Dissipation Coefficient Research Articles

Dissipative Kinematics in Binary Neutron Star Mergers

We highlight the recent progress in the calculation of transport coefficients pertinent to binary neutron star mergers. Specifically, we analyze the bulk viscosity coefficient driven by both the DURCA and MURCA processes and electron transport coefficients in dense and hot plasma relevant to the merger scenario. The study considers high temperatures (T>6×1010 K) and dense environments (nB∼n0−3n0). Bulk viscosity exhibits resonant behavior, with peak values and Peak positions dependent on particle interaction rates and thermodynamic susceptibilities. Susceptibilities are calculated by modeling the nuclear matter in the density functional approach. The bulk viscosity coefficient peaks at T∼1011 K, with a compression–rarefaction oscillation dissipation time scale of 20–50 ms. Electrical transports incorporate frequency-dependent dynamical screening in quantized electron–ion scattering rates. Consequently, dynamical screening reduces the maxima of electrical and thermal conductivities, shortening corresponding dissipation time scales. These results highlight the crucial role of dissipation coefficients in understanding binary neutron star mergers.

Warm inflation in a Universe with a Weylian boundary

We investigate the influence of boundary terms in the warm inflationary scenario, by considering that in the Einstein–Hilbert action the boundary can be described in terms of a Weyl-type geometry. The gravitational action, as well as the field equations, are thus extended to include new geometrical terms, coming from the non-metric nature of the boundary, and depending on the Weyl vector, and its covariant derivatives. We investigate the effects of these new boundary terms by considering the warm inflationary scenario of the early evolution of the Universe, in the presence of a scalar field. We obtain the generalized Friedmann equations in the Universe with a Weylian boundary by considering the Friedmann–Lemaitre–Robertson–Walker metric. We consider the simultaneous decay of the scalar field, and of the creation of radiation, by appropriately splitting the general conservation equation through the introduction of the dissipation coefficient, which can depend on both the scalar field, and the Weyl vector. We consider three distinct warm inflationary models, in which the dissipation coefficients are chosen as different functions of the scalar field and of the Weyl vector. The numerical solutions of the cosmological evolution equations show that the radiation is created during the very early phases of expansion, and, after the radiation reaches its maximum value, the transition from an accelerating inflationary phase to a decelerating one takes place. Moreover, it turns out that the Weyl vector, describing the boundary effects on the cosmological evolution, plays a significant role during the process of radiation creation.

Seismic behaviors of steel-FRP composite bar-reinforced engineered cementitious composites columns under reversed cyclic loads

The combination of steel-FRP composite bar (SFCB) and engineered cementitious composites (ECC) in structures exposed to harsh conditions can offer benefits in mechanical performance and durability. In this study, the seismic behaviors of SFCB-reinforced ECC and concrete columns were investigated through reversed cyclic loading tests and the effects of matrix types, axial load ratios, and reinforcing bar types were discussed. The results showed that the SFCB-reinforced ECC columns experienced flexural failure characterized by SFCB fracture, whereas the SFCB-reinforced concrete columns failed owing to concrete crushing. The SFCB-reinforced ECC columns showed a 41.5 %− 116.3 % enhancement in deformation capacity and a 34.7 %− 65.2 % improvement in average energy dissipation coefficient compared with SFCB-reinforced concrete columns, which demonstrated that using ECC in SFCB-reinforced columns addressed issues of their low deformation and low energy dissipation capacity. In addition, the plastic hinge length of SFCB-reinforced columns increased substantially with the application of ECC, and the stiffness degeneration and residual deformation were reduced.

Preparation and Evaluation of Epoxy Based Material for High Performance Electronic Packaging through the Surface Modification of Fillers

The continuous integration and refinement of electronic equipment results in the more stringent requirements for epoxy resin (EP) based materials, such as excellent heat dissipation and low coefficient of thermal expansion (CTE). In order to improve the dispersion of silica powder (SP) in EP and thus expand the application of EP in the field of electronic packaging, our research described in this paper adopted the KH-550 coupling agent to modify the surface of SP (m-SP). The effects of KH-550 coupling agent on the characteristics of the composites were investigated in terms of thermal, rheological, electrical insulation and mechanical properties. The results showed that when the content of KH-550 was 2 wt% of the fillers, the best modification effect was achieved, and the surface properties of the fillers were changed accordingly. In particular, the materials filled with m-SP exhibited lower viscosity end, better mechanical and electrical insulation properties. It was also found that the adding of the KH-550 had different effects on the thermal degradation, dynamic thermo-mechanical properties and the thermal deformation behavior of the materials. According to our study, the thermal conductivity and the CTE of m-SP/EP filled with 70 wt% of modified fillers were 0.787 W/m.K and 28.3 ppm/°C respectively, corresponding to a significant thermal conductivity improvement and low CTE.

