Surface Texture Evolution Research Articles

Porous asphalt mixture performance in cold regions: Case study of Chicago

Porous Asphalt Mixtures (PAMs) improve resilience of flexible pavements in the context of climate change. PAM application in coastal cities like Chicago is of interest; however severe winters compromise the durability of PAMs given their susceptibility to freeze-thaw. This work aimed to evaluate the to-date experience with PAMs in Chicago, exploring benefits and limitations to be considered for future projects in the Southern Lake Michigan region. Full-depth PAM cores were obtained from seven sections, constructed in different years. Tests were conducted to assess the evolution of surface texture, internal structure, and multi-scale material properties. Regarding surface texture, consistent change over time was observed, such as loss of the “channel” structure, and increase in mean profile parameters because of raveling. Also, binder content varies with time within different layer depths. An aging gradient in terms of stiffness from top to bottom within the layer does not necessarily occur. However, binder ductility shows drastic and consistent reduction throughout the layer as aging increases. Analysis of internal structure using a CT scan revealed that there is also a lack of homogeneity in the air void and particle size distributions. Finally, this study suggests that full-depth PAM viscoelastic behavior is sensitive to saturation level, and this is a relevant subject to be considered, since partial saturation may be a condition often observed in the field.

Reconstruction and evolution of 3D model on asphalt pavement surface texture using digital image processing technology and accelerated pavement testing

Asphalt pavement surface texture is the main factor affecting pavement function. Reconstruction of the asphalt pavement surface texture is needed to accurately reveal its evolutionary characteristics for pavement performance and quality evaluation. To reconstruct an optimised 3D model of the asphalt pavement surface texture and to study its evolutionary properties, digital image processing technique and accelerated pavement testing system were used. First, the asphalt pavement surface texture 3D model optimised by three camera parameters and their thresholds. Next, the accelerated pavement testing system simulated traffic loadings on dense-gradation asphalt mixtures to investigate the pavement surface texture evolution properties. Finally, predictive models are developed for the asphalt pavement surface texture evolution. Results show that the optimised pavement texture 3D model resembles actual pavement structure. The surface texture evolutionary characteristics of asphalt pavement can be divided into three periods and six stages. The evolution model can accurately characterise the evolution of the surface texture of asphalt pavement. Abbreviations: MLS11: Accelerated pavement testing system; HP : Mean pixel difference; Df : Fractal Dimension; MTD: Mean Texture Depth; BPN: British Pendulum Number

Skid-resistance durability and wear/polish-resistance behaviors of ultra-thin friction course designed based on the differential polishing of aggregates

To improve the skid-resistance durability of asphalt pavements in a cost-effective manner, this study introduced a differential-polishing principle based on blending various aggregates. SMA-5 ultra-thin friction courses (UTFC) were prepared using mineral aggregates consisting of 88# calcined bauxite and limestone blended in six proportions. Long-term simulated traffic polishing tests were performed on six types of UTFC surfaces in the laboratory. Direct skid-resistance indexes, BPN20 and μ80, were used to evaluate skid resistance at low and high velocities after different polishing cycles, respectively. Surface texture evolution during long-term polishing was analyzed using bearing area ratio, mean profile depth, and fractal dimension D. Additionally, an attenuation prediction model for skid resistance was developed. Aggregate mechanical properties affecting skid-resistance durability of UTFC were investigated through grey correlation analysis. The results show that a significant differential-polishing effect was generated during long-term polishing due to large differences in the two aggregates’ wear/polish resistance, which can effectively reduce the attenuation rate of skid resistance of UTFC and improve skid-resistance durability by decreasing wear loss of UTFC surface aggregate and forming texture structure difference between aggregates to maintain rough surface texture. The reasonable blending proportion of 88# calcined bauxite was determined to be 40%–60% of the mineral aggregate mass. It was also found that the developed predictive model can reflect the attenuation law of skid resistance, and PSV and LAA loss of aggregates are well correlated with the skid-resistance durability of UTFC.

