36Cl/Cl Accelerator-Mass-Spectrometry Standards: Verification of Their Serial-Dilution-Solution Preparations by Radioactivity Measurements

A consortium of accclerator-mass-spectrometry (AMS) laboratories recently prepared a series of ³⁶Cl/Cl isotopic ratio AMS standards by an eight-step serial gravimetric dilution scheme. Of the resulting nine solutions, only the latter six could be assayed by AMS to confirm the gravimetric dilution factors. This paper provides the results of relative radioactivity measurements on the first four solutions to verify the first three dilution factors. The fourth solution was the only dilution capable of being directly measured by both AMS and radionuclidic metrology of ³⁶Cl, and therefore its assay by radioactivity counting was deemed of considerable importance. Assays were performed by 4πβ⁻ liquid scintillation (LS) counting of gravimetric aliquots of the solutions, with confirmatory measurements by 2πβ⁻ gas-flow proportional counting of gravimetrically-prepared solid sources. The radioactivity measurements on the fourth solution were complex and difficult because of the conflicting combination of a low activity concentration (0.036 Bq · g⁻¹) and high salt content (146 mg NaCl per g of solution). These conditions necessitated independent studies of the ³⁶Cl LS efficiency as a function of NaCl loading in the LS cocktails and of the feasibility of LS counting of precipitated samples, both of which are also reported here. The results of the radioactivity measurements confirmed the dilution factors for the first three solutions to absolute differences of about 1%, and that for the fourth solution to about 1% to 2%. The overall uncertainties for these verification measurements, at a relative three standard deviation uncertainty interval, were of comparable magnitude, i.e., in the range of ±1% to ±2% for the first three solutions and roughly ±3% for the fourth solution.     

Standardization of 63Ni by 4πβ Liquid Scintillation Spectrometry With 3H-Standard Efficiency Tracing

The low energy (E_βmax = 66.945 keV ± 0.004 keV) β-emitter ⁶³Ni has become increasingly important in the field of radionuclidic metrology. In addition to having a low β-endpoint energy, the relatively long half-life (101.1 a ± 1.4 a) makes it an appealing standard for such applications. This paper describes the recent preparation and calibration of a new solution Standard Reference Material of ⁶³Ni, SRM 4226C, released by the National Institute of Standards and Technology. The massic activity C_A for these standards was determined using 4πβ liquid scintillation (LS) spectrometry with ³H-standard efficiency tracing using the CIEMAT/NIST method, and is certified as 50.53 kBq ·g⁻¹ ± 0.46 Bq · g⁻¹ at the reference time of 1200 EST August 15, 1995. The uncertainty given is the expanded (coverage factor k = 2 and thus a 2 standard deviation estimate) uncertainty based on the evaluation of 28 different uncertainty components. These components were evaluated on the basis of an exhaustive number (976) of LS counting measurements investigating over 15 variables. Through the study of these variables it was found that LS cocktail water mass fraction and ion concentration play important roles in cocktail stability and consistency of counting results. The results of all of these experiments are discussed.     

Can a Pressure Standard be Based on Capacitance Measurements?

We consider the feasibility of basing a pressure standard on measurements of the dielectric constant ϵ and the thermodynamic temperature T of helium near 0 °C. The pressure p of the helium would be calculated from fundamental constants, quantum mechanics, and statistical mechanics. At present, the relative standard uncertainty of the pressure u_r(p) would exceed 20 × 10⁻⁶, the relative uncertainty of the value of the molar polarizability of helium A_ϵ calculated ab initio. If the relativistic corrections to A_ϵ were calculated as accurately as the classical value is now known, a capacitance-based pressure standard might attain u_r(p) < 6 × 10⁻⁶ for pressures near 1 MPa, a result of considerable interest for pressure metrology. One obtains p by eliminating the density from the virial expansions for p and ϵ − 1. If ϵ − 1 were measured with a very stable, 0.5 pF toroidal cross capacitor, the small capacitance and the small values of ϵ − 1 would require state-of-the-art capacitance measurements to achieve a useful pressure standard.     

