Contact Interaction Research Articles

Estimation of sleeper-ballast contact pressure based on fretting marks: field measurements and FEM modeling

The contact conditions between components of railway infrastructure are complex. This research focuses on the contact interactions between the ballast and steel sleepers. Unlike the prismatic design of concrete and wooden sleepers, steel sleepers are characterized by a unique U-shaped configuration, further contributing to the complexity of the contact conditions. To address this issue, this study focused on analyzing the lower surfaces of steel sleepers commonly used in railroads, which had contact marks resulting from the ballast and train load due to fretting. To simulate these contact marks, virtual ballast geometries were created and simplified to match the observed contact areas. Specifically, these contact areas represented 6% of the bottom area of the steel sleepers. We compared the efficiency of this approach using Finite Element Method simulations.

Mass and momentum balance during particle migration in the pressure-driven flow of frictional non-Brownian suspensions

The transient shear-induced particle migration of frictional non-Brownian suspensions is studied using particle-resolved simulations. The numerical method – the fictitious domain method – is well suited to heterogeneous flows thanks to a frame-invariant formulation of the subgrid (lubrication) corrections that does not involve the ambient flow (Orsi et al., J. Comput. Phys., vol. 474, 2023, 111823). The paper aims to give an accurate quantitative picture of the mass and momentum balance during the flow. The various assumptions and local constitutive laws that together form the suspension balance model (SBM) are thoroughly examined. To this purpose, the various quantities of interest are locally averaged in space and time, and their profile across the channel is extensively studied, with specific attention to the time evolution of the different contributions, either hydrodynamic in nature or from contact interactions, to the shear and normal stresses. The latter, together with the velocity gradient in the wall-normal direction and the volume fraction profile, yield the local constitutive laws, which are compared with their counterpart obtained in homogeneous shear flow. A fair agreement is observed except in a layering area at the boundaries and at the very centre of the channel. In addition, the main assumption of the SBM, i.e. the local relation between the hydrodynamic force on the particles and the particle flux, is meticulously investigated. The hydrodynamic force is found to be mainly a drag, except in the lower range of the probed volume fractions, where a non-drag contribution is observed.

On your terms or mine: pigs’ response to imposed gentle tactile contact vs. free form interaction with a familiar human

AbstractPositive human–animal interactions (HAIs) can be intrinsically rewarding and facilitate positive human–animal relationships. However, HAI paradigms vary across studies, and the influence of different interaction paradigms on the animal’s response has been overlooked. We compared the behavioural responses of pigs (n = 28) individually tested with two types of gentle tactile interactions with a familiar human: ‘free form (FF)’ where the pig could voluntarily approach and interact as they normally would, and ‘imposed contact (IC)’ where the human imposed tactile contact on the pig according to a standardised protocol. Pigs did not differ in their level of engagement with the human between the two types of interactions. However, they differed in their behaviour as they explored the pen more during the FF test, while they emitted more low-pitched vocalisations (grunts) during the IC test. These differences can likely be imputed to the IC test differing to the pigs’ habituation to human contact, which could have evoked greater attention to the human or triggered frustration due to violation of expectation. These findings highlight the influence of the predictability of the interaction or level of agency provided to the animal in HAI tests and relation to their previous experience of interacting.

Realizing multiband states with ultracold dipolar quantum simulators

The manipulation of dipolar interactions within ultracold molecular ensembles represents a pivotal advancement in experimental physics, aiming at the emulation of quantum phenomena unattainable through mere contact interactions. Our study uncovers regimes of multiband occupation which allow to probe more realistic, complex long-range interacting lattice models with ultracold dipolar simulators. By mapping out experimentally relevant ranges of potential depths, interaction strengths, particle fillings, and geometric configurations, we calculate the agreement between the state prepared in the quantum simulator and a target lattice state. We do so by separately calculating numerically exact many-body wave functions in the continuous space and single- or multiband lattice representations, and building their many-body state overlaps. Our findings reveal that for shallow lattices and stronger interactions above half filling, multiband population increases, resulting in fundamentally different ground states than the ones observed in simple lowest-band descriptions, e.g., striped vs checkerboard states. A wide range of probed parameter regimes in its turn provides a systematic and quantitative blueprint for realizing multiband states with two-dimensional quantum simulators employing ultracold dipolar molecules. Published by the American Physical Society 2024

A qualitative approach to describe the viscosity of flowable concrete made with manufactured sand containing different microfines

