Hard Conditions Research Articles

Evaluating the Impact of Washing Conditions on the Color Changes of Naturally Colored Cotton Fabrics: A Focus on Detergents, Water Types, and Temperature

Intrinsically colored cotton is crucial for sustainability as it eliminates the need for chemical dyes, reducing water pollution and carbon footprint. It also preserves biodiversity by using fewer pesticides and supports eco-friendly, ethical product creation. This research aims to examine the factors that influence the color change that occurs in naturally colored organic cotton (NaCOC) fabrics when washed under normal household conditions, and it focuses on special detergents designed for people with skin hypersensitivity. The study observes the impact of various washing conditions on the color changes of the fabrics. Specifically, three specific detergents, two types of water (tap and distilled), and three different temperatures (20, 40, and 60 °C) are taken into consideration as variables. By using colorimetric measures and correlating the results with the significant variables of the experimental design, the study evaluates how washing practices affect both the color and the overall integrity of the fabric. The findings demonstrate that the water hardness is the most influential variable when it comes to the color changes in the fabrics. Additionally, higher washing temperatures exacerbate color changes, particularly in hard water conditions. These results provide valuable insights for maintaining the color integrity of NaCOC fabrics during washing.

Synthesis, (bio)degradation, and utilization of starch-derived biopolymers in defined hard waters

Climate change is causing a change in local rainfall, which generally brings with it a reduction in rainfall and, consequently, an increase in water hardness. This study explores the suitability and stability of various dextrin-derived polymers for cation removal in simulated hard water conditions. Thermal analysis and Fourier-transform infrared spectroscopy confirm the polymers' thermal stability and proper formation. Biodegradability assessments reveal KLEPTOSE®LINECAPS (LC) and GLUCIDEX2® (Glu2) dextrin with pyromellitic dianhydride (PMDA) derivatives have higher durability as they were able to endure enzymatic activity. Adsorption experiments at 300 and 600 ppm indicate significant variations influenced by monomer and crosslinker types, with linear monomers demonstrating superior performance. Notably, different crosslinkers exhibit varying affinities for calcium and magnesium ions, with PMDA derivatives excelling for magnesium and citric acid (CA) derivatives for calcium. Kinetic and isotherm studies reveal a favorable trend towards quasi-second-order kinetics and Freundlich isotherm models, attributed to cavity heterogeneity and diverse attachment points as evidenced in existing literature. These findings suggest promising applications for these polymers, traditionally employed for organic contaminant removal, as additional filters to mitigate water hardness.

Extraction of Rare Earth Elements from Phalaborwa phosphogypsum

Rare earth elements (REE) are present at concentrations of approximately 0.36 % in phosphogypsum stacks located in Phalaborwa, South Africa. The REE are present in the phosphogypsum in solid solution in the gypsum and as fluorine and aluminium rich precipitates. Recovery of the REE offers opportunities for valorization and reducing the environmental impact of the phosphogypsum waste. This paper presents the results of investigations into the leaching behaviour of rare earth elements and other impurities from phosphogypsum using aqueous sulfuric acid. The effects of acid concentration, temperature, residence time, and the influence of impurities were evaluated for their impact on the solubility of rare earth elements in a sulfate medium. It was found that a significant fraction of the REE can be leached from the phosphogypsum in a range of conditions much less severe than traditional hard rock rare earth processing conditions. The REE were leached at a sulfuric acid concentration of 110 g/l, temperature of 30°C - 40°C and a residence time of approximately 8 hours.

Risk factors for cardiovascular diseases in taxi drivers in Tabriz metropolis

Risk factors for cardiovascular diseases in taxi drivers in Tabriz metropolis

On the contact and vibration characteristics of TBM cutter with abnormal damage under hard rock conditions

