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We exploit a time-resolved ultrafast optical technique to study the propagation of point-excited surface acoustic waves on a microscopic two-dimensional phononic crystal in the form of a square lattice of holes in a silicon substrate. Constant-frequency images and the dispersion relation are extracted, and the latter measured in detail in the region around the phononic band gap. Mode conversion and refraction at the interface between the phononic crystal and surrounding non-structured silicon substrate is studied at constant frequencies. Symmetric phonon beam splitting, for example, is shown to lead to a striking Maltese-cross pattern when phonons exit a square region of phononic crystal excited near its center.

We exploit a time-resolved ultrafast optical technique to study the propagation of point-excited surface acoustic waves on a microscopic two-dimensional phononic crystal in the form of a square lattice of holes in a silicon substrate. Constant-frequency images and the dispersion relation are extracted, and the latter measured in detail in the region around the phononic band gap. Mode conversion and refraction at the interface between the phononic crystal and surrounding non-structured silicon substrate is studied at constant frequencies. Symmetric phonon beam splitting, for example, is shown to lead to a striking Maltese-cross pattern when phonons exit a square region of phononic crystal excited near its center.

We exploit a time-resolved ultrafast optical technique to study the propagation of point-excited surface acoustic waves on a microscopic two-dimensional phononic crystal in the form of a square lattice of holes in a silicon substrate. Constant-frequency images and the dispersion relation are extracted, and the latter measured in detail in the region around the phononic band gap. Mode conversion and refraction at the interface between the phononic crystal and surrounding non-structured silicon substrate is studied at constant frequencies. Symmetric phonon beam splitting, for example, is shown to lead to a striking Maltese-cross pattern when phonons exit a square region of phononic crystal excited near its center.

To study the nonlinear saturation mechanism in turbulent plasmas, we plan to obseve ion temperature gradient (ITG) modes in the Plasma Assembly for Nonlinear Turbulence Analysis (PANTA). Linear growth rates of ITG modes in the linear device are analyzed to determine their excitation conditions using a three-field fluid model to describe the ion motion. Parameter scans of the linear growth rate show the threshold for ITG mode excitation, and the typical plasma parameters of the PANTA are found in the unstable domain., source:https://doi.org/10.1585/pfr.8.2403133

The nonlinear dispersion relation of the geodesic acoustic modes (GAMs) is investigated for tokamaks with a high safety factor and low magnetic shear. We focus on the Reynolds stress as a nonlinearity, which is truncated at the third order of the GAM amplitude. The real frequency of the GAM is modified according to the phase of the nonlinear force acting on the GAM, which depends on the turbulence decorrelation rate. The nonlinear frequency shift is much larger than that from the finite gyro-radius effects in the linear theory, when the poloidal turbulent E × B velocities are comparable to the diamagnetic drift velocity. Under such circumstances, the group velocity is strongly enhanced and becomes comparable with the radial phase velocity. In addition, the magnitude of the nonlinear effects is also evaluated using experimental parameters., source:https://doi.org/10.1585/pfr.8.1403010, identifier:0000-0002-7696-6405

We develop a Korteweg-De Vries (KdV) theory for weakly nonlinear waves in discontinuously stratified two-layer fluids with a generally prescribed rotational steady current. With the help of a classical asymptotic power series approach, these models are directly derived from the divergence-free incompressible Euler equations for unidirectional free surface and internal waves over a flat bed. Moreover, we derive a Burns condition for the determination of wave propagation speeds. Several examples of currents are given; explicit calculations of the corresponding propagation speeds and KdV coefficients are provided as well., Mathematical Physics

We develop a Korteweg-De Vries (KdV) theory for weakly nonlinear waves in discontinuously stratified two-layer fluids with a generally prescribed rotational steady current. With the help of a classical asymptotic power series approach, these models are directly derived from the divergence-free incompressible Euler equations for unidirectional free surface and internal waves over a flat bed. Moreover, we derive a Burns condition for the determination of wave propagation speeds. Several examples of currents are given; explicit calculations of the corresponding propagation speeds and KdV coefficients are provided as well., Mathematical Physics

A combination of the Fourier transform and the maximum entropy method for estimating the frequency-wavenumber resolved power spectrum density is proposed. After illustrating the physical insight of the maximum entropy method by using synthetic test data, capability of the proposed method is tested using numerical simulation data. The method is also applied to experimental data obtained by the beam emission spectroscopy in the Large Helical Device. All of those examinations show that the proposed method provides more plausible results than conventional methods when the available spatial points are limited., source:T Kobayashi et al 2021 Plasma Phys. Control. Fusion 63 045011, source:https://doi.org/10.1088/1361-6587/abe024, identifier:0000-0001-6835-1569, identifier:0000-0001-5669-1937, identifier:0000-0002-0585-4561, identifier:0000-0003-1804-2308

Selection rule of the radial propagation direction of geodesic acoustic modes (GAMs) is investigated. Here, we study the influence of nonlinear coupling with drift wave turbulence on the propagation direction of GAMs. Based on wave-kinetic equation for the turbulence, the phase-space dynamics is numerically solved and the nonlinear saturated states are obtained, where the phase-space consists of the real space and the wavenumber space. A wave pattern of the GAM in a nonlinear saturated state varies to form a standing wave, outward and inward propagating waves, depending on the peak radial wavenumber of the turbulence. The impact of nonlinear coupling with turbulence is discussed by deriving the GAM dispersion relation that includes the effect of the turbulence., source:Citation M. Sasaki et al 2018 Nucl. Fusion 58 112005, source:https://doi.org/10.1088/1741-4326/aad251

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the epsilon expansion of the Wilson-Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang-Mills theory in four dimensions.

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the epsilon expansion of the Wilson-Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang-Mills theory in four dimensions.

The numerical determination of dispersion relations in periodic materials via the finite element method is a difficult task in most standard codes. Here, we propose a novel technique which allows the computation of these band structures from local elemental subroutines in contrast with existing methods which impose Bloch boundary conditions on the global arrays. The proposed local approach is thus readily applicable to several physical contexts and space dimensionalities. Here we present the details of this element-based algorithm and provide verification results for three different kinematic assumptions applied to phononic crystals in a classical and a micropolar elastic medium. The paper also includes in the form of supplementary material, a fully-coded user subroutine and a test-problem to be used in a commercial finite element code. © 2019 IMACS.

