1335
1997
eng
preprint
0
2007-07-04
--
--
Bifurcations in two-dimensional Rayleigh-Bénard convection
Two-dimensional bouyancy-driven convection in a horizontal fluid layer with stress-free boundary conditions at top and bottom and periodic boundary conditions in the horizontal direction is investigated by means of numerical simulation and bifurcation-analysis techniques. As the bouyancy forces increase, the primary stationary and symmetric convection rolls undergo successive Hopf bifurcations, bifurcations to traveling waves, and phase lockings. We pay attention to symmetry breaking and its connection with the generation of large-scale horizontal flows. Calculations of Lyapunov exponents indicate that at a Rayleigh number of 2.3×105 no temporal chaos is reached yet, but the system moves nonchaotically on a 4-torus in phase space.
urn:nbn:de:kobv:517-opus-14534
1453
-
Egbert Zienicke
Norbert Seehafer
Fred Feudel
NLD Preprints
42
Physik
open_access
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1335/nld_preprint_042_zienicke_etal.pdf
6863
2014
eng
doctoralthesis
0
2014-07-16
--
2014-07-07
Advances in experimental methods to probe surface relief grating formation mechanism in photosensitive materials
Entstehung von Oberflächengittern in lichtempfindlichen Materialien
When azobenzene-modified photosensitive polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the electric field vector distribution resulting in the formation of surface relief grating (SRG). The exact correspondence of the electric field vector orientation in interference pattern in relation to the presence of local topographic minima or maxima of SRG is in general difficult to determine. In my thesis, we have established a systematic procedure to accomplish the correlation between different interference patterns and the topography of SRG. For this, we devise a new setup combining an atomic force microscope and a two-beam interferometer (IIAFM). With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. To validate our results, we have compared two photosensitive materials named in short as PAZO and trimer. This is the first time that an absolute correspondence between the local distribution of electric field vectors of interference pattern and the local topography of the relief grating could be established exhaustively. In addition, using our IIAFM we found that for a certain polarization combination of two orthogonally polarized interfering beams namely SP (↕, ↔) interference pattern, the topography forms SRG with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures below diffraction limit with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We have also probed for the stresses induced during the polymer mass transport by placing an ultra-thin gold film on top (5–30 nm). During irradiation, the metal film not only deforms along with the SRG formation, but ruptures in regular and complex manner. The morphology of the cracks differs strongly depending on the electric field distribution in the interference pattern even when the magnitude and the kinetic of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. The neutron reflectivity measurements of the metal/polymer interface indicate the penetration of metal layer within the polymer resulting in the formation of bonding layer that confirms the transduction of light induced stresses in the polymer layer to a metal film.
Azobenzolhaltige Polymere gehören zu einer Klasse funktionaler Materialien, bei denen durch ein äußeres Strahlungsfeld eine starke mechanische Reaktion ausgelöst werden kann. Durch die Bindung an das Polymerrückgrat können die Azobenzole, die unter UV-Belichtung eine Photoisomerisierung ausführen, was zum Teil drastische Effekte zur Folge hat. Unter Belichtung mit Intensitätsmustern, d.h. mit räumlich variierender Verteilung der Polarisation oder der Intensität des einfallenden Lichts verändert sich die Topographie der azobenzolhaltigen Filme, was zur Bildung von Oberflächengittern (engl. Surface Relief Gratings, SRG) führt. In dieser Arbeit wurde eine neue Methode vorgeschlagen, bei der das Verhalten elastischer/morphologischer Eigenschaften unter verschiedenen Belichtungsbedingungen, d.h. mit unterschiedlicher Verteilung der Polarisation und der Intensität in situ lokal als Funktion der Position entlang der SRG aufgenommen werden kann. Außerdem wurde hier vorgeschlagen, opto-mechanische Spannungen, die innerhalb der photosensitiven Polymerfilme während der Belichtung entstehen, mit Hilfe dünner aufgebrachter metallischen Schichten abzubilden und zu analysieren.
urn:nbn:de:kobv:517-opus-71213
7121
UV 5400
UV 7000
CC-BY - Namensnennung 4.0 International
Nataraja Sekhar Yadavalli
deu
uncontrolled
Azobenzolhaltige Polymerfilme
deu
uncontrolled
Oberflächengitter
deu
uncontrolled
In-situ Rasterkraftmikroskopie
deu
uncontrolled
Opto-mechanische Spannungen
deu
uncontrolled
Metall/Graphen/Polymer Grenzfläch
eng
uncontrolled
azobenzene polymer films
eng
uncontrolled
surface relief grating
eng
uncontrolled
in-situ atomic force microscopy
eng
uncontrolled
opto-mechanical stresses
eng
uncontrolled
metal/polymer interfaces
Physik
open_access
Institut für Physik und Astronomie
Universität Potsdam
Universität Potsdam
https://publishup.uni-potsdam.de/files/6863/yadavalli_diss.pdf
1325
1997
eng
preprint
0
2007-06-29
--
--
Characterizing the dynamics of stochastic bistable systems by measures of complexity
The dynamics of noisy bistable systems is analyzed by means of Lyapunov exponents and measures of complexity. We consider both the classical Kramers problem with additive white noise and the case when the barrier fluctuates due to additional external colored noise. In case of additive noise we calculate the Lyapunov exponents and all measures of complexity analytically as functions of the noise intensity resp. the mean escape time. For the problem of fluctuating barrier the usual description of the dynamics with the mean escape time is not sufficient. The application of the concept of measures of complexity allows to describe the structures of motion in more detail. Most complexity measures sign the value of correlation time at which the phenomenon of resonant activation occurs with an extremum.
