Institut für Physik und Astronomie
Refine
Year of publication
- 2011 (187) (remove)
Document Type
- Article (150)
- Doctoral Thesis (26)
- Review (3)
- Monograph/Edited Volume (2)
- Other (2)
- Postprint (2)
- Habilitation Thesis (1)
- Master's Thesis (1)
Is part of the Bibliography
- yes (187)
Keywords
- X-rays: stars (5)
- gamma rays: general (5)
- gamma-ray burst: general (4)
- intergalactic medium (4)
- quasars: absorption lines (4)
- Coupled oscillators (3)
- Kuramoto model (3)
- acceleration of particles (3)
- cosmic rays (3)
- radiation mechanisms: non-thermal (3)
- stars: early-type (3)
- stars: massive (3)
- Bose-Einstein condensation (2)
- Ferroelectrets (2)
- Nonlinear coupling (2)
- Oscillator ensembles (2)
- Physikdidaktik (2)
- Quasare (2)
- Sun: magnetic topology (2)
- Wissenschaftstheorie (2)
- binaries: general (2)
- diffuse radiation (2)
- galaxies: active (2)
- galaxies: formation (2)
- gamma rays: ISM (2)
- gamma rays: galaxies (2)
- magnetohydrodynamics (MHD) (2)
- methods: analytical (2)
- methods: numerical (2)
- nonlinear time series analysis (2)
- pattern formation (2)
- piezoelectricity (2)
- stars: Wolf-Rayet (2)
- stars: magnetic field (2)
- stars: magnetic fields (2)
- stars: mass-loss (2)
- techniques: spectroscopic (2)
- turbulence (2)
- AFM (1)
- AGN (1)
- Actuators (1)
- Aerosole (1)
- Aerosols (1)
- African climate (1)
- Aktomyosin (1)
- Allgemeine Relativitätstheorie (1)
- Arctic (1)
- Arktis (1)
- Arnold diffusion (1)
- Astrophysik (1)
- Azobenzen (1)
- BL Lacertae objects: general (1)
- BL Lacertae objects: individual (Mrk 501) (1)
- BL Lacertae objects: individual (RX J0648.7+1516, 1FGL J0648.8+1516, VER J0648+152) (1)
- Be-10 exposure dating (1)
- Bifurcations (1)
- Biomaterial (1)
- Bipolar (1)
- Bose-Einstein-Kondensation (1)
- Bosonic stimulation (1)
- Caged compounds (1)
- Casimir-Polder interaction (1)
- Casimir-Polder-Interaktion (1)
- Cauchy problem (1)
- Cavity quantum electrodynamics (1)
- Cavity-quantum electrodynamics (1)
- Cells (1)
- Chaos spreading (1)
- Chaotic System (1)
- Chemical Abundances (1)
- Convection (1)
- Correlation function (1)
- DFB laser (1)
- DFB-Laser (1)
- Datenanalyse (1)
- Decay semigroups (1)
- Degradable polymer (1)
- Design concepts (1)
- Dictyostelium (1)
- Dictyostelium discoideum (1)
- Dielektrische Spektroskopie (1)
- Diphenyl-oxadiazoles (1)
- Dünnung (1)
- Einstein's field equations (1)
- Einsteins Feldgleichungen (1)
- Electrets (1)
- Electrodes (1)
- Electromagnetic waves (1)
- Electron-phonon coupling (1)
- Elliptic complex (1)
- Enceladus (1)
- Enzymatic degradation (1)
- Eukaryotic chemotaxis (1)
- Excitonic interactions (1)
- Extremereignisse (1)
- Feld-Effekt-Transistoren (1)
- Fernerkundung (1)
- Ferroelectret (1)
- Ferroelectrics (1)
- Ferroelektrete (1)
- Ferroelektrik (1)
- Fluorescence quantum yield (1)
- Flüssigkristalle (1)
- GISAXS (1)
- Galaxie (1)
- Galaxien (1)
- Galaxies (1)
- Galaxy (1)
- Galaxy: halo (1)
- Ganglion (1)
- Gravitationswellen (1)
- Green formulas (1)
- Greenland (1)
- Ground based gamma ray astronomy (1)
- Grönland (1)
- H II regions (1)
- Hohlraum-Quantenelektrodynamik (1)
- Holografie (1)
- Hydrogel (1)
- Hydrolytic degradation (1)
- Hyperbolic chaos (1)
- Hysterese (1)
- ISM: clouds (1)
- ISM: individual objects (G120.1+01.4, Tycho=VER J0025+641) (1)
- ISM: individual objects (RX J1713.7-3946) (1)
- ISM: supernova remnants (1)
- Indian summer monsoon (1)
- Indischer Sommer-Monsun (1)
- Inlandeis (1)
- Integral field spectroscopy (1)
- Integralfeld-Spectroskopie (1)
- Interstellar medium (1)
- Interstellares Medium (1)
- Intrinsically disordered protein (1)
- Kaskade (1)
- Klimawandel (1)
- Komplexe Systeme (1)
- Konvektion (1)
- LCST behavior (1)
- Landslide (1)
- Laser spectroscopy (1)
- Late embryogenesis abundant protein (1)