Electronic conduction in La-based perovskite-type oxides

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo_0.5Ni_0.5O_3±δ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo_0.5Ni_0.5O_3±δ exhibits a high conductivity of 1.9 × 10³ S cm⁻¹ at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 10²² cm⁻³ and a small effective mass m∗ of 0.10 m_e. Notably, LaCo_0.5Ni_0.5O_3±δ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo_0.5Ni_0.5O_3±δ is the most suitable for the fabrication of oxide electrodes and wiring, though La_1−xSr_xCoO_3±δ and La_1−xSr_xMnO_3±δ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 10³ S cm⁻¹ for La_0.5Sr_0.5CoO_3±δ and 1.5 × 10³ S cm⁻¹ for La_0.6Sr_0.4MnO_3±δ because oxygen release occurs in La_1−xSr_xCoO_3±δ as elevating temperature and the electrical conductivity of La_0.6Sr_0.4MnO_3±δ slightly decreases at temperatures above 400 K.     

Measurement of the Parity-Violating Neutron Spin Rotation in 4He

In the meson exchange model of weak nucleon-nucleon (NN) interactions, the exchange of virtual mesons between the nucleons is parameterized by a set of weak meson exchange amplitudes. The strengths of these amplitudes from theoretical calculations are not well known, and experimental measurements of parity-violating (PV) observables in different nuclear systems have not constrained their values. Transversely polarized cold neutrons traveling through liquid helium experience a PV spin rotation due to the weak interaction with an angle proportional to a linear combination of these weak meson exchange amplitudes. A measurement of the PV neutron spin rotation in helium (φ_PV (n,α)) would provide information about the relative strengths of the weak meson exchange amplitudes, and with the longitudinal analyzing power measurement in the p + α system, allow the first comparison between isospin mirror systems in weak NN interaction. An earlier experiment performed at NIST obtained a result consistent with zero: φ_PV (n,α) = (8.0 ±14(stat) ±2.2(syst)) ×10⁻⁷ rad / m[1]. We describe a modified apparatus using a superfluid helium target to increase statistics and reduce systematic effects in an effort to reach a sensitivity goal of 10⁻⁷ rad/m.     

Antibacterial,anti‐inflammatory and antioxidant effects of acetyl‐11‐α‐keto‐β‐boswellic acid mediated silver nanoparticles in experimental murine mastitis

Mastitis is an important economic disease causing production losses in dairy industry. Antibiotics are becoming ineffective in controlling mastitis due to the emergence of resistant strains requiring the development of novel therapeutic agents. In this study, the authors present the phytochemical synthesis of silver nanoparticles (AgNPs) with acetyl‐11‐α‐keto‐β‐boswellic acid and evaluation of their activity in Staphylococcus aureus induced murine mastitis. Boswellic acid mediated AgNP (BANS) were oval, polydispersed (99.8 nm) with an minimum inhibitory concentration of 0.033 µg ml⁻¹ against S. aureus, inhibitory concentration (IC₅₀) of 30.04 µg ml⁻¹ on mouse splenocytes and safe at an in vivo acute oral dose of 3.5 mg kg⁻¹ in mice. Mastitis was induced in lactating mice by inoculating S. aureus (log₁₀ 5.60 cfu) and treated 6 h post‐inoculation with BANS (0.12 mg kg⁻¹, intramammary and intraperitoneal), and cefepime (1 mg kg⁻¹, intraperitoneal). S. aureus inoculated mice showed increased bacterial load, neutrophil infiltration in mammary glands and elevated C‐reactive protein (CRP) in serum. Oxidative stress was also observed with elevated malondialdehyde level, superoxide dismutase (SOD) and catalase (CAT) activities. BANS treatment significantly (P  < 0.05) reduced bacterial load, CRP, SOD, CAT activities and neutrophil infiltration in affected mammary glands. BANS could be a potential therapeutic agent for managing bovine mastitis.Inspec keywords: nanomedicine, nanoparticles, silver, antibacterial activity, drugs, diseases, enzymesOther keywords: antibacterial effects, antiinflammatory effects, antioxidant effects, acetyl‐11‐α‐keto‐β‐boswellic acid, mediated silver nanoparticles, experimental murine mastitis, economic disease, dairy industry, resistant strains, phytochemical synthesis, Staphylococcus aureus, minimum inhibitory concentration, inoculating S. aureus, neutrophil infiltration, mammary glands, elevated C‐reactive protein, superoxide dismutase, catalase, bovine mastitis, Ag     

