Surface Topology Research Articles

Involutions, links, and Floer cohomologies

AbstractWe develop a version of Seiberg–Witten Floer cohomology/homotopy type for a 4‐manifold with boundary and with an involution that reverses the structure, as well as a version of Floer cohomology/homotopy type for oriented links with nonzero determinant. This framework generalizes the previous work of the authors regarding Floer homotopy type for spin 3‐manifolds with involutions and for knots. Based on this Floer cohomological setting, we prove Frøyshov‐type inequalities that relate topological quantities of 4‐manifolds with certain equivariant homology cobordism invariants. The inequalities and homology cobordism invariants have applications to the topology of unoriented surfaces, the Nielsen realization problem for nonspin 4‐manifolds, and nonsmoothable unoriented surfaces in 4‐manifolds.

Topology of Isoenergy Surfaces of Billiard Books Glued of Annuli

Topology of Isoenergy Surfaces of Billiard Books Glued of Annuli

In vivo mechanical response of thigh soft tissues under compression: A two-layer model allows an improved representation of the local tissue kinematics

Biomechanical parameters have the potential to be used as physical markers for prevention and diagnosis. Finite Element Analysis (FEA) is a widely used tool to evaluate these parameters in vivo. However, the development of clinically relevant FEA requires personalisation of the geometry, boundary conditions, and constitutive parameters. This contribution focuses on the characterisation of mechanical properties in vivo which remains a significant challenge for the community. The aim of this retrospective study is to evaluate the sensitivity of the computed elastic parameters (shear modulus of fat and muscle tissues) derived by inverse analysis as a function of the geometrical modelling assumption (homogenised monolayer vs bilayer) and the formulation of the cost function. The methodology presented here proposes to extract the experimental force-displacement response for each tissue layer (muscle and fat) and construct the associated Finite Element Model for each volunteer, based on data previously collected in our group (N = 7 volunteers) as reported in (Fougeron et al., 2020). The sensitivity analysis indicates that the choice of the cost function has minimal impact on the topology of the response surface in the parametric space. Each surface displays a valley of parameters that minimises the cost function. The constitutive properties of the thigh (reported as median ± interquartile range) were determined to be (μ=198±322Pa,α=37) for the monolayer and (μmuscle=1675±1127Pa,αmuscle=22±14,μfat=537±1131Pa,αfat=32±7) for the bilayer. A comparison of the homogenised monolayer and bilayer models showed that adding a layer reduces the error on the local force displacement curves, increasing the accuracy of the local kinematics of soft tissues during indentation. This allows for an increased understanding of load transmission in soft tissue. The comparison of the two models in terms of strains indicates that the modelling choice significantly influences the localization of maximal compressive strains. These results support the idea that the biomechanical community should conduct further work to develop reliable methodologies for estimating in vivo strain in soft tissue.

Biomimetic-inspired piezoelectric ovalbumin/BaTiO3 scaffolds synergizing with anisotropic topology for modulating Schwann cell and DRG behavior

The treatment of peripheral nerve injury is a clinical challenge that tremendously affected the patients' health and life. Anisotropic topographies and electric cues can simulate the regenerative microenvironment of nerve from physical and biological aspects, which show promising application in nerve regeneration. However, most studies just unilaterally emphasize the effect of sole topological- or electric- cue on nerve regeneration, while rarely considering the synergistic function of both cues simultaneously. In this study, a biomimetic-inspired piezoelectric topological ovalbumin/BaTiO3 scaffold that can provide non-invasive electrical stimulation in situ was constructed by combining piezoelectric BaTiO3 nanoparticles and surface microtopography. The results showed that the incorporation of piezoelectric nanoparticles could improve the mechanical properties of the scaffolds, and the piezoelectric output of the scaffolds after polarization was significantly increased. Biological evaluation revealed that the piezoelectric topological scaffolds could regulate the orientation growth of SCs, promote axon elongation of DRG, and upregulate the genes expression referring to myelination and axon growth, thus rapidly integrated chemical-mechanical signals and transmitted them for effectively promoting neuronal myelination, which was closely related to peripheral neurogenesis. The study suggests that the anisotropic surface topology combined with non-invasive electronic stimulation of the ovalbumin/BaTiO3 scaffolds possess a promising application prospect in the repair and regeneration of peripheral nerve injury.

