Reference Filter Research Articles

Multimedia Archives: New Digital Filters to Correct Equalization Errors on Digitized Audio Tapes

Multimedia archives face the problem of obsolescing and degrading analogue media (e.g., speech and music recordings and video art). In response, researchers in the field have recently begun studying ad hoc tools for the preservation and access of historical analogue documents. This paper investigates the active preservation process of audio tape recordings, specifically focusing on possible means for compensating equalization errors introduced in the digitization process. If the accuracy of corrective equalization filters is validated, an archivist or musicologist would be able to experience the audio as a historically authentic document such that their listening experience would not require the recovery of the original analogue audio document or the redigitization of the audio. Thus, we conducted a MUSHRA-inspired perception test (n = 14) containing 6 excerpts of electronic music (3 stimuli recorded NAB and 3 recorded CCIR). Participants listened to 6 different equalization filters for each stimulus and rated them in terms of similarity. Filters included a correctly digitized “Reference,” an intentionally incorrect “Foil” filter, and a subsequent digital correction of the Foil filter that was produced with a MATLAB script. When stimuli were collapsed according to their filter type (NAB or CCIR), no significant differences were observed between the Reference and MATLAB correction filters. As such, the digital correction appears to be a promising method for compensation of equalization errors although future study is recommended, specifically containing an increased sample size and additional correction filters for comparison.

Inter-laboratory comparison of ED-XRF/PIXE analytical techniques in the elemental analysis of filter-deposited multi-elemental certified reference materials representative of ambient particulate matter.

The quantification of the elemental concentration of ambient particulate matter is a challenging task because the observed elemental loadings are not well above the detection limit for most analytical techniques. Although non-destructive nuclear techniques are widely used for the chemical characterization of ambient aerosol, only one multi-element standard reference filter material that mimics ambient aerosol composition has become recently available in the market. To ensure accuracy, reliability and comparability of instruments performance, multiple reference materials with different elemental mass loadings are necessary. In this study, an intercomparison exercise was performed to evaluate the measurement uncertainty and instruments performance using multi-element dust standard reference samples deposited on PTFE filters. The filter samples, produced by means of dust dispersion, were tested in terms of homogeneity, reproducibility and long-term stability (≈40 months). Eight laboratories participated in the exercise. The evaluation of the results reported by the participants was performed by using two sets of reference values: a) the concentrations reported by the Expert Laboratory, b) the robust average concentrations reported by all participants. Most of the reported on the certificate of analysis elements were efficiently detected in the sample loadings prepared as representative for atmospheric samples by the Expert Laboratory. The average absolute relative difference between the reported and the reference values ranged between 0.1% (Ti) and 33.7% (Cr) (CRM-2584). The participants efficiently detected most of the elements except from the elements with atomic number lower than 16 (i.e. P, Al, Mg). The average absolute percentage difference between the participants results and the assigned value as derived by the expert laboratory was 17.5 ± 18.1% (CRM-2583; Cr, Pb excluded) and 16.7 ± 16.7% (CRM-2584; Cr, P excluded). The average "relative robust standard deviation" of the results reported by all participants was 25.1% (CRM-2583) and 22.8% (CRM-2584).

Use of common average reference and large-Laplacian spatial-filters enhances EEG signal-to-noise ratios in intrinsic sensorimotor activity

