Design of a Novel High Frequency Ultrasound Annular Array

AbstractThe design of a novel 50MHz 7-elment annular array is described. Equal-width electrodes are deposited on the rear face of piezoelectric layer to form a kerfless array, instead of mechanical cutting. Compared with equal-area designs, much better performance is achieved by the novel design. The cross talk is down to -20dB, the -6dB bandwidth and insertion loss are 41% and 18dB, respectively. The pulse responses are largely improved compared with conventional kerfless annular arrays. Furthermore, no pre-focus lens for the central element is required in this array, promising simplified fabrication

Observation of Nonlocal Modulation with Entangled Photons

We demonstrate a new type of quantum mechanical correlation where phase modulators at distant locations, acting on the photons of an entangled pair, interfere to determine the apparent depth of modulation. When the modulators have the same phase, the modulation depth doubles; when oppositely phased, the modulators negate each other.Comment: 4 pages, 4 figure

The Core-like Nature of HST-1 in the M87 Jet

We investigate the total flux density, spectral, polarization, and Faraday rotation variability of HST-1 in the M87 jet during the outburst from 2003 to 2007 through multi-epoch VLA observations at 8, 15, and 22 GHz. Contrary to the general case for blazars, the flux densities of HST-1 rise earlier at lower frequencies from radio to X-ray, and the spectra are softening with the growth of outburst, indicating that the newly emerging subcomponents within HST-1 have relatively steep spectra. In particular, the intrinsic EVPA varies monotonically by $\sim90^\circ$ at the 3 wavebands during the period, and all but the stationary subcomponent in the eastern end of HST-1 move downstream superluminally deviating divergently from the overall jet direction, with the motion of the outmost subcomponent bending from one side of the jet axis to another. These strongly argue for the presence of helical magnetic fields around HST-1, which is also supported by the fact that the subcomponents might be accelerated in this region. The fractional polarization is relatively low in the rising stage, and in the decaying stage the polarization levels are almost comparable at the 3 wavebands. In view of the quite large RM values, Faraday rotation is expected to occur dominantly external to HST-1 in the decaying stage, which is well supported by the presence of diffuse emission around HST-1, and consistent with the scenario that RM decrease gets slower with time.Comment: 5 pages, 4 figures, Accepted for publication in MNRAS Lette

A new 2-D model of a thin annular disk using a modified assumption

The work describes an improved 2-D model for a thin annulus by using a modified assumption with regard to coupled vibration. With this approach, the impedance spectrum and displacements due to radial modes, both in radial and thickness direction of a thin ring, are obtained. Bending displacement is investigated by finite element analysis (FEA) and matches our model. The bending in the thickness direction is coupled to radial modes and shows several node circles in the high radial overtone frequency range. The model is validated by FEA with excellent agreement between the new theory and FEA result

Disorder in DNA-Linked Gold Nanoparticle Assemblies

We report experimental observations on the effect of disorder on the phase behavior of DNA-linked nanoparticle assemblies. Variation in DNA linker lengths results in different melting temperatures of the DNA-linked nanoparticle assemblies. We observed an unusual trend of a non-monotonic ``zigzag'' pattern in the melting temperature as a function of DNAlinker length. Linker DNA resulting in unequal DNA duplex lengths introduces disorder and lowers the melting temperature of the nanoparticle system. Comparison with free DNA thermodynamics shows that such an anomalous zigzag pattern does not exist for free DNA duplex melting, which suggests that the disorder introduced by unequal DNA duplex lengths results in this unusual collective behavior of DNA-linked nanoparticle assemblies.Comment: 4 pages, 4 figures, Phys.Rev.Lett. (2005), to appea

Mutual productivity spillovers between foreign and local firms in China

The existing literature treats advanced technology sourcing as the only cause of reverse productivity spillovers from local to foreign firms and implies that mutual spillovers between foreign and local firms can only happen in the developed world. This paper argues that the diffusion of indigenous technology and local knowledge helps the productivity enhancement of multinationals, so that there can be mutual spillovers even in a developing country. The results from a large-sample firm-level econometric analysis and a comparative case study of seven companies in Chinese manufacturing support this new argument, as mutual spillovers are identified between local Chinese firms and overseas Chinese or OECD-invested firms

The International Effects of China's Growth, Trade and Ecucation Booms

China’s international trade flows have increased by 500% since 1992, far outstripping GDP growth. Likewise tertiary education enrollments have increased by 300%. We simulate these changes using a multi-sector growth model of the Chinese and USA economies. A decade of trade biased growth in China is found to have a large effect on the USA economy – raising GDP approximately 3-4.5 percentage points. We also show that the trade bias in China’s growth accounts for more than half of the observed growth in tertiary enrolments in China. In contrast neutral growth has practically no effect on USA incomes or China’s stock of skilled labour. Finally the simulations reveal that China’s education boom per se has practically no long run impact on the USA economy. The results thus indicate that the pattern of productivity growth in exports sectors, as might be caused by falling trade costs, has been critical in transmitting benefits of Chinese growth to the world economy. They also point to an important link between falling trade costs and human capital formation.Economic Growth, China, Human Capital, Trade Costs