Surface Integral Method for the Second Harmonic Generation in Metal Nanoparticles

Second harmonic (SH) radiation in metal nanoparticles is generated by both nonlocal-bulk and local-surface SH sources, induced by the electromagnetic field at the fundamental frequency. We propose a surface integral equation (SIE) method for evaluating the SH radiation generated by metal nanoparticles with arbitrary shapes, considering all SH sources. We demonstrate that the contribution of the nonlocal-bulk SH sources to the SH electromagnetic field can be taken into account through equivalent surface electric and magnetic currents. We numerically solve the SIE problem by using the Galerkin method and the Rao-Wilton-Glisson basis functions in the framework of the distribution theory. The accuracy of the proposed method is verified by comparison with the SH-Mie analytical solution. As an example of a complex-shaped particle, we investigate the SH scattering by a triangular nano-prism. This method paves the way for a better understanding of the SH generation process in arbitrarily shaped nanoparticles and can also have a high impact in the design of novel nanoplasmonic devices with enhanced SH emission

Low field phase diagram of spin-Hall effect in the mesoscopic regime

When a mesoscopic two dimensional four-terminal Hall cross-bar with Rashba and/or Dresselhaus spin-orbit interaction (SOI) is subjected to a perpendicular uniform magnetic field $B$, both integer quantum Hall effect (IQHE) and mesoscopic spin-Hall effect (MSHE) may exist when disorder strength $W$ in the sample is weak. We have calculated the low field "phase diagram" of MSHE in the $(B,W)$ plane for disordered samples in the IQHE regime. For weak disorder, MSHE conductance $G_{sH}$ and its fluctuations $rms(G_{SH})$ vanish identically on even numbered IQHE plateaus, they have finite values on those odd numbered plateaus induced by SOI, and they have values $G_{SH}=1/2$ and $rms(G_{SH})=0$ on those odd numbered plateaus induced by Zeeman energy. For moderate disorder, the system crosses over into a regime where both $G_{sH}$ and $rms(G_{SH})$ are finite. A larger disorder drives the system into a chaotic regime where $G_{sH}=0$ while $rms(G_{SH})$ is finite. Finally at large disorder both $G_{sH}$ and $rms(G_{SH})$ vanish. We present the physics behind this ``phase diagram".Comment: 4 page, 3 figure

Enhancement of second harmonic generation in a doubly resonant metamaterial

We investigate second harmonic (SH) generation in a doubly resonant metamaterial. We show that SH generation can be enhanced when the resonant condition is satisfied for the SH frequency as well as for the fundamental frequency. A unit cell of the doubly resonant metamaterial consists of two coupled resonators, one of which resonates at the fundamental frequency, whereas the other resonates around the SH frequency. We observe that the SH generation in the doubly resonant metamaterial is 4.6 times as large as that in a singly resonant metamaterial.Comment: 4 pages, 4 figure

Sequential star formation at the periphery of the HII regions Sh 217 and Sh 219

The HII regions Sh 217 and Sh 219 are textbook examples of a Stromgren sphere surrounded by an annular photodissociation region (PDR). The annular PDR is observed in both the 21 cm atomic hydrogen emission and the dust (PAH) emission near 8 micron (MSX Survey). An ultracompact radio continuum source is observed in the direction of the annular PDR, in both Sh 217 and Sh 219. JHKobservations show the presence of highly reddened stellar clusters (AV ~ 20 mag) in the directions of these radio sources. These clusters are also IRAS sources, of luminosities 22700 Lo for Sh 217 and 5900 Lo for Sh 219. Each cluster contains at least one luminous star with an IR colour excess; the one in the Sh 219 cluster shows H-alpha emission. The cluster associated with Sh 217 is almost spherical and contains luminous objects at its centre. The cluster associated with Sh 219 is elongated along the ionization front of this HII region. We argue that these are `second-generation clusters', which means that the physical conditions present in the PDRs, close to the ionization fronts, have favoured the formation of clusters containing massive objects. We discuss the physical mechanisms which may be at the origin of the observed triggered star formation.Comment: 12 pages, Late

The triangulated categories of framed bispectra and framed motives

An alternative approach to the classical Morel-Voevodsky stable motivic homotopy theory $SH(k)$ is suggested. The triangulated category of framed bispectra $SH_{nis}^{fr}(k)$ and effective framed bispectra $SH_{nis}^{fr,eff}(k)$ are introduced in the paper. Both triangulated categories only use Nisnevich local equivalences and have nothing to do with any kind of motivic equivalences. It is shown that $SH_{nis}^{fr}(k)$ and $SH_{nis}^{fr,eff}(k)$ recover the classical Morel-Voevodsky triangulated categories of bispectra $SH(k)$ and effective bispectra $SH^{eff}(k)$ respectively. We also recover $SH(k)$ and $SH^{eff}(k)$ as the triangulated category of framed motivic spectral functors $SH_{S^1}^{fr}[\mathcal Fr_0(k)]$ and the triangulated category of framed motives $\mathcal {SH}^{fr}(k)$ respectively constructed in the paper

Abnormal Action Potentials Associated with the Shaker Complex Locus of Drosophila

Intracellular recordings of action potentials were made from the cervical giant axon in Shaker (Sh) mutants and normal Drosophila. The mutants showed abnormally long delays in repolarization. The defect is not due to abnormal Ca2+ channels, because it persists in the presence of Co2+, a Ca2+-channel blocker. On the other hand, the K+-channel blocker 4-aminopyridine causes a similar effect in normal animals, suggesting that the Sh mutant may have abnormal K+ conductance. Gene-dosage analysis of Sh shows that the defect is not due to underproduction of an otherwise normal molecule; it may be due to an abnormal molecule produced by the mutated gene. Gel electrophoresis failed to detect an abnormal protein, suggesting that, if Sh codes for a nervous system protein, it is rare. Genetic analysis of the Sh locus indicates three regions. Mutations or chromosome breaks in the two flanking regions cause Sh mutant physiology; the central region shows a "haplolethal effect"--i.e., heterozygous females are lethal

Discovery of interstellar mercapto radicals (SH) with the GREAT instrument on SOFIA

We report the first detection of interstellar mercapto radicals, obtained along the sight-line to the submillimeter continuum source W49N. We have used the GREAT instrument on SOFIA to observe the 1383 GHz Doublet Pi 3/2 J = 5/2 - 3/2 lambda doublet in the upper sideband of the L1 receiver. The resultant spectrum reveals SH absorption in material local to W49N, as well as in foreground gas, unassociated with W49N, that is located along the sight-line. For the foreground material at velocities in the range 37 - 44 km/s with respect to the local standard of rest, we infer a total SH column density ~ 2.6 E+12 cm-2, corresponding to an abundance of ~ 7 E-9 relative to H2, and yielding an SH/H2S abundance ratio ~ 0.13. The observed SH/H2S abundance ratio is much smaller than that predicted by standard models for the production of SH and H2S in turbulent dissipation regions and shocks, and suggests that the endothermic neutral-neutral reaction SH + H2 -> H2S + H must be enhanced along with the ion-neutral reactions believed to produce CH+ and SH+ in diffuse molecular clouds.Comment: Accepted for publication in Astronomy and Astrophysics (SOFIA/GREAT special issue