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Showing papers on "Tungsten published in 2010"


Journal ArticleDOI
TL;DR: Shaped metal deposition (SMD) is a relatively new technology of additive manufacturing, which creates near-net shaped components by additive manufacture utilizing tungsten inert gas welding as mentioned in this paper, which has great advantages.

501 citations



Journal ArticleDOI
TL;DR: In this article, the tensile and compressive behavior of -oriented body-centered cubic (bcc) metals W, Mo, Ta and Nb with nanometer dimensions was investigated.

309 citations



Journal ArticleDOI
TL;DR: In this article, the authors report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and Henhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls.
Abstract: Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations.

226 citations


Journal ArticleDOI
TL;DR: Mesoporous tungsten carbides displayed an excellent solar conversion efficiency as a counter electrode for dye sensitized solar cells under 100 mW cm(-2), AM 1.5G illumination, which corresponded to ca.

215 citations


Journal ArticleDOI
TL;DR: It is shown that alloying induces a transition from a symmetric to an asymmetric core and a reduction in Peierls stress and this combination ductilizes the alloy as the number of available slip planes is increased and the critical stress needed to start plastic deformation is lowered.
Abstract: Despite exhibiting the highest melting point of all metals, the technological use of tungsten is hampered by its room-temperature brittleness. Alloying with Re significantly ductilizes the material which has been assigned to modified properties of the 1/2(111) screw dislocation. Using density functional theory, we show that alloying induces a transition from a symmetric to an asymmetric core and a reduction in Peierls stress. This combination ductilizes the alloy as the number of available slip planes is increased and the critical stress needed to start plastic deformation is lowered.

213 citations


Journal ArticleDOI
TL;DR: In this article, the binding and trapping properties of hydrogen to point defects in tungsten were investigated and it was concluded that the monovacancy can hold up to five hydrogen atoms at room temperature.
Abstract: First-principles calculations were used in determining the binding and trapping properties of hydrogen to point defects in tungsten. Hydrogen zero-point vibrations were taken into account. It was concluded that the monovacancy can hold up to five hydrogen atoms at room temperature. The hydrogen was found to distort the self-interstitial atom configuration geometry. The interaction of hydrogen with the transmutation reaction impurities Re and Os were studied. It was found that the substitutional Re and Os have a negligible effect on the hydrogen trapping whereas the interstitial Os may increase the hydrogen inventory in tungsten.

207 citations


Journal ArticleDOI
TL;DR: In this paper, femtosecond laser ablation studies of the metals copper, silver and tungsten are presented. But they do not consider the effect of heat diffusion.
Abstract: In this paper we present femtosecond laser ablation studies of the metals copper, silver and tungsten. Measurements of the threshold fluence determined from the hole diameters versus fluence provide incubation coefficients of the three materials, which are found to be equal within one standard deviation. Furthermore, we have determined the single-shot threshold fluences to be 1.7±0.3 J/cm2, 1.5±0.4 J/cm2 and 0.44±0.02 J/cm2 for copper, silver and tungsten, respectively. These are in good agreement with theoretical values calculated neglecting heat diffusion.

196 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of tungsten precursor (silicotungstic (HSiW), phosphotungsts (HPW), and tungstic acids (HW) acids on the activity of partially reduced Ni-W/AC catalysts in phenol hydrodeoxygenation (HDO) was investigated.
Abstract: The aim of this study was to detect any synergistic effect between nickel and tungsten oxide species supported on activated carbon as well as to study the effect of tungsten precursor (silicotungstic (HSiW), phosphotungstic (HPW), and tungstic (HW) acids) on the activity of partially reduced Ni–W/AC catalysts in phenol hydrodeoxygenation (HDO). The catalytic tests were performed in a flow fixed-bed reactor set-up at a hydrogen pressure of 1.5 MPa, temperatures ranging from 423 to 573 K and weight hourly space velocities of 0.5 g phenol /(g catalyst h). Before reaction, the catalysts were heat treated in H 2 flow at soft conditions ( T = 673 K for 4 h). The XPS analysis of spent catalysts revealed that this pre-treatment led to W(VI) species and a mixture of metallic and NiO species. Moreover, XPS and HRTEM analyses of the spent catalysts indicated that the nickel incorporation into W/AC catalysts led to a substantial improvement in surface exposure of the metal oxide species. All catalysts were active in the HDO of phenol and the most active catalysts were those prepared from heteropolyacids (HPAs). Regardless of the tungsten precursor, after Ni incorporation to the base W/AC system, a large enhancement in catalyst performance was observed. Moreover, supporting Ni and W phases on AC induced some beneficial effect because of the lower coke formation on the surface of AC with respect to classical alumina support. Regardless of the reaction temperature, analysis of the products suggests that reaction occurs via two direction pathways: (I) a hydrogenation (HYD) of phenol's aromatics ring (main reaction route) leading to formation of cylohexane, cyclohexene, cyclohexanol and methylcyclopentane and (II) a direct cleavage of the C–O σ bond leading to benzene formation. Total elimination of the O-containing compounds was archived in the HDO reaction at 573 K over oxide Ni–W(P)/AC and Ni–W(Si)/AC catalysts.

