Types Of Filters Research Articles

Restart performance of prolonged stopped down-flow hanging sponge reactor for treating of low-strength domestic sewage

The down-flow hanging sponge (DHS) reactor, a type of trickling filter used as a sponge, is a promising treatment system for low-cost sewage treatment. However, the performance of dried sponges that have been non-operational for 8 months has not been evaluated. Accordingly, herein, the re-startup process performance of a DHS reactor treating low-strength domestic sewage in Thailand that had stopped operation for over eight months was investigated. The dried sponge carrier immediately retained water in the sponge biomass-retained carrier and absorbed organic compounds. High nitrification activity of the DHS reactor was observed after 13 d, which was the same as that of the pure sponge biomass-retained carrier start-up. The tracer test results showed that the restarted DHS reactor had a high hydraulic retention time (HRT)/theoretical HRT ratio of 134.2 % at the beginning of the operation from the water retention property of the sponge carrier. Microbial community analysis showed that nitrifying microorganisms were effectively recovered in the biomass-retained sponge carrier. These results demonstrate that the sponge carriers in the DHS reactor that were left into dry condition are available for reuse and has high potential for rapid re-startup.

A Survey of UV Filters Used in Sunscreen Cosmetics

The aim of this study was to determine the types of UV filters used in adult and children’s sunscreen products sold in Poland (part of the EU market) and their frequency of use. The INCI compositions of sunscreen products were collected and analyzed for the presence of UV filters. The study included 150 randomly selected preparations for adults (from 71 brands) and 50 for children (from 33 brands). The survey concerned the UV filters listed in Annex VI to Regulation (EC) No 1223/2009 of the European Parliament and Council of 30 November 2009 on cosmetic products. The most frequently used UV filters in the child sunscreens were triazine derivatives: bis-ethylhexyloxyphenol methoxyphenyl triazine (60.0%) and ethylhexyl triazone (52.0%), and ethylhexyl salicylate (46.0%), a derivative of salicylic acid. The most common in adult sunscreens were butyl methoxydibenzoylmethane (56.0%), a dibenzoylmethane derivative, followed by the salicylic acid derivative ethylhexyl salicylate (54.7%) and the triazine derivatives bis-ethylhexyloxyphenol methoxyphenyl triazine (54.7%) and ethylhexyl triazone (50.0%). Physical filters, including their nano and non-nano forms, were more popular in sunscreens for children, i.e., 50.0% (TiO2) and 22.0% (ZnO), than for adults: 21.3% (TiO2) and 6.7% (ZnO). For both adults and children, many cosmetic products contained four or five UV filters per preparation; however, the child preparations often used two UV filters. To summarize, the following UV filters dominate in photoprotectors for both adults and children: butyl methoxydibenzoylmethane, bis-ethylhexyloxyphenol methoxyphenyl triazine, ethylhexyl triazone, ethylhexyl salicylate, and diethylamino hydroxybenzoyl hexyl benzoate.

Terahertz narrow-band filter based on 3D-printed periodic waveguides

Terahertz (THz) devices, especially waveguide-type functional devices related to transmission and control, are severely scarce due to the lack of effective design and fabrication methods. Here, we experimentally demonstrate a waveguide type of THz narrow-band filter based on 3D-printed technology, which is realized by a cylindrical hollow metal structure with corrugated tube walls. The semi-cylindrical periodic corrugations are 3D printed on a photosensitive resin substrate material, followed by sputtering a layer of gold film on its surface to endow the structure with THz filtering functions. A hollow cylindrical corrugated waveguide is obtained by assembling two identical semi-circular corrugations together. The periodic structure with Bragg resonances can produce a frequency stop band, in which the propagation of THz waves is significantly suppressed. We print a wider section of corrugations in the middle of the waveguide, which destroys the perfect periodicity of the structure and forms a defect. Due to the local resonance caused by the defect, we observe an additional narrow-band transmission peak within the former stop band, which is a good candidate for THz filtering. The filtering bandwidth and extinction ratio are 1.8 GHz and 28 dB, respectively, and the Q-factor reaches 234. The proposed 3D-printed THz filter has the advantages of the simple structure, excellent performance, and easy integration, which can improve the existing THz systems in various applications.

