Open Filter Research Articles

A Tunable Open Planar Acoustic Notch Filter Utilizing a Pneumatically Modulated Helmholtz Resonator Array

Acoustic filters provide sound insulation unpleasant noises at a specific frequency only. Ordinary passive acoustic filters made up of acoustic metamaterial structures can work without a power supply. However, their working frequency is not adjustable. This study reports a tunable open planar acoustic notch filter that incorporates a pneumatically controlled Helmholtz resonator (HR) array. The HR array consisted of three layers: cavities, a membrane, and microchannels. The cavities function as the HR chambers, whose volume determines the resonant frequency. The acoustic wave is effectively attenuated at this frequency owing to the HR effect. The HR chamber volume can be varied by displacing the stretchable membrane with air pressure through the microchannels. This helps in adjusting the resonant frequency, thereby realizing a tunable acoustic notch filter. We conducted theoretical, and experimental examinations along with simulations of the frequency response for an HR array with three different cavity thicknesses. The prototype device realized a frequency tuning of approximately 4.1–4.9 kHz with 10 dB filtering. Furthermore, an improved notch frequency tunability was observed for the thinner cavities, along with a decrease in the notch performance. Thus, the proposed HR array filter can be useful for high-frequency noise that is generally uncomfortable for humans.

Simulation of horizontal injection wells in Managed Aquifer Recharge facilities using the conduit flow process (CFP) code for MODFLOW-2005

Groundwater management of coastal aquifers is a scientific and engineering challenge, as coastal aquifer systems are hydrogeologic features that are hydraulically connected with the sea while at the same time are stressed with extensive abstraction practices for irrigation. To remedy this, Managed Aquifer Recharge -MAR- is proved to be a sound and effective technology that is able to fill the gap between groundwater supply and demand. Essential part of this procedure is reliable groundwater modeling that simulates effectively all involved hydrologic processes in order to be able to predict the response of the system under different natural or artificially induced conditions. This paper describes the application of a modeling tool, for the simulation of the relative hydrologic processes between the open filter pipe of the injection well and the surrounding aquifer material with the finite difference method. More specifically, a MAR pilot setup with a horizontal direction injection well was simulated with the Conduit Flow Process (CFP) of MODFLOW-2005 code. To investigate further the applicability of CFP code, the HDDW was conceptualized with the simpler MODFLOW WEL package and the results of the two models were compared. For the two models, sensitivity analysis was conducted using UCODE_2014. Both models were calibrated successfully as the simulated values showed an acceptable fit to the observed data. The main difference between the two packages was observed in the rise of groundwater level along the horizontal well. To this end, it was indicated that CFP offered a more realistic representation of the horizontal well pipe.

Utilization of a Miniaturized Brazilian Disc Test for Strength Measurements of C‐Bonded Alumina Filter Materials

Filtration of molten metals using open cell ceramic filters has proven the premises regarding the improvements of the final product quality. The Collaborative Research Center 920 has made a substantive record in developing carbon‐bonded alumina () filters. Considering the mechanical loads carried by these filters, material strength determination is a necessary step to improve their performance. The Brazilian disc test (BDT) is a method to determine mechanical properties of brittle materials with indirect tensile stresses. The simplicity of the specimen production, test application, as well as results evaluation makes this test attractive. Herein, experimental investigations of different variations of the BDT setup on specimens are conducted. Test variations mainly concern the geometry of the load application to ensure a defined failure of the specimens. Digital image correlation (DIC) technique is used to extract the necessary data for the evaluation of the results. Moreover, within an inverse parameter identification method finite element analysis is used to determine strength and elastic material parameters. Additionally, a high‐speed camera is used for the detection of crack formation. It can be concluded that a special variation of the BDT is a suitable method to evaluate the mechanical properties of .

