12,790 research outputs found
Solving job shop scheduling problem using genetic algorithm with penalty function
This paper presents a genetic algorithm with a penalty function for the job shop scheduling problem. In the context of proposed algorithm, a clonal selection based hyper mutation and a life span extended strategy is designed. During the search process, an adaptive penalty function is designed so that the algorithm can search in both feasible and infeasible regions of the solution space. Simulated experiments were conducted on 23 benchmark instances taken from the OR-library. The results show the effectiveness of the proposed algorithm
Quantum Spin Hall Effect in Inverted Type II Semiconductors
The quantum spin Hall (QSH) state is a topologically non-trivial state of
quantum matter which preserves time-reversal symmetry; it has an energy gap in
the bulk, but topologically robust gapless states at the edge. Recently, this
novel effect has been predicted and observed in HgTe quantum wells. In this
work we predict a similar effect arising in Type-II semiconductor quantum wells
made from InAs/GaSb/AlSb. Because of a rare band alignment the quantum well
band structure exhibits an "inverted" phase similar to CdTe/HgTe quantum wells,
which is a QSH state when the Fermi level lies inside the gap. Due to the
asymmetric structure of this quantum well, the effects of inversion symmetry
breaking and inter-layer charge transfer are essential. By standard
self-consistent calculations, we show that the QSH state persists when these
corrections are included, and a quantum phase transition between the normal
insulator and the QSH phase can be electrically tuned by the gate voltage.Comment: 5 pages,4 figures. Submitted to PRL. For high resolution figures see
final published version when availabl
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A refined r-factor algorithm for TVD schemes on arbitrary unstructured meshes
A refined r-factor algorithm for implementing TVD schemes on arbitrary unstructured meshes, referred to henceforth as FFISAM (a Face-perpendicular Far-upwind Interpolation Scheme for Arbitrary Meshes), is proposed based on an extensive review of the existing r-factor algorithms available in the literature. The design principles, as well as the respective advantages and disadvantages, of the existing algorithms are first systematically analyzed before presenting the FFISAM. The FFISAM is designed to combine the merits of various existing r-factor algorithms. The performance of the FFISAM, implemented in ten classical TVD schemes, is evaluated against four two-dimensional pure-advection benchmark test cases where analytical solutions are available. The numerical results clearly show that the FFISAM leads to a better overall performance than the existing algorithms in terms of accuracy and convergence on arbitrary unstructured meshes for the ten classical TVD schemes.The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (Grant No. 51279082) and the support from Australian Research Council through a Discovery Grant (Project ID: DP110105171).This is the author accepted manuscript. The final version is available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/fld.4073/abstract
A review on TVD schemes and a refined flux-limiter for steady-state calculations
This paper presents an extensive review of most of the existing TVD schemes found in literature that are based on the One-step Time-space-coupled Unsteady TVD criterion (OTU-TVD), the Multi-step Time-space-separated Unsteady TVD criterion (MTU-TVD) and the Semi-discrete Steady-state TVD criterion (SS-TVD). The design principles of these schemes are examined in detail. It is found that the selection of appropriate flux-limiters is a key design element in developing these schemes. Different flux-limiter forms (CFL-dependent or CFL-independent, and various limiting criteria) are shown to lead to different performances in accuracy and convergence. Furthermore, a refined SS-TVD flux-limiter, referred to henceforth as TCDF (Third-order Continuously Differentiable Function), is proposed for steadystate calculations based on the review. To evaluate the performance of the newly proposed scheme, many existing classical SS-TVD limiters are compared with the TCDF in eight two-dimensional test cases. The numerical results clearly show that the TCDF results in an improved overall performance.The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (Grant No. 51279082 and 51511130073) and the support from Australian Research Council through a Discovery Grant (Project ID: DP110105171).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.jcp.2015.08.04
Effects of topological edge states on the thermoelectric properties of Bi nanoribbons
Using first-principles calculations combined with Boltzmann transport theory,
we investigate the effects of topological edge states on the thermoelectric
properties of Bi nanoribbons. It is found that there is a competition between
the edge and bulk contributions to the Seebeck coefficients. However, the
electronic transport of the system is dominated by the edge states because of
its much larger electrical conductivity. As a consequence, a room temperature
value exceeding 3.0 could be achieved for both p- and n-type systems when the
relaxation time ratio between the edge and the bulk states is tuned to be 1000.
Our theoretical study suggests that the utilization of topological edge states
might be a promising approach to cross the threshold of the industrial
application of thermoelectricity
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