Degradation of metallic surfaces under space conditions, with particular emphasis on hydrogen recombination processes

The widespread use of metallic structures in space technology brings risk of degradation which occurs under space conditions. New types of materials dedicated for space applications, that have been developed in the last decade, are in majority not well tested for different space mission scenarios. Very little is known how material degradation may affect the stability and functionality of space vehicles and devices during long term space missions. Our aim is to predict how the solar wind and electromagnetic radiation degrade metallic structures. Therefore both experimental and theoretical studies of material degradation under space conditions have been performed. The studies are accomplished at German Aerospace Center (DLR) in Bremen (Germany) and University of Zielona G\'{o}ra (Poland). The paper presents the results of the theoretical part of those studies. It is proposed that metal bubbles filled with Hydrogen molecular gas, resulting from recombination of the metal free electrons and the solar protons, are formed on the irradiated surfaces. A thermodynamic model of bubble formation has been developed. We study the creation process of $\rm{H_2}$-bubbles as function of, inter alia, the metal temperature, proton dose and energy. Our model has been verified by irradiation experiments completed at the DLR facility in Bremen. Consequences of the bubble formation are changes of the physical and thermo-optical properties of such degraded metals. We show that a high surface density of bubbles (up to $10^8$ $\rm{cm^{-2}}$) with a typical bubble diameter of $\sim 0.4$$\rm{\mu}$m will cause a significant increase of the metallic surface roughness. This may have serious consequences to any space mission. Changes in the thermo-optical properties of metallic foils are especially important for the solar sail propulsion technology, ..

Probabilistic Opacity for Markov Decision Processes

Opacity is a generic security property, that has been defined on (non probabilistic) transition systems and later on Markov chains with labels. For a secret predicate, given as a subset of runs, and a function describing the view of an external observer, the value of interest for opacity is a measure of the set of runs disclosing the secret. We extend this definition to the richer framework of Markov decision processes, where non deterministic choice is combined with probabilistic transitions, and we study related decidability problems with partial or complete observation hypotheses for the schedulers. We prove that all questions are decidable with complete observation and $\omega$-regular secrets. With partial observation, we prove that all quantitative questions are undecidable but the question whether a system is almost surely non opaque becomes decidable for a restricted class of $\omega$-regular secrets, as well as for all $\omega$-regular secrets under finite-memory schedulers

THE CHANGING POLISH FOOD CONSUMER

This paper provides an overview of major demographic and food trends in Poland and the rapid changes in Polish food retailing. The demographic changes include the size of the population; birth, death, marriage and divorce rates; the age distribution, education and household types. Two important demographic factors that will affect food consumption are the aging population and the major gap in education between urban and rural areas. In the next 20 years, the number of children will decrease radically, whereas the number of people over 64 years of age will rise significantly. Education levels are much lower in rural than in urban areas. The average household budget share for food was 44.6% in 1988. It reached 55.3% in 1990 at the beginning of the transition to a market economy and fell to 37.8% in 1996. Under central planning, consumers had to adjust to what was made available. There was a limited assortment of goods and many people relied on home-produced food. Since 1989 and the transition to a market economy, food consumption patterns have undergone some substantial changes. Butter consumption has fallen sharply, while plant fat consumption has increased with the introduction of high quality margarine. The change from central planning to a market economy has had a major impact on food retailing. U.S. fast food companies, such as McDonald's, have opened numerous outlets in Poland during the 1990s. Fast food is very popular, especially among young Poles. Under central planning, three government-owned chains dominated grocery retailing in Poland. The food marketing system was producer, not consumer driven. When the right to own private businesses was restored, many new food retailing stores were opened. In 1996, final sales by food retailing stores in Poland were about $100 billion. A large portion of the sales is by small shops. However, foreign-owned grocery retailers have been expanding in Poland and had sales of$5 billion in 1997. The foreign-owned chains open larger stores, supermarkets and even hypermarkets. Many of the major Western European food retailers are now operating in Poland, such as Ahold, a big Dutch company, and Tengelman, a large German company.Food Consumption/Nutrition/Food Safety, Health Economics and Policy,

The DLR Complex Irradiation Facility (CIF)