Poles, shocks, and tygers: The time-reversible Burgers equation.

We construct a formally time-reversible, one-dimensional forced Burgers equationby imposing a global constraint of energy conservation, wherein the constant viscosity is modified to a fluctuating state-dependent dissipation coefficient. The system exhibits dynamical properties which bear strong similarities with those observed for the Burgers equationand can be understood using the dynamics of the poles, shocks, and truncation effects, such as tygers. A complex interplay of these give rise to interesting statistical regimes ranging from hydrodynamic behavior to a completely thermalized warm phase. The end of the hydrodynamic regime is associated with the appearance of a shock in the solution and a continuous transition leading to a truncation-dependent state. Beyond this, the truncation effects such as tygers and the appearance of secondary discontinuity at the resonance point in the solution strongly influence the statistical properties. These disappear at the second transition, at which the global quantities exhibit a jump and attain values that are consistent with the establishment of a quasiequilibrium state characterized by energy equipartition among the Fourier modes. Our comparative analysis shows that the macroscopic statistical properties of the formally time-reversible system and the Burgers equationare equivalent in all the regimes, irrespective of the truncation effects, and this equivalence is not just limited to the hydrodynamic regime, thereby further strengthening the Gallavotti's equivalence conjecture. The properties of the system are further examined by inspecting the complex space singularities in the velocity field of the Burgers equation. Furthermore, an effective theory is proposed to describe the discontinuous transition.

A study on attenuation patterns of acoustic waves in waveguide structures with flexural boundaries

This research article investigates the attenuation patterns of acoustic waves within waveguide structures featuring flexural boundaries. By employing advanced methods in vibrations and controls, the study aims to enhance our understanding of waveguide behavior and offer valuable insights for optimizing acoustic wave propagation in diverse applications. The entire waveguide structure is tuned through cooperative interactions involving elastic plates, membranes, and rigid boundary surfaces. The lower boundary of the expansion chamber consists of a rigid plate, with elastic membranes covering the upper surfaces of the cavity. The problem is formulated in terms of transmission and reflection coefficients of the modes, enabling the solution of the scattering problem. Matching acoustic pressure and velocity at the waveguide junction yields the scattering coefficients. The results reveal that the scattering coefficients are intricately influenced by both the geometric characteristics of the waveguide and the frequency of the incident waves. Notably, the first higher-order mode of the cut-off frequency of the waveguide structure corresponds to the frequency at which the dissipation coefficient reaches its maximum value. This research provides valuable insights into the scattering behavior of acoustic waves in waveguide configurations, contributing to the design of acoustic devices and systems. Rigorous support and justification for all aspects of the mode-matching method, including pressure and velocity matching, eigen properties, physical edge conditions, convergence criteria, and energy conservation, are provided through thorough algebraic and numerical analyses, confirming the validity of the solution methodology.

Research on axial compressive performance of ceramic concrete reinforced with HTPP fibers

This study investigates the influence of High-Toughness Polypropylene (HTPP) fiber content (0 %, 0.3 %, 0.6 %, 0.9 %) on the axial compressive performance of ceramsite concrete. Four sets of ceramsite concrete cube and prism specimens were prepared, and the cube compressive strength and full stress-strain curves for each set were tested. Based on the experimental results, it analyzed the variation characteristics of HTPP fibers on the stress-strain curve of ceramic concrete at different stages, studied the peak stress, peak strain, elastic modulus, toughness, and energy absorption capacity of ceramic concrete. Finally, the stress-strain curve has been fitted. The results indicate that: HTPP fibers can significantly enhance the strength and toughness of ceramic concrete, the compressive strength of the cube increased by 23.8 %, the axial compressive strength increased by 19.0 %, the residual stress increased by 143.0 %, the absolute modulus increased by 164.1 %, the toughness increased by 51.5 %, and the energy dissipation coefficient increased by 9.4 %. By fitting the experimental curve, the mathematical expression for the uniaxial compressive stress-strain curve of ceramic concrete reinforced with high tenacity polypropylene (HTPP) fibers has been proposed. The model matches well with the experimental results, which provides a theoretical basis for the structural analysis and design of this type of concrete.

