| 561. |
|
|
| 562. |
|
|
| 563. |
- Liu, Tian Xiang, et al.
(författare)
-
Coarse-grained tight-binding models
- 2022
-
Ingår i: Journal of Physics Condensed Matter. - 0953-8984. ; 34:12
-
Tidskriftsartikel (refereegranskat)abstract
- Calculating the electronic structure of systems involving very different length scales presents a challenge. Empirical atomistic descriptions such as pseudopotentials or tight-binding models allow one to calculate the effects of atomic placements, but the computational burden increases rapidly with the size of the system, limiting the ability to treat weakly bound extended electronic states. Here we propose a new method to connect atomistic and quasi-continuous models, thus speeding up tight-binding calculations for large systems. We divide a structure into blocks consisting of several unit cells which we diagonalize individually. We then construct a tight-binding Hamiltonian for the full structure using a truncated basis for the blocks, ignoring states having large energy eigenvalues and retaining states with energies close to the band edge energies. A numerical test using a GaAs/AlAs quantum well shows the computation time can be decreased to less than 5% of the full calculation with errors of less than 1%. We give data for the trade-offs between computing time and loss of accuracy. We also tested calculations of the density of states for a GaAs/AlAs quantum well and find a ten times speedup without much loss in accuracy.
|
|
| 564. |
- Liu, Tian Xiang, et al.
(författare)
-
Speeding up tight binding calculations using zone-folding methods
- 2022
-
Ingår i: Computational Materials Science. - : Elsevier BV. - 0927-0256. ; 211
-
Tidskriftsartikel (refereegranskat)abstract
- Tight binding models are widely used in large scale electronic structure calculations of nanostructures. Their atomistic nature makes them flexible, but also means the computational cost increases rapidly with system size. The large number of calculations required to design nanostructures makes computational efficiency desirable. We have developed a method to increase computational speed while retaining most of its accuracy. The method is based on the use of supercells and zone folding combined with a truncation of the Hamiltonians to only include states close to the band-edges. We apply the method to model the band edge energies of a GaAs/AlAs quantum well grown along the [110]-directions with 3D and 2D periodic boundary conditions as well as the density of states and dielectric function of the quantum well. We typically find a speed-up of ten times with only a small loss of accuracy of the calculation result.
|
|
| 565. |
- Liu, Wing Kam, et al.
(författare)
-
Complexity science of multiscale materials via stochastic computations
- 2009
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 80:6-7, s. 932-978
-
Tidskriftsartikel (refereegranskat)abstract
- New technological advances today allow for a range of advanced composite materials, including multilayer materials and nanofiber-matrix composites. In this context, the key to developing advanced materials IS file understanding of the interplay between the various physical scales present. from the atomic level Interactions to the microstructaral composition and the marcoscale behavior Using the developing 'multiresolution data sets mechanics' the 'predictive science-based governing laws of the materials microstructure evolutions' are derived and Melted into a 'stochastic multiresolution design framework' Under such a framework. the governing laws Of the materials microstructure evolution will be essential to assess, across multiple scales. The impact of multiscale material design. geometry design of a structure and the manufacturing process conditions, by following the cause-effect relationship from structure property and then to performance The future Integrated multiscale analysis system will be Constructed based on a probabilistic complexity science-based mathematical framework. its verification, validation and uncertainty quantification tire done through carefully designed experiments, and file life-cycled materials design for products design and manufacturing is performed through the use of petascale computing. The various techniques of microstructure reconstruction result in the genetation of model microstructures that, at some level, has the same statistical properties as the real heterogenous media. Having reconstructed the heterogeneous medium. one can then evaluate Its effective properties via direct numerical simulation and compare these values with experimentally measured properties of the actual medium. The proposed analysis will be dynamic in nature to capture the multi-stage historical evolvement of material/structure performance over the life span of a product. In addition to providing more accurate assessment of structure performance with stochastic multiscale analysis. our development will provide the capability of predicting failures and system reliability to enable more reliable design and decisions in product development.
|
|
| 566. |
|
|
| 567. |
- Liu, Xiang, et al.
(författare)
-
MR diffusion tensor and perfusion-weighted imaging in preoperative grading of supratentorial nonenhancing gliomas.
