Strong Bonds Research Articles

Strong Lewis Electron-Pair Bonding in Vanadium Oxide for Ultra-fast and Long-term Stable Zn-ion Storage

Vanadium-based oxides typically show low electrical conductivity, high repulsion for Zn2+, and severe structure collapse problems, resulting in unsatisfied cathode performance for aqueous Zn-ion batteries (AZIBs). Herein, we propose an advanced structural optimization strategy to address the above issues by constructing strong Lewis electron-pair bonding in vanadium oxide through initial doping Ca and a subsequent in-situ electrochemical activation process. We prepared the precursor of Ca-doped and amorphous carbon-encapsulated V2O3 material (Ca0.17V2O3-x@C) and verified a phase transition into a layered V2O5-typed cathode during the activation process. Importantly, we find the initial-doped Ca and generated abundant oxygen vacancy defects are well restored in the phase-transformed crystal lattice. We reveal that band and bond structures of the phase-transformed cathode are optimized, exhibiting an improved electrical conductivity, optimal Zn2+ binding energy, ultra-low Zn-ion transport barrier, and considerably strong bonds of Ca-O and V-O, thereby realizing enhanced reaction kinetics and stability. The Ca0.17V2O3-x@C exhibits surprisingly high-rate performance (233 mAh g–1 at 40 A g–1) and excellent cycling stability (10,000 cycles with 82% retention at 20 A g–1). This work offers a novel and simple band and bond structure engineering strategy for preparing high-performance phase transformation typed vanadium oxide cathodes for AZIBs.

Functional composite films incorporating triphala-derived carbon dots for extending chicken preservation

Triphala-based carbon dots (T-CDs) were successfully prepared using a simple one-step hydrothermal method. T-CDs were characterized by absorbance, fluorescence, Fourier-transform infrared, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. T-CDs showed bright blue fluorescence at 434 nm upon excitation at 360 nm. Functional composite films were prepared using poly(vinyl alcohol) and gelatin mixture by incorporating T-CDs and applied as a packaging film to extend the shelf life of chicken. The antibacterial activity of T-CDs against Listeria monocytogenes and Staphylococcus aureus was evaluated using well diffusion and colony count methods. T-CDs were evenly dispersed throughout the PVA/Gel solution to form a dense and uninterrupted film. They also formed strong bonds with polymer chains, which improved the tensile strength of the film from 32.44 to 42.70 MPa. Furthermore, the presence of T-CDs significantly enhanced the UV-blocking ability of the PVA/Gel films, achieving 99.7 % for UV-B and 97.2 % for UV-A. In addition, the PVA/Gel/T-CDs composite films showed excellent antioxidant, antimicrobial and UV-barrier properties, extending the shelf life of chicken. Therefore, the PVA/Gel/T-CDs composite films showed great potential as an active food packaging material to extend the shelf life and preserve the visual quality of packaged meat.

Late-stage Functionalization using a Popular Titrating Agent: Aryl-Chlorides and -Fluorides Activation by the Diphenylacetic Acid Dianion.

Aryl-chlorides and -fluorides are common building blocks, but their use in synthesis is limited by the high stability of their Ar-X bonds. The generation of aryl radicals via activation of strong Ar-X bonds is possible through the irradiation of tailor-made organic anions, which become reductants stronger than lithium metal. We report that the combination of visible light with the cheap diphenylacetic acid dianion is an even better tool, showing excellent activity across a variety of complex substrates and providing opportunities for late-stage drug modification. Ar-X bonds are chemoselectively activated in the presence of more easily reducible functions, such as Alk-Cl ones and carbonyl groups. These results pave the way to original synthetic strategies that would be otherwise considered impossible.

