Is the far border of the Local Void expanding?

According to models of evolution in the hierarchical structure formation scenarios, voids of galaxies are expected to expand. The Local Void (LV) is the closest large void, and it provides a unique opportunity to test observationally such an expansion. It has been found that the Local Group, which is on the border of the LV, is running away from the void center at ~260 km/s. In this study we investigate the motion of the galaxies at the far-side border of the LV to examine the presence of a possible expansion. We selected late-type, edge-on spiral galaxies with radial velocities between 3000 km/s and 5000 km/s, and carried out HI 21 cm line and H-band imaging observations. The near-infrared Tully-Fisher relation was calibrated with a large sample of galaxies and carefully corrected for Malmquist bias. It was used to compute the distances and the peculiar velocities of the LV sample galaxies. Among the 36 sample LV galaxies with good quality HI line width measurements, only 15 galaxies were selected for measuring their distances and peculiar velocities, in order to avoid the effect of Malmquist bias. The average peculiar velocity of these 15 galaxies is found to be -419+208-251 km/s, which is not significantly different from zero. Due to the intrinsically large scatter of Tully-Fisher relation, we cannot conclude whether there is a systematic motion against the center of the LV for the galaxies at the far-side boundary of the void. However, our result is consistent with the hypothesis that those galaxies at the far-side boundary have an average velocity of ~260 km/s equivalent to what is found at the position of the Local Group.Comment: 15 pages, 6 figures, and 4 tables. Accepted for publication in A&

Microscopic Study of the Spinodal Decomposition of Supported Eutectic Droplets during Cooling:PtGe/Ge{110}

[Image: see text] We embarked on an in situ low-energy electron microscopy, photo-electron emission microscopy, and selected area low-energy electron diffraction study during the cooling of huge eutectic droplets through the critical stages of the eutectic transition. On this journey through uncharted waters, we revealed an expected initial shrinking of the exposed area of the droplet, followed by an unanticipated expansion. We attribute this behavior to an initial fast amorphization of the interface between the droplet and surface, followed by the recrystallization of Ge expelled from the droplet at the interface. As a major surprise, we discovered the emergence of extensive “spaghetti”-like patterns, which are rationalized in terms of parallel Ge ripples oriented along, mainly, [−554] and [−55–4] directions. They emerge during spinodal decomposition when passing the eutectic temperature of the system. Their sides are defined by Ge{111} and Ge{11–1} vicinals covered with Pt-modified (√3 × √3) superstructures. The distance between adjacent ripples is about 18 nm

Factorization of the Non-Stationary Schrodinger Operator

We consider a factorization of the non-stationary Schrodinger operator based on the parabolic Dirac operator introduced by Cerejeiras/ Kahler/ Sommen. Based on the fundamental solution for the parabolic Dirac operators, we shall construct appropriated Teodorescu and Cauchy-Bitsadze operators. Afterwards we will describe how to solve the nonlinear Schrodinger equation using Banach fixed point theorem.Comment: Accepted for publication in Advances in Applied Clifford Algebra

Photoinduced Changes of Reflectivity in Single Crystals of YBa2Cu3O6.5 (Ortho II)

We report measurements of the photoinduced change in reflectivity of an untwinned single crystal of YBa2Cu3O6.5 in the ortho II structure. The decay rate of the transient change in reflectivity is found to decrease rapidly with decreasing temperature and, below Tc, with decreasing laser intensity. We interpret the decay as a process of thermalization of antinodal quasiparticles, whose rate is determined by an inelastic scattering rate of quasiparticle pairs.Comment: 4 pages, 4 figure

New Reference Galaxy Standards for HI Emission Observations

We have taken advantage of the improved baselines and higher sensitivity available with the upgraded Arecibo 305m telescope to create a new HI spectral line catalog of disk galaxies which can be used as a reference catalog for anyone interested in 21-cm spectral line work. In all 108 galaxies were observed, covering 24h of the sky at declinations between 0 < delta < 36 degrees and velocities between 0 - 25,000 km s-1. The majority of the galaxies were observed at least two times on different nights to avoid problems with RFI, baselines fluctuations, etc. Comparing our measured values with all those available in the literature show that while large individual variations may exist, the average differences between the measurements to be zero. In all we have considerable confidence in our measurements, and the resultant catalog should be extremely useful as a well defined reference catalog for anyone interested in 21-cm spectral line work.Comment: Accepted for publication by AJ. 23 pages, with 10 figures and 3 tables. Data tables, paper, etc. available online at http://www.gb.nrao.edu/~koneil/HIsurvey Replacement paper corrects one error in Table 1 and two errors in Table

Dirac solutions for quaternionic potentials

In this paper, the quaternionic Dirac equation is solved for quaternionic potentials, iV0+jW0. The study shows two different solutions. The first solution contains particles and anti-particles and leads to the diffusion, tunneling and Klein energy zones. The complex limit is recovered from this solution. The second solution, which does not have a complex counterpart, can be seen as a V0-antiparticle or |W0|-particle.Comment: 12 pages, 3 figure

Spectrum Sensing Framework based on Blind Source Separation for Cognitive Radio Environments

El uso eficiente del espectro se ha convertido en un área de investigación activa, debido a la escasez de este recurso y a su subutilización. En un escenario en el que el espectro es un recurso compartido como en la radio cognitiva (CR), los espacios sin uso dentro de las bandas de frecuencias con licencia podrían ser detectados y posteriormente utilizados por un usuario secundario a través de técnicas de detección y sensado del espectro. Generalmente, estas técnicas de detección se utilizan a partir de un conocimiento previo de las características de canal. En el presente trabajo se propone un enfoque de detección ciega del espectro basado en análisis de componentes independientes (ICA) y análisis de espectro singular (SSA). La técnica de detección se valida a través de simulación, y su desempeño se compara con metodologías propuestas por otros autores en la literatura. Los resultados muestran que el sistema propuesto es capaz de detectar la mayoría de las fuentes con bajo consumo de tiempo, un aspecto que cabe resaltar para aplicaciones en línea con exigencias de tiempo.The efficient use of spectrum has become an active research area, due to its scarcity and underutilization. In a spectrum sharing scenario as Cognitive Radio (CR), the vacancy of licensed frequency bands could be detected by a secondary user through spectrum sensing techniques. Usually, this sensing approaches are performed with a priori knowledge of the channel features. In the present work, a blind spectrum sensing approach based on Independent Component Analysis and Singular Spectrum Analysis is proposed. The approach is tested and compared with other outcomes. Results show that the proposed scheme is capable of detect most of the sources with low time consumption, which is a remarkable aspect for online applications with demanding time issues