Tunnel Boring Machines (TBM) play a pivotal role in the construction of modern tunnels, with their performance directly determining the progress, economic benefits, and safety levels of the construction. As the core component interfacing with the rock, the condition of the TBM cutter significantly impacts the machine's boring performance. Faced with increasingly complex geological conditions, the cutters frequently suffer from abnormal damage, including partial wear, polygon wear, and chipping. Such damages are typically accompanied by reduced rock-breaking ability and increased vibration intensity, leading to severe performance degradation. To propose effective monitoring and maintenance strategies to prevent serious consequences of abnormal damage, such as cutterhead damage or personnel injuries, it is necessary to understand the changes in the operational characteristics of the cutter in such conditions and to accurately assess the specific impacts of abnormal damage on cutter performance. This study uses bench tests and discrete element-dynamics coupled simulations to explore the differences in load-bearing, cutter-rock contact, vibration, and noise characteristics between the normal wear cutter and those with abnormal damages. The results show that abnormal damages affect the cutter's load-bearing and cutter-rock contact properties, thereby increasing the proportion of cutting resistance and reducing energy utilization and rock-breaking efficiency. Additionally, partial wear and polygon wear not only significantly increase the noise/vibration levels of the cutter but also cause the mode of noise and vibration to shift from random to periodic, thus increasing the likelihood of forced vibrations in the system. By combining simulation and experimental results, this study elucidates the mechanisms by which different types of abnormal damage affect cutter performance by altering the motion form and cutter-rock contact mode. The operational characteristics of cutters with abnormal damages, as revealed in this study, in terms of load, vibration, and noise, provide theoretical support for the state monitoring and maintenance strategies of TBM cutters.

Development of an Automatic Harvester for Wine Grapes by Using Three-Axis Linear Motion Mechanism Robot

In Japan, the aging and decreasing number of agricultural workers is a significant problem. For wine grape harvesting, especially for large farming areas, there is physical strain to farmers. In order to solve this problem, this study focuses on developing an automated harvesting robot for wine grapes. The harvesting robot needs high dust, water, and mud resistance because grapevines are grown in hard conditions. Therefore, a three-axis linear robot was developed using a rack and pinion mechanism in this study, which can be used in outdoor conditions with low cost. Three brushless DC motors were utilized to drive the three-axis linear robot. The motors were controlled using a control area network (CAN) bus to simplify the hardware system. The accuracy of the robot positioning was evaluated at the automated harvesting condition. The experiment results show that the accuracy is approximately 5 mm, 9 mm, and 9 mm in the x-axis (horizontal), y-axis (vertical), and z-axis (depth), respectively. In order to improve the accuracy, we constructed an error model of the robot and conducted a calibration of the robot. The accuracy was improved to around 2 mm of all three axes after calibration. The experimental results show that the accuracy of the robot is high enough for automated harvesting of the wine grapes.

Indentation size effect in Knoop and Vickers hardness measurement of dental resin-based composites

ObjectivesComparisons of material hardness may be affected by the indentation size effect (ISE), which is characterized by increasing hardness values at decreasing loads. This study aimed to assess the influence of load, dwell time and measurement method on ISE in dental resin-based composites with different filler content. MethodsKnoop (HK) and Vickers (HV) microindentation hardness of Filtek Ultimate Universal Restorative (FU) and Filtek Supreme Flowable Restorative (FF) was measured under different loads (0.098–2.96 N, i.e. 10-300 gf) and dwell times (5–30 s). Their effects on HK and HV were evaluated using repeated measures ANOVA, which was also used to compare the measurement methods. Coefficients of Meyer's equation, proportional specimen resistance (PSR) model and a modified PSR model were calculated using regression analyses. ResultsISE was more pronounced for the highly-filled FU than for the less-filled FF, and HK was more susceptible to ISE than HV. The effect of dwell time was similar for both materials and measurement methods; hardness values decreased with dwell time, significantly between 5 s and 30 s. SignificanceThe possible presence of ISE should be considered when determining measurement conditions for the microindentation hardness of dental resin-based composites. HV was found to be less sensitive to ISE and provided stable hardness values at lower loads than HK. Due to the high variability of composites, any hardness measurement should be preceded by mapping the effect of load to ensure that load-independent hardness is measured. If hardness values continue to decrease in the whole range of increasing loads, load-independent hardness can be calculated using the PSR model.

