Discrete Signal and Systems

At present, semiotics-which in my opinion is the science of signs, sign systems, and sign reality-is undergoing a deep crisis. This was clearly demonstrated by the 15th World Congress of Semiotics, which took place in Thessaloniki, Greece, from August 30 to September 3, 2022. The same was unambiguously stated by the Czech scholar Vladimir Franta in his article "The Crisis of Semiotics against the Background of the Humanities and Natural Sciences." Since the Congress in Thessaloniki, international meetings of semioticians seem to have ceased altogether. In any case, up to this day the next congress has not managed to be organized. I write about this with deep regret-I was present at and actively participated in all the first congresses of semiotics back in the last century, trying to defend its significance and independence throughout this entire time. The aim of this article is to analyze the causes of the crisis and to propose ways of overcoming it.

In this paper, a new numerical method for solving fractional optimal control problems (FOCPs) is presented. The fractional derivative in the dynamic system is described in the Caputo sense. The method is based upon biorthogonal cubic Hermite spline multiwavelets approximations. The properties of biorthogonal multiwavelets are first given. The operational matrix of fractional Riemann-Lioville integration and multiplication are then utilized to reduce the given optimization problem to the system of algebraic equations. In order to save memory requirement and computational time, a threshold procedure is applied to obtain algebraic equations. Illustrative examples are provided to confirm the applicability of the new method.

In this paper, we develop a methodology and a conceptual framework in which manipulations are undertaken for perceiving and characterizing materials. Within this framework, we distinguish different materials (unknown environments) by actively contacting and testing them, and by analyzing the resulting sounds using a microphone. For this implementation, we identify sensor-derived measures that are diagnostic of a material's properties, and use these measures to categorize the objects (or unknown environments) in their different material class. The parameter of characterization is the internal angle of friction of the materials. This parameter is determined by the relation of strain and stress properties. Using this theoretical approach and the experimental results, we conclude that the statement of shape-invariance of materials is critical and invalid in real cases.

Studies on neurophysiological correlates of the functional magnetic resonance imaging (fMRI) signals reveal a strong relationship between the local field potential (LFP) acquired invasively and metabolic signal changes in fMRI experiments. Most of these studies failed to reveal an analogous relationship between metabolic signals and the spiking activity. That would allow for the prediction of the neural activity exclusively from the fMRI signals. However, the relationship between fMRI signals and spiking activity can be inferred indirectly provided that the LFPs can be used to predict the spiking activity of the area. Until now, only the LFP-spike relationship in cortical areas has been examined. Herein, we show that the spiking activity can be predicted by the LFPs acquired in a deep nucleus, namely the subthalamic nucleus (STN), using a nonlinear cascade model. The model can reproduce the spike patterns inside the motor area of the STN that represent information about the motor plans. Our findings expand the possibility of further recruiting non-invasive neuroimaging techniques to understand the activity of the STN and predict or even control movement.

In this paper, we develop a methodology and a conceptual framework in which manipulations are undertaken for perceiving and characterizing materials. Within this framework, we distinguish different materials (unknown environments) by actively contacting and testing them, and by analyzing the resulting sounds using a microphone. For this implementation, we identify sensor-derived measures that are diagnostic of a material's properties, and use these measures to categorize the objects (or unknown environments) in their different material class. The parameter of characterization is the internal angle of friction of the materials. This parameter is determined by the relation of strain and stress properties. Using this theoretical approach and the experimental results, we conclude that the statement of shape-invariance of materials is critical and invalid in real cases.

In this paper, we focus on orthogonal frequency-division multiplexing (OFDM) receiver designs for underwater acoustic (UWA) channels with user-and/or path-specific Doppler scaling distortions. The scenario is motivated by the cooperative communications framework, where distributed transmitter/receiver pairs may experience significantly different Doppler distortions, as well as by the single-user scenarios, where distinct Doppler scaling factors may exist among different propagation paths. The conventional approach of front-end resampling that corrects for common Doppler scaling may not be appropriate in such scenarios, rendering a post-fast-Fourier-transform (FFT) signal that is contaminated by user-and/or path-specific intercarrier interference. To counteract this problem, we propose a family of front-end receiver structures thatutilizemultiple-resampling (MR)branches,eachmatched tothe Doppler scaling factor of a particular user and/or path. Following resampling, FFT modules transform the Doppler-compensated signals into the frequency domain for further processing through linear or nonlinear detection schemes. As part of the overall receiver structure, a gradient-descent approach is also proposed to refine the channel estimates obtained by standard sparse channel estimators. The effectiveness and robustness of the proposed receivers are demonstrated via simulations, as well as emulations based on real data collected during the 2010 Mobile Acoustic Communications Experiment (MACE10, Martha's Vineyard, MA) and the 2008 Kauai Acomms MURI (KAM08, Kauai, HI) experiment.

