Refine
Has Fulltext
- yes (52) (remove)
Year of publication
- 2002 (52) (remove)
Document Type
- Preprint (28)
- Doctoral Thesis (14)
- Postprint (6)
- Habilitation Thesis (2)
- Monograph/Edited Volume (1)
- Master's Thesis (1)
Language
- English (52) (remove)
Keywords
- conormal symbol (3)
- relative index (3)
- Atiyah-Bott obstruction (2)
- edge-degenerate operators (2)
- elliptic families (2)
- elliptic family (2)
- elliptic operators (2)
- 'Peer To Peer' (1)
- (co)boundary operator (1)
- Adipozyt (1)
- Aggression (1)
- American Indians (1)
- Anden (1)
- Anden / Störung <Geologie> / Strukturgeologie / Magnetotellurik / Chile <Nord> (1)
- Andes (1)
- Ausreisser (1)
- Belletristik (1)
- Bioelektrokatalytisches Recycling (1)
- Biokatalytisches Recyc (1)
- Biosensor (1)
- Bistability (1)
- Bistabilität (1)
- Boundary value problems (1)
- Brandenburg (1)
- Brasilien (1)
- Brazil (1)
- Cactus (1)
- Ceará / Semiarides Gebiet / Wasserreserve / Hydrologie / Mathematisches Modell (1)
- Christentum (1)
- Christianisierung (1)
- Christianity (1)
- Christianization (1)
- D'Ar (1)
- D'Arcy McNickle (1)
- Depression (1)
- Diasporenmorphologie (1)
- Differenzierung (1)
- Dispersionsrelationen (1)
- Distributed Computing (1)
- Dreissena polymorpha (1)
- Emotion Regulation (1)
- Emotionsregulation (1)
- Enzymelektrode ; Monophenolmonooxygenase (1)
- Epizoochorie (1)
- Fag (1)
- Fagus syl (1)
- Fault architecture (1)
- Fettzelle (1)
- Genexpression (1)
- Globus (1)
- Glucosedehydrogenase (1)
- Green operator (1)
- Grid (1)
- Grid Computing (1)
- Hochdruck (1)
- Honey bee (1)
- Hydrologie (1)
- Infants (1)
- Junge Mutter / Kind / Aggressivität / Risikoverhalten (1)
- Kleinkinder (1)
- Klimaänderung (1)
- Kolonialisierung (1)
- Kristallstruktur (1)
- Labradorsee ; Thermohaline Konvektion ; Stochastisches Modell (1)
- Lehrer (1)
- Literatur der Indianer Nordamerikas (1)
- Loop-Quantengravitation (1)
- MDS (1)
- MHD ; Röntgenstrahlung ; Jets ; AGN ; Mikro-Quasare (1)
- MHD ; X-rays ; Jets ; AGN ; Microquasars (1)
- Magnetotelluric (1)
- Magnetotellurik (1)
- Meromorphic operator functions (1)
- Microarray (1)
- Migration (1)
- Mother-Child Interaction (1)
- Mutter-Kind Interaktion (1)
- N. Scott Momad (1)
- NE Germany (1)
- Native American literature (1)
- Natural Regions (1)
- Naturräume (1)
- Negative Emotionality (1)
- Negative Emotionalität (1)
- Nichtlineare Dynamik (1)
- Niederschlag-Abfluss-Modellierung (1)
- Noise-induced phenomena (1)
- Nonlinear dynamics (1)
- Nordatlantik (1)
- North Atlantic (1)
- Oxadiazolderivate ; Kristallstruktur ; Hochdruck ; UV-VIS-Spektroskopie ; Raman-Spektroskopie (1)
- PUFA (1)
- Paralleles Rechnen (1)
- Peer-to-Peer-Netz ; GRID computing ; Zuverlässigkeit ; Web Services ; Betriebsmittelverwaltung ; Migration (1)
- Perron's method (1)
- Phenol (1)
- Physiologie-basierte Modelle (1)
- Phänologie (1)
- Preadipozyt (1)
- Quantengravitation (1)
- Raman Streuung (1)
- Raman scattering (1)
- Rauschen (1)
- Rauschinduzierte Phänomene (1)
- Recyclingsystem (1)
- Regressionsanalysen (1)
- Reh (1)
- Religion (1)
- Religiosität (1)
- Riemann-Roch theorem (1)
- Romane (1)
- Schulbindung (1)
- Schulen (1)
- Schüler (1)
- Seitenverschiebung (1)
- Sobolev problem (1)
- Spawning (1)
- Stochastic dynamical systems (1)
- Stochastische Prozesse (1)
- Stochastische Resonanz (1)
- Stochastische dynamische Systeme (1)
- Strike-slip fault (1)
- Störungsbau (1)
- Säugetiere ; Fettgewebe ; Zelldifferenzierung ; Genexpression (1)
- TSL (1)
- Themisch-Stimulierte Lumineszenz (1)
- Thermally stimulated luminescence (1)
- Trends (1)
- Trendwendepunkte (1)
- Trockengebiet (1)
- Tyrosinase (1)
- Tyrosinaseinhibitoren (1)
- UV-Vis Spektroskopie (1)
- UV-Vis spectroscopy (1)