Separated and prime compactifications

We discuss conditions under which certain compactifications of topological spaces can be obtained by composing the ultrafilter space monad with suitable reflectors. In particular, we show that these compactifications inherit their categorical properties from the ultrafilter space monad. We further observe that various constructions such as the prime open filter monad defined by H. Simmons, the prime closed filter compactification studied by Bentley and Herrlich, as well as the separated completion monad studied by Salbany fall within the same categorical framework.

Structural mechanism of TRPV3 channel inhibition by the plant-derived coumarin osthole.

TRPV3, a representative of the vanilloid subfamily of TRP channels, is predominantly expressed in skin keratinocytes and has been implicated in cutaneous sensation and associated with numerous skin pathologies and cancers. TRPV3 is inhibited by the natural coumarin derivative osthole, an active ingredient of Cnidium monnieri, which has been used in traditional Chinese medicine for the treatment of a variety of human diseases. However, the structural basis of channel inhibition by osthole has remained elusive. Here we present cryo-EM structures of TRPV3 in complex with osthole, revealing two types of osthole binding sites in the transmembrane region of TRPV3 that coincide with the binding sites of agonist 2-APB. Osthole binding converts the channel pore into a previously unidentified conformation with a widely open selectivity filter and closed intracellular gate. Our structures provide insight into competitive inhibition of TRPV3 by osthole and can serve as a template for the design of osthole chemistry-inspired drugs targeting TRPV3-associated diseases.

Use of Synchrotron Phase-Sensitive Imaging for the Investigation of Magnetopriming and Solar UV-Exclusion Impact on Soybean (Glycine max) Leaves.

The combined response of exclusion of solar ultraviolet radiation (UV-A+B and UV-B) and static magnetic field (SMF) pre-treatment of 200 mT for 1 h were studied on soybean (Glycine max) leaves using synchrotron imaging. The seeds of soybean with and without SMF pre-treatment were sown in nursery bags kept in iron meshes where UV-A+B (280–400 nm) and UV-B (280–315 nm) from solar radiation were filtered through a polyester filters. Two controls were planned, one with polythene filter controls (FC)- which allows all the UV (280–400 nm); the other control had no filter used (open control-OC). Midrib regions of the intact third trifoliate leaves were imaged using the phase-contrast imaging technique at BL-4, Indus-2 synchrotron radiation source. The solar UV exclusion results suggest that ambient UV caused a reduction in leaf growth which ultimately reduced the photosynthesis in soybean seedlings, while SMF treatment caused enhancement of leaf growth along with photosynthesis even under the presence of ambient UV-B stress. The width of midrib and second-order veins, length of the second-order veins, leaf vein density, and the density of third-order veins obtained from the quantitative image analysis showed an enhancement in the leaves of plants that emerged from SMF pre-treated seeds as compared to untreated ones grown in open control and filter control conditions (in the presence of ambient UV stress). SMF pre-treated seeds along with UV-A+B and UV-B exclusion also showed significant enhancements in leaf parameters as compared to the UV excluded untreated leaves. Our results suggested that SMF-pretreatment of seeds diminishes the ambient UV-induced adverse effects on soybean.

Behavioural effects of cage systems on the G93A Superoxide Dismutase 1 transgenic mouse model for amyotrophic lateral sclerosis.

Environmental factors inherent to animal facilities can impact on the neuro-behavioural phenotype of laboratory mice and genetic mouse models for human diseases. Many facilities have upgraded from traditional 'open filter top' cages (FT) to individually ventilated cage (IVC) systems, which have been shown to modify various behavioural responses of laboratory mice. Importantly, the impact of IVC housing on the G93A superoxide dismutase 1 mouse model of amyotrophic lateral sclerosis (ALS) is currently unknown. Male and female wild type-like (WT) and heterozygous SOD1G93A mice were group-housed in FT or IVC systems from PND 30 ± 5 onwards. Body weight and motor function were assessed weekly from 15 weeks onward. Mice were also tested for cognitive abilities (i.e., fear conditioning and social recognition memory) and sensorimotor gating (i.e., prepulse inhibition: PPI). SOD1G93A mice lost body weight, and their motor function degenerated over time compared with control littermates. Motor impairments developed faster when SOD1G93A females were housed in IVCs. Context and cue freezing were increased in SOD1G93A females compared with controls, whereas all SOD1G93A mice exhibited lower acoustic startle and PPI than WT mice. IVC housing led to an increase in cue freezing in males and reduced the severity of PPI deficits in SOD1G93A females. Overall, IVC housing impacted moderately on the SOD1G93A phenotype but central behavioural deficits were still evident across housing conditions. Nonetheless, our findings indicate the importance of assessing the effect of cage system in genetic mouse models as these systems can modulate the magnitude and onset of genotypic differences.

