Refine
Has Fulltext
- no (376) (remove)
Year of publication
- 2024 (1)
- 2023 (8)
- 2022 (5)
- 2021 (5)
- 2020 (5)
- 2019 (4)
- 2018 (11)
- 2017 (12)
- 2016 (9)
- 2015 (13)
- 2014 (5)
- 2013 (17)
- 2012 (17)
- 2011 (7)
- 2010 (6)
- 2009 (11)
- 2008 (14)
- 2007 (15)
- 2006 (13)
- 2005 (17)
- 2004 (7)
- 2003 (12)
- 2002 (12)
- 2001 (20)
- 2000 (20)
- 1999 (32)
- 1998 (23)
- 1997 (20)
- 1996 (19)
- 1995 (5)
- 1994 (6)
- 1993 (1)
- 1992 (3)
Document Type
- Doctoral Thesis (376) (remove)
Is part of the Bibliography
- yes (376)
Keywords
- Klimawandel (2)
- biophysics (2)
- climate change (2)
- electronic structure (2)
- mechanobiology (2)
- 3d metals (1)
- Astrophotonics (1)
- Astrophotonik (1)
- Atmosphärendynamik (1)
- Auger electron spectroscop (1)
Institute
- Institut für Physik und Astronomie (376) (remove)
Über nichtelastische Kollisionen und ihren Einfluß auf die Strukturbildung in planetaren Ringen
(1996)
Wachsende Filamentbündel
(2006)
Vlijanie solneécnoj aktivnosti na prozraécnost§ atmosfery i optiéceskie svojstva açerozolja
(2005)
Unveiling the Local Universe
(2023)
Untersuchungen kinematischer und dynamisch konsistenter Dynamomodelle in sphärischer Geometrie
(1997)
Untersuchung von InxGA1-xAS / GaAs- Schichtsystemen mit Röntgenbeugung unter streifendem Einfall
(1996)
Thermisch induzierte Strukturumwandlungen von Langmuir-Blodgett-Multischichten aus Fettsäuresalzen
(1996)
Theorie der differentiellen Rotation der Sonne und ihrer magnetfeldbedingten Torsionsschwingungen
(1996)
One of the tremendous discoveries by the Cassini spacecraft has been the detection of propeller structures in Saturn's A ring. Although the generating moonlet is too small to be resolved by the cameras aboard Cassini, its produced density structure within the rings, caused by its gravity can be well observed. The largest observed propeller is called Blériot and has an azimuthal extent over several thousand kilometers. Thanks to its large size, Blériot could be identified in different images over a time span of over 10 years, allowing the reconstruction of its orbital evolution. It turns out that Blériot deviates considerably from its expected Keplerian orbit in azimuthal direction by several thousand kilometers. This excess motion can be well reconstructed by a superposition of three harmonics, and therefore resembles the typical fingerprint of a resonantly perturbed body. This PhD thesis is directed to the excess motion of Blériot. Resonant perturbations are a known for some of the outer satellites of Saturn. Thus, in the first part of this thesis, we seek for suiting resonance candidates nearby the propeller, which might explain the observed periods and amplitudes. In numeric simulations, we show that indeed resonances by Prometheus, Pandora and Mimas can explain the libration periods in good agreement, but not the amplitudes. The amplitude problem is solved by the introduction of a propeller-moonlet interaction model, where we assume a broken symmetry of the propeller by a small displacement of the moonlet. This results in a librating motion the moonlet around the propeller's symmetry center due to the non-vanishing accelerations. The retardation of the reaction of the propeller structure to the motion of the moonlet causes the propeller to become asymmetric. Hydrodynamic simulations to test our analytical model confirm our predictions. In the second part of this thesis, we consider a stochastic migration of the moonlet, which is an alternative hypothesis to explain the observed excess motion of Blériot. The mean-longitude is a time-integrated quantity and thus introduces a correlation between the independent kicks of a random walk, smoothing the noise and thus makes the residual look similar to the observed one for Blériot. We apply a diagonalization test to decorrelated the observed residuals for the propellers Blériot and Earhart and the ring-moon Daphnis. It turns out that the decorrelated distributions do not strictly follow the expected Gaussian distribution. The decorrelation method fails to distinguish a correlated random walk from a noisy libration and thus we provide an alternative study. Assuming the three-harmonic fit to be a valid representation of the excess motion for Blériot, independently from its origin, we test the likelihood that this excess motion can be created by a random walk. It turns out that a non-correlated and correlated random walk is unlikely to explain the observed excess motion.
The contribution of the warm-hot intergalactic medium to the CMB anisotropies and distortions
(2013)
Mechanosensation is a fundamental biological process that provides the basis for sensing touch and pain as well as for hearing and proprioception. A special class of ion-channel proteins known as mechanosensitive proteins convert the mechanical stimuli into electrochemical signals to mediate this process. Mechanosensitive proteins undergo conformational changes in response to mechanical force, which eventually leads to the opening of the proteins' ion channel. Mammalian mechanosensitive proteins remained a long sought-after mystery until 2010 when a family of two proteins - Piezo1 and Piezo2 - was identifed as mechanosensors [1]. The cryo-EM structures of Piezo1 and Piezo2 protein were resolved in the last years and reveal a propeller-shaped homotrimer with 114 transmembrane helices [2, 3, 4, 5]. The protein structures are curved and have been suggested to deform the surrounding membrane into a nano-dome, which mechanically responds to membrane tension resulting from external forces [2]. In this thesis, the conformations of membrane-embedded Piezo1 and Piezo2 proteins and their tension-induced conformational changes are investigated using molecular dynamics simulations. Our coarse-grained molecular dynamics simulations show that the Piezo proteins induce curvature in the surrounding membrane and form a stable protein-membrane nano-dome in the tensionless membrane. These membrane-embedded Piezo proteins, however, adopt substantially less curved conformations in our simulations compared to the cryo-EM structures solved in detergent micelles, which agrees with recent experimental investigations of the overall Piezo nano-dome shape in membrane vesicles [6, 7, 8]. At high membrane tension, the Piezo proteins attain nearly planar conformations in our simulations. Our systematic investigation of Piezo proteins under different membrane tensions indicates a half-maximal conformational response at membrane tension values rather close to the experimentally suggested values of Piezo activation [9, 10]. In addition, our simulations indicate a widening of the Piezo1 ion channel at high membrane tension, which agrees with the channel widening observed in recent nearly flattened cryo-EM structures of Piezo1 in small membrane vesicles [11]. In contrast, the Piezo2 ion channel does not respond to membrane tension in our simulations. These different responses of the Piezo1 and Piezo2 ion channels in our simulations are in line with patch-clamp experiments, in which Piezo1, but not Piezo2, was shown to be activated by membrane tension alone [12].
Synchrotron-based angle-resolved time-of-flight electron spectroscopy for dynamics in dichalogenides
(2018)
Strukturuntersuchungen von organischen Multischichtsystemen mittels Röntgen- und Neutronenstreuung
(1998)
Strukturfaktoränderungen von GaAs und ZnSe unter dem Einfluss eines äußeren elektrischen Feldes
(1999)
Spectroscopy at the limit
(2018)
Shaping via binding
(2018)
Samarium hexaboride
(2018)