Effect of ultrasound on the physicochemical, mechanical and adhesive properties of micro-arc oxidized coatings on Ti13Nb13Zr bio-alloy

Implant surgeries are increasingly challenging due to their rising number. Achieving the desired biomaterial surface properties to ensure a strong bond with human tissue is a significant issue. This study investigates the influence of ultrasound (US) during the micro-arc oxidation (MAO) process on Ti13Zr13Nb bio-alloy, an area not previously explored, to enhance titanium alloy coatings’ properties for biomedical applications. Porous calcium-phosphate-based coatings were successfully deposited on Ti13Zr13Nb using MAO and ultrasound micro-arc oxidation (UMAO). Various properties such as morphology, chemical composition, topography, wettability, surface free energy, thickness, adhesion to the substrate, as well as mechanical and corrosion characteristics were thoroughly analyzed. Cytocompatibility was assessed using human osteoblasts. Using US during the MAO process increased coating roughness (up to ~ 17%), core height (up to 22%), isotropy (up to 17%), thickness (up to ~ 46%), and hardness (up to ~ 18%), depending on MAO parameters and US mode. Optimal coating performance was achieved at 136 mA, 600 s, and a sinusoidal US setting, resulting in the highest isotropy (~ 79%) and rutile quantity (2.6%), the lowest elastic modulus (~ 57 GPa), and the contact angle of ~ 70°, all of which could have contributed to enhancing osteoblast viability in vitro. This study, for the first time, underscores the importance of using the US during the MAO in tailoring the Ti13Zr13Nb for specific biomedical applications.

Effect of Rare Earth Ce on Structure and Properties in 7CrSiMnMoV Die Steel Castings

In this study, rare earth (RE) Ce is used to modify the interaction between atoms in 7CrSiMnMoV die steel castings. The tensile properties are performed, and strengthening mechanism are analyzed by investigated fracture surface, and microstructure by optical microscopy (OM) and scanning electron microscope‐energy dispersive spectrometer (SEM‐EDS). And ab initio molecular dynamics (AIMD) is used to simulate the effect of the Ce element on the local atomic structure of the FeCeC system alloy steel. The results indicate the strength can increase from 722.55 to 1074.27 MPa, and the elongation can increase from 24.86% to 44.22% with a RE Ce concentration of 0.009%. It is attributed to that doping of Ce can inhibit the formation of network eutectic cementite, refine the lamellar spacing of pearlite, and even form granular cementite and martensite structures. AIMD simulation results show that C atoms tend to be surrounded by Fe, and the strong chemical bonds of FeC make the Fe‐centered C more stable with an increase in RE Ce concentration. And doping Ce can introduce new local topological and chemical orderings such that the FeCFe triplets predominantly form small and big angles shifting from near 75° and 136° to 47° and 81°, respectively.

Tailoring the Mechanical Properties and Foaming Behaviors of PLA/P4HB Blends by Using P4HB‐g‐GMA as Compatibilizer

ABSTRACTSynthetic poly(4‐hydroxybutyrate) (P4HB), a flexible and biodegradable polymer, shows great promise in improving the toughness of poly(lactic acid) (PLA), but the inherent immiscibility of PLA and P4HB compromises the toughening efficiency. To address this issue, P4HB grafted glycidyl methacrylate (P4HB‐g‐GMA) is synthesized for the purpose of enhancing the compatibility within the PLA/P4HB blend. The epoxy groups on P4HB‐g‐GMA can form strong chemical bonds with PLA chains and remain compatible with P4HB. Rheological data confirm that adding P4HB‐g‐GMA enhances polymer chain entanglement. Therefore, the phase interface of the blend becomes more diffuse, leading to improved mechanical performance. Specifically, a 3D‐printed PLA/P4HB/P4HB‐g‐GMA blend containing 8% P4HB‐g‐GMA (PLA/P4HB/G8) achieves an elongation at break of 161.5%, approximately 22.7 times higher than that of a PLA/P4HB blend without the modifier. Moreover, the PLA/P4HB/G8 blends show a higher volume expansion ratio (VER) and better cell morphology due to the increased melt strength from P4HB‐g‐GMA. This study demonstrates a simple and efficient method to improve the compatibility between PLA and P4HB, resulting in superior mechanical performance of PLA/P4HB blends and broadening their potential applications in foaming.

