Basic Research Research Articles

Joint identification of groundwater pollution source information, model parameters, and boundary conditions based on a novel ES-MDA with a wheel battle strategy

Groundwater pollution source identification (GPSI) is an important prerequisite for pollution remediation and risk assessment. However, an accurate GPSI is usually difficult to achieve due to the need to simultaneously consider practical problems and theoretical research. For practical problems, the boundary conditions, especially the concentration boundary, are often given as known constants through prior information. However, in most practical situations, the boundary conditions are complex and cannot be accurately estimated in advance, which leads to the distortion of the final identification results. Therefore, this study focused on the concentration boundary, and first proposed to jointly identify three types of unknown variables (source information, model parameters, and boundary conditions) to ensure that the identification results had more practical value. For theoretical research, as the number of unknown variable types increases, the difficulty of solving the inverse problem often increases, which may lead to inaccurate inversion results. Thus, a novel ensemble smoother with multiple data assimilation (ES-MDA) with a wheel battle strategy was proposed, enhancing the identification accuracy. We designed two cases to verify the effectiveness and practicality of the above ideas: a low-dimensional Case 1 (including four different synthetic scenarios: three scenarios with unknown boundary conditions under three concentration boundary modes and a scenario with known boundary conditions) and a high-dimensional complex Case 2. Identifying the boundary conditions in GPSI was found to be of great significance. Compared to the standard ES-MDA method, the ES-MDA with a wheel battle strategy proposed here could improve the inversion accuracy, and had certain effectiveness and practicality.

Organosulfur Cathodes in Lithium Metal Batteries: Bridging the Gap between Fundamentals and Practical Applications

AbstractHigh‐specific energy sulfur‐based cathodes have attracted considerable interest in lithium batteries. Organosulfur cathodes offer inherent advantages of high element abundance and an extended cycling life, aligning with the evolving requirements of future energy storage devices. Over the past decade, research efforts have been devoted to optimizing electrochemical performance through the rich and tunable molecular structures of organosulfur compounds. To further advance the fundamental research and practical application of lithium‐organosulfur batteries, a systematical analysis of the correlation between the molecular structures and electrochemical mechanisms of organosulfur cathodes is imperative. This involves deriving the key parameters at the cell level and investigating the feasibility. In this review, the thermodynamics, reaction processes, and electrochemical kinetics of organosulfur cathodes, grounded in fundamental theories of electrochemistry and materials science are discussed. Expanding the insights, comparisons among elemental sulfur, organosulfur, and n‐type organic cathodes (e.g., carbonyl cathodes) are drawn. The gap between fundamentals and practical applications targeting 500 Wh kg−1 lithium organosulfur batteries is highlighted through energy density calculations and identification of key factors affecting pouch cells. Finally, potential strategies and prospects for the overall design of advanced lithium‐organosulfur batteries are proposed, considering both theoretical foundations and practical implementations.

Impact of surfactant polydispersity on the phase and flow behavior in water: the case of Sodium Lauryl Ether Sulfate

This study delves into the impact of molecular polydispersity on the phase behavior of Sodium Lauryl Ether Sulfate (SLES) surfactant, aiming to deepen understanding of its implications for fundamental science and industrial applications. SLE3S is utilized as a model compound: a comprehensive characterization of molecular polydispersity is conducted using Gas Chromatography–Mass Spectrometry and Nuclear Magnetic Resonance spectroscopy, juxtaposing the findings with those for SLE1S.Our comprehensive investigative approach entails: (i) employing Time-Lapse dissolution experiments in microchannel geometries to observe the dissolution and phase transitions; (ii) utilizing polarized light microscopy, confocal microscopy, and Small Angle X-ray Scattering for microstructure identification assessments; (iii) conducting rheological evaluations at various concentrations and temperatures to determine their effects on the surfactant properties.The findings reveal that SLE3S, being more polydisperse, demonstrates complex phase behavior not observed in the less polydisperse SLE1S. Notably, SLE3S exhibits a unique concentration domain, corresponding to a concentration of about 60 %wt, where hexagonal (H), cubic, and lamellar (Lα) phases coexist, resulting in highly viscoelastic heterogeneous mixtures. This behavior is attributed to the local segregation of surfactant components with varying polarity, underscoring the crucial role of molecular polydispersity in the phase behavior of SLES surfactants.

