Top Part Research Articles

Extracellular enzymes secreted in the mycelial block of Lentinula edodes during hyphal growth

Lentinula edodes (shiitake mushroom) is one of the most widely cultivated edible mushrooms and is primarily cultivated using sawdust medium. While there have been improvements in the cultivation technology, the mechanism of mycelial block cultivation, such as mycelial growth and enzymatic sawdust degradation, has not been clarified. In this study, the mycelium was elongated longitudinally in the bottle sawdust culture for 27 days, and the cultivated sawdust medium was divided into three sections (top, middle, and bottom parts). To determine spatial heterogeneity in the enzyme secretion, the enzymatic activities of each part were analyzed. Lignocellulose degradation enzymes, such as endoglucanase, xylanase, and manganese peroxidase were highly secreted in the top part of the medium. On the other hand, amylase, pectinase, fungal cell wall degradation enzyme (β-1,3-glucanase, β-1,6-glucanase, and chitinase), and laccase activities were higher in the bottom part. The results indicate that the principal sawdust degradation occurs after mycelial colonization. Proteins with the laccase activity were purified from the bottom part of the medium, and three laccases, Lcc5, Lcc6 and Lcc13, were identified. In particular, the expression of Lcc13 gene was higher in the bottom part compared with the level in the top part, suggesting Lcc13 is mainly produced from the tip region and have important roles for mycelial spread and nutrient uptake during early stage of cultivation.

Monitoring of concrete segregation using AC impedance spectroscopy

Segregation is one of the major phenomena decreasing the durability of concrete and increasing its risk of failure. This paper investigates the feasibility of AC Impedance Spectroscopy (ACIS) to serve as a monitoring technique for the concrete segregation during compaction. The impedances of fresh concrete were determined between compaction intervals. Changes in the calculated bulk resistivities were compared to hardened densities of the drilled cores, as well as to aggregate segregation obtained via digital image analysis of the hardened concrete sections. During the compaction process, a significant difference in the bulk resistivity was observed between the top and bottom parts of segregated specimens in comparison to unsegregated specimens. By inspecting the relationship between the measurement methods, it was found that ACIS provides a reliable approach (r=-0.948) for estimating the segregation level in cases where the resistivity is mostly affected by the movement of aggregates.

Geochemical significance for the composition and depositional environments of the Campanian carbonate-rich phosphorite, Abu-Tartur plateau, Western Desert, Egypt

Twenty-six samples involved CFA (carbonate fluor-apatite) and intercalated marl were collected from four outcrops of the Campanian phosphorites horizon extending along 9 km of a minable NE-SW side wall of the Abu Tartur Plateau. Samples were analyzed chemically using XRF (x-ray fluorescence) and ICP-OES (Inductively coupled plasma optical emission spectrometry) techniques for measuring oxides, trace elements, and REE (Rare earth elements) for deducing their implication for the paleo-depositional environment. The CFA samples show an average compositional richness in major oxides of CaO (42.23 wt%) and P2O5 (27.22 wt%) with a considerable amount of F (2.75%). Whilst the main average composition of the intercalated marl is SiO2 (54.17 wt%) and CaO (10.58 wt%). The geochemical classification of this marl shows a type of Fe-sand (Ferro-magnesium potassic sandstone). The P2O5 in the marl samples does not exceed 3.46 wt%. Calculation of the CaO/MgO molar ratio of studied samples reveals evidence of the dolomitization process took place, making a conversion of approximately 65.73% of the entire CFA to be dolomitic- and highly dolomitic-francolite may occur over a long time post of the Campanian age. CFA samples have an amount of Fe2O3 ranging from 3.15 wt% to 5.84 wt% (average 4.31 wt%) whereas Fe2O3 in the marl samples range from 3.81 wt% to 6.03 wt% (average 4.41 wt%). The origin of iron is attributed to being delivered by an ancient river system laden from hot, humid chemically weathered (laterite) soils into the basin simultaneously with the dolomitization process. Less saline mixed water is the suggested medium where dolomitization processes occur based on Rb/Sr and Sr/Ba ratios. The normalized REE pattern of the base, middle and top parts of the CFA samples show a similarity of fingerprint patterns of near-shore and margin-marine of either bottom seawater and shallow-to deep-pore-water below the SWI (sediment-water interface). Dysoxic to oxic depositional environments of the marginal shelf are established based on measured trace elements ratios of V/Cr, Ni/Co and V/(V + Ni). The accumulation rate of P shows a progressively increasing trend toward the NE direction of favourable P depositional conditions. The results of the Ce/Ce* and Pr/Pr* anomalies show no-to + ve Ce/Ce* lie between 0.93 and 1.45 (average 1.04) and the Y/Ho ratio lie between 23.43 and 87.75 (average 51.63) which is attributed to depositional sets within the shelf margin of suboxic to anoxic pore-water chemistry conditions at bottom seawater below the sediment-water interface. The fingerprint shape of the REE patterns and the richest of HREE (Heavy rare earth elements) of the studied CFA samples reflect the chemistry of the shallow to the deep pore-water flux of suboxic-anoxic sulfidic characters.

