Hydrogels for nucleus replacement—Facing the biomechanical challenge

Hydrogels are considered promising for disc regeneration strategies. However, it is currently unknown whether the destruction of the natural interface between nucleus and surrounding structures caused by nucleotomy and an inadequate annulus closure diminishes the mechanical competence of the disc. This in vitro study aimed to clarify these mechanisms and to evaluate whether hydrogels are able to restore the biomechanical behaviour of the disc. Nucleus pressure in an ovine intervertebral disc was measured in vivo during day and night and adapted to an in vitro axial compressive diurnal (15min) and night (30min) load. Effects of different defects on disc height and nucleus pressure were subsequently measured in vitro using 30 ovine motion segments. Following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue; and two different hydrogels repaired by suture and glue. The intradiscal pressure in vivo was 0.75MPa during day and 0.5MPa during night corresponding to an in vitro axial compressive force of 130 and 58N, respectively. The compression test showed that neither the implantation of hydrogels nor the re-implantation of the natural nucleus, assumed as being the ideal implant, was able to restore the mechanical functionality of an intact disc. Results indicate the importance of the natural anchorage of the nucleus with its surrounding structures and the relevance of an appropriate annulus closure. Therefore, hydrogels that are able to mimic the mechanical behaviour of the native nucleus may fail in restoring the mechanical behaviour of the disc.

Romany Families in Romania: Intelligence and Personality of Children Cross-cultural and Specific Problems of Development

Psychogenetic research has emphasised the influence of social factors on a child's intellectual development. In her work, Ms. Dumitrascu examines two such factors; family size and order of birth. However, since these formal parameters tend to be unstable, other more informal factors should be taken into consideration. Of these, perhaps the most interesting is the "style" of parental education, which Ms. Dumitrascu regards as an expression of national traditions at the family level. This educational style is culture dependent. Only a comparative, cross-cultural study can reveal the real mechanism through which educational style influences the development of a child's intellect and personality. Ms. Dumitrascu conducted an experimental cross-cultural study aimed at examining the effects of the family environment on a child's intellectual development. Three distinct populations were involved in her investigation, each having quite a distinct status in their geographical area; Romanians, Romanies (Gypsies) from Romania, and Russians from the Republic of Moldova. She presented her research in the form of a series of articles written in English totalling 85 pages, and also on disc. A significant difference was revealed between the intelligence of a child living in a large family, and that of a child with no brothers or sisters. In the case of Romany children, the gap is remarkably large. Ms. Dumitrascu concludes that the simultaneous action of several negative factors (low socio-economic status, large family size, socio-cultural isolation of a population) may delay child development. Subjected to such a precarious environment, Romany children do not seek self-realisation, but rather struggle to survive the hardship. Most of them remain out of civilisation. Unfortunately, adult Romanies seldom express any concern regarding their children's successful social integration. The school as main socialisation tool has no value for most parents. Ms. Dumitrascu argues the need for a major effort aimed at helping Romany's social integration. She hopes this project will be of some help for psychologists, social workers, teachers, and all those who are interested in the integration into society of minority groups.

The Dynamics of the Policies of Ethnic Cleansing in Silesia in the Nineteenth and Twentieth Centuries

