Cold Flow Research Articles

Improving CONUS Convective‐Scale Forecasting With Simultaneous Multiscale Data Assimilation

AbstractAccurate initialization of CONUS convective‐scale forecasting requires a proper estimate of all resolved scales. This study further develops and examines a simultaneous multiscale data assimilation (MDA) approach in EnVar with modulated cross‐scale and cross‐variable covariances. The method is examined using 10 retrospective cases with the assimilation of both in situ and radar reflectivity observations (hereafter, SimMDA). The necessity of the modulated and therefore weakened cross‐covariances in simultaneous MDA for CONUS convective‐scale forecasting is first demonstrated. The relative benefits of increasing the decomposed‐scale number with increased computational cost in SimMDA are also discussed. The impact of the further developed simultaneous MDA method is revealed by comparing it with a commonly adopted DA approach (Baseline), which separately assimilates in situ and reflectivity observations using individual single‐scale localization. During DA cycling, SimMDA improves analysis accuracy for temperature and reflectivity and reduces biases in all variables compared to Baseline. SimMDA yields significantly better forecasts than Baseline for most lead times. Additional experiments are conducted to attribute such improvements in a case study. Specifically, an experiment the same as Baseline except using simultaneous MDA for reflectivity assimilation enhances cold pools and inflows and thus improves storms by making larger‐scale increments. An experiment the same as Baseline except using simultaneous MDA for in situ assimilation more properly constrains small‐scale covariances, leading to more reasonable correlations along the front and more accurate moisture near the dryline and consequently improved analyses and forecasts. Both effects together largely contribute to the overall improvements of SimMDA compared to Baseline.

Rim Driven Thruster as Innovative Propulsion Element for Dual Phase Flows in Plug Flow Reactors

The purpose of this work was to test a new setup to pump water with entrained air for application in gas fermentation. A mixed flow, where gas is contained in a liquid to be pumped, rapidly reduces the efficiency of a conventional pump, due to the compressibility of the gas. It is not always possible to degas the fluid, for instance in gas fermentation, which is preferably carried out in tubular reactors (loop fermenters) to achieve a high conversion rate of the gaseous feedstocks. Method: In this work, a rim-driven thruster (RDT) was tested in a lab-scale, cold flow model of a loop reactor with 5–30% (by volume) of gas fraction (air) in the liquid (water) as alternative propulsion element (6 m total pipe length, ambient temperature and pressure). As a result, it was found that the RDT, in connection with a guiding vane providing swirling motion to the two-phase fluid, could pump a mixed flow with up to 25.7% of gas content (by volume) at atmospheric pressure and 25 °C and 0.5 to 2 m/s flow speed. In conclusion, an RDT is advantageous over a classic propulsion element like a centrifugal pump or axial flow pump for transporting liquids with entrained gases. This article describes the potential of rim-driven thrusters, as known from marine propulsion, in biotechnology, the chemical industry, and beyond, to handle multiphase flows.

Characterization of biodiesel blends produced from repurpose used cooking oil

Characterising the fuel before it is used in an engine is necessary for a healthy fuel supply for an engine, just as a clean environment is necessary for a healthy life. Used cooking oil (UCO), a third-generation feedstock, is investigated for its physicochemical properties. To ascertain the blend's suitability as an alternative fuel, characterisation was conducted using GC-MS, thermogravimetric, infrared spectroscopy and element analysis. To enhance the characteristics the oxygenated additive (diethyl ether: DEE) was added at higher proportions. In accordance with Indian requirements, the impact of DEE on the physicochemical characteristics of biodiesel blends was examined (IS1448). Oleic acid keeps RUCO-B's fuel mixture well in terms of viscosity, ignition quality and oxidative stability. Sulphur-free technology on the RUCO-B eliminates sulphur oxide emissions automatically. The physical (density and viscosity), chemical (cetane number and calorific value) and cold flow (flash point, pour point and cloud point) characteristics of ternary blends were all enhanced by the addition of DEE. According to ASTM D975, the blend's 4% DEE surpasses the standard's acid value by 36%, potentially causing engine damage. In ternary blends, the DEE proportion (0.8, 1.6, 2.4 and 3.2%) enhances the cold flow, chemical and physical qualities.

