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In this thesis the anti-proton to proton ratio in 197Au + 197Au collisions, measured at mid-rapidity, at a center of mass energy of psNN = 200GeV is reported. The value was measured to be ¹p/p = 0.81+-0.002stat +- 0.05syst: in the 5% most central collisions. The ratio shows no dependence on rapidity in the range jyj < 0:5. Furthermore, a dependence on transverse momentum within 0:4< p? < 1:0 GeV/c is not observed. At higher p?, a slight drop in the ratio is observed. In the present analysis, the highest momentum considered is p? = 4:5 GeV/c yielding ¹p=p = 0:645§0:005stat: §0:10syst:. However, the systematic error is higher in this momentum range. A slight centrality dependence was observed, where a decrease from ¹p=p = 0:83§0:002stat:§0:05syst: for most peripheral collisions (less than 80% central) to ¹p=p = 0:78§0:002stat:§0:05syst: for the 5% most central collisions was measured. An estimate of the feed-down contributions fromthe decay of heavier strange baryons results in ¹p=p = 0:77 § 0:05syst:. The measured ratio indicates a » 12:5 times higher value compared to the highest SPS energy of psNN = 17:3 and an \almost net-baryon free" region, at mid- rapidity. The asymmetry of protons and anti-protons may be explained by the contribution ofvalence quarks in a nucleus break-up picture. In such a scenario, the absolute value of the ratio and the fact that the ratio does not depend on rapidity (at mid-rapidity) is well reproduced. Fragmentation of quarks and anti- quarks into protons and anti-protons is assumed. An estimate of the ratio, when feed-down correction is taken into consideration, agrees well with the prediction of a statistical model analysis at a temperature of T = 177 § 7 MeV and a baryon chemical potential of ¹B = 29 § 8 MeV. The temperature achieved is only slightly higher when compared to the top SPS energy, while the baryochemical potential is factor »10 lower. As in the case of the SPS results, these parameters are close to the phase boundary of Figure 1.6. The measurement of the ratio at high transverse momentum was of special in- terest in this analysis, since at RHIC energies, the cross section for hadrons at high transverse momentum is increased with respect to SPS energies. The weak dependence of the ratio on the transverse momentum is well described by the non- perturbative quenched and baryon junction scenario (i.e. Soft+Quench model), where baryon creation is enhanced by baryon junctions. In comparison the ratio does not decrease within the considered momentum range as predicted by pQCD.
This thesis presented the measurement of antideuteron and antihelium-3 production in central AuAu collisions at V SNN = 200 GeV center-of-mass energy at RHIC. The analysis is based on STAR data, about 3 x 10 high 6 events at top 10% centrality. Within the data sample a total number of about 5000 antideuterons and 193 antihelium-3 were observed in the STARTPC at mid-rapidity. The specific energy loss measurement in the TPC provides antideuteron identification only in a small momentum window, antihelium-3 however can be identified nearly background free with almost complete momentum range coverage. Following the statistical analysis of the hadronic composition at chemical freeze-out of the fireball, the antinuclei abundances were analyzed in terms of the same statistical description. Now applied to the clusterization of the fireball, the statistical analysis yields a fireball temperature of (135+-10) MeV and chemical potential of (5+-10) MeV at kinetic freeze-out. In the same way as the hadronization, the clusterization process is phase-space dominated and clusters are born into a state of maximum entropy. The large sample of observed antihelium-3 allowed for the first time in heavy-ion physics to calculate a differential multiplicity and invariant cross section as a function of transverse momentum. As expected, the collective transverse flow in the fireball flattens the shape of the transverse momentum spectrum and leads to the high inverse slope parameter of (950+-140) MeV of the antihelium-3 spectrum. With the extracted mean transverse momentum of antihelium-3, the collective flow velocity in transverse direction could be estimated. As the average thermal velocity is small compared to the mean collective flow velocity for heavy particles, the mean transverse momentum of antihelium-3 by itself constrains the flow velocity. Here, a simple ideal-gas approximation was fitted to the distribution of the mean transverse momentum as a function of particle mass and provided direct access to the kinetic freeze-out temperature and the flow velocity. A concept, which is complementary to the combined analysis of momentum spectra and two-particle HBT correlation