Through studying German, Polish and Czech publications on Silesia, Mr. Kamusella found that most of them, instead of trying to objectively analyse the past, are devoted to proving some essential "Germanness", "Polishness" or "Czechness" of this region. He believes that the terminology and thought-patterns of nationalist ideology are so deeply entrenched in the minds of researchers that they do not consider themselves nationalist. However, he notes that, due to the spread of the results of the latest studies on ethnicity/nationalism (by Gellner, Hobsbawm, Smith, Erikson Buillig, amongst others), German publications on Silesia have become quite objective since the 1980s, and the same process (impeded by under funding) has been taking place in Poland and the Czech Republic since 1989. His own research totals some 500 pages, in English, presented on disc. So what are the traps into which historians have been inclined to fall? There is a tendency for them to treat Silesia as an entity which has existed forever, though Mr. Kamusella points out that it emerged as a region only at the beginning of the 11th century. These same historians speak of Poles, Czechs and Germans in Silesia, though Mr. Kamusella found that before the mid-19th century, identification was with an inhabitant's local area, religion or dynasty. In fact, a German national identity started to be forged in Prussian Silesia only during the Liberation War against Napoleon (1813-1815). It was concretised in 1861 in the form of the first Prussian census, when the language a citizen spoke was equated with his/her nationality. A similar census was carried out in Austrian Silesia only in 1881. The censuses forced the Silesians to choose their nationality despite their multiethnic multicultural identities. It was the active promotion of a German identity in Prussian Silesia, and Vienna's uneasy acceptance of the national identities in Austrian Silesia which stimulated the development of Polish national, Moravian ethnic and Upper Silesian ethnic regional identities in Upper Silesia, and Polish national, Czech national, Moravian ethnic and Silesian ethnic identities in Austrian Silesia. While traditional historians speak of the "nationalist struggle" as though it were a permanent characteristic of Silesia, Mr. Kamusella points out that such a struggle only developed in earnest after 1918. What is more, he shows how it has been conveniently forgotten that, besides the national players, there were also significant ethnic movements of Moravians, Upper Silesians, Silesians and the tutejsi (i.e. those who still chose to identify with their locality). At this point Mr. Kamusella moves into the area of linguistics. While traditionally historians have spoken of the conflicts between the three national languages (German, Polish and Czech), Mr Kamusella reminds us that the standardised forms of these languages, which we choose to dub "national", were developed only in the mid-18th century, after 1869 (when Polish became the official language in Galicia), and after the 1870s (when Czech became the official language in Bohemia). As for standard German, it was only widely promoted in Silesia from the mid 19th century onwards. In fact, the majority of the population of Prussian Upper Silesia and Austrian Silesia were bi- or even multilingual. What is more, the "Polish" and "Czech" Silesians spoke were not the standard languages we know today, but a continuum of West-Slavic dialects in the countryside and a continuum of West-Slavic/German creoles in the urbanised areas. Such was the linguistic confusion that, from time to time, some ethnic/regional and Church activists strove to create a distinctive Upper Silesian/Silesian language on the basis of these dialects/creoles, but their efforts were thwarted by the staunch promotion of standard German, and after 1918, of standard Polish and Czech. Still on the subject of language, Mr. Kamusella draws attention to a problem around the issue of place names and personal names. Polish historians use current Polish versions of the Silesian place names, Czechs use current Polish/Czech versions of the place names, and Germans use the German versions which were in use in Silesia up to 1945. Mr. Kamusella attempted to avoid this, as he sees it, nationalist tendency, by using an appropriate version of a place name for a given period and providing its modern counterpart in parentheses. In the case of modern place names he gives the German version in parentheses. As for the name of historical figures, he strove to use the name entered on the birth certificate of the person involved, and by doing so avoid such confusion as, for instance, surrounds the Austrian Silesian pastor L.J. Sherschnik, who in German became Scherschnick, in Polish, Szersznik, and in Czech, Sersnik. Indeed, the prospective Silesian scholar should, Mr. Kamusella suggests, as well as the three languages directly involved in the area itself, know English and French, since many documents and books on the subject have been published in these languages, and even Latin, when dealing in depth with the period before the mid-19th century. Mr. Kamusella divides the policies of ethnic cleansing into two categories. The first he classifies as soft, meaning that policy is confined to the educational system, army, civil service and the church, and the aim is that everyone learn the language of the dominant group. The second is the group of hard policies, which amount to what is popularly labelled as ethnic cleansing. This category of policy aims at the total assimilation and/or physical liquidation of the non-dominant groups non-congruent with the ideal of homogeneity of a given nation-state. Mr. Kamusella found that soft policies were consciously and systematically employed by Prussia/Germany in Prussian Silesia from the 1860s to 1918, whereas in Austrian Silesia, Vienna quite inconsistently dabbled in them from the 1880s to 1917. In the inter-war period, the emergence of the nation-states of Poland and Czechoslovakia led to full employment of the soft policies and partial employment of the hard ones (curbed by the League of Nations minorities protection system) in Czechoslovakian Silesia, German Upper Silesia and the Polish parts of Upper and Austrian Silesia. In 1939-1945, Berlin started consistently using all the "hard" methods to homogenise Polish and Czechoslovakian Silesia which fell, in their entirety, within the Reich's borders. After World War II Czechoslovakia regained its prewar part of Silesia while Poland was given its prewar section plus almost the whole of the prewar German province. Subsequently, with the active involvement and support of the Soviet Union, Warsaw and Prague expelled the majority of Germans from Silesia in 1945-1948 (there were also instances of the Poles expelling Upper Silesian Czechs/Moravians, and of the Czechs expelling Czech Silesian Poles/pro-Polish Silesians). During the period of communist rule, the same two countries carried out a thorough Polonisation and Czechisation of Silesia, submerging this region into a new, non-historically based administrative division. Democratisation in the wake of the fall of communism, and a gradual retreat from the nationalist ideal of the homogeneous nation-state with a view to possible membership of the European Union, caused the abolition of the "hard" policies and phasing out of the "soft" ones. Consequently, limited revivals of various ethnic/national minorities have been observed in Czech and Polish Silesia, whereas Silesian regionalism has become popular in the westernmost part of Silesia which remained part of Germany. Mr. Kamusella believes it is possible that, with the overcoming of the nation-state discourse in European politics, when the expression of multiethnicity and multilingualism has become the cause of the day in Silesia, regionalism will hold sway in this region, uniting its ethnically/nationally variegated population in accordance with the principle of subsidiarity championed by the European Union.

Marginality and Integrity: Constructing of Gender Identities in the Post-Communist Bulgaria

Ms. Kotzeva's team aimed to reveal the formation of the new gender identities in the transitional society of Bulgaria since 1989. Their main conclusions (presented in a series of manuscripts written in Bulgarian and German, and also on disc) were reached on the basis of data obtained from a field survey involving a group of 190 women, and interviews conducted with a group of Bulgarian women politicians. Although approving of gender equality and the ideology of emancipation on an abstract level, women predominantly identify themselves with mothering and caring for the family. At the same time they do not fully surrender to their family obligations and support a strategy of balancing between family and extra-family activities. Bulgarian women are highly frustrated by the new requirements of the labour market, insecurity, and lack of safety in their personal life. Ms. Kotzeva and her team observed a high degree of convergence of self-identification strategies amongst Bulgarian women from different generations and educational backgrounds. On the other hand, women from the ethnic minorities, especially Gypsy women, demonstrate radically divergent styles of orientation and behaviour. Women's marginalisation due to the altering economic and political circumstances in Bulgaria, and the decline of female participation in Parliament, have clearly shown that the end of socialist women's politics must lead to critical reflection and the development of new strategies in order to enable women to take part in the process of a new elite in Bulgaria.