Flow characteristic investigation of localized arc filament plasma assisted turbulent jet and Bunsen flame

Localized arc filament plasma actuators (LAFPAs) have shown the capability to alter the entrainment of freestream air into a jet. This paper presents an investigation into the effects of LAFPAs on the air jet and methane/air premixed Bunsen flames at different Reynolds numbers. The flow disturbance covering the laminar to turbulent transient conditions was generated by a high voltage plasma discharge system of LAFPAs. The high speed Z-type Schlieren technique was applied to visualize the instantaneous flow and flame structures, and an optical flow algorithm was used to estimate the velocity distribution and further analyze the turbulent effect induced by the plasma. The results illustrate that, in the presence of LAFPA operation, the turbulence jet was accelerated and the jet mixing enhanced. Meanwhile, with the help of LAFPAs, the global consumption burning velocity increased significantly by the area enhancement via plasma–flame interaction. The flame front response to the flow disturbance consists of more surface stretch and flame separation. Furthermore, turbulence spectra analysis of the images reveals a considerable increase in turbulent fluctuations in both cold flow and reacting flow.

Evaluated the effects of nature α-olefins (limonene, β-caryophyllene and camphene) as additives on the cold flow properties of diesel fuel

Pour Point Depressants (PPDs) are currently deemed the most efficacious methodology to enhance the low-temperature fluidity of diesel fuel. However, the majority of these PPDs present complications such as high costs, intricate synthesis procedures, and exhibit potential biotoxicity. To address these challenges, natural α-olefins (β-caryophyllene, limonene and camphene) with 1-hexadecene in varying ratios (5, 10, 15, 20, 25:1) were successfully polymerized at ordinary temperature as poly-α-olefine pour point depressant (PAO PPD), and designated as 1-hexadecane-β-caryophyllene (C16-SZX), 1-hexadecane-limonene (C16-NMX), 1-hexadecane-camphene (C16-KX). An in-depth examination was conducted on the cold filter plugging point (CFPP) and solid point (SP) of both untreated and PPD-added diesel. Subsequently, the finding clearly demonstrates that the CFPP and SP were separately reduced 10 and 32 °C in diesel treated with a molar ratio of 10:1 of C16-KX at the dosage of 2000 ppm. Meanwhile, a comprehensive study was undertaken to investigate the influence of natural α-olefins on the reduction of low-temperature fluidity in diesel fuel. The inhibitory impacts of natural molecular formations on wax crystals were meticulously scrutinized, particularly their roles in modifying the growth patterns of these crystals. Eventually, a novel mechanism by which poly-α-olefine alters the crystalline behavior of wax crystals is proposed.

IoT-driven monitoring and controlling to improve performance of thermoelectric air conditioning system

Thermoelectric module-based air conditioners (TEM-AC) are scalable, reliable, and have the potential to replace conventional air conditioners. However, the coefficient of performance (COP) of TEM-AC is still relatively low. Improving the COP requires a combination of temperature control, voltage control, heat recovery, airflow control, and material selection. The present study focuses on enhancing COP of the TEM-AC for building space cooling. To control and monitor the parameters of the TEM-AC, a low-cost, IoT-enabled monitoring and controlling system (MCS) is developed. The MCS helps in TEM-AC system designing as it can apply different current pulses to improve cooling capacity and control the temperature difference between both surfaces. MCS also measure all the required parameters of the TEM-AC to calculate the COP of the system and helps in reducing the calculation time for each experiment. Using a developed technique and TEM-AC design, a performance comparison of eight experimental cases has been done. Experiments have been performed in normal and control modes with different heat sinks and airflow of TEM-AC. The TEM-AC system is installed over a 16-inch × 12-inch enclosed space with a TEC-12706 module. The study indicates the COP of the system is enhanced by controlling the cold side temperature and air flow rate. For this study, maximum COP is achieved around 0.44 with control operation. The developed IoT-based monitoring and controlling system offers a promising solution for improving the performance of thermoelectric modules in building space conditioning applications.