179 citations


Journal ArticleDOI
TL;DR: In this paper, first principle calculations were used to study the hydrogen migration properties in bulk bcc tungsten and the hydrogen diffusion coefficient was evaluated using the harmonic transition state theory and was found to agree with the experimental results at temperatures above 1500 K.
Abstract: First principle calculations were used to study the hydrogen migration properties in bulk bcc tungsten. Hydrogen has low solubility in tungsten and occupies the tetrahedral interstitial site with an energy difference of 0.38 eV compared to the octahedral interstitial site. The hydrogen diffusion coefficient was evaluated using the harmonic transition state theory and was found to agree with the experimental results at temperatures above 1500 K. The height of the migration barrier between two adjacent tetrahedral sites was found to be 0.21 eV, which is lower than the value 0.39 eV obtained for the migration barrier from degassing measurements in the temperature range between 1100 and 2400 K. The tunneling correction to the diffusion rate provides much better agreement with the experimental result at 29 K than the extrapolated experimental D from high temperature measurements.

Journal ArticleDOI
TL;DR: In this article, a spin-coated tungsten oxide nanostructured thin film was used for the fabrication of gas sensors and dye-sensitized solar cells, and it was shown that these materials can be rendered into anhydrous or partially or fully hydrated Tungsten oxides.
Abstract: Among the available metal oxide nanostructures, tungsten oxide has remained, at times, troublesome to fabricate, with many synthetic methods often requiring exotic equipment and or reagents. In this work, we present a systematic investigation demonstrating a new method for the deposition of anhydrous and hydrated nanostructured tungsten oxide thin films via spin coating. The attributes of these materials include the following: high surface area, controllable deposition, and compatibility with existing semiconductor fabrication infrastructure making this method a suitable candidate for application in the manufacture of gas sensors and dye sensitized solar cells. We will show that it is possible to form micrometer thick highly crystalline nanostructured thin films and, using Raman, SEM, XRD, XPS, and TEM analysis, will prove that these nanostructures can be rendered into anhydrous or partially or fully hydrated tungsten oxides. We further demonstrate the application of these materials in the fabrication of ...

Journal ArticleDOI
TL;DR: In this article, the effect of microstructure on fracture toughness of tungsten and rhenium alloys was investigated by means of 3-point bending, double cantilever beam and compact tension specimens.
Abstract: Tungsten and tungsten alloys show the typical change in fracture behavior from brittle at low temperatures to ductile at high temperatures. In order to improve the understanding of the effect of microstructure the fracture toughness of pure tungsten, potassium doped tungsten, tungsten with 1 wt.% La 2 O 3 and tungsten rhenium alloys were investigated by means of 3-point bending, double cantilever beam and compact tension specimens. All these materials show the expected increase in fracture toughness with increasing temperature. The experiments demonstrate that grain size, texture, chemical composition, grain boundary segregation and dislocation density seem to have a large effect on fracture toughness below the DBTT. These influences can be seen in the fracture behavior and morphology, where two kinds of fracture occur: on the one hand transgranular and on the other hand intergranular fracture. Therefore, techniques like electron backscatter diffraction (EBSD), Auger electron spectroscopy (AES) and X-ray line profile analysis were used to improve the understanding of the parameters influencing fracture toughness.

Journal ArticleDOI
TL;DR: Efficient visible light-induced photoelectrochemical oxidation of water was achieved using a tungsten(iv) oxide (WO(3)) film composed of perpendicularly oriented plate-like crystallites, a flake-wall film, prepared on a transparent conductive substrate by controlling anisotropic crystal growth of tundsten oxide hydrate (WW(3).H(2)O) followed by calcination.

