Asteroseismology of the DAV star L19-2

L19-2 is a DAV star, which has been intermittently observed from 1976 to 2013. Five independent pulsation modes of 350\,s, 192\,s, 143\,s, 118\,s, and 113\,s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O-C method for modes of 192\,s and 113\,s, which can be used to study the evolution effect of DAV stars. Using the \texttt{WDEC} (2018 version), a large sample DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal model with an absolute difference of $\Phi$ = 0.06\,s. By parameterizing the core oxygen profile, the \texttt{WDEC} (2018 version) procedure can greatly reduce the fitting error of asteroseismological model. According to our optimal model, the distance obtained through the model luminosity is only 1\% different from that reported by the Gaia Data Release 2. The L19-2 is a massive and hot DAV star with relatively a thick H atmosphere and a thick He layer. The stellar parameters and the rates of period change of our optimal model are a little modifications to that of the previous work. Our optimal model has a large central oxygen abundance. The central oxygen abundance is strongly correlated with the previous physical process of stellar evolution. A lot of asteroseismological work on white dwarfs have an opportunity to explore the progenitor stars.Comment: 8 pages, 5 figures, 5 tables. Accepted by ApJ on June 7, 202

Examination on the Relationship between OVX and Crude Oil Price with Kalman Filter

AbstractChicago Board Option Exchange publishes the Crude Oil Volatility Index (OVX) in 2007, which is regarded as a new barometer to research the variance of oil future prices. This paper explores how OVX changes are influenced by crude oil price returns with time-varying coefficients achieved by Kalman filter. The results indicate a negative and asymmetric contemporaneous relationship between OVX changes and crude oil price returns

Temperature dependence of circular DNA topological states

Circular double stranded DNA has different topological states which are defined by their linking numbers. Equilibrium distribution of linking numbers can be obtained by closing a linear DNA into a circle by ligase. Using Monte Carlo simulation, we predict the temperature dependence of the linking number distribution of small circular DNAs. Our predictions are based on flexible defect excitations resulted from local melting or unstacking of DNA base pairs. We found that the reduced bending rigidity alone can lead to measurable changes of the variance of linking number distribution of short circular DNAs. If the defect is accompanied by local unwinding, the effect becomes much more prominent. The predictions can be easily investigated in experiments, providing a new method to study the micromechanics of sharply bent DNAs and the thermal stability of specific DNA sequences. Furthermore, the predictions are directly applicable to the studies of binding of DNA distorting proteins that can locally reduce DNA rigidity, form DNA kinks, or introduce local unwinding.Comment: 15 pages in preprint format, 4 figure

The geometric constraints on Filippov algebroids

Filippov n-algebroids are introduced by Grabowski and Marmo as a natural generalization of Lie algebroids. In this note, we characterize Filippov n-algebroid structures by considering certain multi-input connections, which we call Filippov connections, on the underlying vector bundle. Through this approach, we are able to express the n-ary bracket of any Filippov n-algebroid using a torsion-free type formula. Additionally, we transform the generalized Jacobi identity of the Filippov n-algebroid into the Bianchi-Filippov identity. Furthermore, in the case of rank n vector bundles, we provide a characterization of linear Nambu-Poisson structures using Filippov connections