Distribution Pipelines Research Articles

Detection of underground natural gas pipeline micro-leakage based on UAV hyperspectral remote sensing and GIS

ABSTRACT Detection of underground natural gas pipeline micro-leakage based on unmanned aerial vehicle (UAV) hyperspectral remote sensing and GIS. Hyperspectral images can indirectly detect underground natural gas pipeline micro-leakage through spectral and spatial variation characteristics of surface vegetation. However, most of existing studies were based on ground-mounted platforms, which could only perform small-range single-point detection and might occur misidentifications. UAV hyperspectral remote sensing can allow wide-range detection of surface vegetation. Moreover, underground pipeline distribution GIS data can provide prior knowledge about leakage points to exclude misidentifications. Therefore, a natural gas pipeline micro-leakage experiment was set up. UAV hyperspectral images of grasslands and pipeline distribution vector data were obtained, which led to a proposed new wide-range multi-points detection methodology of underground natural gas micro-leakage. Firstly, the vegetation identification index (WVI) R 470 + R 674 / R 555 + R 750 was designed based on WOA–VMD (whale optimization algorithm – variational modal decomposition) to segment and extract the vegetation stress zones. Then, UAV- and GIS-based natural gas micro-leakage vegetation stress identification model was constructed to obtain the leak points of natural gas micro-leakage. Finally, the recognition ability was evaluated by comparing with three stress vegetation identification indices proposed in previous studies. The result showed that there was no missing or false detection in identification results; the identification and positioning effect was better than other indices, which could meet the practical application requirements.

Fire safety characteristics of natural gas with hydrogen admixture

The increasing pressure to decarbonise energy production leads to the need to use low or zero carbon fuels or energy carriers. One of the promising fuels of the future is hydrogen, which is carbon-free if renewable energy sources are used for its production. However, the capacity for hydrogen production is currently insufficient to make it applicable on a large scale. Adding hydrogen to natural gas allows for a reduced carbon footprint without costly modifications to pipeline distribution network. However, changing the composition of gas in transport and distribution facilities requires a thorough assessment of the impact on operational safety. Fire safety of flammable mixtures is commonly assessed on the basis of explosive limits and other parameters. Although methods are available to calculate these parameters based on the composition of the mixtures being evaluated, the final safety assessment should rely on actual measured values. The scope of this work is to determine the explosion limits of natural gas from the transit system and changes in the limits caused by the addition of hydrogen at the concentration levels of 10% and 20% (v/v). Obtained experimental results were further compared with theoretically calculated values. Attention was also paid to the change in maximum explosion pressure, maximum pressure rise rate and oxygen concentration limits (LOC). As a result, valuable data on the expansion of the explosion limits of natural gas after the addition of hydrogen are presented.

Ultra-Low-Power, Extremely Stable, Highly Linear-Response Thermal Conductivity Sensor Based on a Suspended Device with Single Bare Pt Nanowire.

The continuous and stable monitoring by sensors is crucial for ensuring the safe utilization of hydrogen due to its inherent high explosiveness. Currently, catalyst aging and oxygen dependence often limit the lifetime of most sensors, which stems from the sensing materials and catalytic reaction in comparison to thermal conductivity sensors. Thermal conductivity sensors possess superior sensing characteristics such as lowpower consumption and exceptional stability attributed to their free-catalysts or free-oxygen nature. Herein, we present an ultralow-power hydrogen-thermal conductivity sensor based on suspended bare platinum nanowires. This sensor incorporates two suspended independent working elements (serpentine/bridge), each of which is thermally decoupled from the substrate. Also, the bridge element operates at significantly lower power levels (the lowest ∼3.32 μW) compared to existing direct-current hydrogen-thermal conductivity sensors. Furthermore, it demonstrates a 99.99% linearity between hydrogen concentration and response under various operating powers. Finally, our sensor shows remarkable stability through a repeatability test (>30,000 cycles). This developed platform provides an optimal structure scheme for integrated sensors with ultralow-power, extremely stable, highly linear-response sensing characteristics, which is expected to be widely used for hydrogen detection and leakage warning under various pipeline distribution systems.

