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Fabrication of a high sensitive Ag-nanoparticle substrate and its application to the detection of toxic substances
Surface Enhanced Raman Scattering (SERS) is typically observed with the substrate in a liquid medium and it has been proposed as a promising technique for detecting low levels of pollutants in liquids. A technique is presented for self-assembly to immobilize Ag nanoparticles (Ag-NPs), with diameters ranging from 100 to 800nm on a solid support. Experimental results have been obtained through experiments using Ag-NPs active substrates to detect Rhodamine 6G (R6G) and crystal violet in the deionized water. Further, the SERS spectrum and Raman spectrum of phoxim were also measured, showing the enhancement in the performance of the active substrate as a result
A k-space method for nonlinear wave propagation
A k-space method for nonlinear wave propagation in absorptive media is
presented. The Westervelt equation is first transferred into k-space via
Fourier transformation, and is solved by a modified wave-vector time-domain
scheme [Mast et al., IEEE Tran. Ultrason. Ferroelectr. Freq. Control 48,
341-354 (2001)]. The present approach is not limited to forward propagation or
parabolic approximation. One- and two-dimensional problems are investigated to
verify the method by comparing results to the finite element method. It is
found that, in order to obtain accurate results in homogeneous media, the grid
size can be as little as two points per wavelength, and for a moderately
nonlinear problem, the Courant-Friedrichs-Lewy number can be as small as 0.4.
As a result, the k-space method for nonlinear wave propagation is shown here to
be computationally more efficient than the conventional finite element method
or finite-difference time-domain method for the conditions studied here.
However, although the present method is highly accurate for weakly
inhomogeneous media, it is found to be less accurate for strongly inhomogeneous
media. A possible remedy to this limitation is discussed
Statistical study of free magnetic energy and flare productivity of solar active regions
Photospheric vector magnetograms from Helioseismic and Magnetic Imager on
board the Solar Dynamic Observatory are utilized as the boundary conditions to
extrapolate both non-linear force-free and potential magnetic fields in solar
corona. Based on the extrapolations, we are able to determine the free magnetic
energy (FME) stored in active regions (ARs). Over 3000 vector magnetograms in
61 ARs were analyzed. We compare FME with ARs' flare index (FI) and find that
there is a weak correlation () between FME and FI. FME shows slightly
improved flare predictability relative to total unsigned magnetic flux of ARs
in the following two aspects: (1) the flare productivity predicted by FME is
higher than that predicted by magnetic flux and (2) the correlation between FI
and FME is higher than that between FI and magnetic flux. However, this
improvement is not significant enough to make a substantial difference in
time-accumulated FI, rather than individual flare, predictions.Comment: The paper was submitted to ApJ and it is accepted no
Exponential Decay for Damped Klein-Gordon Equations on Asymptotically Cylindrical and Conic Manifolds
We study the decay of the global energy for the damped Klein-Gordon equation
on non-compact manifolds with finitely many cylindrical and subconic ends up to
bounded perturbation. We prove that under the Geometric Control Condition, the
decay is exponential, and that under the weaker Network Control Condition, the
decay is logarithmic, by developing the global Carleman estimate with multiple
weights
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Can the persistence of a currency crisis be explained by fundamentals? Markov switching models for exchange market pressure
This paper investigates the contribution of fundamentals to the persistence of currency crises by identifying the determinants of high volatility in the exchange market pressure index (empi) for some new EU member states. The Markov switching model is utilised to identify the high volatility of empi, and a linear regression analysis is conducted to find the sources of the transition probability of the high volatility regime. The evidence does not seem to provide strong support for macroeconomic fundamentals, whereas it highlights the adverse movement of interest rates as the major determinant of the persistence of the currency crisis
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