Experimental and Theoretical Study of Kinetics of Bulk Crystallization in Poly(Chlorotrifluoroethylene)

The rate of isothermal bulk crystallization of poly(chlorotrifluoroethylene), T_m=221° C, was measured from 170° to 200° C. The intrinsic bulk crystallization, which accurately followed an n = 2 law, was shown to be a result of the injection of primary nuclei sporadically in time, with one-dimensional growth of centers derived from these nuclei. The crystallites are exceedingly small. The one-dimensional growth process was isolated by nucleating specimens with seed crystals, and its temperature-dependence determined between 191° and 205° C. The seed crystal isotherms followed an n = 1 law. The temperature coefficients of the rate of nucleation and the rate of growth were both strongly negative.A theory of homogeneous nucleation that takes into account the segmental character of the polymer chains is developed in some detail. A cylindrical nucleus is assumed. In the temperature range near the melting point, region A, where the radius and length of the nucleus are unrestricted, the rate of nucleation is shown to be proportional to exp(−α/T³ΔT²). The nucleation rate is proportional to exp (−β/T²ΔT) in region B, which extends from somewhat below the melting point to considerably lower temperatures; the length of the nucleus has a constant value l₀ in this region, but the radius is unrestricted. (In the above expressions, α and β are constants). Finally, at sufficiently low temperatures, region C is entered. Under certain circumstances, the rate of nucleation in region C will be extremely rapid, and correspond to a “nucleative collapse” of the supercooled liquid state. A calculation of the one-dimensional growth rate shows that it is proportional to exp(−γ/T²ΔT) where β=γ.A careful analysis of the experimental data obtained between 170° and 200° C clearly showed that both the rate of nucleation and the rate of growth were proportional to exp(−β/T²ΔT), and not exp(−α/T³ΔT²). The primary nucleation event was thus of type B in this interval. A detailed analysis of the data is given, and surface free energies and the dimensions of the nuclei quoted. Quenching experiments, where the polymer was crystallized well below 170° C, gave a firm indication of the existence of region C.An experimental study was made of the extremely slow crystallization process that prevailed when the degree of crystallinity became high. The onset of this stage of the crystallization was interpreted as being the result of a massive degree of impingement. This interpretation is justified by the calculations of Lauritzen, who has given a theory of impingements that predicts a pseudoequilibrium degree of crystallinity.As indicated above, the growth process originating at homogeneous nuclei is not of a three-dimensional or spherulitic character in the region of study. Such stray spherulites as do appear in this region are shown to originate at heterogeneities. The possibility that the intrinsic growth process may become three-dimensional at crystallization temperatures sufficiently near T_m is discussed.     

A Double-Primary Dead-Weight Tester for Pressures (35–175) kPa in Gage Mode

Primary pressure standards in the atmospheric pressure range are often established using mercury manometers. Less frequently, controlled-clearance dead-weight testers in which one component (normally the piston) has been dimensionally measured have also been used. Recent advances in technology on two fronts i) the fabrication of large-diameter pistons and cylinders with good geometry; and ii) the ability to measure the dimensions of these components, have allowed some dead-weight testers at NIST to approach total relative uncertainties (k = 2) in dimensionally-derived effective areas near 5 × 10⁻⁶. This paper describes a single piston/cylinder assembly (NIST-PG201WC/WC) that serves as both a primary gage in which both piston and cylinder are measured dimensionally and a controlled-clearance primary gage (employing the Heydemann-Welch method). Thus it allows some previous assumptions about the modeling of dead-weight testers to be checked. For the gage described in this paper the piston/cylinder clearance obtained from the two analyses have relative differences of 4 × 10⁻⁶ to 7 × 10⁻⁶ over the pressure range 35 kPa to 175 kPa. Some implications of these results will be discussed. From the dimensional characterizations and auxiliary measurements we have determined that the effective area for this gauge at 20 °C is: A_eff,20 = 1961.0659mm²(1 + 3.75 × 10^?12P/Pa + 3.05 × 10^?12P_J/Pa), where P is the system pressure and P_J is a control pressure. The estimated relative uncertainty in effective area is 8.2 × 10⁻⁶ +1.4 × 10⁻¹¹ P/Pa (k = 2). The temperature coefficient for the area was measured and found to be (9.06 ± 0.04) × 10⁻⁶/K. Thus using the gage at a reference temperature of 23 °C yields an effective area: A_eff,23 = 1961.1192mm²(1 + 3.75 × 10^?12P/Pa + 3.05 × 10^?12P_J/Pa), with almost no increase in the uncertainty over that at 20 °C.     

