Laboratory Experimental Facility for Studying Metamaterial Sound-absorbing Duct Linings with Grazing Sound Propagation and How the Type of Source Influences their Efficiency

Acoustical Physics - The article describes an experimental facility for studying and testing sound-absorbing linings made of acoustic metamaterials designed to reduce the noise generated by a...     

Machine learning-based surrogate modeling for data-driven optimization: a comparison of subset selection for regression techniques

Optimization of simulation-based or data-driven systems is a challenging task, which has attracted significant attention in the recent literature. A very e     

The Peierls instability in one-dimensional conductors with arbitrary bandfilling

Mean field calculations of the Peierls instability have been carried out for arbitrary bandfilling both in the case of free electrons as well as for the tightbinding approximation. New expressions for Δ(0) and T_p are derived which change the experimentally derived λ to a more reasonable value. Δ(0)/k_BT_p may differ significantly from the BCS value 1.76 in the tightbinding approximation.     

Pionic K X-rays in liquid He

Energies and lorentzian widths of pionic K X-ray transitions have been measured in liquid ³He with improved accuracy. The strong interaction on the π³He 1s level is found to be attractive and to produce an increase in the K transition energies of 34 ± 4 eV; the measured lorentzian width is 36 ±7 eV. Measured values are also presented for K X-ray energies in liquid π⁴He and μ⁴He, the lorentzian width of the 1s level in π⁴He, and relative intensities of K X-ray transitions in π³He, π⁴He and μ⁴He. The measurements are compared with those of others and with recent theoretical calculations.     

Simultaneous jumps in two two-level atoms

We demonstrate the importance of collective behaviour in two identical two-level atoms. When the atoms become very close together a cascade three-level atom analysis can be adopted to show the increasing possibility of simultaneous jumps. Due to the dipole-dipole interaction the intermediate one-atom excited state is detuned by a large amount when the atoms are close together but leaving the upper two-atom excited state in two-photon resonance. The relative importance of multiple jumps compared with stepwise independent jumps is then changed dramatically.     

Analysis of creep due to grain-boundary diffusion in hexagonal microstructures

For steady-state deformation caused by grain-boundary diffusion in hexagonal microstructures, the stress distribution on grain boundaries and the macroscopic strain rates are analysed by taking the effects of viscous grain-boundary sliding into account. The maximum normal stress and the extent of stress concentration are shown to decrease as the grain-boundary viscosity increases. For infinite viscosity and/or extremely small grain sizes, the distribution of the normal stress becomes uniform on grain boundaries. The strain rates are predicted by both the stress analysis and the energy balance method, and the two strain rates are consistent with each other. The predicted strain rates also decrease as the grain-boundary viscosity increases. The present analysis reveals that the grain-size exponent is dependent on the grain size and the grain-boundary viscosity: the exponent becomes unity for small grain sizes and/or high viscosity, while it is three for large grain sizes and/or low viscosity. Recent experimental observations that the strain rates of nano-sized grain are much lower than those predicted by grain-boundary diffusion are explained by the increasing contribution of viscous grain-boundary sliding with decreasing grain size.     

Positive Operator Majorization and <Emphasis Type="Italic">p</Emphasis>-hyponormality

In this note we examine the relationships between p-hyponormal operators and the operator inequality . This leads to a method for generating examples of p-hyponormal operators which are not q-hyponormal for any . Our methods are also shown to have implications for the class of Furuta type inequalities.     

Top–bottom mass hierarchy, s-\mu puzzle and gauge coupling unification with split multiplets

Supersymmetric 5D SU(5) grand unification is considered. SU(5) is broken down to by the assignment of the bulk field(s). The matter fields are located at the fixed point(s). In the bulk, a Higgs multiplet (containing the bottom doublet ) and the SU(5) gauge multiplet are located. At one fixed point, (the top doublet) and the standard model matter multiplets are presented. Because of the difference of the locations of and , one can obtain a hierarchy between top and bottom Yukawa couplings. We also present a possible way to understand the s– mass puzzle in this framework of the split multiplet. Received: 10 December 2001 / Revised version: 22 January 2002 / Published online: 5 April 2002     

In vivo mapping of functional domains and axonal connectivity in cat visual cortex using magnetic resonance imaging

Noninvasive cognitive neuroimaging studies based on functional magnetic resonance imaging (fMRI) are of ever-increasing importance for basic and clinical neurosciences. The explanatory power of fMRI could be greatly expanded, however, if the pattern of the neuronal circuitry underlying functional activation could be made visible in an equally noninvasive manner. In this study, blood oxygenation level-dependent (BOLD)-based fMRI and diffusion tensor imaging (DTI) were performed in the same cat visual cortex, and the foci of fMRI activation utilized as seeding points for 3D DTI fiber reconstruction algorithms, thus providing the map of the axonal circuitry underlying visual information processing. The methods developed in this study will lay the foundation for in vivo neuroanatomy and the ability for noninvasive longitudinal studies of brain development.