Sandwich Structure Research Articles

Experimental, numerical and optimization investigation of sandwich structures with 3D-printed sacrificial core under explosive loading

Sandwich panel structures are widely used in aerospace, marine, and automotive applications due to their high stiffness, high strength-to-weight ratio, good vibration damping, and thermal conductivity. The present study investigates the response of 3D printed polylactide acid (PLA) honeycomb structures when used as a crushable core with a protective metal coating in order to analyze the extent of damage and deformation of the center of the back sheet. This research is based on experimental testing and finite element simulation. The purpose of this study is to investigate the effect of three parameters of sandwich panel core, including filling density of the sacrificial core, 3D printer nozzle thickness, and the geometry of printed cells on the strength of sandwich panel under explosive loading. In this study, the effect of these three parameters is investigated at the same time, and finally, the optimal state of these three parameters that leads to the least displacement of the center of the back sheet is introduced. At first, a sandwich structure with a honeycomb core was made by a 3D printing machine, and the filling density of the core was 13 %. Then this set was subjected to explosive loading in open air with C4 explosive and the displacement of the center of the back sheet was measured. Further, considering the cost of experimental tests, the conditions of this test were simulated by the finite element code in LS-DYNA software, and the results of the displacement of the center of the back sheet were verified by experimental testing. In the following, Design-Expert software was used to check the three parameters of filling density, geometry of cells and thickness of the 3D printer nozzle at the same time. Finally, to verify the value obtained for the optimal state, the finite element simulation and experimental test were performed by placing the input parameters of the optimal state and the results were compared.

Gradient 2D re-entrant cores for sandwich structures under low-velocity impact

Auxetic metamaterials, known for their unusual properties, are being explored as cores for sandwich structures to improve impact resistance. This study investigated the low-velocity impact response of sandwich panels with various core designs using finite element method (FEM) and experiments on 3D-printed specimens. These cores include pure honeycomb, pure auxetic, and gradient variations with controlled gradients of Poisson’s ratio, transitioning from negative to positive (NTP), positive to negative (PTN), negative-to-positive-to-negative (NTPTN), and positive-to-negative-to-positive (PTNTP). These gradients were achieved by adjusting the unit cell angle within the core. Under quasi-static indentation, the gradient PTN design improved energy absorption by 26% compared to the honeycomb structure, while the gradient NTP structure showed a 9% improvement over the auxetic core. As for the impact tests, the gradient NTP and PTN structures significantly enhanced the indentation resistance of auxetic and honeycomb structures by 21.3% and 6.5%, respectively. Interestingly, while the optimal core for peak energy absorption varied with impact velocity, gradient structures generally provided superior energy absorption, particularly at lower velocities. FEM results at initial impact velocities of 10, 15, 20 m/s confirmed that structures having negative Poisson’s ratio at their top layer exhibited the lowest penetration depth. Additionally, gradient structures, particularly NTP and NTPTN, demonstrated superior energy absorption capability compared to purely auxetic or honeycomb structures, especially at lower velocities. The study highlights the benefits of utilizing gradient auxetic metamaterial cores in high-performance sandwich structures for impact resistance applications. These structures showed minimal localized damage, reduced densification risk due to uniform crushing, and lower penetration depth.

A simplified design of a concrete sandwich structure containing a reinforcing rib

This article presents the use of a strut and tie analogy for modelling the behaviour of a concrete sandwich structure, which is formed by thin outer concrete layers made of high-performance concrete and reinforcing ribs. The beams transmitting shear are made of a rigid material with low thermal conductivity (Purenit) in combination with a carbon fibre reinforced polymer. The purpose of these ribs is to ensure reliable shear interaction of the outer concrete layers regardless of the thermal insulation of the sandwich structure. A simplified model using the truss analogy in the Scia Engineer software was used for the design of this structure. Furthermore, this design was verified experimentally on a section of the sandwich panel where the feasibility and functionality were tested by a four-point bending test. Finally, the theoretical values from the model were compared with the experimental results. This also includes a simple evaluation of whether this simplified modelling of the structure’s behaviour is appropriate. The paper contains a summary of the conditions that could have affected the results.