- Unsicherheit (1)
- Unsicherheiten (1)
- Variabilität (1)
- Verteiltes Rechnen (1)
- Verteilungen von lokalisierten Zustände (1)
- Viscosity solutions (1)
- Volterra symbols (1)
- Waldbodenpflanzen (1)
- Wasserverfügbarkeit (1)
- Werte (1)
- Werteerziehung (1)
- Werteprioritäten (1)
- West Fault Zone (1)
- Wildschwein (1)
- Zustandsgleichung (1)
- adaptiv (1)
- adaptive (1)
- adipocyte (1)
- amerikanische Ureinwohner (1)
- biocatalytic recycling (1)
- bioelectrocatalytic recycling (1)
- biogenic amines (1)
- biosensor (1)
- boundary value problems (1)
- braunes Fettgewebe (1)
- brown adipose tissue (1)
- bundles (1)
- climate change (1)
- colonization (1)
- combined time series (1)
- compressible Euler equations (1)
- connections (1)
- coupled solution (1)
- crystal structure (1)
- diaspore morphology (1)
- differentiation (1)
- dispersion relations (1)
- distributions of localised states (1)
- division algebras (1)
- drylands (1)
- dynamic (1)
- dynamisch (1)
- edge symbol (1)
- electrical conductivity (1)
- elektrische Leitfähigkeit (1)
- elliptic morphism (1)
- epizoochory (1)
- equation of state (1)
- exterior tensor product (1)
- fatty acid (1)
- fibre coordinates (1)
- fiction (1)
- food quality (1)
- force unification (1)
- forest plant species (1)
- fully non-linear degenerate parabolic equations (1)
- gene expression (1)
- glucose dehydrogenase (1)
- high pressure (1)
- hydrology (1)
- index (1)
- index formulas (1)
- index theory (1)
- insect (1)
- kombinierte Zeitreihen (1)
- life history (1)
- lifespan (1)
- loop quantum gravity (1)
- manifolds with edges (1)
- metamorphosis (1)
- microarray (1)
- noise (1)
- nondegenerate condition (1)
- novels (1)
- order reduction (1)
- organic crystal (1)
- organische Kristalle (1)
- outliers (1)
- parallelizable spheres (1)
- parameter-dependent cone operators (1)
- parameter-dependent ellipticity (1)
- phenol (1)
- phenology (1)
- physiology-based models (1)
- preadipocyte (1)
- proboscis extension response (1)
- quantum gravity (1)
- rainfall-runoff modelling (1)
- recycling system (1)
- regression analysis (1)
- relative index formulas (1)
- religion (1)
- religiosity (1)
- roe deer (1)
- school commitment (1)
- schools (1)
- semi-arid (1)
- semiclassical states (1)
- semiklassische Zustände (1)
- shock wave (1)
- spectral flow (1)
- stochastic processes (1)
- stochastic resonance (1)
- students (1)
- sucrose responsiveness (1)
- surgery (1)
- symmetry conditions (1)
- systems of partial differential equations (1)
- teachers (1)
- trend turning points (1)
- trends (1)
- tyrosinase (1)
- tyrosinase inhibitors (1)
- uncertainties (1)
- uncertainty (1)
- value education (1)
- value priorities (1)
- values (1)
- variability (1)
- water availability (1)
- wild boar (1)
Institute
- Institut für Mathematik (28)
- Institut für Physik und Astronomie (7)
- Institut für Biochemie und Biologie (4)
- Institut für Chemie (3)
- Department Psychologie (2)
- Extern (2)
- Institut für Informatik und Computational Science (2)
- Institut für Umweltwissenschaften und Geographie (2)
- Institut für Anglistik und Amerikanistik (1)
- Institut für Ernährungswissenschaft (1)
Structural and spectroscopical study of crystals of 1,3,4-oxadiazole derivatives at high pressure
(2002)
