Conventional Curing Research Articles

Thermal crosslinking characteristics of dual-curable isocyanate blocked with methacrylate-functionalized amine derivatives for eco-friendly automotive clearcoats

A novel isocyanate blocked with an amine derivative blocking agent (2-(tert-butylamino) ethyl methacrylate, TBEMA) was designed as a thermal crosslinker for an eco-friendly automotive clearcoat system. New dual-curable blocked isocyanate (BITBEMA) was effectively deblocked at curing temperatures of 120 and 130 °C, which are lower than the conventional curing temperature of 150 °C. The deblocking features of BITBEMA were verified through experimental measurements and density functional theory simulations. The amine-based blocking agent with the methacrylate functionality directly participated in free radical polymerization with CC double bonds in the main resin (hydroxyl functionalized urethane methacrylate oligomer) during thermal curing, leading to enhanced crosslinking networks as well as reduced emissions of volatile organic compounds. The real-time crosslinking behaviors and mechanical properties of the clearcoat with BITBEMA were compared to those of clearcoats with mono-curable amine-based blocked isocyanate and a commercial crosslinker, confirming the excellent crosslinking characteristics of the dual-curable isocyanate crosslinker.

Immobilization of lead (Pb) using ladle furnace slag and carbon dioxide

Global sustainable development faces challenges in greenhouse gas emissions, consumption of energy and non-renewable resources, environmental pollution, and waste landfilling. Current technologies for immobilization of heavy metals face similar challenges; for example, the use of cement, magnesia, lime, and other binders for immobilization of heavy metals is associated with carbon dioxide emission and consumption of limestone/magnesite and energy. In these contexts, this study introduced a novel and sustainable method for immobilization of lead (Pb) by using an industrial solid waste (ladle furnace slag, LFS) and a greenhouse gas (carbon dioxide). In this laboratory investigation, LFS was first mixed with the lead nitrate and then treated by conventional curing (without carbon dioxide) and carbonation curing (with carbon dioxide) for different periods. The treated LFS were then analyzed by various chemical analyses and microanalysis. The results showed that LFS with conventional curing is not effective in immobilization of lead, while LFS with carbonation curing can effectively immobilize lead. The leaching concentrations of Pb from carbonated LFS were four orders of magnitude lower than those with conventional curing. LFS can achieve carbon dioxide uptake of up to 8% of LFS mass. During the carbonation process, carbonates were produced and wrapped LFS particles to prevent the release of lead, lead nitrate was also carbonated into lead carbonate, and the pH of LFS was reduced to 9.36–9.58, close to the minimum solubility of lead carbonate; these are the main reasons for lead immobilization. In summary, the use of LFS with carbon dioxide for immobilization of lead can not only sequester carbon dioxide, but also reduce the cost of binders, non-renewable resource consumption, energy use, and LFS landfilling.

Effect of amorphous silica fume as active filler for rapid densification of the geopolymer products formed by warm pressing

Geopolymers are attracting attention in the field of concrete building materials from the viewpoint of reducing CO2 emissions. This study demonstrates the effects of the addition of silica fume in the warm press method on the densification and mechanical properties of a geopolymer. First, geopolymer products hardened by conventional slurry curing, using fly-ash and sodium hydroxide solution as starting materials, were prepared. The hardened geopolymer products were then pulverized into small grains. Subsequently, various amounts of silica fume were mixed into the fine geopolymer particles to form the starting powder mixtures. A series of these mixtures (10 mass% water added) were placed into a steel mold, which was then inserted into a warm press device. An uniaxial pressure of 240 MPa was applied at room temperature and then the temperature was raised from 80 to 180 °C. When the warm press temperature was set at 80 °C, the compressive strength of the hardened bodies increased in line with the amount of added silica fume. Particularly, in the case of a hardened body with 30 wt% silica fume, the compressive strength reached 195 MPa, which was about three times that of a hardened body with 0 wt% silica fume. The added silica fume was found to improve the fine stacking of starting geopolymer particles in the early stages of warm pressing and help form objects with tightly packed voids between the original geopolymer particles. In contrast, for heat treatment at a warm press temperature of 180 °C, the compressive strength of the hardened bodies with 30 wt% silica fume decreased compared to those for the hardened bodies with 0, 10 and 20 wt% silica fume. From the results of nuclear magnetic resonance analysis, this decrease in strength was considered to be due to an increase in the silica-rich phase.