Experimental Study on Spacing Effect in Arrays of Draft-Varying Floating WEC-Dikes

This study examines the impact of the spacing parameter on the efficacy of an array of hybrid modules functioning as both floating breakwaters and wave energy converters. The dual functionality is ensured by the ability of the device to autoadjust its submergence. The behavior of multiple 1:40 scaled modules was tested in the wave tank of the University of Campania “Luigi Vanvitelli”. The objective was to assess the hydraulic performance of the array by analyzing transmission, reflection, and dissipation coefficients under different wave conditions. Specifically, the transmission coefficient ranges between 0.85 and 0.51, depending on the relative wavelength and wave steepness, while the reflection and dissipation coefficients vary, respectively, between 0.70–0.20 and 0.55–0.3. In any case, the results underscore the critical importance of the spacing parameter.

Weak (non)conservation and stochastic dynamics of angular momentum

Angular momentum conservation influences equilibrium statistical mechanics, leading to a generalized microcanonical density for an isolated system and a generalized Gibbs density for a weakly coupled system. We study the stochastic decay of angular momentum due to the weakly imperfect rotational symmetry of the external potential that confines the isolated many-particle system. We present a mesoscopic description of the system, deriving Langevin and Fokker–Planck equations, which are consistent with equilibrium statistical mechanics when rotational symmetry is maintained. When the symmetry is weakly violated, we formulate a coarse-grained stochastic differential equation governing the decay of total angular momentum over time. To validate our analytical predictions, we conduct numerical simulations of the microcanonical ensemble, an isolated system undergoing thermalization due to weak two-body interactions. Our coarse-grained Langevin equation accurately characterizes both the decay of the angular momentum and its fluctuations in a steady state. Furthermore, we estimate the parameters of our mesoscopic model directly from simulations, providing insights into the dissipative phenomenological coefficients, such as friction. More generally, this study contributes to a deeper understanding of the behavior of the integrals of motion when the corresponding symmetry is weakly violated.

Dissipative stratified elastic metamaterials for broadband blast-wave impact mitigation

In this paper, impact attenuation and blast-wave mitigation are effectively realized by the dissipative stratified metamaterials with negative mass mechanism due to the coupling of the different resonators. To create a broad bandgap of the metamaterials, the dispersion curve and effective negative mass property are investigated. It is found that the coupling effect of different resonators produced by the relative movement of different main masses can create a broad bandgap and make the original bandgap by starting with a lower frequency, and thus impact input waves could be blocked effectively. Simulation results show that a stratified elastic metamaterial containing 25 units can reduce the amplitude of the load by two thirds under impact loading and almost completely impede its further propagation. Furthermore, the bandgap is broadened by optimization of the structure parameters and dissipative coefficient for blocking transient shock waves propagation. It is shown in numerical experiment that the wider bandgap produced by the new elastic metamaterials can effectively absorbed the energy of the blast and impact waves. Therefore, the results of this study provide a remarkably novel strategy for the design of new blast-resistant materials.

Multiple scroll attractors and multistability in the collective dynamics of a four chain coupled hopfield inertial neuron network: analysis and circuit design investigations

This work deals with the chain bidirectional coupling of four inertial Hopfield neurons. Each of our cells taken alone is modeled by a second order differential equation having three resting points. Coupling these neurons helps increasing the number of fixed points that is related to the amount of memory assigned to the network. The system having a hyperbolic tangent as nonlinearity is investigated with the help of suitable nonlinear dynamical tools like bifurcation diagrams, Lyapunov exponent diagrams and phase portraits to resort the richness of the model. As the coupling adds the amount of equilibriums, it also helps in generating multiple scroll attractors. The system that was unable of oscillation presents firing patterns such as parallel branches, coexistence of up to sixteen attractors in the phase plane, extreme events and Hopf bifurcation to name a few. All these features are discovered when observing the coupling strengths, the dissipation coefficient and when programming initial states around sensitive equilibriums. The electronic version of the four-chain coupled inertial neurons system is provided and simulated on Pspice with the aim to confirm the results obtained in the numerical scheme.