CEPTNER: Contrastive learning Enhanced Prototypical network for Two-stage few-shot Named Entity Recognition

Few-shot Named Entity Recognition (NER) systems aim to classify unseen named entity types with limited labeled examples. Significant progress has been made in the use of large-scale pre-trained language models. However, boundary information and hidden relationships between entities beyond the sequence, which provide additional information and play crucial roles in few-shot NER, have received little attention in recent methods that achieve the state of the art. In this paper, we propose CEPTNER, a Contrastive learning Enhanced Prototypical network for Two-stage few-shot Named Entity Recognition, which leverages meta-learning and prototypical network to identify unseen entity types with limited labeled data. Concretely, we first detect candidate boundaries of entities in the stage of boundary detector, then we employ a prototypical network to filter false boundaries and type for the remaining spans in the stage of entity classifier. Additionally, we conduct entity-level contrastive learning to explore the internal relationship between entities that provides extra information while optimizing the prototypical network. CEPTNER is evaluated on two widely-used few-shot NER datasets and a few-shot slot tagging dataset: Few-NERD, CrossNER and SNIPS. Extensive experiments on various benchmarks show the superiority of CEPTNER over previous methods for few-shot NER.

A study on the characteristics and geometric optimization of a cyclone filter

Cyclone separator without filter is a common device used for separating solid–liquid/gas–solid/gas–liquid mixtures, which is widely used in chemical and household appliance industries. It has the advantages of high separation efficiency and low susceptibility to clogging. However, its separation efficiency cannot reach 100%, and some particles that enter the separator are not separated and will cause secondary pollution to downstream fluids. Combining the cyclone separator with a mesh filter to form a cyclone filter can achieve the complementary advantages of both, namely, high filtration efficiency and low susceptibility to clogging. For cyclone filters, particle shape has a significant impact on filter clogging, but there are few reports on this issue in the literature. In this paper, a new type of cyclone filter is proposed, and experimental and simulation methods are used to study its resistance characteristics. It is found that compared with the case of no filter, the flow resistance of the cyclone filter is significantly reduced, and the reason for the reduction in resistance is analyzed based on flow field analysis. The movement trajectory of flat and spherical particles in the cyclone filter and the problem of particle clogging on the filter are then studied. It is found that flat particles are more likely to cause clogging on the filter, and the reason for the clogging of the filter in the inlet area of the cyclone filter and the mechanism by which flat particles are more likely to clog the filter in the inlet area are analyzed based on the flow field and particle force in the separator. Finally, the inlet profile of the cyclone filter is optimized, and the changes in the inlet flow field and particle movement trajectory before and after optimization are compared. The problem of flat particle clogging on the filter is ultimately solved.

Неотражающие фильтры CВЧ (обзор)

The subject of the review is non-reflective microwave filters (NF) of various types, also called absorption filters. Brief information from the history of the creation of SF is provided. Directional filters are considered, which served as the prototype of non-reflective filters, NFs on lumped elements, non-reflective filters with loaded sections of transmission lines, non-reflective filters on coupled lines. All of these types of devices differ from conventional filters in that they remain matched both in and out of the operating passband (or non-passband). Part of the unwanted frequency spectrum of the signal entering the input of such filters is not reflected back to the signal source, but is absorbed in the filter itself. This operating principle of the NF ensures effective matching with other devices in the system, which is a key characteristic when designing wideband equipment with multiple output and output channels tuned to different frequencies. An assessment is made of the current state of development, prospects for miniaturization and improvement of the characteristics of non-reflective filters.

Aspects Regarding of Passive Filters Sustainability for Non-Linear Single-Phase Consumers