Initial biocompatibility of novel resins for 3D printed fixed dental prostheses

ObjectivesSeveral materials for 3D printing of fixed dental prostheses (FDP) have been recently introduced. This study aims to evaluate the initial biocompatibility of novel printable resins for manufacturing temporary and permanent FDP. MethodsSpecimens of five printable resins (VarseoSmile Crown plus, NextDent C&B MFH, VarseoSmile Temp, Temp PRINT, P Pro Crown & Bridge), two types of resins for subtractive manufacturing (Tetric CAD, Telio CAD) and two types of resins with conventional curing processes (Tetric EvoCeram, Protemp 4) were produced and finished. Post-processing was strictly performed according to the manufacturer’s protocol. Biocompatibility was evaluated by eluting specimens with cell culture medium and treating human gingival fibroblast cells with the eluates. A 72-hour continuous read cell viability assay measuring the reducing potential of the cells was performed. The cellular inflammatory response in terms of IL-6 and PGE2 levels was determined with specific ELISAs. Oxidative stress was determined by measuring oxidized glutathione concentrations after exposure to the resin eluates. A luminescence-based apoptosis assay was used to detect apoptosis. ResultsTetric CAD and Telio CAD were slightly toxic. All other resins were moderately to severely cytotoxic. VarseoSmile Crown plus and P Pro Crown & Bridge significantly enhanced PGE2 levels. Higher concentrations of oxidized gluthatione were determined in the presence of Telio CAD, VarseoSmile Temp and P Pro Crown & Bridge. Tetric EvoCeram and Protemp 4 reduced intracellular gluthatione levels. All printable resins slightly induced apoptosis. SignificanceFurther post-processing steps such as additional curing and washing may improve the biocompatibility of printable materials.

Effects of content and length/diameter ratio of PP fiber on explosive spalling resistance of hybrid fiber-reinforced ultra-high-performance concrete

Ultra-high-performance concrete (UHPC) is prone to explosive spalling at high temperatures, which compromises the load-bearing capacity of the structures. In this paper, the effects of the content and length/diameter ratio of polypropylene (PP) fibers on the explosive spalling resistance of the steel and PP hybrid fiber-reinforced UHPC were investigated utilizing experimental method. First, the UHPC specimens were prepared using the conventional curing method. Second, the UHPC specimens were heated using the ISO-834 standard heating curve. Thirdly, the appearances, the first spalling time, the first spalling temperature, and the mass loss of the specimens were used to evaluate the explosive spalling resistance of the UHPC. The results demonstrated that the steel and PP hybrid fiber-reinforced UHPC has much greater explosive spalling resistance than the steel fiber-reinforced UHPC. The explosive spalling resistance of the hybrid fiber-reinforced UHPC is strongly influenced by the content and length/diameter ratio of the PP fibers. Generally, the explosive spalling resistance of the hybrid fiber-reinforced UHPC increases with the increase of the PP fiber content and length/diameter ratio.

Bio-preservation of raw hides/skins: A review on greener substitute to conventional salt curing.

Raw hides/skins are considered to be the prime component for leather industry, which once flayed from animals, plummets to microbial attack. Their preservation combats putrefaction wherein curing using sodium chloride (NaCl) is by and large the most widely accepted method. However, there are few stumble blocks in using NaCl in terms of pollution load generated such as high total dissolved solids (TDS), total suspended solids (TSS), biological oxygen demand (BOD), chemical oxygen demand (COD) and chlorides (Cl-). Additionally, this effluent when discharged affects the quality of the water, soil and plants causing huge ecological damage. To evade these problems, researches are being carried out to explore alternative preservation techniques which are either salt free or with reduced amount of salt. Different methods were proposed time and again which remained unfeasible due to associated drawbacks like high cost, health hazards and environmental concerns. Therefore, finding cheaper, eco-friendly and sustainable method for preservation has become the need of the hour for this industry. This review meticulously summarizes the changing trends in preservation techniques for past few decades with special emphasis on bio-based preservation. The diversity of the natural preservatives explored for the said purpose has been systematically reviewed. The enormous environmental benefits that can be obtained by adopting bio-based preservation and future avenues of research have been discussed.