The concrete made with different manufactured sands can exhibit complex rheological properties. The prediction of viscosity is crucial in concrete placement, but remains challenging given the varied content and characteristics of microfines in the sands. This paper studies the influence of tuff (TF) and limestone (LS) microfines with disparate particle size distributions on the pseudo-Newtonian viscosity of concrete prepared with crushed sand. The concrete had a fixed water-to-binder mass ratio of 0.32 and polycarboxylate ether superplasticizer (PCE) dosage of 0.14 % by mass of biner. Test results showed that the microfines in manufactured sand can reduce the aggregate-to-excess cement paste ratio, leading to lower contact interactions between the aggregate grains. But the ratio of total powder particles and entrained air to excess interstitial solutions increased for the fluid paste matrix of the concrete, which caused greater flow resistance related to the powder contacts and air bubble deformations. A qualitative approach correlating the volume ratio of aggregate grains to excess cement pastes and that of total powder particles and entrained air to excess interstitial solutions was proposed to describe the pseudo-Newtonian viscosity of concrete, regardless of the different microfine additions in manufactured sand.

Study of regularities and features of simultaneous contact interaction of active and inert metal melts with zirconia

ABSTRACT The mutual influence of interface processes during simultaneous contact of zirconia ceramic plate with adhesion-active Cu–Ga–Ti melt (on one side of the plate) and inert to oxides liquid copper (on other side of the plate) was studied. Wetting of ceramic with metal melts was studied by sessile drop method, the structure of the interfaces was determined using SEM. Due to the dissolution of ceramic oxygen in Cu–Ga–Ti, non-stoichiometric zirconia (ZrO2-x) is formed, then ‘surplus’ zirconium from the ZrO2-x structure dissolves in the copper melt, the stoichiometry of zirconia is restored and an additional amount of oxygen dissolves in the Cu–Ga–Ti melt. It leads to a decrease in the adhesion of Cu–Ga–Ti to ceramics, while improving the wetting of ZrO2 ceramics with copper. The ZrO2–Cu–Ga–Ti interface contains copper–titanium–oxygen intermetallides with zirconia inclusions, which does not provide adhesion of metals with solid oxides. If the contact of Cu–Ga–Ti with ZrO2 is formed before contact with liquid copper, then the interface layer contains oxidized titanium, which promotes adhesion of metal to ceramic. Thus, the design of the sample affects the processes in the studied systems in the same way as the heating mode and the amount of the active component.

First radial excitations of baryons in a contact interaction: Mass spectrum

We compute masses of twenty positive parity first radial excitations of spin-1/2 and spin-3/2 baryons composed of u, d, s, c, and b quarks in a quark-diquark picture within a contact interaction model. These excitations comprise of two elements; one characterized by a zero in the Faddeev amplitude, representing a radial excitation of the quark-diquark system and the other marked by a zero in the diquark’s Bethe-Salpeter amplitude, corresponding to an intrinsic excitation of the diquark correlation. Wherever possible, we compare our results with other models and/or experiment. We verify that the masses obtained through our model conform to the spacing rules for all the baryons studied, whether light or heavy and whether of spin-1/2 or spin-3/2. The computed masses do not just offer a guide to the future experimental searches but also compare well with the existing candidates for the possible radial excitations of some heavy baryons. Published by the American Physical Society 2024

Tunable interfacial properties of monolayer GeSb2Te4 on metal surfaces

Abstract Atomically thin monolayer (ML) GeSb 2 Te 4 (GST) holds promising prospects in non-volatile memory applications because of its high non-homogeneous crystallization rate. In GST-based devices, the interaction between GST and metals is crucial, as it affects the electronic properties. Herein, based on first-principles calculations, we investigate the interaction and Schottky barrier height of contacts formed by the combination of ML GST with various metals. It is found that the interfaces of GST with Pt, Pd, Ir and W exhibit strong interaction, characterized by large binding energies ranging from 1.394 to 1.015 eV , and the interfaces between GST and Cu, Ag and Au display weak interaction. For the seven contacts, Ag and W form Ohmic contacts with ML GST, while Cu, Au, Pd, Ir, and Pt form n-type Schottky contacts, with Schottky barrier heights ranging from 0.029 to 0.353 eV . The strong Fermi level pinning at GST-metal interface is observed with a pinning factor of 0.378. Additionally, altering the interfacial distance and optimizing the layers of GST enable a transition from Ohmic contact to Schottky contact. These findings provide crucial guidance for the design and optimization of electronic devices based on phase change materials like GST.