- Lax-Phillips theory (1)
- Lidar (1)
- Light-harvesting complex (1)
- Lyapunov exponent (1)
- Magnetospheres (1)
- Markov-Prozesse (1)
- Mathematikdidaktik (1)
- Membrane stability (1)
- Metall-Isolator-Halbleiter (1)
- Microfluidics (1)
- Milchstraße (1)
- Milky Way (1)
- Mischung (1)
- Mixing (1)
- Monolayer (1)
- Monopolar (1)
- Nanofluid (1)
- Nanokomposite (1)
- Nanofluid (1)
- Near edge X-ray absorption fine structure (1)
- Next generation Cherenkov telescopes (1)
- Nichtlinear angeregte Fluoreszenz (1)
- Nichtlineare Dynamik (1)
- Nonlinear polarization spectroscopy in the frequency domain (1)
- Numerical simulations (1)
- Oberflächengitter (1)
- Optical properties (1)
- Optimal control (1)
- Organic electronics (1)
- Oscillator populations (1)
- Ott-Antonsen theory (1)
- PBP10 (1)
- PDLC (1)
- Packing motif (1)
- Paleoclimatology (1)
- Paläoklimatologie (1)
- Paschen's law (1)
- Phase gate (1)
- Phenomenology (1)
- Philosophy of Science (1)
- Physics Education (1)
- Physik (1)
- Phänomenologie (1)
- Pigment-pigment interactions (1)
- Plio-Pleistocene (1)
- Polarisationsverteilung (1)
- Polarization distribution (1)
- Protein folding (1)
- Protein-membrane interaction (1)
- Quasars (1)
- Quaternary glaciations (1)
- Rapid thinning (1)
- Raumzeitgeometrie (1)
- Remote Sensing (1)
- Resonances (1)
- Resonant inelastic X-ray scattering (1)
- Resonant interaction (1)
- Retina (1)
- Rock avalanche (1)
- Rydberg atoms (1)
- SVD (1)
- Satellites, Composition (1)
- Satellites, Surfaces (1)
- Saturn, Rings (1)
- Saturn, Satellites (1)
- Scattering (1)
- Scattering theory (1)
- Schwarze Löcher (1)
- Science Curriculum (1)
- Spectroscopy (1)
- Spektroskopie (1)
- Spontaneous decay (1)
- Stabilität (1)
- Statistik (1)
- Stratton-Chu formulas (1)
- Subretinal (1)
- Sun: activity (1)
- Sun: atmosphere (1)
- Sun: coronal mass ejections (CMEs) (1)
- Sun: photosphere (1)
- Superradiance (1)
- Synchronisation (1)
- Synchronization (1)
- Tensor-Zerlegungen (1)
- Thermal-Pulse Tomography (1)
- Thermoresponsive (1)
- Thin Film (1)
- Thin film (1)
- Tien Shan (1)
- Time-varying Delay (1)
- Transiente Absorption (1)
- Understanding (1)
- Unterrichtsvorschläge (1)
- Vakuumschwankungen (1)
- Verstehen (1)
- Vorstellungen (1)
- Watanabe-Strogatz theory (1)
- Wellenlängenverschiebung (1)
- Wiskostatin (1)
- Wärmepuls-Tomographie (1)
- X-ray absorption spectroscopy (1)
- X-ray emission spectroscopy (1)
- X-ray structure (1)
- X-rays: ISM (1)
- X-rays: binaries (1)
- X-rays: individual (Carina) (1)
- Zustandsmodell (1)
- Zwangsgleichungen (1)
- ab initio (1)
- absorption spectroscopy (1)
- accretion, accretion disks (1)
- acoustic transducers (1)
- actomyosin (1)
- amorphous state (1)
- animal models (1)
- astroparticle physics (1)
- astrophysics (1)
- azobenzene (1)
- biological invasions (1)
- black holes (1)
- black-holes (1)
- broad-spectrum permittivity enhancement (1)
- cGMP (1)
- calibration (1)
- cascade (1)
- cavity quantum electrodynamics (1)
- chaos (1)
- charge carrier processes (1)
- charge stability (1)
- chemical equilibrium (1)
- chemically reactive flow (1)
- chemische Häufigkeiten (1)
- climate change (1)
- climate-driven evolution (1)
- coating (1)
- comets: general (1)
- comets: individual ((596) Scheila) (1)
- complex networks (1)
- complex systems (1)
- conceptions (1)
- constraint equations (1)
- control (1)
- cosmology: dark matter, large-scale structure of the Universe (1)
- cosmology: theory (1)
- critical collapse (1)
- dark ages, reionization, first stars (1)
- dark matter (1)
- data analysis (1)
- design concepts (1)
- dielectric barrier discharge (DBD) (1)
- dielectric barrier discharges (1)
- dielectric elastomers (1)
- dielectric spectroskopie (1)
- dielektrische Elastomere (1)
- dipole grafting (1)
- durability (1)
- dynamical transitions (1)