PET-Based Instant Inkjet-Printed 4 × 4 Butler Matrix Beamforming Network

In this paper, a novel planar Butler matrix (BM) utilizing only 3dB3⁢dBhybrid couplers and a crossover are implemented using a low-cost silver-nano inkjet printing technique. Unlike in the conventional design of BM where a phase shifter is required, this novel design does not need a phase shifter to be implemented. However, the use of delicate substrates like polyethylene terephthalate (PET) in the design makes it unique. This is not possible with the conventional thermal curing process, as PET substrate cannot be subjected to an excessively feverish temperature. The results obtained show good return loss and transmission coefficients better than 26.1026.10 and 23.54dB23.54⁢dB, respectively, at the center frequency. Similarly, an amplitude imbalance of less than 2.4dB2.4⁢dB with phase mismatch within ±0.25∘±0.25∘ is achieved at the center frequency. The BM has a −10dB-10⁢dB bandwidth of 24.79% with a beam pattern produced at +13∘+13∘,−40∘-40∘, +40∘+40∘, and −13∘-13∘ when ports 1-4 of the BM are energized.

Laboratory Study on the Water-Soluble Polymer as a Self-Curing Compound for Cement Concrete Roads in Ethiopia

In this paper, the self-curing process was considered and found to be a better alternative to the conventional curing process for concrete structures in Ethiopia. It is well known that water plays a significant role in the curing process of preparing concrete in the construction industry. A good quality water is required for the conventional curing process, but that is scarce in Ethiopia. Curing concrete for bridges and roads is difficult in Ethiopia due to the poor quality and scarcity of water. In this study, Polyethylene Glycol (PEG) 600, a self-curing process, is considered as an alternative. Using the M40 Grade mix, four different percentages of PEG-600, 0.0, 0.5, 1.0, and 1.5 of cement weight, were studied, and the specimens were tested. Here, M40 grade stands for “a concrete mix with a characteristic compressive strength of 40 N/mm2, i.e., 40 Newton per square millimeter”. Additionally, the mechanical strengths and properties of both conventional and self-cured processed concretes were calculated and compared. The present investigation concludes that PEG 600 offers significant results for self-curing concrete. The study procedure, results, and recommendations are presented in the text of the paper.

XRD INVESTIGATIONS ON COMPRESSIVE STRENGTH GAIN OF UHPC SUBJECTED TO VARIOUS CURING TECHNIQUES

Ultra High Performance Concrete (UHPC) is a relatively novel structural material which can be regarded as an advanced cementitious material with great stiffness, very high mechanical strength, and, extraordinary toughness in a broad sense. Even after cracking, the existence of tiny steel fibers confers the capacity to withstand deformations and, resist flexural and tensile stresses. Curing procedure is a key characteristic to enrich the qualities of the toughened concrete due to the inclusion of the mineral admixtures and a small water to binder ratio. If the process of curing is flawlessly completed, properties such as durability, volume stability, water tightness, strength, abrasion resistance, and resistance to freezing and thawing is highly enhanced. The impact of conventional water curing, hot air curing and, steam curing on the compressive strength of UHPC is explored in this study. UHPC cubes of side 70 mm are cast and the samples are subjected to water curing at 25°C, steam curing at 70°C temperature and, 75% RH and, hot air curing at 200°C. The cured samples are tested for compressive strength at different ages. The powders acquired after crushing the cubes are used for X-ray diffraction (XRD) studies. The variation in the compressive strength when subjected to different types of curing is analyzed using XRD studies, based on the products formed during hydration.

Performance Evaluation of Green Cushion Gum Composite Formulated Based on Hybrid Filler and Curing System

Cushion gum is a type of rubber composite material used as adhesive in the manufacture of retread tires. Therefore, cushion gum should have good processability and mechanical characteristics, particularly tensile property, and adhesion strength. The effect of hybrid filler and curing system on the performance of green cushion gum composite was investigated to determine the appropriate green cushion gum formula designed at a laboratory scale. The content of CB N330/lignin in hybrid filler was arranged at 40/10 phr and 50/10 phr. Meanwhile, the curing system was performed semi-efficient (CBS/S 1.6/1.6 phr) and conventional (CBS/S 1.6/2.2 phr). Green cushion gum composite was also formulated using pine tar oil as a bio plasticizer. Referred to the curing characteristic and mechanical property test result, it showed that green cushion gum composite formula coded by RF1 which composed of CB N330/lignin as 50/10 phr and applied conventional curing system which ratio of CBS/S as 1.6/2.2 phr was regarded as the acceptable combination in designing green cushion gum composite formula. Higher CB N330 loading in hybrid filler composition and conventional curing system attributed to the relatively high crosslink density indicated by MH-ML value. Consequently, green cushion gum composite was obtained using the RF1 formula that has a better optimum curing time accompanied by good tensile property and adhesion strength. The composite was also comparable to conventional commercial cushion gum.

