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301.
We show that rubidium vapor can be produced within the core of a photonic band-gap fiber yielding an optical depth in excess of 2,000. Our technique for producing the vapor is based on coating the inner walls of the fiber core with organosilane and using light-induced atomic desorption to release Rb atoms into the core. As an initial demonstration of the potential of this system for supporting ultralow-level nonlinear optical interactions, we perform electromagnetically induced transparency with control-field powers in the nanowatt regime, which represents more than a 1,000-fold reduction from the power required for bulk, focused geometries. 相似文献
302.
We present "twin Higgs models," simple realizations of the Higgs boson as a pseudo Goldstone boson that protect the weak scale from radiative corrections up to scales of order 5-10 TeV. In the ultraviolet these theories have a discrete symmetry which interchanges each standard model particle with a corresponding particle which transforms under a twin or a mirror standard model gauge group. In addition, the Higgs sector respects an approximate global symmetry. When this global symmetry is broken, the discrete symmetry tightly constrains the form of corrections to the pseudo Goldstone Higgs potential, allowing natural electroweak symmetry breaking. Precision electroweak constraints are satisfied by construction. These models demonstrate that, contrary to the conventional wisdom, stabilizing the weak scale does not require new light particles charged under the standard model gauge groups. 相似文献
303.
Goh SK Paglione J Sutherland M O'Farrell EC Bergemann C Sayles TA Maple MB 《Physical review letters》2008,101(5):056402
The evolution of the Fermi surface of CeRh(1-x)CoxIn5 was studied as a function of Co concentration x via measurements of the de Haas-van Alphen effect. By measuring the angular dependence of quantum oscillation frequencies, we identify a Fermi-surface sheet with f-electron character which undergoes an abrupt change in topology as x is varied. Surprisingly, this reconstruction does not occur at the quantum critical concentration x(c), where antiferromagnetism is suppressed to T=0. Instead we establish that this sudden change occurs well below x(c), at the concentration x approximately 0.4, where long-range magnetic order alters its character and superconductivity appears. Across all concentrations, the cyclotron effective mass of this sheet does not diverge, suggesting that critical behavior is not exhibited equally on all parts of the Fermi surface. 相似文献
304.
This article discusses the effectiveness of a fresh analytical method in solving a prey-predator problem, which is described as a system of two nonlinear ordinary differential equations. The method of interest is the multistage variational iteration method (MVIM), which provides a slight modification of the classical variational iteration method (VIM). We shall compare solutions of the classical VIM along with MVIM and match them against the conventional numerical method, Runge-Kutta (RK4) (fourth-order). 相似文献
305.
A competitive and cooperative co-evolutionary approach to multi-objective particle swarm optimization algorithm design 总被引:1,自引:0,他引:1
Multi-objective particle swarm optimization (MOPSO) is an optimization technique inspired by bird flocking, which has been steadily gaining attention from the research community because of its high convergence speed. On the other hand, in the face of increasing complexity and dimensionality of today’s application coupled with its tendency of premature convergence due to the high convergence speeds, there is a need to improve the efficiency and effectiveness of MOPSO. In this paper a competitive and cooperative co-evolutionary approach is adapted for multi-objective particle swarm optimization algorithm design, which appears to have considerable potential for solving complex optimization problems by explicitly modeling the co-evolution of competing and cooperating species. The competitive and cooperative co-evolution model helps to produce the reasonable problem decompositions by exploiting any correlation, interdependency between components of the problem. The proposed competitive and cooperative co-evolutionary multi-objective particle swarm optimization algorithm (CCPSO) is validated through comparisons with existing state-of-the-art multi-objective algorithms using established benchmarks and metrics. Simulation results demonstrated that CCPSO shows competitive, if not better, performance as compared to the other algorithms. 相似文献
306.
Lin Cheng Kun Wang Jianyong Mao Xiao Ming Goh Zhiqin Chu Yanpeng Zhang Lei Zhang 《Annalen der Physik》2019,531(9)
Subwavelength structures can provide a versatile platform for displaying various colors. Here, a reflection‐type approach to structural colors enabled by an extrinsic polarization‐dependent plasmonic resonance using aluminum nanohole arrays is presented theoretically. Usually, nanohole arrays with small hole sizes support whitish structural colors due to the narrow‐band reflection dip and high‐reflection nonresonant background. Interestingly, the lineshape of the resonance can be converted from a reflection dip with a high background to a reflection peak with negligible background using a pair of linear polarizers to select the polarization states of the incident light and the detected signal. Therefore, the resultant colors can be switched between whitish colors and vibrant colors, which are covert and overt under a white lighting condition, respectively. Due to the huge contrast between the two types of colors, this approach provides a novel scheme for the development of security‐related color labels. 相似文献
307.
H. J.?LiuEmail author T.?Yang W. C.?Goh C. H.?Sow S. N.?Piramanayagam C. K.?Ong 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,48(1):37-40
Nano-constriction array in
La0.67Sr0.33MnO3 film was fabricated by using ion
beam etching masked by a monolayer of packed and ordered array of
SiO2 microspheres. Nano-constrictions of around 50 nm in
width were fabricated. The low field magnetoresistance (LFMR)
exhibited in the samples were observed to be current dependent and
the I-V characteristics of the film were found to be nonlinear.
These observations were attributed to the co-existence of the
ferromagnetic regions and the nano-constricted region of weakened
ferromagnetic coupling where Mn3+-O-Mn4+ bond were
distorted due to the ion beam bombardment. The spin polarized bias
current would strengthen local ferromagnetic coupling when passing
through this nano-constricted regions. This current effect is
relatively large comparing to the external magnetic field to the
drop of resistance. 相似文献
308.
[reaction: see text] The structures of novel gaudichaudiic acids F-I (1-4), isolated from the bark of Indonesian Garcinia gaudichaudii, have been elucidated by detailed spectral analysis. Gaudichaudiic acid I (4) is probably derived from 1 as a result of allylic oxidation at C-24 and C-21, followed by aromatization. 相似文献
309.
Carbon-13 NMR chemical shifts of several series of aliphatic hydrocarbon derivatives–-substituted methanes, ethanes, isopropanes, n-propanes and n-butanes–-were found to have a linear relationship with σ-electron densities (Qσ) calculated by the method of σ-included ω-HMO. A plot of the 13C NMR chemical shift of a given carbon in a substituted propane versus that of the corresponding carbon in a substituted butane showed a good linearity with a slope of unity. The values of the 13C chemical shifts of the n-butyl derivatives converged rapidly to a constant value as the distance from the substituent increased. Accordingly, the value for the δ-carbon was found to be constant regardless of the substituent. These results show that the 13C NMR chemical shifts of aliphatic hydrocarbon derivatives are mainly dependent on inductive effects. The convergence shown by the experimental results is supported by the calculated results of the Qσ values of the n-butyl derivatives. 相似文献
310.