In recent years the search for new materials of technological interest has given new impulses to the study of organic compounds. Organic substances possess a great number of advantages such as the possibility to adjust their properties for a given purpose by different chemical and physical techniques in the preparation process. Oxadiazole derivatives are interesting due to their use as material for light emitting diodes (LED) as well as scintillators. The physical properties of a solid depend on its structure. Different structures induce different intra- and intermolecular interactions. An advantageous method to modify the intra- as well as the intermolecular interactions of a given substance is the application of high pressure. Furthermore, using this method the chemical features of the compound are not influenced. We have investigated the influence of high pressure and high temperature on the super-molecular structure of several oxadiazole derivatives in crystalline state. From the results of this investigation an equation of state for these crystals was determined. Furthermore, the spectroscopical features of these materials under high pressure were characterized.
Deep convection is an essential part of the circulation in the North Atlantic Ocean. It influences the northward heat transport achieved by the thermohaline circulation. Understanding its stability and variability is therefore necessary for assessing climatic changes in the area of the North Atlantic. This thesis aims at improving the conceptual understanding of the stability and variability of deep convection. Observational data from the Labrador Sea show phases with and without deep convection. A simple two-box model is fitted to these data. The results suggest that the Labrador Sea has two coexisting stable states, one with regular deep convection and one without deep convection. This bistability arises from a positive salinity feedback that is due to the net freshwater input into the surface layer. The convecting state can easily become unstable if the mean forcing shifts to warmer or less saline conditions. The weather-induced variability of the external forcing is included into the box model by adding a stochastic forcing term. It turns out that deep convection is then switched "on" and "off" frequently. The mean residence time in either state is a measure of its stochastic stability. The stochastic stability depends smoothly on the forcing parameters, in contrast to the deterministic (non-stochastic) stability which may change abruptly. The mean and the variance of the stochastic forcing both have an impact on the frequency of deep convection. For instance, a decline in convection frequency due to a surface freshening may be compensated for by an increased heat flux variability. With a further simplified box model some stochastic stability features are studied analytically. A new effect is described, called wandering monostability: even if deep convection is not a stable state due to changed forcing parameters, the stochastic forcing can still trigger convection events frequently. The analytical expressions explicitly show how wandering monostability and other effects depend on the model parameters. This dependence is always exponential for the mean residence times, but for the probability of long nonconvecting phases it is exponential only if this probability is small. It is to be expected that wandering monostability is relevant in other parts of the climate system as well. All in all, the results demonstrate that the stability of deep convection in the Labrador Sea reacts very sensitively to the forcing. The presence of variability is crucial for understanding this sensitivity. Small changes in the forcing can already significantly lower the frequency of deep convection events, which presumably strongly affects the regional climate. ----Anmerkung: Der Autor ist Träger des durch die Physikalische Gesellschaft zu Berlin vergebenen Carl-Ramsauer-Preises 2003 für die jeweils beste Dissertation der vier Universitäten Freie Universität Berlin, Humboldt-Universität zu Berlin, Technische Universität Berlin und Universität Potsdam.