Research on discrete element simulation of slump test for fresh self-compacting concrete

A numerical computational modelling of slump tests for fresh self-compacting concrete (SCC) was developed in this investigation based discrete element method (DEM). The coarse aggregates in DEM model were characterized by using spherical shapes and 3D irregular geometries obtained by scanning real aggregates, respectively. By comparing the results of the slump simulation tests corresponding to the two geometric models, it was found that the average error of the latter was smaller, about 2.9%. The results of quantitative analysis of the rotational kinetic energy for both found that the motion of the real coarse aggregate model was more consistent with the actual situation. The effect of coarse aggregate gradation characteristics on the flow properties of fresh SCC was investigated based on the real coarse aggregate model. The results indicated that the increase in the content of large-size coarse aggregate or its replacement of small-size coarse aggregate both resulted in the deterioration of the flow properties of fresh SCC. During the lifting of the bucket at the beginning of the slump test, different velocity distribution patterns existed before and after the complete separation of the bucket from the concrete. The maximum flow velocity, about 0.8 m/s, occurred when the bucket was not completely separated from the SCC and was distributed in the top part of the inner bucket.

Enhanced accumulation of bitumen residue in a highly concentrated tailings flow by microbubbles from in-situ catalytic decomposition of hydrogen peroxide

The massive volume of oil sands tailings has been one of the most challenging environmental issues. In this work, we experimentally explore a simple and effective approach to bitumen residue separation from a highly concentrated slurry flow of the artificial oil sands tailings. By utilizing microbubbles from in-situ catalytic decomposition of H2O2 at low concentrations, bitumen aggregation is enhanced on the top part of the hydrotransport pipeline. The microscopic image analysis revealed the in-situ formation of microbubbles and confirmed that magnetic particles present in the slurries contributed to the fast release of the gas products and bubble formation from hydrogen peroxide decomposition. A high-speed camera was applied to capture images of the tailings flow in the pipeline through a transparent view window. A large number of tiny bubbles were identified post to the injection of H2O2 to the slurry flow. More than 70 % bitumen could be recovered from a lab-scale pipeline loop within 30 mins after H2O2 injection. The bitumen recovery efficiency from the collected froth was quantitatively compared under seven conditions with varied dosages, the concentration of H2O2, and the amount of magnetic solids in the slurries. Our results confirmed that the total dosage of H2O2 is the dominant factor in in-situ microbubble formation for enhanced bitumen aggregation in the flow. Importantly, microbubbles were generated rapidly in the real mature fine tailings. The results from our study provide insights into the preferential distribution of oil residue in the flow during hydrotransport without the requirement for an additional device. Removal of oily residues from concentrated slurries may bring economical and environmental advantages.

Facial nerve palsy following parotid gland surgery: A machine learning prediction outcome approach.

Machine learning (ML)-based facial nerve injury (FNI) forecasting grounded on multicentric data has not been released up to now. Three distinct ML models, random forest (RF), K-nearest neighbor, and artificial neural network (ANN),for the prediction of FNI were evaluated in this mode. A retrospective, longitudinal, multicentric study was performed, including patients who went through parotid gland surgery for benign tumors at three different university hospitals. Seven hundred and thirty-six patients were included. The most compelling aspects related to risk escalation of FNI were as follows: (1) location, in the mid-portion of the gland, near to or above the main trunk of the facial nerve and at the top part, over the frontal or the orbital branch of the facial nerve; (2) tumor volume in the anteroposterior axis; (3) the necessity to simultaneously dissect more than one level; and (4) the requirement of an extended resection compared to a lesser extended resection. By contrast, in accordance with the ML analysis, the size of the tumor (>3 cm), as well as gender and age did not result in a determining favor in relation to the risk of FNI. The findings of this research conclude that ML models such as RF and ANN may serve evidence-based predictions from multicentric data regarding the risk of FNI. Along with the advent of ML technology, an improvement of the information regarding the potential risks of FNI associated with patients before each procedure may be achieved with the implementation of clinical, radiological, histological, and/or cytological data.

