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The planned Galileo global navigation system will employ an array of satellites in medium Earth orbit. Internal charging is one of the primary hazards for any spacecraft in MEO and accordingly the Galileo test spacecraft, Giove-A, carries the dasiaSURFpsila detector to undertake measurements of internal charging currents deposited at three different shielding depths (0.5, 1.0 and 1.5 mm Al). Giove-A was successfully launched on 28th December 2005 into a 23,300 km circular, 56 degree inclination orbit. In this paper we provide data on the charging currents observed in 2006, with particular emphasis on two large charging events, one in April and one in December. Comparisons are made between the flight data and predictions made using ESA's internal charging tool, DICTAT, which employs the FLUMIC dasiaworst casepsila electron belt model. The DICTAT predictions of charging current are exceeded for a few days in the 1.5 mm Al shielded plate in the course of the December event.

In preparation for deployment of the Galileo satellite navigation system, Europe has launched a test satellite, Giove-A. One of its objectives is to measure the radiation environment encountered in medium Earth orbit (MEO) which is a new regime for European missions. Giove-A therefore includes two radiation environment monitors: Merlin supplied by QinetiQ and CEDEX supplied by the University of Surrey. Merlin measures electrostatic charging and electron fluxes, total ionising dose, energetic proton fluxes and heavy ion linear energy transfer (LET) spectra. CEDEX monitors energetic proton fluxes, heavy ion linear energy transfer (LET) spectra and ionising dose rates. Giove-A, which was built by SSTL (UK), was successfully launched on 28th December 2005 into a 23,600 km circular, 56 degree inclination orbit. Data received since launch has been analysed and demonstrates that the MEO environment is highly dynamic due to the influence of space weather. Numerous electron belt enhancement events have been observed and the charging effects of these events been characterised. Total ionising dose is also seen to be delivered almost wholly during electron events.

[1] The European Space Agency (ESA) Space Environment Information System (SPENVIS) provides standardized access to models of the hazardous space environment through a user-friendly Web interface, available at http://www.spenvis.oma.be/. SPENVIS is designed to help spacecraft engineers perform rapid analyses of environmental problems and, with extensive documentation and tutorial information, allows engineers with relatively little familiarity with the models to produce reliable results. SPENVIS is based on internationally recognized standard models and methods in many domains. It uses an ESA-developed orbit generator to produce orbital point files necessary for many different types of problem. It has various reporting and graphical utilities and extensive help facilities. SPENVIS also contains an active, integrated version of the European Cooperation for Space Standardization Space Environment Standard, and access to in-flight data. Apart from radiation and plasma environments, SPENVIS includes meteoroid and debris models, atmospheric models (including atomic oxygen), and magnetic field models. Recently, the radiation sources and effects module have been rewritten, providing enhanced mission analysis features, new radiation effects models, and streamlined navigation between various model pages.

Smart overlay coatings are a functionally gradient coating system designed to provide high temperature corrosion protection over a wide range of operating conditions. The SMARTCOAT design consists of a MCrAlY base, enriched first in chromium, then aluminium to provide a chemically graded structure. At elevated temperatures, above 900°C (1650°F), the coating oxidises to form a protective alumina scale. However, at lower temperatures this alumina scale does not reform rapidly enough to confer protection under type II hot corrosion conditions. The coating is therefore designed with an intermediate chromium-rich interlayer, which permits the rapid formation of chromia healing areas of type II corrosion damage. Laboratory and burner rig tests have been carried out on a series of developmental smart overlay coatings. These have shown that the development of an intermediate chromium-rich phase provides protection under low temperature hot corrosion conditions, while the aluminium-rich surface layer provides resistance to high temperature oxidation and type I hot corrosion. Thus, the single application of SMARTCOAT permits operation over a broad range of industrial and marine turbine conditions.

The creation of Bangladesh in December 1971 was as much a struggle for constitutional justice as it was a movement of ethno-linguistic nationalism. Yet, the country’s experience as a multi-party democracy could be said to have only properly begun in the 1990s. For most of its first two decades of independence, Bangladesh was dominated by regimes that had a hard time reconciling the pressing development priorities of one of the world’s poorest nations — an international basket case to cite Henry Kissinger’s grim metaphor — with the requirements of Western-style democracy. These governments made some progress in improving the country’s socioeconomic condition, but much more still needs to be done. Its Gross Domestic Product (GDP) has averaged a consistent, if unglamorous, 4–5 percent growth since the late 1970s;1 the population growth rate has declined from 3.2 percent in the early 1970s to around 2 percent today;2 average life expectancy has risen from 46 years in the 1970s to an estimated 55 years in the early 1990s;3 and the male literacy rate has steadily increased to almost 50 percent though the female literacy rate remains an abysmally low 22 percent.4

The space radiation environment is highly variable and dynamic. With the increasing number and complexity of space missions, the detailed analysis of the effects of that environment often requires the use of advanced Monte Carlo radiation transport tools. In this presentation, various space-oriented developments and applications based on the Geant4 particle transport toolkit are described.