urn:nbn:de:kobv:517-opus-14556
1455
-
Annette Witt
Alexander Neiman
Jürgen Kurths
NLD Preprints
36
Physik
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1325/nld_preprint_036_witt_etal.pdf
1282
1996
eng
preprint
0
2007-06-13
--
--
Reconstruction of grand minima of solar activity from Delta 14 C data : linear and nonlinear signal analysis
Using a special technique of data analysis, we have found out 34 grand minima of solar activity obtained from a 7,700 years long Δ14C record. The method used rests on a proper filtering of the Δ14C record and the extrapolation of verifiable results for the later history back in time. Additionally, we use a method of nonlinear dynamics, the recurrence rate, to back up the results. Our findings are not contradictory to the record of solar maxima resp. minima by Eddy [5], but constitute a considerable extension. Hence, it has become possible to look closer at the validity of models. This way, we have tested several models for solar activity, esp. the model of Barnes et al. [1]. There are hints for that the grand minima might solely be driven by the 209 year period found in the Δ14C record.
urn:nbn:de:kobv:517-opus-14083
1408
-
Henning Voss
Jürgen Kurths
Udo Schwarz
NLD Preprints
28
Physik
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1282/nld_preprint_028_voss_etal.pdf
1365
1998
eng
preprint
0
2007-07-31
--
--
Nonlinear interaction of Farley-Buneman waves
The nonlinear interaction of waves excited by the modified two-stream instability (Farley-Buneman instability) is considered. It is found that, during the linear stage of wave growth, the enhanced pressure of the high-frequency part of the waves locally generates a ponderomotive force. This force acts on the plasma particles and redistributes them. Thus an additional electrostatic polarization field occurs, which influences the low-frequency part of the waves. Then, the low-frequency waves also cause a redistribution of the high-frequency waves. In the paper, a self-consistent system of equations is obtained, which describes the nonlinear interaction of the waves. It is shown that the considered mechanism of wave interaction causes a nonlinear stabilization of the high-frequency waves’ growth and a formation of local density structures of the charged particles. The density modifications of the charged particles during the non-linear stage of wave growth and the possible interval of aspect angles of the high-frequency waves are estimated.
urn:nbn:de:kobv:517-opus-14851
1485
-
Alexandra V. Volosevich
Claudia-Veronika Meister
NLD Preprints
52
Physik
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1365/nld_preprint_053_volosevich_meister.pdf
1309
1996
eng
preprint
0
2007-06-20
--
--
Absence of magnetohydrodynamic activity in the voltage-driven sheet pinch
We have numerically studied the bifurcation properties of a sheet pinch with impenetrable stress-free boundaries. An incompressible, electrically conducting fluid with spatially and temporally uniform kinematic viscosity and magnetic diffusivity is confined between planes at x1=0 and 1. Periodic boundary conditions are assumed in the x2 and x3 directions and the magnetofluid is driven by an electric field in the x3 direction, prescribed on the boundary planes. There is a stationary basic state with the fluid at rest and a uniform current J=(0,0,J3). Surprisingly, this basic state proves to be stable and apparently to be the only time-asymptotic state, no matter how strong the applied electric field and irrespective of the other control parameters of the system, namely, the magnetic Prandtl number, the spatial periods L2 and L3 in the x2 and x3 directions, and the mean values B¯2 and B¯3 of the magnetic-field components in these directions.
urn:nbn:de:kobv:517-opus-14328
1432
-
Norbert Seehafer
Egbert Zienicke
Fred Feudel
NLD Preprints
32
Physik
Nonlinearity, bifurcation, and symmetry breaking
Plasma dynamics and flow
Magnetohydrodynamics and plasmas (see also 52.30.Cv and 52.72.+v-in physics of plasmas)
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1309/nld_preprint_032_seehafer_etal.pdf
1343
1998
eng
preprint
0
2007-07-06
--
--
Resistivity profile and instability of the plane sheet pinch
The stability of the quiescent ground state of an incompressible, viscous and electrically conducting fluid sheet, bounded by stress-free parallel planes and driven by an external electric field tangential to the boundaries, is studied numerically. The electrical conductivity varies as cosh–2(x1/a), where x1 is the cross-sheet coordinate and a is the half width of a current layer centered about the midplane of the sheet. For a <~ 0.4L, where L is the distance between the boundary planes, the ground state is unstable to disturbances whose wavelengths parallel to the sheet lie between lower and upper bounds depending on the value of a and on the Hartmann number. Asymmetry of the configuration with respect to the midplane of the sheet, modelled by the addition of an externally imposed constant magnetic field to a symmetric equilibrium field, acts as a stabilizing factor.