Dual-mode topological rainbow based on Kagome sandwich structure

Topological slow light offers an attractive platform for enhancing light-matter interaction because of its immunity to backscattering and robustness to defects. Most topological rainbow trapping structures are designed to support only one mode during frequency routing. However, in this work, we have designed a dual-mode topological rainbow trapping structure to enrich the functionality of frequency routing in slow light, based on Kagome sandwich structure. With the expanding perturbation index m decreasing gradually, the proposed structure supports coupled topological dual-mode edge states. Through the theoretical and numerical calculations, the group velocity of dual-mode edge states can be slowed to near-zero areas, resulting in the trapping of light at the corresponding positions. Our work introduces a new approach to utilizing coupled topological edge states for building multifunctional slow light optical devices.

MOFs-based 0D-2D-3D nanoarchitectonics as catalytic converters for peroxymonosulfate activation

Peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) are promising trend for degrading of toxic organic pollutants. In this work, the novel 0D-2D-3D nanoarchitectonics (sandwich structure) are fabricated as advanced catalysts for PMS-AOPs. The distinctive sandwich structure of ZIF-67-AG-CA allows for the complete exposure of the active sites of ZIF-67, which can effectively activate PMS to generate both radical and non-radical species for the degradation of organic pollutants. Furthermore, the nano-reactive sites are distributed uniformly in layers, which provides additional PMS adsorption sites and enhances the efficiency of the catalytic reaction. Consequently, ZIF-67-AG-CA was observed to exhibit an excellent performance in the removal of organic pollutants by activating PMS, achieving a 99% degradation of 4-NP in 60 min and demonstrating good cycling stability through cycling experiments. Furthermore, quenching experiments and EPR demonstrated that SO42− and O2− radicals were involved in a synergistic manner in the catalytic reaction process with 1O2 non-radicals during the catalytic process.

A flexible wearable sensor based on improving the piezoelectric layer performance of sandwich structures with micro-/mesopores for communication with the deaf-mute

Layered H-UiO-66@IL composites with both intraparticle micropores, interparticle mesopores, and multiple active sites were prepared. A key aspect of the technique was the addition of deionized water during solvothermal synthesis, which rapidly nucleated layered nanoparticles. A multifunctional, flexible, and stable polyacrylonitrile (PAN)-based membrane was successfully constructed by incorporating H-UiO-66 nanoparticles, modified by ionic liquid (1-allyl-3-butylimidazole tetrafluoroborate), into polymers with macromolecular chains under mild, controlled conditions. The resulting film exhibited excellent dielectric, ferroelectric, and mechanical properties due to the multilayer fiber design. Furthermore, the PAN matrix showed a higher content (97.41 %) of planar zigzag conformations, enhancing the piezoelectric properties. The composite film demonstrated ultra-high sensitivity (10.98 V/N) and an ultra-low detection limit of 3.5 × 10⁻⁴ N. In addition, the film passed 1,800-cycle stability tests and maintained its initial output value across various environmental conditions. This flexible piezoelectric sensor shows significant potential for aiding deaf and mute individuals in sign language or breathing communication.

Free vibration characteristics of honeycomb sandwich cylindrical shells reinforced with graphene nanoplatelets/polymer coatings

This study conducts a comprehensive analysis of the free vibration characteristics of honeycomb sandwich cylindrical shells reinforced with graphene nanoplatelets (GNPs). The shells are modeled with a hexagonal honeycomb core, which not only provides a lightweight structure but also enhances the stiffness and dynamic stability. This core design is ideal for high-performance applications such as aerospace and light transport equipment. In addition, the incorporation of graphene nanoplatelet/polymer coatings further improves the structural stiffness, making these shells suitable for demanding environments where both strength and lightweight properties are critical. In the theoretical model, the refined trigonometric shear deformation theory (RTSDT) is applied to accurately represent both bending and shear deformations, capturing the complex behavior of honeycomb sandwich cylindrical shells without requiring shear correction factors. Various parameters, including axial and circumferential wave numbers, as well as geometry and material properties, are examined to assess their impact on natural frequencies. Comparisons with existing literature validate the theoretical models, demonstrating strong agreement with previous results. The analysis reveals that the fundamental natural frequency and other natural frequencies are significantly affected by the inclusion of GNPs and variations in sandwich cylindrical shell geometry. The findings underscore the effectiveness of the RTSDT in modeling these complex sandwich structures.