methods commonly used to extract these parameters, and a cross check for the statistical analysis. The upper limit for the transverse collective flow velocity from the antihelium-3 measurement alone is v flow <= (0.68+-0.06)c, whereas the ideal-gas approximation yields a temperature of (130+-40) MeV and v flow = (0.46+-0.08)c. The results indicate, that the kinetic freeze-out conditions at SPS and RHIC are very similar, except for a smaller baryon chemical potential at RHIC. The simultaneous inclusive measurement of antiprotons allowed to study the cluster production in terms of the coalescence picture. With the large momentum coverage of the antihelium-3 momentum spectrum, the coalescence parameter could be calculated as a function of transverse momentum. Due to the difference between antiproton and antihelium-3 inverse slopes, increases with increasing transverse momentum - again a direct consequence of collective transverse flow. Both B2 and B3 follow the common behavior of decreasing coalescence parameters as a function of collision energy. According to the simple thermodynamic coalescence model, this indicates an increasing freeze-out volume for higher energies and is confirmed by the interpretation of the coalescence parameters in the framework of Scheibl and Heinz. Their model includes a dynamically expanding source in a quantum mechanical description of the coalescence process and expresses the coalescence parameter as a function of the homogeneity volume V hom accessible also in two-particle HBT correlation analyzes. The values for the antideuteron and antihelium-3 results agree well with the homogeneity volume from pion-pion correlations, but do not seem to follow the same transverse mass dependence. A comparison with proton-proton correlations may clarify this point and provide an important cross check for this analysis. Compared to SPS the homogeneity volume increases nearly by a factor of two. The analysis of the antinuclei emission at RHIC allowed to study the kinetic freeze-out of the created fireball. The results show, that the temperature and mean transverse velocity in the expanding system does not change significantly, when the collision energy increases by one order of magnitude. Only the source volume, i.e. the homogeneity volume, increases. That leaves open questions for the theoreticians to the details of the system evolution from the initial hot and dense phase - the initial energy density is a factor of two to three higher at RHIC than at SPS - to the final kinetic freeze-out with similar conditions. At the same time, the results are important constraints for the theoretical descriptions. The successful implementation of the Level-3 trigger system in STAR opens the door for the measurement of very rare signals. Indeed, in the coalescence physics perspective, the first observations of anti-alpha 4 He nuclei and antihypertritons 3/Delta H will come within the reach of STAR, in addition to a high statistics sample of antihelium-3.
Vascular occlusive diseases are one of the leading mortality causes in westernised countries. Occlusions of one of the major arteries can be overcome without devastating consequences provided a timely induction of compensating collateral arteries occurs. Perhaps the most outstanding feature of collateral vessel growth is the proliferation of smooth muscle cells (SMCs). Understanding the molecular mechanisms and identifying key molecular players of SMC proliferation would contribute significantly to the development of efficient therapies to intervene with all processes involving neointima formation, including collateral growth. mRNA and protein coding for co-transcription factor Egr1 were found to be up-regulated in growing collateral vessels 6, 12 or 24 hours following femoral artery ligation in mice. Since Egr1 is required for SMC proliferation in vitro and in vivo and likely to be implicated in the initiation of collateral artery growth, the key signalling mediators regulating Egr1 expression specifically in proliferating vascular SMCs were investigated. Northern blot and Western blot analysis revealed a strong up-regulation of Egr1 within 2 hours of stimulation with PDGF-AB and FGF-2. These two potent SMC mitogens involved in neointima formation were used to stimulate vascular SMCs not only to delineate the regulators of Egr1 expression but also to identify additional key mediators of SMC proliferation. FGF-2 but not PDGF-AB led to a drastic reduction of desmin amount in proliferating SMCs, correlating closely with the phenotypic modulation of SMCs in vivo. Both growth factors triggered a dramatic increase in DNA-synthesis rate with a concomitant loss of p27 exp Kip1. Stimulation with PDGF-AB and FGF-2 triggered a rapid and transient activation of PDGFRβ and