National Identity in Lithuania: Processes During the Period of Changes

Under the conditions of rapid and total change in the social, political, economic and legal environment in Lithuania, a re-orientation process is going on in all groups of society. In this process, not only younger but also middle-aged and old people become adherents to what Ms. Liubiniene calls the new, "post-materialist" values, strongly reinforced by powerful agents of socialisation originating in the West, like the media, advertising agencies and lifestyle-consumption models. As a result, the national identity of Lithuania and its inhabitants is being reconstructed. Ms. Liubiniene set out to examine the details of this evolving identity by conducting a survey of 1218 university staff and students. Her conclusions are set out in a 74 page manuscript, written in Lithuanian and available on disc. Change is most noticeable among the young. Indeed, time and time again, Ms. Liubiniene was to find that the age of 36 marks a natural watershed, with, for instance, the younger group valuing individualism highly and the older, collectivism. Ms. Liubiniene ventures to suggest that traditional values are deeply rooted amongst elderly people, women and people with an education in the humanities. Young people on the other hand, and especially those with a professional orientation towards business are more open to change and ready to adapt to new values. Turning to the evaluation of national symbols, Ms. Liubinie finds that those with an education in the humanities might be considered to be the most traditional, placing greater value on the symbols of nature, ethnic culture and religion. Folk songs and the crucifix are also in their top ten. Respondents with a technical education favour symbols of statehood and nature, and respondents with a business orientation assign greater value to the symbols of nature, history, sports and statehood. Ms. Liubinie concludes that the group of respondents most active and ready to adapt to new things is composed of young males of a business orientation. Generally the national identity of the young is weaker compared to that of the old. In the future, the combination of the evolution of values and the process of inter-generational replacement allows us to predict a weakening of the sense of national identity, or at least its transformation into something radically different to what it is today.

Post-War Writers' Memoirs in Romania and France: A Study of Mentalities

Ms. Net wanted to find out if there was what she terms a "collective identity of the intelligentsia" of Romania and France between 1945 and 1989. She conducted her research on a corpus of memoirs from both cultures, and in the process, uncovered some fundamental differences, which she presented in the form of a 178 page manuscript in English, and also on disc. One of the most basic appears to be that French memorialists rarely deal with social, historical and political changes and events. Ms. Net regards these writers as shutting their eyes to reality, and attempting to preserve the past. They are interested in their personal history, and in the genesis of their own works. According to Ms. Net, this tendency is so marked that she doubts whether 20th century French writers share the dominant mentalities of their times. In her opinion all this points to the fact that the French intelligentsia are "trying hard to preserve their cultural hegemony" a task which she maintains has always been an essential aspect of the identity of the French intellectual. In Romania, of course, the situation was very different. To take an example: many Romanian memoirs speak about the campaigns to improve the lot of women, while at the same time recognising and analysing the way that this was simply a "cover" for promoting the most incompetent people, men and women alike. They also express frustration at the way access to information was blocked due to the media being government controlled. Ms. Net concludes, eventually, that, in general, intellectuals, more than any other group in society, ensure the continuity of the dominant mentalities in a given cultural space. Consequently, she feels, we must revise the idea - or myth as she calls it - that intellectuals represent the avant-garde in a given society. Specifically, she concludes that petty bourgeois, patriarchal and elitist mentalities are still prevalent in France. The truth is, she reflects, that intellectuals are always true to their nature, no mater when and where they are living.