The DLR Institute of Space Systems in Bremen has built a new facility to study the behavior of materials under complex irradiation and to estimate their degradation in a space environment. It is named Complex Irradiation Facility (CIF). CIF allows simultaneously irradiating samples with three light sources for the simulation of the spectrum of solar electromagnetic radiation. The light sources are a solar simulator with a Xe-lamp (wavelength range 300-1200nm), a deuterium-UV-source (112-200nm), and an Argon-gas-jet-VUV-simulator. The latter allows irradiating samples with shorter wavelengths below the limitation of any window material. The VUV-simulator has been validated at the PTB (Physikalisch Technische Bundesanstalt) in Berlin by calibration that uses synchrotron radiation in the wavelength range between 40 and 400nm. Beside the different light sources CIF provides also electron and proton sources. Electrons and protons are generated in a low energy range from 1 to 10 keV with currents from 1 to 100 nA and in a higher range from 10 to 100 keV with 0.1 to 100 µA. Both particle sources can be operated simultaneously. In order to model temperature variations as appear in free space, the sample can be cooled down to liquid Nitrogen and heated up to about 450 K during irradiation. The complete facility has been manufactured in UHV-technology with metal sealing. It is free of organic compounds to avoid self-contamination. The different pumping systems achieve a final pressure of 1*1010 mbar (empty sample chamber) Besides the installed radiation sensors that control the stability of the various radiation sources and an attached mass spectrometer for analyzing the outgassing processes in the chamber, the construction of CIF allows adding other in-situ measurement systems to measure parameters that are of the user’s interest. We are currently planning to develop an in-situ measurement system in order to determine changes in the optical properties of the samples caused by irradiation. Within this paper we will show the design of CIF in more detail and discuss the performance of the various radiation sources

Militares, gobierno y sociedad civil, en Israel

Este trabajo trata acerca de las cambiantes relaciones entre las fuerzas armadas, el gobierno y la sociedad civil en Israel. A pesar de que Israel cuenta con una democracia bien establecida, una sociedad civil activa e históricamente las fuerzas armadas han mostrado una subordinación a los gobiernos electos, los cambios que afectan los distintos niveles de la democracia en el país, los desarrollos sociales y la naturaleza evolutiva de sus fuerzas armadas presentan un desafío para el análisis. El marco de este tema es lo que generalmente es conocido como el conflicto Árabe-Israelí, en sus diversas fases. La larga duración de los conflictos en los que Israel ha estado involucrado desde su establecimiento como un estado independiente en 1948, sus múltiples y cambiantes características, ambos generan presiones sobre los distintos actores fuerzas armadas, sociedad y gobierno - y sirven como un recurso para la legitimación y deslegitimación de iniciativas, actitudes y políticas.This article deals with a complex subject: the changing relations between the armed forces, the government and civil society in Israel. Although Israel is a well established democracy with a vibrant civil society and historically the armed forces have shown the due subordination to the elected governments, the changes affecting the levels of democracy in the country, social developments and the evolving nature of its armed forces present an anlytical challenge. The framework of the above stated issue is what is generally known as the Israeli-Arab conflict in its various parts. The long duration of the conflicts in which Israel is involved since its establishment as an independent state in 1948, their multiplicity and changing features, both generate pressures upon the different actors - armed forces, society and government - and serve as sources of legitimization and de-Iegitimization for initiatives, attitudes and policies.Fil: Sznajder, Mario. Universidad Hebrea de Jerusale

Design and performance of a vacuum-UV simulator for material testing under space conditions

This paper describes the construction and performance of a VUV-simulator that has been designed to study degradation of materials under space conditions. It is part of the Complex Irradiation Facility at DLR in Bremen, Germany, that has been built for testing of material under irradiation in the complete UV-range as well as under proton and electron irradiation. Presently available UV-sources used for material tests do not allow the irradiation with wavelengths smaller than about $115$ nm where common Deuterium lamps show an intensity cut-off. The VUV-simulator generates radiation by excitation of a gas-flow with an electron beam. The intensity of the radiation can be varied by manipulating the gas-flow and/or the electron beam. The VUV simulator has been calibrated at three different gas-flow settings in the range from $40$ nm to $410$ nm. The calibration has been made by the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. The measured spectra show total irradiance intensities from $24$ to $58$ mW$\rm{m^{-2}}$ (see Table 4.2) in the VUV-range, i.e. for wavelengths smaller than $200$ nm. They exhibit a large number of spectral lines generated either by the gas-flow constituents or by metal atoms in the residual gas which come from metals used in the source construction. In the range from $40$ nm to $120$ nm where Deuterium lamps are not usable, acceleration factors of $3$ to $26.3$ Solar Constants are reached depending on the gas-flow setting. The VUV-simulator allows studies of general degradation effects caused by photoionization and photodissociation as well as accelerated degradation tests by use of intensities that are significantly higher compared to that of the Sun at $1$ AU

Praca tymczasowa – motywy wyboru i problemy związane z jej realizowaniem

Udostępnienie publikacji Wydawnictwa Uniwersytetu Łódzkiego finansowane w ramach projektu „Doskonałość naukowa kluczem do doskonałości kształcenia”. Projekt realizowany jest ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Wiedza Edukacja Rozwój; nr umowy: POWER.03.05.00-00-Z092/17-00