Space division multiplexing (SDM) has been proposed as the ultimate solution to address the capacity crunch of optical transport networks. The efficient utilization of SDM requires some forms of spatial integration which is expected to bring huge cost savings for the deployment of SDM-based optical networks. Spatially integrated components with different characteristics have been largely explored and demonstrated for the realization of SDM networks, including; transmission media, transceivers with sophisticated digital signal processing (DSP) units, amplifiers, and ultimately optical switching nodes which are the key elements for the realization of transparent optical networks exploiting SDM technologies. As a consequence, in contrast to the currently deployed optical networks based on standard single mode fibers (SSMF), the next generation of optical networks exploiting SDM technologies can be realized utilizing various kinds of transmission media and the other corresponding elements. However, due in part to the physical properties of different components, their complexity, and the technology limitations not all of them meet the economic feasibility and a desired level of network-wide performance. Therefore, careful analysis should be done revealing the most appropriate and costeffective solutions. In this work, we review the recent developments and findings which pave the way for a simplified and efficient implementation of the spectrally and spatially flexible optical networks.

A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of friction material is taken into account, and the asperity load is calculated according to the Greenwood and Tripp approach. In this model, effects of friction material permeability, applied load and driving velocity on the engagement characteristics of the wet clutch were studied. The results show that friction material with high permeability reduces the film thickness rapidly and increases the torque peak; the applied load increases the asperity contact pressure and the friction torque, and reduces the engagement time; the driving velocity mainly increases the engagement time. The theoretical torque and relative velocity curves agree qualitatively with the experimental ones, which verifies the wet clutch engagement model.

We describe a new technique, currently under development, intended to detect the presence of flaws such as cracks and holes in thin-walled mechanical components. This technique combines ultrasonics with optics, both at a low power density, that allows to perform the tests in the non-destructive range. Lamb waves, a kind of surface acoustic waves that propagate in thin plates, are generated to explore metallic samples while double-pulsed TV holography, a whole-field interferometric technique, is used to detect them. This scheme provides maps of the instantaneous surface displacements produced by the waves, where the effects of the flaws can be visualised by contrast against the smooth propagation of the wavefront in defect free plates. Images with reasonable resolution can be achieved almost in real-time. Several examples of detection of typical flaws in plates using the proposed method complete this work.

A mathematical model was developed to analyze the characteristics of the wet clutch during engagement. The lubricant squeeze action was simulated with Patir and Cheng average flow model in which the permeability of friction material is taken into account, and the asperity load is calculated according to the Greenwood and Tripp approach. In this model, effects of friction material permeability, applied load and driving velocity on the engagement characteristics of the wet clutch were studied. The results show that friction material with high permeability reduces the film thickness rapidly and increases the torque peak; the applied load increases the asperity contact pressure and the friction torque, and reduces the engagement time; the driving velocity mainly increases the engagement time. The theoretical torque and relative velocity curves agree qualitatively with the experimental ones, which verifies the wet clutch engagement model.

Nowadays, manufacturing companies are making great efforts to implement an effective machinery maintenance program, which provides incipient fault detection. The machine problem and its irregularity can be detected at an early stage by employing a suitable condition monitoring accompanied with powerful signal processing technique. Among various defects occurred in machines, rotor faults are of significant importance as they cause secondary failures that lead to a serious motor malfunction. Diagnosis of rotor failures has long been an important but complicated task in the area of motor faults detection. This paper intends to review and summarize the recent researches and developments performed in condition monitoring of the induction machine with the purpose of rotor faults detection. The aim of this article is to provide a broad outlook on rotor fault monitoring techniques for the researchers and engineers.