Predicting potential hard materials in Nb[sbnd]B ternary boride: First-principles calculations

To identify potential superhard materials, we conducted a comprehensive theoretical investigation of the thermodynamic and kinetic stability, mechanical properties, electronic structure, Debye temperatures and melting point of sixteen ternary transition metal borides NbTMBx (x = 1, 2, 4 and TM = Ti, V, Fe, Co, Ni, Zr, Ru, Hf, W, Os) using first-principles methods. Our findings indicate that, with the exception of NbFeB, NbRuB, and NbWB, all other borides exhibit both thermodynamic and kinetic stability. Notably, NbTiB4, NbVB4, NbZrB4 and NbHfB4 demonstrate superior hardness and enhanced resistance to deformation, with NbTiB4 showing an impressive hardness value of 40.84 GPa, positioning it as a promising candidate for superhard materials. Both NbVB4 and NbTiB4 have very high Debye temperatures and melting points and can be used in high temperature environments. We further explored the mechanical properties of NbTiB4 at elevated temperatures by employing a combination of first-principles and quasi-static methods. Our analysis reveals that the elastic constants and moduli of NbTiB4 decrease with increasing temperature. Additionally, bonding analysis indicates that all NbB ternary borides exhibit hybridization involving metallic, ionic, and covalent interactions, resulting in the formation of exceptionally strong covalent bonds between boron atoms.

Electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds: the case of Pd2MnTi

Abstract In this study, taking Pd2MnTi as a representative example, the electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds was systematically studied and revealed theoretically. The calculation and theoretical analysis suggest that Pd2MnTi is not stable in cubic structure and prones to transform to low-symmetric tetragonal structure. By tetragonal deformation, the shrinkage of lattice parameters and the decrease of symmetry promote the electron accumulation between Pd and its first nearest neighboring Ti atom, resulting in the increased covalent hybridization. The occurrence of pesudogap in density of states (DOSs) of tetragonal Pd2MnTi near the Fermi level also verifies the enhancement of covalent bond. Comparatively, the stronger interatomic bond in tetragonal Pd2MnTi, i.e., covalent bond here, would strengthen interatomic coupling and consequently lower the energy of the material. By the martensitic phase transition, more stable state in energy was achieved. Thus, based on the analysis of electronic structure evolution, the nature of martensitic phase transition is a process wherein symmetry breaking weakens the original weak chemical bonds in high-symmetric parent phase and induces the strong chemical bond to lower the energy of the materials and achieve a more stable state. This study could help to deepen the understanding of martensitic phase transition and the exploration of novel materials for potential technical applications.

Between deep comradeship and nationalism: The social dynamics of solidarity on the battlefield

AbstractThis article explores the social mechanisms that facilitate the transformation of micro‐level bonds into coherent nationalist narratives of solidarity. The aim is to explain the paradox: while the armed forces are highly nationalist institutions, most ordinary combatants detest nationalist rhetoric on the battlefield. Drawing on the interviews with the combatants who fought in the 1991–1995 wars in Croatia and Bosnia and Herzegovina together with the analysis of the mass media reports, I examine how deep bonds of micro‐solidarity forged in the violent experiences are transformed into coherent nationalist discourses. I explore how social ties generated in the protracted face‐to‐face interactions can be enveloped by the specific social organisations and then ‘translated’ into nationalist ideologies that project deep comradeship as ‘national solidarities’. I aim to show that the direct war experience does not automatically generate strong bonds of national solidarity. Instead, nationalism is always a product of protracted coercive‐organisational, ideological and micro‐interactional work.

Dual metal centers within a water-stable Co/Ni bimetallic metal-triazolate framework contribute to durable photocatalysis for water treatment.

Bimetallic metal-organic frameworks (MOFs) have been studied extensively in various fields, including photocatalytic and electrocatalytic applications. The enhanced catalytic activity is typically attributed to the synergistic effect of the two metals, often without further explanation. Here, we demonstrate a CoNi-bimetallic triazolate MOF with fixed metal occupancy within the MOF's secondary building unit. Due to the difference in electronegativity and so on, the charge redistribution between the two metal centers could be responsible for the enhanced photocatalytic activity. In addition, the metal(II)-triazolate MOFs we synthesized exhibit unique metal-N coordination and a strong bond between the metal center and triazole ring. Therefore, their crystal structure and high porosity are highly retained even after exposure to humid environments for several months or stirring in water for several days. Overall, the CoNi-bimetallic triazolate MOF combines the excellent water stability and high surface area of its two monometallic counterparts. It can be further tailored to yield the highest colloidal stability during photocatalytic water treatment. As a result, the dual metal centers within the bimetallic MOF, combined with boosted colloidal stability, demonstrate the highest reactive oxygen species generation and promising antibacterial performance compared to their Ni- or Co-based counterparts. These findings shed light on the future design of robust MOF-based photocatalysts, particularly bimetallic ones.