FGFR1 respectively, thus providing the basis for activation of down-stream targets. Analysis of an array of signalling pathways demonstrated a strong activation of the Ras-Raf-MEK-ERK cascade in response to both factors as measured by the level of phosphorylation of prominent members MEK, ERK1/2 and c-Myc. SAPK/JNK and p38, which also belong to the superfamily of MAP kinases, did not become activated following stimulation with either PDGF-AB or FGF-2. The analysis of various PKC isoforms identified PKCδ and PKCθ to be the key mediators of PDGF-AB- and FGF-2-induced mitogenesis in proliferating SMCs. Whereas PDGF-AB potently stimulated PKB/Akt with concomitant GSK3β phosphorylation, FGF-2-induced inactivation of GSK3β was independent of PKB/Akt. Specific inhibition in order to evaluate the contribution of individual pathways to Egr1 expression and vascular SMC proliferation revealed that inhibition of the Raf-MEK-ERK module by UO126 completely abolished DNA-synthesis and Egr1 expression without a compensation by alternative pathways. Surprisingly, inhibition of PI3K led to a switch to the mitogenic RafMEK-ERK signalling cascade which resulted in an augmented Egr1 expression. In conclusion, in porcine vascular SMCs, activation of the Ras-Raf-MEK-ERK signalling module appears to be the main prerequisite for Egr1 expression and DNA synthesis induction in response to PDGF-AB and FGF-2 whereas related kinases SAPK/JNK and p38 play no significant role. Inhibition of the PI3K-Akt cascade represents an alternative way to activate ERK1/2 and induce Egr1 expression. Whereas MEK is the central regulator of mitogenic effects in proliferating vascular SMCs, the PI3K-Akt pathway most likely exerts survival function. Inactivation of MEK by its specific inhibitors identified hyperphosphorylation as ayet unknown mechanism of kinase inhibition.
In dieser Arbeit wurde der chemische Ozonverlust in der arktischen Stratosphäre über elf Jahre hinweg, zwischen 1991 und 2002, mit Hilfe der so genannten "Ozon-Tracer Korrelationstechnik" (TRAC), untersucht. Bei dieser Methode werden Korrelationen zwischen Ozon und langlebigen Spurenstoffen im Verlauf des Winters im Polarwirbels beobachtet und so der jährliche akkumulierte Ozonverlust berechnet. Die Ergebnisse dieser Arbeit basieren im wesentlichen auf Messdaten der Satelliteninstrumente: HALOE (Halogen Occultation Experiment) auf UARS (Upper Atmosphere Research Satellite) und ILAS (Improved Limb Atmospheric Spectrometer) Instrument auf ADEOS (Advanced Earth Observing Satellite). Das HALOE Instrument misst seit Oktober 1991 kontinuierlich alle zwei bis drei Monate für einige Tage in höheren nördlichen Breiten. ILAS lieferte ausschließlich für den Winter 1996-97 Messungen, die über sieben Monate hinweg in hohen Breiten aufgenommen wurden. Aufgrund der eingeführten Erweiterungen und Verbesserungen der Methode in dieser Arbeit, konnte die Methode anhand einer detaillierten Studie für den Winter 1996-97 validiert werden. Die ILAS Messreihe wurde dazu verwendet, erstmals die Untersuchung der zeitlichen Entwicklung von Ozon-Tracer Korrelationen kontinuierlich für die gesamte Lebensdauer des Polarwirbels durchzuführen. Dabei wurden auch Korrelationen während der Bildung des Wirbels untersucht und im Besonderen mögliche Mischungsvorgänge zwischen Wirbelluft und Luftmassen außerhalb des Wirbels. Ausserdem wurde ein Vergleich der Ergebnisse von ILAS und HALOE Messdaten durchgeführt und Unterschiede in den Ergebnissen tiefgreifend analysiert. Basierend auf HALOE Messungen konnte die erweiterte TRAC Methode über elf Jahren hinweg angewendet werden. Damit war erstmals eine konsistente Analyse von Ozonverlust und Chloraktivierung über diesen Zeitraum möglich. Die Erweiterungen führten zu einer Verringerung und genauen Quantifizierung von Unsicherheiten der Ergebnisse. Ein deutlicher Zusammenhang zwischen meteorologischen Bedingungen, Chloraktivierung und dem chemischen Ozonverlust wurde deutlich. Weiterhin zeigte sich eine Abhängigkeit zwischen den meteorologischen Bedingungen und der Homogenität des Ozonverlustes innerhalb eines Winters, sowie der mögliche Einfluss von horizontaler Mischung auf Luftmassen in einem schwach ausgeprägten Polarwirbel. In dieser Arbeit wurde eine positive Korrelation zwischen den über die gesamte Lebensdauer des Wirbels auftretenden möglichen PSC-Flächen und den akkumulierten Ozonverlusten für die elf untersuchten Jahre deutlich. Es konnte darüber hinaus gezeigt werden, dass der Ozonverlust von deutlich mehr Einflüssen als nur von der Fläche möglichen PSC Auftretens bestimmt wird, sondern zum Beispiel von der Stärke der Sonneneinstrahlung abhängt. Außerdem lassen sich Auswirkungen von Vulkanausbrüchen, wie zum Beispiel im Jahr 1991 der des Mount Pinatubo, identifizieren.