The Differences in Microstructure, Microtexture, and Tensile Anisotropy of Ti80 Heavy Plate Across the Thickness

Herein, the differences in microstructure, microtexture, and tensile behavior of the Ti80 heavy plate across the thickness are investigated. The Ti80 heavy plate consists of equiaxed α and transformed β grains with high degrees of recrystallization microstructures. Significant differences are observed in the main texture components between the central and surface zones. The inhomogeneous distribution of hot compression and shear leads to different deformation textures during processing. Due to temperature distribution, the combination of the variant selection mechanism and α–β phase interaction is responsible for the evolution of surface texture, while only the former plays a major role in the center. Final fracture areas of tensile samples show ductile fracture characteristics. The anisotropy behaviors in planar tensile of the Ti80 heavy plate at room temperature are evaluated. They are related to the difficulty of activating prismatic slip and basal slip , which are determined by the crystallographic texture of the material. This work helps to explore reasonable thermomechanical processing parameters and establish rolling schedules to weaken the mechanical heterogeneity across the thickness of near‐α‐titanium alloy heavy plates.

Improving vertical charge transport in organic Schottky diodes via interface engineering of large-area conducting polymer thin films fabricated on hydrophilic liquid surface of tunable surface energy

Molecular orientation and stacking genre proved to be one of the decisive factors for the performance of conducting polymer (CP) based electronic devices. In this context, harnessing the key advantages of the ribbon shaped “floating-film transfer method” (FTM) along with an interfacial engineering approach has been utilized for molecular rearrangement in polymer thin-films formed on the surface of a high surface energy hydrophilic liquid mixture. In this novel subphase modified floating-film transfer method (SM-FTM), dodecyl benzene sulfonic acid (DBSA) has been used to control the molecular backbone stacking proximate to the solution-liquid interface and regioregular-poly(3-hexylthiophen-2,5-diyl) (rr-P3HT) was used as the model CP to probe the polymer-DBSA interaction. The molecular arrangements in microcrystalline domains, electronic band structures, and the evolution of surface texture at the solution-liquid interface have been investigated through multiple characterization tools. After that, the electrical performances of Schottky barrier diodes (SBDs) were studied in an ITO/P3HT/AlOx/Al sandwiched structure and a dramatic enhancement of rectification ratio up to 8.2 × 106 at ± 6 V was achieved. Further, an analytical model for SM-FTM, developed using lubrication theory and thin-film dynamics, has also been presented to elucidate the polymer spreading dynamics and the mechanism of molecular rearrangement at the interface.

Understanding the Role of Directional Texture in Tribofilm Evolution

Abstract This paper reports a study of the evolution of directional texture and its role in the manipulation of tribofilm layers under boundary lubrication (BL). The use of surface protective tribofilms/lubricant chemistries along with the use of textured surfaces has gained significant attention as an effective BL strategy to provide advanced lubrication. However, the evolution of surface texture in the direction of motion under continuous asperity-to-asperity contact remains unexplored, especially in correlation with the tribofilm properties on textured surfaces. Mechanical polishing using SiC abrasive paper was used to generate directional and concentric surface texture on 52100 steel discs. Tribological tests of varying time durations were performed using MoS2-based lubricant to systematically study the evolution of texture and tribofilm using a pin-on-disc rotational setup. A laser microscope was used for areal texture characterization while tribofilm was characterized using SEM/EDS, Raman, and FIB/TEM. The results show that directional texture manipulates the early onset and tribo-chemical reactions and the delivery of lubricant tribofilm on the asperities during the evolution process.

Evolution of a Superhydrophobic H59 Brass Surface by Using Laser Texturing via Post Thermal Annealing.