Leak identification and quantification in gas network using operational data and deep learning framework

In this study, we introduce an innovative deep learning framework designed to achieve precise detection, localization, and rate estimation of gas distribution pipeline system leakages. Our method surpasses conventional statistical approaches, particularly those based on Bayesian inference, by accommodating the system’s intricate behaviors, including variable usage and production from both sources and sinks. Notably, our approach demonstrates remarkable accuracy in localizing leakages even amidst multiple occurrences within the system. Specifically, achieving over 98% accuracy in single-leakage scenarios underscores its effectiveness. Furthermore, through data augmentation involving the introduction of noise into the training dataset, we significantly enhance the model’s performance, particularly when tested against real-world-like noisy data. This study not only showcases the efficacy of our proposed deep learning framework but also underscores its adaptability and robustness in addressing complex challenges in gas pipeline systems.

Pipeline incidents and property values

The rapid expansion of pipelines during the U.S. shale oil and gas boom drew attention to the economic consequences of pipeline incidents. This study investigates the impacts of 426 gas distribution pipeline incidents on property values in the United States between 2010 and 2020. We find that only incidents that are both severe (involving explosion, ignition, or fatalities) and occurred on above-ground pipelines, which we define as high-profile incidents, have adverse effects on nearby property values, while other incidents have no measurable housing price effect. A difference-in-differences analysis finds that high-profile incidents significantly decrease property values within 1000 m by 8.2%, and the negative impact can persist for about eight years on average. Furthermore, we find a drop in transaction volume that lasts a short period after the incidents, suggesting an initial demand-side response. In contrast to the strong effects of pipeline incidents, we do not find statistically significant price effects from pipeline installation. We also demonstrate that there is substantial heterogeneity by the type of incident and that results based on studies of individual incidents should be generalized with caution.

A review analysis of corrosion rate on stainless steel pipe in sea water media

Regarding providing energy, few sectors are as massive as the oil and gas business. One of the most crucial parts of oil and gas production is the distribution pipes or pipelines that transport the production fluids, which include oil and gas, from one distribution point to another. The corrosion of A316 material, which can lead to holes or pitting, and the damage it causes in most industrial operations, particularly in the oil and gas industry, has resulted in substantial losses at high prices over an extended period of time. In the study, we will quickly examine what corrosion is, the different kinds of corrosion, inhibitors, and how to assess the corrosion rate of A316 stainless steel in salt water. Analysis of the electrochemical corrosion rate of Inconel 600 nickel alloy and stainless steel 316L subjected to varying amounts of saltwater (freshwater, seawater, mixed water). Because chlorine speeds up corrosion, alloys like Inconel 600 and 316L undergo pitting corrosion. The molybdenum component gives 316 stainless steel its superior corrosion resistance. That's why it works well for gas and oil pipelines that go through saltwater. Nevertheless, materials exposed to maritime environments must have cathodic protection or coating to prolong their life and stop the pipe from continuously corroding.

Techno-Economic Analysis of Clean Hydrogen Production Plants in Sicily: Comparison of Distributed and Centralized Production

This paper presents an assessment of the levelized cost of clean hydrogen produced in Sicily, a region in Southern Italy particularly rich in renewable energy and where nearly 50% of Italy’s refineries are located, making a comparison between on-site production, that is, near the end users who will use the hydrogen, and centralized production, comparing the costs obtained by employing the two types of electrolyzers already commercially available. In the study for centralized production, the scale factor method was applied on the costs of electrolyzers, and the optimal transport modes were considered based on the distance and amount of hydrogen to be transported. The results obtained indicate higher prices for hydrogen produced locally (from about 7 €/kg to 10 €/kg) and lower prices (from 2.66 €/kg to 5.80 €/kg) for hydrogen produced in centralized plants due to economies of scale and higher conversion efficiencies. How-ever, meeting the demand for clean hydrogen at minimal cost requires hydrogen distribution pipelines to transport it from centralized production sites to users, which currently do not exist in Sicily, as well as a significant amount of renewable energy ranging from 1.4 to 1.7 TWh per year to cover only 16% of refineries’ hydrogen needs.