Crystallographic Evidence for Bi(I) as the Heaviest Halogen Bond Acceptor.

Complexation of the green bismuthinidene (RBi) with two equivalents of a highly fluorinated aryl iodide at low temperature allows the crystallographic identification of an unstable red species that can be regarded as an intermediate in an overall Bi(I) → Bi(III) oxidation process. Both C-I bonds are orientated toward the filled 6p orbital of bismuth (Bi-I distances 3.44-3.52 Å), leading to an elongation of the C-I bonds by 0.05 and 0.07 Å. Density functional theory (DFT) calculations confirm that the Bi(I) center is indeed acting as an electron donor, establishing two strong and directional halogen bonds. The color change from green to red upon halogen bond formation is a consequence of the energetic stabilization of a Bi(I) lone pair by interactions with the sigma-holes of the halogen bond donors. Overall, this study presents the first structural proof of bismuth, and more generally of heavy organopnictogen(I) compounds, acting as halogen bond acceptors.

Permeable void-free interface for all-solid-state alkali-ion polymer batteries.

All-solid-state batteries suffer from a loss of contact between the electrode and electrolyte particles, leading to poor cyclability. Here, a void-free ion-permeable interface between the solid-state polymer electrolyte and electrode is constructed in situ during cycling using charge/discharge voltage as the stimulus. During the charge-discharge, the permeation phase fills the voids at the interface and penetrates the electrode, forming strong bonds with the cathode and effectively mitigating the contact problem. Our all-solid-state potassium ion polymer batteries maintain high Coulombic efficiency more than 2000 cycles at a high operating voltage of 4.5 volt and stably cycle more than 500 cycles even at 4.6 volt. Our rational design for mitigating the contact problem is versatile, as demonstrated by the scalability of all-solid-state graphite-based polymer potassium-ion pouch cells and all-solid-state lithium-ion polymer batteries.

Roles of ESIPT and TICT in the Photophysical Process of a Ratiometric Fluorescence Sensor for Al3.

Precise detection of Al3+ with the aid of a fluorescence sensor is of fundamental importance in the fields of water pollution control and food safety. A comprehensive understanding of the photophysical process of the sensor as well as its underlying detection mechanism is a precondition for the design of highly efficient sensors. This contribution performs a thorough investigation of the ratiometric fluorescence sensing mechanism of an Al3+ sensor with the aid of density functional theory and time-dependent density functional theory. Two excited-state intramolecular proton transfer (ESIPT) processes are observed on the S1 state potential energy surface, which leads to emission around 565 nm. A twisted intramolecular charge transfer state is observed after one of the ESIPT processes via cis-trans isomerization of the C═N bond. However, the large energy barrier hinders its occurrence, which is quite unusual. Al3+ is found to form three strong coordination bonds with the sensor, which eliminates ESIPT processes and induces a significant blue shift of the emission spectrum to 480 nm. The origination of the sensor's selectivity is also uncovered by investigating the interaction between the sensor and interfering metal ions.

Study on the adhesive property of sludge-modified magnesium phosphate cement reinforcement coating for steel bars

The synergistic interaction inreinforced concrete systems originates from the strong bond between steel reinforcement and concrete, enabling them to collaborateunder load and optimize structural performance. This study applied various sludge-modified magnesium phosphate cement mixtures to the surfaces of plain round steel bars and ribbed steel bars to prepare steel-reinforced concrete specimens. The characterization of the bond performance of the sludge-modified magnesium phosphate cement reinforcement coating for steel bars and concrete was achieved through analyzing the failure modes, bond strength, and slip values of different groups. Microscopic analysis was performed using a scanning electron microscope. The results revealed that the primary failure mode of the steel-reinforced concrete specimens was steel bar pull-out, with some specimens exhibiting concrete splitting failure. Coating application on plain round steel bars increased bond strength, while on ribbed steel bars, it decreased bond strength. The application of the coating slightly reduced slip values to some extent.

