Effective potential of scalar-tensor gravity with quartic self-interaction of scalar field

One-loop effective potential of scalar-tensor gravity with a quartic scalar field self-interaction is evaluated up to first post-Minkowskian order. The potential develops an instability in the strong field regime which is expected from an effective theory. Depending on model parameters the instability region can be exponentially far in a strong field region. Possible applications of the model for inflationary scenarios are highlighted. It is shown that the model can enter the slow-roll regime with a certain set of parameters.

Variation in Extreme Temperature and Its Instability in China

In this study, the instability of extreme temperatures is defined as the degree of perturbation of the spatial and temporal distribution of extreme temperatures, which is to show the uncertainty of the intensity and occurrence of extreme temperatures in China. Based on identifying the extreme temperatures and by analyzing their variability, we refer to the entropy value in the entropy weight method to study the instability of extreme temperatures. The results show that TXx (annual maximum value of daily maximum temperature) and TNn (annual minimum value of daily minimum temperature) in China increased at 0.18 °C/10 year and 0.52 °C/10 year, respectively, from 1966 to 2015. The interannual data of TXx’ occurrence (CTXx) and TNn’ occurrence (CTNn), which are used to identify the timing of extreme temperatures, advance at 0.538 d/10 year and 1.02 d/10 year, respectively. In summary, extreme low-temperature changes are more sensitive to global warming. The results of extreme temperature instability show that the relative instability region of TXx is located in the middle and lower reaches of the Yangtze River basin, and the relative instability region of TNn is concentrated in the Yangtze River, Yellow River, Langtang River source area and parts of Tibet. The relative instability region of CTXx instability is distributed between 105° E and 120° E south of the 30° N latitude line, while the distribution of CTNn instability region is more scattered; the TXx’s instability intensity is higher than TNn’s, and CTXx’s instability intensity is higher than CTNn’s. We further investigate the factors affecting extreme climate instability. We also find that the increase in mean temperature and the change in the intensity of the El Niño phenomenon has significant effects on extreme temperature instability.

Nuclear Adiabatic Effects of Electron-Positron Pairs on the Dynamical Instability of Very-Massive Stars

The adiabatic effects of electron-positron pair-production on the dynamical instability of very-massive stars is investigated from stellar progenitors of carbon-oxygen cores within the range of 64 M < MCO < 133 M both with and without rotation. At a very high temperature and relatively low density; the production of electron-positron pairs in the centres of massive stars leads the adiabatic index to below 4/3. The adiabatic quantities are evaluated by constructing a model into a thermodynamically consistent electron-positron equation of state (EoS) table. It is observed that the adiabatic indices in the instability regions of the rotating models are fundamentally positive with central temperature and density. Similarly, the mass of the oxygen core within the instability region has accelerated the adiabatic indices in order to compress the star, while the mass loss and adiabatic index in the non-rotating model exponentially decay. In the rotating models, a small amount of heat is required to increase the central temperature for the end fate of the massive stars. The dynamic of most of the adiabatic quantities show a similar pattern for all the rotating models. The non-rotating model may not be suitable for inducing the instability. Many adiabatic quantities have shown great effects on the dynamical instability of the massive stars due to electron-positron pair-production in their centres. The results of this work would be useful for better understanding of the end fate of very-massive stars.

Dynamic Instability Analysis and Design Charts of Curved Panels with Linearly Varying Periodic In-Plane Load

The present paper reports an extensive study on dynamic instability characteristics of curved panels under linearly varying in-plane periodic loading employing finite element formulation with a quadratic isoparametric eight nodded element. At first, the influences of three types of linearly varying in-plane periodic edge loads (triangular, trapezoidal and uniform loads), three types of curved panels (cylindrical, spherical and hyperbolic) and six boundary conditions on excitation frequency and instability region are investigated. Further, the effects of varied parameters, such as shallowness parameter, span to thickness ratio, aspect ratio, and Poisson’s ratio, on the dynamic instability characteristics of curved panels with clamped–clamped–clamped–clamped (CCCC) and simply supported-free-simply supported-free (SFSF) boundary conditions under triangular load are studied. It is found that the above parameters influence significantly on the excitation frequency, at which the dynamic instability initiates, and the width of dynamic instability region (DIR). In addition, a comparative study is also made to find the influences of the various in-plane periodic loads, such as uniform, triangular, parabolic, patch and concentrated load, on the dynamic instability behavior of cylindrical, spherical and hyperbolic panels. Finally, typical design charts showing DIRs in non-dimensional forms are also developed to obtain the excitation frequency and instability region of various frequently used isotropic clamped spherical panels of any dimension, any type of linearly varying in-plane load and any isotropic material directly from these charts without the use of any commercially available finite element software or any developed complex model.