BackgroundOscillations in the resting-state scalp electroencephalogram (EEG) represent various intrinsic brain activities. One of the characteristic EEG oscillations is the sensorimotor rhythm (SMR)—with its arch-shaped waveform in alpha- and betabands—that reflect sensorimotor activity. The representation of sensorimotor activity by the SMR depends on the signal-to-noise ratio achieved by EEG spatial filters. New methodWe employed simultaneous recording of EEG and functional magnetic resonance imaging, and 10-min resting-state brain activities were recorded in 19 healthy volunteers. To compare the EEG spatial-filtering methods commonly used for extracting sensorimotor cortical activities, we assessed nine different spatial-filters: a default reference of EEG amplifier system, a common average reference (CAR), small-, middle- and large-Laplacian filters, and four types of bipolar manners (C3-Cz, C3-F3, C3-P3, and C3-T7). We identified the brain region that correlated with the EEG-SMR power obtained after each spatial-filtering method was applied. Subsequently, we calculated the proportion of the significant voxels in the sensorimotor cortex as well as the sensorimotor occupancy in all significant regions to examine the sensitivity and specificity of each spatial-filter. ResultsThe CAR and large-Laplacian spatial-filters were superior at improving the signal-to-noise ratios for extracting sensorimotor activity from the EEG-SMR signal. Comparison with existing methodsOur results are consistent with the spatial-filter selection to extract task-dependent activation for better control of EEG-SMR-based interventions. Our approach has the potential to identify the optimal spatial-filter for EEG-SMR. ConclusionsEvaluating spatial-filters for extracting spontaneous sensorimotor activity from the EEG is a useful procedure for constructing more effective EEG-SMR-based interventions.

Drivability Optimization by Reducing Oscillation of Electric Vehicle Drivetrains

The drivetrain of electric vehicles differs significantly from vehicles with combustion engines. Current concepts of electric vehicle drivetrains usually have a low damping. Typically, there is no clutch to separate the inertial mass of the electric drive machine from the rest of the vehicle drivetrain. External (road unevenness, potholes, etc.) and internal excitation (torque changes of the electric machine, brake interferences, etc.) cause jerk oscillation and sometimes high component stress. These excitations can be reduced by suitable drivability functions, to which a reference filter can also be assigned. A common approach known from conventional drivetrains is to limit the gradient of the demand torque of the drive machine or the driver′s desired torque in order to influence the torque build-up of the drive machine and to reduce the excitation of jerk oscillations. A second approach is the use of a prefilter. The prefilter uses the inverse dynamics of the drivetrain to influence the demand torque of the drive machine. In this paper, the influence of a prefilter based on the inverse dynamics of electric vehicle drivetrains to reduce oscillations is investigated. In addition, an anti-jerk control enhances the drivability function afterwards. All investigations are made on a hardware-in-the-loop test bench to create reproducible results.

Aluminum Melt Filtration with Carbon Bonded Alumina Filters.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 °C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 °C and 30 min). The conventional test yielded contact angles of around 92°, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157°. Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 µm up to 50 µm and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

Parametric and Nonparametric PID Controller Tuning Method for Integrating Processes Based on Magnitude Optimum

Integrating systems are frequently encountered in power plants, paper-production plants, storage tanks, distillation columns, chemical reactors, and the oil industry. Due to the open-loop instability that leads to an unbounded output from a bounded input, the efficient control of integrating systems remains a challenging task. Many researchers have addressed the control of integrating processes: Some solutions are based on a single closed-loop controller, while others employ more complex control structures. However, it is difficult to find one solution requiring only a simple tuning procedure for the process. This is the advantage of the magnitude optimum multiple integration (MOMI) tuning method. In this paper, we propose an extension of the MOMI tuning method for integrating processes, controlled with a two-degrees-of-freedom (2-DOF) proportional–integral–derivative (PID) controller. This extension allows for calculations of the controller parameters from either time domain measurements or from a process transfer function of an arbitrary order with a time-delay, when both approaches are exactly equivalent. The user has the option to emphasise disturbance-rejection or tracking with the reference weighting factor b or apply two different reference filters for the best overall response. The proposed extension was also compared to other tuning methods for the control of integrating processes and tested on a charge-amplifier drift-compensation system. All closed-loop responses were relatively fast and stable, all in accordance with the magnitude optimum criteria.