Value education of youth
(2002)
The value priorities of students and teachers were measured at eight different schools at the beginning and the end of the school year 2000/2001. This study once again confirmed the theoretical model of a universal structure of human values (Schwartz, 1992). At both measurement times, similar gender differences, as well as positive correlations between religiosity and school commitment were found. The students from the non-religious schools determined Hedonism as their highest, and Tradition as their lowest value priority. In the religious schools, Benevolence and Self-Direction were the highest values, whereas Power was found to be the lowest value priority. The change of the values Conformity, Hedonism, and Universalism was predicted both through the students′ religiosity and their type of school. The change of the values Power, Tradition, Benevolence, and Achievement, however, was mainly predicted through their religiosity. In three out of four schools the student-teacher similarity correlated positively with the school commitment of the students. Across all schools student-teacher similarity correlated positively with academic achievement.
The primary focus on the present study was to identify early risk factors for infant aggression in a sample of high risk, low-income teenager mothers and their infants. Despite the amount of research on externalizing behavior, relatively little is known about its development in early childhood. Because chronically aggressive school-age children tend to be those who first display symptoms during preschool years, an examination of the early manifestations of aggressive behavior and the development of measurements for infants is needed. The present study explored a model of infant aggression development that emphasized infant aggression developing largely through the interaction of infant′s dispositional characteristics with their caregiving environment. The study addressed the following relations: (1) Maternal psychosocial functioning with reported and observed infant aggression and negative emotionality, (2) reported measurements of infant aggression and negative emotionality with observed infant measurements of infant aggression and negative emotionality, (3) infant negative emotionality and infant aggression, (4) infant emotion regulation with infant aggression and negative emotionality, (5) the interaction between emotion regulation and negative emotionality in relation to infant aggression, and (6) attachment classification with infant aggression and negative emotionality. Finally, the question of whether these six relations would differ by gender was also addressed. Maternal psychosocial functioning was assessed with self-reported measurements. Infant aggression, negative emotionality and emotion regulation were measured during two standardized assessments, the Strange Situation and the Bayley Scales of Infant Development Assessment and maternal reported with the Infant-Toddler Social and Emotional Assessment. Several interesting findings emerged. One of the main findings concerned maternal attribution and its possible role as a risk factor for later externalizing behaviors. That is, mothers, especially depressed and stressed mothers, tended to report higher levels of infant aggression and negative emotionality than was noted by more objective observers. This tendency was particularly evident in mothers with girl infants. Another important finding concerned emotion regulation. Even at this early age, clear differences in emotion regulation could be seen. Interestingly, infants with high negative emotionality and low emotion regulation were observed to be the most aggressive. Also significant relations emerged for infant negative emotionality and aggression and vise versa. Thus, for purposes of treatment and scientific study, the three constructs (emotion regulation, negative emotionality, and aggression) should be considered in combination. Investigating each alone may not prove fruitful in future examinations. Additionally, different emotion regulation behaviors were observed for girl and boy infants. Aggressive girls looked more at the environment, their toys and their mother, whereas aggressive boys looked less at the environment and their mother and explored their toys more, although looked at the toys less. Although difficult to interpret at this point, it is nonetheless interesting that gender differences exist at this young age in emotion regulatory behaviors. In conclusion, although preliminary, findings from the present study provide intriguing directions for future research. More studies need to conducted focusing on infant aggression, as well as longitudinal studies following the infants over time.