Journal ArticleDOI
TL;DR: An optimized solar multilayer coating based on W-Al 2 O 3 graded cermet layer was fabricated in our laboratories by magnetron sputtering technique as mentioned in this paper, which has very high structural, physical and chemical stability at high temperature (580°C) under vacuum, maintaining good performances in terms of high solar absorption and low thermal emissivity.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the strain rate dependence of the brittle-to-ductile transition (BDT) temperature in notched and un-notched miniature bars made of high-purity polycrystalline tungsten and in less-pure sintered material.
Abstract: The strain rate dependence of the brittle-to-ductile transition (BDT) temperature was investigated in notched and un-notched miniature bars made of high-purity polycrystalline tungsten and in notched bars of less-pure sintered material. The activation energy, E BDT, for the process controlling the BDT in pure tungsten was equal to 1.0 eV both in un-notched and notched specimens, though the brittle–ductile transition temperature, T BDT, was ≈ 40 K lower at each strain rate for the un-notched samples, indicating that the activation energy, E BDT, is a materials parameter, independent of geometrical factors. The experimental data obtained from pure tungsten are described well by a two-dimensional dislocation-dynamics model of crack-tip plasticity, which is also discussed. For sintered tungsten, E BDT was found to be 1.45 eV; T BDT at a given strain rate was higher than in the pure tungsten by ≈ 90 K, suggesting that the BDT in tungsten is very sensitive to impurity levels.

Journal ArticleDOI
TL;DR: In this article, a 3D-ordered macroporous (3DOM) tungsten(VI) oxide (WO3) was prepared using a colloidal crystal template method.
Abstract: Three-dimensionally ordered macroporous (3DOM) tungsten(VI) oxide (WO3) was prepared using a colloidal crystal template method. Well-ordered 3DOM WO3 was prepared with a high pore fraction using ammonium metatungstate ((NH4)6H2W12O40), a Keggin-type dodecatungstate, as a tungsten precursor; WO3 materials prepared by other commercially available W precursors, tungsten chloride (WCl6), tungsten(V) ethoxide (W(OEt)5), and phosphotungstic acid (H3PW12O40), have a low 3DOM pore fraction. These WO3 materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), powder X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis of nitrogen adsorption isotherm, and Raman spectroscopy. Non-porous WO3 prepared from ammonium metatungstate without a poly(methyl metacrylate) (PMMA) template grew to crystal sizes of up to several micrometres with a low specific surface area (ca. 1–2 m2 g−1). In the presence of a colloidal crystal template of PMMA spheres, WO3 crystal grew in the nanometre-sized voids between the PMMA spheres, and the specific surface area thus increased up to ca. 30 times compared to non-porous WO3. The surface area is tunable by changing the PMMA sphere diameter. Calcination of the 3DOM WO3 produced WO3 nano-crystalline particles by sintering-induced disassembly. After Pt-loading, these WO3 materials showed higher photocatalytic activity compared to non-porous WO3 for decomposition of acetic acid in air under visible light irradiation.

Journal ArticleDOI
TL;DR: In this paper, thin films of BiVO 4 with monoclinic structure were deposited onto indium-doped tin oxide (ITO)-coated glass substrates by ultrasonic spray pyrolysis.

Journal ArticleDOI
TL;DR: An overview of the use of tungsten-containing materials in fuel cells is presented in this paper, where the authors describe the requirements for their use as thermally stable carbon-alternative catalyst supports and Nafion ® -alternative proton conducting electrolytes.
Abstract: Tungsten-based materials can play different roles in fuel cell systems. They are the only compounds which can be used as catalysts, co-catalysts, catalyst supports and electrolytes in different types of fuels cells. In particular, tungsten-based materials fulfill the requirements for their use as thermally stable carbon-alternative catalyst supports and Nafion ® -alternative proton conducting electrolytes in fuel cells operating at intermediate temperature. In this work an overview of the use of tungsten-containing materials in fuel cells is presented.

Journal ArticleDOI
TL;DR: Calculations on the enthalpy-pressure relationship and convex hulls have demonstrated that at zero pressure, the experimentally observed W(2)B-W(2), WB-WB, and assumed WB(2)-ReB( 2) phases are stable against decomposition into other components, suggesting that it is a potentially hard compound.
Abstract: The phase stability and mechanical properties of tungsten borides W2B, WB, WB2, W2B5 and WB4 were extensively studied by first-principles calculations within density functional theory. The thermodynamic and mechanical stabilities were examined. Our calculations on the enthalpy–pressure relationship and convex hulls have demonstrated that at zero pressure, the experimentally observed W2B–W2B (W2B–W2B represents W2B in W2B structure type, the same hereinafter) and WB–WB, and assumed WB2–ReB2 phases are stable against decomposition into other components. The estimated hardness of WB2–ReB2 is 39.4 GPa, suggesting that it is a potentially hard compound. At 60 GPa, the most stable phases are WB–WB and WB2–WB2. WB–WB, WB2–AlB2 and WB4 are the ground state phases at 100 GPa. The phase transition mechanism for WB2 was discussed. The synthesis of WB2–AlB2 could be conducted at high pressures.

