Energy-momentum tensor in QCD: nucleon mass decomposition and mechanical equilibrium

We review and examine in detail recent developments regarding the question of the nucleon mass decomposition. We discuss in particular the virial theorem in quantum field theory and its implications for the nucleon mass decomposition and mechanical equilibrium. We reconsider the renormalization of the QCD energy-momentum tensor in minimal-subtraction-type schemes and the physical interpretation of its components, as well as the role played by the trace anomaly and Poincaré symmetry. We also study the concept of “quantum anomalous energy” proposed in some works as a new contribution to the nucleon mass. Examining the various arguments, we conclude that the quantum anomalous energy is not a genuine contribution to the mass sum rule, as a consequence of translation symmetry.

Condensation tendency and planar isotropic actin gradient induce radial alignment in confined monolayers

A monolayer of highly motile cells can establish long-range orientational order, which can be explained by hydrodynamic theory of active gels and fluids. However, it is less clear how cell shape changes and rearrangement are governed when the monolayer is in mechanical equilibrium states when cell motility diminishes. In this work, we report that rat embryonic fibroblasts (REF), when confined in circular mesoscale patterns on rigid substrates, can transition from the spindle shapes to more compact morphologies. Cells align radially only at the pattern boundary when they are in the mechanical equilibrium. This radial alignment disappears when cell contractility or cell-cell adhesion is reduced. Unlike monolayers of spindle-like cells such as NIH-3T3 fibroblasts with minimal intercellular interactions or epithelial cells like Madin-Darby canine kidney (MDCK) with strong cortical actin network, confined REF monolayers present an actin gradient with isotropic meshwork, suggesting the existence of a stiffness gradient. In addition, the REF cells tend to condense on soft substrates, a collective cell behavior we refer to as the 'condensation tendency'. This condensation tendency, together with geometrical confinement, induces tensile prestretch (i.e., an isotropic stretch that causes tissue to contract when released) to the confined monolayer. By developing a Voronoi-cell model, we demonstrate that the combined global tissue prestretch and cell stiffness differential between the inner and boundary cells can sufficiently define the cell radial alignment at the pattern boundary.

“ hv-Energy Packet floating in Front of the Wave Beam” Hybrid Structure of Photon and its Self-Interference in the Single Photon Double-Slits Experiment

In the single photon double slits experiment, what mechanism makes the interference? Whether it is owing to the external factor or the photon has a special structure it can interfere photon itself to make the interference pattern? Because the photon is a quantum of EM radiation as Einstein proposed, so we start the study from an EM wave beam (an EM radiation). Under the demand of the symmetry and quantization, we found the wave beam is certainly circular polarized and covered by a side membrane. There is a pair of ± charges ±q and the circular tension distributes double helically along the side membrane. Quantization of charges requires ( k=2.3,...). Mechanical equilibrium among the helical distributed or, tension and the circular polarized EM field inside construct a steady structure to keep the quantized EM beam integrity, shape and size. Its energy hv concentrates in a cylindrical packet of radius R max and length , named -(energy) packet. With the aid of Einstein theory of spontaneous emission, we proved that the photon is consisted of the energy packet and accompany with a conical - (EM) wave beam; -packet floats in front of the -wave. It is such hybrid structure that makes photon self interference in the double slits experiment.

Diffusion Mechanisms for the Occurrence of the Instability of Mechanical Equilibrium of a Ternary Gas Mixture Containing Carbon Dioxide

Mixing of carbon dioxide dissolved in a multicomponent gas mixture at different pressures was researched. It was found that the mechanical equilibrium of the ternary gas mixture 0.4163H2 (1) + 0.5837CO2 (2) − N2 (3) is violated at a pressure of p = 0.7 MPa and structured flows appear in the system. The pressure area (from 0.7 to 1.5 MPa) at which the conditions of priority transfer of components with the highest molecular weight in the mixture are realised in the system is fixed. To analyse the effect of pressure on the process of changing “diffusion–convection” modes, a mathematical model, which takes into account the kinetic features of multicomponent mixing, was applied. It was shown that the change in the modes of mass transfer is associated with a significant difference in the diffusion ability of the components. It is noted that the difference in the diffusion coefficients of components results in the nonlinearity of the concentration distribution, which leads to the inversion of the density gradient of the gas mixture, which is the cause of convective flows.