The efficient use of electrical energy (an important component of sustainability) has become increasingly important for electrical consumers (industrial and non-industrial) as we face the challenges of climate change and the need to protect the environment. This theme is essential for guaranteeing a secure and sustainable future for both present and future generations. The power quality and the efficiency of electrical energy are connected to each other. Some power quality problems are caused by natural and unpredictable events, but many disturbances affecting power quality are caused by suppliers and consumers. One of the most important parameters in power engineering is the power factor, which indicates the degree of efficient use of electrical energy. Harmonics is the most important dynamic component of power quality, which affects the operation of electrical equipment and, at the same time, reduces the power factor. Harmonic sources in power systems are generally associated with nonlinear loads. To analyze the operating of passive filters (series L, shunt LC, T type LCL), two groups of experiments (relevant consumers were chosen for the industry as well as from the household sector) were carried out with single-phase nonlinear consumers: in the first group of experiments, a variable-frequency drive is used to supply a three-phase induction motor with variable load; in the second group of experiments, compact fluorescent lamps and LED lamps were used. Following the experiments, it was found that the difficulty of calibrating coils (to size a filter), especially the coils with a core, and the change in electrical properties over time for capacitors. For a certain type of consumer, the improvement of the current waveform depends on the type of filter used, the possibility of improving the power factor (to use electrical energy efficiently), and the role of the source impedance, which is particularly important to improve the efficiency of passive filters. Through the appropriate choice of the passive filter, a decrease in the deforming regime is obtained, with a slight decrease in the active power, and by increasing the power factor, a decrease in the losses of electrical energy from the electrical networks is obtained, with direct implications for the emission of greenhouse gases.

Analysis of Filtered Multicarrier Modulation Techniques Using Different Windows for 5G and Beyond Wireless Systems

In contemporary wireless communication systems, multicarrier modulation schemes have become widely adopted over single-carrier techniques due to their improved capacity to address challenges posed by multipath fading channels, leading to enhanced spectral efficiency. Orthogonal frequency division multiplexing (OFDM), a prevalent multicarrier scheme in 4G, is favored for its ease of implementation, interference resilience, and high data rate provision. But it falls short of meeting the requirements for 5G and beyond due to limitations such as out-of-band (OOB) emissions and cyclic prefixes. This paper introduces the filter bank multicarrier (FBMC) and universal filtered multicarrier (UFMC) with quadrature amplitude modulation (QAM) and phase shift keying (PSK) waveforms through Additive White Gaussian Noise channel (AWGN), Rayleigh fading channel and Rician channel. The objective of this paper is to enhance the performance of UFMC with reduced complexity through the new filtering approach for achieving optimal outcomes. The proposed scheme, incorporating Tukey filtering technique, demonstrates superior performance in reducing peak-to-average power ratio (PAPR) and improving bit error ratio (BER) compared to the original UFMC signal without necessitating additional power increments. Specifically, the UFMC system with Tukey filtering achieves a notable net gain of 5 dB. Simulation results demonstrate that utilizing various filter types in FBMC and UFMC systems, combined with QAM modulation, significantly reduces OOB emissions compared to conventional systems. In aspect to BER, Tukey window showed almost 10−6 at 15 dB SNR in UFMC which is better than FBMC.

Design of fractional-order transitional filters of the Butterworth-Sync-Tuned, Butterworth-Chebyshev, and Chebyshev-Sync-Tuned types: optimization, simulation, and experimental verification

This paper presents the optimal and generalized design of three different fractional-order (FO) transitional filters for the first time in the literature. The transitional filters considered are of the FO Butterworth-sync-tuned, the FO Butterworth-Chebyshev, and the FO Chebyshev-sync-tuned types. A metaheuristic swarm intelligence optimizer, namely the Crow Search Algorithm (CSA), helps to achieve the optimal FO filter model that minimizes the magnitude error with the theoretical function. The accuracy of the proposed approximants is examined for 19 different combinations of orders of the constituent filters for each of the three types of FO transitional filters. Comparisons with the modified stability boundary locus-based second-, third-, and fourth-order filter approximants demonstrate the compactness and superior accuracy of the proposed models. The average performance regarding the approximation accuracy, computational time, and convergence of CSA for solving the proposed filter design problems is investigated. Circuit simulations conducted on the OrCAD PSPICE platform for the proposed filter using the current feedback operational amplifier as an active element highlight good matching between the proposed model and theoretical filter function. Experimental validation is also carried out to justify the practical feasibility of the proposed filter with printed circuit board fabricated FO capacitor emulators.

