Photoacoustic Signal Enhancement by Localized Surface Plasmon of Gold Nanoparticles

Photoacoustic imaging has been widely studied as a deep biological tissue imaging modality combining optical absorption and ultrasonic detection. It enables multi-scale high resolution imaging of optical absorbing intrinsic molecules as well as exogenous molecules. Gold nanoparticles have the primary advantages of large absorption cross section and bioconjugation capability for the imaging contrast agents. In order to design the photoacoustic imaging agents for enhancing the contrast with high specificity to targeted molecules and / or cell, we measured and analyzed time-of-flight photoacoustic signals of aqueous solutions of various shapes and sizes of gold nanoparticles. The signal intensities were sensitive to the shapes and sizes of the gold nanoparticles. We found a strong photoacoustic signal of the polyhedral gold nanoparticle due to the localized surface plasmon resonance. The experimental results derive the strategy of designing the optimum photoacoustic contrast agents. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3543

Polarizations and Nullcone of Representations of Reductive Groups

The paper starts with the following simple observation. Let V be a representation of a reductive group G, and let f_1,f_2,...,f_n be homogeneous invariant functions. Then the polarizations of f_1,f_2,...,f_n define the nullcone of k 0} h(t) x = 0 for all x in L. This is then applied to many examples. A surprising result is about the group SL(2,C) where almost all representations V have the property that all linear subspaces of the nullcone are annihilated. Again, this has interesting applications to the invariants on several copies. Another result concerns the n-qubits which appear in quantum computing. This is the representation of a product of n copies of $SL_2$ on the n-fold tensor product C^2 otimes C^2 otimes ... otimes C^2. Here we show just the opposite, namely that the polarizations never define the nullcone of several copies if n <= 3. (An earlier version of this paper, distributed in 2002, was split into two parts; the first part with the title ``On the nullcone of representations of reductive groups'' is published in Pacific J. Math. {bf 224} (2006), 119--140.

Direct evidence for ferromagnetic spin polarization in gold nanoparticles

We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometry. This result is evidence of intrinsic spin polarization in nano-sized gold.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Effects of nonlinear sweep in the Landau-Zener-Stueckelberg effect

We study the Landau-Zener-Stueckelberg (LZS) effect for a two-level system with a time-dependent nonlinear bias field (the sweep function) W(t). Our main concern is to investigate the influence of the nonlinearity of W(t) on the probability P to remain in the initial state. The dimensionless quantity epsilon = pi Delta ^2/(2 hbar v) depends on the coupling Delta of both levels and on the sweep rate v. For fast sweep rates, i.e., epsilon << l and monotonic, analytic sweep functions linearizable in the vicinity of the resonance we find the transition probability 1-P ~= epsilon (1+a), where a>0 is the correction to the LSZ result due to the nonlinearity of the sweep. Further increase of the sweep rate with nonlinearity fixed brings the system into the nonlinear-sweep regime characterized by 1-P ~= epsilon ^gamma with gamma neq 1 depending on the type of sweep function. In case of slow sweep rates, i.e., epsilon >>1 an interesting interference phenomenon occurs. For analytic W(t) the probability P=P_0 e^-eta is determined by the singularities of sqrt{Delta ^2+W^2(t)} in the upper complex plane of t. If W(t) is close to linear, there is only one singularity, that leads to the LZS result P=e^-epsilon with important corrections to the exponent due to nonlinearity. However, for, e.g., W(t) ~ t^3 there is a pair of singularities in the upper complex plane. Interference of their contributions leads to oscillations of the prefactor P_0 that depends on the sweep rate through epsilon and turns to zero at some epsilon. Measurements of the oscillation period and of the exponential factor would allow to determine Delta, independently.Comment: 11 PR pages, 12 figures. To be published in PR

First application of the Trojan Horse Method with a Radioactive Ion Beam: study of the 18^{18}F(p,αp,{\alpha})15^{15}O}} reaction at astrophysical energies

Measurement of nuclear cross sections at astrophysical energies involving unstable species is one of the most challenging tasks in experimental nuclear physics. The use of indirect methods is often unavoidable in this scenario. In this paper the Trojan Horse Method is applied for the first time to a radioactive ion beam induced reaction studying the $^{18}$F($p,{\alpha}$)$^{15}$O process at low energies relevant to astrophysics via the three body reaction $^{2}$H($^{18}$F,${\alpha}^{15}$O)n. The knowledge of the $^{18}$F($p, {\alpha}$)$^{15}$O reaction rate is crucial to understand the nova explosion phenomena. The cross section of this reaction is characterized by the presence of several resonances in $^{19}$Ne and possibly interference effects among them. The results reported in Literature are not satisfactory and new investigations of the $^{18}$F($p,{\alpha}$)$^{15}$O reaction cross section will be useful. In the present work the spin-parity assignments of relevant levels have been discussed and the astrophysical S-factor has been extracted considering also interference effectsComment: 7 pages, 4 figure