Journal ArticleDOI
TL;DR: Migas et al. as discussed by the authors showed that all Magneli phases of tungsten oxides W Ox (namely, W32O84, W3O8, W18O49, W17O47, W5O14, W20O58, and W25O73) are characterized by metal-like properties.
Abstract: In the first part [D. B. Migas et al., J. Appl. Phys. 108, 093713 (2010)] electronic and optical properties of different phases of WO3 have been considered. In this part we present results of our ab initio calculations which clearly show that all Magneli phases of tungsten oxides WOx (namely, W32O84, W3O8, W18O49, W17O47, W5O14, W20O58, and W25O73) are characterized by metal-like properties. Their band structures display an energy gap in the valence band just below the Fermi level. We discuss how addition (removal) of oxygen atoms to (from) the unit cell of W18O49 affects the position of the Fermi level with respect to the energy gap and the charge carrier concentration. A possible mechanism has been suggested in order to switch from metallic to semiconducting properties for W18O49 and to explain experimental observations.

Journal ArticleDOI
TL;DR: In this article, a gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode, and a viscosity approximation was used to express the diffusion coefficient.
Abstract: A gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode. The whole region of GTA atmosphere including the tungsten cathode, the arc plasma and the anode was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of the shielding gas and metal vapour. The transient two-dimensional distributions of temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the molten pool as a function of time for a 150 A arc current at atmospheric pressure, both for helium and argon gases. It was shown that the thermal plasma in the GTA was influenced by iron vapour from the molten pool surface and that the concentration of iron vapour in the plasma was dependent on the temperature of the molten pool.GTA on high sulfur stainless steel was calculated to discuss the differences between a low sulfur and a high sulfur stainless steel anode. Helium was selected as the shielding gas because a helium GTA produces more metal vapour than an argon GTA. In the GTA on a high sulfur stainless steel anode, iron vapour and current path were constricted. Radiative emission density in the GTA on high sulfur stainless steel was also concentrated in the centre area of the arc plasma together with the iron vapour although the temperature distributions were almost the same as that in the case of a low sulfur stainless steel anode.

Journal ArticleDOI
TL;DR: In this article, the configuration of multiple hydrogen atoms trapped in a tungsten monovacancy was investigated using first-principles calculations, and it was found that the stable sites shift toward tetrahedral interstitial sites as the number of hydrogen atoms increases.
Abstract: The configuration of multiple hydrogen atoms trapped in a tungsten monovacancy is investigated using first-principles calculations. Unlike previous computational studies, which have reported that hydrogen in bcc metal monovacancies occupies octahedral interstitial sites, it is found that the stable sites shift toward tetrahedral interstitial sites as the number of hydrogen atoms increases. As a result, a maximum of twelve hydrogen atoms can become trapped in a tungsten monovacancy.

Journal ArticleDOI
TL;DR: In this paper, the effect of crystal structure on the gas sensitivity of tungsten oxides was studied, and both hexagonal and monoclinic WO 3 samples were tested as gas sensors to CH 4, CO, H 2, NO and H 2 S (1000 and 10ppm) at 200 and 600°C, respectively.

Journal ArticleDOI
Jialei Zhang1, X.L. Wang1, Xin Xia1, Changdong Gu1, Z.J. Zhao1, J.P. Tu1 
TL;DR: In this article, a self-organized macroporous tungsten trioxide (WO3) films are obtained by anodic oxidation of DC-sputtered Tungsten (W) layers on 10mm × 25mm indium tin oxide (ITO)-coated glass.

