Visibility-Based Demodulation of Rhessi Light Curves

The Reuven Ramaty High Energy Spectroscopic Solar Imager (RHESSI) uses the rotational modulation principle to observe temporally, spatially, and spectrally resolved hard X ray and gamma ray images of solar flares. In order to track the flare evolution on time scales that are commensurate with modulation, the observed count rates must be demodulated at the expense of spatial information. The present paper describes improvements of an earlier demodulation algorithm, which decomposes the observed light curves into intrinsic source variability and instrumental modulation.Comment: 6 pages, 3 figure

Microwave spectroscopy of the active sun

In studies of solar active regions and bursts, the ability to obtain spatially resolved radio spectra (brightness temperature spectra) opens a whole new range of possibilities for study of the solar corona. For active regions, two-dimensional maps of brightness temperature over a wide range of frequencies allows one to determine temperature, column density, and magnetic field strength over the entire region in a straightforward, unambiguous way. For flares, the time-dependent electron energy distribution, number of accelerated electrons, and magnetic field strength and direction can be found. In practice, obtaining complete radio images at a large number of frequencies is a significant technical challenge, especially while keeping costs down. Our instrument at Owens Valley Radio Observatory provided the starting point for a modest attempt at meeting this goal. We proposed to build three additional, very low-cost 2-m antennas which, when combined with our existing two 27-m dishes, expands the array to 5 elements. This modest increase in number of solar dedicated antennas, from 2 to 5, increases our maximum number of physical baselines from 1 to 10 and allows the instrument to do true imaging of solar microwave sources, both bursts and active regions. Combined with the technique of frequency synthesis, the new array has up to 450 effective baselines, giving imaging capability that approaches that of a sub-arrayed VLA. The prototype antenna design was finalized and the antenna was put into operation in Nov. 1989

High-spectral resolution solar microwave observations

The application of high-spectral resolution microwave observations to the study of solar activity is discussed with particular emphasis on the frequency dependence of microwave emission from solar active regions. A shell model of gyroresonance emission from active regions is described which suggest that high-spectral resolution, spatially-resolved observations can provide quantitative information about the magnetic field distribution at the base of the corona. Corresponding observations of a single sunspot with the Owens Valley frequency-agile interferometer at 56 frequencies between 1.2 and 14 Ghs are presented. The overall form of the observed size and brightness temperature spectra was consistent with expectations based on the shell model, although there were differences of potential physical significance. The merits and weaknesses of microwave spectroscopy as a technique for measuring magnetic fields in the solar corona are briefly discussed

The role of extension in the Miocene denudation of the Nevado-Filábride Complex, Betic Cordillera (SE Spain)

The Internal Zone of the Betic Cordillera, SE Spain, consists of a nappe stack of three complexes, the deepest of which is the Nevado-Filábride Complex. The zone is separated from the overlying Alpujárride Complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite and zircon fission track results have been obtained from the Nevado-Filábride Complex and these have been used to define regional cooling patterns for the complex. Rapid cooling (105°C–200°C Ma−1) is spatially related to the tectonic contact with the overlying Alpujárride Complex-Cooling to near-surface temperatures occurred first in the east (Sierra de los Filabres) during the mid-Serravallian (12±1 Ma) and was completed by the early Tortonian (9–8 Ma) in the west (Sierra Nevada). There is no correlation between fission track age and sample elevation. These results are consistent with tectonic unroofing of this complex, a finding that favors extension as the mechanism by which the two complexes were brought into contact. Extension spans the middle and earliest upper Miocene (12–8 Ma) in the study area and therefore lasted much longer than previously documented. A hypothesis is advanced which links oblique convergence between the Iberian plate and the Betic Internal Zones, resulting in crustal contraction at depth, with orogen parallel extension in the middle and upper crust

Planned improvements to the Owens Valley frequency-agile interferometer

Three small antennas will be added to the OVRO interferometer to form a five-element solar-dedicated array. This would provide up to 7 or 10 baselines (compared to the present 1 or 3). This would be sufficient to apply microwave diagnostics to most active region and burst sources. By using frequency-synthesis it would also provide an imaging capability comparable to that of an approximately 100 baseline interferometer. Expansion of the array is discussed

Distance education with special reference to the teaching of Christian theology in sub Saharan Africa