Relationship between Ambient Temperature and Reasonable Heat Dissipation Coefficient of Mass Concrete Pouring Blocks.

In engineering practice, similar surface insulation measures are typically applied to different parts of mass concrete surfaces. However, this can lead to cracking at the edges of the concrete surface or the wastage of insulation materials. In comparison to flat surfaces, the edges of mass concrete structures dissipate heat more rapidly, leading to more pronounced stress concentration phenomena. Therefore, reinforced insulation measures are necessary. To reduce energy consumption and enhance overall insulation effectiveness, it is essential to study the specific insulation requirements of both the flat surfaces and edges of concrete separately and implement targeted surface insulation measures. Taking the bridge abutment planned for pouring in Nanjing City as the research object, this study established a finite element model to explore the effects of different ambient temperatures and different surface heat dissipation coefficients on the early-age temperature and stress fields of different parts of the abutment's surface. Based on simulation results, reasonable heat dissipation coefficients that meet the requirements for crack prevention on both the structure's plane and edges under different ambient temperatures were obtained. The results indicate that under the same conditions, the reasonable heat dissipation coefficient at the edges was smaller than that on the flat surfaces, indicating the need for stronger insulation measures at the edges. Finally, mathematical models correlating ambient temperature with reasonable heat dissipation coefficients for the structure's plane and edges at these temperatures were established, with high data correlation and determination coefficients (R2) of 0.95 and 0.92. The mathematical models were validated, and the results from finite element calculations were found to be consistent with those from the mathematical models, validating the accuracy of the mathematical models. The conclusions drawn can provide references for the insulation of similar engineering concrete planes and edges.

Research on mechanical properties of metal rubber based on planar lattice design

Metal rubber is a common vibration is olation material. Because the arrangement of the internal spiral coil will affect the mechanical properties of the metal rubber, this paper draws on the crystal lattice theory in metallurgy, changes the mesoscopic arrangement of the spiral coil through the design of the two-dimensional blank plane lattice structure, and prepares three kinds of lattice structures, and optimizes the mass ratio of the three metal rubber lattice structures, so as to improve the average stiffness and energy dissipation coefficient of the metal rubber. The quasi-static compression experiments passed. The results show that the triangular lattice structure design can reflect the good average stiffness, and the square lattice structure design can obtain the maximum energy dissipation coefficient. The study confirms that the fabrication of metal rubber materials based on planar lattice design is an effective way to improve stiffness and energy dissipation.

A numerical study of electron-magnetohydrodynamics tearing modes in parameter ranges of experimental interest

We perform a numerical study of the linear dynamics of tearing modes in slab incompressible electron-magnetohydrodynamics (EMHD) by considering some parameter ranges, which can be of interest for laboratory plasmas (e.g., helicon devices) or for astrophysics (e.g., solar-wind turbulence). To this purpose, several non-ideal effects are simultaneously retained (finite electron inertia, resistivity, and electron viscosity), and we make distinction between the dissipation coefficients in the direction parallel and perpendicular to the guide field. We thus identify some new reconnection regimes, characterized by a departure from the customary monotonic power-law scalings of the growth rates with respect to the non-ideal parameters. The results here presented can provide a useful indication for future studies of EMHD regimes relevant to experiments and for extensions of the EMHD tearing mode modeling to more complete regimes including kinetic effects (e.g., “electron-only” reconnection in kinetic regimes).

Theory of elastic wave propagation in a fluid-saturated multi-porous medium with multi-permeability

This paper establishes the concept of elastic wave propagation in a multi-porous medium with different permeabilities by assuming there are n distinct pore fluid phases. The dynamic equation of motion of elastic wave propagation through this multi-porous medium is derived based on Lagrangian mechanics. In this regard, the generalized form of mass coefficients and then the energy loss due to the fluid phases in terms of dissipation coefficients are presented for low-frequency limits with the help of Darcy’s Law of multi-phases system. The elastic coefficients of the constitutive equation in terms of compliance matrix are identified using a series of Gedanken experiments. Some significant results regarding the compressional and rotational waves in a multi-porosity medium are derived. The validation of the theory has been shown by comparing it with the existing theory of single and double porosity. It is observed that there are ( n + 1 ) compressional waves corresponding to solid and fluid phases, whereas only one rotational wave is associated with the solid phase. The concept of multi-porosity theory can contribute to a deeper understanding of wave behaviour in a porous medium.