Experimental and theoretical investigation of polygon-based swept-source with continuous adjustable free spectral range

In this paper, a method that enables adjustment of the free spectral range (FSR) of a swept-source is presented by introducing a right-angled prism inside a polygon-based filter. Firstly, the feasibility of this method is analyzed in theory. When adopting the prism at two different cases, the theoretical prediction value of FSR changes differently. In Case 1, when the beam incidents from the hypotenuse surface of the prism, a broader FSR is obtained. In Case 2, when the beam incidents from the right-angled surface of the prism, a narrower FSR is achieved. Then, to verify these two different changes, the filters deployed in these two cases, as well as a standard reference filter, are tested and compared on a seed swept-source. There is no prism in the reference configuration which has the FSR of 187.9 nm. Compared with that, in Case 1 and Case 2, the measured FSR increases to be 234.4 nm and decreases to be 156.6 nm, respectively. The experimental results are not only consistent with the predicted changes, but also show the ability of fine and continuous adjustment of the FSR. This method is promising to improve the performance of swept-sources, as well as the imaging systems which utilize swept-sources as the light sources.

Adaptive virtual metrology method based on Just-in-time reference and particle filter for semiconductor manufacturing

The prediction of the average Material Removal Rate (MRR) for Chemical Mechanical Planarization (CMP) process has been recognized to be a critical factor of Virtual Metrology (VM) modeling as well as wafer-to-wafer process control. In this paper, a novel method is proposed to dynamically predict MRR in CMP process by using a Just-in-time (JIT) model-based strategy. First, the proposed method applies a reference search procedure to query similar data samples from the historical dataset. Second, a Support Vector Regression (SVR) model is used to fuse the similar data samples with the past MRR. Finally, Particle Filter (PF) is employed to estimate and update the fusion result. The application of PF ensures that the method can track the CMP process change and continuously learn from the current dataset. Compared with static models, the proposed method, named JIT-PF model is an online dynamic method with enhanced accuracy. Compared with pure JIT model, JIT-PF model keeps the historical knowledge in the process. A public dataset is used to validate JIT-PF model with the benchmarks from the recent literature. The model outperforms other peer dynamic models and some static models from the literature.

Influence of Ceramic Foam Filters with Al2O3 Nanocoating on the Aluminum Filtration Behavior Tested With and Without Grain Refiner

In industrial applications, filter materials are often chosen according to cost as well as their processing and thermomechanical properties, but rarely in terms of their behavior during filtration, which is largely due to there being insufficient information available on the influence of filter materials and surface quality on filtration behavior. In this study, the manufacture of functionalized Al2O3 nanofilters was investigated, along with their filtration performance in short- and long-term filtration trials. In addition, sessile drop tests were performed to measure the contact angle of the nanofunctionalized materials, and yielded an approximately 10 deg (11 pct) higher contact angle for nanocoated materials sintered at 800 °C and 1250 °C than for those sintered at 1600 °C and an approximately 23 deg (23 pct) higher contact angle compared to surfaces without a nanocoating. The filtration mechanism was assessed by means of Porous Disk Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) monitoring systems, as well as by analysis of the used and infiltrated filters using Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM/EDX) technology. Both short-term and long-term filtration trials showed that the filtration behaviors of the reference and nanocoated filters were comparable. It was therefore determined that nanocoating of such filters with Al2O3 does not provide any improvement with regard to filtration performance.

Comparison of a priori and interlaboratory-measurement-consensus approaches for value assignment of multi-element reference materials on PTFE filters

Multi-element reference materials (ME-RM) were prepared with 28 elements on polytetrafluoroethylene (PTFE) filters utilizing a custom aerosol deposition system and certified multi-element solutions designed to mimic atmospheric particulate composition. ME-RM were then distributed to eight participating laboratories who provided measurement results via X-ray fluorescence (XRF), particle induced X-ray emission (PIXE), and inductively coupled plasma mass spectrometry (ICP-MS). Lab-consensus loadings computed following an international methodology agreed well with a priori ones for Na, Al, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, As, Se, Rb, Sr, Cd, and Pb. The lab results were in good agreement with a priori reference loadings for S, K, Ca, V, Mn, Fe, Co, As, Se, Rb, Sr, Cd, and Pb. This work demonstrates the ability of the custom aerosol chamber to generate consistent reference filters that can be used for instrument calibration and quality control, interlaboratory comparison, and proficiency testing purposes, filling a much-needed gap hitherto lacking because of unavailability of suitable reference materials.