Quantum sensing with tunable superconducting qubits: optimization and speed-up

Abstract Sensing and metrology are crucial in both fundamental science and practical applications. They meet the constant demand for precise data, enabling more dependable assessments of theoretical models’ validity. Sensors, now a common feature in many fields, play a vital role in applications like gravity imaging, geology, navigation, security, timekeeping, spectroscopy, chemistry, magnetometry, healthcare, and medicine. The advancements in quantum technologies have sparked interest in employing quantum systems as sensors, offering enhanced capabilities and new possibilities. This article describes the optimization of the quantum-enhanced sensing
of magnetic fluxes with a Kitaev phase estimation algorithm based on frequency tunable transmon qubits. It provides the optimal flux biasing point for sensors with different qubit transition frequencies and gives an estimation of decoherence rates and achievable sensitivity. The use of 2- and 3-qubit entangled states are compared in simulation with the single-qubit case. The flux sensing accuracy reaches 10-8·Φ0 and scales inversely with time, which proves the speed-up of sensing with high ultimate accuracy.

Single-Step Control of Liquid-Liquid Crystalline Phase Separation by Depletion Gradients.

Fine-tuning nucleation and growth of colloidal liquid crystalline (LC) droplets, also known as tactoids, is highly desirable in both fundamental science and technological applications. However, the tactoid structure results from the trade-off between thermodynamics and nonequilibrium kinetics effects, and controlling liquid-liquid crystalline phase separation (LLCPS) in these systems is still a work in progress. Here, a single-step strategy is introduced to obtain a rich palette of morphologies for tactoids formed via nucleation and growth within an initially isotropic phase exposed to a gradient of depletants. The simultaneous appearance is shown of rich LC structures along the depleting potential gradient, where the position of each LC structure is correlated with the magnitude of the depleting potential. Changing the size (nanoparticles) or the nature (polymers) of the depleting agent provides additional, precise control over the resulting LC structures through a size-selective mechanism, where the depletant may be found both within and outside the LC droplets. The use of depletion gradients from depletants of varying sizes and nature offers a powerful toolbox for manipulation, templating, imaging, and understanding heterogeneous colloidal LC structures.

Customs services and ways to improve their quality in the context of digitalisation

This article is devoted to problems of the process of rendering services in the field of customs during digitalisation of the economy. The observed mechanism of rendering state customs services, as well as improving their quality, naturally affect the entire service sector and the development of the country’s economy as a whole. The main purposes of the article are to analyse the mechanism of rendering services in the field of customs and to search for effective methods of assessing their quality. The relevance of the article is determined by the need to improve the operations performed to be able to manage the quality of provided customs services. The main objective of this article is to propose possible ways to reduce time costs without losing the quality of customs control in the process of providing the services. The article used both theoretical (analysis of the current legislation) and empirical research methods (giving practical examples of improving the efficiency of customs operations and the quality of customs services). The results of the study are the following: development of sequential operations performed by customs authorities in the process of rendering services in the field of customs; proposal of possible criteria for assessing their quality; formulation of options for managing this quality.

Uncovering the molecular mechanism of Mume Fructus in treatment of Sjögren's syndrome.

Modern medicine has no cure for the xerostomia caused by the early onset of Sjögren's syndrome. Mume Fructus is a common Chinese herbal medicine used to relieve xerostomia. However, the molecular mechanisms of the effects of Mume Fructus are unknown. In this study, network pharmacology and molecular docking were used to investigate the mechanisms of action of Mume Fructus on Sjögren's syndrome. The Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform database was used to identify the active components and targets of Mume Fructus, and the UniProt database was used to identify the genes encoding these targets. SS-related targets were also identified from the GeneCards and OMIM databases. By finding the intersection of the targets of the compounds and the targets of Sjögren's syndrome, the predicted targets of Mume Fructus in the treatment of Sjögren's syndrome were obtained. Further investigation of the active compounds and their targets was carried out by constructing a network of "medicine-candidate compound-target-disease" using Cytoscape 3.7.2, the Protein-Protein Interaction network using the STRING database and Cytoscape 3.7.2, and key targets were identified by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis on R software. Finally, molecular docking was used to verify the affinity of the candidate compounds to the key targets. Quercetin, beta-sitosterol, and kaempferol in Mume Fructus interact with AKT1, IL-6, IL-1B, JUN, CASP3, and MAPK8. These results suggest that Mume Fructus exerts its therapeutic effects on the peripheral gland injury of Sjögren's syndrome and its secondary cardiovascular disease and tumorigenesis through anti-inflammatory, anti-oxidant, and anti-tumor pathways. With network pharmacology, this study systematically identified the main active components, targets, and specific mechanisms of the therapeutic effects of Mume Fructus on Sjögren's syndrome, providing both a theoretical basis and research direction for further investigations on Mume Fructus.