Compensation, Incentives and Risk: Economic Theory and Russian Practise

Mr. Pechersky set out to examine a specific feature of the employer-employee relationship in Russian business organisations. He wanted to study to what extent the so-called "moral hazard" is being solved (if it is being solved at all), whether there is a relationship between pay and performance, and whether there is a correlation between economic theory and Russian reality. Finally, he set out to construct a model of the Russian economy that better reflects the way it actually functions than do certain other well-known models (for example models of incentive compensation, the Shapiro-Stiglitz model etc.). His report was presented to the RSS in the form of a series of manuscripts in English and Russian, and on disc, with many tables and graphs. He begins by pointing out the different examples of randomness that exist in the relationship between employee and employer. Firstly, results are frequently affected by circumstances outside the employee's control that have nothing to do with how intelligently, honestly, and diligently the employee has worked. When rewards are based on results, uncontrollable randomness in the employee's output induces randomness in their incomes. A second source of randomness involves the outside events that are beyond the control of the employee that may affect his or her ability to perform as contracted. A third source of randomness arises when the performance itself (rather than the result) is measured, and the performance evaluation procedures include random or subjective elements. Mr. Pechersky's study shows that in Russia the third source of randomness plays an important role. Moreover, he points out that employer-employee relationships in Russia are sometimes opposite to those in the West. Drawing on game theory, he characterises the Western system as follows. The two players are the principal and the agent, who are usually representative individuals. The principal hires an agent to perform a task, and the agent acquires an information advantage concerning his actions or the outside world at some point in the game, i.e. it is assumed that the employee is better informed. In Russia, on the other hand, incentive contracts are typically negotiated in situations in which the employer has the information advantage concerning outcome. Mr. Pechersky schematises it thus. Compensation (the wage) is W and consists of a base amount, plus a portion that varies with the outcome, x. So W = a + bx, where b is used to measure the intensity of the incentives provided to the employee. This means that one contract will be said to provide stronger incentives than another if it specifies a higher value for b. This is the incentive contract as it operates in the West. The key feature distinguishing the Russian example is that x is observed by the employer but is not observed by the employee. So the employer promises to pay in accordance with an incentive scheme, but since the outcome is not observable by the employee the contract cannot be enforced, and the question arises: is there any incentive for the employer to fulfil his or her promises? Mr. Pechersky considers two simple models of employer-employee relationships displaying the above type of information symmetry. In a static framework the obtained result is somewhat surprising: at the Nash equilibrium the employer pays nothing, even though his objective function contains a quadratic term reflecting negative consequences for the employer if the actual level of compensation deviates from the expectations of the employee. This can lead, for example, to labour turnover, or the expenses resulting from a bad reputation. In a dynamic framework, the conclusion can be formulated as follows: the higher the discount factor, the higher the incentive for the employer to be honest in his/her relationships with the employee. If the discount factor is taken to be a parameter reflecting the degree of (un)certainty (the higher the degree of uncertainty is, the lower is the discount factor), we can conclude that the answer to the formulated question depends on the stability of the political, social and economic situation in a country. Mr. Pechersky believes that the strength of a market system with private property lies not just in its providing the information needed to compute an efficient allocation of resources in an efficient manner. At least equally important is the manner in which it accepts individually self-interested behaviour, but then channels this behaviour in desired directions. People do not have to be cajoled, artificially induced, or forced to do their parts in a well-functioning market system. Instead, they are simply left to pursue their own objectives as they see fit. Under the right circumstances, people are led by Adam Smith's "invisible hand" of impersonal market forces to take the actions needed to achieve an efficient, co-ordinated pattern of choices. The problem is that, as Mr. Pechersky sees it, there is no reason to believe that the circumstances in Russia are right, and the invisible hand is doing its work properly. Political instability, social tension and other circumstances prevent it from doing so. Mr. Pechersky believes that the discount factor plays a crucial role in employer-employee relationships. Such relationships can be considered satisfactory from a normative point of view, only in those cases where the discount factor is sufficiently large. Unfortunately, in modern Russia the evidence points to the typical discount factor being relatively small. This fact can be explained as a manifestation of aversion to risk of economic agents. Mr. Pechersky hopes that when political stabilisation occurs, the discount factors of economic agents will increase, and the agent's behaviour will be explicable in terms of more traditional models.

Poverty in Slovenia: A Conseqence of Economic Transition

Slovenia is considered to be one of the most successful Central and Eastern European countries undergoing the process of transition. It has a high GDP per capita (the highest in the Visegrad group) amounting to about 7200 US dollars (at the exchange rates pertaining during Ms. Stropnik's research). In 1994, a low rate of inflation, a low level of public debt and almost balanced public finances, were all positive elements. However, there is a darker side, for instance the dramatic increase in unemployment and (somewhat less dramatic) fall in production during the transition period. This analysis aimed to provide insights into what is actually happening at the household level, since households are the ultimate bearers of macroeconomic and social change. The final output totalled 166 pages in English and Slovenian, available also on disc. The income concept used by Ms. Stropnik is that of the disposable (monetary) household income, i.e. the cash income of all household members - including social security transfers and family benefits, and the net sum of taxes and social security contributions - plus the equivalent of domestic production, used in the household. Non-monetary income sources, such as household own production, benefits in kind, subsidies for goods and services, and fringe benefits, were not taken into account. The concept of relative and objective poverty was followed. Poverty means having less than others in society, it is a state of relative deprivation. Objective aspects of the situation, e.g. command over resources (i.e. the household income) and the relative position of the household in the income distribution, determine who is poor and who is not. Changes in household composition - an increase in the number of pensioners, unemployed and self-employed, concomitant with a large decrease in the number of employees - obviously played a part in the changing structure of household income sources during this period. The overall decrease in the share of wages and salaries from primary employment in 1993 is to be observed in all income deciles. On the other hand, the importance of salaries gained from secondary employment has increased in all deciles. The lower seven deciles experienced a sharp rise in the share of social benefits in the period 1988-1993, mostly because of the increase in the number of persons entitled to claim unemployment benefits. In Slovenia, income inequality has increased considerably during the 1988-1993 period. To make matters worse, the large increase in income inequality occurred in a period of falling real incomes. In 1983 the bottom decile disposed of 3.8 percent and the top decile disposed of 23.4 percent of total monetary income in Slovenia, whereas by 1993 the same statistics revealed 3.1 percent and 18.9 percent respectively. Unemployment greatly increases the risk of living in poverty. In 1993, 35 per cent of all unemployed persons in Slovenia were living in the lowest income quintile. Ms. Stropnik found certain features that were specific to Slovenia and not shared by most countries in transition. For example, the relative income position of pensioners has improved. Retirement did not increase the risk of poverty in 1993 as much as it did in 1983 and 1988. Also, it appears that children have not been particularly hard-hit by the transition upheavals. The incidence of poverty amongst children has not increased in the period 1983-1993. Children were also fairly evenly distributed across income quintiles. In 1983, 11.8 percent of households with children aged 18 or less were poor. In 1993, this figure was 8.4 per cent. On the other hand, poor households with children were, in comparison with other households of the same type, poorer in 1993 than in 1983. Ms. Stropnik also analysed the impact of social transfers. Her conclusion was that the level of social transfers prevented them from being successful in alleviating poverty. Family policy transfers (child allowances, child tax allowances, subsidised child care) did, however, contribute to the lowering of income inequality between families with and without children, and amongst families with different numbers of children. Ms. Stropnik is determined that the results of her research be used in the creation of social policy aimed at helping the poor. She quotes Piachaud approvingly: "If the term 'poverty' carries with it the implication and moral imperative that something should be done about it, then the study of poverty is only ultimately justifiable if it influences individual and social attitudes and actions."