A novel reservoir simulation model based on physics informed neural networks

Surrogate models are widely used for reservoir simulations in the petroleum industry to improve computational efficiency. However, the traditional surrogate model mainly relies on the data collected from production wells (e.g., well bottom pressure data and well production data) and ignores the physical mechanism of underground fluid flow; therefore, the surrogate model will be invalid in the case of insufficient data samples. In response to these challenges, a Hard-Soft physics informed neural network (HS-PINN) was proposed to simulate pressure fluctuations around producing wells without relying on any labeled data, where two coupled fully connected neural networks were comprised to control the Hard and Soft constraint conditions. Specifically, in the “Soft Constraint” condition, we employ a modified Lorentz function to incorporate underground flow theory and permeability fields into the loss function. Meanwhile, in the “Hard Constraint” condition, we incorporate an enforcement function in the “output layer” to ensure the network outputs satisfy the boundary and initial conditions. To demonstrate the HS-PINN model's robustness and accuracy abilities, we tested it for single and multi-well production in both noisy low-fidelity and high-fidelity geologic reservoir environments, and the HS-PINN prediction errors were less than 1% in both cases compared to simulation results by the commercial software “COMSOL.” Additionally, we assessed the impacts of varying well interference intensities, adjustments in collocation points counts within the control equations, and diverse geological characteristics on model performance to validate the generalization and stability of HS-PINN. Moreover, the HS-PINN-based surrogate model significantly improves the efficiency of uncertainty quantification tasks compared to simulation-based approaches, requiring only 8% of the computational time. The deep-learning surrogate models developed in this work offer a novel and efficient approach for simulating reservoir development.

Pushing boundaries in slurry microtunneling: Innovations in microtunnel boring machine design for hard rock conditions

AbstractFor microtunneling in hard rock, as it is encountered very often in alpine tunneling, the continuous further development of technologies plays a key role to overcome the limitations in drive length and to improve performance. During the last decades, the application range of slurry microtunneling has been considerably extended and more demanding projects have been designed for underground utilities installations worldwide, including many sewage tunnels and hydropower plants. The prevailing ground conditions still play a key role and determine the limits for alignment design and the possible use of trenchless construction methods. In hard rock conditions with high rock strength and/or abrasivity, the applicability of slurry microtunneling has been especially limited in the non‐accessible diameter range in the past. With the new AVN 800 HR for hard rock microtunneling, Herrenknecht has developed a machine concept, enabling drives of up to 200 m, with precise steering of the MTBM. Longer drives, even through hard rock, make microtunneling a more economic, flexible, and more environmentally friendly construction method. New opportunities for clients and consultants in the planning of tunnel routes in alpine environments for different infrastructure installations can be considered, making trenchless installations even more cost‐effective, while improving public acceptance.

A semi-analytical approach for dynamic responses of monopile-supported offshore wind turbines subjected to accidental loads

Offshore wind energy is leading the way in sustainable energy generation. Offshore wind turbines (OWTs) need to be designed to withstand extreme or accidental loads in Ultimate Limit States (ULS) and Accidental Limit States (ALS), whereby high order eigenmodes may become significant. This paper introduces a semi-analytical approach for efficient and reliable analysis of the dynamic responses of monopile-supported OWTs subjected to accidental loads. A Rayleigh-Ritz solution is initially adopted to determine the high-order natural frequencies and eigenmodes of monopile OWTs, explicitly considering tapered towers and soil-pile interactions. Dynamic responses of OWTs are then calculated depending on the interaction schemes between accidental loads and the structures, e.g. soft contact loads (e.g. slamming, wind) and hard contact loads (e.g. ship collisions, ice impact). For soft contact loading conditions, the loads are considered independent of turbine responses, and the transient dynamic response is computed using the classical modal superposition method. While for hard contact loading conditions, the load actions depend on the contact stiffnesses and responses of the interacting bodies. A numerical contact algorithm is thus developed, and numerical iterations are performed to ensure convergence. The proposed approach is applied to the DTU 10 MW monopile-supported OWT subjected to extreme water slamming and ship collisions, respectively as example applications of soft and hard contact scenarios. The results are verified against nonlinear finite element analysis using USFOS and discussed with respect to the turbine natural frequencies and eigenmodes, contact forces and dynamic responses. A parametric analysis is conducted for ship-OWT collisions, exploring different impact scenarios by varying ship sizes, contact stiffnesses, and initial impact velocities. The proposed approach can serve as a promising tool for accidental load response analysis and the design of monopile OWTs.