A prospective method to assess thermo-acoustic instabilities based on two reflection coefficients measured from the upstream side of the burner is presented and experimentally validated. In order to compose a model which allows predicting the onset of thermo-acoustic instability of combustion in a practical appliance, one has to characterize the thermo-acoustic properties of the burner including the flame as an acoustically active element and acoustic properties of all other (usually passive) components of the combustion appliance both upstream as well as downstream of the burner. This kind of modeling strategy usually faces serious practical problems related to the need of measurements/modeling at the hot downstream part of the system. In the present work, we propose a measurement and a system modeling approach which relies on two acoustic measurements, namely reflection coefficients, only at the cold (burner upstream) part of the combustion appliance. Both reflection coefficients, termed upstream and input, can be readily measured using standard acoustic techniques. The need to measure the input reflection coefficient of an acoustically active subsystem may impose difficulties related to the acoustic instability of the measurement setup itself. The approach and technical solution to handle this problem via a special modification of the excitation source (loudspeaker box) is proposed. The dispersion relation to search for system eigen frequencies is represented in a form that couples the reflection coefficients of the upstream part of the appliance and input reflection coefficient from the downstream part as observed through the burner with flame. This form of the dispersion relation is commonly used in the theory of radio-frequency circuits and recently introduced for thermo-acoustic problems. The proposed method is applied to burners with premixed burner-stabilized Bunsen-type flames. The observed instability conditions and oscillation frequencies are compared wi, QC 20210305

Photons are elementary particles of light, and their interactions in vacuum are extremely weak. The seclusion of photons makes them perfect carriers of classical and quantum information, but also poses difficulties for employing them in quantum information technologies. Recent years have seen tremendous experimental progress in the development of synthetic quantum systems where strong and controllable coupling between single photons is achieved. In a variety of solid-state and optical platforms, propagating photons are coupled with local emitters such as atoms, quantum dots, NV centers, or superconducting qubits. Despite the different nature of the platforms, many of these systems can be described using the same theoretical framework called waveguide quantum electrodynamics (WQED). Dissipation is an inevitable ingredient of many synthetic quantum systems and is a source of error in quantum information applications. Despite its important role in experimental systems, the implications of dissipation in scattering theory havenot been fully explored. Chapter 2 discusses our discovery of the dissipation-induced bound states in WQED systems. The appearance of these bound states is in a one-to-one correspondence with zeros in the single-photon transmission. We also formulate a dissipative version of Levinson's theorem by looking at the relation between the number of bound states and the winding number of the transmission phases. In Chapter 3, we study three-body loss in Rydberg polaritons. Despite past theoretical and experimental studies of the regime with dispersive interaction, the dissipative regime is still mostly unexplored. Using a renormalization group technique to solve the quantum three-body problem, we show how the shape and strength of dissipative three-body forces can be universally enhanced for Rydberg polaritons. We demonstrate how these interactions relate to the transmission through a single-mode cavity, which can be used as a probe of the three-body physi

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the epsilon expansion of the Wilson-Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang-Mills theory in four dimensions.

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the epsilon expansion of the Wilson-Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang-Mills theory in four dimensions.

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the epsilon expansion of the Wilson-Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang-Mills theory in four dimensions.

The three electromagnetic form factors for the transition from a spin-3/2 Σ* hyperon to the ground-state Λ hyperon are studied. At low energies, combinations of the transition form factors can be deduced from Dalitz decays of the Σ* hyperon to Λ plus an electron-positron pair. It is pointed out how more information can be obtained with the help of the self-analyzing weak decay of the Λ. In particular, it is shown that these transitionform factors are complex quantities already in this kinematical region. Such measurements are feasible at hyperon factories such as, for instance, the Facility for Antiproton and Ion Research (FAIR). At higher energies, the transition form factors can be measured in electron-positron collisions. The transition form factors are related to decay distributions and differential cross sections. Using dispersion theory, the low-energy electromagneticform factors for the Σ*-to-Λ transition are related to the pion vector form factor. The additionally required input, i.e., the two-pion–Σ*–Λ amplitudes, is determined from relativistic next-to-leading-order (NLO) baryon chiralperturbation theory, including the baryons from the octet and the decuplet. A poorly known NLO parameter is fixed to the experimental value of the Σ*→Λ γ decay width. Pion rescattering is taken into account by using dispersion theory and solving a Muskhelishvili-Omnès equation. Subtracted and unsubtracted dispersion relations are discussed. However, in view of the fact that the transition form factors are complex quantities, the current data situation does not allow for a full determination of the subtraction constants. To reduce the numberof free parameters, unsubtracted dispersion relations are used to make predictions for the transition form factors in the low-energy space- and timelike regions.

The three electromagnetic form factors for the transition from a spin-3/2 Σ* hyperon to the ground-state Λ hyperon are studied. At low energies, combinations of the transition form factors can be deduced from Dalitz decays of the Σ* hyperon to Λ plus an electron-positron pair. It is pointed out how more information can be obtained with the help of the self-analyzing weak decay of the Λ. In particular, it is shown that these transitionform factors are complex quantities already in this kinematical region. Such measurements are feasible at hyperon factories such as, for instance, the Facility for Antiproton and Ion Research (FAIR). At higher energies, the transition form factors can be measured in electron-positron collisions. The transition form factors are related to decay distributions and differential cross sections. Using dispersion theory, the low-energy electromagneticform factors for the Σ*-to-Λ transition are related to the pion vector form factor. The additionally required input, i.e., the two-pion–Σ*–Λ amplitudes, is determined from relativistic next-to-leading-order (NLO) baryon chiralperturbation theory, including the baryons from the octet and the decuplet. A poorly known NLO parameter is fixed to the experimental value of the Σ*→Λ γ decay width. Pion rescattering is taken into account by using dispersion theory and solving a Muskhelishvili-Omnès equation. Subtracted and unsubtracted dispersion relations are discussed. However, in view of the fact that the transition form factors are complex quantities, the current data situation does not allow for a full determination of the subtraction constants. To reduce the numberof free parameters, unsubtracted dispersion relations are used to make predictions for the transition form factors in the low-energy space- and timelike regions.