Predicted effectiveness of EnChroma multi-notch filters for enhancing color perception in anomalous trichromats

EnChroma filters are aids designed to improve color vision for anomalous trichromats. Their use is controversial because the results of lab-based assessments of their effectiveness have so far largely failed to agree with positive anecdotal reports. However, the effectiveness of EnChroma filters will vary depending on the conditions of viewing, including whether the stimuli are broadband reflective surfaces or colors presented on RGB displays, whether illumination spectra are broadband or narrowband, the transmission spectra of particular filters, and the cone spectral sensitivity functions of the observer. We created a model of anomalous trichromatic color vision to predict the effects of EnChroma filters on the color signals impaired in anomalous trichromacy. Using the model we varied illumination, filter type and observer cone sensitivity functions, and tested the effect of presenting colors as broadband reflective surfaces or on RGB displays. We also used hyperspectral images to assess the impact of the filters on anomalous trichromats’ color vision for natural scenes. Model results predicted that the filters should be broadly effective at enhancing anomalous trichromats’ equivalent to L/(L + M) chromatic contrasts under a range of viewing conditions, but are substantially more effective for deuteranomals than for protanomals. The filters are predicted to be more effective for broadband reflective surfaces presented under broadband illuminants than for surfaces presented under narrowband illuminants or for colors presented on RGB displays. Since the potential impacts of contrast adaptation and perceptual learning are not considered in the model, it needs to be empirically validated. Results of empirical tests of the effects of EnChroma filters on deuteranomalous color vision in comparison with model predictions are presented in an accompanying paper (Somers et al., in prep.).

A feasible approach to measure metal concentrations in drill hole waters on site for mineral exploration

The new technologies used in the green transition towards carbon-free societies typically demand extensive use of metals. This leads to a heavily growing need for exploration and extraction of ore deposits. Exploration can be facilitated by measuring metal concentrations in ground and surface waters carrying trace concentrations of metals leached from nearby deposits. Currently, measuring metal concentrations in water is slow and expensive and it cannot be done on-site, which hinders the discovery of new ore deposits. To address this challenge, we have developed a method to collect and concentrate the dissolved metals in a solid filter and measure the metal concentrations directly from the filter with a portable X-ray fluorescence spectrometer. The permeable filter is made of mesoporous silicon modified with bisphosphonates. Two types of adsorbing materials for the filters were prepared based on scalable production methods: i) regenerative etching of metallurgical grade silicon powder, and ii) magnesiothermic reduction of silica from barley husks. Empirical calibrations were prepared in a concentration range of 10–200 μg/L for Mn, Co, Ni, Cu, Zn, and Pb using water samples prepared by spiking well water with standard metal solutions. Both filter types were tested for their ability to adsorb metals from the real water samples taken from drill holes. The developed system was able to detect metal concentrations down to 12 μg/L (ppb) showing its potential for on-site measurements of dissolved metals in water samples, which could be feasible in the discovery of new mineral deposits. This innovation enables smart sampling during exploration and provides real-time information on metal concentrations in water.

Remote Sensing Extraction of Crown Planar Area and Plant Number of Papayas Using UAV Images with Very High Spatial Resolution

The efficient management of commercial orchards strongly requires accurate information on plant growing status for the implementation of necessary farming activities such as irrigation, fertilization, and pest control. Crown planar area and plant number are two very important parameters directly relating to fruit growth conditions and the final productivity of an orchard. In this study, in order to propose a novel and effective method to extract the crown planar area and number of mature and young papayas based on visible light images obtained from a DJ Phantom 4 RTK, we compared different vegetation indices (NGRDI, RGBVI, and VDVI), filter types (high- and low-pass filters), and filter convolution kernel sizes (3–51 pixels). Then, Otsu’s method was used to segment the crown planar area of the papayas, and the mean–standard deviation threshold (MSDT) method was used to identify the number of plants. Finally, the extraction accuracy of the crown planar area and number of mature and young papayas was validated. The results show that VDVI had the highest capability to separate the papayas from other ground objects. The best filter convolution kernel size was 23 pixels for the low-pass filter extraction of crown planar areas in mature and young plants. As to the plant number identification, segmentation could be set to the threshold with the highest F-score, i.e., the deviation coefficient n = 0 for single young papaya plants, n = 1 for single mature ones, and n = 1.4 for crown-connecting mature ones. Verification indicated that the average accuracy of crown planar area extraction was 93.71% for both young and mature papaya orchards and 95.54% for extracting the number of papaya plants. This set of methods can provide a reference for information extraction regarding papaya and other fruit trees with a similar crown morphology.

