Directional emission of light from a nano-optical Yagi-Uda antenna

The plasmon resonance of metal nanoparticles can enhance and direct light from optical emitters in much the same way that radio frequency (RF) antennas enhance and direct the emission from electrical circuits. In the RF regime, a typical antenna design for high directivity is the Yagi-Uda antenna, which basically consists of a one-dimensional array of antenna elements driven by a single feed element. Here, we present the experimental demonstration of directional light emission from a nano-optical Yagi-Uda antenna composed of an array of appropriately tuned gold nanorods. Our results indicate that nano-optical antenna arrays are a simple but efficient tool for the spatial control of light emission.Comment: 4 pages, including 4 figure

Direct Test of the Scalar-Vector Lorentz Structure of the Nucleon- and Antinucleon-Nucleus Potential

Quantum Hadrodynamics in mean field approximation describes the effective nucleon-nucleus potential (about -50 MeV deep) as resulting from a strong repulsive vector (about 400 MeV) and a strong attractive scalar (about -450 MeV) contribution. This scalar-vector Lorentz structure implies a significant lowering of the threshold for $p\bar{p}$ photoproduction on a nucleus by about 850 MeV as compared to the free case since charge conjugation reverses the sign of the vector potential contribution in the equation of motion for the $\bar{p}$ states. It also implies a certain size of the photon induced $p\bar{p}$ pair creation cross section near threshold which is calculated for a target nucleus $^{208}$Pb. We also indicate a measurable second signature of the $p\bar{p}$ photoproduction process by estimating the increased cross section for emission of charged pions as a consequence of $\bar{p}$ annihilation within the nucleus.Comment: 18 pages latex, 5 PS figure

Gauged Inflation

We propose a model for cosmic inflation which is based on an effective description of strongly interacting, nonsupersymmetric matter within the framework of dynamical Abelian projection and centerization. The underlying gauge symmetry is assumed to be $SU(N+1)$ with $N \gg 1$. Appealing to a thermodynamical treatment, the ground-state structure of the model is classically determined by a potential for the inflaton field (dynamical monopole condensate) which allows for nontrivially BPS saturated and thereby stable solutions. For $T<M_P$ this leads to decoupling of gravity from the inflaton dynamics. The ground state dynamics implies a heat capacity for the vacuum leading to inflation for temperatures comparable to the mass scale $M$ of the potential. The dynamics has an attractor property. In contrast to the usual slow-roll paradigm we have $m\gg H$ during inflation. As a consequence, density perturbations generated from the inflaton are irrelevant for the formation of large-scale structure, and the model has to be supplemented with an inflaton independent mechanism for the generation of spatial curvature perturbations. Within a small fraction of the Hubble time inflation is terminated by a transition of the theory to its center symmetric phase. The spontaneously broken $Z_{N+1}$ symmetry stabilizes relic vector bosons in the epochs following inflation. These heavy relics contribute to the cold dark matter of the universe and potentially originate the UHECRs beyond the GZK bound.Comment: 23 pages, 4 figures, subsection added, revision of text, to app. in PR

Bispectrum speckle interferometry of the massive protostellar outflow source IRAS 23151+5912

We present bispectrum speckle interferometry of the massive protostellar object IRAS 23151+5912 in the near-infrared K' band. The reconstructed image shows the diffuse nebulosity north-east of two point-like sources in unprecedented detail. The comparison of our near-infrared image with mm continuum and CO molecular line maps shows that the brighter of the two point sources lies near the center of the mm peak, indicating that it is a high-mass protostar. The nebulosity coincides with the blue-shifted molecular outflow component. The most prominent feature in the nebulosity is a bow-shock-like arc. We assume that this feature is associated with a precessing jet which has created an inward-pointed cone in the swept-up material. We present numerical jet simulations that reproduce this and several other features observed in our speckle image of the nebulosity. Our data also reveal a linear structure connecting the central point source to the extended diffuse nebulosity. This feature may represent the innermost part of a jet that drives the strong molecular outflow (PA ~80 degr) from IRAS 23151+5912. With the aid of radiative transfer calculations, we demonstrate that, in general, the observed inner structures of the circumstellar material surrounding high-mass stars are strongly influenced by the orientation and symmetry of the bipolar cavity.Comment: accepted by Astronomy & Astrophysics; preprints with high-resolution images can be obtained from http://www.mpifr-bonn.mpg.de/staff/tpreibis/iras23151.htm