Resistive Plate Chambers (RPCs) are gaseous parallel plate avalanche detectors that implement electrodes made from a material with a high volume resistivity between 10 high 7 and 10 high 12 omega cm. Large area RPCs with 2mm single gaps operated in avalanche mode provide above 98% efficiency and a time resolution of around 1 ns up to a flux of several kHz/cm high 2. These Trigger RPCs will, as an example, equip the muon detector system of the ATLAS experiment at CERN on an area of 3650 m high 2 and with 355.000 independent read out channels. Timing RPCs with a gas gap of 0.2 to 0.3mm are widely used in multi gap configurations and provide 99% efficiency and time resolution down to 50 ps. While their performance is comparable to existing scintillator-based Time-Of-Flight (TOF) technology, Timing RPCs feature a significantly, up to an order of magnitude, lower price per channel. They will for example equip the 176 m high 2 TOF barrel of the ALICE experiment at CERN with 160.000 independent read out cells. RPCs were originally operated in streamer mode providing large signals which simplifies readout electronics and gap uniformity requirements. However, high rate applications and detector aging issues made the operation in avalanche mode popular. This was also facilitated by the development of new highly quenching C2F4H2-based gas mixtures with small contents of SF6. While the physics of streamers is difficult to study, the avalanche mode opened the possibility for a detailed simulation of the detector physics processes in RPCs. Even though RPCs were introduced in the early eighties and have been (will be) used in experiments, there are still disagreements about the explanation of several aspects of the RPC performance. The high efficiency of single gap RPCs would require a large ionization density of the used gases, which according to some authors contradicts measurements. Even in the case of a large ionization density the gas gain has to be extremely large, in order to arrive at the observed RPC efficiency. This raises other questions: A very strong space charge effect is required to explain the observed small avalanche charges around 1 pC. Doubts have been raised whether an avalanche can progress under such extreme conditions without developing into a streamer. To overcome these difficulties, other processes, like the emission of an electron from the cathode, were suggested. Moreover, the shape of measured charge spectra of single gap RPCs differs largely from what is expected from the statistics of the primary ionization and the avalanche multiplication. In this thesis we discuss the detector physics processes of RPCs, from the primary ionization and the avalanche statistics to the signal induction and the read out electronics. We present Monte-Carlo simulation procedures that implement the described processes. While the fundament of the described model and some results were already published elsewhere [1], the subject of this thesis is the implementation of the space charge effect. We present analytic formulas for the electrostatic potential of a point charge in the gas gap of an RPC. These formulas were developed in collaboration with the University of Graz [2] and were published in [3, 4]. The simulation model presented in [1] is completed by the dynamic calculation of the space charge field using these formulas. Since the gas parameters like drift velocity and the Townsend and attachment coefficients depend on the electric field, they are calculated dynamically as well. The functional dependence of these parameters on the field is obtained with the simulation programs MAGBOLTZ and IMONTE. For the primary ionization parameters, we use the values that are predicted by the program HEED. While the described procedure only simulates the longitudinal avalanche development towards the anode of the RPC, we also present more dimensional models that allow a careful study of the transverse repulsive and attractive forces of the space charge fields, and of the consequences for the avalanche propagation. We shall show that the efficiencies of single gap Timing RPCs is indeed explained by the high primary ionization density (about 9.5 /cm as predicted by HEED) and a large effective Townsend coefficient (around 113 /mm as predicted by IMONTE). We show that the space charge field reaches the same magnitude as the applied electric field in avalanches at large gas gain. This strong space charge effect effectively suppresses large values for the avalanche charges. The shape of the simulated charge spectra is very similar to the measurements. Also the simulated average charges are close to the experimental results. RPCs are operated in a strong space charge regime over a large range of applied voltage, contrary to wire chambers. We apply only standard detector physics simulations to RPCs. The performance of Timing and Trigger RPCs is well reproduced by our simulations. The results concerning the space charge effect were presented and discussed at the 'RPC 2001' workshop [5] and on the '2002 NSS/MIC' conference [6].