Effect of Silicon Carbide Particulates on Mechanical Behavior of Al5052 Alloy Metal Matrix Composites for Mining Applications

In particular, the impact of Silicon Carbide (SiC) particles on the mechanical properties of stir-cast Al5052 alloy Metal Matrix Composites (MMCs) for rotor blade applications is examined in this work. The goal of integrating SiC particles is to improve mechanical characteristics including wear resistance, tensile strength, and hardness while preserving the ideal weight-tostrength ratio, which is essential for rotor blade performance. The Al5052 matrix was filled with SiC in a variety of compositions (0%, 2%, 4%, 6%, and 8% by weight), and the resultant composites underwent mechanical testing and microstructural examination. Due to the efficient load transfer and reinforcing processes, the results show a considerable improvement in tensile strength and hardness with the addition of SiC particles. Furthermore, microstructural analyses demonstrate a uniform dispersion of SiC in the matrix, which supports the improved performance attributes. Wear resistance of Al5052 alloy is greatly increased when Silicon Carbide (SiC) particles are added as reinforcement. This makes the composite material perfect for applications requiring great durability and longevity to survive hard mining conditions, such as wear plates, conveyor liners, and drill bits in mining machinery components.

АНАЛІЗ ДІЯЛЬНОСТІ БАНКІВ НА ФІНАНСОВОМУ РИНКУ УКРАЇНИ

The article analyzes the activity of domestic banks in Ukraine's financial market and examines the state and dynamics of the banking system's assets, capital, and liabilities for 2020-2023. Ukraine's financial market is experiencing significant challenges due to martial law, but these hard conditions also driving radical change and innovation in the sector. Due to the specificity of their activity, banks occupy a special place in the market economy and have a significant impact on the development of the financial market and the economy of the country. The integration of the national banking system into the world financial space is one of the leading directions of economic globalization, which strengthens the requirements for domestic banking institutions to increase their competitiveness and efficiency in providing financial services. This makes it necessary to study the essence and peculiarities of the functioning of banking institutions in the financial market of Ukraine in the modern, changing conditions of the development of economic relations between subjects of the national and international economy. The trend of consolidation of the banking system and withdrawal from the market of unreliable banks or banks whose capital belongs to under-sanctioned owners has been revealed. It was determined that despite the decrease in the number of these institutions, there was no significant deterioration of the main quantitative and qualitative indicators of the bank's activity, which indicates the stability of the efficiency of their activity. The state, dynamics, and quality of the banking system's credit portfolio were studied, and banks' compliance with NBU prudential regulations regarding credit risk was analyzed. The consistently high value of 45% of the share of bank assets in GDP confirms the overall efficiency of these financial institutions. A positive thing is the reduction of NPL before the full-scale invasion, but with its onset, this indicator increased again. A characteristic feature of the activity of domestic banks at present is a significant increase in the interest of institutions in investments in securities, in particular, military government bonds, the share of investments in these securities in the total assets of banks is rapidly increasing. To stabilize the financial state of the country's economy under the influence of "force majeure" circumstances, the banking system must constantly adapt its activities on the financial market, acting as an intermediary in the circulation of capital and financial resources

Manifestations of exile and diaspora in the poetry of Abdullah al-Baradouni

ABSTRACT This paper attempts to shed light on the contemporary issue of exile and diaspora and their manifestations in the poetry of Abdullah al-Baradouni, a modern Yemeni poet. Within the postcolonial hermeneutics and postmodernist theory, exile in the poetry of al-Baradouni becomes a signifier indicating not only being expelled outside one’s homeland but experiencing the feelings of isolation, exile, and diaspora caused by hard conditions, power struggle, ideological heterodoxy, and identity loss. Al-Baradouni’s dialectics of exile revolves on the concept that exile is a human condition beyond physical boundaries. Thus, exile is no longer treated as a singular event, it rather becomes a heterogeneous and multifaceted phenomenon. He succeeds in depicting the impactful consequences of exile and diaspora through the employment of bizarre, macabre, and surrealistic images and techniques. Hence, this piece of research adopts surrealism as a theoretical framework in illuminating and investigating al-Baradouni’s poetic texts under study. In his poetry, al-Baradouni becomes the voice of the voiceless and embodies a collective national consciousness as he engages himself in poetic enterprises that demand intrepidity, determination, articulateness, genius, vision, and prophecy. His contribution to the literature of exile and diaspora is significant.