Insights into the Mechanism of Catalytic Activity of Plasmodium Parasite Malate-Quinone Oxidoreductase.

Plasmodium malate-quinone oxidoreductase (MQO) is a membrane flavoprotein catalyzing the oxidation of malate to oxaloacetate and the reduction of quinone to quinol. Recently, using a yeast expression system, we demonstrated that MQO, expressed in place of mitochondrial malate dehydrogenase (MDH), contributes to the TCA cycle and the electron transport chain in mitochondria, making MQO attractive as a promising drug target in Plasmodium malaria parasites, which lack mitochondrial MDH. However, there is little information on the structure of MQO and its catalytic mechanism, information that will be required to develop novel drugs. Here, we investigated the catalytic site of P. falciparum MQO (PfMQO) using our yeast expression system. We generated a model structure for PfMQO with the AI tool AlphaFold and used protein footprinting by acetylation with acetic anhydride to analyze the surface topology of the model, confirming the computational prediction to be reasonably accurate. Moreover, a putative catalytic site, which includes a possible flavin-binding site, was identified by this combination of protein footprinting and structural prediction model. This active site was analyzed by site-directed mutagenesis. By measuring enzyme activity and protein expression levels in the PfMQO mutants, we showed that several residues at the active site are essential for enzyme function. In addition, a single substitution mutation near the catalytic site resulted in enhanced sensitivity to ferulenol, an inhibitor of PfMQO that competes with malate for binding to the enzyme. This strongly supports the notion that the substrate binds to the proposed catalytic site. Then, the location of the catalytic site was demonstrated by structural comparison with a homologous enzyme. Finally, we used our results to propose a mechanism for the catalytic activity of MQO by reference to the mechanism of action of structurally or functionally homologous enzymes.

Bioinspired Plateau–Rayleigh Instability on Fibers: From Droplets Manipulation to Continuous Liquid Films

AbstractThe Plateau–Rayleigh instability (PRI) of a liquid column, which always spontaneously breaks into droplets to minimize surface energy, underlies a variety of fascinating phenomena in daily life and industrial applications. Different from the free liquid column, the evolution of the liquid film on a fiber involves solid‐liquid interfaces which allow for regulating the PRI. Recently, natural fibers with certain topologies have witnessed various dynamic liquid behaviors from droplet manipulation to continuous liquid films. Tailoring the topology of local curved liquid film by the structural‐confinement is the key to manipulating liquids, where the asymmetric Laplace pressure generated by the asymmetric/non‐spherical liquid film promotes the liquid motion. In nature, the spider silk collects droplets efficiently by the spindle‐knot structure; while the mulberry silk enables a smooth surface‐coating on dual‐parallel fibers. Drawing inspirations, many artificial structured fibers are developed to precisely regulate liquid behaviors in the form of either separated droplets or continuous liquid films, which have demonstrated applications as fluidic coating, micro‐patterning, and materials fabrication. Here, recent research progress on bioinspired fibrous PRI from the viewpoints of tailoring the Laplace pressure by rationally designing the surface topology, which offers inspiration for liquid manipulation using open fibrous media, is reviewed.

Surface Topology of Redox- and Thermoresponsive Nanogel Droplets.

Hydrogels are usually depicted as a homogenous polymer block with a distinct surface. While defects in the polymer structure are looked into frequently, structural irregularities on the hydrogel surface are often neglected. In this work, thin hydrogel layers of ≈100nm thickness (nanogels) are synthesized and characterized for their structural irregularities, as they represent the surface of macrogels. The nanogels contain a main-chain responsiveness (thermo responsive) and a responsiveness in the cross-linking points (redox responsive). By combining data from ellipsometry using box-model and two-segment-model analysis, as well as atomic force microscopy, a more defined model of the nanogel surface can be developed. Starting with a more densely cross-linked network at the silica wafer surface, the density of cross-linking gradually decreases toward the hydrogel-solvent interface. Thermo-responsive behavior of the main chain affects the entire network equally as all chain segments change solubility. Cross-linker-based redox-responsiveness, on the other hand, is only governed by the inner, more cross-linked layers of the network. Such dual responsive nanogels hence allow for developing a more detailed model of a hydrogel surface from free radical polymerization. It provides a better understanding of structural defects in hydrogels and how they are affected by responsive functionalities.

