Scale, Pittsburg Sleep Quality Index, Wagnild and Young’s Resilience Scale; and the WHOQOL-BREF. ANOVA (Test F) was applied for data analysis.Results and conclusions: A total of 49 first-year and 37 fourth-year students were sampled for this study. Fourth- year nursing students showed higher levels of stress, lower intensity of depressive symptoms and higher quality of life and resilience levels. The poor sleep quality was prevalent in both groups. Conclusion: although the nursing education potentially contributes for students’ sickness, the experiences lived in this period may strength the resilience skills.Conclusions: Video indexing and retrieval are accomplished by using hashing and $k$-d tree methods, while visual signatures containing color, shape and texture information are estimated for the key-frames, by using image and frequency domain techniques. Experimental results with the dataset of a multimedia information system especially developed for managing television broadcast archives demonstrate that our approach works efficiently, retrieving videos in 0.16 seconds on average and achieving recall, precision and F1 measure values, as high as 0.76, 0.97 and 0.86 respectively.

Railway Ballast Monitoring by GPR: A Test-Site Investigation

Effective maintenance of railways requires a comprehensive assessment of the actual condition of the construction materials involved. In this regard, Ground-Penetrating Radar (GPR) stands as a viable alternative to the invasive and time-consuming traditional techniques for the inspection of these infrastructures. This work reports the experimental activities carried out on a test-site area within a railway depot in Rome, Italy. To this purpose, a 30 m-long railway section was divided into ten sub-sections reproducing different various physical and structural conditions of the track-bed. For more detail, combinations of varying scenarios of fragmentation and fouling of the ballast were reproduced. The set-up was then investigated using different multi-frequency GPR horn antenna systems. The effects of the different physical conditions of ballast on the electromagnetic response of the material were analysed for each scenario using time- and frequency-domain signal processing techniques. Parallel to this, modelling was provided to estimate fouling content. Interpretation of results has proven the viability of the GPR method in detecting signs of decay at the network level, thereby proving this technique to be worthy of implementation in asset management systems.

Two-Dimensional Algebraic Codes for Multiple Burst Error Correction

We construct native binary 2D binary cyclic codes capable of correcting multiple occurrences of multiple non-overlapping pre-defined 2D error shapes using frequency domain techniques. The starting location of each error shape is determined using a novel decoding algorithm based on a careful selection of the common zero set. The proposed code construction is generic and offers superior coding rates compared to the native 2D BCH code with the same error correction ability.

Intensity-Modulated Photocurrent Spectroscopy and Its Application to Perovskite Solar Cells

Frequency domain techniques are useful tools to characterize processes occurring on different time scales in solar cells and solar fuel devices. Intensity-modulated photocurrent spectroscopy (IMPS)...

A FREQUENCY-DOMAIN APPROACH TO DYNAMIC MACROECONOMIC MODELS

This article proposes a unified framework for solving and estimating linear rational expectations models with a variety of frequency-domain techniques, some established, some new. The solution methodology is applicable to a wide class of models and leads to straightforward construction of the spectral density for performing likelihood-based inference. We also generalize the well-known spectral decomposition of the Gaussian likelihood function to a composite version implied by several competing models. Taken together, these techniques yield fresh insights into the model’s theoretical and empirical implications beyond conventional time-domain approaches can offer. We illustrate the proposed framework using a prototypical new Keynesian model with fiscal details and two determinate monetary–fiscal policy regimes. The model is simple enough to deliver an analytical solution that makes the policy effects transparent under each regime, yet still able to shed light on the empirical interactions between US monetary and fiscal policies along different frequencies.

Tonal signal detection in passive sonar systems using atomic norm minimization

Frequency estimation of a tonal signal in passive sonar systems is crucial to the identification of the marine object. In the conventional techniques, a basis mismatch error caused by the discretization of the frequency domain is unavoidable, resulting in a severe degradation of the object detection quality. To overcome the basis mismatch error, we propose a tonal frequency estimation technique in the continuous frequency domain. Towards this end, we formulate the frequency estimation problem as an atomic norm minimization problem. From the numerical experiments, we show that the proposed technique is effective in identifying the tonal frequency components of marine objects.

