Libstatmech and Applications to Astrophysics

In this work an introduction to Libstatmech is presented and applications especially to astrophysics are discussed. Libstatmech is a C toolkit for computing the statistical mechanics of fermions and bosons, written on top of libxml and gsl (GNU Scientific Library). Calculations of Thomas-Fermi Screening model and Bose-Einstein Condensate based on libstatmech demonstrate the expected results. For astrophysics application, a simple Type Ia Supernovae model is established to run the network calculation with weak reactions, in which libstatmech contributes to compute the electron chemical potential and allows the weak reverse rates to be calculated from detailed balance. Starting with pure 12C and T9=1.8, we find that at high initial density (&rho~ 9× 109 g/cm3) there are relatively large abundances of neutron-rich iron-group isotopes (e.g. 66Ni, 50Ti, 48Ca) produced during the explosion, and Ye can drop to ~0.4, which indicates that the rare, high density Type Ia supernovae may help to explain the 48Ca and 50Ti effect in FUN CAIs

CHEMICAL EVOLUTION OF THE NEUTRON-RICH IRON-GROUP ISOTOPES AND IMPLICATIONS FOR THE FORMATION OF FUN CAIS

Calcium-aluminum-rich inclusions (CAIs) are millimeter-sized refractory objects found in primitive meteorites. CAIs are considered as some of the first solids to form in the solar system, because they are refractory. FUN CAIs, those with Fractionated and Unknown Nuclear effects, are a small subset of CAIs. These FUN CAIs show correlated excesses and deficits in the neutron-rich iron-group isotopes such as 48 Ca and 50 Ti which regular CAIs do not. Interestingly, these isotopes are most likely produced infrequently but in huge quantities in a rare class of thermonuclear (Type Ia) supernovae. I propose that the isotopic effects in the neutron-rich iron-group nuclei in FUN CAIs arise from the rarity (~2%) of the Type Ia supernovae that produce them. To quantitatively test this hypothesis we built a simple Ia model to get the yields and trajectories, and then estimated the chemical forms and sizes of dust grains into which those isotopes condense. Our results show that these rare dense Type Ia supernovae can produce a large quantity of neutron-rich iron-group isotopes; with unburned carbon and oxygen added the chemical perovskite (CaTiO 3 ) would form and may count for more than 5% of total atoms in the outflow; the size of dust grains can grow up to the order of 0.1 micron. All these findings suggest the rare dense Type Ia supernovae may be the source of these isotopes and the outflows may form Ca-Ti carriers which will bring the heterogeneity of these isotopes to the early solar system. The future Galactic Chemical Evolution simulation with these inputs would help constrain the Solar System formation in the nucleosynthetic and dust formation aspects

Continuum damage mechanics models and their applications to composite components of aero-engines

Built on top of a consistent continuum damage mechanics (CDM) damage representation formulation, a novel damage evolution law based on the concept of damage driving force is proposed for modelling the evolution of matrix damage in UD composites. This damage evolution law has the advantage of allowing different damage evolution constants to be associated with different loading modes (corresponding to the fracture modes in Fracture Mechanics) when dealing with mixed-mode loading conditions, which avoids the unrealistic assumption in many existing theories that different loading modes make the same contribution to damage evolution. A new CDM model for UD composites is developed incorporating this damage evolution law. Thanks to the laminate test cases designed and conducted in this project, it is found that the damage initiation and propagation related material constants can be determined using these tests. These damage-related material constants served as inputs to the UD composite CDM model. Apart from the tests on laminates, detailed experimental investigation was carried out regarding damage in two types of layer-to-layer interlock 3D woven composites which are reinforced by IM7 carbon fibre (CF) and E-glass fibre (GF), respectively. The experimental data obtained and the damage processes recorded for these 3D woven composites can serve as a good reference for future interest in this area, since currently only limited studies are available in the literature regarding damage in this type of 3D woven composites. The new UD composite CDM model is applied to predict intra-laminar damage in laminates and intra-tow damage in the 3D woven composites. Compared to the experimental results, it is found that the model produced satisfactory predictions but lacking the capability to predict a severe stress-strain nonlinearity caused by shear. A new pragmatic continuum damage model is developed to capture the damage effect of inter-tow cracks in the 3D woven composites caused by warp direction tensile loading. This model works in conjunction with the intra-tow damage predicted by the aforementioned UD composite CDM model. With the successful development of these damage models, a novel damage modelling methodology for textile composites is made possible and implemented in conjunction with the UnitCells© composite characterisation tool and the artificial neural network tool developed. Through the artificial neural network for data interpolation, the constitutive behaviour of textile composite incorporating the effect of damage can be interpolated for any load combination, which is then readily available for engineering applications

Continuum damage mechanics models and their applications to composite components of aero-engines