Polygonum hydropiper in goatskin preservation: A sustainable leather processing approach

In conventional preservation of hides and skins, the use of NaCl (50%) evolves enormous salinity and total dissolved solids (TDS) in soaking effluent during leather processing. Plant-based skins preservation is a sustainable solution in reducing salinity and TDS from leather industry to replace conventional curing. In this study, the application of Polygonum hydropiper-based dry powder paste over flesh side of goatskin following 10%, 10%, and 15% paste mixing with 5%, 10%, and 5% salt, respectively, was done with periodical monitoring of organoleptic properties, moisture content, hydrothermal stability, and bacterial load. As compared to conventional curing, these Phyto-based salt minimized curing formulations had preserved goatskin for 30 days, resulting in a maximum 81% and 52% salinity and TDS reduction, respectively, in soaking liquor. The preserved skins were processed into shoe-upper leather in the same manner, and the ultimately produced leather offered the equivalent physical qualities. SEM images corroborated the structural orientation of collagen fibers was more suited than leather produced from salt-preserved skins. The correlation analysis demonstrated strong interdependencies among goatskin preservation efficacy metrics, particularly moisture content and hydrothermal stability, with the highest correlation (r = −0.919). Phytochemicals like alkaloids, flavonoids, coumarin, quinones, terpenoids, tannin, and phlobatannin were present in P. hydropiper extracts. The acetonic and water extract of the examined plant demonstrated modest antibacterial efficacy (11 mm) against Staphylococcus aureus compared to chloramphenicol (27 mm). Therefore, P. hydropiper can be a potential curing agent with comparable leather strength while minimizing the environmental impact and endorsing sustainable developments of leather industry.

The use of alkaline CO2 solvent for the CO2 curing of blast-furnace slag mortar

Moving toward carbon neutrality in the construction industry involves utilizing CO2 to produce construction materials. CO2 curing of cement-based materials induces carbonation at an early age, which enhances strength and performance. A new process for the CO2 curing is proposed using CO2-dissolved curing water, which needs no massive CO2-gas chamber encasing cement-based materials in mild pressure. Gaseous CO2 was dissolved in 1 M aqueous KOH solution beforehand, and mortar samples made with ground-granulated blast furnace slag were submerged and cured. The CO2-water curing for 3 days carbonated the samples, but was not beneficial for their 3-day strengths. Successive moist curing resulted in further hydration of the mortar with carbonate seeds. Finally, the samples’ strengths at 28 days were enhanced, and their CO2 uptake was as much as the conventional CO2 curing provides.

XRD INVESTIGATIONS ON COMPRESSIVE STRENGTH GAIN OF UHPC SUBJECTED TO VARIOUS CURING TECHNIQUES

Ultra High Performance Concrete (UHPC) is a relatively novel structural material which can be regarded as an advanced cementitious material with great stiffness, very high mechanical strength, and, extraordinary toughness in a broad sense. Even after cracking, the existence of tiny steel fibers confers the capacity to withstand deformations and, resist flexural and tensile stresses. Curing procedure is a key characteristic to enrich the qualities of the toughened concrete due to the inclusion of the mineral admixtures and a small water to binder ratio. If the process of curing is flawlessly completed, properties such as durability, volume stability, water tightness, strength, abrasion resistance, and resistance to freezing and thawing is highly enhanced. The impact of conventional water curing, hot air curing and, steam curing on the compressive strength of UHPC is explored in this study. UHPC cubes of side 70 mm are cast and the samples are subjected to water curing at 25°C, steam curing at 70°C temperature and, 75% RH and, hot air curing at 200°C. The cured samples are tested for compressive strength at different ages. The powders acquired after crushing the cubes are used for X-ray diffraction (XRD) studies. The variation in the compressive strength when subjected to different types of curing is analyzed using XRD studies, based on the products formed during hydration.