Organization оf Electrochemical Protection оf Steel Underground Pipelines Against Corrosionin the Gas Distribution Industry of the Republic of Belarus

Steel underground gas pipelines occupy a significant share of the total length of gas distribution pipelines, and therefore their maintenance in proper condition is a constant and very urgent task. Due to its global nature, the main influencing factor affecting the technical condition of any steel underground pipelines, including gas pipelines, is corrosion, primarily soil corrosion. To protect against it on pipeline networks, along with insulating coatings, electrochemical protection (ECP) is applied, that is, following the definition of STO [Standard of Organization] 17330282.27.060.001–2008, protection of metal against corrosion in an electrolytic environment, carried out by establishing a protective potential on it or eliminating the anodic potential shift from the stationary potential. In the gas distribution industry of the country, methods and means of electrochemical protection have been applied since the beginning of gasification and the construction of the first gas pipelines. All gas supplying organizations of the State Production Association for Fuel and Gasification “Beltopgaz” (six regional and Minsk city), which operate gas distribution facilities, have specialized corrosion protection services. These services provide maintenance of available ECP equipment, conduct electrical measurements on gas pipelines and corrosion studies of soils, and have certified laboratories. This paper is devoted to the analysis of domestic experience in organizing electrochemical protection of steel underground gas distribution pipelines, searching for promising directions for its improvement and increasing efficiency through the implementation of a unified industry technical policy, automation and telemechanization of ECP equipment in the general context of digital transformation, optimization of the timing and volume of maintenance.

Data-Driven Inline Leak Detection for Pipelines Using Flow-Induced Acoustics Analysis

Fluid and water distribution networks are essential to the modern world. However, these systems are prone to leaks, which can lead to significant water loss, damage to infrastructure, and environmental pollution. The proposed solution makes use of Acoustic Emission sensors placed in discrete locations in the pipeline which measures the sound in the pipeline caused by the flow of fluids. Computation models are used to deduce the location from the input provided by the sensors. In case of leak, the leak is localized through cross correlation and TDOA methods. This solution is particularly developed for water distribution pipelines. Keyword: Acoustic data analysis, Data-driven models, Cross-Correlation, Time Difference of Arrival (TDOA)

Simulation of the Jet Fire Using Atmospheric Dispersion Modeling (ALOHA): A Case Study of Natural Gas Pipeline in Istanbul, Türkiye

Natural gas is known as a widely used energy source in residential, business and industrial areas. During the transportation of natural gas by pipelines, accidents occur due to various reasons, which can also lead to gas output. These accidents are events that have the potential to pose important risks in terms of life and property safety, particularly in urban areas and surrounding of pipeline routings. In this study, accident scenarios were generated based on a natural gas distribution pipeline fire that occurred in Istanbul (NW Türkiye) on 28 April 2020 and the impact areas of the jet fire were calculated using the ALOHA program. The effects of source release factors (i.e., pipe length and diameter) and atmospheric conditions (i.e., wind speed, cloud cover, air temperature and relative humidity) on the thermal radiation threat distances associated with jet fire were calculated for the current and worst scenarios. As a result, it was found that pipe length and diameter have a significant effect on threat distances. In addition to the role of the synoptic circulation mechanism on the jet fire for the selected episodic event (position of low/high pressure centers), local atmospheric conditions also have an effect on the threat distance. From the modeling analysis, significant impact of wind speed, air temperature and relative humidity values on the threat distances were found. In the worst scenario, if there were strong northeasterly winds reaching 30.9 m per hour at the time of the jet fire, the threat distances would have been 21 m (red), 28 m (orange) and 42 m (yellow). This case shows that if a natural gas jet fire occurs under the influence of strong northeasterly winds (passing over the Black Sea without encountering any topographic obstacles), poisonous gas will be transported to long distances in a short time and will negatively affect social life and economy.

ГИДРАВЛИЧЕСКИЙ РАСЧЕТ ТРУБОПРОВОДА С РАССРЕДОТОЧЕННЫМ СБРОСОМ РАССОЛА В АКВАТОРИЮ

When producing water using desalination technologies, significant volumes of highly concentrated brines are formed. The solution of the problem of wastes recycling is an important global issue for water protection organizations, and the studies of the last decade confirm this. The article discusses an environmentally friendly method of dispersed uniform brine discharge into the water area, presents the developed technical solution and describes the principle of its operation. As an example, the authors calculate the hole diameters of the distribution pipeline for uniform brine discharge along the length. We calculated the radius and the scattering jet rate at a given distance from the hole in the distribution pipeline. The difference in brine salt concentrations at a depth of 20 m from the discharge point between the background concentration in the sea and the salt concentration was found to be from 0.439 % to 0.524 % along the length of the discharge pipeline. Dissolution of brines to safe concentrations becomes even more intense in the presence of sea currents. The research results can be used in the design and operation of such systems.