Application of magnetism in tissue regeneration: Recent progress and future prospects

Abstract Tissue regeneration is a hot topic in the field of biomedical research in this century. Material composition, surface topology, light, ultrasonic, electric field and magnetic fields (MFs) all have important effects on the regeneration process. Among them, MFs can provide nearly non-invasive signal transmission within biological tissues, and magnetic materials can convert MFs into a series of signals related to biological processes, such as mechanical force, magnetic heat, drug release, etc By adjusting the MFs and magnetic materials, desired cellular or molecular-level responses can be achieved to promote better tissue regeneration. This review summarizes the definition, classification, and latest progress of MFs and magnetic materials in tissue engineering. It also explores the differences and potential applications of MFs in different tissue cells, aiming to connect the applications of magnetism in various subfields of tissue engineering and provide new insights for the use of magnetism in tissue regeneration.

Theoretical Investigation of Mechanical and Electronic Properties of Hexagonal BaB2

A comprehensive investigation of the electronic and mechanical properties in the hexagonal BaB2 binary system using state of the art first-principles computational techniques is critical for an in-depth understanding of the fundamental properties unique to this binary system. In this context, we derived elastic constants using the metric-tensor formulation, which allowed us to find important mechanical properties such as Bulk Modulus, Shear Modulus, and Vickers's hardness which are fundamental mechanical quantities. Also, this research includes a detailed analysis of the electronic band structures and a study comparison of Fermi surface topologies. The charge density at the Fermi level (N(EF)), which is very important in superconductivity theories, was found to be 1.43 states/eV.uc. Furthermore, we have explored whether there exists a close relationship between these properties and the superconducting behavior of the BaB2 material. Nevertheless, our calculations unequivocally demonstrate that the information derived from electronic band structures and Fermi surfaces alone is insufficient for a comprehensive explanation of the superconductivity phenomenon observed in such materials.

Study of Microstructure, Texture, and Cooking Qualities of Reformulated Whole Wheat Flour Pasta by Substituting Water with Stearic Acid–Candelilla Wax–Groundnut Oil Oleogel

Oleogels, which are traditionally utilized to reduce saturated and trans fats in bakery foods, have recently shown promising applications in non-bakery foods, particularly in the enhancement of their food texture and cooking qualities. This study investigates the impact of incorporating stearic acid-containing candelilla wax–groundnut oil oleogel in various proportions on the production of whole wheat pasta. Five different pasta samples were prepared by replacing water with oleogels in varying concentrations (2.5%, 5%, 10%, and 15%), and their physicochemical attributes were evaluated using a range of analytical methods for both cooked and uncooked pasta (like microscopy, colorimetry, dimensional analysis, texture, cooking qualities, moisture content, and FTIR). Significant differences in width, thickness, and color properties were observed between the control sample (0% oleogel) and those containing oleogel, with notable variations in surface texture and color intensities, particularly with the higher oleogel content (p < 0.05). Cooked pasta exhibited lower L* values and higher a* values than uncooked pasta. Stereo zoom microscope and field emission scanning electron microscope (FESEM) micrographs demonstrated a change in the pasta surface topology and microstructures. Dark spots on the pasta with greater oleogel concentrations (samples with 10% and 15% oleogel replacement) suggest the formation of starch–lipid complexes. Cooking induced pore formation, which was more pronounced when the oleogel content was increased, impacted the water absorption capacity, swelling index, and moisture content. The cooked samples exhibited higher moisture content and improved polymer network stability compared to the uncooked ones, indicating the potential of oleogel incorporation to modulate pasta properties in a concentration-dependent manner. These findings underscore the versatility of oleogels when their applications are diversified in non-bakery foods to enhance food texture and quality.