Thermal-Conductivity Apparatus for Steady-State,Comparative Measurement of Ceramic Coatings

An apparatus has been developed to measure the thermal conductivity of ceramic coatings. Since the method uses an infrared microscope for temperature measurement, coatings as thin as 20 μm can, in principle, be measured using this technique. This steady-state, comparative measurement method uses the known thermal conductivity of the substrate material as the reference material for heat-flow measurement. The experimental method is validated by measuring a plasma-sprayed coating that has been previously measured using an absolute, steady-state measurement method. The new measurement method has a relative standard uncertainty of about 10 %. The measurement of the plasma-sprayed coating gives 0.58 W·m⁻¹·K^−l which compares well with the 0.62 W·m⁻¹·K^−l measured using the absolute method.     

Interlaboratory Comparison of Magnetic Thin Film Measurements

A potential low magnetic moment standard reference material (SRM) was studied in an interlaboratory comparison. The mean and the standard deviation of the saturation moment m_s, the remanent moment m_r, and the intrinsic coercivity H_c of nine samples were extracted from hysteresis-loop measurements. Samples were measured by thirteen laboratories using inductive-field loopers, vibrating-sample magnetometers, alternating-gradient force magnetometers, and superconducting quantum-interference-device magnetometers. NiFe films on Si substrates had saturation moment measurements reproduced within 5 % variation among the laboratories. The results show that a good candidate for an SRM must have a highly square hysteresis loop (m_r/m_s > 90 %), H_c ≈ 400 A·m⁻¹ (5 Oe), and m_s ≈ 2 × 10⁻⁷ A·m² (2 × 10⁻⁴ emu).     

Measurement of the Neutron Lifetime by Counting Trapped Protons

We measured the neutron decay lifetime by counting in-beam neutron decay recoil protons trapped in a quasi-Penning trap. The absolute neutron beam fluence was measured by capture in a thin ⁶LiF foil detector with known efficiency. The combination of these measurements gives the neutron lifetime: τ_n = (886.8 ± 1.2 ± 3.2) s, where the first (second) uncertainty is statistical (systematic) in nature. This is the most precise neutron lifetime determination to date using an in-beam method.     

Self-Broadening of Carbon Monoxide in the 2 v and 3 v Bands

The self-broadening of carbon monoxide has been measured for the 2 v and 3 v bands with pressures up to 3.5 atmospheres. A grating spectrometer of high resolving power was used for the measurements and the correction for finite slits was small. The corrections varied from 3 to 20 percent for the different conditions of measurement. The half-widths per atmosphere, γ°, decreased from 0.089 cm⁻¹ for |m| = 1 to 0.053 cm⁻¹ for |m| = 21. The half-widths are compared with those obtained by other investigators and it is shown that the results reported in this work fall in between the self-broadening values previously obtained.     

Measurement of Parity Violation in np Capture: the NPDGamma Experiment

The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry A_γ in the reaction n→+p→d+γ. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, providing a theoretically clean determination of the weak pion-nucleon coupling. A new beam-line at the Los Alamos Neutron Science Center (LANSCE) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized ³He spin filter and captured in a liquid para-hydrogen target. The 2.2 MeV gamma rays from the capture reaction are detected in an array of CsI(Tl) scintillators read out by vacuum photodiodes operated in current mode. We will complete commissioning of the apparatus and carry out a first measurement at LANSCE in 2004–05, which would provide a statistics-limited result for A_γ accurate to a standard uncertainty of ±5 × 10⁻⁸ level or better, improving on existing measurements in the neutron-proton system by a factor of 4. Plans to move the experiment to a reactor facility, where the greater flux would enable us to make a measurement with a standard uncertainty of ±1 × 10⁻⁸, are actively being pursued for the longer term.     