The three electromagnetic form factors for the transition from a spin-3/2 Σ* hyperon to the ground-state Λ hyperon are studied. At low energies, combinations of the transition form factors can be deduced from Dalitz decays of the Σ* hyperon to Λ plus an electron-positron pair. It is pointed out how more information can be obtained with the help of the self-analyzing weak decay of the Λ. In particular, it is shown that these transitionform factors are complex quantities already in this kinematical region. Such measurements are feasible at hyperon factories such as, for instance, the Facility for Antiproton and Ion Research (FAIR). At higher energies, the transition form factors can be measured in electron-positron collisions. The transition form factors are related to decay distributions and differential cross sections. Using dispersion theory, the low-energy electromagneticform factors for the Σ*-to-Λ transition are related to the pion vector form factor. The additionally required input, i.e., the two-pion–Σ*–Λ amplitudes, is determined from relativistic next-to-leading-order (NLO) baryon chiralperturbation theory, including the baryons from the octet and the decuplet. A poorly known NLO parameter is fixed to the experimental value of the Σ*→Λ γ decay width. Pion rescattering is taken into account by using dispersion theory and solving a Muskhelishvili-Omnès equation. Subtracted and unsubtracted dispersion relations are discussed. However, in view of the fact that the transition form factors are complex quantities, the current data situation does not allow for a full determination of the subtraction constants. To reduce the numberof free parameters, unsubtracted dispersion relations are used to make predictions for the transition form factors in the low-energy space- and timelike regions.

Non-reciprocity of wave phenomena describes the situation where wave dispersion depends on the sign of the wave-vector, i.e., counter-propagating waves exhibit di↵erent wavelengths for the same frequency. Such behavior has been recently observed in heavy-metal/ferromagnetic interfaces with Dzyaloshinskii-Moriya coupling, and has also been known for coupled magnetic bilayers, where non-reciprocity is enhanced when the two layers are antiparallel aligned. Besides the conventional uses of spin-waves, non-reciprocity adds further functionalities, such as its potential applications in communications technologies and logical operations. In the current manuscript, we thus examine the spin-wave non-reciprocity induced by dipolar interactions in a coupled bilayer consisting of two ferromagnetic layers separated by a non-magnetic spacer. We derive an easy-to-use formula to estimate the frequency di↵erence provided by the non-reciprocity, which allows for choosing an optimal system in order to maximize the e↵ect. For small wave-numbers, non-reciprocity scales linearly, while for larger wave-vectors the non-reciprocity behaves non-monotonically, with a well-defined maximum. The study is carried out by means of analytical calculations that are complemented by micromagnetic simulations. Furthermore, we confirmed our model by experimental investigation of the spin-wave dispersion in a prototype antiparallel-coupled bilayer system. Since the relative magnetic orientation can be controlled through a bias field, the magnon non-reciprocity can be then turned on and o↵, which lends an important functionality to the coupled ferromagnetic bilayers.

Non-reciprocity of wave phenomena describes the situation where wave dispersion depends on the sign of the wave-vector, i.e., counter-propagating waves exhibit di↵erent wavelengths for the same frequency. Such behavior has been recently observed in heavy-metal/ferromagnetic interfaces with Dzyaloshinskii-Moriya coupling, and has also been known for coupled magnetic bilayers, where non-reciprocity is enhanced when the two layers are antiparallel aligned. Besides the conventional uses of spin-waves, non-reciprocity adds further functionalities, such as its potential applications in communications technologies and logical operations. In the current manuscript, we thus examine the spin-wave non-reciprocity induced by dipolar interactions in a coupled bilayer consisting of two ferromagnetic layers separated by a non-magnetic spacer. We derive an easy-to-use formula to estimate the frequency di↵erence provided by the non-reciprocity, which allows for choosing an optimal system in order to maximize the e↵ect. For small wave-numbers, non-reciprocity scales linearly, while for larger wave-vectors the non-reciprocity behaves non-monotonically, with a well-defined maximum. The study is carried out by means of analytical calculations that are complemented by micromagnetic simulations. Furthermore, we confirmed our model by experimental investigation of the spin-wave dispersion in a prototype antiparallel-coupled bilayer system. Since the relative magnetic orientation can be controlled through a bias field, the magnon non-reciprocity can be then turned on and o↵, which lends an important functionality to the coupled ferromagnetic bilayers.

In order to account for non-Fourier heat transport, occurring on short time and length scales, the often-praised Dual-Phase-Lag (DPL) model was conceived, introducing a causality relation between the onset of heat flux and the temperature gradient. The most prominent aspect of the first-order DPL model is the prediction of wave-like temperature propagation, the detection of which still remains elusive. Among the challenges to make further progress is the capability to disentangle the intertwining of the parameters affecting wave-like behaviour. This work contributes to the quest, providing a straightforward, easy-to-adopt, analytical mean to inspect the optimal conditions to observe temperature wave oscillations. The complex-valued dispersion relation for the temperature scalar field is investigated for the case of a localised temperature pulse in space, and for the case of a forced temperature oscillation in time. A modal quality factor is introduced showing that, for the case of the temperature gradient preceding the heat flux, the material acts as a bandpass filter for the temperature wave. The bandpass filter characteristics are accessed in terms of the relevant delay times entering the DPL model. The optimal region in parameters space is discussed in a variety of systems, covering nine and twelve decades in space and time-scale respectively. The here presented approach is of interest for the design of nanoscale thermal devices operating on ultra-fast and ultra-short time scales, a scenario here addressed for the case of quantum materials and graphite.

Different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, were studied by means of the electrically detected ferromagnetic resonance (ED-FMR). The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength.

Here we present a study of different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, by means of the electrically detected ferromagnetic resonance (ED-FMR). The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength. For asymmetric samples, mode intermixing occurs for certain resonance fields, accompanied by abrupt jumps in both mode frequencies. Such behavior is not observed for symmetric samples, in accordance with predictions based on VNA-FMR experiments and simulations performed elsewhere.

Different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, were studied by means of the electrically detected ferromagnetic resonance (ED-FMR). The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength.

Here we present a study of different ferromagnetic resonance (FMR) modes in micron-sized antiferromagnetically interlayer exchange coupled SiO2/Ta(5nm)/Py(t)/Ru(0.85 nm)/Py(3nm)/Ru(3nm) structures, with t = 3, 6 and 9 nm, by means of the electrically detected ferromagnetic resonance (ED-FMR). The main magnetoresistance effect used in ED-FMR was anisotropic magnetoresistance (AMR). Bilinear and biquadratic coupling strengths for each sample were determined by fitting SQUID-VSM measurements on 4×4 mm² thin films, using equilibrium total energy minimization. The existence of two different resonance modes (in-phase (acoustic) and out-of-phase (optic)) is shown for asymmetric samples. For the symmetric sample only the acoustic mode was observed, due to the compensation of AMR response from Py layers for the out-of-phase mode. The obtained dispersion relations show a clear dependence of the acoustic mode frequency minimum on the bilinear coupling strength. For asymmetric samples, mode intermixing occurs for certain resonance fields, accompanied by abrupt jumps in both mode frequencies. Such behavior is not observed for symmetric samples, in accordance with predictions based on VNA-FMR experiments and simulations performed elsewhere.