- effective polarization (1)
- electric sensing devices (1)
- electromagnetic counterparts (1)
- electromechanical response (1)
- electrostatic energy density (1)
- elektromagnetische Strahlung (1)
- elektromechanische Reaktion (1)
- elektrostatische Energiedichte (1)
- elementary particles (1)
- elliptic systems (1)
- elliptisches Gleichungssystem (1)
- extreme events (1)
- ferroelectric polarization (1)
- ferroelektrische Polarisation (1)
- galaxies: ISM (1)
- galaxies: general (1)
- galaxies: groups, clusters (1)
- galaxies: halos (1)
- gamma rays: diffuse background (1)
- general relativity (1)
- genetic Allee effects (1)
- granular gas (1)
- gravitational waves (1)
- ground based gamma ray astronomy (1)
- high permittivity (1)
- histomorphometry (1)
- hohe Permittivität (1)
- holography (1)
- hydrodynamics (1)
- hysteresis (1)
- ice sheet (1)
- imidazolium (1)
- instabilities (1)
- interspecific competition (1)
- ionic liquid (1)
- komplexe Netzwerke (1)
- kritischer Kollaps (1)
- life history evolution (1)
- light polarisation (1)
- liquid crystal (1)
- liquid crystal polymers (1)
- magnetic fields (1)
- magnetic reconnection (1)
- man-made dipole (1)
- manufacturing automation (1)
- markov processes (1)
- mathematics education (1)
- metal nanoparticles (1)
- minor planets, asteroids: general (1)
- mobility (1)
- molecular dynamics method (1)
- molecular motors (1)
- molekulare Motoren (1)
- morphology (1)
- nanocomposite (1)
- nanocomposites (1)
- next generation Cherenkov telescopes (1)
- nichtlineare Datenanalyse (1)
- non-volatile memory (1)
- nonadaptive evolution (1)
- nonlinear dynamics (1)
- nonlinear excited fluorescence (1)
- numerical relativity (1)
- numerische Relativitätstheorie (1)
- open clusters and associations: individual (Cl Bochum 10, Cl Bochum 11, Cl Collinder 228, Cl Trumpler 14, Cl Trumpler 15, Cl Trumpler 16) (1)
- open clusters and associations: individual (Trumpler 16) (1)
- optical hole burning (1)
- optical interconnections (1)
- organic electronic (1)
- organische Elektronik (1)
- osteoporosis (1)
- pQCT (1)
- packaging (1)
- permittivity enhancement (1)
- philosophy of science (1)
- photochemistry (1)
- physics (1)
- piezoelectret (1)
- planetary rings (1)
- polyethylene (1)
- polymers (1)
- polytetrafluoroethylene (1)
- position control (1)
- quasars (1)
- quasars: individual (SDSS J092447.36+485242.8, SDSS J110155.74+105302.3) (1)
- r and K selection (1)
- raumartige Unendliche (1)
- reaction kinetics theory (1)
- reaction-advection-diffusion equation (1)
- reaction-diffusion system (1)
- relativistic hydrodynamics (1)
- relativistic processes (1)
- relativistische Hydrodynamik (1)
- reproduction (1)
- schwarze Löcher (1)
- science education (1)
- shock waves (1)
- silicone based dielectric elastomer actuators (1)
- solar cells (1)
- space-like infinity (1)
- space-time geometry (1)
- spatiotemporal phenomena (1)
- stability (1)
- stars: AGB and post-AGB (1)
- stars: abundances (1)
- stars: individual (1A 0535+262) (1)
- stars: individual (HD 93250, HD 93129A, HD 93403, HD 93205, HD 93343, QZ Car, SS73 24, FO 15, Cl Trumpler 16 22, CPD-59 2610, HD 93501) (1)
- stars: individual: zeta Ophiuchi (1)
- stars: kinematics (1)
- stars: kinematics and dynamics (1)
- stars: mass loss (1)
- stars: pre-main sequence (1)
- stars: winds, outflows (1)
- state model (1)
- statistical physics (1)
- statistics (1)
- statistische Physik (1)
- stochastic quench (1)
- structure analysis (1)
- surface relief grating (1)
- surface treatment (1)
- synchronization (1)
- synthetic eumelanin (1)
- synthetisches Eumelanin (1)
- techniques: polarimetric (1)
- tensor decompositions (1)
- trabecular bone (1)
- transient absorption (1)
- uniform spatial arrangement (1)
- vacuum fluctuations (1)
- van der Waals forces (1)
- van der Waals-Kräfte (1)