Benzotriazole loaded polypyrrole/cerium oxide synthesized composite blend within epoxy resin designed as superior coatings against mild steel oxidative corrosion in sodium chloride medium

In the present research work, benzotriazole or BTA-loaded polypyrrole/CeO2 (PCeB) coatings with different weight fractions as 0.5 %, 1.0 %, and 1.5 % blended with epoxy resin (EPR) were prepared and used to inspect the self-healing and corrosion protection behavior of the composite polypyrrole/CeO2 or PCe prior and after the loading of BTA. The synthesized composites were characterized structurally by XRD and FTIR studies and morphologically by SEM analysis. The surface topology of the coatings over mild steel was analyzed through SEM and AFM studies, furthered with the wettability/water resistance of coated surfaces through contact angle measurements, wherein BTA as inhibitor release rate was studied by the ultra-violet spectroscopy to assess the release amount of BTA within 220–400 nm. The corrosion protection of coated samples was evaluated by the potentiodynamic polarization method and electrochemical impedance spectroscopy or EIS, immersing the steel samples in 3.5 % NaCl solutions. There is a positive shift in Ecorr values and the composite PCeB/EPR (1 %) showed a stupendous protection efficiency of 99.95 % after 3 h immersion obtained through the EIS studies. These findings indicate that Polypyrrole/CeO2@BTA could be a potential substitute for persistent anticorrosive coatings for mild steel against aggressive chloride ions.

Basic Remarks on Lagrangian Submanifolds of Hyperkähler Manifolds

Abstract This note presents basic restrictions on the topology of Lagrangian surfaces of hyper-Kähler $4$-folds and a remark on the interaction of a Lagrangian subvariety of a hyper-Kähler variety with a Lagrangian fibration of the latter.

Remnant polarization and structural arrangement in P(VDF-TrFE) electrospun fiber meshes affect osteogenic differentiation of human mesenchymal stromal cells

Many tissues and cells are influenced by mechano-electric stimulation, thus the application of piezoelectric materials has recently received considerable attention in tissue engineering. This report investigated electrospun fiber meshes based on poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] as instructive biomaterials for osteogenic differentiation of human mesenchymal stromal cells (hMSCs). The influence played by methyl ethyl ketone (MEK), used as a solvent in place of dimethylformamide (DMF)/acetone mixture, and the effect of rotating velocity of the electrospinning collector on fiber morphology, mechanical and piezoelectric properties were studied. The solvent had noticeable effects on morphology and piezoelectric properties of electrospun fibers, with MEK outperforming DMF/acetone. By increasing the collector velocity up to 4000 rpm, the fiber diameter reduced and the mutual alignment of the fibers increased, corresponding to enhanced mechanical properties and piezo-active β-phase content. However, as a consequence of the diverse mechanical properties of random and aligned fibrous architectures, which ultimately affected the piezoelectric properties, randomly-oriented fibers exhibited higher remnant piezoelectric properties (Vout and d31 piezoelectric coefficient) than aligned ones. On these scaffolds, hMSCs showed an excellent capability of early osteogenic differentiation, leading to high calcium production. Fiber surface topology, fiber mesh morphology and remnant piezoelectric properties played a determinant role on hMSC osteogenic commitment.

A DFT study of the adsorption of fouling molecules (metal sulfides and hydroxides) onto TiZrO4 ceramic membranes

Ceramic membrane fouling is a constraint in the treatment of acid mine drainage (AMD), leading to a decrease in efficiency over time. Here, it is described via first-principles calculations the physical and chemical phenomena occurring on the surface of TiZrO4 filtration membranes due to the adsorption of eight potential fouling compounds [CuS, FeS, Fe2S3, CaS, Al(OH)3, Fe(OH)3, Fe(OH)2, and Cu(OH)2]. The interaction of these fouling molecules was performed onto nanostructured TiZrO4 surfaces with several pores representing the filtration membranes employed in the treatment of AMD. The adsorption energies reveal that the adsorption is feasible with all the fouling molecules studied, and it is strongly related to the molecular polarity of the adsorbate. Consequently, the adsorption of metal sulfides is more feasible than hydroxides with adsorption orders of CaS>FeS>CuS>Fe2S3, and Al(OH)3>Fe-hydroxides>Cu(OH)2. The outcomes suggest that the metal sulfide adsorption depends on the adsorbate intrinsic polarity, solvent effects, adsorbate van der Waals radius, and membrane surface topology, while the adsorption of hydroxides is less influenced by the last two factors. Density-based binding and energy decomposition analyses indicate strong electrostatic attractions and covalent bonds at the adsorbate-membrane interface supporting the chemical fouling onto ceramic filtration membranes. According to our theoretical results and the elevated concentration of Cu and Fe in AMD, we propose that FeS and CuS are mainly responsible for the fouling onto TiZrO4 membrane surfaces. These results offer valuable information on the adsorption phenomena at TiZrO4 membrane surfaces, which can be useful for metallurgy, industrial water treatment, food industry, biotechnology, and pharmaceutical applications.