Accessing the NASA trapped radiation models AP-8 and AE-8 with (B,L) values obtained with modern geomagnetic field models causes an unrealistic secular increase of the predicted flux over low altitude orbits. We show the secular variation of the orbit-averaged particle flux along the LDEF orbit and the mission dose, obtained using the AP-8 trapped radiation models with an epoch-dependent magnetic field. The artificially increased epoch-dependent fluxes and doses are compared to the flux and dose obtained with a consistent and more correct procedure for predicting fluxes with the NASA models. This procedure has been implemented in the radiation analysis software package UNIRAD developed and distributed by BIRA-IASB.

Samples of silicon dioxide on silicon and hydrogen‐implanted silicon were studied using a low‐energy positron beam. The Doppler S parameter vs. positron implantation energy curves were analysed using a positron diffusion model. Results reveal positron trapping at an interface 950 A beneath the surface on the SiO2/Si sampler and the defect distribution resulting from implantation in the H+ implanted specimen.

SmCo alloys form the basis of excellent permanent magnets with potential service applications to 500°C. It is suspected, however, that their oxidation behavior may limit their usefulness but this is a relatively unstudied subject. Two grades of Sm2(Co,Fe,Cu,Zr)17-based alloys were aged in air at temperatures between 300 and 600°C and the oxidation reaction characterized by post-test scanning electron microscopy examination. Both alloys formed a thin external oxide scale composed of Cu and mixed Fe∕Co oxides and an extensive internal oxidation layer consisting of Sm-rich oxide within a CoFe matrix. The depth of the internal oxidation zone was typically an order of magnitude thicker than the surface oxides and increased parabolically with time. This internal oxidation is an important degradation phenomenon because the transformation to CoFe causes a loss of magnetic properties proportional to the volume consumed. The morphologies of the oxidation zones, nature, and mechanisms of various precipitated phases ...

A lock (19) which by physical or logical means controls human access to an objective (29) such as a restricted area or a computer system is controlled by a data processing system (10) which has access to a store of authorised users (14) and a store of complex images (15), specifically images of human faces. Each authorised user knows certain ones of the complex images, and these key images are linked to an identity statement unique to that user. On receipt of an identity statement signifying an authorised user, a matrix of images including the key images is presented to the user on a display (12), and by means of a suitable input device (20) the user must identify which images are his key images in order to confirm authorisation and be permitted access. The user and image stores (18) may be carried in credit card form as a section of an optical disk. The high security of the system results from the inability of a person to communicate adequately to another the ability to recognise a third person or other complex image.

A patient with duplication of a short segment of 3q (3q21 leads to 26) without apparent deletion of 3 or of other chromosomes provided a further opportunity to study manifestations of this abnormality. The proposita had a broad nasal bridge, anteverted nostrils, webbed neck, and clinodactyly V in addition to congenital heart disease, limb abnormalities, cleft palate, and severe developmental delay. The infant did not have the hirsutism and synophrys present in other cases.