The length of the vegetation period (VP) plays a central role for the interannual variation of carbon fixation of terrestrial ecosystems. Observational data analysis has indicated that the length of the VP has increased in the last decades in the northern latitudes mainly due to an advancement of bud burst (BB). This phenomenon has been widely discussed in the context of Global Warming because phenology is correlated to temperatures. Analyzing the patterns of spring phenology over the last century in Southern Germany provided two main findings: - The strong advancement of spring phases especially in the decade before 1999 is not a singular event in the course of the 20th century. Similar trends were also observed in earlier decades. Distinct periods of varying trend behavior for important spring phases could be distinguished. - Marked differences in trend behavior between the early and late spring phases were detected. Early spring phases changed as regards the magnitude of their negative trends from strong negative trends between 1931 and 1948 to moderate negative trends between 1948 and 1984 and back to strong negative trends between 1984 and 1999. Late spring phases showed a different behavior. Negative trends between 1931 and 1948 are followed by marked positive trends between 1948 and 1984 and then strong negative trends between 1984 and 1999. This marked difference in trend development between early and late spring phases was also found all over Germany for the two periods 1951 to 1984 and 1984 to 1999. The dominating influence of temperature on spring phenology and its modifying effect on autumn phenology was confirmed in this thesis. However, - temperature functions determining spring phenology were not significantly correlated with a global annual CO2 signal which was taken as a proxy for a Global Warming pattern. - an index for large scale regional circulation patterns (NAO index) could only to a small part explain the observed phenological variability in spring. The observed different trend behavior of early and late spring phases is explained by the differing behavior of mean March and April temperatures. Mean March temperatures have increased on average over the 20th century accompanied by an increasing variation in the last 50 years. April temperatures, however, decreased between the end of the 1940s and the mid-1980s, followed by a marked warming after the mid-1980s. It can be concluded that the advancement of spring phenology in recent decades are part of multi-decadal fluctuations over the 20th century that vary with the species and the relevant seasonal temperatures. Because of these fluctuations a correlation with an observed Global Warming signal could not be found. On average all investigated spring phases advanced between 5 and 20 days between 1951 and 1999 for all Natural Regions in Germany. A marked difference be! tween late and early spring phases is due to the above mentioned differing behavior before and after the mid-1980s. Leaf coloring (LC) was delayed between 1951 and 1984 for all tree species. However, after 1984 LC was advanced. Length of the VP increased between 1951 and 1999 for all considered tree species by an average of ten days throughout Germany. It is predominately the change in spring phases which contributes to a change in the potentially absorbed radiation. Additionally, it is the late spring species that are relatively more favored by an advanced BB because they can additionally exploit longer days and higher temperatures per day advancement. To assess the relative change in potentially absorbed radiation among species, changes in both spring and autumn phenology have to be considered as well as where these changes are located in the year. For the detection of the marked difference between early and late spring phenology a new time series construction method was developed. This method allowed the derivation of reliable time series that spanned over 100 years and the construction of locally combined time series increasing the available data for model development. Apart from analyzed protocolling errors, microclimatic site influences, genetic variation and the observers were identified as sources of uncertainty of phenological observational data. It was concluded that 99% of all phenological observations at a certain site will vary within approximately 24 days around the parametric mean. This supports to the proposed 30-day rule to detect outliers. New phenology models that predict local BB from daily temperature time series were developed. These models were based on simple interactions between inhibitory and promotory agents that are assumed to control the developmental status of a plant. Apart from the fact that, in general, the new models fitted and predicted the observations better than classical models, the main modeling results were: - The bias of the classical models, i.e. overestimation of early observations and underestimation of late observations, could be reduced but not completely removed. - The different favored model structures for each species indicated that for the late spring phases photoperiod played a more dominant role than for early spring phases. - Chilling only plays a subordinate role for spring BB compared to temperatures directly preceding BB.