In this thesis, we analyze the electromagnetic wave propagation in waveguidestructuresexhibiting periodical geometry, including glide symmetry. The analysisis performed using a mode matching technique which correlates the different modecoefficients from separate but, connected regions in the structure. This technique isused to obtain the dispersion diagrams for two one-dimensional periodic structures:a glide-symmetric corrugated metasurface and a coaxial line loaded with periodicholes. The mode matching formulation is presented in Cartesian and cylindricalcoordinate system for the former and the later, respectively. The mode matchingresults are compared to simulated results obtained from the Eigenmode Solver inCST Microwave Studio and are found to agree very well., I detta examensarbete, analyseras elektromagnetisk v°agutbredning i periodiskav°agledarstrukturer som uppvisar glid symmetri. Analysen genomf¨ordes genom enmod matchnings-teknik som korrelerar de olika mod-koefficienterna fr°an separeraderegioner i strukturen med varandra. Denna teknik anv¨ands f¨or att ta framdispersionsrelationen f¨or tv°a endimensionella periodiska strukturer: en glid symmetriskkorrugerad meta-yta och en koaxial ledare belagd med periodiskt urgr¨opdah°aligheter. Mod matchnings-formuleringen presenteras i Kartesiska och cylindriskakoordinatsystem respektive f¨or de ovan n¨amnda fallen. Mod matchnings-resultatenj¨amf¨ors med data-simulerade resultat erh°allna fr°an CST Microwave Studio och de¨overenst¨ammer v¨al med varandra.

In this thesis, we analyze the electromagnetic wave propagation in waveguidestructuresexhibiting periodical geometry, including glide symmetry. The analysisis performed using a mode matching technique which correlates the different modecoefficients from separate but, connected regions in the structure. This technique isused to obtain the dispersion diagrams for two one-dimensional periodic structures:a glide-symmetric corrugated metasurface and a coaxial line loaded with periodicholes. The mode matching formulation is presented in Cartesian and cylindricalcoordinate system for the former and the later, respectively. The mode matchingresults are compared to simulated results obtained from the Eigenmode Solver inCST Microwave Studio and are found to agree very well., I detta examensarbete, analyseras elektromagnetisk v°agutbredning i periodiskav°agledarstrukturer som uppvisar glid symmetri. Analysen genomf¨ordes genom enmod matchnings-teknik som korrelerar de olika mod-koefficienterna fr°an separeraderegioner i strukturen med varandra. Denna teknik anv¨ands f¨or att ta framdispersionsrelationen f¨or tv°a endimensionella periodiska strukturer: en glid symmetriskkorrugerad meta-yta och en koaxial ledare belagd med periodiskt urgr¨opdah°aligheter. Mod matchnings-formuleringen presenteras i Kartesiska och cylindriskakoordinatsystem respektive f¨or de ovan n¨amnda fallen. Mod matchnings-resultatenj¨amf¨ors med data-simulerade resultat erh°allna fr°an CST Microwave Studio och de¨overenst¨ammer v¨al med varandra.

We report the lattice dynamics of 0.8Pb(Zr0.52Ti0.48)O3−(0.2−x)Pb(Zn1/3Nb2/3)O3−xPb(Al1/2Nb1/2)O3 (0.8PZT−(0.2−x)PZN−xPAN, 0.02≤x≤0.08) ceramics around morphotropic phase boundary (MPB) by infrared and Raman spectra. The dielectric functions in the wavenumbers range between 50 and 1000 cm−1 were extracted from the factorized oscillator model. The addition of PAN to PZT-PZN system introduces Al3+ ions to the B-site and all of these Raman-active modes in the measured range are related to B-site atoms vibration. The effect of PAN addition leads to infrared and Raman modes shifting to higher wavenumbers, because the atomic weight of Al is smaller than that of Zn. Therefore, the substitution of B-site atom in PZT-PZN system is the dominant reason to influence the frequency shift of infrared and Raman modes.

We report the lattice dynamics of 0.8Pb(Zr0.52Ti0.48)O3−(0.2−x)Pb(Zn1/3Nb2/3)O3−xPb(Al1/2Nb1/2)O3 (0.8PZT−(0.2−x)PZN−xPAN, 0.02≤x≤0.08) ceramics around morphotropic phase boundary (MPB) by infrared and Raman spectra. The dielectric functions in the wavenumbers range between 50 and 1000 cm−1 were extracted from the factorized oscillator model. The addition of PAN to PZT-PZN system introduces Al3+ ions to the B-site and all of these Raman-active modes in the measured range are related to B-site atoms vibration. The effect of PAN addition leads to infrared and Raman modes shifting to higher wavenumbers, because the atomic weight of Al is smaller than that of Zn. Therefore, the substitution of B-site atom in PZT-PZN system is the dominant reason to influence the frequency shift of infrared and Raman modes.