Metallography has been carried out on specimens of 20 Cr/25 Ni/Nb, 20 Cr/25 Ni/Ti, 20 Cr/25 Ni/TiN steels which had been exposed at 923 K, 1023 K and 1123 K in CO2/CO gases with CO contents varying from 2 ↪ 100%. The variation of surface oxide thickness with all test parameters was determined. It was shown that the oxide formed on the 20/25/Nb steel at short exposure times in high CO environments at 923 K was absent after more prolonged exposure. This is a consequence of the coarse surface grain size retarding chromia formation and of the proximity of the test conditions to the Fe/Fe3O4/Fe3C triple point. The finer surface grain size of the Ti-bearing steels ensured the formation of a Cr-rich oxide in all test atmospheres. Coinciding with the absence of a surface oxide in the 20 Cr/25 Ni/Nb steel at 923 K, pitting oxidation occurred which developed parabolically with time. The data were used to obtain an estimate of the oxygen diffusion coefficient at this temperature. Severe carburisation was also observed under these conditions. Additionally, measurements were made of the depth of intergranular oxidation. This was found to be most severe in the 20 Cr/25 Ni/Ti alloy and increased with temperature and environmental CO content. The 20/25/TiN steel also exhibited sub-surface voidage (globular attack) but its rate of development was insensitive to gas composition. Bestandigkeit von 20 Cr 25 Ni-Stahlen gegen Kohlenstoffablagerungen. II. Innere Oxidation und Aufkohlung Mit Hilfe von metallographischen Methoden wurden Proben der Stahle 20 Cr 25 NiNb, 20 Cr 25 NiTi und 20 Cr25 NiTiN nach Einwirkung von Kohlendioxid/Kohlenmonoxid-Gemischen (2–100% CO) bei 923, 1023 und 1123 K untersucht; dabei wurde die Anderung der Dicke des Oberflachenoxids in Abhangigkeit der Versuchsparameter ermoglicht. Es zeigte sich, das das Oxid, das bei kurzzeitiger Einwirkung von Gasen mit hohem CO-Gehalt bei 923 K auf 20/25 Nb-Stahl entsteht, nach langerer Expositionsdauer fehlt. Als Ursache hierfur ist die Grobkornigkeit der Oberflache anzusehen, welche die Bildung von Chromoxid verzogert; auserdem spielt auch eine Rolle, das die Prufbedingungen in der Nahe des Fe/Fe3O4/Fe3C-Tripelpunkts liegen. Die kleineren Korner an der Oberflache der titanhaltigen stahle ermoglichen die Bildung des chromreichen Oxids in allen untersuchten Atmospharen. Gleichlaufend mit dem Verschwinden des Oberflachenoxids im 20 Cr 25 NiNb-Stahl bei 923 K kam es zu lochkorrosionsahnlicher Oxidation, die einem parabolischen Zeitgesetz folgte. Die dabei erhaltenen Daten wurden zur Abschatzung des Diffusionskoeffizienten von Sauerstoff bei dieser Temperature benutzt. Zusatzlich wurde die Tiefe der interkristallinen Oxidation bemessen. Diese was in der 20 Cr 25 NiTi-Legierung am starksten und nahm mit der Temperatur und mit dem Kohlenmonoxid-Gehalt in der umgebenden Atmosphare zu. Auch der 20/25 TiN-Stahl zeigte Fehlstellenbildung (globularer Angriff) unterhalb der Oberflache, jedoch war dieser Angriff unabhangig von der Gaszusammensetzung.

High temperature oxidation tests have been performed at 973–1123 K in a CO2 based gas on specimens of 20Cr-25Ni-Nb stainless steel in which the surface chromium concentration was reduced by prior vacuum annealing at 1273 K. It is shown that the rapid initial oxidation rate decreases as a result of the formation of a chromium-rich ‘healing’ layer at the oxide-metal interface. For oxidation temperatures ≥ 1073 K, a chromia-type layer readily forms whereas lower oxidation temperatures favour the formation of a chromium-rich spinel after considerably longer oxidation times. Use of electron probe micro-analysis to determine the pre-existing chromium depletion profile and measurements of the depth into the steel at which this ‘healing’ layer forms enable an assessment to be made of the chromium concentration necessary to form this layer. This concentration increased from 15.2 w/o at 1123 K to ≥ 18.5 w/o at 973 K.

The oxidation behavior of 20%Cr-25%Ni stainless steels and a similar but stronger alloy containing a dispersion of titanium nitride particles has been studied over the temperature range 1023 to 1173°K. The dispersion-strengthened steel oxidized slightly more slowly than its dispersion-free counterpart at 1023°K, but above this temperature it was inferior in terms of gross weight gain. The parabolic growth kinetics of the chromic oxide layer in each alloy were similar, however, with an activation energy compatible with the rate-controlling step being chromium ion diffusion across the oxide. The evidence suggests that the role of the dispersed phase is to produce an oxide of finer grain size than that of the standard steel, which increases the rate of oxygen transport inward. The consequent formation of internal oxide increases the tendency for oxide rupture and spalling with subsequent enhanced local attack. This leads to the observed higher overall weight gains compared with the dispersion-free alloy.