Enhanced Diffusion and Non-Gaussian Displacements of Colloids in Quasi-2D Suspensions of Motile Bacteria

In the real world, active agents interact with surrounding passive objects, thus introducing additional degrees of complexity. The relative contributions of far-field hydrodynamic and near-field contact interactions to the anomalous diffusion of passive particles in suspensions of active swimmers remain a subject of ongoing debate. We constructed a quasi-two-dimensional microswimmer–colloid mixed system by taking advantage of Serratia marcescens’ tendency to become trapped at the air–water interface to investigate the origins of the enhanced diffusion and non-Gaussianity of the displacement distributions of passive colloidal tracers. Our findings reveal that the diffusion behavior of colloidal particles exhibits a strong dependence on bacterial density. At moderate densities, the collective dynamics of bacteria dominate the diffusion of tracer particles. In dilute bacterial suspensions, although there are multiple dynamic types present, near-field contact interactions such as collisions play a major role in the enhancement of colloidal transport and the emergence of non-Gaussian displacement distributions characterized by heavy exponential tails in short times. Despite the distinct types of microorganisms and their diverse self-propulsion mechanisms, a generality in the diffusion behavior of passive colloids and their underlying dynamics is observed.

Inflaton production of scalar dark matter through fluctuations and scattering

We study the effects on particle production of a Planck-suppressed coupling between the inflaton and a scalar dark matter candidate, χ. In the absence of this coupling the dominant source for the relic density of χ is the long wavelength modes produced from the scalar field fluctuations during inflation. In this case, there are strong constraints on the mass of the scalar and the reheating temperature after inflation from the present-day relic density of χ (assuming χ is stable). When a coupling σϕ2χ2 is introduced, with σ=σ˜mϕ2/MP2∼10−10σ˜, where mϕ is the inflaton mass, the allowed parameter space begins to open up considerably even for σ˜ as small as ≳10−7. For σ˜≳916, particle production is dominated by the scattering of the inflaton condensate, either through single graviton exchange or the contact interaction between ϕ and χ. In this regime, the range of allowed masses and reheating temperatures is maximal. For 0.004<σ˜<50, constraints from isocurvature fluctuations are satisfied, and the production from parametric resonance can be neglected. Published by the American Physical Society 2024

МЕТОД ТА ДОСЛІДЖЕННЯ ТОЧНОСТІ ОБЧИСЛЮВАННЯ МАТЕМАТИЧНОЇ МОДЕЛІ ЕЛЕКТРОГІДРАВЛІЧНОГО ЕФЕКТУ

The mathematical model of the electrohydraulic effect (EHE) is a nonlinear non-stationary system of partial differential equations (PDE), which reflects the motion and contact interaction of two media, gaseous and liquid, under the action of pulsed thermal excitation. Such PDE systems generally do not have analytical solutions and are solved only by numerical methods, which are approximate in nature, i.e. they provide a solution with some error. The peculiarity of the motion of media in the case of EHE is large deformations in the form of flows and vortices. This feature imposes significant restrictions on the choice of the method for solving the PDE model. The widely known Lagrangian finite element method used to solve contact problems, in the case of EHE modeling leads to a pathological change in the shape of the finite elements, and therefore to instability of the calculation process and an unlimited increase in error. In calculation practice, a variant of the finite element method, FEM-ALE, has become widespread. It uses both Lagrangian and Eulerian grids of nodes and a special advection procedure, i.e., transfer by interpolation of the solution from the Lagrangian grid to the Eulerian one, and then vice versa from the Eulerian one to another new Lagrangian grid. Such an additional interpolation procedure, which is used repeatedly in the calculation, leads to additional (in comparison with the Lagrangian FEM) errors. If the causes and kinetics, as well as the methods of error control in the case of the Lagrangian FEM, have been sufficiently studied in the literature, then the kinetics of error development in the simulation of the EGE using the FEM-ALE method has been practically not studied. The article is devoted to the study of the development of errors in the numerical solution in this particular case. An analytical solution of the problem in the asymptotic case for a technological system with a rigid chamber is obtained. This solution is analyzed in comparison with the numerical solution using the FEM-ALE method. Conclusions are made regarding the errors in calculating pressure as the main factor of mechanical impact of EGE on the technological object and technological equipment, as well as errors in calculating deformations of gaseous and liquid media.The scientific novelty consists in the development of a method for determining the accuracy of EHE parameter calculations using the MSE-ALE method. The practical value lies in determining the accuracy of calculating the parameters of the EHE mathematical model, which makes it possible to justify the use of numerical modeling as a method of researching technological processes and systems using EHE