Recubrimientos autolubricantes cuasicristalinos tipo composite depositados mediante proyección térmica para aplicaciones espaciales y de alta temperatura

Los recubrimientos lubricantes sólidos son requeridos para reducir la fricción y prevenir el desgaste en componentes que operan a altas temperaturas o en vacío (vehículos espaciales, industria química, motores diésel, turbinas aeronáuticas y de generación de energía…). Los lubricantes líquidos pierden sus características cuando las condiciones de presión, temperatura o ambientales son severas (oxidación, inestabilidad térmica, volatilidad,…), por ejemplo los aceites minerales convencionales se descomponen a temperaturas próximas a 200 ºC. Por tanto, la única manera de poder conseguir una adecuada lubricación a temperaturas extremas es por medio de sólidos, que cada vez más, se aplican en forma de recubrimientos. Estos recubrimientos podrían ser empleados en componentes de vehículos espaciales reutilizables, donde se pueden alcanzar, en la reentrada en la atmósfera, temperaturas de 700 ºC (bisagras, rodamientos, articulaciones y zonas de sellado en las superficies de control, y rodamientos de las turbobombas y las cajas de engranajes). Dichos recubrimientos también deberían ser capaces de proporcionar una lubricación efectiva a bajas temperaturas para las operaciones en tierra, para las operaciones de arranque en frío, incluso en el espacio. El conjunto de requisitos que tendrían que satisfacer las capas tribológicas relacionadas con estas condiciones extremas es muy diverso, lo que hace que el concepto de capas tipo composite (aquéllas constituidas por varios componentes) sea, en principio, muy adecuado para estas aplicaciones. Recubrimientos composite proyectados térmicamente constituidos por una matriz dura y conteniendo lubricantes sólidos pueden ser una buena solución desde el punto de vista tribológico. El “Lewis Research Centre” de la NASA ha estado desarrollando recubrimientos autolubricantes tipo composite, constituidos por la combinación de materiales duros como el carburo de cromo, junto con lubricantes sólidos como plata o la eutéctica de fluoruros de calcio y bario, en una matriz de NiCr, para su uso en aplicaciones terrestres a alta temperatura. Estos recubrimientos han sido aplicados mediante proyección térmica, siendo denominados como series PS100, PS200, PS300 y PS400, reduciendo de forma significativa el coeficiente de fricción y mejorando la resistencia al desgaste en un amplio margen de temperaturas. Otra nueva familia de materiales con comportamiento tribológico prometedor son las aleaciones cuasicristalinas (QC). Presentan características muy atractivas: alta dureza, baja fricción, alto límite elástico de compresión... Son muy frágiles como materiales másicos, por lo que se intentan aplicar en forma de recubrimientos. Se pueden depositar mediante proyección térmica. Algunos de estos materiales cuasicristalinos, como AlCoFeCr, poseen coeficientes de dilatación próximos al de los materiales metálicos, alta estabilidad térmica, baja conductividad térmica y una elevada resistencia a la oxidación y a la corrosión en caliente. En esta tesis se han desarrollado recubrimientos tipo composite conteniendo cuasicristales como componente antidesgaste, NiCr como componente tenaz, y Ag y la eutéctica de BaF2-CaF2, como lubricantes sólidos. Estos recubrimientos han sido depositados con diferentes composiciones (denominadas TH100, TH103, TH200, TH400, TH600…) mediante distintos procesos de proyección térmica: plasma en aire (PS), plasma en baja presión (LPPS) y combustión a alta velocidad (HVOF). Los recubrimientos se han generado sobre el sustrato X-750, una superaleación base níquel, endurecible por precipitación, con muy buena resistencia mecánica y a la oxidación hasta temperaturas de 870 ºC y, además, es empleada en aplicaciones aeroespaciales e industriales. Los recubrimientos han sido caracterizados microestructuralmente en INTA (Instituto Nacional de Técnica Aeroespacial), mediante SEM-EDS (Scanning Electronic Microscopy-Energy Dispersive Spectroscopy) y XRD (X-Ray Diffraction), y tribológicamente mediante medidas de microdureza y ensayos en tribómetro POD (Pin On Disc) para determinar los coeficientes de fricción y de desgaste. Los recubrimientos han sido ensayados tribológicamente a alta temperatura en INTA y en vacío en AMTTARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), en Seibersdorf (Austria). Se ha estudiado la influencia de la carga normal aplicada, la velocidad lineal y el material del pin. De entre las diferentes series de recubrimientos cuasicristalinos tipo composite desarrolladas, dos de ellas, TH100 y TH103 han presentado una excelente calidad microestructural (baja porosidad, distribución uniforme de fases…) y se han mostrado como excelentes recubrimientos antidesgaste. Sin embargo, estas capas presentan un pobre comportamiento como autolubricantes a temperatura ambiente, aunque mejoran mucho a alta temperatura o en vacío. Los resultados del trabajo presentado en esta tesis han proporcionado nuevo conocimiento respecto al comportamiento tribológico de recubrimientos autolubricantes cuasicristalinos