Stacking-dependent interlayer magnetic interactions in CrSe2.

Recently, CrSe2, a new ferromagnetic van der Waals two-dimensional material, was discovered to be highly stable under ambient conditions, making it an attractive candidate for fundamental research and potential device applications. Here, we study the interlayer interactions of bilayer CrSe2using first-principles calculations. We demonstrate that the interlayer interaction depends on the stacking structure. The AA and AB stackings exhibit antiferromagnetic (AFM) interlayer interactions, while the AC stacking exhibits ferromagnetic (FM) interlayer interaction. Furthermore, the interlayer interaction can be further tuned by tensile strain and charge doping. Specifically, under large tensile strain, most stacking structures exhibit FM interlayer interactions. Conversely, under heavy electron doping, all stacking structures exhibit AFM interlayer interactions. These findings are useful for designing spintronic devices based on CrSe2.

Large control of friction and wear enabled by Ti3AlC2 MAX- multilayer graphene-polydopamine composites

Friction and wear pose significant challenges in moving mechanical systems. Despite efforts to address these challenges with MAX phase materials, many of these materials lack effective lubrication and wear protection under ambient conditions. Here, we developed a composite coating that addresses these challenges through a combination of materials chemistry and engineering. This coating, composed of polydopamine-functionalized Ti3AlC2 MAX (F-MAX) and multilayer graphene (MGr), known as F-MAX + MGr, demonstrated exceptional tribological performance. At its best composition, the F-MAX + MGr composite coating reduced the friction at sliding interfaces by 82 % and decreased the wear on the counterpart ball by 99.76 % compared to bare surfaces. Importantly, its tribological performance surpassed that of pristine MAX, F-MAX, and MGr coatings. This improvement is attributed to the synergistic lubricating effect of the inherently low shear strengths of Ti3AlC2 MAX and MGr, the chemical properties of PDA, and the occurrence of incommensurate contacts at the interfaces. This work pioneers slippery and wear-resistant surfaces via a combination of chemical modification and materials engineering, with implications for both fundamental science and technological advancement.

Impact of Some Immunological Parameters (antioxidant – cytokines) in Cutaneous leishmaniasis in a Sample of Patients in the Al-Ramadi City.

Background: Cutaneous leishmaniasis is one of the endemic diseases in Iraq. Both types of cutaneous leishmaniasis that cause different ulcers are present, namely Leishmania major and Leishmania tropica, The disease also represents a major public and global health problem all over the world. Objective: Investigation of the relationship between parasitic infection with cutaneous leishmaniasis and some antioxidants Superoxide, Nitric oxide and immune cytokines tumor necrosis factor-alpha, Interferon-gamma. Materials and Methods: The demographic and epidemiological study included 55 cases suspected of being infected with cutaneous leishmaniasis. They visited Ramadi Teaching Hospital, with 25 volunteers. After obtaining their consent, they were used as control samples, where blood serum samples were obtained from both study groups. After that, work was done in laboratories. Department of Biology - College of Education for Pure Sciences - Anbar University. Results: The patients and healthy people were of different genders, and among the 55 samples from the infected, the number of males was 36 (65.5)% and females 19 (34.5)%, with statistically significant differences p<0.05, and the age groups of the patients were from one year to 60 years. With an average age of (31 years), they were distributed into 6 groups. Also, among the 25 samples from the control group, the number of males was 12 (48%) and females were 13 (52%), Their ages also ranged from one year to 60 years, with an average age of (13) years, the enzyme-linked immunoabsorbent assay (ELISA) technique was used to detect the level of immunological indicators TNF-α, IFN-γ, SOD, NO, where the results showed High levels in the serum of cutaneous leishmaniasis patients (120.00 ± 52.11, 123.00 ± 44.21, 3.10 ± 1.21 and 121.93 ± 33.22), respectively compared to healthy subjects (72.86 ± 14.94, 21.91 ± 45.40, 0.88 ± 0.12, and 81.46 ± 4.50 ) respectively With statistically significant differences at the level of p < 0.05, p < 0.001. Conclusions: The inflammatory cytokines TNF-α, IFN-γ play a vital role in increasing or decreasing the severity in the pathogenesis of the disease and eliminating it.