Eating Problems in Young Adults: The Role of Unbalanced Family Cohesion and Difficulties in Emotion Regulation

Strong emotional bonds with the family often result in many positive consequences for human functioning, including emotional regulation and eating patterns. The study aimed to determine the relationship between unbalanced family cohesion, emotion regulation, and eating problems in young adults. A correlation research design was used with a non-probability purposive sampling technique to recruit a sample consisting of 300 university students, 50% men and 50% women, with an age range from 18 to 25 years ( M = 21.60, SD = 1.95) from the four universities of Lahore. Demographic performa, Family Cohesion Scale (FCS), Difficulties in Emotion Regulation Scale (DERS), and Eating Problem Scale (EPS) were used to explore the study variables. Data was analyzed using SPSS 21. Pearson product-moment correlation indicated a significant positive relationship between unbalanced family cohesion, difficulties in emotion regulation, and eating problems. It also revealed that a positive relationship was found among unbalanced family cohesion, difficulties in emotion regulation, and eating problems in young adults. Mediation analysis shows that emotion regulation fully mediates the relationship between unbalanced family cohesion and eating problems in young adults. The findings will help students and family counselors identify risk factors of eating problems and its impact on their transition into marriage life. They will contribute to a deeper understanding of unbalanced family dynamics, difficulties in emotion regulation, and eating problems.

Local and Symmetry-Resolved Electronic Structure of Liquid Dimethyl Sulfoxide from Resonant Inelastic Soft X-ray Scattering.

Dimethyl sulfoxide (DMSO) is an important polar solvent that derives its unique properties from the lone pair and the strong polar bond at the sulfinyl functional group. To derive the local and symmetry-resolved electronic structure of liquid DMSO, we have used resonant inelastic soft X-ray scattering (RIXS) maps at the S L2,3, C K, and O K edges. The experimental data are compared to calculations of spectra based on density functional theory, which allows a detailed analysis of the molecular orbitals throughout the molecule. In the RIXS maps, we find the signature of molecular-field splitting of the S 2p core levels, vibronic coupling, and ultrafast nuclear dynamics on the time scale of the RIXS process.

Controllable structure, super adhesion, multifunctional, conductive pressure-sensitive adhesive for electronic skin: Enhancing cohesion by cellulose-derived covalent crosslinking

Ensuring firm adhesion to the skin is essential for improving the detection of temperature and movement signals in electronic skin (E-skin). Self-adhesive eutectogel, an ideal material for E-skin, could act as an innovative pressure-sensitive adhesives (PSAs) that can be easily applied through simple pressing without requiring heating or irradiation. Herein, we synthesized a cellulose-derived polymer crosslinking agent (MCCAC) to create a eutectogel-based conductive PSA (CPSA). The MCCAC formed strong covalent bonds with polymer chains, significantly enhancing the cohesion of the CPSAs. As a result, the CPSAs exhibited high tensile lap-shear strength (99.5 kPa) among self-adhesive eutectogels. Unlike the construction of double-network structures, this method included a straightforward chemical reaction and a cohesion-enhancing strategy, and could adjust crosslinking density by changing the MCCAC content. The preparation process was simple, and the products were controllable. More importantly, this cohesion-enhancing strategy did not compromise the fluidity of polymer chains, which ensured that CPSAs maintain effective interfacial adhesion to adhere on skin, offering exceptional capabilities for capturing body temperature signals (−3.66 %/℃) as well as applications in motion detection and information transmission. This work resolved the cohesion and interfacial adhesion imbalances observed in previous self-adhesive eutectogels and provided a promising approach for designing the novel cellulose-reinforced CPSA for E-skins.

Comparative evaluation of the strength of adhesion by push-out bond strength tests on endodontic posts cemented with different resinous types of luting cements: An in vitro study

INTRODUCTION. Endodontic posts play a vital role in strengthening debilitated teeth. They are luted into the radicular space using dental cements that are generally resinous. Given that the forces faced by human teeth are loading in nature and the stresses are accumulative, the bond strength of the interfaces at both the radicular dentin and luting agent and the endodontic post and the luting agent needs to be evaluated. Micro pushout bond strength (POBS) testing is done to determine these strengths. This experimental, in vitro study evaluated the adhesion strength of endodontic posts cemented with different resin-based luting agents using micro-POBS.MATERIALS AND METHODS. A total of 30 human lower incisors were selected and divided into three groups (n=10), based on the type of adhesive resin cement used for luting. Prefabricated endodontic fiber posts were inserted into the root canals of each tooth, and different resin types of cement – Estecem II, Multilink Automix, and Relyx Ultimate. were used to cement the fiber posts. The micro-POBS test measured the bond strength of the cemented pins to the root canal dentin.RESULTS. The results showed that the mean POBS of Group B was higher than that of Group A and Group C. The difference between the mean POBSs of Group A and Group C was not statistically significant (p>0.05).CONCLUSION. The resin adhesive cement used can affect the POBS of endodontic posts to root canal dentin. Clinicians should choose the appropriate resin cement for cementing endodontic posts to ensure a strong and durable bond for a good clinical prognosis.