Compressibility of Natural Rubber at Pressures Below 500 kg/cm2

The specific volumes of unvulcanized natural rubber and of a peroxide-cured vulcanizate of natural rubber were measured at pressures of 1–500 kg/cm² at temperatures from 0 to 25 °C. Observations on mercury-filled dilatometers were made through a window in the pressure system. No time effects or hysteresis phenomena were observed. The specific volume V in cm³/e over the range studied can be represented by V = V_0,25{1 + A(t ? 25)}{1 + [α₂₅ + k₁(t ? 25)]P + [β₂₅ + k₂(t ? 25)]P²}where P is the pressure in kg/cm², and t the temperature in °C. The constants for the unvulcanized and for the peroxide-cured samples are:

• V₀,₂₅= 1.0951 and 1.1032 cm³/g;
• 10⁴A = 6.54 and 6.36 per degree;
• 10⁶α₂₅= −50.5 and −50.4 (kg/cm²)⁻¹;
• 10⁶k₁ = −0.227 and −0.203 per degree;
• 10⁹β₂₅= 10 and 11.5 (kg/cm²)⁻²;
• and 10⁹k₂=0.048 and 0.073 per degree, respectively. The compressibility of unvulcanized natural rubber at 25° and 1 kg/cm² is thus 50.5×10⁻⁶ (kg/cm²)⁻¹ falling to 40.6×10⁻⁶ (kg/cm²) ⁻¹ at a pressure of 500 kg/cm². It is concluded that a low degree of vulcanization produces no significant changes in the constants listed. The values are not far different from those obtained by extrapolating to zero sulfur content the observations of Scott on the rubbersulfur system. Calculations of values of compressibility (and its reciprocal the bulk modulus), “internal pressure”, bulk wave velocity, difference between specific heats, and several other physical properties are in reasonable agreement with those obtained by direct observation by other workers. For the prediction of values at pressures above 500 kg/cm² the use of the Tait equation is recommended.

     

Light Scattering by Commercial Sugar Solutions

Using a direct measure of scattered light, it was found that commercial sugar solutions scatter light predominantly in a forward direction. The scattering at angles less than 30° was as much as one hundred times that at right angles to the incident beam.It was found that the light scattering by commercial sugar solutions is inversely dependent on wavelength to a power of between 2 and 3, and that severe multiple scattering occurs when the turbidity of the solution is larger than 2×10⁻¹cm⁻¹ at 436 mµ. The scattering of commercial sugar solutions is compared with that of highly purified sucrose.A method is discussed that will enable a good approximation of the turbidity of commercial sugar solutions to be made from a single forward scattering measurement at an angle of about 20° with respect to the incident light beam. A correction for scattered light in transmission measurements of these solutions is also introduced.     

Commissioning of the NPDGamma Detector Array: Counting Statistics in Current Mode Operation and Parity Violation in the Capture of Cold Neutrons on B4C and 27Al

The NPDGamma γ-ray detector has been built to measure, with high accuracy, the size of the small parity-violating asymmetry in the angular distribution of gamma rays from the capture of polarized cold neutrons by protons. The high cold neutron flux at the Los Alamos Neutron Scattering Center (LANSCE) spallation neutron source and control of systematic errors require the use of current mode detection with vacuum photodiodes and low-noise solid-state preamplifiers. We show that the detector array operates at counting statistics and that the asymmetries due to B₄C and ²⁷Al are zero to with- in 2 × 10⁻⁶ and 7 × 10⁻⁷, respectively. Boron and aluminum are used throughout the experiment. The results presented here are preliminary.     

Measurement of the Neutron Lifetime Using a Gravitational Trap and a Low-Temperature Fomblin Coating

We present a new value for the neutron lifetime of 878.5 ± 0.7_stat. ± 0.3_syst. This result differs from the world average value by 6.5 standard deviations and by 5.6 standard deviations from the previous most precise result. However, this new value for the neutron lifetime together with a β-asymmetry in neutron decay, A₀, of −0.1189(7) is in a good agreement with the Standard Model.     