Effect of palm oil methyl ester on coconut oil as a viable bio‐lubricant alternative to traditional mineral‐based oils

AbstractVegetable oils are promoted as a base oil for automobile lubricants due to increased concerns about the environmental damage caused by synthetic and mineral oils‐derived lubricants. Coconut oil exhibits excellent tribological properties but poor cold flow properties. This work investigates the effect of the addition of palm oil methyl ester (POME), obtained from the transesterification of palm oil, on coconut oil by blending it in three proportions with varying volumes and evaluating for lubricant properties namely tribological properties, rheological properties, thermal properties, chemical properties and corrosion and oxidative stabilities. Fatty acid composition are evaluated for the base oil and the blends. The findings show that the addition of POME improves the base oil's pour point and reduces friction and wear. The corrosion test shows only slight tarnishing of copper strips, while the HOOT and chemical tests indicate appreciable resistance to oxidation. Therefore, this blended mixture has the potential to be a viable bio‐lubricant alternative to traditional mineral‐based oils.

Synergistic effect of selenium and gibberellic acid for enhanced biomass, lipid and improved biodiesel quality from Tetradesmus obliquus through response surface methodology

Biodiesel production from microalgae presents an innovative solution for renewable energy. This study investigates biodiesel production using Tetradesmus obliquus ON506010.1 by optimizing substrates, selenium and gibberellic acid. Using 15 µg/L selenium, lipid content and biomass productivity reached 35.45 %±0.92 and 0.178 g/L/day ± 0.051. With 50 µM gibberellic acid, biomass productivity and lipid content peaked at 0.785 ± 0.101 g/L/day and 38.95 %±0.35, surpassing the control. Fatty acid composition, biodiesel properties, and mRNA expression of lipid synthesis enzymes (acetyl CoA carboxylase (ACC) and fatty acid desaturase (FAD)) correlated. Combining 10 µg/L selenium with 75 µM gibberellic acid with response surface methodology (RSM) increased lipid content (42.80 % ±0.11) and biomass productivity (0.964 g/L/day ± 0.128). ACC and FAD upregulation validated this enhancement, with a 4.4-fold increase in FAD expression. Fatty acid composition and most biodiesel properties met international standards demonstrating Tetradesmus obliquus ON506010.1′s potential for sustainable biodiesel production with better cold flow property and oxidative stability.

DirectProduction of Sustainable Aviation Fuel by Deoxygenation and Isomerization of TriglyceridesoverBifunctional Ir-ReOx/SAPO-11 Catalyst.

Catalytic thermochemical conversion offers a sustainable method to upgradeoil-based feedstocks into highly valuable biofuel, aligning with the modern biorefinery concept. Herein,aseries of IrRe/SAPO-11 catalysts with different Ir to Re molar ratios compared to reference Ir/SAPO-11 and Re/SAPO-11 catalysts was prepared using a wetness impregnation method. These catalysts were used for the direct production of sustainable aviation fuels (SAFs) via efficient hydrodeoxygenation and hydroisomerization of triglycerides.The catalyst screening confirmed that the optimum IrRe/SAPO-11 catalyst, with an equivalent Ir to Re molar ratio, exhibited the highesthydrodeoxygenation activity under milder operation conditions thanthe conditions used in previous studies. Increasing thereaction temperature up to 330 °C enhanced the formation of iso-alkanes in the liquid product, achieving a freezing point of -31.4 °C without additional cold flow improvers. Furthermore, a long-term stability experiment demonstrated that the developed Ir-Re system exhibited exceptional performance over 150 h. This excellent catalytic activity and stability of the bifunctional IrRe/SAPO-11 catalyst was owing to its suitable interface between metallic and oxide sites, mixed mesoporous structures, reduced catalyst size, and increased Lewis acid ratio, as confirmed by our comprehensive characterizations.

