Engineering topics
Yang, Li-Ping
Publications and source records attributed to Yang, Li-Ping.
Probing the conformal Calabrese-Cardy scaling with cold atoms
We demonstrate that current experiments using cold bosonic atoms trapped in one-dimensional optical lattices and designed to measure the second-order Rényi entanglement entropy S 2 can be used to verify detailed predictions of conformal field theory (CFT) and estimate the central charge c. We discuss the adiabatic preparation of the ground state at half filling and small hopping parameter J/U, where we expect a CFT with c = 1. We provide two complementary methods to estimate and subtract the classical entropy generated by the experimental preparation and imaging processes. We compare numerical calculations for the classical O(2) model with a chemical potential on a (1 + 1)-dimensional lattice, and the quantum Bose-Hubbard Hamiltonian implemented in the experiments. S 2 is very similar for the two models and follows closely the Calabrese-Cardy scaling, (c/8) ln (N s ) , for N s sites with open boundary conditions, provided that the large subleading corrections are taken into account.
Analysis and statistics of discontinuities as obtained from 3D simulation of MHD turbulence
The turbulent solar wind abounds with MHD discontinuities, and such discontinuities are often found in close connection with turbulence intermittency, constituting a possible main contributor to the turbulence dissipation and solar wind heating. Among the discontinuities, tangential (TD) and rotational (RD) ones are two most important types. Recently, the connection between turbulence intermittency and proton thermodynamics has been being intensively investigated. Such connections are founded to be involved with MHD instablilities, but the difference of TDs an RDs in this process has not yet been covered. Herewith we define new methods for identifying TDs and RDs obtained from a three-dimensional MHD simulation with pressure anisotropy. Especially, we define the Total Variance of Increments (TVI) as a new measure of magnetic field changes. Based on the identified cases, we compare their occurrence rates and heating effects. More specifically, we find that the thermal states embedding TDs, compared with their RD counterparts, tend to be more associated with extreme plasma parameters or instabilites. Some other possible applications of TVI-like norms are also herewith discussed.
Identification and quantification analysis of nonlinear dynamics properties of combustion instability in a diesel engine
The cycling combustion instabilities in a diesel engine have been analyzed based on chaos theory. The objective was to investigate the dynamical characteristics of combustion in diesel engine. In this study, experiments were performed under the entire operating range of a diesel engine (the engine speed was changed from 600 to 1400 rpm and the engine load rate was from 0% to 100%), and acquired real-time series of in-cylinder combustion pressure using a piezoelectric transducer installed on the cylinder head. Several methods were applied to identify and quantitatively analyze the combustion process complexity in the diesel engine including delay-coordinate embedding, recurrence plot (RP), Recurrence Quantification Analysis, correlation dimension (CD), and the largest Lyapunov exponent (LLE) estimation. The results show that the combustion process exhibits some determinism. If LLE is positive, then the combustion system has a fractal dimension and CD is no more than 1.6 and within the diesel engine operating range. We have concluded that the combustion system of diesel engine is a low-dimensional chaotic system and the maximum values of CD and LLE occur at the lowest engine speed and load. This means that combustion system is more complex and sensitive to initial conditions and that poor combustion quality leads to the decrease of fuel economy and the increase of exhaust emissions.
Progress towards quantum simulating the classical O ( 2 ) mode
We connect explicitly the classical $O(2)$ model in 1+1 dimensions, a model sharing important features with $U(1)$ lattice gauge theory, to physical models potentially implementable on optical lattices and evolving at physical time. Using the tensor renormalization group formulation, we take the time continuum limit and check that finite dimensional projections used in recent proposals for quantum simulators provide controllable approximations of the original model. We propose two-species Bose-Hubbard models corresponding to these finite dimensional projections at strong coupling and discuss their possible implementations on optical lattices using a $^{87}$Rb and $^{41}$K Bose-Bose mixture.