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Li, Meng-Lei,Kim, Seungil ALLERTON PRESS INC 2014 CHINESE PHYSICS LETTERS Vol.31 No.5
<P>It has been realized that resonance frequencies of imperfect acoustic cloaking based on a small perturbation of the transformation acoustics in ℝ<SUP>2</SUP> are located near Dirichlet eigenvalues of the cloaked region [Chin. Phys. Lett. <A HREF='http://dx.doi.org/10.1088/0256-307X/26/1/014301'>26 (2009) 014301</A>; <A HREF='http://dx.doi.org/10.1088/0256-307X/29/12/124301'>29 (2012) 124301</A>]. In this work, we study the performance of the three-dimensional approximate cloaking system based on the transformation acoustics and show that the cloaking effect may be deteriorated at zeroth order Neumann eigenvalues of the concealed region. In particular, transmitted fields into the concealed region can be extremely resonated at frequencies corresponding to the zeroth-order Neumann eigenvalues while scattered fields are suppressed well for any frequency. To enhance the cloaking effect at resonance frequencies, we introduce a lossy medium inside the cloaked region and show that the new proposal can reduce the intensity of transmitted fields significantly due to the lossy medium.</P>
Deuterium Clusters Fusion Induced by the Intense Femtosecond Laser Pulse
Hong-Jie, Liu,Zhi-Jian, Zheng,Yu-Qiu, Gu,Bao-Han, Zhang,Yong-Joo, Rhee,Sung-Mo, Nam,Jae-Min, Han,Yong-Woo, Rhee,Kwon-Hae, Yea,Jia-Bin, Chen,Hong-Bin, Wang,Chun-Ye, Jiao,Ying-Ling, He,Tian-Shu, Wen,Xia ALLERTON PRESS INC 2007 CHINESE PHYSICS LETTERS Vol.24 No.2
<P>Neutrons (2.45 MeV) from deuterium cluster fusion induced by the intense femtosecond (30 fs) laser pulse are experimentally demonstrated. The average neutron yield 10<SUP>3</SUP> per shot is obtained. It is found that the yield slightly increases with the increasing laser spot size. No neutron can be observed when the laser intensity I < 4.3×10<SUP>15</SUP> W/cm<SUP>2</SUP>.</P>
Kim, Chung-Seok,Jhang, Kyung-Young ALLERTON PRESS INC 2012 CHINESE PHYSICS LETTERS Vol.29 No.6
<P>We present innovative nonlinear acoustics for characterizing fatigue-induced micro-damage of austenitic stainless steel 316 subjected to high-cycle fatigue. Various fatigue-driven deformations are accumulated at several positions near the middle of hourglass-shaped specimens. A bell-shaped curve of acoustic nonlinearity as a function of position is observed, and the variation in acoustic nonlinearity is attributed to the evolution of a lattice defect (dislocation) and stress-induced martensite based on transmission electron microscopy (TEM) observations. An oblique incidence technique using a longitudinal waveform is a potentially viable method for characterizing the high-cycle fatigue deformation of austenitic stainless steel 316 alloys.</P>