To fabricate an industrial and highly efficient super-hydrophobic brass surface, annealed H59 brass samples have here been textured by using a 1064 nm wavelength nanosecond fiber laser. The effects of different laser parameters (such as laser fluence, scanning speed, and repetition frequency), on the translation to super-hydrophobic surfaces, have been of special interest to study. As a result of these studies, hydrophobic properties, with larger water contact angles (WCA), were observed to appear faster than for samples that had not been heat-treated (after an evolution time of 4 days). This wettability transition, as well as the evolution of surface texture and nanograins, were caused by thermal annealing treatments, in combination with laser texturing. At first, the H59 brass samples were annealed in a Muffle furnace at temperatures of 350 °C, 600 °C, and 800 °C. As a result of these treatments, there were rapid formations of coarse surface morphologies, containing particles of both micro/nano-level dimensions, as well as enlarged distances between the laser-induced grooves. A large number of nanograins were formed on the brass metal surfaces, onto which an increased number of exceedingly small nanoparticles were attached. This combination of fine nanoparticles, with a scattered distribution of nanograins, created a hierarchic Lotus leaf-like morphology containing both micro-and nanostructured material (i.e., micro/nanostructured material). Furthermore, the distances between the nano-clusters and the size of nano-grains were observed, analyzed, and strongly coupled to the wettability transition time. Hence, the formation and evolution of functional groups on the brass surfaces were influenced by the micro/nanostructure formations on the surfaces. As a direct consequence, the surface energies became reduced, which affected the speed of the wettability transition—which became enhanced. The micro/nanostructures on the H59 brass surfaces were analyzed by using Field Emission Scanning Electron Microscopy (FESEM). The chemical compositions of these surfaces were characterized by using an Energy Dispersive Analysis System (EDS). In addition to the wettability, the surface energy was thereby analyzed with respect to the different surface micro/nanostructures as well as to the roughness characteristics. This study has provided a facile method (with an experimental proof thereof) by which it is possible to construct textured H59 brass surfaces with tunable wetting behaviors. It is also expected that these results will effectively extend the industrial applications of brass material.

Finite element model for topography prediction of electrical discharge textured surfaces considering multi-discharge phenomenon

The prediction of surface topography obtained with electrical discharge texturing (EDT) process is very challenging, due to stochastic nature and complex physics in occurrence of sparks. Though there are a few models for surface texture prediction in the literature, there are still ample opportunities to improve upon by adopting more realistic assumptions and formulations for simulation. This paper presents a numerical simulation of progressive development of surface topography due to sequential application of spark discharges on an instantaneous textured surface formed by all previous spark discharges. The model incorporates major single-spark features such as, Gaussian distribution of heat flux, temperature-dependent work material properties, latent heat of melting, and operating parameter dependent variation of factors such as, cathode energy fraction, spark radius, and plasma flushing efficiency; besides the multi-spark features such as, stochastic distribution of sparks with respect to: i) location, ii) energy level, and iii) chronological order. Finite element simulation of EDT is performed in ABAQUS with the help of user-defined subroutines for the dynamic simulation of spark discharges, flagging of elements attaining evaporation temperature from further heat flux application and storage of the highest temperatures attained by each element. An evolution of surface texture through the progress of spark erosions has been studied. As EDT continues, the number of craters overlapping generally tend to increase, whereas the center-to-center distance between a crater with its nearest neighbour tends to decrease. The simulated surface textures are validated with the experimental ones using two methods: error function method and Ra distribution method, and were found to be in good agreement.

Surface Texture Evolution of Fused Silica in a Combined Process of Atmospheric Pressure Plasma Processing and Bonnet Polishing

The increasing demand for precision optical components invokes the requirement of advanced fabrication techniques with high efficiency. Atmospheric pressure plasma processing (APPP), based on chemical etching, has a high material removal rate and a Gaussian-shaped influence function, which is suitable to generate complex structures and correct form errors. Because of the pure chemical etching, an optically smooth surface cannot be achieved using only APPP. Thus, bonnet polishing (BP) with a flexible membrane tool, also delivering a Gaussian influence-function, is introduced to smooth the surface after APPP. In this paper, the surface texture evolution in the combined process of APPP and BP is studied. The etched texture with increased removal depth of APPP is presented and analyzed. Subsequently, the processed substrates are smoothed by BP. The texture smoothing and the roughness improvement is investigated in detail. The experimental results show that the APPP etched pits coalesce with each other and transform into irregular convex-concave structures, with roughness degraded to about 25 nm arithmetical mean deviation (Ra). The APPP etched texture can be successfully smoothed to 1.5 nm Ra, with 0.2–1 μm material removal of BP.

Comprehensive investigation on mechanisms of dry belt grinding on AISI52100 hardened steel

Abstract In order to further understand the grinding mechanisms of dry belt grinding process, this paper provides a comprehensive investigation both on the evolution of the belt wear and the evolution of part's surface texture, simultaneously. The results have shown that grains' wear mode can be evaluated by surface roughness parameters Sz, Sdq and Spc. The belt wear in open-loop belt grinding has been quantitatively proved to keep stable after a few of turns due to constant working conditions. The blockage has been found in this paper and primary studied. It has been revealed that the blockage can further improve the surface roughness, ignoring the limit set by original working condition, but with a sacrifice on material removal and waviness improvement.