Specimens of annealed 20 Cr/25Ni/Nb, selectively pre-oxidised 20Cr/25Ni/Nb, cold worked 20Cr/25Ni/Nb and TiN-strengthened 20Cr-25Ni steels have been exposed to a 75% CO/CO2 gas atmosphere for periods up to 2000 hrs at 923 K (650°C). Whereas the cold-worked and TiN-strengthened steels show high resistance to this environment, the annealed Nb-stabilised alloy exhibited large amounts of carbon deposition. Associated with these were extensive regions of oxide pitting and gross carburisation of the substrate. By contrast, the selectively preoxidised specimens suffered much less deposition and no evidence for carburisation was found. It was also shown that small quantities of defects in the original preoxidised layer increased the propensity for deposition but did not result in local carburisation. Bestandigkeit von 20Cr-25Ni-Stahlen gegen Kohleablagerungen. III. Kaltverformung und selektive Voroxidation Proben aus angelassenem Stahl 20Cr/25Ni/Nb, selektiv voroxidiertem Stahl dieses Typs sowie kaltverformtem 20Cr/25NiNb-Stahl und TiN-verfestigtem 20Cr/25Ni-Stahl wurden bis 2000 h lang in 75% CO/CO2 bei 923 K exponiert. Wahrend die kaltverformten TiN-versteiften Stahle unter diesen Bedingungen sehr verfestigt sind, wird auf den angelassenen Nb-stabilisierten Stahl Kohle in betrachtlichen Mengen abgeschieden. In Verbindung damit kommt es zu Oxid-Lochkorrosion auf groseren Teilen der Oberflache und zu einer Aufkohlung des Substrats. Im Gegensatz dazu sind die selektiv voroxidierten Proben weit weniger anfallig fur Kohleablagerung und Aufkohlung. Geringe Mengen von Fehlstellen in der voroxidierten Schicht steigern zwar die Anfalligkeit fur Kohleablagerung, fuhren jedoch nicht zu ortlicher Aufkohlung.

This paper discusses the role of thermal stresses on the mechanical integrity of oxide layers. It is shown that the processes of cracking and spalling of oxides differ depending on the stress state (tensile or compressive) and on the relative strengths of oxide and oxide-metal interface. Under tensile conditions, through-thickness cracks develop from pre-existing defects in the oxide layer and these generate shear stresses along the interface which may result in decohesion. Under compressive conditions, spallation may result either from the growth of a tensile, wedge crack along the interface or by buckling and cracking of the oxide layer. Initial results of a finite element analysis are provided for both mechanisms.

The processes leading to oxide spallation are discussed in terms of two routes depending on the relative strengths of the surface oxide and the oxide-metal interface. Assuming that the major source of stress is the differential contraction strains produced during a temperature decrease, simple equations are developed which predict the critical temperature decrease to initiate spallation in terms of the oxide thickness and its elastic properties. The concepts are checked using a 20Cr-25Ni-Nb-stabilized stainless steel oxidized in sensitive thermobalances. It is shown that this material exhibits cracking and spallation behaviour commensurate with a relatively strong oxide-metal interface. An upper-limit estimate is made of the energy required to produce decohesion at this interface.

The carbon deposition behaviour of sheet specimens of nine experimental alloys, based on the composition of a 20 Cr/25 Ni/Nb stabilised steel but containing silicon in the range 0.0 to 2.23 w/o, has been studied. The tests were conducted in an environment of 75% CO/CO2 at 1 atmosphere total pressure at a temperature of 923 K. It was found that the resistance to carbon deposition increased with increasing silicon content. By using two heat treatments, it was shown, for steels containing ≲ 1.5 w/o Si, that the alloy's surface grain size was a key parameter in determining its response to carbon deposition; finegrained structures exhibited greater resistance than coarse-grained. At the highest alloy silicon contents (1.8, 2.2 w/o), no effect of grain size was found. The results are interpreted in terms of the ease of formation of protective chromia and silica layers. Bestandigkeit von 20 Cr-25 Ni-Stahlen gegen Kohleablagerungen. IV: Einflus des Siliciumgehalts Untersucht wurde die Kohleablagerung auf Blechproben neun verschiedener experimenteller Legierungen (Typ 20 Cr/25 Ni/Nb) mit Siliciumgehalten zwischen 0,0 und 2,23%. Die Untersuchungen wurden in einem Gasgemisch mit 75% CO, Rest CO2m bei 923 K durchgefuhrt. Aufgrund der Ergebnisse nimmt die Bestandigkeit gegen Kohleablagerung mit dem Siliciumgehalt zu. Die nach zwei Methoden durchgefuhrte Warmebehandlung zeigt, das im Falle der Stahle mit maximal etwa 1,5 Gew. % Si die Korngrose an der Legierungsoberflache ein entscheidender Parameter fur die Kohleablagerung ist: feinkornige Oberflachen sind danach widerstandsfahiger als grobkornige. Bei den hochsten verwendeten Siliciumgehalten (1,8 bzw. 2,2%) wurde hingegen kein Einflus der Korngrose mehr gefunden. Die Ergebnisse werden damit erklart, das die Bildung der schutzenden Chromoxid- und Siliciumoxidschichten mit unterschiedlicher Leichtigkeit erfolgt.