8596 Brain Type 3 Deiodinase Is Induced in Two Disease Models That Lead to Cognitive Impairment: Liver Dysfunction and Alzheimer Disease

Abstract Disclosure: S. Wajner: None. T. Oliveira: None. M. Dreher: None. R. Ribeiro: None. C. Gonçalves: None. M.R. Alveres-da-Silva: None. Thyroid hormone is the leading regulator of cell energy production in most tissues, mainly the brain. While the activation process of T4 into T3 depends on D1 and D2 deiodinases, type 3 is the main enzyme that inactivates T3. Several mechanisms, among them oxidative stress, led by disease, imbalances and induces D3, diminishing T3 levels. The response of D3 in the brain in the context of different disease models has yet to be studied. Here we evaluated D3 induction in the brain in two animal disease models, one systemic and the other local. Methodology: To the metabolic dysfunction-associated steatosis liver disease model Male/adult Sprague Dawley rats (n=20) were assigned to control group (standard diet-2.93kcal/g) or high-fat-diet group (CDHF-4.3kcal/g). In the streptozotocin-induced (STZ) Alzheimer's model Adult Wistar rats (n=16) were allocated to the control group (5uL of citrate) or 5uL of streptozotocin. Sham animals were used as controls. D3 expression, oxidative stress parameters, endoplasmic stress and mitochondrial amount measured in the brain. Levels of D3 increased in the brain (∼30% in each group, P<0.0001) in both MASLD and STZ groups. Cerebral tissue from both groups had augmented carbonyl levels (P<0.001) and reduced sulfhydryl (P<0.001). Glutathione was diminished. Antioxidant defenses endoplasmic reticulum function and mitochondrial concentration were altered (P=0.001). The augmented T3 inactivation by D3 dysfunction in brain due to oxidative stress disrupts ER-mitochondrial contact interaction, changing the function of organelles in both brain disease models, shedding light to new mechanisms of action of thyroid hormone in severe brain disease. Presentation: 6/3/2024

Rapidly rotating quantum droplets confined in a harmonic potential

We consider a “symmetric” quantum droplet in two spatial dimensions, which rotates in a harmonic potential, focusing mostly on the limit of “rapid” rotation. We examine this problem using a purely numerical approach, as well as a semianalytic Wigner-Seitz approximation (first developed by Baym, Pethick, and their co-workers) for the description of the state with a vortex lattice. Within this approximation we assume that each vortex occupies a cylindrical cell, with the vortex-core size treated as a variational parameter. Working with a fixed angular momentum, as the angular momentum increases and depending on the atom number, the droplet accommodates none, few, or many vortices, before it turns to center-of-mass excitation. For the case of a “large” droplet, working with a fixed rotational frequency of the trap Ω, as Ω approaches the trap frequency ω, a vortex lattice forms, the number of vortices increases, the mean spacing between them decreases, while the “size” of each vortex increases as compared to the size of each cell. In contrast to the well-known problem of contact interactions, where we have melting of the vortex lattice and highly correlated many-body states, here no melting of the vortex lattice is present, even when Ω=ω. This difference is due to the fact that the droplet is self-bound. For Ω=ω, the “smoothed” density distribution becomes a flat top, very much like the static unconfined droplet. When Ω exceeds ω, the droplet maintains its shape and escapes to infinity, via center-of-mass motion. Published by the American Physical Society 2024

Study of self-assembly between two magnetic particle chains in magnetorheological fluids

The self-assembly behavior of individual magnetic particles in magnetorheological liquids has been extensively analyzed in previous studies, but the self-assembly behavior between chains of magnetic particles has rarely been investigated. In this paper, the self-assembly mechanism between chains of magnetic particles is investigated using simulation and experimental methods. Firstly, a two-dimensional coupling simulation numerical model of particle-magnetic field-flow field is constructed by analyzing the magnetic force, fluid force and contact interaction force between magnetic particles. The accuracy of the simulation model was verified through experiments. Then the attraction and repulsion dividing line of two magnetic particle chains are analytically calculated by simulation combined with parametric scanning. And analyze the law of the influence of the number of magnetic particles between magnetic particle chains on the attraction and repulsion dividing line. Finally, the different self-assembly behaviors that occur when magnetic particle chains are in different regions of attraction and repulsion between them are experimentally verified. Thus, this study provides new insights into the self-assembly mechanism between chains of magnetic particles in magnetorheological fluids in terms of the effect of the number of magnetic particles on the attraction–repulsion dividing line.