First validation of high-resolution satellite-derived methane emissions from an active gas leak in the UK

Abstract. Atmospheric methane (CH4) is the second-most-important anthropogenic greenhouse gas and has a 20-year global warming potential 82 times greater than carbon dioxide (CO2). Anthropogenic sources account for ∼ 60 % of global CH4 emissions, of which 20 % come from oil and gas exploration, production and distribution. High-resolution satellite-based imaging spectrometers are becoming important tools for detecting and monitoring CH4 point source emissions, aiding mitigation. However, validation of these satellite measurements, such as those from the commercial GHGSat satellite constellation, has so far not been documented for active leaks. Here we present the monitoring and quantification, by GHGSat's satellites, of the CH4 emissions from an active gas leak from a downstream natural gas distribution pipeline near Cheltenham, UK, in the spring and summer of 2023 and provide the first validation of the satellite-derived emission estimates using surface-based mobile greenhouse gas surveys. We also use a Lagrangian transport model, the UK Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME), to estimate the flux from both satellite- and ground-based observation methods and assess the leak's contribution to observed concentrations at a local tall tower site (30 km away). We find GHGSat's emission estimates to be in broad agreement with those made from the in situ measurements. During the study period (March–June 2023) GHGSat's emission estimates are 236–1357 kg CH4 h−1, whereas the mobile surface measurements are 634–846 kg CH4 h−1. The large variability is likely down to variations in flow through the pipe and engineering works across the 11-week period. Modelled flux estimates in NAME are 181–1243 kg CH4 h−1, which are lower than the satellite- and mobile-survey-derived fluxes but are within the uncertainty. After detecting the leak in March 2023, the local utility company was contacted, and the leak was fixed by mid-June 2023. Our results demonstrate that GHGSat's observations can produce flux estimates that broadly agree with surface-based mobile measurements. Validating the accuracy of the information provided by targeted, high-resolution satellite monitoring shows how it can play an important role in identifying emission sources, including unplanned fugitive releases that are inherently challenging to identify, track, and estimate their impact and duration. Rapid, widespread access to such data to inform local action to address fugitive emission sources across the oil and gas supply chain could play a significant role in reducing anthropogenic contributions to climate change.

DIGITAL CADASTRE FOR POTABLE WATER DISTRIBUTION NETWORK IN LOKOJA, KOGI STATE

Water is one of the most important natural resources, and as a resource to any nation, it should be well-planned, developed, conserved, distributed, and managed. Its infrastructure should also be properly maintained to avoid future water problems. This project sought to evaluate the water infrastructure in Lokoja with a focus on identifying areas requiring improvement. The scope of the study encompassed mapping the primary water pipeline distribution network and gathering geometric and attribute data concerning storage tanks and reservoirs within the designated area. Employing a combination of remote sensing and ground survey techniques, data was collected and utilized to generate a detailed spatial distribution map illustrating the major water supply networks and reservoirs. ArcGIS 10.2 was utilized for data processing and analysis, with the 3D analyst tool utilized to generate an elevation map and ascertain optimal site selection for gravity reservoir placement. The outcomes of the analysis included a visual representation of major pipeline connections, the precise location of tanks and reservoirs, and a comprehensive database containing both location and attribute information for these structures within the study area. The study findings revealed a pressing need for enhancing maintenance practices for water reservoir tanks, as a significant portion were found to be in substandard condition. Additionally, the study highlighted the necessity for pipeline extension to incorporate newly developed suburban areas within the study vicinity. The collated data serves as a pivotal resource for informed decision-making regarding the establishment of new reservoirs and the expansion of existing pipeline networks. Overall, this...

