Establishment of the Physical and Technical Prerequisites for the Determination of the Relative Biological Effectiveness of Low-energy Monochromatic X-rays

A superconducting electron linear accelerator of high brilliance and low emittance (ELBE) is under operation at Forschungszentrum Rossendorf since January 2003. The first stage of ELBE is based on an electron energy of 20 MeV, whereas in the future a 40 MeV beam will be provided. The relativistic electron beam is used to drive various kinds of secondary radiation sources. Among all, X-rays in a wide energy range can be obtained. One method for production of intensive, quasi-monochromatic Xrays in the energy range 10 - 100 keV, tunable in photon energy, is by channeling of relativistic electrons in a perfect crystal. This unconventional photon source with variable time structure will be optimised and used for radiobiological studies. Its first test operation was in October 2003. This thesis is part of the first radiobiological project – the determination of relative biological effectiveness (RBE) of the X-rays in this energy range. The most important aspects of medical application of low-energy X-rays are imaging and radiation therapy, but they can also be helpful in the study of radiation effects in living matter. However, the RBE depends on the photon energy, dose range, cell line and biological endpoint. Up to now no definitive conclusions can be made about their biological effectiveness due to the large spread of the published data. Therefore, in order to precisely determine the RBE, studies have to be performed at an intensive, tunable photon source, for several practically relevant cell lines and biological endpoints. The possibility of using channeling radiation (CR) for medical applications has been widely discussed in the literature, but building and optimisation of a dedicated source is for the first time performed at the ELBE accelerator

The Rent-Price Ratio for the Aggregate Stock of Owner-Occupied Housing

We construct a time series of the rent-price ratio for the owner- occupied stock of housing, starting in 1960:1, by merging micro data from the last five Decennial Censuses of Housing with price indexes for house prices and rents.House Prices, Housing, Rents, CMHPI, Capitalization Rates

A superconducting microwave multivibrator produced by coherent feedback

We investigate a coherent nonlinear feedback circuit constructed from pre-existing superconducting microwave devices. The network exhibits emergent bistable and astable states, and we demonstrate its operation as a latch and the frequency locking of its oscillations. While the network is tedious to model by hand, our observations agree quite well with the semiclassical dynamical model produced by a new software package [N. Tezak et al., arXiv:1111.3081v1] that systematically interpreted an idealized schematic of the system as a quantum optic feedback network.Comment: 9 double-spaced pages, 5 figures and supplement. To appear in Phys. Rev. Let

The age structure of stellar populations in the solar vicinity. Clues of a two-phase formation history of the Milky Way disk

We analyze high quality abundances data of solar neighborhood stars and show that there are two distinct regimes of [alpha/Fe] versus age which we identify as the epochs of the thick and thin disk formation. A tight correlation between metallicity and [alpha/Fe] versus age is clearly identifiable on thick disk stars, implying that this population formed from a well mixed ISM, over a time scale of 4-5 Gyr. Thick disk stars vertical velocity dispersion correlate with age, with the youngest objects having as small scale heights as those of thin disk stars. A natural consequence of these two results is that a vertical metallicity gradient is expected in this population. We suggest that the thick disk set the initial conditions for the formation of the inner thin disk. This provides also an explanation of the apparent coincidence between the step in metallicity at 7-10 kpc in the thin disk and the confinment of the thick disk at about R<10 kpc. We suggest that the outer thin disk developped outside the influence of the thick disk, but also that the high alpha-enrichment of the outer regions may originate from a primordial pollution by the gas expelled from the thick disk. Local metal-poor thin disk stars, whose properties are best explained by an origin in the outer disk, are shown to be as old as the youngest thick disk (9-10 Gyr), implying that the outer thin disk started to form while the thick disk formation was still on-going in the inner Galaxy. We point out that, given the tight age-abundance relations in the thick disk, an inside-out process would give rise to a radial gradient in abundances in this population which is not observed. Finally, we argue that the data discussed here leave little room for radial migration, either to have contaminated the solar vicinity, or, to have redistributed stars in significant proportion across the solar annulus.Comment: Accepted in A&A, Revised version with new figures and extended discussio