Gegenstand dieser Arbeit sind Eigenschaften angeregter hadronischer Materie sowie physikalische Systeme, in denen diese Materie auftritt bzw. produziert wird. Die Beschreibung der stark wechselwirkenden Materie erfolgt in einem hadronischen, chiral-symmetrischen SU(3)L x SU(3)R Modell, welches die Saturierungseigenschaften von Kernmaterie und die Eigenschaften von Atomkernen reproduziert. Die Untersuchung heißer und dichter unendlicher hadronischor Materie zeigt, dass das vom Modell vorhergesagte Phasendiagramm stark von den Kopplungen der Baryonenresonanzen abhängt. Für kalte hadronische Materie ergibt die Einbeziehung des Baryonendekupletts und die Freiheit in deren Vektorkopplungen eine sehr große Bandbreite an verschiedenen Zustandsgleichungen. Für heiße hadronische Materie mit verschwindendem baryochemischen Potential zeigt sich ebenfalls eine starke Abhängigkeit der Eigenschaften hadronischer Materie von der Ankopplung der baryonischen Resonanzen. Es werden drei verschiedene Parametrisierungen betrachtet. Das resultierende Phasenübergangsverhalten variiert von einem "Crossover" über einen schwachen, zu einem doppelten Phasenübergang erster Ordnung. Es zeigt sich jedoch, dass die beobachteten Eigenschaften von Neutronensternen die Unbestimmtheit bzgl. der Vektorkopplung dieser Freiheitsgrade und damit der Zustandsgleichung deutlich verringern. Das Raum-Zeit Verhalten relativistischer Schwerionenkollisionen bei SPS- und RHIC-Energien wird mittels einer hydrodynamischen Simulation unter Benutzung der chiralen Zustandsgleichungen untersucht. Dabei spiegelt sich das unterschiedliche Phasenübergangsverhalten deutlich im Ausfrierverhalten der hadronischen Materie wider. Die im chiralen Modell berechneten Teilchenzahlverhältnisse werden mit den aus Schwerionenkollisionen von AGS- bis RHIC-Energien erhaltenen experimentellen Daten verglichen. Dabei zeigt sich, dass die verschiedenen Parametersätze des chiralen Modells und die Rechnungen für ein nichtwechselwirkendes, ideales Hadronengas eine ähnlich gute Beschreibung der gemessenen Weite liefern. Die deduzierten Ausfrierwerte für die Temperatur sind sensitiv auf das Phasenübergangsverhalten und liegen unterhalb der jeweiligen kritischen Temperatur. Die vorhergesagten Ausfriermassen sind in allen Parametrisierungen sehr ähnlich mit Abweichungen bis zu 15% von den entsprechenden Vakuumwerten. Die Untersuchung der Eigenschaften von Vektormesonen in dichter Materie erfolgt in der Mittleren-Feld- und in der HartreeNäherung. Hierbei zeigt sich eine signifikante Reduzierung der Teilchenmassen durch Vakuumpolarisationseffekte.