The natural dynamics are not ideal or linear. To understand their complex behavior, we needs to study the nonlinear dynamics in more simple models. This thesis is consist of two main setups. Both setups are simplified models for the behavior occurs in the complex systems. We studied in both systems the same nonlinear dynamics such as higher-harmonics, sub-harmonics, solitary waves,...etc. In Chapter (2), the propagation of nonlinear waves in a lattice of repelling particles is studied theoretically and experimentally. A simple experimental setup is proposed, consisting in an array of coupled magnetic dipoles. By driving harmonically the lattice at one boundary, we excite propagating waves and demonstrate different regimes of mode conversion into higher harmonics, strongly in influenced by dispersion. The phenomenon of acoustic dilatation of the chain is also predicted and discussed. The results are compared with the theoretical predictions of FPU equation, describing a chain of masses connected by nonlinear quadratic springs. The results can be extrapolated to other systems described by this equation. We studied theoretically and experimentally the generation and propagation of kinks in the system. We excite pulses at one boundary of the system and demonstrate the existence of kinks, whose properties are in very good agreement with the theoretical predictions, that is the equation that approaches, under the conditions of our experiments, the one corresponding to full model describing a chain of masses connected by magnetic forces. The results can be extrapolated to other systems described by this equation. Also, In the case of a lattice of finite length, where standing waves are formed, we report the observation of subharmonics of the driving wave. In chapter (3), we studied the propagation of intense acoustic waves in a multilayer crystal. The medium consists in a structured fluid, formed by a periodic array of fluid layerswith alternating linear acoustic propertie, La dinámica natural no es ideal ni lineal. Para entender su comportamiento complejo, necesitamos estudiar la dinámica no lineal en modelos más simples. Esta tesis consta de dos configuraciones principales. Ambas configuraciones son modelos simplificados de el comportamiento que se produce en los sistemas complejos. Estudiamos en ambos sistemas la misma dinámica no lineal como son la generación de armónicos superiores, los sub-armónicos, las ondas solitarias, etc. En elCapítulo (2), se estudia, tanto teórica comoexperimentalmente, la propagación de ondas no lineales en sistemas periodicos de partículas acopladas mediante fuerzas repulsivas. Se propone una configuración experimental simple, que consiste en una matriz de dipolos magnéticos acoplados. Inyectando armónicamente la señal en un extremo, excitamos ondas de propagación y demostramos diferentes regímenes de conversión de modos en armónicos, fuertemente influenciados por la dispersión. También se predice y se discute el fenómeno de dilatación acústica de la cadena. Los resultados se comparan con las predicciones teóricas de la ecuación FPU, describiendo una cadena de masas conectadas por muelles cuadráticos no lineales. Los resultados pueden ser extrapolados a otros sistemas descritos por esta ecuación. Estudiamos también teórica y experimentalmente la generación y propagación de kinks. Excitamos pulsos en la frontera del sistema y demostramos la existencia de kinks cuyas propiedades están en muy buen acuerdo con las predicciones teóricas, es decir, con la ecuación que aproxima bajo las condiciones de nuestros experimentos la correspondiente al modelo completo que describe un cadena de masas conectadas por fuerzas magnéticas. Los resultados pueden ser extrapolados a otros sistemas descritos por esta ecuación. Además, en el caso de una red finita, donde se forman ondas estacionarias, describimos la observación de subarmónicos del armónico principal. En el capítulo (3), estudiamos la propagación de ondas acústica, La dinàmica natural no és ideal ni tampoc lineal. Per entendre el seu comportament complex, es necessita estudiar la dinàmica no lineal dels models més simples. Aquesta tesi consisteix en l'estudi de dues configuracions principals, que són models simplificats del comportament que es produeix en els sistemes complexos. Estudiem en ambdós sistemes la mateixa dinàmica no lineal, com és la generació d'harmònics superiors, sub-harmònics, ones solitàries, etc. En el capítol (2), estudiem, tant teòrica com experimentalment, la propagació de les ones no lineals en sistemes periòdics de partícules acoblades mitjançant forces repulsives. Es proposa una configuració experimental simple, que consisteixen en una matriu de dipols magnètics acoblats. En conduint harmònicament la xarxa en un límit, excitemla propagació de les ones i demostrem diferents règims de conversió de modes en harmònics més alts, força influenciada per la dispersió. El fenomen de la dilatació acústica de la cadena també es prediu i es discuteix. Els resultats es comparen amb les prediccions teòriques que descriu una cadena de masses conectades per molls quadràtics no lineals. Els resultats es poden extrapolar a altres sistemes descrits per aquesta equació. Hem estudiat teòrica i experimentalment la generació i propagació de Kinks. Excitem polsos a la frontera del sistema i demostrem l'existència d'Kinks, les propietats desl quals estan en molt bon acord amb les prediccions teòriques, és a dir, de l'equació que aproxima sota les condicions dels nostres experiments la corresponent al model complet que descriu un cadena demasses connectades per forcesmagnètiques. Els resultats es poden extrapolar a altres sistemes descrits per aquesta equació. A més, en el cas d'una xarxa finita, on es formen ones estacionàries, descrivim l'observació de subarmónicos de l'harmònic principal. En el capítol (3), s'estudia la propagació d'ones acústiques intenses en un medi multicapa. El medi consisteix en un fluid estructurat, fo