Energy evolution and strain localization in fractured sandstone under freeze-thaw cycling and uniaxial loading-unloading

In cold regions, combined cyclic freeze-thaw (F-T) and loading-unloading can cause rock slope instability and sliding. The macro-failure of rock masses originates from the expansion of strain localization areas driven by energy. Therefore, a deep understanding of the energy evolution and strain distribution can reveal the instability process. Along these lines, in this work, intact and intermittently jointed sandstones were subjected to a cyclic F-T environment and subsequently carried out uniaxial graded loading-unloading to obtain their mechanical parameters and X-ray computed tomography images. By investigating the energy density, it was found that the input, elastic, dissipated, and damage energies all increased with loading according to a quadratic polynomial function, with the energies obeying a linear allocation law. Meanwhile, F-T changed the energy storage capacity and energy dissipation coefficient of the rock by causing meso-damage. To measure the meso-scale strain localization characteristics, the advanced digital volume correlation technique was also used to obtain three-dimensional strain fields. In terms of local strain, the failure behavior of intact specimens under the application of low and high numbers of F-T cycles was controlled by potential fracture bands and frost-heave cracks, respectively, while fractured specimens were mainly dependent on the macro-fracture arrangement. However, both frost heaving and thawing transformed sandstone from brittle to ductile. In terms of statistical strain, the equivalent strain (εeq) showed a log-normal distribution and continued to deviate to the right due to loading-unloading. Meanwhile, the normal strain (εxx, εyy, εzz) exhibited a normal distribution, where fractured sandstone mainly developed along with the slip direction. Finally, the intrinsic correlations among the energy parameters, meso-damage, and macro-failure were discussed. From our analysis, three stages of energy allocation and transformation were revealed, namely the uniform allocation of damage energy, banded accumulation of damage energy, and fracture caused by the elastic energy release.

Myocardial biomechanical effects of fetal aortic valvuloplasty

Fetal critical aortic stenosis with evolving hypoplastic left heart syndrome (CAS-eHLHS) can progress to a univentricular (UV) birth malformation. Catheter-based fetal aortic valvuloplasty (FAV) can resolve stenosis and reduce the likelihood of malformation progression. However, we have limited understanding of the biomechanical impact of FAV and subsequent LV responses. Therefore, we performed image-based finite element (FE) modeling of 4 CAS-eHLHS fetal hearts, by performing iterative simulations to match image-based characteristics and then back-computing physiological parameters. We used pre-FAV simulations to conduct virtual FAV (vFAV) and compared pre-FAV and post-FAV simulations. vFAV simulations generally enabled partial restoration of several physiological features toward healthy levels, including increased stroke volume and myocardial strains, reduced aortic valve (AV) and mitral valve regurgitation (MVr) velocities, reduced LV and LA pressures, and reduced peak myofiber stress. FAV often leads to aortic valve regurgitation (AVr). Our simulations showed that AVr could compromise LV and LA depressurization but it could also significantly increase stroke volume and myocardial deformational stimuli. Post-FAV scans and simulations showed FAV enabled only partial reduction of the AV dissipative coefficient. Furthermore, LV contractility and peripheral vascular resistance could change in response to FAV, preventing decreases in AV velocity and LV pressure, compared with what would be anticipated from stenosis relief. This suggested that case-specific post-FAV modeling is required to fully capture cardiac functionality. Overall, image-based FE modeling could provide mechanistic details of the effects of FAV, but computational prediction of acute outcomes was difficult due to a patient-dependent physiological response to FAV.

