Presence Of Compressive Force Research Articles

Gravity wave interaction with an articulated submerged plate resting on a Winkler foundation

Surface gravity wave interaction with an articulated flexible submerged plate in the presence of lateral compressive force is investigated within the framework of blocking dynamics, assuming that the submerged plate is resting on a uniform Winkler foundation. The problem is studied considering small-amplitude plate response and linearised water wave theory in finite water depth. The loci of the dispersion relation reveal the occurrence of wave blocking in the submerged plate mode for a range of wave frequency and compressive force when the submerged plate is resting on a Winker foundation. However, in the absence of the Winkler foundation, no wave blocking occurs in the plate mode irrespective of the values of compressive force, and plane wave propagation in plate mode does not happen for particular values of compressive force. Four propagating wavenumbers exist within the blocking frequencies, of which one is in the surface mode, and others are in the submerged plate mode. Thus, to account for the four propagating wave modes, the existing solution approach for a pair of propagating wave modes is modified in an appropriate manner within the limit of blocking frequencies. Consequently, the energy relation is obtained using Green’s identity, in which the reflection and transmission coefficients are a combination of the amplitudes of different reflected and transmitted wave modes and the associated energy transfer rates. The reflection coefficient in the submerged plate mode jumps from one to zero for very small values of frequency due to the introduction of the Winkler foundation in the presence of compressive force. In addition, zero wave reflection occurs for a higher frequency range with an increase in the values of the Winkler constant. Removable discontinuities are observed at the blocking and saddle points, whilst jump discontinuities occur in the reflection and transmission coefficients due to the change of incident wave mode within the blocking frequencies. Linear time-dependent displacements in surface and submerged plate modes are presented prior to the blocking limit.

Immunorthodontics: Role of HIF-1α in the Regulation of (Peptidoglycan-Induced) PD-L1 Expression in Cementoblasts under Compressive Force.

Patients with periodontitis undergoing orthodontic therapy may suffer from undesired dental root resorption. The purpose of this in vitro study was to investigate the molecular mechanisms resulting in PD-L1 expression of cementoblasts in response to infection with Porphyromonas gingivalis (P. gingivalis) peptidoglycan (PGN) and compressive force (CF), and its interaction with hypoxia-inducible factor (HIF)-1α molecule: The cementoblast (OCCM-30) cells were kinetically infected with various concentrations of P. gingivalis PGN in the presence and absence of CF. Western blotting and RT-qPCR were performed to examine the protein expression of PD-L1 and HIF-1α as well as their gene expression. Immunofluorescence was applied to visualize the localization of these proteins within cells. An HIF-1α inhibitor was added for further investigation of necroptosis by flow cytometry analysis. Releases of soluble GAS-6 were measured by ELISA. P. gingivalis PGN dose dependently stimulated PD-L1 upregulation in cementoblasts at protein and mRNA levels. CF combined with P. gingivalis PGN had synergistic effects on the induction of PD-L1. Blockade of HIF-1α inhibited the P. gingivalis PGN-inducible PD-L1 protein expression under compression, indicating an HIF-1α dependent regulation of PD-L1 induction. Concomitantly, an HIF-1α inhibitor decreased the GAS-6 release in the presence of CF and P. gingivalis PGN co-stimulation. The data suggest that PGN of P. gingivalis participates in PD-L1 up-regulation in cementoblasts. Additionally, the influence of compressive force on P. gingivalis PGN-induced PD-L1 expression occurs in HIF-1α dependently. In this regard, HIF-1α may play roles in the immune response of cementoblasts via immune-inhibitory PD-L1. Our results underline the importance of molecular mechanisms involved in bacteria-induced periodontics and root resorption.

Scattering of long flexural gravity wave due to structural heterogeneity in the framework of wave blocking