Structural, chemical states, electrical properties and forward transport phenomena of Ti/MnO2/p-InP heterostructure with a transition metal oxide MnO2 interlayer

The study examines the surface topology, optical, structural and electrical characteristics of e-beam evaporated manganese dioxide (MnO2) films on p-InP using AFM, FESEM, UV–Vis, XRD, XPS and I–V procedures. The surface roughness of the MnO2 was smooth from AFM and FESEM analysis. The optical bandgap of MnO2 film was extracted from Tauc's plot. The outcomes endorse that the MnO2 layer deposited on InP. Then, the Ti/MnO2/p-InP heterostructure (HS) was created with an MnO2 interlayer to check the consequence of MnO2 on the electrical features of the Ti/p-InP Schottky diode (SD). The I–V results demonstrated that the higher Φb is acquired for the HS (0.90 eV) than the SD (0.84 eV), implying the MnO2 layer alters the Фb. Also, the Фb, ‘n’ and RS of the SD and HS can be determined by utilizing Cheung's and Norde's functions. The estimated Фb was almost similar, indicating the methodologies applied here are sturdy and effective. The determined NSS of the HS is lesser than the SD, implying that the MnO2 interlayer has a significant role in the decrease in NSS. The forward bias log (I)-log(V) plot of the SD and HS indicates that the ohmic behavior and space charge limited the conduction process at lower-bias and higher-bias segments, respectively. The study outcomes suggested that the transition metal oxide MnO2 layer would be favourable for creating MIS devices.

Multi‐Material Digital Light Processing (DLP) Bioprinting of Heterogeneous Hydrogel Constructs with Perfusable Networks

AbstractThe challenges of replicating the complex mechanical and structural diversity of natural tissues in vitro by leveraging multi‐material digital light processing (DLP) bioprinting are addressed. This technique utilizes PEGDA‐AAm bio‐ink to develop multi‐component, cell‐laden hydrogel constructs with varying moduli. These constructs not only possess heterogeneous mechanical properties but also feature complex architectures and precisely engineered surface microstructures. The hydrogel microfluidic chips are successfully fabricated with perfusable microchannels, embedding various cell types within the matrix. This approach enables the bioprinting of intricate cell‐laden structures with unique surface topologies, such as spiral grooves and triply periodic minimal surfaces (TPMS), which effectively influence cell alignment, spreading, and migration. By integrating various cell‐laden PA hydrogels, the diverse mechanical moduli of biological tissues, including bone, liver lobules, and vascular networks are replicated. This technique ensures high‐fidelity differentiation between cell types and regions. These findings provide valuable insights into the impact of substrate modulus and structure on cell behavior, underscoring the potential of multi‐component, multi‐modulus hydrogel constructs in creating sophisticated structures with custom‐tailored mechanical properties. This study significantly advances the field by demonstrating the feasibility and effectiveness of multi‐material DLP bioprinting in developing complex, functionally relevant tissue models for tissue engineering and regenerative medicine.

Effects of liquid water injection on flame surface topology and propagation characteristics in spray flames: A direct numerical simulation analysis

The effects of water injection on flame surface topology and local flame propagation characteristics have been analyzed for statistically planar turbulent n-heptane spray flames with an overall (i.e., liquid + gaseous) equivalence ratio of unity using carrier-phase direct numerical simulations. Most fuel droplets have been found to evaporate as they approach the flame even though some droplets can survive until the burnt gas side is reached, whereas water droplets do not significantly evaporate ahead of the flame and the evaporation of water droplets starts to take place in the reaction zone and is completed within the burnt gas. However, the gaseous-phase combustion occurs predominantly in fuel–lean mode although the overall equivalence ratio remains equal to unity. The water injection has been found to suppress the fuel droplet-induced flame wrinkling of the progress variable isosurface under the laminar condition, and this effect is particularly strong for small water droplets. However, turbulence-induced flame wrinkling masks these effects, and thus, water injection does not have any significant impact on flame wrinkling for the turbulent cases considered here. The higher rate of evaporation and the associated high latent heat extraction for smaller water droplets induce stronger cooling effects, which weakens the effects of chemical reaction. This is reflected in the decrease in the mean values of density-weighted displacement speed with decreasing water droplet diameter. The weakening of flame wrinkling as a result of injection of small water droplets is explained through the curvature dependence of the density-weighted displacement speed. The combined influence of cooling induced by the latent heat extraction of water droplets and flame surface flattening leads to a decrease in volume-integrated burning rate with decreasing water droplet diameter in the laminar cases, whereas the cooling effects are primarily responsible for the drop in burning rate with decreasing water droplet diameter in the turbulent cases.