Steam oxidation of Zircaloy-2 produces tensile extension; at a given temperature the strain increases parabolically with time. Oxygen dissolution in Zircaloy-2 during oxidation stabilises the α-phase and causes lattice dilatation. These two observations are used to develop a model of the oxidation-induced deformation behaviour of the stabilised α-layer and hence to calculate the stress distribution across the layer.

A study of the localized pitting attack of 20% Cr/25%Ni stainless steel and a similar alloy containing a dispersion of titanium nitride particles has been made over the temperature range 1023 to 1173 K. Pitting is initiated when localized spoiling of the protective chromic oxide film occurs. Rapid oxidation of the chromium-depleted substrate then proceeds with the formation of an iron-rich oxide mound on the alloy surface and spinels containing nickel, chromium, and iron within the pit itself. A silica layer which, in general, remains on the alloy surface acts as a diffusion barrier during this stage of the reaction. With increasing depth of attack the local chromium concentration in the alloy at the base of the pit attains a critical value (∼16%) for a protective chromium oxide film to reform; the pitting attack then effectively ceases, although a a subsequent slow rate of growth continues through the protective film at the base. The observed maximum depth of pitting as a function of time is consistent with the parabolic variation predicted by the proposed mechanism. There is no significant difference in the kinetics of attack between the alloys examined.

Influence de la presence de COS dans l'oxydant lorsqu'il y a formation d'une couche riche en chrome, a diverses temperatures dans l'intervalle 973-1123 K

A recent model of creep deformation in pure materials is compared with published data on β-zirconium and β-zircaloy. It is shown that the zircaloys behave like the pure metal in this phase range and that the model is capable of predicting their creep rates to within a factor of 2 on tubing material. A condition is that the curved Arrhenius plot for diffusion in zirconium represents the intrinsic behaviour of point defects in the lattice and that solute atoms have an insignificant effect on the process. A corollary is that the contribution from dislocation short-circuiting both to diffusion and to creep is negligible.

1 14.8 4.1 0.009 0 -0.001 2 21.0 4.2 0.013 -0.001 0.001 3 6.0 6.7 0.006 0.001 0.001 4A 14.0 2.4 0.005 0 0.001 4B 14.6 3.2 0.007 0.001 0 4C 16.0 3.4 0.008 0 0.002 5 17.6 8.0 0.021 0 0 6 16.4 4.3 0.011 0.001 0.002 7 8.4 5.6 0.007 0 0.001 8A 18.4 2.9 0.008 0 -0.001 8B 15.2 2.6 0.006 0 0.001 9 16.4 7.8 0.019 0.002 0 10 20.6 6.8 0.021 -0.001 -0.001 1 l 6.2 5.4 0.005 -0.002 -0.001 12 6.6 8.2 0.008 0 0.001 Mean 0.010 0 0 _+ SD + 0.006 + 0.001 + 0.001

Highly polarized settlement systems in developing countries reflect and tend to reinforce strong disparities in levels of development between the largest city and other regions and between urban centres and their hinterlands in rural regions. Integrated regional development planning seeks to create a more diffuse and articulated system of settlements in order to diversify the services and facilities available to rural residents, increase their access to town-based markets, new sources of agricultural inputs and non-agricultural employment opportunities, and to provide guidelines for sectoral investment and location decisions. One approach to integrated regional development planning — ‘Urban Functions in Rural Development’ - was tested in the Department of Potosi, Bolivia, and its results provide insights not only into the methodology of analysis but also into the complex relationships among rural development, patterns of human settlement and processes of spatial interaction.