tipo composite depositados por proyección térmica. Sin embargo, dichos resultados, aunque son muy prometedores, no han puesto de manifiesto el adecuado comportamiento autolubricante que se pretendía y, además, como ocurre en cualquier trabajo de investigación, durante el desarrollo del mismo siempre aparecen nuevas dudas por resolver. Se proponen nuevas líneas de trabajo futuro que complementen los resultados obtenidos y que puedan encaminar hacia la obtención de un recubrimiento que mejore su comportamiento autolubricante. ABSTRACT Solid lubricant coatings are required to reduce friction and prevent wear in components that operate at high temperatures or under vacuum (space vehicles, chemical industry, diesel engines, power generation turbines and aeronautical turbines, for instance). In these cases neither greases nor liquid lubricants can be employed and the only practicable approach to lubrication in such conditions is by means of solids. These are increasingly applied in the form of coatings which should exhibit low shear strength, whilst maintaining their chemical stability at extremes temperatures and in the space environment. In the space field, these coatings would be employed in re-usable space plane applications, such as elevon hinges, where temperatures of 700 ºC are reached during re-entry into the Earth’s atmosphere. These coatings should also be capable of providing effective lubrication at lower temperatures since “cold start” operation may be necessary, even in the space environment. The diverse and sometimes conflictive requirements in high temperature and space-related tribological coatings make the concept of composite coatings highly suitable for these applications. Thermal-sprayed composites containing solid lubricants in a hard matrix perform well tribologically. NASA‘s Lewis Research Centre had developed self-lubricating composite coatings for terrestrial use, comprising hard materials like chromium carbide as well as solid lubricant additives such as silver and BaF2-CaF2 eutectic on a Ni-Cr matrix. These coatings series, named PS100, PS200, PS300 and PS400, are applied by thermal spray and significantly reduce friction coefficients, improving wear resistance over a wide temperature range. Quasicrystalline alloys (QC) constitute a new family of materials with promising tribological behaviour. Some QC materials exhibit a combination of adequate antifriction properties: low friction coefficient, high hardness and high yield strength under compression, and can be easily produced as coatings on top of metallic and non-metallic materials. Among these QC alloys, AlCoFeCr has high hardness (700 HV0.1), a thermal expansion coefficient close to that of metals, high thermal stability, low thermal conductivity and good oxidation and hot corrosion resistance. However most QC materials have the disadvantage of being very brittle. In order to take advantage of the excellent tribological properties of QCs, thick composite lubricant coatings were prepared containing them as the hard phase for wear resistance, Ag and BaF2-CaF2 eutectic as lubricating materials and NiCr as the tough component. These coatings were deposited in different composition mixtures (named TH100, TH103, TH200, TH400, TH600…) by different thermal spray processes: air plasma spray (PS), low pressure plasma spray (LPPS) and high velocity oxy-fuel (HVOF), on X-750 substrates. X-750 is an age-hardenable nickel-base superalloy with very good strength and a good resistance to oxidising combustion gas environments at temperatures up to about 870 ºC and it is widely used in aerospace and industrial applications. Coatings have been characterized microstructurally, at INTA (National Institute for Aerospace Technology), by means of SEM-EDS (Scanning Electronic Microscopy- Energy Dispersive Spectroscopy) and XRD (X-Ray Diffraction), and tribologically by microhardness measurements and pin-on-disc testing to determine friction coefficients as well as wear resistance. The coatings were tested tribologically at high temperature at INTA and under vacuum at AMTT-ARC (Aerospace and Space Materials Technology Testhouse – Austrian Research Centres), in Seibersdorf (Austria). Different loads, linear speeds and pin materials were studied. TH100 and TH103 QC alloy matrix composite coatings were deposited by HVOF with excellent microstructural quality (low porosity, uniform phase distribution) and showed to be excellent wear resistant coatings. However these QC alloy matrix composite coatings are poor as a self-lubricant at room temperature but much better at high temperature or in vacuum. The results from the work performed within the scope of this thesis have provided new knowledge concerning the tribological behavior of self-lubricating quasicrystalline composite coatings deposited by thermal spraying. Although these results are very promising, they have not shown an adequate self-lubricating behavior as was intended, and also, as in any research, the results have in addition raised new questions. Future work is suggested to complement the results of this thesis in order to improve the selflubricating behaviour of the coatings.