Effects of water and other filters on fracture resolution in industrial micro-CT scanning

Filtering is known to improve image quality of CT scans. Water immersion is one type of filtering that has been used for CT scanning dry (skeletonized) bones, and it has been suggested that this approach can increase measurement accuracy and improve fracture resolution. These tests have previously involved clinical CT scanners. Here we use an industrial micro-CT scanner and test whether water immersion and other x-ray filtering options increases fracture resolution in reconstructed scans of dry bones.Eleven dry non-human bones were CT scanned using the same acquisition parameters, while varying filter options. Bones were scanned (1) in an unfiltered “dry” air environment, (2) using metal filters at the x-ray source, and (3) with the bones immersed in water. A small subset of bones (N = 3) was also scanned using the same parameters except increasing the number of projections acquired from 500 to 1500. Reconstructed scans were evaluated by the authors, in part using a Likert scale comparing filtered with unfiltered scans, to assess fracture resolution (overall appearance and extent).Results showed that increasing the projections resulted in the greatest improvement in fracture resolution, followed by filtering at the x-ray source. Water immersion performed poorly overall, possibly due to movement artifacts that result from this type of scanning, in which the specimen rotates on a stage during the scan. When using this type of CT scanner, if increased fracture resolution is desired, water immersion is not recommended; increasing the number of projections or filtering at the x-ray source is suggested instead.

Elementary Negative Group Delay Filter Functions

A theoretical study of the behavior of some elementary first- and second-order functions, which are suitable for realizing negative group delay, is performed in this work. As both the gain and phase responses are simultaneously considered, important derivations related to the actual bandwidth of operation are derived accompanied by useful design tips. The presented theory is supported by simulation and experimental results obtained through the utilization of typical active-RC filter structures, as well as from a field-programmable analog array device.

A framework for the systematic evaluation of a novel cigarette filter technology

Any functional change in cigarette filter design warrants a rigorous assessment to ensure comparability to existing filter functionality.This study compares the functionality of a standard CA filter with a novel cellulose-based alternative using a combination of emissions, in silico approaches, pre-clinical assessments and behavioural studies. We assess the challenges faced with a significant filtration change, the substantiation of this change and the limitations of such assessments. We explore cigarette emission chemical profiles; assess the potential toxicological impacts (in vitro and statistical modelling) of the differing chemical profiles of cigarette smoke aerosol resulting from the respective filter types; and, finally investigate the behavioural aspects associated with use of the novel filter as compared to the traditional one. The aim of the study was to establish a weight of evidence assessment framework for the comprehensive evaluation of a novel cigarette filter design as part of robust stewardship approach.The data show comparability to a standard CA filter across all assessments and highlight potential areas of investigation for future novel filter product iterations. The approach demonstrates the applicability of a comprehensive step-wise assessment framework to identify any potential increased toxicant emissions and exposures associated with using the novel filter.

Retention of per- and polyfluoroalkyl substances by syringe filters

Per- and polyfluoroalkyl substances (PFAS) are being increasingly measured in water and wastewater due to emerging toxicity concerns and strict regulatory limits. Previous studies have filtered water samples to remove suspended solids before PFAS analysis. However, filtration may introduce negative bias to measured PFAS concentrations. Using a well-controlled syringe pump assembly, we evaluated retention of six perfluoroalkyl carboxylates, three perfluoroalkyl sulfonates, one fluorotelomer sulfonate, and two perfluorooctane sulfonamides by glass-fiber, glass-fiber cellulose acetate, nylon, polyethersulfone, polypropylene, polyvinylidene fluoride/ difluoride, and surfactant-free cellulose acetate filters. The impacts of water quality and operational parameters were also investigated for select filter types. We found that PFAS were retained on all filters, with the glass-fiber cellulose acetate filters demonstrating the lowest retention. For all filters, PFAS retention was linearly related to chain length and hydrophobicity above certain thresholds (i.e., log D higher than 1.5). Importantly, more PFAS were retained at low filtrate volumes, and ~ 30 mL filtrate was required before the retention efficiencies stabilized. Solution pH only affected the retention of perfluorooctane sulfonamides. Pore size (i.e., 0.20, 0.45, 0.70 µm), filtration rate (i.e., 0.5, 1.0 mL min−1), and PFAS concentration (i.e., 10, 100 µg L−1), did not exert major influences on PFAS retention. The presence of dissolved organic matter improved PFAS permeation. Based on the reported results, filtration introduces bias and is not recommended for sample pretreatment.