- wavelength shift (1)
- wässrige Filme (1)
Institute
Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light
(2011)
Among the possibly most intriguing aspects of quantum entanglement is that it comes in free and bound instances. The existence of bound entangled states certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this Letter, we present a first unconditional, continuous-variable preparation and detection of a bound entangled state of light. We use convex optimization to identify regimes rendering its bound character well certifiable, and continuously produce a distributed bound entangled state with an extraordinary and unprecedented significance of more than 10 standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering, and high precision metrology.
We present the results of 16 Swift-triggered Gamma-ray burst (GRB) follow-up observations taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) telescope array from 2007 January to 2009 June. The median energy threshold and response time of these observations were 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter timescale determined by the maximum VERITAS sensitivity to a burst with a t(-1.5) time profile. This temporal model is characteristic of GRB afterglows with high-energy, long-lived emission that have been detected by the Large Area Telescope on board the Fermi satellite. No significant very high energy (VHE) gamma-ray emission was detected and upper limits above the VERITAS threshold energy are calculated. The VERITAS upper limits are corrected for gamma-ray extinction by the extragalactic background light and interpreted in the context of the keV emission detected by Swift. For some bursts the VHE emission must have less power than the keV emission, placing constraints on inverse Compton models of VHE emission.
Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 degrees C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.
Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution
(2011)
Potential paleoclimatic driving mechanisms acting on human evolution present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the past 5 Ma has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Middle Pliocene (3.35-3.15 Ma B. P.), (ii) Early Pleistocene (2.25-1.6 Ma B. P.), and (iii) Middle Pleistocene (1.1-0.7 Ma B. P.). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Middle Pleistocene, respectively. A reexamination of the available fossil record demonstrates statistically significant coincidences between the detected transition periods and major steps in hominin evolution. This result suggests that the observed shifts between more regular and more erratic environmental variability may have acted as a trigger for rapid change in the development of humankind in Africa.
A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non-optimized (chloroform cast) and nearly optimized (solvent-annealed o-dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H-aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent-annealed o-dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra- and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges.
Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Peclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Peclet number. We investigate the effect of the chaperone size on the translocation process. In particular, for large chaperone size, the translocation progress and the mean waiting time as function of the reaction coordinate exhibit pronounced sawtooth-shapes. The effects of a heterogeneous polymer sequence on the translocation dynamics is studied in terms of the translocation velocity, the probability distribution for the translocation progress, and the monomer waiting times. (C) 2011 American Institute of Physics.