Design of QAM-FBMC Waveforms Considering MMSE Receiver

Due to its high spectral confinement characteristics and spectral efficiency, QAM-FBMC is considered a candidate waveform to replace CP-OFDM. QAM-FBMC has inevitable non-orthogonality both in time and frequency, and the system and filter must be well-designed to minimize the interferences. However, existing QAM-FBMC studies utilize a matched filter as the receiver filter, which is not suitable for a non-orthogonal system. Therefore, in this paper, we design the prototype filters considering the MMSE criterion, and propose a system providing the highest SINR in QAM-FBMC which cannot avoid non-orthogonality. In addition, we confirm that the proposed filters show best performance at target SNR than the reference filters.

КОМБИНИРОВАННЫЙ РЕГУЛЯТОР СИСТЕМЫ С НЕЯВНЫМ ЭТАЛОНОМ ДЛЯ УПРАВЛЕНИЯ ПО ВЫХОДУ СТРУКТУРНО НЕОПРЕДЕЛЕННЫМ НЕАФФИННЫМ ОБЪЕКТОМ С НЕИЗВЕСТНЫМ ЗАПАЗДЫВАНИЕМ ПО СОСТОЯНИЮ

We study the problem of controlling the output of a non-affine plant with a state delay, the mathemati-cal model of which is structurally and parametrically a priori uncertain. Within the framework of ap-plying the hyperstability criterion and L-dissipativity conditions, as well as using an implicit reference model and filter correctors in the control system, we consider the use of a combined controller with minimal structural complexity, but ensuring the achievement of the set control goal in a given class of non-affine objects with an unknown state delay.

A Phasor Measurement Unit Algorithm Using IIR Filters for FPGA Implementation

Phasor measurement units (PMU) are increasingly used in electrical power transmission networks, to maintain stability and protect the network. PMUs accurately measure voltage, phase, frequency, and rate of change of frequency (ROCOF). For reliability, it is desirable to implement a PMU using an FPGA. This paper describes a novel algorithm, suited to implementation in an FPGA and based on a simple PMU block diagram. A description of its realization using low hardware complexity infinite impulse response (IIR) filters is given. The IEC/IEEE standard 60255-118-1:2018 Part 118-1: Synchrophasor measurements for power systems, describes “reference” Finite Impulse Response (FIR) filters for implementing PMU hardware. At the 10 kHz sampling frequency used for our implementation, each “reference” FIR filter requires 100 multipliers, while an 8th order IIR filter only requires 12 multipliers. This paper compares the performance of different order IIR filter-based PMUs with the performance of the same PMU algorithm using the IEC/IEEE FIR reference filter. The IIR-based PMU easily satisfies all the requirements of IEC/IEEE standard and has a much better out of band signal rejection performance than a FIR-based PMU. Steady state errors for a rated voltage ± 10% and a rated frequency ± 5 Hz are < 0.000001% for total vector error (TVE) and < 1 µHz for frequency, with a latency of two mains cycles.

Laboratory evaluation of low-cost PurpleAir PM monitors and in-field correction using co-located portable filter samplers