Model order reduction for discrete-time linear systems with the discrete-time polynomials

In this article, the two-sided model order reduction (MOR) method based on the Charlier and discrete Laguerre polynomials is proposed for large-scale discrete-time linear systems. We first introduce some definitions and results of Charlier polynomials, which are extended from continuous orthogonal polynomial. Then we design the algorithm. The main assumption is that the solution is in the space spanned by Charlier orthogonal polynomials, and then the expansion coefficients of the solution are calculated to generate the projection matrix. Further, combining the frequency-domain techniques with the discrete-time domain techniques, we develop the two-sided projection MOR method, which is a hybrid reduction technique that can possess the nice properties of these two methods. The proposed approach has good computational efficiency and preserves the internal stability under certain condition. Numerical experiments verify the feasibility and effectiveness of the proposed method.

Generalized Huang-Rhys factors for molecular aggregates

Stimulated Raman spectra of molecular aggregates are often remarkably dissimilar to other vibrational spectra e.g. resonance Raman and hole-burning. Particularly in photosynthetic proteins, extremely sparse and predominantly low-frequency spectra are common, unlike the rich structure typical in spectra obtained by frequency-domain techniques. Thus, a mechanism which selectively enhances the intensity of only a small subset of vibronic transitions under stimulated Raman conditions in molecular complexes seems to be required. In this work, we explore how pigment-localized vibrations couple to the excitonic states of molecular aggregates – and the consequences for spectral observables. To aid in the analysis we introduce the concept of a generalized Huang-Rhys factor for molecular aggregates, we derive an analytical expression for this quantity, and establish two conditions required for strong vibronic coupling. We illustrate the effect of such coupling by simulation of absorption and resonance Raman spectra of a two-mode model dimer.

Optimized dithering technique in frequency domain for high-quality three-dimensional depth data acquisition**Project supported by the Science and Technology Major Projects of Zhejiang Province, China (Grant No. 2017C31080).

On the basis of the objective functions, dithering optimization techniques can be divided into the intensity-based optimization technique and the phase-based optimization technique. However, both types of techniques are spatial-domain optimization techniques, while their measurement performances are essentially determined by the harmonic components in the frequency domain. In this paper, a novel genetic optimization technique in the frequency domain is proposed for high-quality fringe generation. In addition, to handle the time-consuming difficulty of genetic algorithm (GA), we first optimize a binary patch, then join the optimal binary patches together according to periodicity and symmetry so as to generate a full-size pattern. It is verified that the proposed technique can significantly enhance the measured performance and ensure the robustness to various amounts of defocusing.

Mitigating Oscillations in Hydraulic Pumping Systems by Using a Supplementary Damping Controller

A feedback control strategy for mitigating pressure oscillations in centrifugal pumping systems is proposed herein. Severe system damage may occur if such oscillations are not adequately damped. According to the experimental data observed, this dominant oscillating mode is operating point-dependent and may become poorly damped under low-speed regime. By using a theoretical control approach, the key parameters that affect the damping of the dominant oscillating mode are investigated. Linear model analysis show that the relative damping of the oscillations depends on the pumping system’s average rotational speed and it is almost zero at low-speed operating condition. To cope with such a dangerous condition, a supplementary feedback damping controller is designed. The damping controller actuates via motor–pump variable-speed drive subsystem. The proposed controller modulates the rotational speed setpoint of the centrifugal pump rotor to produce an extra damping torque. Controller design is performed by using frequency domain techniques, and performance thereof is assessed through experimental tests in a laboratory rig pumping system. The results obtained show that by using the proposed control methodology, it is possible to safely operate the pumping at a low-speed regime, thus preventing damage to the equipment.

Novel non-fiber optical metamaterial waveguide for monitoring canal and pipeline structures

The electromagnetic metamaterials are the recent entrants, into the classification of smart materials for structural health monitoring (SHM). Their applications in SHM have raised the curiosity due to their rapid executable speeds in wide-frequency domains. The speed of obtaining health output signals for engineering structures is about 1/100th of the time taken by existing smart material-based frequency domain techniques such as piezoelectric material-based techniques. Recently, we developed an ultra-sensitive near-field sensing technique using metamaterial localized surface plasmon (LSP) ‘sensor’ which produced diagnosable ‘confined surface electromagnetic waves’ for SHM. This paper presents the same near-field sensing technique in the frequency domain but using metamaterial ‘waveguides’ based on propagating surface plasmon polaritons (SPPs)/surface waves. For the experiments, a novel robust metamaterial waveguide coupling zone was designed and applied for monitoring longitudinal and lateral displacements in civil engineering prototype structures such as channels and pipelines. In the context of SHM, coupling zone and metamaterial waveguide resemble fiber Bragg grating (FBG) sensor and optical fiber waveguide, respectively. Thus, if properly realized, these metamaterials can co-exist with the existing FBG/optical fiber techniques for applications in civil engineering.