Study on the Influence of Hydrogen Blended Transportation on the Safety of Existing X70 Steel in Gas Distribution Pipeline Network

Coal to gas is one of the natural gas sources utilized in Beijing, with a hydrogen blend concentration range from 1% to 3% and reaching up to 5% in specific cases. In order to evaluate the safety of transporting hydrogen blended natural gas with X70 pipeline steel in distribution pipelines, this study first conducted the slow strain rate tensile tests under a total pressure of 4 MPa in hydrogen environment. The results show that X70 steel exhibits highly sensitive to a hydrogen blending ratio of 5%. Subsequently, four types of hydrogen compatibility tests were conducted in the above sensitive hydrogen partial pressure include the impact toughness test, fracture toughness test, fatigue crack growth test, and fastening disk pressure test. The findings demonstrated that hydrogen blended natural gas has virtual no effect on the impact and fracture toughness, with only 10% reduction in fatigue crack growth threshold. Finally, based on fatigue life analysis by fracture mechanics evaluation, it can be concluded that the existing natural gas pipe of X70 steel is capable to operate safely over 40 years under a total pressure of 4 MPa with a hydrogen blend concentration of 5%.

Kajian Kehilangan Air pada Perencanaan District Meter Area PDAM Kota Pasuruan

Water loss that occurred in the service area of the Pleret 1 Reservoir managed by PDAM Pasuruan City from January to November was 42.92%. The highest water loss occurred in January of 46.85% and the lowest in May of 33.43%. This is still very far from the standard 20%. The current condition of the Pasuruan City PDAM distribution pipeline network is that all systems are connected to each other, so that there are no separate systems. Efforts that can be made by PDAM Kota Pasuruan to reduce water loss and interconnection networks are to isolate the piping network by establishing a DMA (District Area Meter). Formation of DMA requires hydrolysis modeling simulation of distribution pipeline network using Epanet 2.2 software. Besides using Epanet 2.2 software, Quantum GIS 3.16.16 software is needed to create a pipeline. The validity test in the field uses the discharge parameter with a correlation coefficient between EPANET and field discharge data obtained at 0.61. The formation of DMA with good results to reduce air loss is by reducing air pressure, if the air pressure decreases, the air loss will be lower.

Damage to Natural Gas Distribution Steel Pipelines caused by Rigid Bodies resulting from the Excavation of Laying Trenches

The present paper focuses on analyzing the occurrence of defects such as dents and local deformations by laboratory simulations of a real case of a defect detected on a natural gas distribution pipeline lain at a depth of approximately 0.6 m. The defect is caused by a river stone which due to the compression forces, damages the pipe to the point of cracking. In the laboratory, the simulation was carried out on a steel pipe insulated with extruded polyethylene which was acted upon by a mandrel made of duralumin. The purpose of the tests is to determine the maximum values at which the pipe material fractures. It was found that the fracture of the pipes when there are rigid bodies in the protective layer of sand is accelerated by the sand existing between them and the pipe and by the change in the properties of the steel the pipes are made of when they are kept in water.

Increasing Oil Recovery by Varying Surfactant Concentrations and Expanding the Well Drainage Area

Surfactant flooding plays a crucial role in advanced techniques for boosting oil recovery. There remains a significant volume of unrecovered oil in reservoirs, particularly in carbonate reservoirs. These reservoirs often face challenges with low primary and water-flood recovery due to inadequate sweep efficiency, resulting in the presence of bypassed or trapped oil. Chemical flooding approaches, including surfactant flooding, have demonstrated their effectiveness in the retrieval of this trapped oil. The fundamental concept of surfactant flooding involves injecting a surface-active agent, known as a surfactant, to reduce the interfacial tension and mobilize the residual oil saturation. Surfactants have been widely utilized for various purposes in the petroleum industry since its early years, owing to their capacity to modify interfacial interactions between two immiscible fluids in contact with one another. Interfacial phenomena play a significant role in rock-fluid interactions and the interactions between fluids from the reservoir to distribution pipelines. Consequently, surfactants find application in a variety of activities within the petroleum industry. Laboratory experiments, pilot-scale projects, and field-scale initiatives worldwide have yielded diverse outcomes regarding the use of surfactants for enhancing oil recovery. Multiple types of surfactants have been investigated to determine highly effective chemical formulations for enhanced oil recovery, with anionic and non-ionic surfactants being commonly employed in sandstone reservoirs.