In summary, the cooled heavy-ion beams of the ESR storage ring offer excellent experimental conditions for a precise study of the effects of QED in the groundstate of high-Z one- and two-electron ions. This has been demonstrated within the series of experiments conducted at the electron cooler device as well as at the gasjet target. In this work we have used a recently developed experimental approach to obtain the first direct measurement of the two-electron contributions to the ground state binding energy of helium-like uranium. By employing our method, all one-electron contributions to the binding energy such as finite-nuclear size corrections and the one-electron self energy cancel out completely. Note, this is a distinctive feature of this particular kind of QED test and is in contrast to all other tests of bound state QED for high-Z ions such as 1s Lamb shift (in one-electron systems), g-factor of bound electrons, or hyperfine splitting. Compared to former investigations conducted at the superEBIT in Livermore we could already substantially improve the statistical accuracy and extend studies to the higher-Z regime. Moreover, our result has reached a sensitivity on specific two-electron QED contributions. Our value agrees with the theoretical predictions within the experimental uncertainty. Similar to the superEBIT experiment possible sources of systematic errors are essentially eliminated and the final result is limited only by counting statistics. For the case of the 1s Lamb shift in hydrogen-like uranium, the achieved accuracy of +- 4.2 eV is a substantial improvement by a factor of 3 compared to the most precise value up to now [44] (see Fig. 5.6). Our result already provides a test of the first-order QED contributions at the 1.5% level and only a slight improvement is required in order to achieve a sensitivity to QED contributions beyond first-order SE and VP.
The objective of this study is the avifauna of the North American Green River Formation. Five new Green River bird species as well as several new specimens of already known species are described. * Galliformes: Gallinuloides wyomingensis EASTMAN 1900 A second specimen of the galliform Gallinuloides wyomingensis could be identified. Gallinuloides wyomingensis resembles closely Paraortygoides MAYR 1999, which is known from Messel and the London Clay. The new specimen exhibits characters such as a cup-like cotyla scapularis of the coracoid that clearly indicate that Gallinuloides is a stem-group representative of galliforms. * Eurypygidae: Eoeurypyga olsoni gen. et sp. nov. Eoeurypyga is the only fossil representative of the Eurypygidae. Eoeurypyga and the modern sunbittern Eurypyga helias share the typical long bill, the caudally situated neck and the elongated vertebrae cervicales. Additional synapomorph characters were found. The new species indicates a North American origin for the Eurypygidae. * Messelornithidae: Messelornis nearctica HESSE 1992 The original description of Messelornis nearctica was based on a single specimen. Ten new specimens, described in this study, reveal additional information. Messelornis nearctica shows the same large intraspecific size range as Messelornis cristata HESSE 1988 from Messel, the type species of the genus. * Apodidae: Wyomingcypselus pohli gen. nov. sp. nov. Wyomingcypselus pohli is the first described fossil apodiform bird for North American. Due to characters of the wing, especially the position of the processus musculi extensor metacarpi radialis, Wyomingcypselus is referrred to the Apodidae. * Trogoniformes: unnamed species The Green River birds include a poorly preserved, but apparently heterodactyl specimen, which also resembles trogons in overall appearance. * Primobucconidae: Primobucco mcgrewi BRODKORB 1970 Originally, Primobucco mcgrewi was only known from a partial skeleton consisting of the right wing. Three new specimens could be referred to the species. Primobucco mcgrewi clearly exhibits an anisodactyl foot, which makes the assignment to the zygodactyl Bucconidae highly doubtful. Instead, Primobucco mcgrewi is referrred to the Coraciiformes s.s. Thus, Primobucconidae are the first New World representatives of stem-group Coraciiformes. * ?Leptosomidae: Plesiocathartes wyomingensis sp. nov. and Plesiocathartes major sp. nov. Plesiocathartes wyomingensis and Plesiocathartes major represent the first North American record for the genus. Both species exhibit the diagnostic characters for the Leptosomidae as listed by MAYR (2002a, b). * Primoscenidae: Eozygodactylus americanus gen. et sp. nov. and unnamed species Eozygodactylus americanus is the first North American member of this taxon. Both Eozygodactylus americanus and the unnamed species show the zygodactyl foot and the large processus intermetacarpalis of the carpometacarpus, which are typical for Primoscendiae. Due to differences mainly of the humerus, it was placed in a new genus. Besides the descriptionof new species, the avifauna of the Green River Formatin was studied and compared with the avifauna of Messel. The formations show a high concordance, more than 60 % of the Green River taxa also occur in Messel. Such a high concordance is also found for mammals. This is due to the existence of two landbridges, the Thule landbridge and the de Geer landbridge, between Europe and North America during the early Eocene.
