Unusually low coronal radio emission at the solar minimum

We present two-dimensional observations of the quiet Sun at 73.8, 50.0, and 38.5 MHz obtained with the Clark Lake Radioheliograph during the sunspot minimum period of September 1986. The observed peak brightness temperatures during the entire period of sunspot minimum are found to be extremely low, lying in the range (0.6 × 10⁵ K – 2.5 × 10⁵ K). It is shown that these low values cannot be explained by the generally adopted models for N _e and T _e in a homogeneous corona. The effect of scattering by random density fluctuations is introduced in order to decrease the values of predicted T _b . The value of peak T _b is computed as a function of relative r.m.s. density fluctuations = <N _e >/N _e ; and it is found that should be in the range from 0.07 to 0.19, 0.1 to 0.25, and 0.15 to 0.35, respectively, at 38.5, 50.0, and 73.8 MHz, respectively, to explain the observed low brightness temperatures.On leave from Indian Institute of Astrophysics, Bangalore, India.     

Labour circulation and the village economy in Fiji

The author examines circular labor migration in Fiji. "This paper is organized into five sections. The first section provides a brief discussion of two major perspectives of labour circulation in developing countries. The second section presents the state of the Fijian village in the context of the current pattern of uneven development in Fiji. The practice of labour circulation by Fijian villagers is dealt with in the third section. In the last two sections, issues concerning the maintenance of the polarized pattern and the preservation of the village mode of production are discussed."     

A model of an exploding,radiating star in general relativity

In a previous paper Adams, Cary and Cohen (1994) presented a model of a supernova. In that paper the equations of General Relativity describing the evolution of a spherically symmetric, radiating star were solved analytically. The evolution of the star was determined by the application of boundary conditions at the center and at the edge. Due to lmitations in the presupernova model, only the very slow inward motion of an unstable, degenerate core could be considered. The solution was also limited by the need to exclude a runaway term, one that increased exponentially with time. Without the exclusion of the runaway, the luminosity would have increased without bound and the mass would have become negative.This paper presents a completely analytic solution to the equations of General Relativity describing the evolution of a Type II supernova. Professor S.E. Woosley kindly gave us data on the physical variables of a 12M ₀ presupernova star. In our model the core collapses within 1 s, leaving a 1.3M ₀ remnant. Shortly afterward 10.6M ₀ is ejected to infinity, and 0.17M ₀ is radiated away in the form of neutrinos. The distance of the edge from the center increases proportionally to the two-thirds power of the time. The luminosity decreases proportionally to the inverse four-thirds power.Although the runaway solution was modified by the exploding rather than a static envelope, it must still be excluded by adjusting initial conditions. Its character is changed from an exponential to a very large power (55) of time. The removal of a degree of freedom by this exclusion leads to physically non-sensical results such as negative luminosity. The inclusion of a term describing motion of the mantle due to neutrino interactions provides the additional degree of freedom necessary for physically reasonable results.     

Coronal magnetic fields from microwave polarization observations

The solar active region (AR) 7530 was observed at 6 cm on July 3 and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a multi-channel receiver with very narrow bandwidth. We compare the radio data with Yohkoh SXT observations and with the magnetic field extrapolated from the Marshall vector magnetograms in the force-free and current-free approximations. The comparison with soft X-rays shows that, although a general agreement exists between the shape of the radio intensity map and the X-ray loops, the brightness temperature, T _b, obtained using the parameters derived from the SXT is much lower than that observed. The comparison with the extrapolated photospheric fields shows instead that they account very well for the observed T _b above the main sunspots, if gyroresonance emission is assumed. In the observation of July 4 an inversion and strong suppression of the circular polarization was clearly present above different portions of the AR, which indicates that particular relationships exist between the electron density and the magnetic field in the region where the corresponding lines of sight cross the field quasi-perpendicularly. The extrapolated magnetic field at a much higher level ( 10¹⁰ cm), satisfies the constraints required by the wave propagation theory all over the AR. However, a rather low electron density is derived.     

Singular points of the polarization tensor

The problem to compute the magnetic field above the chromosphere using data of the vector = B _t/Bt that gives the projected field direction can be solved with different approximations. The field of direction vectors is, however, not the only field accessible to observations. The Stokes parameters, which are components of the radiation tensor, can be measured at each point of the image plane. The directions of the eigenvectors of the radiation tensor define two mutually orthogonal systems of integral curves in the image plane. These families of curves have singular points, which are generally of different type than those of the vector field. When the morphology of H chromospheric fibrils are used to infer the topology of the magnetic field, a similar problem is met, suggesting that singular points should also be present there.     

Refugee flow or brain-drain? The humanitarian policy and post-Tiananmen mainland Chinese immigration to Canada

"The humanitarian policy that the Canadian government implemented in response to the 1989 Tiananmen Square crackdown changed a migration system primarily based on personal networks into a brain drain. Post-Tiananmen mainland Chinese immigrants (MCIs) were better educated than those arriving in Canada previously. Among the post-Tiananmen MCIs, those who landed under the policy were better educated than those landing in other categories. The analysis suggests that post-Tiananmen MCIs represented a brain-drain rather than a refugee flow, that the humanitarian policy implicitly contained ideological and human capital concerns in addition to humanitarian concerns, and that Canada benefited from the policy by obtaining human capital as well as satisfying its humanitarian obligations and ideological aspirations."     

Search for low energyν e,μ,τ andv e,μ,τ in coincidence with BATSE gamma ray bursts

A search for low energy neutrinos of all flavours in correlation with 553 ray bursts detected by BATSE aboard the Compton Observatory has been performed by the LSD (Liquid Scintillator Detector) neutrino telescope. No excess ofe,, orv _e,, candidate has been detected by LSD during the time interval in which BATSE detected the 90% of the photon flux for any of the GRBs analyzed. Upper limits on the neutrino fluxes are given in the paper.     

Electromagnetic bursting of a rapidly rotating magnetized neutron star in a close binary system

We examine a possible manifestation of the electromagnetic activity of a magnetized, rotating neutron star in a binary system. Accreting matter from the companion is initially accumulated at the magnetosphere. When the accumulated mass is such that the inflow can start, together with the accretion flare there will be a burst due to the closure of electric currents. The luminosity associated to the latter effect may be as large as 10⁴² erg/s, if a neutron star possesses the following characteristics: massM =M , period of rotationP = 5 ms, magnetic fieldB ₀ = 10¹² G, and radiusr ₀ = 10⁶ cm. The electromagnetic activity might be relevant for understanding soft gamma ray repeaters.