Variation of Hydraulic Resistance in Pressure Pipelines of an Open-Type Hydraulic System

Pressure distributive pipelines with path distribution of fluid are part of various technical systems. Pressure losses at abrupt and smooth pipe reductions are components of total pressure losses in these pipelines. After all, the equalization of fluid distribution along the length of distributive pipelines is achieved, in particular, by reducing their diameter in the direction of flow. Depending on the configuration of the pipe reductions, pressure losses at this pipeline element can vary. For an open-type hydraulic system, a regulatory characteristics of pressure in the pipeline has been obtained with a constant fluid flow in a general form. The influence of measures necessary to change energy losses in the pipeline on the hydraulic resistance of the unregulated section of the pipeline has been taken into account. Options for these measures have been proposed for a pressure pipeline with pipe reduction.

The hydrogen perspective for Türkiye, which is on the Asia-Europe energy transition route. Can Türkiye become hydrogen hub?

This study examines the potential for hydrogen to undertake a leading role in the transition to sustainable energy in Türkiye. Türkiye, with its well-established energy infrastructure and increasing focus on renewable energy, has the potential to undertake a significant part in the worldwide hydrogen market. The research uses a multi-level perspective to analyse the interactions between different region connected with Türkiye, and the processes and strategies within the national energy system. The findings suggest that hydrogen production and transport in Türkiye has the potential to significantly contribute to the decarbonization of the industry and flexibility services in Asia, Europe and Africa. However, the ongoing advancement in the field of hydrogen in Türkiye is at a critical juncture where coordinated efforts are necessary to fully realize its potential. Türkiye recently announced the Hydrogen Technologies Strategy and Roadmap. Under the new Hydrogen Technologies Strategy and Roadmap, Türkiye plans to significantly increase the production of hydrogen. Türkiye plans to significantly increase its installed electrolyser capacity to support the production of hydrogen. Specifically, the plan aims to increase the installed capacity to 2 GW by 2030, 5 GW by 2035, and 70 GW by 2050. Turkey's strategic investments and policy adjustments could propel its green hydrogen production to 3.4 million tons yearly by 2050. With an anticipated domestic demand for hydrogen at 1.9 million tons annually, Turkey could potentially export between 1.5 and 1.9 million tons yearly by 2050. Türkiye boasts an extensive network of transmission and distribution pipelines for natural gas, totalling 10,000 km, including those with large diameters. The existing pipelines could transport hydrogen in its pure form or blended with natural gas. The natural gas pipeline capacity in Turkey stands at 32 billion cubic meters. This infrastructure enables the transportation of an estimated 575 million tons of hydrogen yearly to neighboring countries by employing a mix of 20 % hydrogen and natural gas. With an extensive network of natural gas transmission and distribution pipelines, Turkey positions itself as an integral part of the interconnected hydrogen energy infrastructure, linking the nation with Europe and neighboring regions. The results of this study present new approaches into the dynamics of the energy system and contribute to ongoing discussions about transition routes and consider the current status of hydrogen in Türkiye, the country's renewable energy potential, the policy and regulatory framework, and the infrastructure and market conditions necessary in order to foster the growth of a hydrogen hub.

MUNICIPAL INFRASTRUCTURE AT THE LEVEL OF PROTECTED NATURAL AREAS ROSCI0045 JIU CORRIDOR, BISTREȚ ROSPA0010 AND NATURAL RESERVES DRĂNC FOSSIL PLACE-2391 AND ZAVAL FOREST - IV.33 + A6

The paper aims to highlight the aspects related to the urban infrastructure for the protected areas ROSCI0045 Jiu Corridor, Bistreț ROSPA0010 and the Drănic Fossil Place-2391 and Zaval Forest Nature Reserves – IV.33+A6, given that they group a significant number of species of plant and animal origin. These protected areas play an essential role in biodiversity conservation at the level of the 56 ATUs (37 in Dolj County, 17 in Gorj County, one in Mehedinţi County, one in Olt County), on whose territory they are located. The paper refers to the drinking water distribution network, the sewerage network and the natural gas distribution network (including adjacent aspects related to them).The area has 740 km of city streets, of which 578 km modernized, 1971.2 km drinking water network, 936.0 km sewerage network, produces about 342 thousand cubic meters of water per day, achieving a daily consumption of 19,956 cubic meters. Within the area, there are 940.2 km of pipelines for natural gas distribution (two thirds located in the urban area), which facilitated a consumption of 133,040 thousand cubic meters of gas annually. The urban infrastructure improved during 2017-2021, but certain aspects related to it need to be properly analyzed in order not to have a high negative impact on the state of the environment.