Cyclic behavior and constitutive relations of HRB400E steel under large strain range

To study the differences in material performance between HRB400E steel and conventional strength steel, this paper performed monotonic and cyclic loading tests on HRB400E and Q355B steels under a series of loading protocols. Additionally, the self-designed fixtures were used to achieve large strain rate loading. The ductility, monotonic behavior and hysteretic characteristics of HRB400E and Q355B steels were assessed, along with the energy dissipation capacity evaluated through the energy dissipation coefficients. The cyclic skeleton curves of both steels were fitted using the Ramberg-Osgood model, with further investigation into the influence of kinematic hardening parameters on hysteretic curves. The combined hardening parameters of the Voce-Chaboche model were calibrated based on the experimental results, and the hysteretic curves were simulated under different loading protocols via ANSYS. The analysis results reveal that the energy dissipation coefficients of HRB400E steel are larger than that of Q355B steel, yet smaller than those of Q460D, LYP100, LY100, LY160, and LY225 steels. Both HRB400E and Q355B steels demonstrate significantly improved material strength under cyclic loading. Excellent agreement between simulated and experimental curves is achieved when using four pairs of kinematic hardening parameters. Additionally, the hysteretic performance of HRB400E and Q355B steels under different cyclic loading protocols can be precisely simulated by employing calibrated combined hardening parameters. Through this paper, the cyclic behavior and constitutive relations of HRB400E steel are comprehensively understood, which provides a reliable theoretical basis for engineering design and structural analysis. Furthermore, this research provides a scientific basis for material applications of HRB400E steel.

Модельные технологические решения по обеспечению качества изделий при обработке точением

Model technological solutions for ensuring the quality of products during turning processing are proposed. A study of the workability of materials based on the ISO classification was carried out. To clarify the workability group, the MS code system was used, which allowed not only to clarify the workability group and the terms of delivery of the workpiece, but also to determine the specific cutting force. Based on the classifier-handbook, the parameters of the prefabricated cutting tool were selected and the technological modes for the prescribed processing conditions were determined. Based on the obtained specific cutting force, an algorithm for simplified determination of the cutting force is implemented. A study of the vibrations of the technological machining system was performed, which made it possible to formulate dynamic models for the system as a whole, subsystems of the workpiece and cutting tool. In relation to the dynamic model of the workpiece subsystem. The model has been simplified. A dynamic cutting characteristic was constructed, which made it possible to build an autonomous dynamic model of the technological system. In relation to this model, parameterization was performed, which made it possible to determine the stiffness coefficients of the fixed workpiece, as well as the inertia and dissipation coefficients. In relation to the selected processing conditions, the accuracy and roughness of the treated surface were checked. A study of the stability of the technological system of mechanical processing based on the algebraic Hurwitz criterion is carried out. In the general formulation, the Hurwitz determinant and stability conditions are obtained. The performed complex of calculations showed that the conditions determined by the Hurwitz stability criterion are met. This indicates that when processing in the selected modes, quiet cutting is carried out, which ensures the requirements for the quality of the product. The construction of the stability boundary can be performed in the space of variable technological parameters using the D-partitioning method or based on the R. Loeb algorithm. As a result of constructing the stability boundary in the space of variable parameters, the area of permissible technological modes is highlighted, which is the basis for solving the problem of processing control in accordance with the formed efficiency criteria. The complex of technological solutions presented in the article was deployed and implemented in relation to the turning of coating discs, as well as discs of turbines and compressors of gas turbine engines.

Fatigue characteristics and energy evolution analysis of red sandstone under the coupling of freeze–thaw and cyclic loading

In order to improve the safety of rock mass engineering in cold regions, this paper discusses the fatigue characteristics and energy evolution of red sandstone under the coupling of freeze–thaw and cyclic loading. Firstly, the correlation between the fatigue life, failure stress, and the number of freeze–thaw cycles of the red sandstone samples was calculated using the Pearson correlation coefficient method. Secondly, the energy evolution of the samples was analyzed using the image integration method and the least squares method. Finally, the damage mechanism of the samples under the coupled effect of freeze–thaw and cyclic loading was discussed using a conceptualized model. The results show that freeze–thaw cycles are negatively correlated with fatigue life and failure stress. The increase in freeze–thaw and fatigue damage leads to an increase in ductility and a decrease in the stiffness of the samples. The total energy density, elastic energy density, and dissipated energy density of the samples all show a quadratic polynomial relationship with the stress level. The energy storage and dissipation coefficients are negatively and positively correlated with the number of freeze–thaw cycles, respectively.