Comparison of heat transfer characteristics of a heat exchanger with straight helical tube and a heat exchanger with coiled flow reverser

Vertical shell and coiled tube heat exchangers are an important aspect of numerous industrial processes and are renowned for their high heat transfer efficiency, versatility, compact design, easy manufacturability and maintenance. As a novel technique, a coiled flow reverser was used to enhance the thermal performance of shell and coiled tube heat exchangers. Therefore, the impact of employing a coiled flow reverser on the heat transfer characteristics and pressure drop in a counter-current shell and tube heat exchanger is investigated using both numerical and experimental approaches. The results are compared to a straight helical coiled tube heat exchanger. The numerical simulations were carried out by employing computational fluid dynamics (CFD) techniques, and the SIMPLE scheme was implemented through the second-order upwind discretization method. The laboratory device used for experimentation features a shell with an inner diameter of 15 cm, and the coil pitch and coil diameter of both coiled tubes are set at 3 cm and 12.1 cm, respectively. Results reveal that the overall heat transfer coefficient of the heat exchanger with a coiled flow reverser is 39.5 % to 49.9 % higher than that of the heat exchanger with a straight helical tube. The effectiveness ratio of the heat exchanger with coiled flow reverser to the straight helical tube heat exchanger ranges from 1.254 to 1.379. Optimal results are observed at a cold flow rate of 6 LPM and a hot flow rate of 1 LPM for both heat exchangers. Additionally, the coiled flow reverser enhances heat transfer performance at the cost of increased pressure drop. Numerical results are in good agreement with experimental findings, establishing the reliability of the study.

Investigation on Cold Flow Properties of Natural Ester Insulating Oils Based on Molecular Dynamics

Investigation on Cold Flow Properties of Natural Ester Insulating Oils Based on Molecular Dynamics

A Cold Flow Model of Interconnected Slurry Bubble Columns for Sorption-Enhanced Fischer–Tropsch Synthesis

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors < 6%. With an extension of the models, particle circulation can be studied in the future.

The effects of grafted multiple phenolic antioxidants onto polymethacrylate type pour point depressants on the low-temperature flowability and oxidation stability of biodiesel blends

The enhancement of cold flow properties (CFPs) and oxidative stability (OS) in biodiesel-diesel blends typically involves the use of pour point depressants and antioxidants. However, a scant number of additives are capable of manifesting both pour point depression and antioxidant functionalities concurrently. This study explored the grafting of syringic acid (SA), 3,5-di-tert-butyl-4-hydroxybenzoic acid (DTBHA), and gallic acid (GA) onto polymethacrylate (PMA) type copolymers, culminating efficacious copolymers, namely PTG-SA, PTG-DTBHA and PTG-GA. The findings reveal that with the addition of 1500 ppm of PTG-GA, the CFPP and PP of B20 (20 vol% soybean biodiesel+80 vol% diesel) decrease by 10 and 18 °C respectively, and with the addition of 2000 ppm, the induction period (IP) of B20 can be extended from 1.34 to 8.69 h. In contrast, the application of PTG-SA and PTG-DTBHA to B20 led to inferior OS and CFPs as compared to PTG-GA. The inherent scientific mechanism that underlies this performance discrepancy was thoroughly investigated, scrutinizing it through the lens of co-crystallization and nucleation processes. This research underscores the potential of post-modification of PMA type pour point depressants with antioxidants, a strategy that not only bolsters the CFPs of B20 but also confers antioxidant attributes to the pour point depressants.

Condenser operating conditions effects on dielectric liquid boiling and condensation heat transfer in closed systems

Localized boiling and enclosed condensation of a dielectric liquid in a thermosyphon can be used as an alternative to traditional air cooling for high performance microprocessors. A small quantity of dielectric fluid boils at the surface of the microprocessor and is condensed by a heat exchanger, which removes the heat from the system. Here, the heat exchanger was a water-fed cold plate cooling a round fins heat sink. Such a thermosyphon can remove large heat fluxes and increase the energy efficiency of data centers.An experimental setup was built to measure the impact of various operating parameters on the thermal resistances of the thermosyphon. The thermal resistances that were considered were the boiling resistance between the heater and the dielectric fluid, the condensation resistance between the dielectric fluid and the cold water feeding the cold plate, and their sum (the total thermal resistance). The operating parameters tested were the cold plate inlet flow rate (0.2 L/min and 1 L/min), the cold plate inlet temperature (15 °C and 24 °C) and the filling ratio of the enclosure (33 %, 66 % and 88 %).It was observed that changing the filling ratio did not have a significant impact on the thermal resistances of the thermosyphon. Increasing the cold plate inlet flow rate from 0.2 L/min to 1 L/min and decreasing the cold plate inlet temperature from 24 °C to 15 °C both led to significantly lower total thermal resistance. However, increasing the flow rate lowered the rate at which the pressure increased with the amount of heat removed from the system, while this rate did not change when decreasing the cold plate inlet temperature.These observations could be properly explained by a simple analytical model, with a single free parameter (increasing the thermal resistance of the heat sink for the lowest cold plate flow rates). With the free parameter adjusted to the data, the model had a root-mean square error of 1.8 °C and a maximum error of 6 °C, over all measured conditions.This study demonstrates how changing the filling ratio or the cold plate inlet temperature and flow rate have an impact on the pressure, the temperature and the thermal resistances inside the thermosyphon. This is a first step in evaluating the energetic and economic efficiency of the thermosyphon solution for its future integration in data centers.