Scattering of flexural gravity waves due to an abrupt change in structural heterogeneity is studied within the framework of blocking dynamics in time-space under shallow water approximations. As a special case, wave scattering due to a crack in the ice sheet is obtained. In the presence of compressive force, primary and secondary wave blocking occur at two different time-periods where group velocities vanish. Moreover, for each time-period within the primary and secondary blocking points, three propagating wave modes exist of which two are related with positive group velocities and the other one corresponds to negative group velocity. Subsequently, the energy relation of the scattering problem is derived in the case of multiple propagating wave modes using the conservation of energy flux. Out of the two propagating wave modes having positive group velocities, the energy transfer rate associated with the highest wavenumber is contributing significantly to the energy relation in the vicinity of the primary blocking point, whilst the other mode behaves in a similar manner near the secondary blocking point. Moreover, between the primary and secondary blocking points the incident wave mode changes to account for law of conservation of energy flux. Further, the study reveals that the energy transfer rate and the transmission coefficient are inversely proportional to each other. In case of wave scattering due to heterogeneity in ice sheet, the reflection and transmission coefficients pattern can have more than two removable discontinuities at the blocking points, whilst in the case of wave scattering due to a crack in the ice sheet, only two removable discontinuities appear at the primary and secondary blocking points. However, a jump discontinuity occurs at the point where incident wave mode conversion takes place in both the cases of wave scattering due to heterogeneity/crack in the ice sheet. Besides, irregular behaviour in plate deflection is observed due to the superposition of multiple propagating wave modes for a certain time-period within the blocking limits.

Phase evolution based thermomechanical crack closure mechanism of shape memory polymers

In this article, the thermomechanical fracture responses of shape memory polymers (SMPs) under two common stress free- strain recovery and fixed strain- stress recovery loading cycles are investigated. The shape memory properties of cracked SMPs for both single and mixed fracture modes are examined. The effect of phase transformation on the fracture parameters of the material is evaluated by the extended finite element method (XFEM). In addition, the fracture behavior is studied when the crack is created during the thermomechanical process. The results show that the initially cracked SMPs can fully preserve the shape memory property for both stress free- strain recovery and fixed strain- stress recovery cycles. Moreover, as a promising application, SMPs can be well employed in self-healing materials due to complete closure of the crack at the end of the shape recovery cycle. In cases where a crack is created in the midst of the fixed strain- stress recovery thermomechanical process, it is observed that the performance of the structure in providing desired reaction forces is reduced by increase of the crack length. Nevertheless, the presence of compressive forces in the initial steps of the force recovery cycle may potentially contribute to crack healing if additive healing agents are employed.

The role of viscoelastic foundation on flexural gravity wave blocking in shallow water

A hydroelastic model is developed to study the interaction of linear long gravity waves with a very large floating flexible plate resting on a viscoelastic foundation, which is based on the Kelvin–Voigt model. Flexural gravity wave blocking occurs for specific values of the compressive force in the absence of viscous damping. During wave blocking, the group velocity vanishes, and mode swapping occurs. Within wave blocking and plate buckling limit in the presence of compressive force, three distinct propagating modes occur in the absence of viscous damping. Moreover, the study reveals that irrespective of the values of viscous damping constant, the blocking/buckling points shift to a higher wavenumber with an increase in the value of elastic foundation constant. On the other hand, the flexural gravity wave modes become complex in the presence of a viscoelastic foundation. The complex wave modes are classified as predominant progressive wave modes and rapidly decaying modes. In the presence of viscous damping, wave blocking does not happen before the buckling limit of the compressive force. However, the phase velocity vanishes, and the group velocity becomes continuous irrespective of the value of non-zero viscous damping at the buckling limit for the compressive force. The detailed behavior of the roots of the dispersion equation and the mode shapes are illustrated through contour plots and by analyzing the roots’ loci. Furthermore, plate deflections are exhibited for different wave and structural parameters.

Adiponectin as Well as Compressive Forces Regulate in vitro β-Catenin Expression on Cementoblasts via Mitogen-Activated Protein Kinase Signaling Activation

We aimed to investigate the molecular effect that adiponectin exerts on cementoblasts especially in the presence of compressive forces. OCCM-30 cells (M. Somerman, NIH, NIDCR, United States) were used. Real-time reverse transcriptase–polymerase chain reaction (RT-PCR) and western blots were employed to verify if the mRNA and protein levels of adiponectin receptors (AdipoRs), mitogen-activated protein kinase (MAPK), and β-catenin signaling were influenced by compressive forces or adiponectin. Moreover, siRNAs targeting P38α, JNK1, ERK1, ERK2, and AdipoRs as well as pharmacological MAPK inhibition were performed. We found that compressive forces increase the expression of AdipoRs. Adiponectin and compression up-regulate P38α,JNK1, ERK1, and ERK2 as well as β-catenin gene expression. Western blots showed that co-stimuli activate the MAPK and β-catenin signaling pathways. MAPK inhibition alters the compression-induced β-catenin activation and the siRNAs targeting AdipoRs, P38α, and JNK1, showing the interaction of single MAPK molecules and β-catenin signaling in response to compression or adiponectin. Silencing by a dominantly negative version of P38α and JNK1 attenuates adiponectin-induced TCF/LEF reporter activation. Together, we found that light compressive forces activate β-catenin and MAPK signaling pathways. Adiponectin regulates β-catenin signaling principally by inactivating the GSK-3β kinase activity. β-Catenin expression was partially inhibited by MAPK blockade, indicating that MAPK plays a crucial role regulating β-catenin during cementogenesis. Moreover, adiponectin modulates GSK-3β and β-catenin mostly through AdipoR1. P38α is a key connector between β-catenin, TCF/LEF transcription, and MAPK signaling pathway.