Small angle X-ray scattering and in silico based structure and function analysis of a novel xylobiohydrolase (AcGH30A) from Acetivibrio clariflavus

Xylobiohydrolase plays a crucial role in the hydrolysis of xylan, a complex polysaccharide present in the cell walls of plants. This study focuses on the solution structure and substrate binding analysis of a novel xylobiohydrolase, AcGH30A, from Acetivibrio clariflavus. Secondary structure analysis of AcGH30A in an aqueous environment using Circular Dichroism and in silico modeling revealed an α/β/α sandwich structure with a central β-barrel comprising eight β-strands. Superposition of the homology-modelled structure of AcGH30A with its closest homolog showed that the active-site contains Glu175 and Glu268 as the catalytic residues. Molecular docking confirmed xylobiose as the preferred ligand, showcasing polar interactions with the catalytic amino acids, indicating its xylobiohydrolase activity. AcGH30A displayed a high binding affinity with xylobiose with an association constant (Ka ) of 7.83 × 105 M−1, as determined by isothermal titration calorimetry. Molecular dynamics (MD) simulations of AcGH30A and AcGH30A-xylobiose complex in solution showed reduced RMSD, Rg and SASA values, confirming the stability and compactness of the complex. MD simulations further highlighted the crucial role of Glu175 in hydrogen bonding with the ligand, which acts as an acid or base. Small-angle X-ray scattering (SAXS) analysis of AcGH30A showed its molecular shape as an earbud with a globular structure existing in a monodispersed state, which was corroborated by dynamic light scattering (DLS). The hydrodynamic radius (Rh ) of AcGH30A, determined by DLS, was 3.7 nm. This study significantly contributed valuable insights into the structure and functional aspects of AcGH30A.

The Sandwich Structure of a Polyimide/PTFE Composite Film Designed to Achieve a Low Dielectric Constant and Excellent Thermal Performance at High Frequency

The Sandwich Structure of a Polyimide/PTFE Composite Film Designed to Achieve a Low Dielectric Constant and Excellent Thermal Performance at High Frequency

Reverse design of load-bearing broadband metamaterial absorber assisted by deep learning

Abstract In response to the current challenges of narrow absorption bandwidth, weak load-bearing capacity, and low design efficiency in absorbing structures, this study focuses on the reverse design of load-bearing broadband metamaterial absorber. A parameterized model of load-bearing metamaterial absorber was developed by integrating the composite sandwich structure with the electromagnetic resonant layers. The resonant layer was constructed using the combination of Vicsek-fractal and circular rings, with resistive films employed to broaden the absorption bandwidth. A deep learning-based forward prediction model was established to accurately predict the absorbance of the metamaterial absorber. The SHapley Additive exPlanations (SHAP) framework was utilized to analyze the forward prediction network, revealing the influence of various design parameters on the absorbance at center frequencies across the L to K band spectrum. Additionally, the Group Teaching Optimization Algorithm (GTOA) was introduced into the design process, leading to the development of an automated reverse design method for metamaterial absorber that can achieve specific design objectives. Using the GTOA-based reverse design method, a metamaterial absorber capable of effectively absorbing vertically incident electromagnetic waves within the 3-20 GHz frequency range was designed. The designed absorbing structure was fabricated, and its absorption performance was measured using the arch method. The measurement results were found to be in good agreement with the simulation data. The absorbing mechanism of the designed metamaterial absorber was analyzed based on the calculation of equivalent electromagnetic parameters and the electromagnetic resonance observed at the resonant frequency. It was determined that the primary absorbing effect is induced by electric resonance triggered by electromagnetic waves. The proposed metamaterial absorber can be applied to radar stealth design for military targets such as naval vessels. The research methodology and approach demonstrate significant generalizability and engineering applicability.

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Amplification of the Surface-Enhanced Raman Scattering Signal from a Monolayer of Organic Molecules in Sandwich Structures Containing Plasmonic Silver Nanoplates

Single-Molecule Detection of Serum MicroRNAs for Medulloblastoma with Biphasic Sandwich Hybridization-Assisted Plasmonic Resonant Scattering Imaging.