Biological and Physical Clogging in Infiltration Wells: Effects of Well Diameter and Gravel Pack.

Gravity-driven infiltration into the shallow subsurface via small-diameter wells (SDWs), i.e., wells with an inner diameter smaller than 7.5cm (3inches) and no gravel pack) has proven to be a cost-efficient and flexible tool for managed aquifer recharge (MAR), as it provides relatively high recharge rates with minimal construction effort. SDWs have a significantly smaller open filter area than larger diameter wells with gravel pack, making the infiltration of low-quality waters through these wells more at risk clogging. To investigate their susceptibility for biological and physical clogging, 24 physical models with different well setups were evaluated by infiltrating either nutrient-poor but turbid water or nutrient-rich but clear water. The experiments showed that smaller diameters and the lack of a gravel pack increase the well's susceptibility to both kinds of clogging. However, this effect was observed to be much more pronounced for physical than for biological clogging. Our conclusion is that SDWs show severe disadvantages with respect to the infiltration of highly turbid waters in comparison to large diameter wells with a gravel pack. Nevertheless, this disadvantage is much less severe when it comes to the infiltration of clear but nutrient-rich waters (e.g., treated wastewater). Depending on the economic and geological circumstances of a MAR-project, this disadvantage could be outweighed by the significantly lower construction costs of SDWs.

Acaricidal activity against Ixodes ricinus nymphs of essential oils from the Libyan plants Artemisia herba alba, Origanum majorana and Juniperus phoenicea.

Ixodes ricinus (L.) (Acari: Ixodidae) is a major vector for the transmission of several important human pathogens. The aim of the present study was to evaluate the in vitro efficacy of different concentrations of essential oils (Eos) on I. ricinus tick nymphs. Oils were obtained from the leaves of three plants native to Libya: white wormwood (Artemisia herba alba Asso), marjoram (Origanum majorana L.) and Arâr (Juniperus phoenicea L., English common name Phoenician juniper). Assays were done using the "open filter paper method". Two concentrations from each oil, 0.5 and 1μl/cm, were tested. The acaricidal effect was measured in terms of the lethal concentrations (LC50, LC95) and lethal time (LT50, LT95). Mortality rates were obtained by counting the surviving nymphs every 30min for the first five hours and then at 24, 48 and 72h. A mortality of 100% was recorded at the higher concentration of oils (1μl/cm2) from A. herba alba and J. phoenicea at the first 2h of exposure. Exposure to O. majorana led to 100% mortality on the third day (72h), and this effect decreased noticeably with 0.5μl/cm2 oil at the same exposure time. However, 50% of ticks showed a paralysis effect and less movement after 2h. The LC50 of mortality was reached within the first 24h of exposure time at 0.5μl/cm2 of O. majorana, which produced 60% tick's mortality. Chemical composition of the essential oils was elucidated by gas chromatography-mass spectrometry analyses. These results suggest that essential oils deserve further investigation as components of alternative approaches for I. ricinus tick control.

Algebraic representation of frame-valued continuous lattices via the open filter monad

With a frame L as the truth value table, we prove that the collections of open filters of T0L-topological spaces form a monad. By means of L-Scott topology and the specialization L-order, we get the main results: (1) the Eilenberg-Moore algebras of the open filter monad are precisely L-continuous lattices; (2) the category of L-continuous lattices is strictly monadic over the category of T0L-topological spaces.