Oxidation tests have been performed at 1123°K in CO 2 on a 20 wt.% Cr-25 wt.% Ni stainless steel containing a dispersion of titanium nitride particles produced by prior nitriding. Two forms of internal attack are distinguished: inger-like, grain boundary penetrations of internally oxidized silicon and globular, discrete voids extending to greater depths within the alloy. The latter are the result of the dissociation of chromium-rich particles in the depleted zones formed near the specimen surface during the oxidation process. The kinetics of this globular attack are parabolic and are closely related to the growth of the depleted zone. The theoretical expectation of a linear relationship between the depth of attack and the thickness of the surface chromic oxide is confirmed. The effect of variation in the chromium and residual nitrogen contents on the depth of attack is discussed in detail.

Specimens of 20Cr/25Ni/Nb, 20Cr/25Ni/Ti and 20Cr/25/Ni/TiN steels have been exposed to CO2/CO-based gases with CO contents ranging from 2% ∼ 100% at 923, 1023 and 1123 K. The 20Cr/25Ni/Nb alloy was particularly susceptible to carbon deposition in high CO environments at all temperatures whereas the TiN-strengthened steel was much more resistant. This difference is interpreted by correlating deposition propensity with the formation of iron-rich regions produced on the metal surface in the early stages of reaction. Thus, the 20Cr/25/Ni/TiN alloy readily formed a “chromia” layer under all test conditions and this inhibited the deposition process. The ease of formation of this oxide was associated with the relatively fine surface grain size of this metal. By contrast, the Nb-stabilised steel required significant periods to develop such protective conditions and this also was associated with its relatively coarse surface grain size. The Tistabilised steel exhibited intermediate behaviour. The critical CO content in the gaseous environment required to initiate carbon deposition on the 20Cr/25Ni/Nb steel increased with test temperature. This was shown to be in accord with the thermodynamics of the Boudouard reaction and indicated that the surface composition of this alloy permitted this reaction to approach equilibrium. Bestandigkeit von 20Cr-25Ni-Stahlen gegen Kohlenstoffablagerungen. I. Die Rolle der Oberflachenkorngrose Proben der Stahle CrNiNb20 25, CrNiTi20 25 und CrNiTiN20 25 wurden in Gemischen von Kohlendioxid und Kohlenmonoxid mit CO-Gehalten zwischen 2 und etwa 100% bei 923, 1023 und 1123 K exponiert. Die Nb-haltige Legierung war besonders anfallig fur Kohleablagerungen in Gasen mit hohem CO-Gehalt, und zwar bei allen Veruchstemperaturen, wahrend der durch Zusatz von Titan und Stickstoff verfestigte Stahl wesentlich bestandiger war. Dieses unterschiedliche Verhalten wird mit der Annahme erklart, das die Ablagerungsneigung mit der Bildung eisenreicher Zonen auf der Metalloberflache wahrend der Anfangsstadien der Reaktion zusammenhangt. So bildet beispielsweise der Stahl CrNiTiN20 25 unter allen Versuchsbedingungen eine Deckschicht auf Chromoxid, wodurch die Ablagerung gehemmt wird. Die Leichtigkeit dieser Deckschichtbildung hangt wiederum zusammen mit der verhaltnismasigen Feinkornigkeit der Metalloberflache. Im Gegensatz dazu war bei dem mit Niob stabilisierten Stahl eine betrachtliche Zeit zur Bildung der Schutzschicht erforderlich, was wiederum mit der verhaltnismasig grobkornigen Metalloberflache zusammenhangt. Der Titan-stabilisierte Stahl lag in seinem Verhalten zwischen den beiden anderen. Der kritische CO-Gehalt, bei dem die Kohleablagerung auf dem Nb-stabilisierten Stahl beginnt, nimmt mit der Temperatur zu. Dieses Verhalten entspricht der Thermodynamik der Boudouard-Reaktion und ist ein Hinweis darauf, das aufgrund der Oberflachenzusammensetzung dieser Legierung diese Reaktion einem Gleichgewicht zustrebt.

This paper considers the kinetics of the in-reactor oxidation of zircaloy, using results from the post-irradiation examination of fuel from both BWRs and PWRs. It is shown that the growth rate of the continuous film type of oxide is similar in all reactors considered, at about 2–3 times the out-of-reactor rate, and that stainless steel components do not accelerate the oxidation. It is concluded that the rate-limiting factor is anion diffusion. By contrast, the nodular form of zircaloy oxidation is affected by both coolant chemistry and the presence of stainless steel components nearby, and it is shown that both these effects probably occur at the nodule nucleation stage. Subsequent growth must then be controlled by similar factors to the continuous oxide form. These observations support a simple, repeated mechanical cracking model of nodule growth.