Estimation of the polishing time for different metallic alloys in surface texture removal

ABSTRACTThe aim of this work is to propose a novel analytical model for predicting the polishing time and behavior of the surface texture removal in different metal alloys. The surface texture, resulting from a previous milling process, is characterized and investigated by the Abbott–Firestone curve, the relative speed of the abrasive material, the applied force, the type of material and the size of the abrasive grains. Consequently, a model that predicts the surface texture evolution based on the mechanism of abrasion is proposed, in which a constant of the wear model is found to behave linearly with the size of the abrasive grain for each metal alloy. Based on the good agreement between the experimental and the estimated values (R2 equal to 0.993), operational parameters are recommended to predict the required surface texture for AlCu4PbMg, 30CrNiMo8, C45E and X6CrNiMo8 when using abrasive grade between P180 and P1200.

FEM-simulation of machining induced surface plastic deformation and microstructural texture evolution of Ti-6Al-4V alloy

When high speed machining polycrystalline metal, severe plastic deformation usually undergoes in the machined surface layer, accompanied by the microstructural variation of the crystallographic orientation. In the present paper, the machined surface plastic deformation and microstructural texture evolution during high speed machining of titanium alloy Ti-6Al-4V were investigated using finite element method (FEM) simulation. Firstly, a two dimensional FEM model was established, and was validated in terms of cutting forces and chip shape characteristics with experimental results of orthogonal machining. The plastic deformation on the machined surface was analyzed on the basis of finite element simulation. Results revealed that the plastic shear strain was much larger than the other strains in different directions. In addition, the variation of plastic shear strain and strain rate versus cutting time was obtained. When the feed rate was constant, the strain decreased and the maximum strain rate increased as cutting speed increased. Finally, the machined surface texture was simulated and analyzed using the Viscoplastic Self-consistent (VPSC) program based on the variation of plastic shear strain and strain rate, combined with polycrystalline plasticity theory. The machined surface texture evolution during machining was expressed by pole figures and orientation distribution function (ODF) diagrams. And the cylinder texture was identified from the pole figures. Four typical shear textures, including Y, C1, C2, and B fiber textures, were obtained from the ODF diagrams. Meanwhile, the orientation density of texture decreased with the increasing of cutting speed.

Sublimation of water ice mixed with silicates and tholins: Evolution of surface texture and reflectance spectra, with implications for comets

The surfaces of many objects in the Solar System comprise substantial quantities of water ice sometimes mixed with minerals and/or organic molecules. The sublimation of the ice changes the structural and optical properties of these objects. We present laboratory data on the evolution of the structure and the visible and near-infrared spectral reflectance of icy surface analogues of cometary ices, made of water ice, complex organic matter (tholins) and silicates, as they undergo sublimation under low temperature (<−70°C) and pressure (10−5mbar) conditions inside the SCITEAS simulation chamber. As the water ice sublimated, we observed in situ the formation of a porous sublimation lag deposit, or sublimation mantle, at the top of the ice. This mantle is a network of filaments made of the non-volatile particles. Organics or phyllosilicates grains, able to interact via stronger inter-particulate forces than olivine grains, can form a foam-like structure having internal cohesiveness, holding olivine grains together. As this mantle builds-up, the band depths of the sub-surface water ice are attenuated until complete extinction under only few millimeters of mantle. Optically thick sublimation mantles are mainly featureless in the near infrared. The absorption bands of the minerals present in the mantle are weak, or even totally absent if minerals are mixed with organics which largely dominate the VIS–NIR reflectance spectrum. During sublimation, ejections of large fragments of mantle, triggered by the gas flow, expose ice particles to the surface. The contrast of brightness between mantled and ice-exposed areas depends on the wavelength range and the dust/ice ratio considered. We describe how the chemical nature of the non-volatiles, the size of their particles, the way they are mixed with the ice and the dust/ice mass ratio influence the texture, activity and spectro-photometric properties of the sublimation mantles. These data provide useful references for interpreting remote-sensing observations of comets and also icy satellites or trans-neptunian objects.