On the removal of the open earcanal high-pass filter effect due to its occlusion: A bone-conduction occlusion effect theory

The occlusion effect is commonly experienced by in-ear device wearers as an increased loudness sensation of bone-conducted low frequency sounds. A widespread theory proposed by Tonndorf and based on a simplified electro-acoustic model describes the phenomenon as the removal of the open earcanal high-pass filter effect due to a perfect or partial occlusion. However, this filter has not been clearly defined and several ambiguities remain. Revisiting the model, a second order high-pass filter effect for the volume velocity transferred between the earcanal wall and the eardrum is highlighted. This filter remains for partial occlusion but vanishes for perfect occlusion. In the latter case, the volume velocity transferred from the earcanal cavity to the middle ear through the eardrum drastically increases, which explains the predominance of the occluded outer ear pathway on the hearing by bone-conduction at low frequencies.

Denoising for Improved Parametric MRI of the Kidney: Protocol for Nonlocal Means Filtering.

In order to tackle the challenges caused by the variability in estimated MRI parameters (e.g., T2* and T2) due to low SNR a number of strategies can be followed. One approach is postprocessing of the acquired data with a filter. The basic idea is that MR images possess a local spatial structure that is characterized by equal, or at least similar, noise-free signal values in vicinities of a location. Then, local averaging of the signal reduces the noise component of the signal. In contrast, nonlocal means filtering defines the weights for averaging not only within the local vicinity, bur it compares the image intensities between all voxels to define "nonlocal" weights. Furthermore, it generally compares not only single-voxel intensities but small spatial patches of the data to better account for extended similar patterns. Here we describe how to use an open source NLM filter tool to denoise 2D MR image series of the kidney used for parametric mapping of the relaxation times T2* and T2.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers.

Read counts from environmental DNA (eDNA) metabarcoding reflect fish abundance and biomass in drained ponds

The sampling of environmental DNA (eDNA) coupled with cost-efficient and ever-advancing sequencing technology is propelling changes in biodiversity monitoring within aquatic ecosystems. Despite the increasing number of eDNA metabarcoding approaches, the ability to quantify species biomass and abundance in natural systems is still not fully understood. Previous studies have shown positive but sometimes weak correlations between abundance estimates from eDNA metabarcoding data and from conventional capture methods. As both methods have independent biases a lack of concordance is difficult to interpret. Here we tested whether read counts from eDNA metabarcoding provide accurate quantitative estimates of the absolute abundance of fish in holding ponds with known fish biomass and number of individuals. Environmental DNA samples were collected from two fishery ponds with high fish density and broad species diversity. In one pond, two different DNA capture strategies (on-site filtration with enclosed filters and three different preservation buffers versus lab filtration using open filters) were used to evaluate their performance in relation to fish community composition and biomass/abundance estimates. Fish species read counts were significantly correlated with both biomass and abundance, and this result, together with information on fish diversity, was repeatable when open or enclosed filters with different preservation buffers were used. This research demonstrates that eDNA metabarcoding provides accurate qualitative and quantitative information on fish communities in small ponds, and results are consistent between different methods of DNA capture. This method flexibility will be beneficial for future eDNA-based fish monitoring and their integration into fisheries management.