Assessing Local Statistics of a Premixed Turbulent Bunsen Flame

The local interactions between the flame-front and turbulence control the dynamics, morphology, and propagation of a premixed turbulent flame. To investigate such complex dynamics of a flame–turbulence interaction, we present an experimental exposition of a premixed turbulent Bunsen flame. Several quantities have been evaluated to assess the flame–turbulence interaction. We first measured the statistics of the flowfield adjacent to the flame and compared it with the cold flow. This allowed us to evaluate the effect of the flame on the upstream turbulence. Subsequently, we performed statistical analyses of the local values of various stretch rates and quantified how their distribution changes with turbulence intensity and flame temperature. We also evaluated the pairwise relation among various stretch rates to assess their dependence on each other. Finally, we used flame particles to evaluate the Lagrangian evolution of stretch rates conditioned on flame-fronts. All the analyses presented in this work point out Karlovitz number as a key factor in determining the flame–turbulence interaction. Specifically, we observe a stronger influence of turbulent eddies on flames with increasing Karlovitz number, as evidenced by the reduced effect of flame on upstream flow, wider probability distribution functions of stretch rates, and increased persistence timescales for stretches.

Design and performance test of a fluidized bed dryer using dry cold air flow for drying marungga leaves

The Marungga tree is a plant that offers numerous benefits. Its leaves can be processed into flour for further processing for various needs. Marungga leaves need to be dried before they can be made into flour. Marungga leaves are sensitive to heat, so high temperature drying should be avoided. Drying in the sun, or at room temperature takes a long time and is unhygienic. To address these issues, a fluidized bed dryer that utilises dry, cold air flow through dehumidification of the air is required. This research aims to design and test the performance of a fluidized bed dryer that uses dry cold air flow. The method used in the research starts from literature study, design, component manufacturing, assembly and performance testing of the dryer. The design results resulted in specifications of the dryer components as follows: dimensions of the drying chamber 500 mm in diameter and 800 mm in height, evaporator, condenser, compressor, blower each 1 HP. The results of the dryer performance test are as follows: dryer air temperature 34.2 °C, relative humidity 54.3%, and dryer air mass rate 0.25 kg/s, with a drying rate of 0.57 kgH2O/s. The evaporator of the cooling system can decrease the absolute humidity of the drying air by 1.6 kgH2O/kg dry air.

Exergy analysis and improvement of helium internal purifier

Exergy analysis was applied to the evaluation of helium internal purifier in this paper. The important operating parameters has been given to determine the exergy destructions in components as well as in the entire cycle of internal purifier. The analysis results show that the recovery of liquefied air energy can improve the performance of purifier and the exergy destruction of different heat exchanger is different. Results from the analysis helped evolving guidelines for designing appropriate technological process for practical helium internal purifier. An internal purifier with an optimized structure was designed to remove air impurities up to 10 mol%, beyond previous maximum impurity content. The impact on liquefaction capacity is minimized because of the small consumption of cold flow. The achievable performance was also provided in this paper. The purifier could remove air impurities up to 8 mol%.