Comparative study of gene expression during the differentiation of white and brown preadipocytes
(2002)
Introduction Mammals have two types of adipose tissue: the lipid storing white adipose tissue and the brown adipose tissue characterised by its capacity for non-shivering thermogenesis. White and brown adipocytes have the same origin in mesodermal stem cells. Yet nothing is known so far about the commitment of precursor cells to the white and brown adipose lineage. Several experimental approaches indicate that they originate from the differentiation of two distinct types of precursor cells, white and brown preadipocytes. Based on this hypothesis, the aim of this study was to analyse the gene expression of white and brown preadipocytes in a systematic approach. Experimental approach The white and brown preadipocytes to compare were obtained from primary cell cultures of preadipocytes from the Djungarian dwarf hamster. Representational difference analysis was used to isolate genes potentially differentially expressed between the two cell types. The thus obtained cDNA libraries were spotted on microarrays for a large scale gene expression analysis in cultured preadipocytes and adipocytes and in tissue samples. Results 4 genes with higher expression in white preadipocytes (3 members of the complement system and a fatty acid desaturase) and 8 with higher expression in brown preadipocytes were identified. From the latter 3 coded for structural proteins (fibronectin, metargidin and a actinin 4), 3 for proteins involved in transcriptional regulation (necdin, vigilin and the small nuclear ribonucleoprotein polypeptide A) and 2 are of unknown function. Cluster analysis was applied to the gene expression data in order to characterise them and led to the identification of four major typical expression profiles: genes up-regulated during differentiation, genes down-regulated during differentiation, genes higher expressed in white preadipocytes and genes higher expressed in brown preadipocytes. Conclusion This study shows that white and brown preadipocytes can be distinguished by different expression levels of several genes. These results draw attention to interesting candidate genes for the determination of white and brown preadipocytes (necdin, vigilin and others) and furthermore indicate that potential importance of several functional groups in the differentiation of white and brown preadipocytes, mainly the complement system and extracellular matrix.
Today, analytical chemistry does not longer consist of only the big measuring devices and methods which are time consuming and expensive, which can furthermore only be handled by the qualified staff and in addition the results can also only be evaluated by this qualified staff. Usually, this technique, which shall be described in the following as 'classic analytic measuring technique', requires also rooms equipped especially and often a relative big quantity of the test compounds which should be prepared especially. Beside this classic analytic measuring technique, limited on definite substance groups and requests, a new measuring technique has gained acceptance particularly within the last years, which one can often be used by a layman, too. Often the new measuring technique has very little pieces of equipment. The needed sample volumes are also small and a special sample preparation isn't required. In addition, the new measuring instruments are simple to handle. They are cheap both in their production and in the use and they permit even a continuous measurement recording usually. Numerous of this new measuring instruments base on the research in the field of Biosensorik during the last 40 years. Since Clark and Lyon in the year 1962 were able to measure glucose with a simple oxygen electrode, completed by an enzyme the development of the new measuring technique did not have to be held back any longer. Biosensors, special pickups which consists of a combination from a biological component (permits a specific recognition of the analyte also without purification of the sample previously) and a physical pickup (convert the primary physicochemical effect into an electronically measurable signal), conquered the market. In the context of this thesis different tyrosinasesensors were developed which fulfilling the various requests, depending on origin and features of the used tyrosinase. One of the tyrosinasesensors for example was used for quantification of phenolic compounds in river and sea water and the results could correlated very well with the corresponding DIN-test for the determination of phenolic compounds. An other developed tyrosinasesensor showed a very high sensitiveness for catecholamines, substances which are of special importance in the medical diagnostics. In addition, the investigations of two different tyrosinases, which were carried out also in the context of this thesis, have shown, that a special tyrosinase (tyrosinase from Streptomyces antibioticus) will be the better choice as tyrosinase from Agaricus bisporus, which is used in the area of biosensor research till now, if one wants to develop in future even more sensitive tyrosinasesensors. Furthermore, first successes became reached on a molecular biological field, the production of tyrosinasemutants with special, before well-considered features. These successes can be used to develop a new generation of tyrosinasesensors, tyrosinasesensors in which tyrosinase can be bound directionally both to the corresponding physical pickup or also to another enzyme. From this one expects to achieve ways minimized which the substance to be determined (or whose product) otherwise must cover. Finally, this should result in an clearly visible increase of sensitivity of the Biosensor.