Zahnwale sind die einzige Säugetiergruppe, die umfassend an ein Leben im Wasser angepasst ist und dabei ein aktives Sonarsystem zur Orientierung nutzt. Wahrscheinlich produzieren alle Zahnwalarten sonische oder ultrasonische Klicklaute, deren Echos die Tiere zu einem drei-dimensionalen "akustischen Bild" zusammensetzen. Im Gegensatz zu den meisten anderen Säugetieren produzieren Zahnwale diese Laute im Nasen-Komplex durch einen pneumatisch betriebenen Mechanismus. Jedoch spielt auch der Kehlkopf dabei eine wichtige Rolle, indem er den nötigen Luftdruck in der Nase erzeugt. Die Ergebnisse werden in Bezug auf die physikalischen Voraussetzungen eines Bio-Sonars in einer aquatischen Umwelt interpretiert. Um die morphologischen Eigenschaften (Struktur, Form, Topographie) der Organe im Kopf verschiedener Zahnwalarten vollständig zu erfassen, wurden diese mittels Computertomographie und Magnetresonanztomographie gescannt. Daraufhin wurden die Köpfe makroskopisch präpariert und histologische Schnitte von Gewebeproben angefertigt. Schließlich wurden die Ergebnisse durch digitale dreidimensionale Rekonstruktionen vervollständigt. Diese Studie basiert zum größten Teil auf der Untersuchung von Schweinswalen (Phocoena phocoena) und Pottwalen (Physeter macrocephalus). Zum Vergleich wurden fetale und postnatale Individuen anderer Zahnwalarten herangezogen wie Delphinartige (Delphinus delphis, Stenella attenuata, Tursiops truncatus), Flussdelphinartige (Pontoporia blainvillei, Inia geoffrensis) und der Zwergpottwal (Kogia breviceps). Im Allgemeinen konnte durch die morphologischen Daten dieser Studie die einheitliche "phonic lips-Hypothese der Schallproduktion bei Zahnwalen, wie sie von Cranford, Amundin und Norris [J. Morphol. 228 (1996): 223-285] aufgestellt wurde, bestätigt werden. Diese Hypothese beschreibt eine ventilartige Struktur in der Nasenpassage, den sogenannten "monkey lips/dorsal bursae complex" (MLDB) als Schallgenerator. Der pneumatische Mechanismus lässt die beiden Hälften des MLDB aufeinanderschlagen und erzeugt damit die initiale Schallschwingung im Gewebe ("phonic lips"). Diese Vibration wird über die Melone, einen großen Fettkörper in der vorderen Nasenregion der Zahnwale, fokussiert und in das umgebende Wasser übertragen. Die akzessorischen Nasensäcke und spezielle Schädel- und Bindegewebestrukturen können zu der Fokussierung beitragen. Obwohl die Echolotsignale der Schweinswale sehr spezialisiert zu sein scheinen, weisen die Übereinstimmungen in der Topographie und in der Form der Nasenstrukturen im Vergleich zu Delphinen und Flussdelphinartigen (Pontoporia und Inia) auf eine ganz ähnliche Funktion der Nase bezüglich der Produktion und Emission von Echolotschall hin. Allerdings gibt es einige anatomische Besonderheiten im Nasenkomplex des Schweinswals, welche die besondere Pulsstruktur der Sonarsignale erklären könnte. Diese werden in der Dissertation diskutiert. Bei einem Vergleich der Nasenmorphologie der Pottwale einerseits und der nicht-pottwalartigen Zahnwale andererseits fällt vor allem der Grad der Asymmetrie ins Auge. Im Gegensatz zu dem oben für Delphine und Schweinswale beschrieben Mechanismus betreiben Pottwale die Schallproduktion an den "monkey lips" mit Luft, die im rechten Nasengang unter Druck gesetzt wird (und nicht im nasopharyngealen Raum). Zudem könnte durch Änderung des Luftvolumens im rechten Nasengang die Schalltransmission zwischen den Fettkörpern, und somit die Schallemission, kontrolliert werden. In diesem theoretischen Szenario fungiert der breite rechte Nasengang als eine Art "akustische Schranke", welche zwischen zwei verschiedenen Modi der Klickproduktion wechselt: Der erste Modus mit luftgefülltem Nasengang führt zur Produktion der Kommunikationsklicks ("coda clicks") und der zweite Modus zur Aussendung von Echolotklicks, wenn der Nasengang kollabiert ist. Somit