MicroRNA (miRNA) dysregulation is closely related to the occurrence and progression of medulloblastoma (MB). However, the full potential of serum circulating miRNAs in MB diagnosis is restricted by their ultralow abundance in peripheral blood due to blood-brain barrier. Here, we report the direct preamplification-free detection of aberrant expression of oncogenic miRNAs in serum from MB patients by proposing a simple yet robust single-molecule assay that combines biphasic sandwich hybridization in nucleic acids and the dark-field single-particle plasmonic imaging (B2S2PI). In this strategy, signal DNA was prehybridized with target miRNA in homogeneous solution to form sDNA-RNA complexes. Then the captured DNA strands with rationally adjusted surface densities could efficiently capture the sDNA-RNA complexes to generate a well-separated DNA-RNA sandwich structure. The combination of homogeneous and heterogeneous reactions enabled interface-mediated hybridization reactions to maintain molecular stability with fewer bases, making it suitable for the direct amplification-free assays of short miRNA targets. Labeling the DNA-RNA hybrids with plasmatic gold nanotags allowed nondestructive recognition and imaging of individual miRNA targets under mild conditions with high signal-to-noise ratio. By digitally counting and analyzing the bright plasmonic resonant scattering spots, B2S2PI enabled both the measurement of a low femtomolar concentration of circulating miRNA-21 in 5 μL sample volume within a turnaround of 2 h and the discrimination of single base mismatches. Moreover, B2S2PI was universal for detecting miRNAs with different sequences and secondary structures. Further analysis of clinical serum samples revealed that B2S2PI was capable of accurately distinguishing MB patients from noncancer controls with an area under the curve (AUC) of 0.99, which was superior to that of qRT-PCR. B2S2PI holds promise as a novel alternative means for single-molecule miRNA assay and sheds light on the circulating nucleic acid-based liquid biopsy of intracranial malignant tumors.

Static and Transient Response Analysis of Arbitrary Laminated Composite and Sandwich Shells by the FSDT Meshless Method

This paper, for the first time, presents a novel meshless method based on the first-order shear deformation theory (FSDT) and moving-least squares (MLS) approximation to carry out static and transient response analysis on arbitrary laminated and sandwich shell structures. The novelty of the method lies in the implementation of MLS in the curvilinear shell formulation, and the derivation of meshless governing equations on the static and transient response of arbitrary laminated and sandwich shells according to the principle of minimum potential energy and Hamilton’s principle, respectively. The concept of a Convected coordinate system is adopted to deal with arbitrary curvilinear surfaces. Both the position and displacement vectors of shells are approximated by MLS, which is conceptually the same procedure as that in the isoparametric finite element method (FEM). The numerical integration of the stiffness matrices is conducted by the simple Gaussian integral in the Convected coordinate system. Because the moving-least squares (MLS) approximation does not satisfy the Kronecker delta condition, the full transformation method is used to modify the meshless governing equations. Numerical examples are calculated to investigate the static and transient response analysis of laminated and sandwich structures with different geometrical shell shapes, including square plates, spherical shells, doubly-curved shells, and cylindrical shells. The numerical tests show that the proposed method is reliable, and robust and produces accurate results compared to the analytical and numerical solutions taken from the previous literature.

Experimental and Numerical Analysis of the Impact Resistance of Polyurethane Foam Aluminum-Concrete Sandwich Structures

The objective of this research paper is to examine the shock-absorption capabilities of sandwich structures that utilize polyurethane foam and aluminum as energy-absorbing materials. A series of drop weight impact tests were conducted on sandwich structures comprising polyurethane foam, aluminum, and concrete. The investigation encompasses variations in the thickness of the polyurethane foam-aluminum absorption layer, the impact height, and different structural combinations, coupled with numerical simulations. Results indicate that as the thickness of the polyurethane foam-aluminum energy absorption layer increases, the energy absorbed by the composite structure also increases. However, the rate of this increase tapers off as the layer thickness continues to grow. The impact height influences energy absorption within a defined range, enabling optimal utilization of the deformation and energy absorption capacities of the polyurethane foam-aluminum layer. Notably, the double-sandwich structure outperforms the single-sandwich structure in terms of impact resistance. The incorporation of the polyurethane foam-aluminum sandwich structure significantly enhances the impact resilience of concrete. Among the tested configurations, the double-sandwich structure composed of polyurethane foam, aluminum, and concrete exhibits the optimal absorption performance. Nevertheless, the layered nature of the structure significantly increases its construction complexity, potentially impacting the practical feasibility of utilizing the polyurethane foam-aluminum-concrete composite structure in real-world applications.