Alternative fixation mechanisms for complete removable dentures: a literature review and pilot study

Adhesives for removable dentures are specialized alternative products designed to enhance the retention of dentures. They help prevent dentures from shifting, ensuring comfortable and secure wear. Adhesives come in various forms, such as creams, powders, pads, strips, and gels. Creams and gels are applied to the inner surface of the denture, creating a strong bond with the gums, while powders provide a thin layer of fixation. Pads and strips can be conveniently attached to the denture, distributing the fixation evenly. Choosing the right adhesive is important for ensuring comfort and preventing possible allergic reactions. Regular cleaning of dentures and proper use of adhesives contribute to oral health and the longevity of the dentures. This literature review presents contemporary aspects and developments in materials aimed at improving the quality of retention for removable dentures.

Determinants of Nyumba Kumi Community Policing Initiative on Maintenance of Law and Order in Migori County, Kenya

Purpose: The study sought to determine the key factors influencing the success or failure of the Nyumba Kumi initiative in maintaining law and order within Suna West Sub-County, Migori County, Kenya. More specifically, it set out to explore how community awareness, collaboration with law enforcers, technology in use, and information sharing influence the success of this community policing endeavor. The study further points out difficulties inhibiting the success of this initiative, such as frayed relations between the community and police force, mistrust, and issues related to personal vendettas, which have undermined the initiative's goal of reducing insecurity. Methodology: This study utilized a descriptive cross-sectional research type to investigate the extent to which selected associated factors affected the implementation of the Nyumba Kumi initiative in Suna West Sub-County. Local community members, Nyumba Kumi leaders, and local administration officials were interviewed using structured questionnaires. A total sample of 210 respondents was represented from all key stakeholder groups using a stratified random sampling technique. Statistical analyses were performed to summarize variables of interest with the help of descriptive statistics like means, and standard deviations (SD) using SPSS version 26. The study also used inferential statistics (Pearson product-moment correlation) to examine the relationships between variables. Findings were tabulated and graphically displayed for trends and comparisons between indicators. Findings: The study achieved a high response rate, highlighting strong positive relationships between the maintenance of law and order and several key factors. Significant associations were found with community awareness (r = 0.759, p < 0.001), collaboration with law enforcement (r = 0.793, p < 0.001), technology use (r = 0.450, p < 0.001), and information sharing (r = 0.673, p < 0.001), all of which contributed to enhanced security in Suna West sub-county, Migori County. These findings indicate that the Nyumba Kumi initiative thrives on increased community awareness, effective collaboration with security agencies, and the integration of technology. Despite challenges such as strained relationships between community members and law enforcement, the initiative has led to reduced crime rates, quicker emergency response times, and more peaceful conflict resolution in the area. Unique Contribution to Theory, Practice and Policy: The study reinforces key theories related to community policing. It supports Collective Efficacy Theory by demonstrating how communities contribute to law and order through informal support and social control. It also bolsters Social Cohesion Theory, emphasizing the significance of strong social bonds for effective community policing. Furthermore, it validates social cognitive theory by illustrating how observational learning and social interactions influence community behavior in security initiatives. From a practical standpoint, the study recommends enhancing community training, fostering collaboration with law enforcement, integrating technologies such as mobile applications and GIS, and improving information sharing. These strategies serve as a practical framework for strengthening grassroots security efforts and enhancing the effectiveness of community policing within the Nyumba Kumi initiatives. Additionally, the study offers valuable policy recommendations that advocate for supporting community training, encouraging collaboration with law enforcement, promoting technology use, and enhancing information sharing. Implementing these policies would significantly improve community policing outcomes by facilitating better cooperation between communities and law enforcement agencies.