The natural dynamics are not ideal or linear. To understand their complex behavior, we needs to study the nonlinear dynamics in more simple models. This thesis is consist of two main setups. Both setups are simplified models for the behavior occurs in the complex systems. We studied in both systems the same nonlinear dynamics such as higher-harmonics, sub-harmonics, solitary waves,...etc. In Chapter (2), the propagation of nonlinear waves in a lattice of repelling particles is studied theoretically and experimentally. A simple experimental setup is proposed, consisting in an array of coupled magnetic dipoles. By driving harmonically the lattice at one boundary, we excite propagating waves and demonstrate different regimes of mode conversion into higher harmonics, strongly in influenced by dispersion. The phenomenon of acoustic dilatation of the chain is also predicted and discussed. The results are compared with the theoretical predictions of FPU equation, describing a chain of masses connected by nonlinear quadratic springs. The results can be extrapolated to other systems described by this equation. We studied theoretically and experimentally the generation and propagation of kinks in the system. We excite pulses at one boundary of the system and demonstrate the existence of kinks, whose properties are in very good agreement with the theoretical predictions, that is the equation that approaches, under the conditions of our experiments, the one corresponding to full model describing a chain of masses connected by magnetic forces. The results can be extrapolated to other systems described by this equation. Also, In the case of a lattice of finite length, where standing waves are formed, we report the observation of subharmonics of the driving wave. In chapter (3), we studied the propagation of intense acoustic waves in a multilayer crystal. The medium consists in a structured fluid, formed by a periodic array of fluid layerswith alternating linear acoustic propertie, La dinámica natural no es ideal ni lineal. Para entender su comportamiento complejo, necesitamos estudiar la dinámica no lineal en modelos más simples. Esta tesis consta de dos configuraciones principales. Ambas configuraciones son modelos simplificados de el comportamiento que se produce en los sistemas complejos. Estudiamos en ambos sistemas la misma dinámica no lineal como son la generación de armónicos superiores, los sub-armónicos, las ondas solitarias, etc. En elCapítulo (2), se estudia, tanto teórica comoexperimentalmente, la propagación de ondas no lineales en sistemas periodicos de partículas acopladas mediante fuerzas repulsivas. Se propone una configuración experimental simple, que consiste en una matriz de dipolos magnéticos acoplados. Inyectando armónicamente la señal en un extremo, excitamos ondas de propagación y demostramos diferentes regímenes de conversión de modos en armónicos, fuertemente influenciados por la dispersión. También se predice y se discute el fenómeno de dilatación acústica de la cadena. Los resultados se comparan con las predicciones teóricas de la ecuación FPU, describiendo una cadena de masas conectadas por muelles cuadráticos no lineales. Los resultados pueden ser extrapolados a otros sistemas descritos por esta ecuación. Estudiamos también teórica y experimentalmente la generación y propagación de kinks. Excitamos pulsos en la frontera del sistema y demostramos la existencia de kinks cuyas propiedades están en muy buen acuerdo con las predicciones teóricas, es decir, con la ecuación que aproxima bajo las condiciones de nuestros experimentos la correspondiente al modelo completo que describe un cadena de masas conectadas por fuerzas magnéticas. Los resultados pueden ser extrapolados a otros sistemas descritos por esta ecuación. Además, en el caso de una red finita, donde se forman ondas estacionarias, describimos la observación de subarmónicos del armónico principal. En el capítulo (3), estudiamos la propagación de ondas acústica, La dinàmica natural no és ideal ni tampoc lineal. Per entendre el seu comportament complex, es necessita estudiar la dinàmica no lineal dels models més simples. Aquesta tesi consisteix en l'estudi de dues configuracions principals, que són models simplificats del comportament que es produeix en els sistemes complexos. Estudiem en ambdós sistemes la mateixa dinàmica no lineal, com és la generació d'harmònics superiors, sub-harmònics, ones solitàries, etc. En el capítol (2), estudiem, tant teòrica com experimentalment, la propagació de les ones no lineals en sistemes periòdics de partícules acoblades mitjançant forces repulsives. Es proposa una configuració experimental simple, que consisteixen en una matriu de dipols magnètics acoblats. En conduint harmònicament la xarxa en un límit, excitemla propagació de les ones i demostrem diferents règims de conversió de modes en harmònics més alts, força influenciada per la dispersió. El fenomen de la dilatació acústica de la cadena també es prediu i es discuteix. Els resultats es comparen amb les prediccions teòriques que descriu una cadena de masses conectades per molls quadràtics no lineals. Els resultats es poden extrapolar a altres sistemes descrits per aquesta equació. Hem estudiat teòrica i experimentalment la generació i propagació de Kinks. Excitem polsos a la frontera del sistema i demostrem l'existència d'Kinks, les propietats desl quals estan en molt bon acord amb les prediccions teòriques, és a dir, de l'equació que aproxima sota les condicions dels nostres experiments la corresponent al model complet que descriu un cadena demasses connectades per forcesmagnètiques. Els resultats es poden extrapolar a altres sistemes descrits per aquesta equació. A més, en el cas d'una xarxa finita, on es formen ones estacionàries, descrivim l'observació de subarmónicos de l'harmònic principal. En el capítol (3), s'estudia la propagació d'ones acústiques intenses en un medi multicapa. El medi consisteix en un fluid estructurat, fo

We present a procedure for constructing Summation-by-Parts operators with minimal dispersion error both near and far from numerical interfaces. Examples of such operators are constructed and compared with a higher order non-optimised Summation-by-Parts operator. Experiments show that the optimised operators are superior for wave propagation and turbulent flows involving large wavenumbers, long solution times and large ranges of resolution scales.

We present a procedure for constructing Summation-by-Parts operators with minimal dispersion error both near and far from numerical interfaces. Examples of such operators are constructed and compared with a higher order non-optimised Summation-by-Parts operator. Experiments show that the optimised operators are superior for wave propagation and turbulent flows involving large wavenumbers, long solution times and large ranges of resolution scales.

We present a procedure for constructing Summation-by-Parts operators with minimal dispersion error both near and far from numerical interfaces. Examples of such operators are constructed and compared with a higher order non-optimised Summation-by-Parts operator. Experiments show that the optimised operators are superior for wave propagation and turbulent flows involving large wavenumbers, long solution times and large ranges of resolution scales.

We present a procedure for constructing Summation-by-Parts operators with minimal dispersion error both near and far from numerical interfaces. Examples of such operators are constructed and compared with a higher order non-optimised Summation-by-Parts operator. Experiments show that the optimised operators are superior for wave propagation and turbulent flows involving large wavenumbers, long solution times and large ranges of resolution scales.

We present a procedure for constructing Summation-by-Parts operators with minimal dispersion error both near and far from numerical interfaces. Examples of such operators are constructed and compared with a higher order non-optimised Summation-by-Parts operator. Experiments show that the optimised operators are superior for wave propagation and turbulent flows involving large wavenumbers, long solution times and large ranges of resolution scales.

Using the recent observation of gravitational waves (GW) produced by a black-hole merger, we place a lower bound on the energy above which a multifractal spacetime would display an anomalous geometry and, in particular, violations of Lorentz invariance. In the so-called multifractional theory with q-derivatives, we show that the deformation of dispersion relations is much stronger than in generic quantum-gravity approaches (including loop quantum gravity) and, contrary to the latter, present observations on GWs can place very strong bounds on the characteristic scales at which spacetime deviates from standard Minkowski. The energy at which multifractal effects should become apparent is E∗>1014GeV (thus improving previous bounds by 12 orders of magnitude) when the exponents in the measure are fixed to their central value 1 / 2. We also estimate, for the first time, the effect of logarithmic oscillations in the measure (corresponding to a discrete spacetime structure) and find that they do not change much the bounds obtained in their absence, unless the amplitude of the oscillations is fine tuned. This feature, unavailable in known quantum-gravity scenarios, may help the theory to avoid being ruled out by gamma-ray burst (GRB) observations, for which E∗>1017GeV or greater.

The paper deals with analytically studying transverse waves propagation in an axially moving string with periodically modulated cross section. The structure effectively models various relevant technological systems, e.g. belts, thread lines, band saws, etc., and, in particular, roller chain drives for diesel engines by capturing both their spatial periodicity and axial motion. The Method of Varying Amplitudes is employed in the analysis. It is shown that the compound wave traveling in the axially moving periodic string comprises many components with different frequencies and wavenumbers. This is in contrast to non-moving periodic structures, for which all components of the corresponding compound wave feature the same frequency. Due to this "multi-frequency" character of the wave motion, the conventional notion of frequency band-gaps appears to be not applicable for the moving periodic strings. Thus, for such structures, by frequency band-gaps it is proposed to understand frequency ranges in which the primary component of the compound wave attenuates. Such frequency band-gaps can be present for a moving periodic string, but only if its axial velocity is lower than the transverse wave speed, and, the higher the axial velocity, the narrower the frequency band-gaps. The revealed effects could be of potential importance for applications, e.g. they indicate that due to spatial inhomogeneity, oscillations of axially moving periodic chains always involve a multitude of frequencies.