Surface force spectroscopic point load measurements and viscoelastic modelling of the micromechanical properties of air flow sensitive hairs of a spider (Cupiennius salei)

The micromechanical properties of spider air flow hair sensilla (trichobothria) were characterized with nanometre resolution using surface force spectroscopy (SFS) under conditions of different constant deflection angular velocities (rad s⁻¹) for hairs 900–950 μm long prior to shortening for measurement purposes. In the range of angular velocities examined (4×10⁻⁴−2.6×10⁻¹ rad s⁻¹), the torque T (Nm) resisting hair motion and its time rate of change (Nm s⁻¹) were found to vary with deflection velocity according to power functions. In this range of angular velocities, the motion of the hair is most accurately captured by a three-parameter solid model, which numerically describes the properties of the hair suspension. A fit of the three-parameter model (3p) to the experimental data yielded the two torsional restoring parameters, S _3p=2.91×10⁻¹¹ Nm rad⁻¹ and =2.77×10⁻¹¹ Nm rad⁻¹ and the damping parameter R _3p=1.46×10⁻¹² Nm s rad⁻¹. For angular velocities larger than 0.05 rad s⁻¹, which are common under natural conditions, a more accurate angular momentum equation was found to be given by a two-parameter Kelvin solid model. For this case, the multiple regression fit yielded S _2p=4.89×10⁻¹¹ Nm rad⁻¹ and R _2p=2.83×10⁻¹⁴ Nm s rad⁻¹ for the model parameters. While the two-parameter model has been used extensively in earlier work primarily at high hair angular velocities, to correctly capture the motion of the hair at both low and high angular velocities it is necessary to employ the three-parameter model. It is suggested that the viscoelastic mechanical properties of the hair suspension work to promote the phasic response behaviour of the sensilla.     

Acid Dissociation Constant and Related Thermodynamic Quantities for Triethanolammonium Ion in Water From 0 to 50°C

Earlier studies of the dissociation constants of monoethanolammonium and diethanolammonium ions and the thermodynamic constants for the dissociation processes have been supplemented by a similar study of triethanolammonium ion from 0° to 50° C. The dissociation constant (K_bh) is given by the formula ?log K_bh = 1341.16/T + 4.6252 ? 0.0045666Twhere T is in degrees Kelvin. The order of acidic strengths of the ions is as follows: Triethanolammonium >diethanolammonium>monethanolammonium. Conversely, monoethanolamine is the strongest of the three bases. The thermodynamic constants for the dissociation of one mole of triethanolammonium ion in the standard state at 25° C are as follows: Heat content change (ΔH°) 33.450 joule mole⁻¹; entropy change (ΔS°), −36.4 joule deg⁻¹ mole⁻¹; heat-capacity change (ΔCp°), 52 joule deg⁻¹ mole⁻¹.     

Standardization of 68Ge/68Ga Using Three Liquid Scintillation Counting Based Methods

A solution containing ⁶⁸Ge in equilibrium with its daughter, ⁶⁸Ga, has been standardized for the first time at the National Institute of Standards and Technology (NIST) using 3 liquid scintillation-based techniques: live-timed 4πβ -γ anticoincidence (LTAC) counting, the Triple-to-Double Coincidence Ratio (TDCR) method, and ³H-standard efficiency tracing with the CIEMAT¹/NIST (CNET) method. The LTAC technique is much less dependent on level scheme data and model-dependent parameters and was thus able to provide a reference activity concentration value for the master solution with a combined standard uncertainty of about 0.3 %. The other two methods gave activity concentration values with respective differences from the reference value of +1.2 % and −1.5 %, which were still within the experimental uncertainties. Measurements made on the NIST “4π”γ secondary standard ionization chamber allowed for the determination of calibration factors for that instrument, allowing future calibrations to be made for ⁶⁸Ge/⁶⁸Ga without the need for a primary measurement. The ability to produce standardized solutions of ⁶⁸Ge presents opportunities for the development of a number of NIST-traceable calibration sources with very low (<1 %) relative standard uncertainties that can be used in diagnostic medical imaging.