Реконструкция величин фотосинтеза в Онежском озере по концентрации хлорофилла а

Phytoplankton photosynthesis in Lake Onego was measured in 1989-2006. An attempt was made to calculate photosynthesis by daily assimilation numbers and chlorophyll a concentration measured in 2007-2021 to supple-ment data on the primary production. Daily assimilation numbers were calculated by simultaneously measured photosynthesis and chlorophyll in 1989-2006 for different areas and seasons of a limnically complex water body. A comparative statistical analysis of the size-structural characteristics of phytoplankton in 1989-2006 and 2007-2021 was performed to assess the possibility of using the obtained assimilation numbers to restore photosynthesis values. Comparison of the average cell volume for the phytocenosis and the ratio of diatoms and smaller non-diatoms showed their similarity in both periods in the main water area of the lake. Only in the central sector of Kondopoga Bay, which has been influenced by biogenic loads from the trout farms since the 2000s, the average cell volume decreased significantly and the proportion of diatom plankton also decreased. Photosynthesis was not calculated for this sector. The calculated assimilation numbers were similar for almost the entire water area of the lake. The maximum daily values were observed in summer with medians from 11.8 to 18.4 µg C/µg Chl in different parts of the water body. In Kondopoga Bay, which during both study periods was experiencing a biogenic load of wastewater from the pulp and paper mill, their median values in summer reached 40.3 and 29.6 µg C/µg Chl day–1 in the top and open parts, respectively. It was possible to restore 197 values of photosynthesis by chlorophyll a measured in 2007-2021and by the calculated assimilation numbers in the surface water layer of different areas in Lake Onego in different seasons.

Experimental study on convectional heat transfer characteristics of argon space in the pool-type fast reactor vessel

A large amount of sodium is used as coolant in the pool-type fast reactor, and argon is used as covering gas in the top part of main vessel. At the top of the main vessel, an annular cavity is formed between the rotating plug and its support, where natural convection of argon is formed. This kind of structure makes the heat transfer complicated at the top of main vessel. Excessive temperature or large temperature gradient at the top of main vessel may occur. Therefore, it is necessary to carry out analysis of the temperature distribution at the top of the main vessel. Many researches based on CFD have been carried out on the analysis of the top domain, but few of them are verified by experiment. In addition, a few experiments have been performed using simplified facility, which is not so similar to the real geometry. Therefore, a scaled-down Heat-transfer Experimental Facility for Argon space at the top of main vessel (HEFA) is established, which is much similar to the real geometry. In HEFA, the annular gap is kept, in addition, a heated stainless bottom plate is used to simulate the liquid sodium surface. Two conditions were set up, one for vacuum, the other for argon. The temperature of the facility was measured in the two conditions. By comparing the results of two condition, the results show that convection of the argon increases the overall temperature of the roof slab and reduces its temperature gradient of roof slab. The circumferential temperature difference at annular gap around rotating plug was observed in the argon condition. It is judged that the circumferential temperature difference is caused by natural convection in the annular gap with one side rising and the other falling. This phenomenon must be paid much attention in the design of SFR.

The Impact of Profile Genesis and Land Use of Histosol on Its Organic Substance Stability and Humic Acid Quality at the Molecular Level