We study the semiclassical asymptotic approximation of the spectrum of the two-dimensional Schrödinger operator with a potential periodic in x and increasing at infinity in y. We show that the lower part of the spectrum has a band structure (where bands can overlap) and calculate their widths and dispersion relations between energy and quasimomenta. The key role in the obtained asymptotic approximation is played by librations, i.e., unstable periodic trajectories of the Hamiltonian system with an inverted potential. We also present an effective numerical algorithm for computing the widths of bands and discuss applications to quantum dimers. © 2016, Pleiades Publishing, Ltd.

A comprehensive understanding of the stability of shear flows is a fundamental problem in fluid mechanics and it has been a subject of both theoretical and practical interest in engineering research. A key aspect of these dynamic flows is the behaviour exhibited by the instabilities as it evolves from initial small perturbations of an equilibrium state, and may lead to fluctuations. In order to control these fluctuations, a study on the spatial and temporal evolution of the perturbations must be carried out. The objective of this thesis is to perform the spatio-temporal stability analysis on the plane, incompressible shear layers representing confined and unconfined shear flows. The analysis requires the estimation of the response of the flow to the initial perturbations for fixed values of relevant parameters. The numerical tools are developed for the low order piecewise linear profile approximations to the shear layers. The influence of typical flow features, like single and multiple shear dynamics, on the stability behaviour is studied and the convective/absolute instability boundary for various parameter combinations are identified. After validation for the analytical models, the numerical tools are extended to the non-analytical models. The analysis is then performed for higher order approximations of the experimental base flows in order to validate the results from the toolkit. A variation of the flow features and variables can change the stability behaviour of the shear flows. The single shear layer dynamics cannot contribute to absolute instability in the absence of a dispersive medium, like surface tension. The surface tension acts as a stabilising mechanism for perturbations of short wavelength. The multiple shear layer dynamics dictates that the unconfined jet or wake flow is more unstable than the single shear layer with equivalent parameter values, and that very high values of surface tension stabilises all perturbations. For confined jet or wake flows, Mechanical, Maritime and Materials Engineering, Process and Energy

Mit dem Begriff Wellenleiterquantenelektrodynamik (WQED) wird gemeinhin die Physik des quantisierten und in eindimensionalen Wellenleitern geführten Lichtes in Wechselwirkung mit einzelnen Emittern bezeichnet. In dieser Arbeit untersuche ich Effekte der WQED für einzelne Dreiniveausysteme (3NS) bzw. Paare von Zweiniveausystemen (2NS), die in den Wellenleiter eingebettet sind. Hierzu bediene ich mich hauptsächlich numerischer Methoden und betrachte die Modellsysteme im Rahmen der Drehwellennäherung. Ich untersuche die Dynamik der Streuung einzelner Photonen an einzelnen, in den Wellenleiter eingebetteten 3NS. Dabei analysiere ich den Einfluss dunkler bzw. nahezu dunkler Zustände der 3NS auf die Streuung und zeige, wie sich mit Hilfe stationärer elektrischer Treibfelder gezielt auf die Streuung einwirken lässt. Ich quantifiziere Verschränkung zwischen dem Lichtfeld im Wellenleiter und den Emittern mit Hilfe der Schmidt-Zerlegung und untersuche den Einfluss der Form der Einhüllenden eines Einzelphotonpulses auf die Ausbeute der Verschränkungserzeugung bei der Streuung des Photons an einem einzelnen Lambda-System im Wellenleiter. Hier zeigt sich, dass die Breite der Einhüllenden im k-Raum und die Emissionszeiten der beiden Übergänge des 3NS die maßgeblichen Parameter darstellen. Abschließend ergründe ich die Emissionsdynamik zweier im Abstand L in den Wellenleiter eingebetteter 2NS. Diese Dynamik wird insbesondere durch kavitätsartige und polaritonische Zustände des Systems aus Wellenleiter und Emitter ausschlaggebend beeinflusst. Bei der kollektiven Emission der 2NS treten - abhängig vom Abstand L - Sub- bzw. Superradianz auf. Dabei nimmt die Intensität dieser Effekte mit längerem Abstand L zu. Diese Eigenart lässt sich auf die Eindimensionalität des Wellenleiters zurückführen., The field of waveguide quantum electrodynamics (WQED) deals with the physics of quantised light in one-dimensional (1D) waveguides coupled to single emitters. In this thesis, I investigate WQED effects for single three-level systems (3LS) and pairs of two-level systems (2LS), respectively, which are embedded in the waveguide. To this end, I utilise numerical techniques and consider all model systems within the rotating wave approximation. I investigate the dynamics of single-photon scattering by single, embedded 3LS. In doing so, I analyse the influence of dark and almost-dark states of the 3LS on the scattering dynamics. I also show, how stationary electrical driving fields can control the outcome of the scattering. I quantify entanglement between the waveguide''s light field and single emitters by utilising the Schmidt decomposition. I apply this formalism to a lambda-system embedded in a 1D waveguide and study the generation of entanglement by scattering single-photon pulses with different envelopes on the emitter. I show that this entanglement generation is mainly determined by the photon''s width in k-space and the 3LS''s emission times. Finally, I explore the emission dynamics of a pair of 2LS embedded by a distance L into the waveguide. These dynamics are primarily governed by bound states in the continuum and by polaritonic atom-photon bound-states. For collective emission processes of the two 2LS, sub- and superradiance appear and depend strongly on the 2LS''s distance: the effects increase for larger L. This is an exclusive property of the 1D nature of the waveguide.