The fabrication of graphene supported Ni nanoparticles and its doping influence on the microstructure and superconductivity of MgB2

A highly dispersed Ni nanoparticle supported on a graphene matrix (nano-Ni/G) has been successfully synthesized using a novel chemical reduction process to overcome agglomeration in traditional MgB2 preparation methods. The influence of the reduction technique on nanoparticle size and structure was thoroughly investigated using a model system. The resulting nanoparticles were small enough (10 nm) to decorate the 2D graphene layers as sandwich structures. This unique morphology contributes to providing more effective flux pinning centers by forming tiny MgNi2.5B2 and efficiently substituting C for B in MgB2 bulks through the principle of double action. Moreover, the low-melting eutectic liquid formed by Mg-Ni at 506 °C is beneficial for the fast fabrication of well-connected MgB2 at low temperatures. Furthermore, a small enhancement of critical current density (Jc) was observed in the doped sample with respect to the undoped ones. However, the advantages of the as-prepared nanoparticles were greatly suppressed by the large presence of MgO during the deposition process, leading to lower superconducting performance than undoped MgB2 bulks. Based on the analysis, further investigation should focus on inducing more flux pinning centers by controlling impurities during the deposition process for achieving optimal performance.

Life Cycle Assessment and Experimental Mechanical Investigation of Test Samples for High-Performance Racing Boats

This paper investigates the environmental impact and mechanical performance of two composite sandwich structures, named Series 1 and Series 2, used in high-performance racing boats. Mechanical tests, including four-point bending and drop impact tests, were performed. It was found on a general basis that Series 2 has higher load-bearing capacity and limited deflection. Series 1, which has a higher density, was able to absorb more impact energy but was more susceptible to damage. A Life Cycle Assessment (LCA) was conducted to evaluate the environmental impact associated with the materials, considering also the testing phase, which plays an important role in the life cycle of materials and structures for advanced marine applications. In addition, two performance indexes were introduced to correlate the mechanical and environmental properties of the analyzed materials. This study emphasizes the importance of considering the testing phase in LCA, as the energy-intensive nature of mechanical testing contributes significantly to the overall environmental impact. The introduced indexes allow for a more comprehensive understanding of the balance between mechanical performance and environmental sustainability. The findings suggest a trade-off between mechanical performance and sustainability, calling for further research into recyclable composites and greener manufacturing processes to balance these competing priorities.

Blast resistance analysis of butterfly-like reentrant circular honeycomb sandwich structure

Negative Poisson honeycomb has great potential in the field of protection against explosive shock due to its unique tensile expansion characteristics and excellent energy absorption capacity. However, there are limitations in the types and performance enhancement of the current negative Poisson honeycomb sandwich structure (HSS), so to further improve the blast resistance of conventional HSS and reduce the mass of the structures, a butterfly-type reentrant circular HSS is designed in this paper. In this analysis, the JC constitutive model related to the mechanical properties of AL-6XN304 alloy steel was used for simulation, and the explosion load was applied to the sandwich structure using the CONWEP loading mode in ABAQUS, and its explosion process was analyzed numerically in detail. Explosive simulation of square-core HSS is first performed, and the precision of the numerical model is verified by comparing it with the experimental result in the existing literature. Secondly, the dynamic response of the imitation butterfly-type HSS under air loading was investigated, and the blast resistance performance of this structure was compared with that of four HSSs under the same air loading. The effects of explosive mass, cell thickness, cell wall radius, and cell length parameters on the blast resistance of imitation butterfly-type reentrant circular sandwich structure were also explored. Findings indicate that the dynamic response of the butterfly-like reentrant circular HSS is divisible into three distinct phases: core compression, overall deformation, and equilibrium vibration. Compared with the square, circular, reentrant hexagonal, and star HSSs, the center displacement of the front panel of the structure is 22.4, 20.2, 8.8, and 23.0% lower, respectively, and the center displacement of the rear panel is 24.4, 20.6, 7.1, and 8.2% lower, respectively. In addition, the central area of the structure is also the lowest deflection. Therefore, the butterfly-like reentrant circular HSS has the best explosion resistance. The butterfly-like reentrant circular HSS of the front and rear panel deflection and the displacement at the center point escalates as the explosive mass grows, diminishes with the thickening of the cell wall, lessens as the radius of the cell wall shrinks, and lessens as the cell length shortens, the blast resistance of the structure can be further improved.