Physiklehrer bestimmen durch die Gestaltung des Unterrichts und damit durch ihr professionelles Handeln maßgeblich mit, wie die individuellen Lernprozesse der Schüler zu Inhalten der Physik ablaufen. Für die Entwicklung ihrer professionellen Handlungskompetenz müssen zukünftige Physiklehrer einerseits physikalisches, physikdidaktisches und pädagogisches Wissen erwerben und andererseits motiviert sein, dieses Wissen auch anzuwenden. In ihrer Vorlesung geht Thorid Rabe der Frage nach, welche physikdidaktischen Kompetenzen Studierende im Rahmen der universitären Ausbildung erwerben sollten. Am Beispiel der Lehrveranstaltung "Physikalische Schulexperimente" zeigt sie, wie physikdidaktische Theorie und praktisches Lehrerhandeln aufeinander bezogen werden können. Zudem wird sie ein Forschungsprojekt vorstellen, das einem bisher vernachlässigten Aspekt professioneller Handlungskompetenz nachgeht, nämlich den domänenspezifischen Selbstwirksamkeitserwartungen - dem Zutrauen in sich selbst, als Physiklehrer angemessen und erfolgreich handeln zu können.
Interaction of land surface processes and the atmophere in the Arctic - senitivities and extremes
(2011)
The inspiral and merger of two black holes is among the most exciting and extreme events in our universe. Being one of the loudest sources of gravitational waves, they provide a unique dynamical probe of strong-field general relativity and a fertile ground for the observation of fundamental physics. While the detection of gravitational waves alone will allow us to observe our universe through an entirely new window, combining the information obtained from both gravitational wave and electro-magnetic observations will allow us to gain even greater insight in some of the most exciting astrophysical phenomena. In addition, binary black-hole mergers serve as an intriguing tool to study the geometry of space-time itself. In this dissertation we study the merger process of binary black-holes in a variety of conditions. Our results show that asymmetries in the curvature distribution on the common apparent horizon are correlated to the linear momentum acquired by the merger remnant. We propose useful tools for the analysis of black holes in the dynamical and isolated horizon frameworks and shed light on how the final merger of apparent horizons proceeds after a common horizon has already formed. We connect mathematical theorems with data obtained from numerical simulations and provide a first glimpse on the behavior of these surfaces in situations not accessible to analytical tools. We study electro-magnetic counterparts of super-massive binary black-hole mergers with fully 3D general relativistic simulations of binary black-holes immersed both in a uniform magnetic field in vacuum and in a tenuous plasma. We find that while a direct detection of merger signatures with current electro-magnetic telescopes is unlikely, secondary emission, either by altering the accretion rate of the circumbinary disk or by synchrotron radiation from accelerated charges, may be detectable. We propose a novel approach to measure the electro-magnetic radiation in these simulations and find a non-collimated emission that dominates over the collimated one appearing in the form of dual jets associated with each of the black holes. Finally, we provide an optimized gravitational wave detection pipeline using phenomenological waveforms for signals from compact binary coalescence and show that by including spin effects in the waveform templates, the detection efficiency is drastically improved as well as the bias on recovered source parameters reduced. On the whole, this disseration provides evidence that a multi-messenger approach to binary black-hole merger observations provides an exciting prospect to understand these sources and, ultimately, our universe.
Eumelanin ist ein Fluorophor mit teilweise recht ungewöhnlichen spektralen Eigenschaften. Unter anderem konnten in früheren Veröffentlichungen Unterschiede zwischen dem 1- und 2-photonen-angeregtem Fluoreszenzspektrum beobachtet werden, weshalb im nichtlinearen Anregungsfall ein schrittweiser Anregungsprozess vermutet wurde. Um diese und weitere optische Eigenschaften des Eumelanins besser zu verstehen, wurden in der vorliegenden Arbeit vielfältige messmethodische Ansätze der linearen und nichtlinearen Optik an synthetischem Eumelanin in 0,1M NaOH verfolgt. Aus den Ergebnissen wurde ein Modell abgeleitet, welches die beobachteten photonischen Eigenschaften konsistent beschreibt. In diesem kaskadierten Zustandsmodell (Kaskaden-Modell) wird die aufgenommene Photonenenergie schrittweise von Anregungszuständen hoher Übergangsenergien zu Anregungszuständen niedrigerer Übergangsenergien transferiert. Messungen der transienten Absorption ergaben dominante Anteile mit kurzen Lebensdauern im ps-Bereich und ließen damit auf eine hohe Relaxationsgeschwindigkeit entlang der Kaskade schließen. Durch Untersuchung der nichtlinear angeregten Fluoreszenz von verschieden großen Eumelanin-Aggregaten konnte gezeigt werden, dass Unterschiede zwischen dem linear und nichtlinear angeregten Fluoreszenzspektrum nicht nur durch einen schrittweisen Anregungsprozess bei nichtlinearer Anregung sondern auch durch Unterschiede in den Verhältnissen der Quantenausbeuten zwischen kleinen und großen Aggregaten beim Wechsel von linearer zu nichtlinearer Anregung begründet sein können. Durch Bestimmung des Anregungswirkungsquerschnitts und der Anregungspulsdauer-Abhängigkeit der nichtlinear angeregten Fluoreszenz von Eumelanin konnte jedoch ein schrittweiser 2-Photonen-Anregungsprozess über einen Zwischenzustand mit Lebendsdauern im ps-Bereich nachgewiesen werden.