Analysis of the phase structure of fluid vibrations with floating longitudinally compressed elastic plate in nonlinear interaction of the surface progressive waves

Based on the asymptotic expansions obtained by the multi-scale method up to the third order of smallness for the potential velocity of liquid particles and the plate-fluid surface elevation, the dispersion properties of the vibrations generated by the interaction of progressive surface wave harmonics of finite amplitude are analyzed in the article. The effect of nonlinearity of acceleration of vertical displacements of an elastic plate on the dispersion characteristics of wave disturbances is studied. The dependence of the vibration frequency is estimated by taking into account the nonlinearity of the first and second approximations values, the plate thickness, and the longitudinal compressive force. It is shown that the sign of the amplitude of the second interacting harmonic and the nonlinearity of the acceleration of vertical displacements of the longitudinally compressed elastic plate affect the vibration phase. It was found that with a decrease in the wavelength of the initial harmonic, the influence of the plate’s nonlinearity vertical acceleration is enhanced. The presence of compressive force is manifested in a decrease in the frequency of vibrations of the wave disturbance in comparison with the frequency obtained in the absence of longitudinal compression, both with a positive and negative sign of the second interacting harmonic amplitude.

Comparison of nonlocal continualization schemes for lattice beams and plates

This paper investigates both stability and vibration of nonlocal beams or plates in the presence of compressive forces. Various nonlocal structural models have been proposed to capture the inherent scale effects of lattice-based beams or plates. These nonlocal models are either based on continualization of the difference equations of the original lattice problem (labeled as continualized nonlocal models), or developed from phenomenological nonlocal approaches such as Eringen’s type nonlocality. Considered herein are several continualization schemes that lead to either fourth or sixth order spatial governing differential or partial differential equation. Even if the new continualized nonlocal plate models differ in their mathematical description, they appear to furnish very close macroscopic results as shown from asymptotic expansion arguments. The continualized nonlocal beam and plate models and the phenomenological approaches are also introduced from variational arguments. The key role of boundary conditions is shown especially for Eringen’s nonlocal model that is not necessarily variationally based. For each of them, the buckling load and the natural frequencies are determined for simply supported beams and plates and compared to their counterparts obtained from the lattice model. The small length scale coefficient of the nonlocal beam or plate models is intrinsically constant and problem independent for the continualized approaches, whereas it is calibrated for the phenomenological models based on the equivalence with the reference microstructured model and consequently, depends on the load, the buckling or vibration mode or the aspect ratio. It is found that the nonlocal continualized approaches are more efficient than the nonlocal phenomenological ones. For beam problems, continualized nonlocal and phenomenological approaches such as Eringen’s nonlocal theory can become the same. However, for plate problems, phenomenological approaches may differ significantly from continualized nonlocal ones; thereby offering one the opportunity to have a new class of two-dimensional nonlocal models.

Isogeometric rotation-free bending-stabilized cables: Statics, dynamics, bending strips and coupling with shells

An isogeometric cable formulation is derived from a 3D continuum, where large-deformation kinematics and the St. Venant–Kirchhoff constitutive law are assumed. It is also assumed that the cable cross-sections remain circular, planar, and orthogonal to the cable middle curve during the deformation. The cable geometry representation reduces to a curve in 3D space, and, because only displacement degrees of freedom are employed, only membrane and bending effects are accounted for in the modeling. Torsion is neglected and bending is confined to an osculating plane of the curve. In the case structural loading and response are confined to a plane, the formulation is reduced to a 2D Euler–Bernoulli beam of finite thickness. Bending terms also stabilize the cable formulation in the presence of compressive forces. The resulting cable formulation is validated in the regime of linear and nonlinear statics, and nonlinear dynamics. The concept of bending strips is extended to the case of multiple cables, and cable-shell coupling is also investigated. The formulation is presented in sufficient mathematical detail for straightforward computer implementation.