It is suggested that, during the oxidation of stainless steels, matter is conserved at the oxide-metal interface by the creation of a dynamic balance between the chromium diffusion fluxes in the alloy and in the oxide. It is shown that the rate of oxidation is insensitive to alloy composition so that a necessary consequence is that the rate-controlling process is always diffusion through the oxide. In addition, the interfacial concentration of chromium remains invariant with time at a value higher than that in thermodynamic equilibrium with the oxide. Some of the predictions made with regard to the depth and kinetics of growth of chromium-depleted zones within the alloy have been checked experimentally inoxidation tests in CO2 at 1123° K on a 20Cr-25Ni stainless steel containing a dispersion of TiN particles. It is concluded that the matter-conservation hypothesis is valid for this material.

Coupon specimens of 20% Cr-25% Ni-Nb-stabilized steel have been oxidized in an atmosphere of CO2-2%CO-670 vppb COS at 0.1 MPa pressure for periods up to 500 hr at 1123 K. Standard specimens, annealed at 1203 K prior to testing, showed an enhancement of iron in the surface scale and a much increased propensity to spall compared with control tests in a sulfur-free atmosphere. The main purpose of the work was to examine the effect of sulfur on the ease of formation of a “healing” layer under duplex attack produced by depleting specimens in chromium by prior vacuum annealing. It is shown that although a chromium-rich layer had formed, extensive breakdown occurred in the sulphidizing atmosphere leading to continued internal oxidation. Sulfur was found to partition at the base of this attack and to be associated with a large concentration of nickel. Spaliation was also enhanced in the depleted specimens, the favored site being the interface between the spinel and outer iron-rich oxide of the duplex structure. Partitioning of both sulfur and carbon was observed at this interface in those regions of the specimen showing “healing” layer breakdown.

Oxidation tests in CO2 at 1123 K have been performed on samples of a 20%Cr-25%Ni-Nb-stabilized stainless steel contaminated by a mixture of sea salt. The test temperature is above the anticipated liquidus of the salt mixture but the quantity of the latter was limited and the oxidation reaction was not prevented. It is shown that the effect of the contaminant is to increase the formation of duplex oxides through spoiling of the protective chromia film. The effect is equally severe for all salt concentrations examined. Towards the upper end of the experimental range, however, the integrity of chromium-rich healing layers formed at the base of the duplex attack is reduced and the depth of internal oxidation increases.

Oxidation tests in a CO2-based atmosphere at 1123 K have been conducted on a series of 20Cr-25Ni stainless steels containing a dispersion of TiN particles and with silicon contents ranging from 0.05 to 2.35 wt.%. In all cases, a chromia surface film whose thickness increased parabolically with time was formed. The parabolic rate constant was a minimum at an intermediate alloy silicon content when an interlayer of silica was formed between the outer oxide and the metal. The significance of this duplex structure on the processes determining the oxidation rate and the extent of oxide spalling is discussed. An additional feature of the attack was the formation of subsurface voidage whose depth again increased parabolically with time. The appropriate rate constant also showed a minimum at an intermediate silicon level and the relationships between this form of attack and the development of the surface oxides are highlighted.

The theory developed in this paper considers the depletion produced by the selective oxidation of an alloy which oxidizes under non-protective conditions and exhibits linear oxidation kinetics. The development is applicable to the case where a pre-existing depletion profile exists within the alloy prior to the advent of non-protective conditions and, thus, is of relevance to the behaviour of a metal substrate after spallation of a protective oxide. Detailed calculations are presented which demonstrate the perturbation to this profile as a function of the recession rate of the oxide-metal interface. The size of the perturbation zone is found to be independent of the velocity of the oxidation front at low values but approaches zero at higher velocities. A limited comparison of the theory is made on a 20 Cr-25 Ni stainless steel in which a pre-existing chromium depletion profile had been produced by vacuum annealing.

A method suitable for the determination of the solubilities of single or mixed solutes in liquid metals has been developed and used for the determination of the solubility of antimony in sodium. By monitoring the distribution of a known amount of radioactive material in a sealed capsule containing the liquid metal and comparing the activity in regions of the capsule with and without an adsorber foil the percentage of the solute actually in solution can be determined. Thus the solubility at various temperatures can be estimated. The method avoids errors due to sampling difficulties, particulates in suspension and failure to attain equilibrium which have vitiated much earlier work. The solubility of antimony from 190° to 550 °C was found to be given by the expression log10S(sb)ppm = (8.662 ± 0.007) −(3.943 ± 0.023)/T. This leads to values of 75.48 ± 0.48 kJ/moleand −121.3 ± 25.5 kJ/mole for the partial molal heats of solution of Na3Sb and Sb, respectively, in sodium. Evidence of reversible adsorption of antimony on stainless steel in liquid sodium was obtained.