CHEMICAL AND MECHANICAL PRINT STABILITY OF SUBSTRATES CONTAINING ALTERNATIVE NON-WOOD FIBRES

The aim of this research has been to demonstrate the use and applicability of substrates containing non-wood fibres in the printing industry, with an emphasis on flexographic printing for packaging. To obtain such substrates, laboratory papers were produced with the addition of 30% non-wood fibres (wheat, barley and triticale), in combination with recycled wood pulp. These substrates were tested for chemical and mechanical resistance after flexographic printing with conventional and ultraviolet curing inks. The results showed that all laboratory papers with the addition of 30% non-wood fibres, printed with water-based inks, had fairly good chemical and mechanical resistance, except for the prints treated with sodium hydroxide. Thus, such papers should not be used as packaging materials for alkaline products. UV-curable inks on these substrates showed low chemical resistance, thus should only be used on substrates intended for secondary packaging. The mechanical resistance of UV prints was very good, thus papers containing straw pulp could be used for various applications.

Influence of curing temperatures on the performances of fiber-reinforced concrete

In cold regions or even permafrost areas, it shows growing interests in engineering infrastructures, and more engineering projects have been constructing, e.g. Sichuan-Tibet railway. Undoubtedly, the concrete needs to be cured at the temperature below the conventional curing temperature (about 20 °C). This paper investigated the effect of curing temperatures (i.e. −6 °C, −2 °C, 2 °C and 6 °C) on the performances (compressive strength, stress–strain relationship, microstructure, and hydration products) of steel fiber-reinforced concrete (SFRC), polypropylene fiber-reinforced concrete (PPFRC), and basalt fiber-reinforced concrete (BFRC). The results show that the curing temperature and curing age have positive effects on the compressive strength of concrete samples, and the compressive strength increases with the curing temperatures and curing ages. Besides, regardless of curing temperatures, the type and dosage of added fibers would greatly affect the compressive strength, and there is an optimum fiber content for the compressive strength of FRCs cured at the low temperature to resist loads, and the optimum fiber contents for the SFRC, PPFRC and BFRC are 2.0%, 2.0‰ and 0.5‰, respectively. Additionally, the axial stress–strain curves can be divided into four-section characteristics, i.e. linear ascending stage, plastic yield stage, descending stage and residual stress stage. The addition of fibers into concrete remarkably improves the ductility of concrete due to the fiber bridging effect. Moreover, the negative curing temperatures drastically inhibit the hydration reaction of concrete. Denser microstructure, more hydration products and good fiber–matrix binding quality can be observed in the concrete samples cured at the higher temperatures.

Effect of the Thermal Insulation Cover Curing on Temperature Rise and Early-Age Strength of Concrete.

In the present paper, the effects of thermal insulation cover curing on the rise in temperature of concrete, and further on the mechanical properties of the concrete are measured experimentally. In the experiments, polyurethane foam boards of 100 mm thickness were used for thermal insulation, and three concrete strength grades of C30, C50 and C80, were used as concrete samples. Conventional standard curing, and two heat curing methods with a constant temperature of 40 °C and 60 °C were used for comparison. The pore structure of the cement paste subject to the different curing procedures, including insulation cover curing, heat curing and standard curing, was experimentally measured using mercury intrusion porosimetry. The test results show that rate of increase in compressive strength compared with standard curing is 22–34%, 16–26%, and 23–67%, respectively, for C30, C50, C80 concrete after being subject to 1 to 3 days thermal insulation cover curing in the initial period after concrete casting. As expected, initial heat curing of concrete will result in a reduction in the long-term strength of the concrete. At 28 days, the strength reduction rate compared with standard curing due to the insulation cover curing is 3.1–5.9%, 0.6–3.0%, 0–3.2%, respectively, for C30, C50, C80 concrete. By contrast, the compressive strength reduction compared with standard curing at 28 days is 8.6–10.5%, 8.6–9.1%, 4.7–5.6%, respectively, for C30, C50, C80 concrete after being subject to a constant heat curing of 40 °C and 60 °C in the initial period after concrete casting. Measurement of the pore structure of the paste subject to different curing procedures initially after casting shows that rising curing temperature leads to coarser pores, especially an increase in capillary pore fraction. Among the four curing methods used in the present study, the effect of insulation cover curing and low temperature (40 °C) heat curing on the capillary pore content is small, while the effect of high temperature (60 °C) heat curing is significant.