Elastic optical networking has recently been proposed for use in optical transport networks to cope with increasingly heterogeneous and dynamic demand patterns. In this paper, we study the blocking performance of a multi-class elastic optical link for which a demand needs to be allocated a contiguous subset of the entire spectrum. This problem is different than the well-known blocking problem in multi-class multi-server loss systems due to the contiguous allocation constraint. We first propose a non-work-conserving aligned spectrum allocation policy which is shown to outperform the conventional first fit-based work-conserving allocation policy without alignment. Subsequently, for blocking performance of an aligned elastic optical link with up to three different traffic classes, we propose a novel and systematic order reduction procedure for MMPPs (Markov Modulated Poisson Process) and use this procedure as the numerical engine to approximately obtain the blocking probabilities. The proposed numerical algorithm is validated under various system and traffic parameters and is shown to be effectively usable as an instrument to dimension elastic optical links.

An experimental investigation has been carried out in order to evaluate the detection of cavitation in actual hydraulic turbines. The methodology is based on the analysis of structural vibrations, acoustic emissions and hydrodynamic pressures measured in the machine. The proposed techniques have been checked in real prototypes suffering from different types of cavitation. In particular, one Kaplan, two Francis and one Pump-Turbine have been investigated in the field. Additionally, one Francis located in a laboratory has also been tested. First, a brief description of the general features of cavitation phenomenon is given as well as of the main types of cavitation occurring in hydraulic turbines. The work presented here is focused on the most important ones which are the leading edge cavitation due to its erosive power, the bubble cavitation because it affects the machine performance and the draft tube swirl that limits the operation stability. Cavitation detection is based on the previous understanding of the cavity dynamics and its location inside the machine. This knowledge has been gained from flow visualisations and measurements in laboratory devices such as a high-speed cavitation tunnel and a reduced scale turbine test rig. The main techniques are the study of the high frequency spectral content of the signals and of their amplitude demodulation for a given frequency band. Moreover, low frequency spectral content can also be used in certain cases. The results obtained for the various types of cavitation found in the selected machines are presented and discussed in detail in the paper. Conclusions are drawn about the best sensor, measuring location, signal

Structures experience various types of loads along their lifetime, which can be either static or dynamic and may be associated to phenomena of corrosion and chemical attack, among others. As a consequence, different types of structural damage can be produced; the deteriorated structure may have its capacity affected, leading to excessive vibration problems or even possible failure. It is very important to develop methods that are able to simultaneously detect the existence of damage and to quantify its extent. In this paper the authors propose a method to detect and quantify structural damage, using response transmissibilities measured along the structure. Some numerical simulations are presented and a comparison is made with results using frequency response functions. Experimental tests are also undertaken to validate the proposed technique.

In this paper, we focus on orthogonal frequency-division multiplexing (OFDM) receiver designs for underwater acoustic (UWA) channels with user-and/or path-specific Doppler scaling distortions. The scenario is motivated by the cooperative communications framework, where distributed transmitter/receiver pairs may experience significantly different Doppler distortions, as well as by the single-user scenarios, where distinct Doppler scaling factors may exist among different propagation paths. The conventional approach of front-end resampling that corrects for common Doppler scaling may not be appropriate in such scenarios, rendering a post-fast-Fourier-transform (FFT) signal that is contaminated by user-and/or path-specific intercarrier interference. To counteract this problem, we propose a family of front-end receiver structures thatutilizemultiple-resampling (MR)branches,eachmatched tothe Doppler scaling factor of a particular user and/or path. Following resampling, FFT modules transform the Doppler-compensated signals into the frequency domain for further processing through linear or nonlinear detection schemes. As part of the overall receiver structure, a gradient-descent approach is also proposed to refine the channel estimates obtained by standard sparse channel estimators. The effectiveness and robustness of the proposed receivers are demonstrated via simulations, as well as emulations based on real data collected during the 2010 Mobile Acoustic Communications Experiment (MACE10, Martha's Vineyard, MA) and the 2008 Kauai Acomms MURI (KAM08, Kauai, HI) experiment.