Visual/infrared interferometry of Orion Trapezium stars: Preliminary dynamical orbit and aperture synthesis imaging of the Theta 1 Orionis C system

Located in the Orion Trapezium cluster, Theta 1 Orionis C is one of the youngest and nearest high-mass stars (O5-O7) and also known to be a close binary system. Using new multi-epoch visual and near-infrared bispectrum speckle interferometric observations obtained at the BTA 6 m telescope, and IOTA near-infrared long-baseline interferometry, we trace the orbital motion of the Theta 1 Ori C components over the interval 1997.8 to 2005.9, covering a significant arc of the orbit. Besides fitting the relative position and the flux ratio, we apply aperture synthesis techniques to our IOTA data to reconstruct a model-independent image of the Theta 1 Ori C binary system. The orbital solutions suggest a high eccentricity (e approx. 0.91) and short-period (P approx. 10.9 yrs) orbit. As the current astrometric data only allows rather weak constraints on the total dynamical mass, we present the two best-fit orbits. From these orbital solutions one can be favoured, implying a system mass of 48 M_sun and a distance to the Trapezium cluster of 434 pc. When also taking the measured flux ratio and the derived location in the HR-diagram into account, we find good agreement for all observables, assuming a spectral type of O5.5 for Theta 1 Ori C1 (M=34.0 M_sun) and O9.5 for C2 (M=15.5 M_sun). We find indications that the companion C2 is massive itself, which makes it likely that its contribution to the intense UV radiation field of the Trapezium cluster is non-negligible. Furthermore, the high eccentricity of the preliminary orbit solution predicts a very small physical separation during periastron passage (approx. 1.5 AU, next passage around 2007.5), suggesting strong wind-wind interaction between the two O stars.Comment: 13 pages, 9 figures, Accepted for publication in Astronomy & Astrophysic

A stopped Delta-Matter Source in Heavy Ion Collisions at 10 GeV/n

We predict the formation of highly dense baryon-rich resonance matter in Au+Au collisions at AGS energies. The final pion yields show observable signs for resonance matter. The Delta(1232) resonance is predicted to be the dominant source for pions of small transverse momenta. Rescattering effects -- consecutive excitation and deexcitation of Deltas -- lead to a long apparent lifetime (> 10 fm/c) and rather large volumina (several 100 fm^3) of the Delta-matter state. Heavier baryon resonances prove to be crucial for reaction dynamics and particle production at AGS.Comment: 17 pages, 5 postscript figures, uses psfig.sty and revtex.st

Non-polynomial Worst-Case Analysis of Recursive Programs

We study the problem of developing efficient approaches for proving worst-case bounds of non-deterministic recursive programs. Ranking functions are sound and complete for proving termination and worst-case bounds of nonrecursive programs. First, we apply ranking functions to recursion, resulting in measure functions. We show that measure functions provide a sound and complete approach to prove worst-case bounds of non-deterministic recursive programs. Our second contribution is the synthesis of measure functions in nonpolynomial forms. We show that non-polynomial measure functions with logarithm and exponentiation can be synthesized through abstraction of logarithmic or exponentiation terms, Farkas' Lemma, and Handelman's Theorem using linear programming. While previous methods obtain worst-case polynomial bounds, our approach can synthesize bounds of the form $\mathcal{O}(n\log n)$ as well as $\mathcal{O}(n^r)$ where $r$ is not an integer. We present experimental results to demonstrate that our approach can obtain efficiently worst-case bounds of classical recursive algorithms such as (i) Merge-Sort, the divide-and-conquer algorithm for the Closest-Pair problem, where we obtain $\mathcal{O}(n \log n)$ worst-case bound, and (ii) Karatsuba's algorithm for polynomial multiplication and Strassen's algorithm for matrix multiplication, where we obtain $\mathcal{O}(n^r)$ bound such that $r$ is not an integer and close to the best-known bounds for the respective algorithms.Comment: 54 Pages, Full Version to CAV 201

Discovery of a dust cloud next to sigma Orionis

We report on the discovery of a mid-infrared source at a projected distance of only 1200 AU from the O9.5 V star sigma Orionis. The spatially resolved, fan-shaped morphology and the presence of an ionization front, as well as evidence in the spectrum for processed dust grains, all suggest that it is a proto-planetary disk being dispersed by the intense ultraviolet radiation from sigma Orionis. We compute the mass budget and the photo-evaporation timescale, and discuss the possible nature of this remarkable object.Comment: Accepted for publication in A&A Letters: 4 pages, 3 figure