Scintillation Caustics in Planetary Occultation Light Curves

We revisit the GSC5249-01240 light curve obtained during its occultation by Saturn's North polar region. In addition to refractive scintillations, the power spectrum of intensity fluctuations shows an enhancement of power between refractive and diffractive regimes. We identify this excess power as due to high amplitude spikes in the light curve and suggest that these spikes are due to caustics associated with ray crossing situations. The flux variation in individual spikes follows the expected caustic behavior, including diffraction fringes which we have observed for the first time in a planetary occultation light curve. The presence of caustics in scintillation light curves require an inner scale cut off to the power spectrum of underlying density fluctuations associated with turbulence. Another possibility is the presence of gravity waves in the atmosphere. While occultation light curves previously showed the existence of refractive scintillations, a combination of small projected stellar size and a low relative velocity during the event have allowed us to identify caustics in this occultation. This has led us to re-examine previous data sets, in which we have also found likely examples of caustics.Comment: 4 pages, 3 figures; ApJL submitte

Poverty and inequality in Britain: 2006

This Commentary provides an update on trends in poverty and inequality in Great Britain, based on the latest official government statistics. It uses the same approach to measuring incomes and poverty in Great Britain as the government employs in its Households Below Average Income (HBAI) publication

Excess mortality during heat waves in Ireland

Ireland is not known for having extreme high temperatures, with values above 30C uncommon. Ireland has significant excess winter mortality compared to summer. The objective of this study is to estimate the impact of nation-wide heat waves on the total, cardiovascular and respiratory relationship, for the period 1981–2003, to determine if there are any periods of excess summer mortality

Helical Magnetorotational Instability in Magnetized Taylor-Couette Flow

Hollerbach and Rudiger have reported a new type of magnetorotational instability (MRI) in magnetized Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields. The salient advantage of this "helical'' MRI (HMRI) is that marginal instability occurs at arbitrarily low magnetic Reynolds and Lundquist numbers, suggesting that HMRI might be easier to realize than standard MRI (axial field only). We confirm their results, calculate HMRI growth rates, and show that in the resistive limit, HMRI is a weakly destabilized inertial oscillation propagating in a unique direction along the axis. But we report other features of HMRI that make it less attractive for experiments and for resistive astrophysical disks. Growth rates are small and require large axial currents. More fundamentally, instability of highly resistive flow is peculiar to infinitely long or periodic cylinders: finite cylinders with insulating endcaps are shown to be stable in this limit. Also, keplerian rotation profiles are stable in the resistive limit regardless of axial boundary conditions. Nevertheless, the addition of toroidal field lowers thresholds for instability even in finite cylinders.Comment: 16 pages, 2 figures, 1 table, submitted to PR

Storm severity detection (RF)

Measurement of lightning location data which occur together with continental thunderstorms and hurricanes was examined, and a second phase linear interferometer was deployed. Electrical emission originating from tropical storms in the Gulf of Mexico were monitored. The time span between hurricane ALLEN (10 August 1980) and hurricane ALICIA (18 August 1983) represents the longest period that the United States has gone without hurricane landfall. Both systems were active and data were acquired during the landfall period of hurricane ALICIA

Microarcsecond Radio Imaging using Earth Orbit Synthesis

The observed interstellar scintillation pattern of an intra-day variable radio source is influenced by its source structure. If the velocity of the interstellar medium responsible for the scattering is comparable to the earth's, the vector sum of these allows an observer to probe the scintillation pattern of a source in two dimensions and, in turn, to probe two-dimensional source structure on scales comparable to the angular scale of the scintillation pattern, typically $\sim 10 \mu$as for weak scattering. We review the theory on the extraction of an ``image'' from the scintillation properties of a source, and show how earth's orbital motion changes a source's observed scintillation properties during the course of a year. The imaging process, which we call Earth Orbit Synthesis, requires measurements of the statistical properties of the scintillations at epochs spread throughout the course of a year.Comment: ApJ in press. 25 pages, 7 fig

Radiobiological studies with monoenergetic neutrons

The Radiological Research Accelerator Facility (RARAF) has the capability of producing essentially monoenergetic neutron beams, ranging in energy from 16.4 MeV down to 220 keV. In addition, two lower energy neutron beams are available which consist of a wide spectrum of energies and are described as the 110 keV and 60 keV spectra. Seedlings of Vicia faba have been used to measure the oxygen enhancement ratio (OER) and the relative biological effectiveness (RBE) of each of these neutron beams. The OER decreases as the neutron energy is reduced between 15.4 MeV and 220 keV, but does not appear to decrease further for lower energy neutrons. RBE increases as the neutron energy is reduced from 15.4 AleV to 440 keV; the curve then goes through a maximum at around 350 keV, and for lower energies the RBE falls again