Synthesis, performance and application of environmental protection scale inhibitorβ-CD-MA-SSS copolymer——in electric power industry

The issue of water scaling in the treatment of cooling water has become an imperative problem that should be solved urgently for the sake of safe operation in large-scale flexible DC converter stations. However, the coexistence of Ca2+ and Mg2+ in high content in this sort of pending raw water is quite hard to tackle. β-CD-MA-SSS, an eco-friendly ternary co-polymer antiscalant with good performance of inhibiting the formation of scale, was applied to address this conundrum in this paper. The efficacy of the antiscalant β-CD-MA-SSS was investigated in cooling water systems under the conditions of low hardness, low alkalinity, a temperature not exceeding 80 °C, and a pH range of 6–8. After optimization, this reagent dem onstrated an excellent scale inhibition rate up to 80% for both calcium carbonate and calcium-magnesium mixed scales. Scanning electron microscopy (SEM) analysis revealed a noticeable reduction in the size of CaCO3 particles when subjected to the action of β-CD-MA-SSS. It was postulated from FTIR analysis that nanoinpurity and chelation effects mainly contributed to the mixed scale inhibition. Further, the effect of β-CD-MA-SSS on the actual production wastewater was comprehensively evaluated from the technical, economic and environmental aspects.

Improved Power Control Based Variable Speed Wind-Turbine DFIG under Hard Work Conditions: Application of Sliding Mode Theory

This paper introduces an efficient and simple power control for the Wind Energy Conversion System (WECS) based on the Doubly-Fed Induction Generator (DFIG). Due to the limitation performance of the conventional PI controller against DFIG parameters change and wind speed variation; the sliding mode theory is applied in order to overcome these drawbacks. To improve the performances of a WECS, robust and nonlinear control techniques, namely; Conventional Sliding Mode Control (C-SMC) and Third Order Sliding Mode Control (3O-SMC), were implemented to independently control the stator active and reactive powers. However, both techniques exhibited a chattering phenomenon, an undesirable phenomenon caused by discontinuous signals. To overcome this drawback and further enhance previous control techniques, an advanced Variable Gain Super Twisting Algorithm (VGSTA) is proposed and compared to SMC and 3O-SMC. Furthermore, to validate the effectiveness of the proposed VGSTA strategy in comparison to two previous control methods, the WECS was simulated and validates using the MATLAB/Simulink environment. The simulation results clearly demonstrated the superiority of the proposed VGSTA strategy over the previous SMC and 3O-SMC techniques. This was obvious in terms of both fast convergence velocity and reduce chattering phenomenon.

Research progress and clinical application of veneer materials for implant-fixed restoration in edentulous jaws

Commonly used materials for fixed restorations in edentulous jaws include acrylic resins, polymerized ceramics, ceramics and zirconia, which have distinct physicochemical properties and clinical application features. The selection of these materials in clinical practice is related to the prosthodontic space, oral soft and hard tissue conditions, occlusal force, lifestyle habits, oral parafunctions, opposing dentition materials, and expectations of patients. Common mechanical complications associated with fixed restorations in edentulous jaws are cracking/chipping and abrasion of the facing materials, which can be avoided through occlusal adjustment, restoration design and processing, and the selection of appropriate restorative materials. This article reviews the characteristics, selection, and design considerations of commonly used materials for fixed restorations in edentulous jaws, as well as the causes and management of common clinical complications related to restorative materials, aiming to provide references for the selection of appropriate materials in fixed restorations for edentulous jaws in clinical practice.

A Review of Radiology and Optical Coherence Tomography in Dental Diagnostics

Background: The rapid evolution of imaging technologies has significantly transformed dentistry, improving the diagnosis and treatment of various dental conditions. While traditional radiological methods such as X-rays and Cone Beam Computed Tomography (CBCT) remain the cornerstone of dental imaging, the emergence of Optical Coherence Tomography (OCT) offers a non-invasive, radiation-free alternative. This review examines the comparative efficacy of X-ray and OCT technologies in diagnosing hard tissue conditions in the oral cavity. Methods: The review analyzed the application of OCT and radiology in dental diagnostics through a custom-built Swept-Source OCT system, assessing its performance against traditional radiological methods. The study utilized both in vivo and ex vivo evaluations, considering variables such as resolution, depth penetration, and image clarity across different dental conditions. Results: OCT demonstrated superior capabilities in detecting early-stage cavities, fractures, and minor imperfections, particularly when high-resolution imaging was required. However, its limited penetration compared to X-rays restricted its application in comprehensive bone assessments. Radiology, especially CBCT, provided essential volumetric data crucial for evaluating bone density, fractures, and post-surgical conditions, though it posed concerns related to radiation exposure. Combining both modalities proved beneficial, offering complementary insights that enhanced overall diagnostic accuracy. Conclusion: While X-ray-based radiology remains indispensable for broad evaluations of dental and bone structures, OCT presents a valuable adjunct, particularly for high-precision assessments of soft tissues and small surface defects. The synergistic use of these technologies can provide a more holistic approach to dental diagnostics, potentially improving patient care and treatment outcomes. Future advancements in OCT could further expand its role in routine dental practice, enhancing diagnostic accuracy while minimizing radiation exposure risks.

