Numerical investigation of the Rayleigh hypothesis for electromagnetic scattering by a particle

The validity of the Rayleigh hypothesis has been a long-standing issue in the applicability of the T-matrix method to near-field calculations, and despite numerous theoretical works, the practical consequences for numerical simulations have remained unclear. Such calculations are increasingly important in the field of nanooptics, for which accurate and efficient modeling tools are in high demand. We here tackle this challenge by investigating numerically the convergence behavior of series expansions of the electric field around spheroidal particles, which provides us with unambiguous examples to clarify the conditions of convergence. This study is made possible by the combination of alternative methods to compute near-fields accurately, and crucially, the recent improvements in the calculation of T-matrix elements free from numerical instabilities, as such errors would otherwise obfuscate the intrinsic convergence properties of the field series. The resulting numerical confirmation for the range of validity of the Rayleigh hypothesis, complemented by a better understanding of the convergence behavior of the field expansions, is a crucial step toward future developments

π\pi-J/ψJ/\psi Correlation and Elliptic Flow Parameter v2v_2 of Charmed Mesons at RHIC Energy

We study the correlation between the trigger $\pi$ and the associated $J/\psi$ on near and away sides in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. In the region of trigger momentum $p_t>4$ GeV/$c$, the $\pi$ spectrum is composed of thermal-shower and shower-shower recombinations in the frame work of the recombination model. We consider the azimuthal anisotropy in the quenched hard parton distribution and then calculate the elliptic flow parameter $v_2$ of charmed mesons ($J/\psi$, $D^0$ and $D_s$) for different centralities.Comment: 17 pages, 6 figure

STM Studies of TbTe3: Evidence for a fully Incommensurate Charge Density Wave

We observe unidirectional charge density wave ordering on the cleaved surface of TbTe3 with a Scanning Tunneling Microscope at ~6 K. The modulation wave-vector q_{CDW} as determined by Fourier analysis is 0.71 +/- 0.02 * 2 pi/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of ~(1/3) * 2 pi/a ordering perpendicular to the CDW. Our analysis indicates that the CDW is incommensurate.Comment: 4 pages, 4 figure

Effects of retro-nasal aroma release on satiation

It is suggested that the brain response of a food odour sensed retro-nasally is related to satiation. The extent of retro-nasal aroma release during consumption depends on the physical structure of a food, i.e. solid foods generate a longer, more pronounced retro-nasal aroma release than liquid foods. The aim of this study was to investigate if a beverage becomes more satiating when the retro-nasal aroma release profile coincides with the profile of a (soft) solid food. In a double-blind placebo-controlled randomised cross-over full factorial design, twenty-seven healthy subjects (fourteen males and thirteen females; aged 16-65 years; BMI 19-37 kg/m(2) were administered aroma profiles by a computer-controlled stimulator based on air dilution olfactometry. Profile A consisted of a profile that is obtained during consumption of normal beverages. Profile B is normally observed during consumption of (soft) solids. The two profiles were produced with strawberry aroma and administered in a retro-nasal fashion, while the subjects consumed a sweetened milk drink. Before, during and after the sensory stimulation, appetite profile measurements were performed. Subjects felt significantly more satiated if they were aroma stimulated with profile B (P = 0.04). After stimulation with sweet strawberry aroma, there was a significant decrease in desire to eat sweet products (P = 0.0001). In conclusion, perceived satiation was increased by altering the extent of retro-nasal aroma release

On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping

We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.Comment: To be submitted to J. Phys. Chem.

Silver Nanoparticle Aggregates as Highly Efficient Plasmonic Antennas for Fluorescence Enhancement

The enhanced local fields around plasmonic structures can lead to enhancement of the excitation and modification of the emission quantum yield of fluorophores. So far, high enhancement of fluorescence intensity from dye molecules was demonstrated using bow-tie gap antenna made by e-beam lithography. However, the high manufacturing cost and the fact that currently there are no effective ways to place fluorophores only at the gap prevent the use of these structures for enhancing fluorescence-based biochemical assays. We report on the simultaneous modification of fluorescence intensity and lifetime of dye-labeled DNA in the presence of aggregated silver nanoparticles. The nanoparticle aggregates act as efficient plasmonic antennas, leading to more than 2 orders of magnitude enhancement of the average fluorescence. This is comparable to the best-reported fluorescence enhancement for a single molecule but here applies to the average signal detected from all fluorophores in the system. This highlights the remarkable efficiency of this system for surface-enhanced fluorescence. Moreover, we show that the fluorescence intensity enhancement varies with the plasmon resonance position and measure a significant reduction (300×) of the fluorescence lifetime. Both observations are shown to be in agreement with the electromagnetic model of surface-enhanced fluorescence