Low-resolution spectroscopy and spectral energy distributions of selected sources towards σ Orionis

Aims. We study in detail nine sources in the direction of the young σ Orionis cluster, which is considered to be a unique site for studying stellar and substellar formation. The nine sources were selected because of their peculiar properties, such as extremely-red infrared colours or excessively strong Hα emission for their blue optical colours. Methods. We acquired high-quality, low-resolution spectroscopy (R ∼ 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analysed [24]-band photometry from MIPS/Spitzer and compiled the highest quality photometric dataset available at the ViJHK_s passbands and the four IRAC/Spitzer channels, for constructing accurate spectral energy distributions between 0.55 and 24 μm. Results. The nine targets were classified into: one Herbig Ae/Be star with a scattering edge-on disc; two G-type stars; one X-ray flaring, early-M, young star with chromospheric Hα emission; one very low-mass, accreting, young spectroscopic binary; two young objects at the brown-dwarf boundary with the characteristics of classical T Tauri stars; and two emission-line galaxies, one undergoing star formation, and another whose spectral energy distribution is dominated by an active galactic nucleus. We also discovered three infrared sources associated with overdensities in a cold cloud of the cluster centre. Conclusions. Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and evolution of young stars and candidates in the σ Orionis cluster.

The boundary lubricated friction and wear of low alloy steel

Pin on disc wear machines were used to study the boundary lubricated friction and wear of AISI 52100 steel sliding partners. Boundary conditions were obtained by using speed and load combinations which resulted in friction coefficients in excess of 0.1. Lubrication was achieved using zero, 15 and 1000 ppm concentrations of an organic dimeric acid additive in a hydrocarbon base stock. Experiments were performed for sliding speeds of 0.2, 0.35 and 0.5 m/s for a range of loads up to 220 N. Wear rate, frictional force and pin temperature were continually monitored throughout tests and where possible complementary methods of measurement were used to improve accuracy. A number of analytical techniques were used to examine wear surfaces, debris and lubricants, namely: Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), Powder X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), optical microscopy, Back scattered Electron Detection (BSED) and several metallographic techniques. Friction forces and wear rates were found to vary linearly with load for any given combination of speed and additive concentration. The additive itself was found to act as a surface oxidation inhibitor and as a lubricity enhancer, particularly in the case of the higher (1000 ppm) concentration. Wear was found to be due to a mild oxidational mechanism at low additive concentrations and a more severe metallic mechanism at higher concentrations with evidence of metallic delamination in the latter case. Scuffing loads were found to increase with increasing additive concentration and decrease with increasing speed as would be predicted by classical models of additive behaviour as an organo-metallic soap film. Heat flow considerations tended to suggest that surface temperature was not the overriding controlling factor in oxidational wear and a model is proposed which suggests oxygen concentration in the lubricant is the controlling factor in oxide growth and wear.

Oxidational wear of low alloy steel in gases other than air

A pin on disc wear machine has been used to study the oxidational wear of low alloy steel in a series of experiments which were carried out under dry wear sliding conditions at range of loads from 11.28 to 49.05 N and three sliding speeds of 2 m/s, 3.5 m/s and 5 m/s, in atmosphere of air, Ar, CO2, 100% O2, 20% O2-80% Ar and 2% O2-98% Ar. Also, the experiments were conducted to study frictional force, surface and contact temperatures and surface parameters of the wearing pins. The wear debris was examined using x-ray diffraction technique for the identification of compounds produced by the wear process. Scanning electron microscopy was employed to study the topographical features of worn pins and to measure the thickness of the oxide films. Microhardness tests were carried out to investigate the influence of the sub-surface microhardness in tribological conditions. Under all loads, speeds and atmospheres parabolic oxidation growth was observed on worn surfaces, although such growth is dependent on the concentration of oxygen in the atmospheres employed. These atmospheres are shown to influence wear rate and coefficient of friction with change in applied load. The nature of the atmosphere also has influence on surface and contact temperatures as determined from heat flow analysis. Unlubricated wear debris was found to be a mixture of αFe2O3, Fe3O4 and FeO oxide. A model has been proposed for tribo-oxide growth demonstrating the importance of diffusion rate and oxygen partial pressure, in the oxidation processes and thus in determination of wear rates.

