We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the ＂Asqtad＂ improved staggered fermion formulation, we measure full ππ four-point correlators for iso...We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the ＂Asqtad＂ improved staggered fermion formulation, we measure full ππ four-point correlators for isospin I = 0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass yields scattering lengths as mna01=2 = -0.041 6（2） and mna01= 0.186（2） for isospin I = 2 and 0 channels, respectively. Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are carried out with MILC 2 ＋ 1 flavor gauge configurations at lattice spacing a ≈0.15 fm.展开更多
Using photonic crystals (PCs), the extraction efficiency of the light-emitting diodes (LEDs) can be greatly enhanced by the effects of photonic band gap (PBG) and grating diffraction. The two theoretical methods are a...Using photonic crystals (PCs), the extraction efficiency of the light-emitting diodes (LEDs) can be greatly enhanced by the effects of photonic band gap (PBG) and grating diffraction. The two theoretical methods are also discussed. Meanwhile, we demonstrate that LEDs can achieve high extraction efficiency by employing photonic crystal as diffraction grating. PCs with square lattice of cylindrical unit cells are fabricated in GaN layer of GaN-based blue LED. We present a theoretical discussion on the extraction efficiency of PC-LED, which relies on the effective medium theory and transmission matrix method to investigate the effect of lattice constant. The results show that the extraction efficiency of the high performance LEDs can achieve 61.8% when the lattice constant is 270 nm.展开更多
基金Supported by Fundamental Research Funds for the Central Universities under Grant No. 2010SCU23002the Startup Grant fromthe Institute of Nuclear Science and Technology of Sichuan University
文摘We study s-wave pion-pion scattering length in lattice QCD for pion masses ranging from 330 MeV to 466 MeV. In the ＂Asqtad＂ improved staggered fermion formulation, we measure full ππ four-point correlators for isospin I = 0 and 2 channels, and use chiral perturbation theory at next-to-leading order to extrapolate our simulation results. Extrapolating to the physical pion mass yields scattering lengths as mna01=2 = -0.041 6（2） and mna01= 0.186（2） for isospin I = 2 and 0 channels, respectively. Our lattice simulation for ππ scattering length in I = 0 channel is an exploratory study, where we include the disconnected contribution, and our preliminary result is near to its experimental value. These simulations are carried out with MILC 2 ＋ 1 flavor gauge configurations at lattice spacing a ≈0.15 fm.
基金supported by the National Natural Science Foundation of China (No.60877047)the Natural Science Foundation of Hebei Province (No.2010002002)
文摘Using photonic crystals (PCs), the extraction efficiency of the light-emitting diodes (LEDs) can be greatly enhanced by the effects of photonic band gap (PBG) and grating diffraction. The two theoretical methods are also discussed. Meanwhile, we demonstrate that LEDs can achieve high extraction efficiency by employing photonic crystal as diffraction grating. PCs with square lattice of cylindrical unit cells are fabricated in GaN layer of GaN-based blue LED. We present a theoretical discussion on the extraction efficiency of PC-LED, which relies on the effective medium theory and transmission matrix method to investigate the effect of lattice constant. The results show that the extraction efficiency of the high performance LEDs can achieve 61.8% when the lattice constant is 270 nm.