Assessing the impact of Medical Education's Innovation & Entrepreneurship Program in China

ObjectiveA growing number of clinical undergraduates are chosen to enter institutions for higher education biotechnology and industry workforce, though most need more laboratory experience training and business practice. Innovation and Entrepreneurship Program (I&E Program) can benefit from biological experiment and commercialization training largely absent from standard clinical medical educational curricula. Our study investigates the impact and status of the I&E Program in enhancing medical students’ research and entrepreneurial abilities and provides recommendations for improving this program.MethodsA cross-sectional study was applied by delivering a questionnaire to survey medical students from Central South University who participated in the I&E Program. The questionnaire consisted of three parts: basic information, the impact of the I&E Program on medical students’ research and entrepreneurial abilities, and attitudes and recommendations regarding the I&E Program.ResultsMany students participating in the I&E Program have received competition awards and improved their academic experience, article writing, and application patents. Their research-related abilities have been enhanced, including in-lab techniques, theoretical research skills, data analysis knowledge, clinical research skills, experimental research skills, entrepreneurship, data analysis ability, teamwork, and communication. While 73.93% of students express satisfaction with the I&E Program, there are still several areas of improvement, including more robust practical components, increased support, and enhanced teamwork.ConclusionThe scale of the I&E Program is rapidly expanding to address scientific research or business skills needed by college students in the new era. However, more programs still need to be discontinued during their further study. The I&E Program significantly enhances research abilities and fosters confidence in their study. This analysis emphasizes the importance of research-oriented and interdisciplinary education for students’ holistic development in medical schools compared with formal medical education.

Theoretical research of impact vibration of multi-section serial pipeline inspection gauge in large drop pipeline

When operating in large drop pipelines, pipeline inspection gauge may experience severe impact vibration at elbows, potentially leading to its failure. This paper focuses on serial pipeline inspection gauges with multiple sections in large drop pipelines, analyzes the force acting on the pipeline inspection gauge during the descent phase, and establishes a multi-body dynamics model of the gauge under pipe-soil coupling conditions. In addition, a correction formula is developed for the pressure changes in the medium at the front and rear of the pipeline inspection gauge. To solve the model, MSC/ADAMS and MATLAB/Simulink are used for the bi-directional fluid–structure-interaction joint simulation. Moreover, the results are compared with the pipeline inspection gauge motion model established by OLGA. The study investigates the dynamic responses, vibration superposition and laws of dynamic evolution at the upper and lower elbows of the large drop pipeline. The results show that the speed of the gauge increases suddenly during the descent in large drop sections and then stabilizes, with different effects of the fluid medium pressure difference at various stages. The vibration responses along the axial, horizontal radial, and vertical directions at the elbows vary, with the second section experiencing stronger vibrations due to superposition effects. Compared to fixed boundaries, the acceleration extremes of the gauge are lower under the constraints of pipe-soil model, indicating significant soil buffering and vibration damping effects.

The structure, magnetism and mechanical properties of L21-type full-Heusler alloy Cr2ZrSi: A first-principles study

Heusler alloy is a widely studied spintronic material in recent years, which has played a huge role in the field of spintronic devices due to its high spin polarization and high Curie temperature. Using first-principles calculation to predict the basic properties of Heusler alloy can not only save experimental costs and time but also provide a reliable theoretical basis for experimental research. This study used a first-principles calculation to study the magnetic and mechanical properties of full-Heusler alloy Cr2ZrSi with an L21-type structure. The research results indicate that the alloy is a half-metallic ferromagnetic material with a theoretical value of 100% spin polarization. The magnetism mainly comes from the asymmetric spin contribution of d-orbital electrons of transition metal atoms and their hybridization. At the same time, this complex hybridization coupling process is also a possible reason for the half-metallic band gaps. In terms of mechanical properties, the Cr2ZrSi alloy exhibits good ductility and anisotropy, with a Debye temperature of 303.848K. Our theoretical research results provide more choices and theoretical basis for subsequent experimental research.

