Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders

In this Letter, we present a theoretical analysis of the acoustic transmission through two-dimensional arrays of straight rigid cylinders placed parallelly in the air. Both periodic and completely random arrangements of the cylinders are considered. The results for the sound attenuation through the periodic arrays are shown to be in a remarkable agreement with the reported experimental data. As the arrangement of the cylinders is randomized, the transmission is significantly reduced for a wider range of frequencies. For the periodic arrays, the acoustic band structures are computed by the plane-wave expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure

Gauge-invariant Green function in 3+1 dimensional QED (QCD) and 2+1 dimensional Abelian (Non-Abelian) Chern-Simon theory

By applying the simple and effective method developed to study the the gauge-invariant fermion Green function in $2+1$ dimensional non-compact QED, we study the gauge-invariant Green function in $3+1$ dimensional QED and $2+1$ dimensional non-compact Chern-Simon theory. We also extend our results to the corresponding $SU(M)$ non-Abelian gauge theories. Implications for Fractional Quantum Hall effect are briefly discussed.Comment: 8 pages, 4 figures, published versio

Light scattering detection of quantum phases of ultracold atoms in optical lattices

Ultracold atoms loaded on optical lattices can provide unprecedented experimental systems for the quantum simulations and manipulations of many quantum phases. However, so far, how to detect these quantum phases effectively remains an outstanding challenge. Here, we show that the optical Bragg scattering of cold atoms loaded on optical lattices can be used to detect many quantum phases which include not only the conventional superfluid and Mott insulating phases, but also other important phases such as various kinds of density waves (CDW), valence bond solids (VBS), CDW supersolids and VBS supersolids.Comment: 4 pages, 3 colour figures, to appear in Phys. Rev. A, Rapid Communicatio

Abelian bosonization approach to quantum impurity problems

Using Abelian Bosonization, we develop a simple and powerful method to calculate the correlation functions of the two channel Kondo model and its variants. The method can also be used to identify all the possible boundary fixed points and their maximum symmetry, to calculate straightforwardly the finite size spectra, to demonstrate the physical picture at the boundary explicitly. Comparisons with Non-Abelian Bosonization method are made. Some fixed points corresponding to 4 pieces of bulk fermions coupled to s=1/2 impurity are listed.Comment: 12 pages, REVTEX, 1 Table, no figures. To appear in Phys. Rev. Letts. July 21, 199

How do top construction companies diversify in the international construction market?

This article won the Best Paper Award in the symposiumGlobalization has created an international market that allows construction companies transcend traditional national boundaries and conduct business overseas. With new opportunities being brought to contractors, competition also grows exponentially in this market. Diversification is frequently adopted by these contractors as a strategy by the contractors for either growth, or risk management, or both in this competitive environment. However, the pattern of diversification has not been well measured, mapped, and analyzed. The aim of this research is to develop a Diversify Index (DI) and examine international contractors’ diversification pattern. The data is from the Top 225 International Contractors’ reports ranked by ENR (Engineering News-Record) from 1995 to 2014. Distributions of the DI were explored first and then case studies were used to investigate the specific diversification strategies adopted by the top international contractors. It is discovered that a downward trend of DI with subsequent changes in rankings expresses that larger contractors increasingly adopt various diversification strategies in international competition. The results provide valuable sights on the relationship between the competitive success and their diversification strategies as well as the tendency of diversification strategies adopted by top international contractors in different regions.postprin

Precision spectroscopy and density-dependent frequency shifts in ultracold Sr

By varying the density of an ultracold $^{88}$Sr sample from $10^9$ cm$^{-3}$ to $> 10^{12}$ cm$^{-3}$, we make the first definitive measurement of the density-related frequency shift and linewidth broadening of the $^1S_0$ - $^3P_1$ optical clock transition in an alkaline earth system. In addition, we report the most accurate measurement to date of the $^{88}$Sr $^1S_0 - ^3P_1$ optical clock transition frequency. Including a detailed analysis of systematic errors, the frequency is ($434 829 121 312 334 \pm 20_{stat} \pm 33_{sys}$) Hz.Comment: 4 pages, 4 figures, 1 table. submitte