Iron oxide thin film growth on Al2O3/NiAl(1 1 0)

The electronic structure and the growth morphology of iron oxide thin films were studied by means of Synchrotron Radiation Photoelectron Spectroscopy (SRPES) and Low Energy Electron Diffraction (LEED). A thin well-ordered alumina film on a NiAl(1 1 0) single crystal surface as a template for iron oxide growth was employed. Two different methods of iron oxide film preparation were applied. In the first attempt, iron deposited at room temperature was subsequently annealed in oxygen. Even though a whole layer of iron was oxidized, an expected long-range order was not achieved. The second attempt was to perform reactive deposition. For this reason iron was evaporated in oxygen ambient at elevated substrate temperature. This method turned out to be more efficient. Diffused but clear LEED patterns of six-fold symmetry indicating hexagonal surface atoms arrangement were observed. From the PES measurements, binding energies for Fe2p for grown iron oxide film were established as well as energy distribution curves for the valence band. Growth curves based on Fe3p core-level peak intensities for iron and iron oxide were plotted identifying type of film growth for both deposition methods. Based upon these results we have found evidence for interdiffusion in the interface between alumina and iron oxide at the early stages of growth. Further deposition led to formation of Fe₃O₄(1 1 1) (magnetite) overlayer. Moreover, the quality of the film could also be improved by long-time annealing at temperatures not exceeding 575 K. Higher annealing temperature caused disappearance of LEED pattern indicating loss of long-range ordering.     

Continuous benchmark selections

The existence of benchmark selections that are continuous both in production factors and technology is examined. If the class of technologies display non-convexities, continuous selections do not exist in general. For probabilistic benchmarks, i.e., lotteries over efficient productions, existence of continuous selections holds only under additional conditions of well-behavedness.     

Examples of Coorbit Spaces for Dual Pairs

In this paper we summarize and give examples of a generalization of the coorbit space theory initiated in the 1980’s by H.G. Feichtinger and K.H. Gröchenig. Coorbit theory has been a powerful tool in characterizing Banach spaces of distributions with the use of integrable representations of locally compact groups. Examples are a wavelet characterization of the Besov spaces and a characterization of some Bergman spaces by the discrete series representation of SL₂(?). We present examples of Banach spaces which could not be covered by the previous theory, and we also provide atomic decompositions for an example related to a non-integrable representation.     

Influence of ion implantation on titanium surfaces for medical applications

The implantation of ions into the near surface layer is a new approach to improve the osseointegration of metallic biomaterials like titanium. Meanwhile it is well known that surface topography and surface physico-chemistry as well as visco-elastic properties influence the cell response after implantation of implants into the human body. To optimize the cell response of titanium, ion implantation techniques have been used to integrate calcium and phosphorus, both elements present in the inorganic bone phase. In this context, the concentration profile of the detected elements and their chemical state have been investigated using X-ray photoelectron spectroscopy and Auger electron spectroscopy depth profiling. Ion implantation leads to strong changes of the chemical composition of the near surface region, which are expected to modify the biofunctionality as observed in previous experiments on the cell response. The co-implantation of calcium and phosphorus samples, which showed best results in the performed tests (biological and physical), leads to a strong modification of the chemical surface composition.     

Acoustic characteristics of urban streets in relation to scattering caused by building facades

The relationship between scattering and the acoustic characteristics of urban streets is examined by computer simulation. The simulation method is a combination of the image method for specular reflection and the radiosity method for scattering reflection. The findings are as follows: (1) the effect of scattering on the SPL appears as an increase at short distances and as a decrease at great distances. The range of the increase in SPL is larger in high-facade streets. In low-facade streets, the primary effect of scattering on SPL is a decrease in SPL. (2) In low-facade streets the reverberation time is determined by the sum of absorption coefficient and scattering coefficient. In contrast, in high-facade streets, the reverberation time is determined by the absorption coefficient. (3) The simulated result for the reverberation time shows good agreement with measured value in actual streets. (4) The estimated values for the sum of absorption coefficient and scattering coefficient of facades of actual urban streets range from 0.1 to 0.25.     

The asymptotic spectrum of the EWMA covariance estimator

The exponentially weighted moving average (EWMA) covariance estimator is a standard estimator for financial time series, and its spectrum can be used for so-called random matrix filtering. Random matrix filtering using the spectrum of the sample covariance matrix is an established tool in finance and signal detection and the EWMA spectrum can be used analogously. In this paper, the asymptotic spectrum of the EWMA covariance estimator is calculated using the Mar?enko-Pastur theorem. Equations for the spectrum and the boundaries of the support of the spectrum are obtained and solved numerically. The spectrum is compared with covariance estimates using simulated i.i.d. data and log-returns from a subset of stocks from the S&P 500. The behaviour of the EWMA estimator in this limited empirical study is similar to the results in previous studies of sample covariance matrices. Correlations in the data are found to only affect a small part of the EWMA spectrum, suggesting that a large part may be filtered out.