Evaluation of T-stress in an infinite plate with double-crack under compression and shear

The T-stress at the crack tip under compression and shear has received more and more attention, but most of the theoretical researches have focused on single-crack, with little reported on the closed form solutions of T-stress at the double-crack or multi-crack tips. Therefore, the single-crack problem under compression and shear is first analyzed in this paper, the formulas for calculating the three components of T-stress (Tx, Ty and Txy) are obtained. According to the principle of superposition, the origins of the three components of T-stress are examined. Then the basic equations for solving the double-crack problems under compression and shear are established, leading to the formulas for calculating the three components of T-stress at the double-crack tips. Finally, the effects of the spacing between two cracks, the ratio of double-crack half-length, the dip angle of rock-bridge and the absolute angle between two cracks on the three components of T-stress are discussed. The results indicate that the Tx and Ty are unaffected by the friction on the crack surface, but the Txy is significantly correlated with it. Each component of T-stress at the inner and outer tips of double-crack is influenced by different geometrical factors and shows a different variation curve, which may be a potential factor contributing to the complexity of the double-crack or multi-crack problems under compression shear.

Christopher Tam: Brief history and accomplishments

This introduction provides a brief personal background and highlights the scientific accomplishments of Professor Christopher Tam. He has maintained extremely high standards of research and an enviable track record for productivity, spanning more than five decades. The depth and breadth of his technical output are truly breathtaking, and he has inspired scores of researchers and graduate students. When the first author was an Acoustics Engineer at Lockheed, Georgia, he started collaborating with Chris in the early 1990s. There were several joint projects when the author moved to Boeing, which encompassed both fundamental research and applications. The second author has an even longer association with Chris, initially as a PhD advisee in the late 1980s and then as a co-researcher. In this special volume we pay tribute to Chris’s many achievements, an endeavor that provides us with great satisfaction and which is long overdue.

Theoretical research on efficient electrocatalysis of CO2 reduction reaction by borophene loaded transition metals

Electrocatalytic conversion of CO2 into chemical or fuel is regarded as a viable approach to attain energy conversion, chemical energy storage and carbon neutrality. Borophene exhibits great potential as an electrocatalyst owing to its exceptional physical and chemical attributes. β12-borophene incorporated transition metal (TM) as single atom catalysts (SACs) have been devised for the electrocatalysis of the carbon dioxide reduction reaction (CO2RR). Through the exploration of the most favorable CO2RR pathway and the comparison of Gibbs free energy (ΔG) during the potential determination step (PDS), the catalyst exhibiting remarkable catalytic activity for CO2RR are chosen. Wherein, the overpotential of Nb-β12 and Ru-β12 produce CO is only 0.02 and 0.03 V. The overpotential of Ru-β12 and Rh-β12 in generation of HCOOH product is only 0.03 and 0.06 V. Additionally, the catalytic performance of Rh-β12 in CO2 reduction to CH3OH and CH4 showcases exceptional performance, with overpotential of 0.65 and 0.79 V. Unexpectedly, the overpotential of Cd-β12 and Mo-β12 are 0.01 and 0.09 V for hydrogen evolution reaction (HER). The research offers invaluable insight for systematic designs and screening of catalysts for the electrochemical CO2RR.

The influence of principals’ personal traits on leadership outcomes of change in Vietnamese secondary schools

This paper addresses the influence of personal traits on the leadership outcomes of change by principals in primary, lower secondary, and upper secondary levels in Vietnamese schools. The research employed a survey questionnaire method to collect data, which was processed using SPSS software version 22. The design of the practical study was carried out based on the literature review and theoretical research. The paper did not use the original research ideas of previous authors but made certain adjustments to align with the research objectives and context. Linear regression analysis was utilized, with six categories of personal traits as independent variables consisting of thirteen specific traits, and two dependent variables representing leadership outcomes, including teacher leadership outcomes and general leadership outcomes. The analysis results revealed that teacher leadership outcomes are negatively influenced by arrogance, dominance, authoritarian thinking, emotionality, and balanced thinking, and they are positively influenced by proactivity, adaptability and discipline, perfectionism, curiosity, and eagerness to learn. The initial study results provide a foundation for applying the role of school leaders’ personal traits in management, leadership, evaluation policies, and personnel appointments in schools today.