Effect of compression on wave diffraction by a floating elastic plate

In the present paper, the water wave diffraction by a two-dimensional floating elastic plate is analyzed in the presence of compressive force. The solutions in the cases of infinite and finite water depths are derived based on integro-differential equation method in the presence of compressive force under the assumption of small amplitude water wave theory and plate deflection. Further, wave diffraction by the floating elastic plate is analyzed under the assumption of shallow water approximation. The role of compressive force and its limiting values are obtained by using the hydroelastic analysis of the flexural gravity waves. The limiting values of oblique angle of incidence are obtained in different cases and the effect of compressive force on the oblique angle is analyzed. Effect of compressive force and angle of incidence on the hydroelastic behavior of the floating plate are studied by analyzing the reflection coefficients in different cases.

Wave structure interaction problems for two-layer fluids in three dimensions

The effect of compressive force on flexural gravity waves in two-layer fluids is analysed. Wave characteristics for surface and interfacial modes in the cases of deep and shallow water are studied and the effect of compression on these modes is analysed in special cases from the general problem. Generalized expansion formulae and associated orthogonal mode-coupling relations are derived for the velocity potentials to deal with wave structure interaction problems in three dimensions in both the cases of finite and infinite water depths in channels of finite and semi-infinite widths. Several characteristics of the eigenfunctions are derived in specific cases. As an application of the expansion formulae, wave scattering due to partially frozen cracks in floating ice sheet is analysed in a channel of finite width and depth in the presence of compressive force in two-layer fluids.

Generation of long waves in ice-covered lakes by moving disturbances of atmospheric pressure

The effect of ice cover on the oscillations of water in a two-dimensional constant-depth basin within the linear theory of long waves is considered. The ice cover is treated as thin elastic plate in the presence of compressive force. The ice is fastened hardly to a shore. The eigenfrequencies and eigenfunctions of free oscillations (seishes) are obtained. The forced oscillations of fluid and ice cover under the action of a moving disturbance of atmospheric pressure are investigated. The input data are taken to have values typical of Lake Baikal. The time dependence of total mechanical energy of the fluid is calculated for different velocities of pressure motion. The variations in ice-bending stresses are determined and the causes of shore-ice breaking are explained.

Biomechanical principles in diarthroses and synarthroses. I: Basic concepts in diarthroses

The incongruity of the articulating surfaces is one of the main constructional characteristics of human joints. Unfortunately, this has virtually been neglected in studying of the mechanism of joints. Only in incongruent articulating surfaces does the force locking, which is permanently produced by gravity and/or compressively acting muscular forces (muscular tonus), engender mechanically stable states of balance of the connected limbs. From the incongruity one can conclude that the dimeric link chain represents the most simple constructional element of the human joints. They are force locked, constrained gear systems composed by dimeric link chains. In this context the overlapped dimeric link chain deserves special attention since it is the only mechanically stable device in the presence of compressive forces. We present fundamental terms and characteristics of the gear mechanisms of human joints.

Application of unified fatigue damage approach to compression–tension region

A Unified Approach to fatigue crack growth developed earlier is extended to include the fatigue behavior over the entire load ratio ( R) regime, from compression–tension to tension–tension. This approach provides a self consistent description of cyclic damage using the two loading parameters, Δ K and K max, applicable over the entire crack growth regime. Crack growth behavior in the R>0 regime has been classified into five distinct classes. This classification is extended here to include the negative R-ratio region. When compression loads are included with the tension cycle, each classification is further divided into three additional subsets, reflecting a characteristic change in crack growth mechanisms. The current overall classification provides a methodology for understanding the combined effects of tension and compression loads on crack tip forces and their effect on material crack growth resistance. Like wise the role of environmental effect will also be altered in the presence of compressive forces.

Plastic-Wave Propagation Effects in Transverse Impact of Membranes

The paper is concerned with the plane motion of a rigid-strain-hardening membrane attached to two parallel fixed supports. The membrane is subjected to a uniformly distributed transverse impulse and the subsequent motion of the membrane is to be determined with the particular emphasis on the variation of thickness in the final deflected shape. It is first shown that two essentially different initial modes of deformation exist depending on the average rate of hardening. For both modes, the analysis can be based on two types of waves of discontinuity until the moment when the compressive membrane forces occur in the middle region of the membrane. The presence of compressive forces will generally preclude the existence of a unique solution for further motion. The bending rigidity will probably have to be included into the analysis in order to obtain a unique solution. However, for the technically important rates of hardening and velocities, the kinetic energy of the membrane at the moment of occurrence of compressive forces is small compared with the initial energy, so that significant information could be obtained from the present analysis about the variation of thickness and hardening throughout the membrane.