The origin of the radio emission from beta Lyrae

In this paper we present new observational evidence that supports the presence of an extra source of continuum emission in the binary system beta Lyrae. New VLA and IRAM observations, together with published data from the literature and ISO archive data, allow us to build the Spectral Energy Distribution of the binary between 5x10^9 Hz and 5x10^15Hz. The radio-millimeter part of the spectrum is consistent with free-free emission from a symbiotic-like wind associated with the primary component and ionized by the radiation field of the hidden companion. Furthermore, we also consider the possibility that the observed radio flux originates from collimated radio structures associated with the mass gaining component and its disk (Conical thermal jets). An extrapolation of this emission to the far-IR part of the spectrum indicates that in both cases the free-free contribution at these frequencies cannot explain the observations and that the observed infrared excess flux is due principally to the secondary component and its associated disk.Comment: 8 pages, 3 figures, A&A in pres

The radio lighthouse CU Virginis: the spindown of a single main sequence star

The fast rotating star CU Virginis is a magnetic chemically peculiar star with an oblique dipolar magnetic field. The continuum radio emission has been interpreted as gyrosyncrotron emission arising from a thin magnetospheric layer. Previous radio observations at 1.4 GHz showed that a 100% circular polarized and highly directive emission component overlaps to the continuum emission two times per rotation, when the magnetic axis lies in the plane of the sky. This sort of radio lighthouse has been proposed to be due to cyclotron maser emission generated above the magnetic pole and propagating perpendicularly to the magnetic axis. Observations carried out with the Australia Telescope Compact Array at 1.4 and 2.5 GHz one year after this discovery show that this radio emission is still present, meaning that the phenomenon responsible for this process is steady on a timescale of years. The emitted radiation spans at least 1 GHz, being observed from 1.4 to 2.5 GHz. On the light of recent results on the physics of the magnetosphere of this star, the possibility of plasma radiation is ruled out. The characteristics of this radio lighthouse provides us a good marker of the rotation period, since the peaks are visible at particular rotational phases. After one year, they show a delay of about 15 minutes. This is interpreted as a new abrupt spinning down of the star. Among several possibilities, a quick emptying of the equatorial magnetic belt after reaching the maximum density can account for the magnitude of the breaking. The study of the coherent emission in stars like CU Vir, as well as in pre main sequence stars, can give important insight into the angular momentum evolution in young stars. This is a promising field of investigation that high sensitivity radio interferometers such as SKA can exploit.Comment: Accepted to MNRAS, 8 pages, 7 figures, updated versio

A three-dimensional model for the radio emission of magnetic chemically peculiar stars

In this paper we present a three-dimensional numerical model for the radio emission of Magnetic Chemically Peculiar stars, on the hypothesis that energetic electrons emit by the gyrosynchrotron mechanism. For this class of radio stars, characterized by a mainly dipolar magnetic field whose axis is tilted with respect to the rotational axis, the geometry of the magnetosphere and its deformation due to the stellar rotation are determined. The radio emitting region is determined by the physical conditions of the magnetosphere and of the stellar wind. Free-free absorption by the thermal plasma trapped in the inner magnetosphere is also considered. Several free parameters are involved in the model, such as the size of the emitting region, the energy spectrum and the number density of the emitting electrons, and the characteristics of the plasma in the inner magnetosphere. By solving the equation of radiative transfer, along a path parallel to the line of sight, the radio brightness distribution and the total flux density as a function of stellar rotation are computed. As the model is applied to simulate the observed 5 GHz lightcurves of HD37479 and HD37017, several possible magnetosphere configurations are found. After simulations at other frequencies, in spite of the large number of parameters involved in the modeling, two solutions in the case of HD37479 and only one solution in the case of HD37017 match the observed spectral indices. The results of our simulations agree with the magnetically confined wind-shock model in a rotating magnetosphere. The X-ray emission from the inner magnetosphere is also computed, and found to be consistent with the observations.Comment: 15 pages, 10 figures, A&A in pres

Resolving the radio nebula around beta Lyrae

In this paper we present high spatial resolution radio images of the puzzling binary system beta Lyrae obtained with MERLIN at 5 GHz. We find a nebula surrounding the binary with a brightness temperature of 11000+-700K approximately 40AU across. This definitively confirms the thermal origin of the radio emission, which is consistent with emission from the wind of the B6-8II component (mass loss of order of 10^-7 Msun per year), ionized by the radiation field of the hotter companion. This nebula, surrounding the binary, is the proof that beta Layrae evolved in a non-conservative way, i. e. not all the mass lost by the primary is accretted by the secondary, and present measurements indicate that almost 0.015Msun had been lost from the system since the onset of the Roche lobe overflow phase. Moreover, the nebula is aligned with the jet-like structures inferred from recent optical measurements, indicating a possible connection among them.Comment: 5 pages, 2 figures. Accepted for publication in A&