Wear and corrosion of mechanical seals

Mechanical seals are used extensively to seal machinery such as pumps, mixers and agitators in the oil, petrochemical and chemical industries. The performance of such machinery is critically dependent on these devices. Seal failures may result in the escape of dangerous chemicals, possibly causing injury or loss of life. Seal performance is limited by the choice of face materials available. These range from cast iron and stellited stainless steel to cemented and silicon carbides. The main factors that affect seal performance are the wear and corrosion of seal faces. This research investigated the feasibility of applying surface coating/treatments to seal materials, in order to provide improved seal performance. Various surface coating/treatment methods were considered; these included electroless nickel plating, ion plating, plasma nitriding, thermal spraying and high temperature diffusion processes. The best wear resistance, as evaluated by the Pin-on-Disc wear test method, was conferred by the sprayed tungsten carbide/nickel/tungsten-chromium carbide deposit, produced by the high energy plasma spraying (Jet-Kote) process. In general, no correlation was found between hardness and wear resistance or surface finish and friction. This is due primarily to the complexity of the wear and frictional oxidation, plastic deformation, ploughing, fracture and delamination. Corrosion resistance was evaluated by Tafel extrapolation, linear polarisation and anodic potentiodynamic polarisation techniques. The best corrosion performance was exhibited by an electroless nickel/titanium nitride duplex coating due to the passivity of the titanium nitride layer in the acidified salt solution. The surface coating/treatments were ranked using a systematic method, which also considered other properties such as adhesion, internal stress and resistance to thermal cracking. The sealing behaviour of surface coated/treated seals was investigated on an industrial seal testing rig. The best sealing performances were exhibited by the Jet-Kote and electroless nickel silicon carbide composite coated seals. The failure of the electroless nickel and electroless nickel/titanium nitride duplex coated seals was due to inadequate adhesion of the deposits to the substrate. Abrasion of the seal faces was the principal wear mechanism. For operation in an environment similar to the experimental system employed (acidified salt solution) the Jet-Kote deposit appears to be the best compromise.

The transition from severe to mild wear in law alloy steel

The wear rates of sliding surfaces are significantly reduced if mild oxidational wear can be encouraged. It is hence of prime importance in the interest of component life and material conservation to understand the factors necessary to promote mild, oxidational wear, The present work investigates the fundamental mechanism of the running-in wear of BS EN 31!EN 8 steel couples. under various conditions of load. speed and test duration. Unidirectional sliding experiments were carried out on a pin-on~disc wear machine where frictional force, wear rate, temperature and contact resistance were continuously monitored during each test. Physical methods of analysis (x-ray, scanning electron microscopy etc.) were used to examine the wear debris and worn samples. The wear rate versus load curves revealed mild wear transitions, which under long duration of running, categorized mild wear into four distinct regions.α-Fe20s. Fe304, FeO and an oxide mixture were the predominant oxides in four regions of oxidational wear which were identified above the Welsh T2 transition. The wear curves were strongly effected by the speed and test duration. A surface model was used to calculate the surface parameters, and the results were found to be comparable with the experimentally observed parameters. Oxidation was responsible for the transition from severe to mild wear at a load corresponding to the Welsh T2 transition. In the running-in period sufficient energy input and surface hardness enabled oxide growth rate to increase and eventually exceeded the rate of removal, where mild wear ensued. A model was developed to predict the wear volume up to the transition. Remarkable agreement was found between the theoretical prediction and the experimentally-measured values. The oxidational mechanjsm responsible for transitjon to mild wear under equilibrium conditions was related to the formation of thick homogenous oxide plateaux on subsurface hardened layers, FeO was the oxide formed initially at the onset of mild wear but oxide type changed.during the total running period to give an equilibrium oxide whose nature depended on the loads applied.

Nitrogen implantation of tool steels and engineering coatings

Ion implantation modifies the surface composition and properties of materials by bombardment with high energy ions. The low temperature of the process ensures the avoidance of distortion and degradation of the surface or bulk mechanical properties of components. In the present work nitrogen ion implantation at 90 keV and doses above 1017 ions/cm2 has been carried out on AISI M2, D2 and 420 steels and engineering coatings such as hard chromium, electroless Ni-P and a brush plated Co-W alloy. Evaluation of wear and frictional properties of these materials was performed with a lubricated Falex wear test at high loads up to 900 N and a dry pin-on-disc apparatus at loads up to 40 N. It was found that nitrogen implantation reduced the wear of AISI 420 stainless steel by a factor of 2.5 under high load lubricated conditions and by a factor of 5.5 in low load dry testing. Lower but significant reductions in wear were achieved for AISI M2 and D2 steels. Wear resistance of coating materials was improved by up to 4 times in lubricated wear of hard Cr coatings implanted at the optimum dose but lower improvements were obtained for the Co-W alloy coating. However, hardened electroless Ni-P coatings showed no enhancement in wear properties. The benefits obtained in wear behaviour for the above materials were generally accompanied by a significant decrease in the running-in friction. Nitrogen implantation hardened the surface of steels and Cr and Co-W coatings. An ultra-microhardness technique showed that the true hardness of implanted layers was greater than the values obtained by conventional micro-hardness methods, which often result in penetration below the implanted depth. Scanning electron microscopy revealed that implantation reduced the ploughing effect during wear and a change in wear mechanism from an abrasive-adhesive type to a mild oxidative mode was evident. Retention of nitrogen after implantation was studied by Nuclear Reaction Analysis and Auger Electron Spectroscopy. It was shown that maximum nitrogen retention occurs in hard Cr coatings and AISI 420 stainless steel, which explains the improvements obtained in wear resistance and hardness. X-ray photoelectron spectroscopy on these materials revealed that nitrogen is almost entirely bound to Cr, forming chromium nitrides. It was concluded that nitrogen implantation at 90 keV and doses above 3x1017 ions/cm2 produced the most significant improvements in mechanical properties in materials containing nitride formers by precipitation strengthening, improving the load bearing capacity of the surface and changing the wear mechanism from adhesive-abrasive to oxidative.