Channel adjustments to a succession of water pulses in gravel bed rivers

AbstractGravel bed rivers commonly exhibit a coarse surface armor resulting from a complex history of interactions between flow and sediment supply. The evolution of the surface texture under single storm events or under steady flow conditions has been studied by a number of researchers. However, the role of successive floods on the surface texture evolution is still poorly understood. An experimental campaign in an 18 m‐long 1 m‐wide flume has been designed to study these issues. Eight consecutive runs, each one consisting of a low‐flow period of variable duration followed by a sudden flood (water pulse) lasting 1.5 h, have been conducted. The total duration of the experiment was 46 h. The initial bed surface was created during a 280 h‐long experiment focused on the influence of episodic sediment supply on channel adjustments. Our experiments represent a realistic armored and structured beds found in mountain gravel bed rivers. The armor surface texture persists over the duration of the experiment. The experiment exhibits downstream fining of the bed‐surface texture. It was found that sorting processes were affected by the duration of low‐flow between flood pulses. Since bed load transport is influenced by sediment sorting, the evolution of bed load transport is impacted by the frequency of the water pulses: short interpulse durations reduce the time over which fine material (transported as bed load) can be winnowed. This, in turn, contributes to declining reduction of the bed load transport over time while the sediment storage increases.

Size Effects on Strength in the Transition from Single-to-Polycrystalline Behavior

During the transition from single crystalline to polycrystalline behavior, the available data show the strength increasing or decreasing as the number of grains in a cross section is reduced. Tensile experiments were conducted on polycrystalline Ni with grain sizes (d) between 16 and 140 mu m and varying specimen thickness (t), covering a range of lambda (-t/d) between similar to 0.5 and 20. With a decrease in lambda, the data revealed a consistent trend of strength being independent of lambda at large lambda, an increase in strength, and then a decrease in strength. Microstructural studies revealed that lower constraints enabled easier rotation of the surface grains and texture evolution, independent of the specimen thickness. In specimen interiors, there was a greater ease of rotation in thinner samples. Measurements of misorientation deviations within grains revealed important differences in the specimen interiors. A simple model is developed taking into account the additional geometrically necessary dislocations due to variations in the behavior of surface and interior grains, leading to additional strengthening. A suitable combination of this strengthening and surface weakening can give rise to wide range of possibilities with a decrease in lambda, including weakening, strengthening, and strengthening and weakening.

Surface–texture evolution of different chemical-vapor-deposited zinc sulfide flats polished with various magnetorheological fluids

The macro-structure of chemical-vapor-deposited (CVD) zinc sulfide (ZnS) substrates is characterized by cone-like structures that start growing at the early stages of deposition. As deposition progresses, these cones grow larger and reach centimeter size in height and millimeter size in width. It is challenging to polish out these features from the top layer, particularly for the magnetorheological finishing (MRF) process. A conventional MR fluid tends to leave submillimeter surface artifacts on the finished surface, which is a direct result of the cone-like structure.Here we describe the MRF process of polishing four CVD ZnS substrates, manufactured by four different vendors, with conventional MR fluid at pH 10 and zirconia-coated-CI (carbonyl iron) MR fluids at pH 4, 5, and 6. We report on the surface–texture evolution of the substrates as they were MRF polished with the different fluids. We show that performances of the zirconia-coated-CI MR fluid at pH 4 are significantly higher than that of the same fluid at pH levels of 5 and 6 and moderately higher than that of a conventional MR fluid at pH 10. An improvement in surface–texture variability from part to part was also observed with the pH 4 MR fluid.

Effects of vitamin E blending on plastic deformation mechanisms of highly crosslinked ultrahigh molecular weight polyethylene (HXL-UHMWPE) in total hip arthroplasty

The molecular mobility and crystalline texture development in highly crosslinked ultrahigh molecular weight polyethylene (HXL-UHMWPE) blended with antioxidant vitamin E (VE, dl-α-tocopherol) were studied via uniaxial compression at room temperature by means of confocal/polarized Raman spectroscopy. The results were compared to morphological analyses under the same compression conditions performed on HXL-UHMWPE prepared in exactly the same way but blending VE into the polyethylene resin (VE-free HXL-UHMWPE). These comparative analyses allow us to evaluate the physical role of VE in morphological alterations of HXL-UHMWPE induced by compression deformation, which can greatly affect its micromechanical behavior. Molecular rearrangement and phase transitions in crystalline and non-crystalline phase, i.e. amorphous and intermediate (third) phase, were found to be part of a reconstruction process after plastic deformation in the samples. Although VE-blended HXL-UHMWPE exhibited more pronounced molecular mobility, as evidenced by its significant deformation-induced texturing, crystallinity change was totally inhibited by the presence of VE during deformation. On the other hand, amorphous-to-intermediate phase transition was confirmed. VE-free HXL-UHMWPE also presented significant crystallization after deformation, but its surface texture evolution occurred to a much lesser extent. This study suggests that the addition of VE induced earlier activation of compression deformation modes in crystalline and non-crystalline phases (e.g. chain slip, interlamellar shear and rotation) due to an increase in polyethylene chain mobility.