Complexity transitions in global algorithms for sparse linear systems over finite fields

We study the computational complexity of a very basic problem, namely that of finding solutions to a very large set of random linear equations in a finite Galois Field modulo q. Using tools from statistical mechanics we are able to identify phase transitions in the structure of the solution space and to connect them to changes in performance of a global algorithm, namely Gaussian elimination. Crossing phase boundaries produces a dramatic increase in memory and CPU requirements necessary to the algorithms. In turn, this causes the saturation of the upper bounds for the running time. We illustrate the results on the specific problem of integer factorization, which is of central interest for deciphering messages encrypted with the RSA cryptosystem.Comment: 23 pages, 8 figure

Ohio's statewide land use inventory: An operational approach for applying LANDSAT data to state, regional and local planning programs

The programmatic, technical, user application, and cost factors associated with the development of an operational, statewide land use inventory from LANDSAT data are described. The LANDSAT multispectral data are subjected to geometrical and categorical processing to produce map files for each of the 200 fifteen (15) minute quads covering Ohio. Computer compatible tapes are rescanned to produce inventory tapes which identify eight (8) Level I land use categories and a variety of Level II categories. The inventory tapes are processed through a series of ten (10) software programs developed by the State of Ohio. The net result is a computerized inventory which can be displayed in map or tabular form for various geographic units, at a variety of scales and for selected categories of usage. The computerized inventory data files are applied to technical programs developed by the various state agencies to be used in state, regional, and local planning programs

Statistical Approach to Fiber Laser Microcutting of NIMONIC® C263 Superalloy Sheet Used in Effusion Cooling System of Aero Engines

AbstractIn order to reduce thermal stress and avoid premature failure of turbine blades in the hot section of aero-engines, a diffusion cooling system is often adopted. This system is a thin sheet, with a closely spaced holes array allowing a uniform cooling of the turbine blade thanks to the evenly distributing of the cooling fluid within its wall. The holes diameters vary in the range of 0.3-1.0 mm. Furthermore, tight tolerances, perpendicular surfaces, no burr, no recast layer, are required. In order to satisfy the hole requirements, typically EDM technique is adopted. However, EDM micro-drilling needs long process time (about 20 s for hole). A promising alternative is laser trepanning. In this technique, a laser beam, with a very small focused spot, is used to make a hole by circular cutting. The hole is obtained in few seconds (<3 s). In this work a preliminary study on laser microcutting of NIMONIC® C263 sheet is presented in order to verify the possibility to adopt a low-power Yb:YAG fiber laser for the microdrilling. Linear cutting tests were carried out on NIMONIC® C263 superalloy sheet, 0.38 mm thick, using a 100 W Yb:YAG fiber laser working in modulated regime. A systematic approach based on Design of Experiment (DoE) has been successfully adopted with the aim to detect which and how the process parameters affect the kerf geometry in term of kerf width, taper angle and tolerances. The examined process parameters were scan speed, on-time, pulse duration and gas pressure. A full factorial design and ANalysis Of VAriance (ANOVA) were applied. Experimental results show the possibility to obtain kerf characterized by narrow width (<100 μm), low taper angle values (<1.8°) and small tolerance (<0.22 μm). Then, the possibility to produce in-tolerance holes was proved

Dietary patterns of school-age children in Scotland : association with socio-economic indicators, physical activity and obesity

Peer reviewedPublisher PD

Coherent radio emission from the magnetic chemically peculiar star CU Virginis

Radio observations of the magnetic chemically peculiar star CU Vir, carried out with the VLA in three different days, show that the radio emission at 20 cm is characterized by a strong enhancement at particular rotational phases. This radio emission is found to be right hand polarized with a degree of polarization close to 100 %. As common for this class of stars, the magnetic axis of CU Vir is oblique with respect to the rotational axis. By comparing the 20 cm radio light curve with the effective magnetic field available from the literature, a coincidence of the main peaks of the radio emission with the magnetic nulls has been found. This happens when the magnetic axis lies in the plane of the sky. We suggest that the high degree of polarization, together with the high directivity of the radiation, can be explained in terms of coherent radio emission. The data have been interpreted on the basis of the Electron Cyclotron Maser Emission from electrons accelerated in current sheets out of the Alfven radius toward the stellar surface and eventually reflected outward by magnetic mirroring.Comment: 9 pages, 12 figures. To be published in A&