Nonlinear Rayleigh wave propagation in a three-layer sandwich structure in dual-phase-lag

Plane, nonlinear Rayleigh wave propagation is investigated in a three-layer sandwich structure of a thermoelastic medium, within the frame of dual-phase-lag theory. The thermal conductivity is taken as a linear function of temperature. This induces nonlinearity in the evolution equations for the heat flux components. A particular solution is found in the form of Poincaré expansion in a small parameter that reflects the fluctuations of temperature about a steady value. This solution is discussed and plots are provided for a special case when both external faces of the structure are traction-free and under prescribed temperature regime. It is noted, in particular, that some quantities of practical interest suffer jumps at the interfaces. Some of the jumps appear only starting from the second order of approximation. The existence of jumps may be favourably used to carry out some measurements of material parameters.

Fibrillated Films for Suspension Catalyst Immobilization-A Kinetic Study of the Nitrobenzene Hydrogenation.

The immobilization of suspension catalysts in flexible, fibrillated films offers a promising solution to the mass transfer limitations often encountered in three-phase hydrogenation reactions. This study investigates the catalytic performance and mass transfer properties of fibrillated films in the hydrogenation of nitrobenzene to aniline, comparing them to free-flowing powdered catalysts. Fibrillated films were prepared from Pd/C catalysts with varying thicknesses (100-400 µm), and their performance was evaluated through kinetic studies in both batch reactors and microreactors. The specific activity of the films was significantly influenced by film thickness with thinner films demonstrating lower mass transfer limitations. However, mass transfer limitations were observed in thicker films, prompting the development of alternative film designs, including enhanced macro-porous films and sandwich structures. These modifications successfully minimized diffusion limitations, achieving similar specific activity to the powder catalysts while maintaining the mechanical stability of the films. This work demonstrates the feasibility of using fibrillated films for continuous catalytic processes and highlights their potential for efficient catalyst reuse, avoiding filtration steps and enhancing process sustainability. Furthermore, while PTFE remains indispensable for producing such films due to its mechanical and thermal stability, ongoing research focuses on identifying more environmentally friendly alternatives without compromising performance.

Application of Hybrid Conventional Filter and PVDF-TiO<sub>2</sub>/SBE Hollow Fibre Membrane for Peat Water Treatment

South Kalimantan-Indonesia is known to have extensive peatlands reaching 15% of a total peatland in Kalimantan. Due to that peat land water is mostly found and claim as abundant water sources. However, based on quality, peat land water has poor characteristic with high natural organic matter content. Therefore, peat water treatment is necessary to treat using effective method such as hybrid conventional filter and membrane using hollow fibre PVDF-TiO2/SBE. This study aims to investigate the variation of media filter thickness and filtration pressure of hollow fibre (HF) PVDF-TiO2/SBE membrane peat water treatment by filtration pre-treatment and HF membrane ultrafiltration. HF PVDF-TiO2/SBE membrane was prepared by wet spinning method using spinneret set up. Hybrid process was divided into two steps: 1) conventional filter as pre-treatment and 2) HF ultrafiltration membrane under cross flow system. The filter media was used in this work is silica sand and activated carbon with varied thickness 30:10 and 10:30 cm. The HF membrane structure was analysed via scanning electron microscopy (SEM) to investigate the membrane morphology. The results show the fabricated HF membrane has a finger like-sponge sandwich structure morphology. In addition, 30:10 cm (silica sand: activated carbon) thickness exhibits TDS and turbidity removal of 92.18 and 61.37%, respectively as conventional filter pre-treatment. In other hand, HF membrane successfully removed TDS and turbidity of peat water up to 98.68% and 92.41% at 2 bar of filtration pressure. The highest permeate flux of HF membrane conducted of 13.055 Kg.m-2.h-1 at 3 bar. Conclusion of this work is the peat water treatment using activated carbon: silica filtration pre-treatment and HF membrane ultrafiltration can provide clean water with maximum turbidity and TDS removal.