Open Inferior Vena Cava Filter Removal

The last several decades have seen dramatic changes in the standards for both the insertion and removal of inferior vena cava (IVC) filters. Retrievable and nonretrievable IVC filters can frequently be removed by endovascular techniques. Because IVC filters rarely cause symptoms or result in complications, those that cannot be easily removed are usually left in place. Open removal is reserved for IVC filters with complications or causing symptoms that cannot be removed by endovascular techniques. The results of open IVC filter removal at a single academic medical center from January 2011 through June 2019 were reviewed. Nine open IVC filter removals were performed. Six (68%) patients were female. The mean age was 46 years (range, 26-65 years). The filters had been in place for a mean of 6.6 years (range, 1-12 years). Six (68%) of the filters were originally placed because of deep venous thrombosis with pulmonary embolus in patients with contraindications to anticoagulation. Three (33%) were placed prophylactically in high-risk trauma patients not able to be anticoagulated. The most common indication for IVC filter removal was severe malposition of the filter with filter erosion through the IVC wall (n = 4; Fig). Other indications included chronic back pain with filter struts eroding into vertebral bodies (n = 3) and strut erosion into the duodenum (n = 2). The mean length of stay was 6 days (range, 4-16 days). Complications included one case of postoperative ileus and two wound complications, one requiring reoperation. In seven (78%) cases, the filer was captured through a small venotomy after mobilization of the vena cava and cutting of the protruding struts. Two patients required an extensive venotomy to remove the filter. Only one of the three patients with back pain had symptom resolution. IVC filters that cannot be removed by endovascular techniques can be safely removed with an open procedure. In most patients, the filter can be captured and removed through a small venotomy; an extensive venotomy is not usually required. The majority of patients with back pain do not have relief of symptoms after IVC filter removal.

Integrated graphene oxide resistive element in tunable RF filters

Adaptable communication systems are of great interest as they provide dynamic front end to accommodate the tunable spectrum management in advanced wireless systems. Memristor (acronym of memory resistor) is an emerging technology part of resistive RAM (RRAM) that has good potential for application in reconfigurable RF devices. The potentiality of using resistive switches for frequency tuning of high frequency RF filters is successfully explored in this article for the first time. Tunable RF filter is designed with detailed simulation using Ansys HFSS, and then correlated with measured results from experiment. As a proof of concept, a prototype of the tunable RF filter is fabricated by using a graphene oxide (GO) integrated with a conventional microstrip open stub notch filter. The resistor switching ability of the device is exploited for the frequency tuning. The resonating length of the notch filter is varied by changing the resistance of the active GO material between ‘HIGH’ (OFF) and ‘LOW’ (ON) resistance states. The measured results demonstrate the great potential of using RRAM in tunable RF devices. It also proves the possibility of tuning RF devices without any localized surface mount device (SMD) element or complex realization technique.

Outcomes of Innominate Artery Revascularization Through Endovascular, Hybrid, or Open Approach

Atherosclerotic disease of the innominate artery (IA) is rare and can lead to cerebral, upper extremity, and vertebral steal symptoms. Nonocclusive lesions can be treated with endovascular interventions, often with a hybrid approach while performing a right carotid endarterectomy (RCEA). Calcified IA lesions have a high risk of embolization to bilateral cerebral hemispheres. Occlusive lesions may require treatment through a median sternotomy and bypass. The purpose of our study is to review our short-term and long-term outcomes of IA revascularization. Our operative database was used to identify patients who underwent IA revascularization between January 1998 and December 2018. Patients who underwent innominate artery stenting (IAS), combined with RCEA and IAS as well as aortoinnominate bypass (AIB), were identified. Our primary end points were freedom from neurologic event, all-cause mortality, and need for reintervention. Thirty-three patients (18 females [55%]) who underwent IA revascularization were identified. Average age was 67±8years, and mean clinical follow-up was 51±21months. Most patients (30 [91%]) were on a statin and antiplatelet therapy. Twenty-one patients (64%) were symptomatic. Twelve patients (36%) were asymptomatic and underwent combined RCEA with retrograde IAS for critical right carotid stenosis and IA stenosis. Preoperative imaging included a carotid duplex and computed tomography angiography. Eighteen patients (55%) underwent RCEA+IAS, 11 patients (33%) underwent isolated IAS, and 4 patients (12%) underwent AIB. In our attempt to protect bilateral hemispheres during IAS for heavily calcified lesions, we used right common carotid artery (CCA) clamping although open exposure and left CCA embolic protection filter was placed through transfemoral approach. Patients who underwent AIB had chronic heavily calcified IA occlusions or occluded IA stents with failed endovascular interventions. Perioperative stroke rate was 3%, involving 1 patient who developed reperfusion syndrome after RCEA+IAS. Perioperative mortality was 0%. Long-term stroke rate was 0%, and long-term mortality was 15% (5 of 33) because of cardiac disease. Overall restenosis rate was 9%, involving 3 patients who required secondary interventions for IA in-stent restenosis. IA interventions through a hybrid approach or an open approach are safe, with acceptable perioperative stroke and mortality rates. Long-term patency of these interventions is acceptable. Bilateral cerebral embolic protection can be accomplished by clamping the right CCA through an open exposure and placing a filter in the left CCA through a transfemoral approach. Patients undergoing IAS appear to have a higher rate of restenosis compared with AIB, and therefore, close follow-up with noninvasive imaging is recommended.