Low-cost aerosol monitors can provide more spatially- and temporally-resolved data on ambient fine particulate matter (PM2.5) concentrations than are available from regulatory monitoring networks; however, concentrations reported by low-cost monitors are sometimes inaccurate. We investigated laboratory- and field-based approaches for calibrating low-cost PurpleAir monitors. First, we investigated the linearity of the PurpleAir response to NIST Urban PM and derived a laboratory-based gravimetric correction factor. Then, we co-located PurpleAirs with portable filter samplers at 15 outdoor sites spanning 3 × 3-km in Fort Collins, CO, USA. We evaluated whether PM2.5 correction factors calculated using ambient relative humidity data improved the accuracy of PurpleAir monitors (relative to reference filter samplers operated at 16.7 L min−1). We also (1) evaluated gravimetric correction factors derived from periodic co-locations with portable filter samplers and (2) compared PM2.5 concentrations measured using portable and reference filter samplers. Both before and after field deployment, a linear model relating NIST Urban PM concentrations reported by a tapered element oscillating microbalance and PurpleAir monitors (“PM2.5 ATM”) had R2 = 99%; however, an F-test identified a significant lack of fit between the model and the data. The laboratory-based correction did not translate to the field. Over a 35-day period, time-averaged ambient PM2.5 concentrations and RHs measured during 72- or 48-h filter samples ranged from 1.5 to 8.3 μg m−3 and 47%–77%, respectively. Corrections calculated using ambient RH data increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference concentration from 24% (for uncorrected measurements) to 66%. Corrections derived from monthly, weekly, and concurrent in-field co-locations with portable filter samplers increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference to 46%, 54%, and 72%. PM2.5 concentrations measured using portable filter samplers were within 20% of the reference for 69% of samples.

Non-linear data assimilation via trust region optimization

In this paper, we propose an efficient and practical implementation of the ensemble Kalman filter based on trust region method for non-Gaussian data assimilation. The proposed method works as follows: the empirical moments of an ensemble of model realizations are employed to estimate the parameters of the background error distribution, then an iterative method is proposed to, among iterations, build quadratic surrogate models of the three-dimensional variational (3D-Var) cost function, these models are utilized to approximate solutions of the 3D-Var optimization problem, and the quality of solutions are assessed using the trust region framework. Furthermore, the global convergence of the proposed trust region implementation is theoretically proven. Experimental tests are carried out making use the Lorenz 96 model. Even more, two different observation operators are considered during the experiments: a linear observation operator, and a non-convex and discontinuous one. Different ensemble sizes as well as number of observations (and their time frequencies) are employed to enrich the numerical results. The Maximum Likelihood Ensemble Filter (MLEF) is utilized as a reference filter to estimate the performance of our proposed filter implementation. Ten experiments (repetitions) are performed for each configuration of parameters. The results reveal that, in average, the proposed filter outperforms the MLEF in terms of root mean square errors and even more, it converges to posterior modes of error distributions in cases wherein filter divergence can be possible in the MLEF context.

Pathogenic aspects of palmoplantar keratodermas

Objective — to study level of pro- and anti-inflammatory cytokines and expression of the endogenous intoxication in the patients of palmoplantar keratodermas (PPK).Materials and methods. We examined 23 patients with different variants of PPK in the age from 3 to 60 years. Indicators of cytokines (interleukin4 and TNF-a) in blood serum were determined by the method of immunoassay. The results of the immunoassay (ELISA) were recorded using a spectrophotometer, measuring the optical density in the two-wave mode: the main filter — 450 nm, the reference filter — in the range 620—650 nm. The presence of endogenous intoxication was established using laboratory tests according to A.A. Togobayeva et al. (sorption capacity of erythrocytes) and N.I. Gabrie­lyan et al. (mediomolecular peptides) methods.Results and discussion. With the use of ELISA we studied parameters of proinflammatory (TNF-a) and anti-inflammatory (IL-4) cytokines in the blood serum of the patients with palmoplantar keratoderma. Biochemical methods were used to determine levels of the sorption ability of the erythrocytes (%) and mean molecular peptides (un. ext.). A reliable increase of TNF-a was established in the blood of patients with PPK in comparison with control group: (86.7 ± 11.4) vs (4.0 ± 0.31) pg/ml, respectively, p < 0.001. The level of proinflammatory cytokine IL-4 was unreliably lower than in the control group: (1.65 ± 0.17) and (1.9 ± 0.28) pg/ml, respectively, p < 0.05. The revealed disorders of the cytokine status resulted in increase of endogenous intoxication, which was expressed by reliable rising of values of the erythrocyte sorption ability of erythrocytes (32.4 ± 2.8) vs (29.62 ± 1.69) % at p < 0.05 and the level of mediomolecular peptides ((0.286 ± 0.02) vs (0.215 ± 0.003) un. ext. with p < 0.05).Conclusions. The results obtained show the presence of endogenous intoxication in the patients with palmoplantar keratoderma along with disorders of cytokine status of patients. The data received allow development of the methods of anticytokine and detoxication therapy in the patients suffering from palmoplantar keratoderma as pathogenically confirmed methods of treatment.