This study is designed to evaluate soil organic matter (SOM) quality indicators: molecular indicators of dissolved organic matter (DOM) and hydrophobicity of humic acid (HA), distribution of quantity in humified and labile fractions of histosols during renaturalization. The aim is to determine the differences in the qualitative composition of humic acids at the molecular level, which are decided by the previous tillage and genesis, and to evaluate the impact of anthropogenization on the peat soil according to hydrophobicity, as well as to estimate the impact of soil genesis and removing peat layer. Soil samples were taken from the three Sapric Histosol (according to WRB2022) profiles and the 0–30 cm layer in three field replicates (Lithuania, Radviliskis mun.). Our study suggested that in the differently managed drained Sapric Histosol under renaturalization, the most significant changes occurred in the topsoil layer (0–30 cm), in which an increase in the content of SOM particles 106–2 µm in size. It is expedient to grow perennial grasses and legumes to maintain the soil organic carbon stability mobile humic acids to mobile fulvic acids ratio (MHA:MFA 0.83 to 0.86). An evaluation of the quality of HA (E4:E6) revealed their highest maturity in the unfertilized perennial grasses (3.88) and crop rotation (3.87) with grasses. The highest concentrations of hydrophilic groups (ratio of the C=O to O-H) were found in Sapric Histosol under deciduous hardwood forest (12.33). The lowest hydrophilicity (9.25 and 9.36) was of the crop rotation Sapric Histosol with removed peat layer. The most sustainable use of drained Sapric Histosol in the context of the sustainability and quality of its humus substances should be associated with the formation of perennial grass and clover grassland and the cultivation of deciduous hardwood. Therefore, the horizon forms on the top part of the profile, which protects deeper Histosolic material layers from its mineralization.

Energy losses during driving due to tapered section of monopile

Efficient pile driving and accurate pile driving predictions are essential for the continued use of monopiles as an optimised foundation for the offshore wind energy sector, especially as the offshore wind industry continuously pushes limits of wind turbine and foundation size. For monopile foundation a crucial part of the structure from an installation perspective is the transition tapered section of the monopile between the top and bottom parts of the monopile and its interaction with the water column during pile driving. To evaluate the impact of this interaction on the driving energy, two monopile foundations installed at an offshore wind farm (OWF) site in the North Sea were instrumented and their installation was monitored in 2019. For the monitoring, optical fibre strain gauges and resistive accelerometers were placed at different levels above, below, and on to the tapered section of the monopiles. As an innovative part, all sensors were glued on the monopile shaft surface instead of the traditional welded/screwed approach. The driving energy loss between different sensor levels was calculated post installation. The measurement data were used to benchmark a series of finite element analyses (FEA) that were performed to identify and quantify the different factors affecting the energy loss.The study evaluates the effect of various parameters, such as wave reflections due impedance changes caused by diameter increase and wall thickness variation, bending of tapered section, and vertical acceleration of water due to interaction with the tapered section of the monopile. Measurements and the finite element analysis both reveal that a large part of the driving energy applied by the hammer is dissipated due to the above-mentioned factors with the water-pile interaction playing the most important role, resulting in a significant impact on the monopile installation.

Study of Phase Evolution Behavior of Ti6Al4V/Inconel 718 by Pulsed Laser Melting Deposition

In this study, a pulsed laser was used as the heat source for the additive work. The Ti6Al4V/Inconel 718 alloy wire was deposited on the substrate by melting using a pulsed laser. Using the above method, single-layer and double-layer samples were printed. The sample material printed in this way is highly utilized. Compared to the complicated pre-preparation work of metal powder pre-mixing, this printing method is simple to prepare and only requires changing the wire feeding speed. The study of this paper provides a theoretical guide for the subsequent fusion deposition of heterogeneous wire materials. The samples were analyzed after molding using SEM, EDS and XRD to characterize the microstructure of the samples. The samples can be divided into three zones depending on the microstructure, the bottom columnar crystal zone, the middle mixed phase zone, and the bottom equiaxed crystal zone. From the bottom to the top of the sample, the phase microstructure changes as γ + Laves → α + β + Ti2Ni + TiNi + Ni3Ti → α + β. The hardness data show that the highest value in the transition zone is 951.4 HV. The hardness of the top part is second only to the transition zone due to a large number of equiaxed crystals. The bottom region is dominated by columnar crystals and is the softest of the three regions with the lowest hardness value of 701.4 HV.

Erratum for Zhao et al., "N-Acetyltransferase 8 Promotes Viral Replication by Increasing the Stability of Enterovirus 71 Nonstructural Proteins".

Volume 96, no. 6, e00119-22, 2022, https://doi.org/10.1128/JVI.00119-22. Fig. 5A: The top part of the image on the left should be labeled “NAT8B” rather than “NAT8”, and the top part of the image on the right should be labeled “NAT8” rather than “NAT8B.” Panel A should appear as shown in this erratum.