- 2011
-
Ingår i: Neuro-oncology. - : Oxford University Press (OUP). - 1523-5866 .- 1522-8517. ; 13:4, s. 447-55
-
Tidskriftsartikel (refereegranskat)abstract
- We evaluate the value of MR diffusion tensor imaging (DTI) and dynamic susceptibility-weighted contrast material-enhanced perfusion-weighted imaging (PWI) in preoperative grading of supratentorial nonenhancing gliomas. This institutional review board-approved, Health Insurance Portability and Accountability Act-compliant retrospective study involved 52 patients: 37 with low-grade gliomas (LGGs) and 15 with high-grade gliomas (HGGs). The mean trace apparent diffusion coefficient (ADC), minimal ADC, mean fractional anisotropy (FA), maximal FA, and maximal relative cerebral blood volume (rCBV) ratio of the lesions were measured and compared between LGG and HGG. The efficacy of the above parameters in grading supratentorial nonenhancing gliomas was evaluated. There was no significant difference in rCBV ratio, minimal ADC, and mean ADC between LGG and HGG (p > 0.05). The mean and maximal FA values of LGG were significantly lower than the values of HGG (p < 0.001). The receiver operating characteristic analysis showed that the mean FA with a cutoff value of 0.129 and the maximal FA with a cutoff value of 0.219 could differentiate between LGG and HGG with specificity of 69.2% and 76.9%, respectively, and sensitivity of 93.3% and 100.0%, respectively. The combination of mean FA and maximal FA based on the linear discriminant analysis improved the diagnostic accuracy with specificity of 92.3% and sensitivity of 86.7%. These findings were better than maximal rCBV ratio, mean ADC, and minimum ADC. The mean FA and maximal FA, used individually or combined, may be useful in preoperative grading of supratentorial nonenhancing gliomas.
|
|
| 568. |
- Liu, Yanrong, et al.
(författare)
-
Ionic liquids as a new cornerstone to support hydrogen energy
- 2023
-
Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 25:13, s. 4981-4994
-
Forskningsöversikt (refereegranskat)abstract
- As a fuel or energy carrier, hydrogen has been identified as a key way to decarbonize electricity, industry, transportation, and heating sectors. Hydrogen can be produced by a variety of methods, among which water electrolysis driven by renewable energy is sustainable and nearly carbon-free. To use hydrogen widely, storage and transportation over long distances are another key issue. Apart from storage at high pressure and low temperature, hydrogen can be stored in organic compounds via chemical bonding under relatively mild conditions. Efficient utilization of hydrogen includes hydrogen fuel cells as an alternative to internal combustion engines. From the above scenarios, catalysis and reaction media are the key factors for realizing hydrogen energy implementation. Ionic liquids (ILs) offer new opportunities due to their tunable functional groups, low vapor pressure, and stable structures as additives, solvents, and charge transfer materials. ILs are known to produce solid catalysts with controllable properties, decorate solid catalysts with modified electrons and geometric structures, and serve as electrolytes and hydrogen storage media. This review summarizes and recaps the recent progress in how ILs act as a cornerstone to support the production, storage, and utilization of hydrogen. Furthermore, critical challenges and future research directions of ILs in hydrogen energy applications are also outlined.
|
|
| 569. |
- Liu, Y, et al.
(författare)
-
Tree-ring-based annual precipitation reconstruction in Kalaqin, Inner Mongolia for the last 238 years
- 2011
-
Ingår i: Chinese Science Bulletin. ; 56:28-29, s. 2995-3002
-
Tidskriftsartikel (refereegranskat)abstract
- A tree-ring-width chronology of Pinus tabulaeformis from Kalaqin, Inner Mongolia was developed using modern dendrochronological techniques. Based on the results of correlation function analysis, the total precipitation from the previous August to current July was reconstructed for 1771–2008 AD with an explained variance of 49.3%. The reconstruction correlated well with the dryness/ wetness series derived from historical documents, as well as the precipitation reconstruction of the Chifeng-Weichang region. There were eight intervals with greater precipitation than the average (associated with the strong East Asian summer monsoon) and seven intervals lower than the average (weak monsoon). A power spectrum analysis showed that there were 120 a, 80 a, 8 a and 2 a periodicities.
|
|
| 570. |
|
|