Incorporation of adaptive compression into a GPU parallel computing framework for analyzing large-scale vessel trajectories

Automatic Identification System (AIS) offers a wealth of vessel navigation data, which underpins research in maritime data mining, situational awareness, and knowledge discovery within the realm of intelligent transportation systems. The flourishing marine industry has prompted AIS satellites and base stations to generate massive amounts of vessel trajectory data, escalating both data storage and calculation costs. The conventional Douglas-Peucker (DP) algorithm used for trajectory compression sets a uniform threshold, which hampers effective compression. Additionally, compressing and accelerating the computation of large datasets poses a significant challenge in real-world applications. To address these limitations, this paper aims to develop a new Graphics Processing Unit (GPU) parallel computing and compression framework that enables the acceleration of the optimal threshold calculation for each trajectory automatically in maritime big data mining. It achieves this by incorporating a new Adaptive DP with Speed and Course (ADPSC) algorithm, which utilizes the dynamic navigation characteristics of different vessels. It can effectively solve the associated computational time cost concern when using the ADPSC algorithm to compress vast trajectory datasets in the real world. Additionally, this paper proposes a novel evaluation metric for assessing compression efficacy based on the Dynamic Time Warping (DTW) method. Comprehensive experiments encompass vessel trajectory datasets from three representative research areas: Tianjin Port, Chengshan Jiao Promontory, and Caofeidian Port. The experimental results demonstrate that 1) the newly developed ADPSC method outperforms in terms of compression, and 2) the designed GPU parallel computing framework can significantly shorten the compression time for extensive datasets. The GPU-accelerated compression methodology not only minimizes storage and transmission costs for data from both manned and unmanned vessels but also enhances data processing speed, supporting real-time decision-making. From a theoretical perspective, it provides the key to the puzzle of realizing the real-time anti-collision of manned and unmanned ships, particularly in complex waters. It hence makes significant contributions to maritime safety in the autonomous shipping era.

Mapping the application research on machine learning in the field of ionic liquids: A bibliometric analysis

The aim was to gain a deep understanding of the research status and application of machine learning in the field of ionic liquids, and to identify the research hotspots and frontiers. Co-occurrence analysis, co-citation analysis, key literature citation temporal analysis and emerging word analysis were used. The results show that the knowledge base of applying machine learning in the field of ionic liquids can be divided into three parts: fundamental properties and application research, thermodynamics and phase equilibrium research, and the combination of machine learning with computational chemistry methods. The research hotspots mainly include the prediction and optimization of properties, the prediction of phase behavior, and research on machine learning algorithms. The current research frontiers in applying machine learning in the field of ionic liquids include the prediction of ionic liquid performance, the structure-property relationships of ionic liquids, and the optimization and design of ionic liquid processes.

Empowering pro-environmental behavior in tourists through digital media: the influence of eco-guilt and empathy with nature.

In the digital economy era, leveraging digital media to foster tourists' pro-environmental behavioral intention (TPEBI) has become crucial in the field of sustainable tourism. While existing studies have mainly focused on the driving mechanism of TPEBI within physical tourism contexts, the correlation between digital media information sharing and TPEBI remains unclear. Our study employs the cognitive-affective-conative framework to construct a theoretical model, considering eco-guilt and empathy with nature as mediating variables. It aims to explore the influencing mechanism of destination environmental information sharing through digital media on TPEBI from a presence perspective. Thereby, two scenario experiments were designed: Study 1 examined the impact of different formats of destination environmental threat information presentation on digital media on the sense of presence, while Study 2 explored the influencing mechanism of presence on TPEBI based on the conclusions of Study 1. Results indicate that (1) vivid and visible presentation formats of destination environmental threat information on digital media enhance individuals' sense of presence; (2) sense of presence positively influences TPEBI; and (3) eco-guilt and empathy with nature mediate between presence and TPEBI. These findings not only contribute to theoretical and empirical research on digital media information sharing in sustainable tourism but also offer guidance for governments and tourism destinations to effectively stimulate TPEBI through digital media, achieve the sustainable development of destinations.