Printing Formation of Flexible (001)-Oriented PZT Films on Plastic Substrates.

High-quality, uniaxially oriented, and flexible PbZr0.52Ti0.48O3 (PZT) films were fabricated on flexible RbLaNb2O7/BaTiO3 (RLNO/BTO)-coated polyimide (PI) substrates. All layers were fabricated by a photo-assisted chemical solution deposition (PCSD) process using KrF laser irradiation for photocrystallization of the printed precursors. The Dion-Jacobson perovskite RLNO thin films on flexible PI sheets were employed as seed layers for the uniaxially oriented growth of PZT films. To obtain the uniaxially oriented RLNO seed layer, a BTO nanoparticle-dispersion interlayer was fabricated to avoid PI substrate surface damage under excess photothermal heating, and the RLNO has been orientedly grown only at around 40 mJ·cm-2 at 300 °C. The prepared RLNO seed layer on the BTO/PI substrate showed very high (010)-oriented growth with a very high Lotgering factor (F(010) = 1.0). By using the flexible (010)-oriented RLNO film on BTO/PI, PZT film crystal growth was possible via KrF laser irradiation of a sol-gel-derived precursor film at 50 mJ·cm-2 at 300 °C. The obtained PZT film showed highly (001)-oriented growth on the flexible plastic substrates with F(001) = 0.92 without any micro-cracks. The RLNO was only uniaxial-oriented grown at the top part of the RLNO amorphous precursor layer. The oriented grown and amorphous phases of RLNO would have two important roles for this multilayered film formation: (1) triggering orientation growth of the PZT film at the top and (2) the stress relaxation of the underneath BTO layer to suppress the micro-crack formation. This is the first time that PZT films have been crystallized directly on flexible substrates. The combined processes of photocrystallization and chemical solution deposition are a cost-effective and highly on-demand process for the fabrication of flexible devices.

우유 균질 조건 예측을 위한 반응표면방법론의 활용

Response surface methodology (RSM) is a statistical approach widely used in food processing to optimize the formulation, processing conditions, and quality of food products. The homogenization process is achieved by subjecting milk to high pressure, which breaks down fat globules and disperses fat more evenly throughout milk. This study focuses on an application of RSM including the logit transformation to predict the efficiency of milk homogenization, which can be maximized by minimizing the relative difference in fat percentage between the top part and the remainder of milk. To avoid a negative predicted value of the minimum of this proportion, the logit transformation is used to turn the proportion into the logit, whose possible values are real numbers. Then, the logit values are modeled and optimized. Subsequently, the logistic transformation is used to turn the predicted logit into the predicted proportion. From our model, the optimum condition for the maximized efficiency of milk homogenization was predicted as the combination of a homogenizer pressure of 30 MPa, a storage temperature of 10°C, and a storage period of 10 days. Additionally, with a combination of a homogenizer pressure of 30 MPa, a storage temperature of 10°C, and a storage period of 50 days, the level of milk homogenization was predicted to be acceptable, even with the problem of extrapolation taken into account.

Cover Image

AbstractThis cover (DOI: 10.1002/inf2.12396) displays a quasi‐2D perovskite solar cellwithreverse‐gradedquantum well distribution, which promotes the charge carrier transport. The small‐n phase at the top part of the quasi‐2Dperovskite film protects the surface from the damage of water and oxygen. Intermediate phase assisted sequential deposition is demonstrated firstly to fabricate MA‐free quasi‐2D ACI perovskiteswith reverse‐graded QW distribution and improved vertical orientation. image

Residual rocky forms in the landscape of the Outer Carpathians (Silesian Beskid Mts, Poland) – geotourist and sedimentological case study

This study investigated residual landforms developed within of the flysch bedrock in the Outer Western Carpathians as sandstone-to-conglomeratic tors. The studied relic rocky forms are locally exposed on the valley slopes in the top and plateau parts of the Silesian Beskid Mts. The cognitive values of such relic landforms, especially in the context of their morphogenetic traits and shaping of their macro- and microrelief, are well known and described. In contrast to epigenetic processes, the sedimentological aspect of the origin of such siliciclastic rocky deposits is still subject to different approaches in terms of terminology and interpretation. Thus, the aim of this study is to describe the conditions of environmental settings and character of the sediment transport and deposition processes from gravity flows, and to present a depositional system model for such a variety of flysch deposits. This study also attempts to present geotourist and geoeducational attractiveness of the tors against the background of regional geodiversity, geoheritage, and geoprotection. The results yielded a synthetic morpho-litho-sedimentological and geotouristic specification of the rocky forms analysed. The residual rocky landforms are polygenic geomorphological elements developed as a consequence of multistage and different scale of morph-forming activity operating on the basis of litho-sedimentological and tectonic assumptions under the influence of denudation processes.