Built on top of a consistent continuum damage mechanics (CDM) damage representation formulation, a novel damage evolution law based on the concept of damage driving force is proposed for modelling the evolution of matrix damage in UD composites. This damage evolution law has the advantage of allowing different damage evolution constants to be associated with different loading modes (corresponding to the fracture modes in Fracture Mechanics) when dealing with mixed-mode loading conditions, which avoids the unrealistic assumption in many existing theories that different loading modes make the same contribution to damage evolution. A new CDM model for UD composites is developed incorporating this damage evolution law. Thanks to the laminate test cases designed and conducted in this project, it is found that the damage initiation and propagation related material constants can be determined using these tests. These damage-related material constants served as inputs to the UD composite CDM model. Apart from the tests on laminates, detailed experimental investigation was carried out regarding damage in two types of layer-to-layer interlock 3D woven composites which are reinforced by IM7 carbon fibre (CF) and E-glass fibre (GF), respectively. The experimental data obtained and the damage processes recorded for these 3D woven composites can serve as a good reference for future interest in this area, since currently only limited studies are available in the literature regarding damage in this type of 3D woven composites. The new UD composite CDM model is applied to predict intra-laminar damage in laminates and intra-tow damage in the 3D woven composites. Compared to the experimental results, it is found that the model produced satisfactory predictions but lacking the capability to predict a severe stress-strain nonlinearity caused by shear. A new pragmatic continuum damage model is developed to capture the damage effect of inter-tow cracks in the 3D woven composites caused by warp direction tensile loading. This model works in conjunction with the intra-tow damage predicted by the aforementioned UD composite CDM model. With the successful development of these damage models, a novel damage modelling methodology for textile composites is made possible and implemented in conjunction with the UnitCells© composite characterisation tool and the artificial neural network tool developed. Through the artificial neural network for data interpolation, the constitutive behaviour of textile composite incorporating the effect of damage can be interpolated for any load combination, which is then readily available for engineering applications

Formation of Cn Molecules in Oxygen-Rich Interiors of Type II Supernovae

Two reaction-rate-based kinetic models for condensation of carbon dust via the growth of precursor linear carbon chains are currently under debate: the first involves the formation of C2 molecules via radiative association of free C atoms, and the second forms C2 molecules by the endoergic reaction CO + C → C2 + O.Bothare followedby C captures until the linear chain eventually makes an isomeric transition to ringed carbon on which rapid growth of graphite may occur. These two approaches give vastly different results. Because of the high importance of condensable carbon for current problems in astronomy, we study these competing claims with an intentionally limited reaction rate network which clearly shows that initiation by C + C → C2 + γ is the dominant pathway to carbon rings. We propose an explanation for why the second pathway is not nearly as effective as its proponents calculated it to be

The Birth of Quark Stars: Photon-driven Supernovae?

In this letter we propose a possible mechanism trying to alleviate the current difficulty in core-collapse supernovae by forming a strange quark star inside the collapsing core. Although the initial longtime cooling behavior of nascent strange stars is dominated by neutrino emissions, thermal emissions including photons and $e^\pm$ pair plasma do play a significant role in the explosion dynamics under this picture. The key to promote a successful shock outside a bare strange star is more likely to be the radiation pressure caused by thermal photons rather than neutrinos in conventional models. We observed through calculation that radiation pressure can push the overlying mantle away through photon-electron scattering with energy (the work done by radiation pressure) as much as ~10^{51} erg if protoquark stars are born with temperatures higher than ~ (30-40) MeV. This result not only indicates that strange quark stars should be bare ever since their formations, it could also provide a possible explanation to the formation of fireballs in cosmic long-soft $\gamma$-ray bursts associated to supernovae.Comment: 13 pages, 3 figures, last version accepted to ApJ Letter

The Analysis of Electricity Deployment Under the Government Involvement in Holidays

As the power load is less on holidays compared with the annual electricity load, we built a model to analyze the feasibility of the use of electricity for enterprises on holidays. This paper paid attention to the electric deployment under the government involvement. We set up a discounted electricity price, the industrial enterprises may restart production of the preferential tariff during holidays. It analyzed all of the situations that the power enterprises would like to do with the change of the public subsidies and encouragement of the government. It is helpful to deploy electricity and provide a reference for government to make a decision

Fault Diagnosis for Micro-Gas Turbine Engine Sensors via Wavelet Entropy

Sensor fault diagnosis is necessary to ensure the normal operation of a gas turbine system. However, the existing methods require too many resources and this need can’t be satisfied in some occasions. Since the sensor readings are directly affected by sensor state, sensor fault diagnosis can be performed by extracting features of the measured signals. This paper proposes a novel fault diagnosis method for sensors based on wavelet entropy. Based on the wavelet theory, wavelet decomposition is utilized to decompose the signal in different scales. Then the instantaneous wavelet energy entropy (IWEE) and instantaneous wavelet singular entropy (IWSE) are defined based on the previous wavelet entropy theory. Subsequently, a fault diagnosis method for gas turbine sensors is proposed based on the results of a numerically simulated example. Then, experiments on this method are carried out on a real micro gas turbine engine. In the experiment, four types of faults with different magnitudes are presented. The experimental results show that the proposed method for sensor fault diagnosis is efficient