Thermomechanical Analysis of Cement Hydration Effects in Multi-layered Pier Head Concrete: Finite Element Approach

Mass concrete plays a crucial role in infrastructure development, yet its complex thermo-mechanical behavior poses challenges, especially in the construction of multi-layered structures like pier heads. This study investigated the thermo-mechanical behavior of a pier head during its concreting process in three stages, including the influence of temperature differences that impact the thermomechanical balance of the concrete. By utilizing the ABAQUS software, thermo-mechanical analysis was conducted to simulate temperature fluctuations during cement hydration. The model integrates thermal analysis to simulate temperature fluctuations during cement hydration and stress distribution during construction, validated through mesh convergence studies and field data comparison. The mechanical analysis considered concrete properties, temperature variations, and construction phase. Nonlinear material behavior and contact interactions between layers were incorporated to obtain a realistic simulation. The results indicated that a multi-layer system can balance temperatures, reducing thermal stress-induced cracking risks. Furthermore, specific test points within the pier head were assessed, revealing potential internal cracks by comparing thermal stresses to the concrete’s tensile strength. This research offers insight into pier head conditions during construction, highlighting critical stress zones, crack prediction, and construction sequence efficacy.

Enhanced Impedance Control of Cable-Driven Unmanned Aerial Manipulators Using Fractional-Order Nonsingular Terminal Sliding Mode Control with Disturbance Observer Integration

The article presents a novel control strategy for cable-driven aerial manipulators (UAMs) aimed at enhancing impedance control during contact operations in complex environments. A fractional-order nonsingular terminal sliding mode control (FONTSMC) integrated with a disturbance observer (DOB) is proposed to improve the robustness and precision of the UAM under lumped disturbances. This developed approach utilizes the flexibility of fractional calculus, the finite-time stability of nonsingular terminal sliding mode, and the real-time disturbance estimation capabilities of the DOB to ensure smooth and compliant contact interactions. The effectiveness of the proposed control strategy is validated through comprehensive simulation studies, which demonstrate significant improvements in control performance, stability, and disturbance rejection when compared to traditional methods. The results indicate that the FONTSMC-DOB framework is highly suitable for complex aerial manipulation tasks, offering both theoretical and practical insights into the design of advanced control systems for UAMs.

Tribotechnical processes of the soil environment interaction with the working bodies of soil tillage and earthmoving machines reinforced with composite materials

The work presents the study results of the stress-strain state of the soil, as a continuous medium filled with abrasive particles under the action of the working bodies of soil tillage and earthmoving machines. One of the main properties of the soil, which determines the specifics of the force interaction of the working surfaces of the working bodies of soil tillage and earthmoving machines with the technological environment, is taken into account, namely the tendency of the contact layer of the treated layer to compaction. The relationship between stress in the soil and the wear of the working bodies of soil tillage and earthmoving machines has been established experimentally. A theoretical analysis is presented for the stress-strain state of the local region of the strengthened surface layer that is used in the working bodies of soil tillage and earthmoving machines, in which the filler, inclusion or strengthening phase is placed. An analysis of the contact characteristics of the stress-strain state and their changes during friction and wear was carried out based on the formulation and solution of the contact interaction problems of abrasive soil particles with the inhomogeneities of the composite coatings components based on ultra-high molecular weight polyethylene with fillers during strengthening of the working bodies of soil tillage and earthmoving machines. Computer modeling was performed to study the nature of stress distribution in the reinforced surface layer of the working bodies of soil tillage and earthmoving machines in the area of the contact zone in stationary and dynamic conditions. The contact problem is formulated, the boundary conditions and the solution in the form of components of the stress field are given. The characteristics of the filler, their content in the composite material and coating are taken into account, the relationship between the stress-strain state and wear is established.