Mechanical Equilibrium Dynamics Controlling Wetting State Transition at Low-Temperature Superhydrophobic Array-Microstructure Surfaces

Superhydrophobic materials are significant for engineering applications in the anti-icing field because of their non-wetting property. The interface physical mechanisms of non-wetting properties are important to promote real applications of superhydrophobic surfaces, especially under low-temperature conditions. Here, we found that low temperature could induce the wetting state transition from a Cassie–Baxter state to a Wenzel state. This transition occurred at 14 °C (and 2 °C) on superhydrophobic surfaces with pillar heights of 250 μm (and 300 μm). As a consequence, the driving-force of the Cassie-Wenzel (C-W) wetting transition was induced by the contraction of air pockets on cooling, and the pressure of air pockets supporting the droplet decreased with the contraction degree. Decreasing the pressure of air pockets broke the mechanical equilibrium at the solid–liquid contact interface, and the continuous contraction overcame the resistance in the C-W wetting transition. Based on the analysis of work against resistance in the C-W wetting transition, lower C-W wetting transition temperature was mainly attributed to a higher pillar, which produced more work against resistance to require more energy. This energy was directly reflected by the energy required for continuous contraction of air pockets. Superhydrophobic surfaces with higher pillar structure remain stable non-wetting property at low-temperature conditions. This work provides theoretical support for the application of superhydrophobic materials in low-temperature environments.

STUDY OF CONVECTIVE FLOWS IN THREE-COMPONENT GAS MIXTURES BY THE METHOD OF NUMERICAL SIMULATION

The characteristics of convective flows arising in three-component gas mixtures are investigated by the method of numerical simulation. The time variation of the isoconcentration lines of the heavy component of the mixture and the average velocity are considered as characteristics of convective flows. To calculate the characteristics of convective flows arising in a vertical cylindrical channel, we used a numerical model based on the splitting scheme according to physical parameters. It was shown that in three-component gas mixtures, where special diffusion regimes are manifested, non-monotonic distributions of component concentrations and velocities are possible. The time of loss of stability of mechanical equilibrium and the time of developed convective flows are determined.

A new equation for period vectors of crystals under external stress and temperature in statistical physics: mechanical equilibrium condition and equation of state

Starting with the rigorous derivation of the work done on the center cell by external forces, a new equation is derived for the period vectors (cell edge vectors) in crystals under external stress and temperature. Since the equation is based on the principles of statistical physics, it applies to both classical and quantum systems. The existing theory for crystals under external pressure is covered as a special case. The new equation turns out to be the mechanical equilibrium condition and the equation of state for crystals under external stress and temperature. It may be used to predict crystal structures and to study structural phase transitions and crystal expansions. For linear elastic crystals, it takes the microscopic and temperature-dependent form of the generalized Hooke’s law, and may therefore be used to calculate the corresponding elastic constants. It should be helpful in studying piezoelectric and piezomagnetic materials, as the period vectors change with external stress. It is also consistent and can be combined with the previously derived corresponding one for Newtonian dynamics.

Notch in mechanotransduction – from molecular mechanosensitivity to tissue mechanostasis

ABSTRACTTissue development and homeostasis are controlled by mechanical cues. Perturbation of the mechanical equilibrium triggers restoration of mechanostasis through changes in cell behavior, while defects in these restorative mechanisms lead to mechanopathologies, for example, osteoporosis, myopathies, fibrosis or cardiovascular disease. Therefore, sensing mechanical cues and integrating them with the biomolecular cell fate machinery is essential for the maintenance of health. The Notch signaling pathway regulates cell and tissue fate in nearly all tissues. Notch activation is directly and indirectly mechanosensitive, and regulation of Notch signaling, and consequently cell fate, is integral to the cellular response to mechanical cues. Fully understanding the dynamic relationship between molecular signaling, tissue mechanics and tissue remodeling is challenging. To address this challenge, engineered microtissues and computational models play an increasingly large role. In this Review, we propose that Notch takes on the role of a ‘mechanostat’, maintaining the mechanical equilibrium of tissues. We discuss the reciprocal role of Notch in the regulation of tissue mechanics, with an emphasis on cardiovascular tissues, and the potential of computational and engineering approaches to unravel the complex dynamic relationship between mechanics and signaling in the maintenance of cell and tissue mechanostasis.