Frequency dependence of pulsar radiation patterns

We report on new results from simultaneous, dual frequency, single pulse observation of PSR B0329+54 using the Giant Metrewave Radio Telescope. We find that the longitude separation of subpulses at two different frequencies (238 and 612 MHz) is less than that for the corresponding components in the average profile. A similar behaviour has been noticed before in a number of pulsars. We argue that subpulses are emitted within narrow flux tubes of the dipolar field lines and that the mean pulsar beam has a conal structure. In such a model the longitudes of profile components are determined by the intersection of the line of sight trajectory with subpulse-associated emission beams. Thus, we show that the difference in the frequency dependence of subpulse and profile component longitudes is a natural property of the conal model of pulsar emission beam. We support our conclusions by numerical modelling of pulsar emission, using the known parameters for this pulsar, which produce results that agree very well with our dual frequency observations.Comment: 24 pages, 8 figures. Accepted for publication in Ap

Persistence on airline accidents

This paper analyses airline accidents data from 1927-2006. The fractional integration methodology is adopted. It is shown that airline accidents are persistent and (fractionally) cointegrated with airline traffic. Thus, there exists an equilibrium relation between air accidents and airline traffic, with the effect of the shocks to that relationship disappearing in the long run. Policy implications are derived for countering accidents events.

Semipurity of tempered Deligne cohomology

In this paper we define the formal and tempered Deligne cohomology groups, that are obtained by applying the Deligne complex functor to the complexes of formal differential forms and tempered currents respectively. We then prove the existence of a duality between them, a vanishing theorem for the former and a semipurity property for the latter. The motivation of these results comes from the study of covariant arithmetic Chow groups. The semi-purity property of tempered Deligne cohomology implies, in particular, that several definitions of covariant arithmetic Chow groups agree for projective arithmetic varieties

How to generate pentagonal symmetry using Turing systems

We explore numerically the formation of Turing patterns in a confined circular domain with small aspect ratio. Our results show that stable fivefold patterns are formed over a well defined range of disk sizes, offering a possible mechanism for inducing the fivefold symmetry observed in early development of regular echinoids. Using this pattern as a seed, more complex biological structures can be mimicked, such as the pigmentation pattern of sea urchins and the plate arrangements of the calyxes of primitive camerate crinoids

Spontaneous patterning of quantum dots at the air-water interface

Nanoparticles deposited at the air-water interface are observed to form circular domains at low density and stripes at higher density. We interpret these patterns as equilibrium phenomena produced by a competition between an attraction and a longer-ranged repulsion. Computer simulations of a generic pair potential with attractive and repulsive parts of this kind, reproduce both the circular and stripe patterns. Such patterns have a potential use in nanoelectronic applications

On the calibration of the relation between geometric albedo and polarimetric properties for the asteroids

We present a new extensive analysis of the old problem of finding a satisfactory calibration of the relation between the geometric albedo and some measurable polarization properties of the asteroids. To achieve our goals, we use all polarimetric data at our disposal. For the purposes of calibration, we use a limited sample of objects for which we can be confident to know the albedo with good accuracy, according to previous investigations of other authors. We find a new set of updated calibration coefficients for the classical slope - albedo relation, but we generalize our analysis and we consider also alternative possibilities, including the use of other polarimetric parameters, one being proposed here for the first time, and the possibility to exclude from best-fit analyzes the asteroids having low albedos. We also consider a possible parabolic fit of the whole set of data.Comment: Accepted by MNRA

Seeing Star Formation Regions with Gravitational Microlensing

We qualitatively study the effects of gravitational microlensing on our view of unresolved extragalactic star formation regions. Using a general gravitational microlensing configuration, we perform a number of simulations that reveal that specific imprints of the star forming region are imprinted, both photometrically and spectroscopically, upon observations. Such observations have the potential to reveal the nature and size of these star forming regions, through the degree of variability observed in a monitoring campaign, and hence resolve the star formation regions in distant galaxies which are too small to be probed via more standard techniques.Comment: 7 pages, 8 figures, ApJ accepte

The redshift and broad band spectral energy distribution of NRAO 150

Context. NRAO 150 is one of the brightest radio and mm AGN sources on the northern sky. It has been revealed as an interesting source where to study extreme relativistic jet phenomena. However, its cosmological distance has not been reported so far, because of its optical faintness produced by strong Galactic extinction. Aims. Aiming at measuring the redshift of NRAO 150, and hence to start making possible quantitative studies from the source. Methods. We have conducted spectroscopic and photometric observations of the source in the near-IR, as well as in the optical. Results. All such observations have been successful in detecting the source. The near-IR spectroscopic observations reveal strong H$\alpha$ and H$\beta$ emission lines from which the cosmological redshift of NRAO 150 ($z=1.517\pm0.002$) has been determined for the first time. We classify the source as a flat-spectrum radio-loud quasar, for which we estimate a large super-massive black-hole mass $\sim5\times 10^{9} \mathrm{M_\odot}$. After extinction correction, the new near-IR and optical data have revealed a high-luminosity continuum-emission excess in the optical (peaking at $\sim2000$\,\AA, rest frame) that we attribute to thermal emission from the accretion disk for which we estimate a high accretion rate, $\sim30$\,% of the Eddington limit. Conclusions. Comparison of these source properties, and its broad-band spectral-energy distribution, with those of Fermi blazars allow us to predict that NRAO 150 is among the most powerful blazars, and hence a high luminosity -although not detected yet- $\gamma$-ray emitter.Comment: 8 pages, 4 figure