The role of blank filter mass in attenuation measurements using an off-line transmissometer

We describe how reference filter characteristics (unexposed weights) can influence instrument-reported attenuation (thereby black carbon concentrations) using the OT21 (SootScan Optical Transmissometer), in the case of Emfab filters. Reference filters (unexposed filters) with higher unexposed weights (pre-weights) compared to that of sample filters are found to reduce the instrument-reported aerosol sample attenuation measurement; reference filters weighing less than the sample filter results in the reverse outcome. This sensitivity can lead to significant under- and over-estimation by the instrument (estimated mean absolute error: ∼ 10 and 16 ATN units for infrared (IR) and ultraviolet (UV) channels, respectively, in our tests, which represent 44% and 15% errors, respectively). We find that the error is linear with respect to difference in the unexposed filter weights of the sample and reference filters. We report two equations (one for IR, one for UV) for correcting the Transmissometer output based on experimental data, which allow use of any unexposed Emfab filter as the reference filter; application of correction parameters to data here reduces the error to 2 and 3 ATN units, respectively, for IR and UV (10% and 3% errors, respectively).

Power Efficiency and EMI Attenuation Optimization in Filter Design

This paper presents a discrete conducted electromagnetic (EM) interference filter optimization procedure, based on a genetic algorithms. A macromodeling technique taking into account the load impedance, the source emissions and the filter parasitic components, including the filter layout, is used to obtain an accurate solution for the optimization process. The latter searches among supplier passive component databases and provides, for a given filter topology, an optimal set of components available on the market. This approach has been applied to a differential Class-D audio amplifier for validation. By considering the electromagnetic interference (EMI), the additional power losses introduced by the filter and the audio gain, two different optimization formulations have been tested. The first corresponds to maximizing the power efficiency of the system while respecting a determined level of EM emissions. The second corresponds to minimizing the EMI without exceeding a determined level of power loss. The optimized filters are built and measurements are carried out. The results show a remarkable power efficiency improvement and a significant EM emission reduction when compared to a reference filter.

Distributed stereo vision‐based 6D localization and mapping for multi‐robot teams

AbstractJoint simultaneous localization and mapping (SLAM) constitutes the basis for cooperative action in multi‐robot teams. We designed a stereo vision‐based 6D SLAM system combining local and global methods to benefit from their particular advantages: (1) Decoupled local reference filters on each robot for real‐time, long‐term stable state estimation required for stabilization, control and fast obstacle avoidance; (2) Online graph optimization with a novel graph topology and intra‐ as well as inter‐robot loop closures through an improved submap matching method to provide global multi‐robot pose and map estimates; (3) Distribution of the processing of high‐frequency and high‐bandwidth measurements enabling the exchange of aggregated and thus compacted map data. As a result, we gain robustness with respect to communication losses between robots. We evaluated our improved map matcher on simulated and real‐world datasets and present our full system in five real‐world multi‐robot experiments in areas of up 3,000 m2 (bounding box), including visual robot detections and submap matches as loop‐closure constraints. Further, we demonstrate its application to autonomous multi‐robot exploration in a challenging rough‐terrain environment at a Moon‐analogue site located on a volcano.

Optimized decentralized adaptive control of noise and vibration for periodic disturbances.

Decentralized control has great potential to facilitate the implementations of multichannel active noise/vibration control systems. The main drawback, however, is its inherent risk of system instability. In this letter an optimized decentralized adaptive control algorithm subject to periodic disturbances is reported. The algorithm employs the scheme of a decentralized filtered-x least mean square algorithm and utilizes optimized reference filters so that the stability of the control system can be ensured. Simulation results based on a realistic vibration isolation system demonstrate that both the stability and the convergent speed could be significantly improved.