Fourier-domain filtering analysis for color-polarization camera demosaicking.

We review Fourier-domain methods for demosaicking Bayer-filter color cameras and monochrome polarization cameras, and then generalize the approach for the quad-Bayer-filter mosaic and for color-polarization cameras. For each of these four mosaic filter types, we provide theoretical expressions for the sampling functions, the Fourier-domain channels, and the linear combination of reconstructed channels (the demosaicking algorithm) needed to estimate the input (presampled) image. A useful advantage of the Fourier-domain approach is that it provides a direct means of visualizing and quantifying when aliasing is likely or unlikely to be present. For the Bayer and quad-Bayer-filter types, we provide simulated images, while for the polarization camera types we provide experimental images and videos to illustrate the algorithm and analyze crosstalk error.

Optimal filter materials for protist quantification via droplet digital PCR

The use of droplet digital polymerase chain reaction (ddPCR) has greatly improved the quantification of harmful protists, outperforming traditional methods like quantitative PCR. Notably, ddPCR provides enhanced consistency and reproducibility at it resists PCR inhibitors commonly found in environmental DNA samples. This study aimed to determine the most effective filter material for ddPCR protocols by assessing the reproducibility of species-specific gene copy numbers and filtration time across six filter types: cellulose acetate (CA), mixed cellulose ester (MCE), nylon (NY), polycarbonate (PC), polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The study used two species of Chattonella marina complexes as a case study. Filtration rates were slower for NY, PC, and PVDF filters. Moreover, MCE, NY, PES, and PVDF yielded lower DNA amounts than other filters. Importantly, the CA filter exhibited the lowest variance (38–39%) and the highest determination coefficients (R2 = 0.92–0.96), indicating superior performance. These findings suggest that the CA filter is the most suitable for ddPCR quantification of marine protists, offering quick filtration and reliable reproducibility.

Analysis of Phase-Locked Loop Filter Delay on Transient Stability of Grid-Following Converters

To ensure precise phase estimation within the q-axis of the phase-locked loop (PLL), integrating a filter into the q-axis loop is essential to mitigate grid-voltage harmonics. Nevertheless, the intrinsic delay characteristics of this filter impede PLL synchronization during significant grid disturbances. This study begins by developing mathematical models for three types of filters—moving-average filter (MAF) for eliminating odd harmonic components, dq-frame cascaded delayed signal cancellation (dqCDSC) filter, and notch filter (NF). Following the reduction in filter orders, a third-order nonlinear large-signal model of the PLL, incorporating an additional q-axis internal filter, is formulated. Using phase plane analysis, this study investigates the transient synchronism of the grid-following converter (GFL) and explores the influence of delay time constants from the three PLL filters on its behavior while delineating the boundaries of their basins of attraction. Theoretical findings indicate that, relative to the traditional SRF-PLL, incorporating an internal filter into the PLL compromises the transient synchronous stability of GFL. Specifically, greater filter delay time constants exacerbate the GFL’s vulnerability to transient instability amid substantial grid disturbances. Hence, careful consideration is essential when using MAF-PLL and NF-PLL in situations demanding high synchronization stability. The theoretical analyses are validated using Matlab/Simulink to verify their accuracy.

Characteristics in the Fourier spectrum of images associated with discontinuities such as cracks and fissures in concrete structures.

Increasing An algorithm is developed to identify differences between concrete slabs with some type of Crack and Fissure discontinuity. The Fourier transform is used as a basis. Different types of fil-ters were evaluated within the image processing algorithm, in order to adapt favorably to the discontinuity detection process, allowing the image data to be read in the frequency domain, generating a figure of merit to compare the image. where there are no discontinuities and those that have some alteration in their structure.