Study of the microhardness ensuring the contact endurance of structural materials

The strength of the working surfaces of gears depends on the mechanical properties of the material and the quality of parts. We present the results of studying the strength of materials and working surfaces of a gear mechanism due to structural changes attributed to chemical and thermal treatment. The surface strength of the gears of gas turbine engines was studied. Nitrocementation and ion nitriding were used for chemical and thermal treatment of the contacting surfaces of steel samples under study (20Kh3MVF-Sh, 16Kh3NVFMB-Sh, 18Kh2H4MA, and 12Kh2H4A). Changes in the microhardness of the component layers (diffusion, transition and basic) of the toothed crown were analyzed. Metallographic analysis of the structure of materials was carried out to describe the factors determining the surface strength of working surfaces. Systematized data on the change in the microhardness of materials obtained experimentally in conditions of mass production are presented. Presented experimental results on changes in the mechanical properties of materials are based on data on the microhardness and structural state of the surface layers of the working profiles of gears. A comparative assessment of the surface strength of the studied samples during contact interaction was performed. The dependence of the surface strength on the multifactorial volumetric structure and structure formation of the material in the process of operation is determined. It is shown that the method of surface saturation forms the structure of a material with different mechanical properties accompanied with the formation of a transition zone having characteristic distinctive values of the hardness. The results obtained can be used in the design of gears, taking into account changes in the mechanical properties and structure of materials to ensure the necessary operational requirements.

Analysis of Structures at the Boundary of Contact Melting Al–Mg–Mn and Zn Based Alloys

The processes of contact melting of the AMg6 (Al-6%Mg-1%Mn) alloy with Zn–Cu–Al solder and the model Zn–Al alloy, as well as the structure of the contact fusion zone, are studied. Samples were obtained in two stages. At the first step, the solder was mechanically applied (tinned) to the surface of the AMg6 plates. Аt the second step, the resulting composite samples were subjected to heat treatment with a varied exposure time in the liquid state. According to the data of metallographic and X-ray diffraction analyses, as well as differential scanning calorimetry, it was shown that already at the tinning stage the active interaction between Zn and Al occurs, which leads to the formation of a developed microstructure in the joint zone. The presence of copper in the solder HTS-2000 reduces the melting point of the Zn-Al alloy by 30-40°C and improves the conditions for contact interaction with the grade AMg6 matrix. Active diffusion of zinc ensures the formation of an extensive melting zone during heat treatment, while zinc-rich areas during crystallization contain the Zn5Cu intermetallic phase, which prevents the formation of intermetallic ZnxMgy compounds, which does not lead to embrittlement of the contact zone.

1,25-dihydroxyvitamin-D3 distinctly impacts the paracrine and cell-to-cell contact interactions between hPDL-MSCs and CD4+ T lymphocytes.

Human periodontal ligament-derived mesenchymal stromal cells (hPDL-MSCs) possess a strong ability to modulate the immune response, executed via cytokine-boosted paracrine and direct cell-to-cell contact mechanisms. This reciprocal interaction between immune cells and hPDL-MSCs is influenced by 1,25-dihydroxyvitamin-D3 (1,25(OH)2D3). In this study, the participation of different immunomodulatory mechanisms on the hPDL-MSCs-based effects of 1,25(OH)2D3 on CD4+ T lymphocytes will be elucidated using different co-culture models with various cytokine milieus. hPDL-MSCs and CD4+ T lymphocytes were co-cultured indirectly and directly with inserts (paracrine interaction only) or directly without inserts (paracrine and direct cell-to-cell contact interaction). They were stimulated with TNF-α or IL-1β in the absence/presence of 1,25(OH)2D3. After five days of co-cultivation, the CD4+ T lymphocyte proliferation, viability, and cytokine secretion were analyzed. Additionally, the gene expression of soluble and membrane-bound immunomediators was determined in hPDL-MSCs. In the indirect and direct co-culture model with inserts, 1,25(OH)2D3 decreased CD4+ T lymphocyte proliferation and viability. The direct co-culture model without inserts caused the opposite effect. 1,25(OH)2D3 mainly decreased the CD4+ T lymphocyte-associated secretion of cytokines via hPDL-MSCs. The degree of these inhibitions varied between the different co-culture setups. 1,25(OH)2D3 predominantly decreased the expression of the soluble and membrane-bound immunomediators in hPDL-MSCs to a different extent, depending on the co-culture models. The degree of all these effects depended on the absence and presence of exogenous TNF-α and IL-1β. These data assume that 1,25(OH)2D3 differently affects CD4+ T lymphocytes via the paracrine and direct cell-to-cell contact mechanisms of hPDL-MSCs, showing anti- or pro-inflammatory effects depending on the co-culture model type. The local cytokine microenvironment seems to be involved in fine-tuning these effects. Future studies should consider this double-edged observation by executing different co-culture models in parallel.