This MA thesis examines novels by Native American authors of the 20th century in regard to their representation of conflicts between the indigenous population of North America and the dominant Christian religion of the mainstream society. Several major points can be followed throughout the century, which have been presented repeatedly and discussed in various perspectives. Historical conflicts of colonization and Christianization, as well as the perpetual question of Native American Christians -- 'How can you go to a church that killed so many Indians?' [Alexie, Reservation Blues] -- are debated in these novels and analyzed in this paper. Furthermore, I have tried to position and classify the works according to their representation of these problems within literary history. Following Charles Larson's chronologic and thematic examination of American Indian Fiction, the categories rejection, (syncretic) adaptation, and postmodern-ironic revision are introduced to describe the various forms of representation. On the basis of five main examples, we can observe an evolution of contemporary Native American literature, which has liberated itself from the narrow definition of the 1960s and 1970s, in favor of a broader and more varied approach. In so doing, and by means of intercultural and intertextual referencing, postmodern irony, and a new Indian self-confidence, it has also taken a new position towards the religion of the former colonizer.
In the honey bee, responsiveness to sucrose correlates with many behavioural parameters such as age of first foraging, foraging role and learning. Sucrose responsiveness can be measured using the proboscis extension response (PER) by applying sucrose solutions of increasing concentrations to the antenna of a bee. We tested whether the biogenic amines octopamine, tyramine and dopamine, and the dopamine receptor agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (6,7-ADTN) can modulate sucrose responsiveness. The compounds were either injected into the thorax or fed in sucrose solution to compare different methods of application. Injection and feeding of tyramine or octopamine significantly increased sucrose responsiveness. Dopamine decreased sucrose responsiveness when injected into the thorax. Feeding of dopamine had no effect. Injection of 6,7-ADTN into the thorax and feeding of 6,7-ADTN reduced sucrose responsiveness significantly. These data demonstrate that sucrose responsiveness in honey bees can be modulated by biogenic amines, which has far reaching consequences for other types of behaviour in this insect. (C) 2002 Elsevier Science B.V. All rights reserved.
Highly collimated, high velocity streams of hot plasma – the jets – are observed as a general phenomenon being found in a variety of astrophysical objects regarding their size and energy output. Known as jet sources are protostellar objects (T Tauri stars, embedded IR sources), galactic high energy sources ("microquasars"), and active galactic nuclei (extragalactic radio sources and quasars). Within the last two decades our knowledge regarding the processes involved in astro-physical jet formation has condensed in a kind of standard model. This is the scenario of a magnetohydrodynamically accelerated and collimated jet stream launched from the innermost part of an accretion disk close to the central object. Traditionally, the problem of jet formation is divided in two categories. One is the question how to collimate and accelerate an uncollimated low velocity disk wind into a jet. The second is the question how to initiate that outflow from a disk, i.e. how to turn accretion of matter into an ejection as a disk wind. My own work is mainly related to the first question, the collimation and acceleration process. Due to the complexity of both, the physical processes believed to be responsible for the jet launching and also the spatial configuration of the physical components of the jet source, the enigma of jet formation is not yet completely understood. On the theoretical side, there has been a substantial advancement during the last decade from purely station-ary models to time-dependent simulations lead by the vast increase of computer power. Observers, on the other hand, do not yet have the instruments at hand in order to spatially resolve observe the very jet origin. It can be expected that also the next years will yield a substantial improvement on both tracks of astrophysical research. Three-dimensional magnetohydrodynamic simu-lations will improve our understanding regarding the jet-disk interrelation and the time-dependent character of jet formation, the generation of the magnetic field in the jet source, and the interaction of the jet with the ambient medium. Another step will be the combina-tion of radiation transfer computations and magnetohydrodynamic simulations providing a direct link to the observations. At the same time, a new generation of telescopes (VLT, NGST) in combination with new instrumental techniques (IR-interferometry) will lead to a "quantum leap" in jet observation, as the resolution will then be sufficient in order to zoom into the innermost region of jet formation.