Journal ArticleDOI
TL;DR: In this paper, a facile route to control the morphology of tungsten oxide hierarchical hollow structures was demonstrated, with no need for catalysts, surfactants, or templates.
Abstract: A facile route to control the morphology of tungsten oxide hierarchical hollow structures was demonstrated. The morphology of the tungsten oxide nanostructures could be tuned from size-controlled hollow urchins to nanowires by adjusting the concentration of the tungsten precursor, with no need for catalysts, surfactants, or templates. The tungsten oxide nanostructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The as-prepared tungsten oxide hierarchical hollow nanostructures showed a very high specific surface area and demonstrated an excellent ability to remove organic pollutants. The adsorption capability of our tungsten oxide hierarchical hollow nanostructure was much higher than those of previously reported transition metal oxide nanostructures including Mn3O4, Fe2O3, and MnO2 as well as other alternative adsorbents such as MCM-22, fly ash, and red mud. This study provides a simple strategy for template/surfactant-free synthesis of hierarchical hollow nanostructures. Also, the as-prepared products are expected to be new promising materials for environmental remediation.

Journal ArticleDOI
TL;DR: In this article, the development of the PM processing steps and tools used by William D. Coolidge in 1909 marks the breakthrough for the usage of tungsten filaments in the lighting industry and the beginning of the industrial era of modern powder Metallurgy.
Abstract: From a historical point of view, the development of the PM processing steps and tools “for making tungsten ductile” by William D. Coolidge in 1909 marks the breakthrough for the usage of tungsten filaments in the lighting industry and the beginning of the industrial era of modern Powder Metallurgy. Some important technological developments before introducing the Coolidge process will be described briefly (Just and Hanaman procedures, Kuzel process, Pintsch method) together with the corresponding implications for today's modern technologies and materials (Sol-Gel, CVD, MIM, ODS alloys, W-RE welding electrodes). With regard to the Coolidge process some always recurring misunderstandings, especially of the doping process, will be corrected. In addition, some accompanying discoveries and inventions (Tungsten Heavy Metals, Gradient Materials, Cemented Carbides) will be mentioned too. Finally, the scientific importance of the potassium bubbles as the strongest pinning points at highest temperatures against the movement of dislocations and grain boundaries will be highlighted shortly. Considering geometrical dimensions, the microstructural features of the finest wires and the corresponding fabrication of diamond dies, necessary for the deformation of wires, also represent precursors of today's nanotechnology and micromachining.

Journal ArticleDOI
TL;DR: In this article, WO3 nanoparticles in the 5−30 nm range have been prepared by solvothermal treatment of tungsten chloride in benzyl alcohol up to 210 °C followed by annealing in air.
Abstract: WO3 nanoparticles in the 5−30 nm range have been prepared by solvothermal treatment of tungsten chloride in benzyl alcohol up to 210 °C followed by annealing in air. The solvothermal treatment has been performed by resistive or microwave heating and leads to agglomerates of tungsten oxide nanoparticles covered by organic residues. As determined by thermogravimetric measurements in air, the organic residues have been removed at 350 °C for samples prepared by microwave heating and at least at 420 °C for those prepared by resistive heating. When resistive heating is used, the specific surfaces are in the 20−90 m2/g range corresponding to particles of 10−30 nm, but smaller sizes, 140 m2/g of specific surface and 6 nm in diameter, can been obtained by fast microwave heating.

Journal ArticleDOI
17 Aug 2010-Sensors
TL;DR: This work fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and E-beam evaporation technique, and is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E- beam method.
Abstract: In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method.

Journal ArticleDOI
TL;DR: In this article, the fracture behavior of several tungsten-based alloys was characterized by standard Charpy tests which have been performed up to 1100°C in vacuum, and the influence of the microstructure characteristics like grain size, anisotropy, texture, or chemical composition as well as the effect of notch machining was investigated.
Abstract: Refractory materials, in particular tungsten base materials are considered as primary candidates for high heat load applications in future nuclear fusion power plants. Promising design outlines make use of the high heat conductivity and strength of W-1%La2O3 (WL10) as structural material. Here, the lower temperature range is restricted by the transition to a steel part and the upper operation temperature limit is defined by the onset of recrystallization and/or loss of strength, respectively. The most critical issue of tungsten materials in connection with structural applications, however, is the ductile-to-brittle transition. Another problem consists in the fact that especially refractory alloys show a strong correlation between microstructure and their manufacturing history. Since mechanical properties are defined by the underlying microstructure, refractory alloys can behave quite different, even if their chemical composition is the same. Therefore, the fracture behavior of several tungsten based alloys was characterized by standard Charpy tests which have been performed up to 1100 °C in vacuum. Due to their fabrication history (powder mixing, pressing, sintering, rolling or swaging) all materials had specific microstructures which often led to typical delamination fractures. The influence of the microstructure characteristics like grain size, anisotropy, texture, or chemical composition as well as the effect of notch machining was investigated. All results are discussed and assessed with respect to the optimization of future component fabrication for high temperature nuclear fusion applications.