A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too.
This Thesis puts its focus on the physics of neutron stars and its description with methods of numerical relativity. In the first step, a new numerical framework the Whisky2D code will be developed, which solves the relativistic equations of hydrodynamics in axisymmetry. Therefore we consider an improved formulation of the conserved form of these equations. The second part will use the new code to investigate the critical behaviour of two colliding neutron stars. Considering the analogy to phase transitions in statistical physics, we will investigate the evolution of the entropy of the neutron stars during the whole process. A better understanding of the evolution of thermodynamical quantities, like the entropy in critical process, should provide deeper understanding of thermodynamics in relativity. More specifically, we have written the Whisky2D code, which solves the general-relativistic hydrodynamics equations in a flux-conservative form and in cylindrical coordinates. This of course brings in 1/r singular terms, where r is the radial cylindrical coordinate, which must be dealt with appropriately. In the above-referenced works, the flux operator is expanded and the 1/r terms, not containing derivatives, are moved to the right-hand-side of the equation (the source term), so that the left hand side assumes a form identical to the one of the three-dimensional (3D) Cartesian formulation. We call this the standard formulation. Another possibility is not to split the flux operator and to redefine the conserved variables, via a multiplication by r. We call this the new formulation. The new equations are solved with the same methods as in the Cartesian case. From a mathematical point of view, one would not expect differences between the two ways of writing the differential operator, but, of course, a difference is present at the numerical level. Our tests show that the new formulation yields results with a global truncation error which is one or more orders of magnitude smaller than those of alternative and commonly used formulations. The second part of the Thesis uses the new code for investigations of critical phenomena in general relativity. In particular, we consider the head-on-collision of two neutron stars in a region of the parameter space where two final states a new stable neutron star or a black hole, lay close to each other. In 1993, Choptuik considered one-parameter families of solutions, S[P], of the Einstein-Klein-Gordon equations for a massless scalar field in spherical symmetry, such that for every P > P⋆, S[P] contains a black hole and for every P < P⋆, S[P] is a solution not containing singularities. He studied numerically the behavior of S[P] as P → P⋆ and found that the critical solution, S[P⋆], is universal, in the sense that it is approached by all nearly-critical solutions regardless of the particular family of initial data considered. All these phenomena have the common property that, as P approaches P⋆, S[P] approaches a universal solution S[P⋆] and that all the physical quantities of S[P] depend only on |P − P⋆|. The first study of critical phenomena concerning the head-on collision of NSs was carried out by Jin and Suen in 2007. In particular, they considered a series of families of equal-mass NSs, modeled with an ideal-gas EOS, boosted towards each other and varied the mass of the stars, their separation, velocity and the polytropic index in the EOS. In this way they could observe a critical phenomenon of type I near the threshold of black-hole formation, with the putative solution being a nonlinearly oscillating star. In a successive work, they performed similar simulations but considering the head-on collision of Gaussian distributions of matter. Also in this case they found the appearance of type-I critical behaviour, but also performed a perturbative analysis of the initial distributions of matter and of the merged object. Because of the considerable difference found in the eigenfrequencies in the two cases, they concluded that the critical solution does not represent a system near equilibrium and in particular not a perturbed Tolmann-Oppenheimer-Volkoff (TOV) solution. In this Thesis we study the dynamics of the head-on collision of two equal-mass NSs using a setup which is as similar as possible to the one considered above. While we confirm that the merged object exhibits a type-I critical behaviour, we also argue against the conclusion that the critical solution cannot be described in terms of equilibrium solution. Indeed, we show that, in analogy with what is found in, the critical solution is effectively a perturbed unstable solution of the TOV equations. Our analysis also considers fine-structure of the scaling relation of type-I critical phenomena and we show that it exhibits oscillations in a similar way to the one studied in the context of scalar-field critical collapse.