Immediate Insertion and Restoration of a Single Implant to Replace Two Adjacent Periodontally Compromised Lower Incisors: A Technique Report with up-to-8 Years Follow-up.

The study investigated the cumulative survival rate (CSR) and marginal bone loss (MBL) of single implants immediately placed and restored with two-unit cantilevered fixed dental prostheses after extraction of two adjacent mandibular incisors with a compromised periodontal condition. Patients in need of extraction and replacement of two adjacent mandibular incisors due to advanced periodontal loss of attachment were treated consecutively. Following a flapless procedure, a single implant was inserted at the time of extraction in one of the two fresh alveoli sockets and immediately restored with a screw retained two-unit provisional FDP. The area of extraction was grafted using xenograft particulate material. Peri-implant soft tissue and hard tissue condition at the last follow-up appointment, marginal bone loss at the last follow-up appointment at least 1 year after the delivery of the final prosthesis, and the final aesthetic result were evaluated. Twenty patients were recruited between January 2014 and December 2019 in a single private practice and each received single implants and immediate provisional restoration with a two-unit cantilevered fixed dental prosthesis. Patients were followed for 22 to 94 months (average follow-up = 4 years) and none of the implants failed resulting in 100% CSR. Cumulative MBL -measured using the VixWin Platinum software -was 1.08 +/- 0.35. A lower MBL was observed in the presence of platform switching (0.63 +/- 0.11 mm) compared to the absence of platform switching (1.27 +/- 0.20 mm). The preliminary results obtained from this study suggest that patients in need of replacing two adjacent periodontally compromised mandibular incisors can be treated with an immediately inserted and restored single implant.

Identification of cutter flat wear for rock TBMs using vibration signal of shield

Identification of cutter wear status is one of the critical issues for the successful operation of tunnel boring machines (TBM). This study proposed a novel model for predicting the locations of cutters experiencing flat wear, leveraging measured vibration signals from the TBM shield. Field tests were conducted to collect vibration acceleration data using accelerometers. This paper outlines the equipment and setup for monitoring vibration acceleration and develops procedures for signal processing. Analysis of vibration acceleration patterns reveals distinct characteristics corresponding to varying numbers and locations of cutters with flat wear. A linear relationship can be identified between the frequency of different vibration acceleration peak intervals and the extent of flat wear on the cutters (number and location of wear cutters). The proposed model is then applied to a TBM tunnelling section in Guangzhou, China, and validated using on-site wear data. This method offers real-time insight into the potential need for cutter replacement during tunnelling operations in challenging hard rock conditions.

Ultralow-frequency absorption mechanism of a hybrid membrane resonator with acoustic soft boundary condition

Hybrid membrane resonator (HMR) as a typical metamaterial-based absorber with acoustic hard boundary condition (AHBC) has demonstrated excellent noise absorption abilities, but the challenge lies in achieving broadband absorption of ultralow-frequency noise in the tens of Hz to 150 Hz regime. In this research, we investigate systematically the absorption characteristics, absorption mechanisms, and casual optimality of an HMR with three openings in lower surface of the cavity, which functioned as an acoustic soft boundary condition (ASBC). Compared to the well-studied HMR with AHBC, a new absorption mechanism, which states that most energy dissipates occur in the opening region rather than in the membrane, has been found first. As a result, the HMR with ASBC can demonstrate outstanding ultralow-frequency sound absorption performance with a very small thickness, and the full width at half maximum of the HMR can be enlarged over 7 times. Furthermore, the causal inequalities of the absorbers with ideal AHBC and ASBC are derived based on the Cauchy integral and causality principle. The causal optimality of the proposed absorber is also achieved. This research provides valuable guidelines for the design of excellent ultralow-frequency sound absorbers which could contribute to solving the major issue of noise reduction.