Nonlinear Instability and Reliability Analysis of Composite Laminated Beams

The wide range of high performance engineering applications of composite laminated structures demands a proper understanding of their dynamics performance. Due to the complexity and nonlinear behaviour of such structures, developing a mathematical model to determine the dynamic instability boundaries is indispensable and challenging. The aim of this research is to investigate the dynamic behaviour of shear deformable composite laminated beams subjected to varying time conservative and nonconservative loads. The dynamic instability behaviour of non-conservative and conservative system are dissimilar. In case of conservative loading, the instability region intersects the loading axis, but in case of non-conservative loads the region will be increased with loading increases. The extended Hamilton’s principle and the first order shear deformation theory are employed in this investigation to establish the integral form of the equation of motion of the beam. A five node beam model is presented to descritize the integral form of the governing equations. The model has the capability to capture the dynamic effects of the transverse shear stress, warping, and bending-twisting, bending-stretching, and stretching-twisting couplings. Also, the geometric and loading nonlinearities are included in the equation of system. The beam model incorporates, in full form, the non-classical effects of warping on stability and dynamic response of symmetrical and unsymmetrical composite beams. In case of nonlinear elasticity, the resonance curves are bent toward the increasing exciting frequencies. The response of the stable beam is pure periodic and follow the loading frequency. When the beam is asymptotically stable the response of the beam is aperiodic and does not follow the loading frequency. In unstable state of the beam response frequency increases with time and is higher than the loading frequency, also the amplitude of the beam will increases, end to beam failure. The amplitude of the beam subjected to substantial excitation loading parameters increases in a typical nonlinear manner and leads to the beats phenomena. The principal regions of dynamic instability are determined for various loading and boundary conditions using the Floquet’s theory. The beam response in the regions of instability is investigated. Axially loaded beam may be unstable not just in load equal to critical load and/or loading frequency equal to beam natural frequency. In fact there are infinite points in region of instability in plane load vs. frequency that the beam can be unstable. The region of instability of the shear deformable beams is wider compare to non-shear deformable beams. The lower bound of the instability region of the shear deformable beams changes faster than upper bound. Probabilistic stability analysis of the uncertain laminated beams subject to both conservative and nonconservative loads is studied. The effects of material and geometry uncertainties on dynamics instability of the beam, is investigated through a probabilistic finite element analysis and Monte Carlo Simulation methods. For non-conservative systems variations of uncertain material properties has a smaller influence than variations of geometric properties over the instability of the beam.