Behavioral modeling and digital pre-distortion techniques for RF PAs in a 3 × 3 MIMO system

AbstractModern telecommunications are moving towards (massive) multi-input multi-output (MIMO) systems in 5th generation (5G) technology, increasing the dimensionality of the systems dramatically. In this paper, the impairments of radio frequency (RF) power amplifiers (PAs) in a 3 × 3 MIMO system are compensated in both the time and the frequency domains. A three-dimensional (3D) time-domain memory polynomial-type model is proposed as an extension of conventional 2D models. Furthermore, a 3D frequency-domain technique is formulated based on the proposed time-domain model to reduce the dimensionality of the model, while preserving the performance in terms of model errors. In the 3D frequency-domain technique, the bandwidth of the system is split into several narrow sub-bands, and the parameters of the model are estimated for each sub-band. This approach requires less computational complexity, and also the procedure of the parameters estimation for each sub-band can be implemented independently. The device-under-test consists of three RF PAs including input and output cross-talk channels. The proposed techniques are evaluated in both behavioral modeling and digital pre-distortion (DPD) perspectives. The experimental results show that the proposed DPD technique can compensate the errors of non-linearity and memory effects in the both time and frequency domains.

Detection and Quantification of Non-Linear Structural Behavior Using Frequency Domain Methods

ABSTRACTMost of the practical engineering structures exhibit nonlinearity due to nonlinear dynamic characteristics of structural joints, nonlinear boundary conditions, and nonlinear material properties. In this paper, we investigate the effectiveness of five selected frequency domain techniques for the detection of nonlinear behaviour of the structure. Numerical simulation studies have been carried out by choosing a typical benchmark problem i.e., spring-mass system. The strength and weaknesses of each of the technique are evaluated with respect to their sensitivity to measurement noise. Efforts are also made in this paper to estimate the degree of nonlinearity present in the system using all the five techniques. Numerical investigations are later complemented with experimental studies to demonstrate their practical applicability. The investigations carried out in this paper clearly highlight the effectiveness of the bispectrum technique in robustly identifying the presence and also the degree of nonlinearity in the system.

Identification of discrete Hammerstein systems by using adaptive finite rational orthogonal basis functions

In this paper, an adaptive identification method is presented, it is developed for discrete Hammerstein systems. We adopt a frequency-domain technique by using sampled input–output data. The excitation signals are chosen to be the fundamental harmonics, by which one could get approximating estimate of frequency responses to linear subsystem. By using adaptive rational orthogonal basis functions, we obtain approximations of linear subsystem, it is carried out through selecting poles of the basis functions under some criterion. Meanwhile, efficient estimates of both the nonlinear part and linear part could be obtained in the presence of noise.

Vibrational analysis for surge precursor definition in gas turbines

Compressor behaviour analysis in critical working conditions, such as incipient surge, represents a significant aspect in the turbomachinery research field. Turbines connected with large-size volumes present critical issues related to surge prevention especially during transient operations. Investigations based on acoustic and vibrational measurements appear to provide an interesting diagnostic and predictive solution by adopting suitable quantifiers calculated from microphone and accelerometer signals. For this scope a wide experimental activity has been conducted on a T100 microturbine connected with different volume sizes. A machine dynamical characterisation has been useful for better interpretation of signals during its transient to the surge. Hence, different possible methods of incipient surge identification have been developed through the use of different signal processing techniques in time, frequency and angle domain. These results will be useful for control system development to prevent compressor failures.

The causal relationship between financial development and economic growth in Africa

ABSTRACTPrevious empirical studies on the causal relationship between financial development and economic growth are not instructive given their failure to unearth the causality trend across the different time periods. Using a more recently developed and robust indicator of financial development, we revisit the causal relationship between financial development and economic growth within the framework of a frequency-domain spectral causality technique which allows the causality to vary across time. Using data from 47 African countries over the period 1980–2016, our findings largely suggest that, even though there is some evidence of demand-following, supply-leading and feedback hypotheses, for most part, we find strong support of neutrality hypothesis. Thus, financial development and economic growth at most frequency levels evolve independently. We infer that caution must be exercised in making general conclusions about the causal nexus between financial development and economic growth.