A Machine Learning Based Email Spam Classification Framework Model: Related Challenges and Issues

Spam emails, also known as non-self, are unsolicited commercial emails or fraudulent emails sent to a particular individual or company, or to a group of individuals. Machine learning algorithms in the area of spam filtering is commonly used. There has been a lot of effort to render spam filtering more efficient in classifying e-mails as either ham (valid messages) or spam (unwanted messages) through the ML classifiers. We may recognize the distinguishing features of the material of documents. Much important work has been carried out in the area of spam filtering which cannot be adapted to various conditions and problems which are limited to certain domains. Our analysis contrasts the positives methods as well as some shortcomings of current ML methods and open spam filters study challenges. We suggest some of the new ongoing approaches towards deep leaning as potential tactics that can tackle the challenge of spam emails efficiently.

Comparison of granular and open cell foam filter models by numerical simulation

A comparison of granular and highly porous mesh filter models is based on the results of numerical simulation. We created models filters with an equal diameter of granules and cells. In order to avoid calculation errors associated with a random arrangement of cells, we averaged the results for five geometries. The values of the pressure drop obtained based on numerical simulation correlate well with the data obtained by the experimental Ergun equation. We calculated particle deposition efficiency and filter quality factor for models with equal porosity, and pressure drop value. Additionally, the filter quality factor for geometries with equal particle deposition efficiency was estimated. The calculation results show that it is advisable to compare the filter models by the value of the differential pressure.

Determination of the particle deposition efficiency value in a granular and open cell foam filter

We constructed a model of a granular filter with spherical granules with a diameter of dc = 5 mm and a porosity of ε = 0.44, as well as two models of a highly porous cellular filter. The first model has a porosity equal to the porosity of the granular filter, and the second model has a surface area equal to the surface area of the granular filter. A numerical and experimental study of the change in pressure drop depending on the average filtration rate was carried out; the results are in a good agreement. In the case of porosity of the granular filter. In the velocity field found, the trajectories of the particles are calculated, by which the efficiency of particle deposition is determined as the ratio of the number of particles deposited in the filter to the total number started. The deposition efficiency curves are the closest for models with a same filter surface area. The surface area of the material is the determining parameter when choosing a filter.

Investigation of the multi-layer open cell foam filter model using numerical simulation and experimental studies

In this work, we studied the influence of the internal features of an open cell foam material structure on the efficiency of particle deposition and the pressure drop value of the medium. Constructing of the open cell foam filter models is based on the Distinct Element Method, which allows creating geometry with a random arrangement of pores in space. Calculations of the flow field and particle trajectories were performed using the ANSYS Fluent software package (v. 19.0). Experimental studies were conducted using samples created on the basis of the inverse matrix of 3D printed computational models. Also, models of various geometries with a fixed porosity of the medium are considered. Conducted numerical and experimental studies show that the filter model with the lowest porosity provides the highest deposition efficiency of particles. For a given fixed porosity of the medium, a filter with a change in the cells in diameter across the layers gives a lower value of the pressure drop, which is a significant advantage. The results can serve as the basis for creating aerosol filters with improved characteristics.