Residual rocky forms in the landscape of the Outer Carpathians (Silesian Beskid Mts, Poland) - geotourist and sedimentological case study

This study investigated residual landforms developed within of the flysch bedrock in the Outer Western Carpathians as sandstone-to-conglomeratic tors. The studied relic rocky forms are locally exposed on the valley slopes in the top and plateau parts of the Silesian Beskid Mts. The cognitive values of such relic landforms, especially in the context of their morphogenetic traits and shaping of their macro- and microrelief, are well known and described. In contrast to epigenetic processes, the sedimentological aspect of the origin of such siliciclastic rocky deposits is still subject to different approaches in terms of terminology and interpretation. Thus, the aim of this study is to describe the conditions of environmental settings and character of the sediment transport and deposition processes from gravity flows, and to present a depositional system model for such a variety of flysch deposits. This study also attempts to present geotourist and geoeducational attractiveness of the tors against the background of regional geodiversity, geoheritage, and geoprotection. The results yielded a synthetic morpho-litho-sedimentological and geotouristic specification of the rocky forms analysed. The residual rocky landforms are polygenic geomorphological elements developed as a consequence of multistage and different scale of morph-forming activity operating on the basis of litho-sedimentological and tectonic assumptions under the influence of denudation processes.

Multi-scale textured PEEK surfaces obtained by direct laser interference patterning using IR ultra-short pulses

In this work, we aimed at getting the first insight into the influence of the laser processing parameters on the production of functional multi-scale PEEK surfaces using the Direct Laser Interference Patterning technology. An infrared ultra-short pulsed laser source (1064 nm, 10 ps) and a two-beam interference setup were used. The fabricated structures morphology was analyzed by Scanning Electron Microscopy and Confocal Microscopy. As a result, line-like structures with periodic spatial repetition (p) at two levels were produced: main structures with p = 5 µm and mean depth values up to ∼2.5 µm (aspect ratio of ∼0.5) and secondary structures, perpendicularly oriented relative to the main structures, formed at DLIP maxima position (top part of ridges) with p≈1 µm (LIPSS).

Advanced Manufacturing Design of an Emergency Mechanical Ventilator via 3D Printing—Effective Crisis Response

Nowadays, there is a market need that is pushing manufacturers to support more sustainable product designs regardless of any crisis. Two important lessons that society inferred from the COVID-19 pandemic are that the industry needs an improved collaboration efficiency that can handle such emergencies and improve its resource conservation to avoid having shortages. Additive manufacturing technologies use 3D object scanners to direct hardware to deposit material, layer upon layer, in precise geometric shapes, and are positioned to provide a disruptive transformation in how products are designed and manufactured. They can provide for the planet in fighting against crisis from a materials and applications perspective. In this context, the optimization and production of emergency ventilators in health systems were investigated with plans for 3D printing received from the University of Illinois Urbana–Champaign. An evaluation of the printability of CAD files and a partial redesign to limit dimensional variability, acceptable surface finish, and a more efficient printing process were performed. Six parts of the design were redesigned to make printing easier, faster, and less expensive. In the case of the O2 inlet attachment, the necessary supports were difficult to remove due to the part’s geometry, leading to redesign. The modulator top and bottom part, the patient tee, the manometer body, and the pop-off valve cap were also redesigned in order to avoid dimensional variability and possible rough surfaces. Metallic and thermoplastic composite ventilators were produced and then tested in real operating conditions, such as in a hospital setting with a realistic oxygen supply. The preliminary findings are promising compared to the initial design, both in terms of construction quality and performance such as exhalation rate adjustment and emergency valve operation. Also, a combination of manufacturing technologies was evaluated. The modifications allowed optimal casting (injection molding) of the parts and therefore faster production, instead of printing each part, when high output is required.

Making the Invisible Audible: A Simple Sound-Emitting Water Level Meter.

Making the Invisible Audible: A Simple Sound-Emitting Water Level Meter.