Mechanism of surface texture evolution in pure copper strips subjected to double rolling

Developing ultra-thin copper foils with different surface roughness and microstructure has important significance for improving the service performance and reducing the production cost of high-end circuit boards. In this paper, pure copper strips with initial cube texture were subjected to a double rolling process (deformation amount ranges from 50% to 95%), and the surface textures evolution law and mechanism of double-rolled strips were studied by an X-ray diffraction technique. The results show that when a deformation amount increased from 50% to 70%, the grains of two surfaces rotate away from the cube orientation, and the formed textures of two surfaces mainly consisted of C, S and B orientation components. The orientation density values for these three components on bright surface only had slight difference; the orientation density values for C and S components were much larger than that for B components on a matt surface. When the deformation amount increased to 90%, the increase extents of orientation density values for C and S components were obviously larger than that for B components on a bright surface; the increase extents of orientation density values for these three components were almost the same on the matt surface. It has been found that when deformation amount reaches 95%, the grains orientation of bright surface were relatively concentrated, and the orientation density value for C texture obviously increased to 11.68 and that for B texture was only 3.15; the grains orientation of matt surface were relatively dispersed, and the orientation density value for C texture increased to 9.26 and that for B texture obviously increased to 6.35, and the density values of these two textures had less difference. For the condition of strong compressive and shear stress on the bright surface, grains were mainly rotating to C texture orientation; compared with the bright surface, “semi-free” deformation condition on the matt surface is beneficial to promote much more grains to rotate to the B texture orientation.

The Innovative Application of Surface Texture in Fashion and Textile Design

This study focuses on 'texture' as one of the most important fashion and textile design elements; in addition, it proposes various applications of it. Surface texture is indispensable in fashion and textile design that also factors heavily into innovative creations. Along with technological advances in the fashion industry, surface texture has derived many new and attractive features that provide more opportunities for designers to show various design concepts. Rather than the surface quality of fabrics, surface texture in fashion design creates its identity through a manipulation of materials- an application that tends to be primarily for visual effects without being restricted to decorative purposes. The status and significance of surface texture in various creative fields is explored and the evolution of surface texture is traced by analyzing a number of fashion design cases with representative surface textures. The latest feature of surface texture in fashion and textile design is identified to establish a new classification of surface texture with five groups and technical suggestions. This study provides a theoretical basis for this field of study and a new framework that can be employed in the development of surface textures that use innovative techniques as well as the future application of newly-developed textures.

Simulation of Roughness and Surface Texture Evolution at Macroscopic Scale During Cylinder Honing Process

The honing process produces surface liners with specific functional properties. Engine performances and life expectancy are directly impacted by the quality of honed surface. The form quality, the roughness and the surface appearance manufactured by honing determine the friction of the piston in the liner. The process is however mechanically complex and the selection of the process parameters is currently based on empirical methods. The aim of this paper is thus to develop a macroscopic simulation environment which will help end-users during this setting-up stage. The development of this virtual tool is based on a space-time discretization and a macroscopic cutting model taking into account local contacts between the workpiece and the abrasive stones. The space-time discretization allows representing the machine environment including the tool, the workpiece and the machine kinematics. The cutting model allows converting kinematics and abrasive contacts in dynamic data and material removal rate by calculation. The cutting model is initially adjusted based on simple experiments. The stock removal equation is then extrapolated to the whole range of stone cutting conditions. This approximation allows simulating the real process and a whole honing cycle. Results are validated by comparison with industrial context experiments. The simulation of the whole honing cycle allows predicting the form quality, one of the roughness criteria and the surface appearance. Moreover, simulation results are represented by means of maps that allow looking at quality criteria for each point of the surface.