scheinen die zentrale Position und die nahezu horizontale Orientierung des rechten Nasengangs im Kopf der Pottwale als Schnittstelle (Schranke) zwischen den beiden großen Fettkörpern mit dem Mechanismus der Schallproduktion bei veränderten Luftvolumina korreliert zu sein. Die hier beschriebenen und andere Ergebnisse dieser Dissertation deuten darauf hin, dass die Gestalt und das Ausmaß der Nasenasymmetrie nicht mit der systematischen Zugehörigkeit der jeweiligen Art korrelieren, sondern durch den jeweiligen Typus des Sonarsystems als Ausdruck einer bestimmten ökologischen Anpassung bedingt sind. Bei Zahnwalen ist der Kehlkopf charakterisiert durch eine rostrale Verlängerung des Kehldeckels und der beiden Stellknorpel, die ein gänseschnabelartiges Rohr bilden, das von einem starken Sphinktermuskel umrundet und dabei in Position gehalten wird. Auf diese Weise ist das Atemrohr vollständig vom Digestionstrakt getrennt. Aus anatomischer Sicht ist es wahrscheinlich, dass die Schallerzeugung bei Zahnwalen durch eine Kolbenbewegung des Kehlkopfes in Richtung der Choanen zustande kommt, wodurch der Luftdruck im Nasenbereich erzeugt wird. Die Kontraktion des Sphinktermuskels als einem muskulösen Schlauch erzeugt wahrscheinlich die größte Kraft für diese Kolbenbewegung. Jedoch dürften die Muskelgruppen, die den Kehlkopf und das Zungenbein am Unterkiefer und an der Schädelbasis aufhängen, signifikant zur Druckerhöhung beitragen.
Hepatitis E virus (HEV) is a positive-stranded RNA virus with a 7.2 kb genome that is capped and polyadenylated. The virus is currently unclassified : the organisation of the genome resembles that of the Caliciviridae but sequence analyses suggest that it is more closely related to the Togaviridae. HEV is an enterically transmitted virus that causes both epidemics and sporadic cases of acute hepatitis in many countries of Asia and Africa but only rarely causes disease in more industrialised countries. Initially the virus was believed to have a limited geographical distribution. However, serological studies suggest that that HEV may be endemic also in the United states and Europe even though it infrequently causes overt disease in these countries. Many different animal species worldwide recently have been shown to have antibodies to HEV suggesting that hepatitis E may be zoonotic. Although two related strains have been experimentally transmitted between species, direct transmission from animal to a human has not been documented. Our main objective in this study is to evaluate the suitability of current available HEV antibody assays for use in low-endemicity areas such as in Germany. Methods: We selected sera on the basis of at least borderline reactivity in the routinely used Abbot EIA. Most were tested as part of routine screening of long-term expatriates in endemic countries. The following assays (recombinant antigens : ORF2 and ORF3) were used: Abbot EIA, Genelabs ELISA, Mikrogen recomBlot and a 'Prototype' DSL-ELISA. We observed a wide range of sensitivity ( average of 56.8%) and specificity ( an average of 61.4%) in these used assays. These results implies that , these assays might be unreliable for detection of HEV infection in areas where hepatitis E is not endemic. However, most anti- HEV assays have not been correlated with the HEV RNA determined by reverse transcription. Many of these unexpected results and discrepancies can be alluded to the following reasons: I. The choice and the size of the HEV antigen. II. Duration of the antibody persistence III. A cross reactivity with different agent IV. Due to geographic species V. A low sensitivity of the available assays. VI. And infection with non-pathogenic HEV strain. (zoonotic strain?). We therefore suggest that, further studies will be required to improve the sensitivity and specificity of the available commercial assays on the market.