The origin of cold gas in the circumgalactic medium

Context. The presence of cold gas (T ≲ 104 K) in the circumgalactic medium (CGM) of galaxies has been confirmed in observations and in high-resolution simulations, but its origin is still a puzzle. Possible mechanisms are cold accretion from the intergalactic medium (IGM), clumps embedded in outflows and transported from the disk, and gas detaching from the hot CGM phase via thermal instabilities. Aims. In this work we characterize the history of cold CGM gas in order to identify the dominant origin channels at different evolutionary stages of the main galaxy. Methods. To this end, we tracked gas particles in different snapshots of the smoothed particle hydrodynamics (SPH) cosmological zoom-in simulation Eris2k. We performed a backward tracking of cold gas, starting from different redshifts until we could identify one of the followings origins for the particle: cold inflow, ejection from the disk, cooling down in situ, or stripping from a satellite. We also performed a forward tracking of gas in different components of the galaxy (such as the disk and outflows). Results. We find a clear transition between two epochs. For z > 2, most cold gas (up to 80%) in the CGM comes from cold accretion streams as the galaxy is accreting in the cold mode from the IGM. At lower z, gas either cools down in situ after several recycles (with 10–20% of the gas cooling in outflow), or it is ejected directly from the disk (up to 30%). Outflows have a major contribution to the cold CGM gas budget at z < 1, with almost 50% of the hot gas cooling in outflow. Finally, we discuss possible mechanisms for CGM cooling, showing that the thermally unstable gas with tcool/tff < 1 (precipitation-regulated feedback) is abundant up to r ∼ 100 kpc and cooling times are shorter than 50 Myr for densities n > 10−2 cm−3.

Cold-Flow Properties of Estolides: The Older (D97 and D2500) versus the Mini-(D5773 and D5949) Methods

There is growing research on developing new and sustainable lubricants. Sustainable lubricants with adequate cold-flow properties are of particular interest for many applications. One limitation of the established methods for measuring cold flow properties is the large volume needed to test samples. This makes initial screening of many hard-to-synthesize samples difficult. In the current study, we compared the results of the older, widely accepted ASTM methods D97 (pour point, PP) and D2500 (cloud point, CP) to the newer, smaller-volume, and easier-to-perform methods D5949 and D5773 for bio-based base oils (estolides and iso-estolides). The CP results were in good agreement for less colored samples, but D5773 gave lower values for some darker (Gardner color >8) samples, especially esters. The D5949 showed a tendency to report slightly higher PP, especially for the lower values. Viscosities and densities in a wide temperature range (15 to 120 °C) were also measured. The surface tensions were estimated by a literature group method. Viscosity and density effects can only partially explain the differences in the PP values from the two methods. In conclusion, the newer mini-methods are an acceptable substitution when larger volumes are not accessible, unless the sample is too dark.

A semi-interpenetrating network acrylic pressure-sensitive adhesive for efficient transdermal application with high cohesion and adhesion

The application of pressure-sensitive adhesives (PSAs) in transdermal drug delivery systems (TDDSs) is limited. Insufficient cohesion in TDDS can lead to cold flow, patch displacement, dose inaccuracies, and the ‘dark ring’ phenomenon. To address these issues, we developed a semi-interpenetrating network (semi-IPN) PSA using a 2-hydroxyethylacrylate-modified acrylic copolymer as the linear polymer and poly[tri(propylene glycol) diacrylate] as the cross-linked network. Semi-IPN PSAs have better mechanical properties compared to traditional PSAs. The cohesion of the semi-IPN PSA was 31 times and 1.6 times that of commercially available DURO-TAK®87-2287 and DURO-TAK® 87–4098, respectively, and the cold flow of the semi-IPN PSA was significantly reduced. Furthermore, the semi-IPN PSA adhered to the human forearm for longer time and did not exhibit the ‘dark ring’ phenomenon after removal. When loaded with flurbiprofen, the semi-IPN PSA was found to maintain high levels of drug release and skin permeation amount, and flurbiprofen loading did not affect its superior cohesive performance. In conclusion, the innovative application of the semi-IPN PSA for TDDS showed excellent mechanical properties, effective adhesion to the skin without irritation, and highly effective drug release. These findings indicate that the use of the semi-IPN is both simple and highly effective for TDDS.