First authorized in 1968, then significantly expanded in 1970, the New Communities Program was, according to its former administrator, “reduced to a salvage operation in exactly four years.”1 The program was dismantled in the fall of 1978, three years after even its modest objectives had been jettisoned in an effort to bolster the precarious financial positions of individual projects.

The role of biotic mechanisms in baculovirus (BV) dispersal was investigated using three Lepidopteran pests; Plodia interpunctella (Hubner), Ephestia cautella Walker and Mamestra brassicae L. and their respective BVs. The first two, pyralid moths, are pests of stored products, and the third is a pest of brassicas. Detailed host biology and virus mortality studies were undertaken to provide background information for the main investigation of virus dispersal using P.interpunctella. BV infectionincreased larval activity and thus BV dispersal in all three species until the disease at an advanced stage caused sluggish behaviour and mortality. However, larva to larva virus transmission was limited, especially as the integuments of diseased pylarids did not rupture and cannibalism was rare when a suitable food supply was available. P.interpunctella adults which received a sub-lethal BV dose in the larval stages appeared normal but the proportion of eggs oviposited, the viability of the eggs and the survival of the progeny were reduced. However, no BV was detected in the adult stage. Transovum transmission occurred if the adults were externally contaminated with BV. Scavangers, predators and adult parasitoids which fed on diseased prey voided viable BV in their faeces. This contaminated the larval medium and resulted in larval infection. The predators tested readily fed on diseased prey but the parasitoids were less able to compete with BV for hosts, Bracon hebetor Say preferentially avoided diseased hosts. There was little evidence to indicate that BV can be mechanically vectored between host larvae on the ovipositor of a parasitoid or the mouthparts of a predator. The relative potential of the host and other biotic mechanisms to cause BV dispersal is discussed.

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Serious illness requiring rehospitalization of low birth weight infants following discharge from the nursery was related to four specific sociomedical factors. These were failure of the mother to receive prenatal care, absence of the father from the home, receipt of public assistance, and presence of other children in the home. These factors formed the basis of a weighted prognostic index, permitting prospective assignment of a score to each low birth weight infant. Those at highest risk of inadequate follow-up care and rehospitalization were identified prior to discharge from the nursery. This may permit direction of intensive medical nursing and social services toward this high risk group.

Radiation shielding analysis is a crucial process in the spacecraft and space instrument development cycle. A number of dedicated tools have been developed in the last decades for the study of the effects of radiation on materials and instruments in space. We present here a set of detailed analyses based on Monte Carlo radiation transport simulations, and new tools for space applications, both based on the Geant4 simulation toolkit, developed as part of the European Space Agency (ESA) activities in the Geant4 collaboration. Finally we present some activities initiated by ESA for the creation of a Geant4 space users' community.

Detailed studies of underlying phenomena in radiation interaction with spacecraft devices are enabled by the development of a new Geant4-based application for SEE, degradation and background analyses in 3D geometries with simple user-interfaces.

International audience; Pine wilt disease, which can rapidly kill pines, is caused by the pine wood nematode, Bursaphelenchus xylophilus. It is expanding its range in many countries in Asia and measures are being taken at the EU level to prevent its spread from Portugal. Due to the threat to European forests, it is important to prevent additional introductions and target surveillance to the points of entry that pose the greatest risk. In this study, we present a model to identify the European ports from which the nematode can spread most rapidly across Europe. This model describes: (1) the potential spread of the pine wood nematode based on short-distance spread (the active flight of the vector beetles) and long-distance spread (primarily due to human-mediated transportation), and (2) the development of pine wilt disease based on climate suitability and the potential spread of the nematode. Separate introductions at 200 European ports were simulated under various climate change scenarios. We found that the pine wood nematode could invade 19–60% of the study area (30°00 N–72°00 N, 25°00 W–40°00 E) by 2030, with the highest spread from ports located in Eastern and Northern Europe. Based on climate change scenarios, the disease could affect 8–34% of the study area by 2030, with the highest spread from ports located in South-Eastern Europe. This study illustrates how a spread model can be used to determine the critical points of entry for invasive species, so that surveillance can be targeted more accurately and control measures prioritised.