Experimentally detected aerodynamic drag coefficient of the agricultural tractor form considering effects of windshield angle and hood front shape

Agricultural tractors are improving their capacity, speed, and performance. However, the characteristic form of the agricultural tractors is not known in terms of aerodynamics. This is required in modeling transportational duties and their impacts on energy and environment, especially considering tractor-trailer couples. In this work, this characteristic form solely investigated apart from the couple to base a foundation. The geometry was adapted from a commercial model. The model was simplified greatly to isolate numerous parameters yielding a generic shape. Only geometrical features as parameters were selected as the nose shape as the leading surface and the windshield angle. Scaled models were tested in a wind tunnel. Drag coefficients independent from Reynolds number, drag forces, pressure distributions on the symmetry planes and pressure coefficients were obtained. An extrapolation was made in order to predict drag force related fuel consumption and CO2 emission for a full-scale tractor on-road transportation scenario based on experimentally obtained drag coefficient. It is understood that changes in tractor front surface topology and wind shield angle can lead to drag changes up to 3%. A 0.72 value of drag coefficient may be assumed for the generic agricultural tractor form. Based on this value, an on-road agricultural tractor cruising with 70 km h−1 is predicted to have a drag sourced fuel consumption of 3.9 kg h−1 and CO2 emission of 10.19 kg h−1. Tractor trailer couples and their platoons are of interest in terms of research and computational simulations that may utilize present results as validator.

Investigation of Wettability Behavior and Surface Topology of PVC Materials Used in Outdoor Applications

The wettability behavior is crucial in determining the materials' applications and durability. To assess the wettability behavior, the measurement of contact angle is utilized. In this study, commercially produced PVC profiles were sampled, and a contact angle measurement system, consisting of both software and hardware, was developed to measure the contact angle of the samples. The contact angle measurements were conducted by placing approximately 20 µl of distilled water on the samples, and each sample was measured six times, with the average being taken. A device for measuring roughness was used to determine the surface roughness of the samples, and the average roughness value was obtained from four different parts of each sample. Additionally, SEM images of each sample were taken to conduct surface and structural analyses. The correlation between roughness, SEM image analysis results, and contact angle was examined in the research study. Moreover, the wettability behavior of PVC materials was analyzed by evaluating the impact of the elements in their structure and their homogeneity on the contact angle values.

Thin-film photodiode based on novel SiC/MoS2 composite by RF-sputtering for fast response photodetection

A Schottky -photodiode and pn-photodiode were fabricated based on a SiC/MoS2 composite semiconductor material using a physical vapour deposition (PVD) method. The surface topology and structural features of the nanostructured SiC/MoS2 thin films were investigated using scanning electron microscope (SEM), Fourier Transform Infrared spectroscopy (FTIR), and grazing incidence X-Ray diffraction (GIXRD) analysis. The two-dimensional nature of these materials enables easiness integration for vertical device design with novel properties. The performance parameters of the fabricated devices were characterized. The electrical performance of the fabricated SiC/MoS2 Schottky and pn photodiodes were investigated according to their current-voltage (I–V) characteristics within a bias voltage range from −4 to 4 V. Here, we report highly efficient photocurrent generation from vertical SiC/MoS2 composite device fabricated using asymmetric metal contacts, exhibiting an external quantum efficiency (EQE) of up to 14.68% for pn -photodiode and 6.68% for Schottky -photodiode. Evaluated to in-plane MoS2 devices, the vertical design of these devices has a much larger junction area which is essential for achieving highly efficient photovoltaic devices. As well as spectral responsivity of 28.25 mA/W and 63.22 mA/W for Schottky and pn-photodiodes respectively also, response time of 1 ms for Schottky-photodiode and 977.5 μs for pn-photodiode were measured and discussed.