The Thesis begins by considering the situations of three ideal typical students learning theology through a Theological Education by Extension' programme which, in Africa, is the most common form of Distance Education in Christian Theology. Use of the 'ideal typical' device is justified and then a brief survey of Extension Schemes in Africa is made. This is followed by a consideration of the principles of’ Distance Education. The problems facing Africa at the present time are listed as these provide the background and context of the study of Theology. As Distance Education deals primarily with adults, adult learning is discussed in some depth followed by the learning of Christian Theology which has its own particular issues and problems. African Traditional Religion plays a part in forming the view of the African thought world and belief in God and the main aspects of this are considered alongside. the teaching of Christian Theology. Schemes of Distance Learning in Theology currently or recently in use are then considered with references to texts. Finally conclusions are drawn to suggest ways forward for good Distance Learning in Christian Theology

Colour imagery in the poetry of Gautier : a thesis presented in partial fulfilment of the requirements for the degree of Master of Arts in French at Massey University

Some French throughout.Dans son pourpoint de satin rose, Qu'un gout hardi coloria, Il semble chercher une pose Pour Boulanger ou Devéria." (Le Château du souvenir, p 109, v 40) "A rose-coloured doublet," - unforgettably the words are linked with the night of February 25th 1830, when the young revolutionaries of the Romantic movement arrived in force to support the first staging of Victor Hugo's play, Hernani, and to do battle with the traditionalists. Prominent among the revolutionaries was Théophile Gautier, wearing the famous garment, which was to become known as the "gilet rouge", a fitting symbol for a man who was above all a visual poet - a poet of colour. Years later, in describing his career as a Romantic writer, he remarked, "J'etais le peintre de la bande." 1. It is the purpose of this thesis to explore how and to what extent Gautier used colour as a means of expression in his poems, with particular reference to what is probably his finest and most mature work - the collection entitled Emaux et Camées

Solar flare hard X-ray spikes observed by RHESSI: a case study

In this paper, we analyze hard X-ray spikes observed by RHESSI to understand their temporal, spectral, and spatial properties. A recently developed demodulation code was applied to hard X-ray light curves in several energy bands observed by RHESSI. Hard X-ray spikes were selected from the demodulated flare light curves. We measured the spike duration, the energy-dependent time delay, and count spectral index of these spikes. We also located the hard X-ray source emitting these spikes from RHESSI mapping that was coordinated with imaging observations in visible and UV wavelengths. We identify quickly varying structures of <1 s during the rise of hard X-rays in five flares. These hard X-ray spikes can be observed at photon energies over 100 keV. They exhibit sharp rise and decay with a duration (FWHM) of less than 1 s. Energy-dependent time lags are present in some spikes. It is seen that the spikes exhibit harder spectra than underlying components, typically by 0.5 in the spectral index when they are fitted to power-law distributions. RHESSI clean maps at 25-100 keV with an integration of 2 s centered on the peak of the spikes suggest that hard X-ray spikes are primarily emitted by double foot-point sources in magnetic fields of opposite polarities. With the RHESSI mapping resolution of ~ 4 arsec, the hard X-ray spike maps do not exhibit detectable difference in the spatial structure from sources emitting underlying components. Coordinated high-resolution imaging UV and infrared observations confirm that hard X-ray spikes are produced in magnetic structures embedded in the same magnetic environment of the underlying components. The coordinated high-cadence TRACE UV observations of one event possibly reveal new structures on spatial scales <1-2 arsec at the time of the spike superposed on the underlying component. They are probably sources of hard X-ray spikes.Comment: 20 pages, 11 figure

Relevance of Tidal Heating on Large TNOs

We examine the relevance of tidal heating for large Trans-Neptunian Objects, with a focus on its potential to melt and maintain layers of subsurface liquid water. Depending on their past orbital evolution, tidal heating may be an important part of the heat budget for a number of discovered and hypothetical TNO systems and may enable formation of, and increased access to, subsurface liquid water. Tidal heating induced by the process of despinning is found to be particularly able to compete with heating due to radionuclide decay in a number of different scenarios. In cases where radiogenic heating alone may establish subsurface conditions for liquid water, we focus on the extent by which tidal activity lifts the depth of such conditions closer to the surface. While it is common for strong tidal heating and long lived tides to be mutually exclusive, we find this is not always the case, and highlight when these two traits occur together.Comment: Submitted to Icaru