Nonlinear Instability and Reliability Analysis of Composite Laminated Beams

The wide range of high performance engineering applications of composite laminated structures demands a proper understanding of their dynamics performance. Due to the complexity and nonlinear behaviour of such structures, developing a mathematical model to determine the dynamic instability boundaries is indispensable and challenging. The aim of this research is to investigate the dynamic behaviour of shear deformable composite laminated beams subjected to varying time conservative and nonconservative loads. The dynamic instability behaviour of non-conservative and conservative system are dissimilar. In case of conservative loading, the instability region intersects the loading axis, but in case of non-conservative loads the region will be increased with loading increases. The extended Hamilton’s principle and the first order shear deformation theory are employed in this investigation to establish the integral form of the equation of motion of the beam. A five node beam model is presented to descritize the integral form of the governing equations. The model has the capability to capture the dynamic effects of the transverse shear stress, warping, and bending-twisting, bending-stretching, and stretching-twisting couplings. Also, the geometric and loading nonlinearities are included in the equation of system. The beam model incorporates, in full form, the non-classical effects of warping on stability and dynamic response of symmetrical and unsymmetrical composite beams. In case of nonlinear elasticity, the resonance curves are bent toward the increasing exciting frequencies. The response of the stable beam is pure periodic and follow the loading frequency. When the beam is asymptotically stable the response of the beam is aperiodic and does not follow the loading frequency. In unstable state of the beam response frequency increases with time and is higher than the loading frequency, also the amplitude of the beam will increases, end to beam failure. The amplitude of the beam subjected to substantial excitation loading parameters increases in a typical nonlinear manner and leads to the beats phenomena. The principal regions of dynamic instability are determined for various loading and boundary conditions using the Floquet’s theory. The beam response in the regions of instability is investigated. Axially loaded beam may be unstable not just in load equal to critical load and/or loading frequency equal to beam natural frequency. In fact there are infinite points in region of instability in plane load vs. frequency that the beam can be unstable. The region of instability of the shear deformable beams is wider compare to non-shear deformable beams. The lower bound of the instability region of the shear deformable beams changes faster than upper bound. Probabilistic stability analysis of the uncertain laminated beams subject to both conservative and nonconservative loads is studied. The effects of material and geometry uncertainties on dynamics instability of the beam, is investigated through a probabilistic finite element analysis and Monte Carlo Simulation methods. For non-conservative systems variations of uncertain material properties has a smaller influence than variations of geometric properties over the instability of the beam.

Effect of a High Mg Solute Content on the Hot Workability of Al–Mg Alloys

The workability of Al–xMg alloys with a high Mg content (Al–6Mg, Al–8Mg, Al–9Mg) was evaluated by investigating the microstructure and processing map. Hot torsion tests were conducted in the range of 350–500 °C between 0.1 and 1 s−1. Constitutive equations were derived from various effective stress–strain curves, and the thermal activation energies for deformation obtained were 171 kJ/mol at Al–6Mg, 195 kJ/mol at Al–8Mg, and 220 kJ/mol at Al–9Mg. In the case of the processing map, the instability region, which widened with increasing Mg content, was due mainly to the influence of the Mg solute, which activated grain boundary cracking and flow localization.

Evidence that short-period AM CVn systems are diverse in outburst behaviour

ABSTRACT We present results of our analysis of up to 15 yr of photometric data from eight AM CVn systems with orbital periods between 22.5 and 26.8 min. Our data have been collected from the GOTO, ZTF, Pan-STARRS, ASAS-SN, and Catalina all-sky surveys and amateur observations collated by the AAVSO. We find evidence that these interacting ultracompact binaries show a similar diversity of long-term optical properties as the hydrogen accreting dwarf novae. We found that AM CVn systems in the previously identified accretion disc instability region are not a homogenous group. Various members of the analysed sample exhibit behaviour reminiscent of Z Cam systems with long superoutbursts (SOs) and standstills, SU UMa systems with regular, shorter SOs, and nova-like systems that appear only in a high state. The addition of TESS full frame images of one of these systems, KL Dra, reveals the first evidence for normal outbursts appearing as a precursor to SOs in an AM CVn system. Our results will inform theoretical modelling of the outbursts of hydrogen deficient systems.

Comparing turbulence in a Kelvin-Helmholtz instability region across the terrestrial magnetopause

The properties of turbulence observed within the plasma originating from the magnetosheath and the magnetospheric boundary layer, which have been entrained within vortices driven by the Kelvin-Helmholtz Instability (KHI), are compared. The goal of such a study is to determine similarities and differences between the two different regions. In particular, we study spectra, intermittency and the third-order moment scaling, as well as the distribution of a local energy transfer rate proxy. The analysis is performed using the Magnetospheric Multiscale (MMS) data from a single satellite that crosses longitudinally the KHI. Two sets of regions, one set containing predominantly magnetosheath plasma and the other containing predominantly magnetospheric plasma, are analyzed separately, thus allowing us to explore turbulence properties in two portions of very different plasma samples. Results show that the turbulence in the two regions is different, with the boundary layer plasma including current structures that may not be originated by the turbulent cascade. This suggests that the observed turbulence is affected by the KHI.