Impact of Carbon di-oxide Curing on Basalt Rock Fibre Reinforced Concrete

Concrete is the fundamental element in the construction activity which advancement enhances the durability properties. To achieve the strength of concrete within short time various curing techniques are available. One such curing technique is exposing concrete to carbon dioxide gas. Carbon dioxide gas is the abundantly released gas from the industries which pollutes the environment & also a main reason for the greenhouse effect. By utilizing carbon dioxide gas in construction activities, environmental pollution can be minimized. This study is about the investigation of mechanical properties of basalt fibre reinforced concrete subjected to conventional and carbon dioxide curing methods. Specimens are prepared of M25 grade concrete with 0, 1, 2, and 3, 4 Kg/m3 basalt fibres. Compressive strength and split tensile strength tests are performed to specimens after 28 days of conventional curing and 2.5 hours of carbon dioxide curing.

Salt Free Preservation of Raw Goat Skin Using Swietenia Mahogany (Seed) Extract

Curing of hides and skins using sodium salt is a well-established and economical preservation technique worldwide. But it contributes to generating a large amount of total dissolved solids (TDS) and increasing the salinity of water during leather processing which is a threat to the environment. The current research is an attempt to preserve goat skin using mahogany (Swietenia mahogany) seed’s extract. In real practice different percentages of mahogany seed extract were applied on raw goat skin and 3% (by weight of skin) of it showed best result. To evaluate the preservation efficiency, related parameters of preservation viz. odor, hair slip, shrinkage temperature, moisture content, bacterial count etc. were monitored regularly for 30 days. The obtained results were compared with conventional salt curing process. The experimental trial showed efficiency in lessening TDS value and chloride content. The preserved goat skins of both trials were treated following conventional leather processing techniques and physical properties were studied. The discussed preservation method exhibited comparable result in every index.

Durability assessment of Self-Curing high performance concretes containing zeolite admixture

The infrastructural development activities are accompanied with construction of various facilities to provide safe and sustainable livelihood to the society. Concrete being one of the most extensively used construction material, there has been a growing demand in terms of consumption of cement fine aggregate, coarse aggregate and water. There have been numerous attempts to utilize alternate binding materials as a partial replacement of cement. Scarcity in aggregates are also being addressed through alternate filler materials like manufactured sand or artificial aggregates. Water scarcity in many locations has been forcing the researchers to look for alternate methods of curing either through addition of self-curing compounds or through coatings which doesn’t permit the internal water to evaporate. There have been numerous attempts to quantify the functioning characteristics of the selfcuring mortars and self-curing concretes. However, the research on zeolite as admixture in self-curing concrete have not been addressed to a great extent. The current work was focused to study the durability aspects of self-curing concretes containing calcined zeolite and uncalcined zeolite as a partial replacement of cement. A relative comparison of performance characteristics of air cured self-curing concretes with conventional concrete cured in water have been presented. Also, attempts were made to evaluate the corrosion characteristics of embedded reinforcement through half-cell potential measurements. The extensive study on these proposed concretes revealed the fact, that it is possible to develop high strength concretes without conventional curing practices. However, these concretes had superior durability characteristics which was witnessed through resistivity, rapid chloride penetration test (rcpt) and cyclic wet and dry test.

Internal carbonation curing base on molecular sieve: Influence and mechanism on cement-based materials

Carbonation curing of cement-based materials can not only store CO2, but also improve the mechanics and durability. But there are still many problems limiting its application. For example, the water cement ratio should be low, the carbonation reaction only occurs at the surface and the high-pressure curing equipment is hard to be used in-situ. In this paper, the molecular sieve adsorbed CO2 was adopted as internal carbonation curing agent to investigate its influence and mechanism on the strength of cement-based materials. And the mechanism was investigated through the methods including X-Ray Diffraction and scanning electron microscope. Results indicated that under the action of internal carbonation curing agent, the strength of the cement paste at 3d, 7d and 28d increased by 22.5%, 18.6% and 12.8%, respectively. It would provide more possibilities for in-situ application of carbonation curing on cement-based materials which cannot be achieved by conventional carbonation curing.