urn:nbn:de:kobv:517-opus-14686
1468
-
Norbert Seehafer
Jörg Schumacher
NLD Preprints
44
Physik
Plasma dynamics and flow
Magnetohydrodynamics and plasmas (see also 52.30.Cv and 52.72.+v-in physics of plasmas)
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1343/nld_preprint_044_seehafer_schumacher.pdf
1333
1997
eng
preprint
0
2007-07-04
--
--
Squire‘s theorem for the magnetohydrodynamic sheet pinch
The stability of the quiescent ground state of an incompressible viscous fluid sheet bounded by two parallel planes, with an electrical conductivity varying across the sheet, and driven by an external electric field tangential to the boundaries is considered. It is demonstrated that irrespective of the conductivity profile, as magnetic and kinetic Reynolds numbers (based on the Alfvén velocity) are raised from small values, two-dimensional perturbations become unstable first.
urn:nbn:de:kobv:517-opus-14628
1462
-
Norbert Seehafer
Jörg Schumacher
NLD Preprints
40
Physik
Plasma dynamics and flow
Magnetohydrodynamics and plasmas (see also 52.30.Cv and 52.72.+v-in physics of plasmas)
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1333/nld_preprint_040_seehafer_schumacher.pdf
1314
1997
eng
preprint
0
2007-06-22
--
--
Nonlinear Galerkin methods for the 3D magnetohydrodynamic equations
The usage of nonlinear Galerkin methods for the numerical solution of partial differential equations is demonstrated by treating an example. We desribe the implementation of a nonlinear Galerkin method based on an approximate inertial manifold for the 3D magnetohydrodynamic equations and compare its efficiency with the linear Galerkin approximation. Special bifurcation points, time-averaged values of energy and enstrophy as well as Kaplan-Yorke dimensions are calculated for both schemes in order to estimate the number of modes necessary to correctly describe the behavior of the exact solutions.
urn:nbn:de:kobv:517-opus-14431
1443
-
Olaf Schmidtmann
Fred Feudel
Norbert Seehafer
NLD Preprints
35
Physik
open_access
Institut für Physik und Astronomie
Interdisziplinäres Zentrum für Dynamik komplexer Systeme
Universität Potsdam
https://publishup.uni-potsdam.de/files/1314/nld_preprint_035_schmidtmann_etal.pdf
6746
2014
deu
article
0
2014-03-14
--
--
Zur Anwendung des Skalarprodukts von Kraft und Weg auf reversible Prozesse (Druck-Volumen-Änderung, Dehnung, Elektrostatische Wechselwirkung, Hub)
To the application of the scalar product of force and displacement to reversible processes (pressure-volume change, elongation, electrostatic interaction, raising)
Wir schlagen einen allgemein anwendbaren Algorithmus vor, der unter Verwendung des Skalarprodukts von Kraft und Weg zum richtigen Vorzeichen in den Gleichungen für die Arbeit und die Potentielle Energie bei reversiblen Prozessen (Druck-Volumen-Änderung, Dehnung, Elektrostatische Wechselwirkung, Hub)führt. Wir zeigen, dass es dabei möglich ist, systemimmanente oder externe Kräfte zu benutzen. Wir zeigen, dass bei Verwendung von systemimmanenten Kräften das Skalarprodukt mit negativem Vorzeichen anzusetzen ist. Zudem ist es sehr wichtig, nötige Vorzeichenwechsel bei den einzelnen Schritten zu beachten. Wir betonen dies, weil gelegentlich übersehen wird, dass ein Vorzeichenwechsel nötig ist, wenn das Wegdifferential ds durch das Höhendifferential dh beziehungsweise durch das Abstandsdifferential dx oder dr ersetzt werden muss.
die Verwendung äußerer oder systemimmanenter Kräfte
the use of external or system-immanent forces
urn:nbn:de:kobv:517-opus-69732
6973
Keine öffentliche Lizenz: Unter Urheberrechtsschutz
Joachim Schmidt
Wolfgang Bechmann
deu
uncontrolled
Skalarprodukt von Kraft und Weg
deu
uncontrolled
systemimmanente Kräfte
deu
uncontrolled
Druck-Volumen-Änderung
deu
uncontrolled
Dehnung
deu
uncontrolled
Elektrostatische Wechselwirkung
deu
uncontrolled
Gravitation
eng
uncontrolled
scalar product of force and displacement
eng
uncontrolled
system-immanent forces
eng
uncontrolled
pressure-volume change
eng
uncontrolled
elongation
eng
uncontrolled
electrostatic interaction
eng
uncontrolled
gravitation
Physik
open_access
Institut für Chemie
Universität Potsdam
https://publishup.uni-potsdam.de/files/6746/schmidt_bechmann.pdf