We propose a robust algorithm to detect the arrival of a vehicle of arbitrary type when other noises are present. It is done via analysis of its acoustic signature against an existing database of recorded and processed acoustic signals. To achieve it with minimum number of false alarms, we combine a construction of a training database of acoustic signatures signals emitted by vehicles using the distribution of the energies among blocks of wavelet packet coefficients with a procedure of random search for a near-optimal footprint (RSNOFP). The number of false alarms in the detection is minimized even under severe conditions such as: the signals emitted by vehicles of different types differ from each other, whereas the set of non-vehicle recordings (the training database) contains signals emitted by planes, helicopters, wind, speech, steps, etc. The proposed algorithm is robust even when the tested conditions are completely different from the conditions where the training signals were recorded. The proposed technique has many algorithmic variations. For example, it can be used to distinguish among different types of vehicles. The proposed algorithm is a generic solution for process control that is based on a learning phase (training) followed by an automatic real time detection.

Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/fA times the photodetector-army sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.

Multiresponse imaging is a process that acquires A images, each with a different optical response, and reassembles them into a single image with an improved resolution that can approach 1/fA times the photodetector-army sampling lattice. Our goals are to optimize the performance of this process in terms of the resolution and fidelity of the restored image and to assess the amount of information required to do so. The theoretical approach is based on the extension of both image restoration and rate distortion theories from their traditional realm of signal processing to image processing which includes image gathering and display.

Blade vibration reduction is an important task in high performance turbo machinery for power generation, in order to avoid the risk of blade failure due to the overcoming of fatigue limit. A possible way to obtain this result is a contact related phenomenon, i.e. by physically limiting the vibration amplitude on the blade tip leaving a small gap between the shrouds of adjacent blades. When the relative displacement between adjacent blades exceeds the gap, in a certain vibration mode of the blade row, a contact occurs between the shrouds, the relative motion is restricted and energy is dissipated by friction and impact during the contact. This is called the snubbing mechanism. In this paper, an original simplified model of bladed disks, in which the snubbing mechanism can occur, is presented and numerical integration in time domain furnishes the time histories of the vibrations of the blades. The level of vibration reduction is then evaluated in some different modes that could be excited for instance by the fluid flow. It is also shown that unlucky combinations of system and excitation parameters can effect also a certain magnification instead of a reduction of the vibration amplitudes. Experimental results on single blades and blade groups of a steam turbine are used to tune the parameters of the system.

It is believed that the acoustic emissions (AE) signal contains potentially valuable information for monitoring precision cutting processes, as well as to be employed as a control feedback signal. However, AE stress waves produced in the cutting zone are distorted by the transmission path and the measurement systems. In this article, a bicepstrum based blind system identification technique is proposed as a valid tool for estimating both, transmission path and sensor impulse response. Assumptions under which application of bicepstrum is valid are discussed and diamond turning experiments are presented, which demonstrate the feasibility of employing bicepstrum for AE blind identification.

We present a method for construction of multiwavelet frames for manipulation of discrete signals. The frames are generated by three-channel perfect reconstruction oversampled multifilter banks. The design of the multifilter bank starts from a pair of interpolatory multifilters. We derive these interpolatory multifilters from the cubic Hermite splines. We use original preprocessing algorithms, which transform scalar signals into vector arrays that serve as inputs to the oversampled analysis multifilter banks. These pre-processing algorithms do not degrade the approximation accuracy of the transforms of the vectors by multifilter banks. The postprocessing algorithms convert the vector output of the synthesis multifilter banks into scalar signal. The discrete framelets, generated by the designed filter banks, are symmetric and have short support. The analysis framelets have four vanishing moments, whereas the synthesis framelets converge to Hermite splines supported on the interval [-1,1].

The problem of stabilizability of the 2D continuous-time saturated systems under state-feedback control is solved in this paper. Two cases are considered: the first one, the control may saturate and limits may be attained. The second one, the control does not saturate and limits are avoided. Sufficient conditions of asymptotic stability are presented. The synthesis of the required controllers is given under LMIs form. Illustrative examples are treated.

The problem of stabilizability of the 2D continuous-time saturated systems under state-feedback control is solved in this paper. Two cases are considered: the first one, the control may saturate and limits may be attained. The second one, the control does not saturate and limits are avoided. Sufficient conditions of asymptotic stability are presented. The synthesis of the required controllers is given under LMIs form. Illustrative examples are treated.