Mit dem Begriff Wellenleiterquantenelektrodynamik (WQED) wird gemeinhin die Physik des quantisierten und in eindimensionalen Wellenleitern geführten Lichtes in Wechselwirkung mit einzelnen Emittern bezeichnet. In dieser Arbeit untersuche ich Effekte der WQED für einzelne Dreiniveausysteme (3NS) bzw. Paare von Zweiniveausystemen (2NS), die in den Wellenleiter eingebettet sind. Hierzu bediene ich mich hauptsächlich numerischer Methoden und betrachte die Modellsysteme im Rahmen der Drehwellennäherung. Ich untersuche die Dynamik der Streuung einzelner Photonen an einzelnen, in den Wellenleiter eingebetteten 3NS. Dabei analysiere ich den Einfluss dunkler bzw. nahezu dunkler Zustände der 3NS auf die Streuung und zeige, wie sich mit Hilfe stationärer elektrischer Treibfelder gezielt auf die Streuung einwirken lässt. Ich quantifiziere Verschränkung zwischen dem Lichtfeld im Wellenleiter und den Emittern mit Hilfe der Schmidt-Zerlegung und untersuche den Einfluss der Form der Einhüllenden eines Einzelphotonpulses auf die Ausbeute der Verschränkungserzeugung bei der Streuung des Photons an einem einzelnen Lambda-System im Wellenleiter. Hier zeigt sich, dass die Breite der Einhüllenden im k-Raum und die Emissionszeiten der beiden Übergänge des 3NS die maßgeblichen Parameter darstellen. Abschließend ergründe ich die Emissionsdynamik zweier im Abstand L in den Wellenleiter eingebetteter 2NS. Diese Dynamik wird insbesondere durch kavitätsartige und polaritonische Zustände des Systems aus Wellenleiter und Emitter ausschlaggebend beeinflusst. Bei der kollektiven Emission der 2NS treten - abhängig vom Abstand L - Sub- bzw. Superradianz auf. Dabei nimmt die Intensität dieser Effekte mit längerem Abstand L zu. Diese Eigenart lässt sich auf die Eindimensionalität des Wellenleiters zurückführen., The field of waveguide quantum electrodynamics (WQED) deals with the physics of quantised light in one-dimensional (1D) waveguides coupled to single emitters. In this thesis, I investigate WQED effects for single three-level systems (3LS) and pairs of two-level systems (2LS), respectively, which are embedded in the waveguide. To this end, I utilise numerical techniques and consider all model systems within the rotating wave approximation. I investigate the dynamics of single-photon scattering by single, embedded 3LS. In doing so, I analyse the influence of dark and almost-dark states of the 3LS on the scattering dynamics. I also show, how stationary electrical driving fields can control the outcome of the scattering. I quantify entanglement between the waveguide''s light field and single emitters by utilising the Schmidt decomposition. I apply this formalism to a lambda-system embedded in a 1D waveguide and study the generation of entanglement by scattering single-photon pulses with different envelopes on the emitter. I show that this entanglement generation is mainly determined by the photon''s width in k-space and the 3LS''s emission times. Finally, I explore the emission dynamics of a pair of 2LS embedded by a distance L into the waveguide. These dynamics are primarily governed by bound states in the continuum and by polaritonic atom-photon bound-states. For collective emission processes of the two 2LS, sub- and superradiance appear and depend strongly on the 2LS''s distance: the effects increase for larger L. This is an exclusive property of the 1D nature of the waveguide.

The paper deals with analytically predicting the effects of weak nonlinearity on the dispersion relation and frequency band-gaps of a periodic Bernoulli– Euler beam performing bending oscillations. Two cases are considered: (i) large transverse deflections, where nonlinear (true) curvature, nonlinear material and nonlinear inertia owing to longitudinal motions of the beam are taken into account, and (ii) midplane stretching nonlinearity. A novel approach is employed, the method of varying amplitudes. As a result, the isolated as well as combined effects of the considered sources of nonlinearities are revealed. It is shown that nonlinear inertia has the most substantial impact on the dispersion relation of a nonuniform beam by removing all frequency band-gaps. Explanations of the revealed effects are suggested, and validated by experiments and numerical simulation.

A comprehensive understanding of the stability of shear flows is a fundamental problem in fluid mechanics and it has been a subject of both theoretical and practical interest in engineering research. A key aspect of these dynamic flows is the behaviour exhibited by the instabilities as it evolves from initial small perturbations of an equilibrium state, and may lead to fluctuations. In order to control these fluctuations, a study on the spatial and temporal evolution of the perturbations must be carried out. The objective of this thesis is to perform the spatio-temporal stability analysis on the plane, incompressible shear layers representing confined and unconfined shear flows. The analysis requires the estimation of the response of the flow to the initial perturbations for fixed values of relevant parameters. The numerical tools are developed for the low order piecewise linear profile approximations to the shear layers. The influence of typical flow features, like single and multiple shear dynamics, on the stability behaviour is studied and the convective/absolute instability boundary for various parameter combinations are identified. After validation for the analytical models, the numerical tools are extended to the non-analytical models. The analysis is then performed for higher order approximations of the experimental base flows in order to validate the results from the toolkit. A variation of the flow features and variables can change the stability behaviour of the shear flows. The single shear layer dynamics cannot contribute to absolute instability in the absence of a dispersive medium, like surface tension. The surface tension acts as a stabilising mechanism for perturbations of short wavelength. The multiple shear layer dynamics dictates that the unconfined jet or wake flow is more unstable than the single shear layer with equivalent parameter values, and that very high values of surface tension stabilises all perturbations. For confined jet or wake flows, Mechanical, Maritime and Materials Engineering, Process and Energy

With the unique possibilities for controlling light in nanoscale devices, graphene plasmonics has opened new perspectives to the nanophotonics community with potential applications in metamaterials, modulators, photodetectors, and sensors. This paper briefly reviews the recent exciting progress in graphene plasmonics. We begin with a general description for optical properties of graphene, particularly focusing on the dispersion of graphene-plasmon polaritons. The dispersion relation of graphene-plasmon polaritons of spatially extended graphene is expressed in terms of the local response limit with intraband contribution. With this theoretical foundation of graphene-plasmon polaritons, we then discuss recent exciting progress, paying specific attention to the following topics: excitation of graphene plasmon polaritons, electron-phonon interactions in graphene on polar substrates, and tunable graphene plasmonics with applications in modulators and sensors. Finally, we seek to address some of the apparent challenges and promising perspectives of graphene plasmonics. [Front. Phys. 11(2), 117801 (2016) doi:10.1007/s11467-016-0551-z].

Tesis por compendio, [EN] Phononic crystals are artificial materials formed by a periodic arrangement of inclusions embedded into a host medium, where each of them can be solid or fluid. By controlling the geometry and the impedance contrast of its constituent materials, one can control the dispersive properties of waves, giving rise to a huge variety of interesting and fundamental phenomena in the context of wave propagation. When a propagating wave encounters a medium with different physical properties it can be transmitted and reflected in lossless media, but also absorbed if dissipation is taken into account. These fundamental phenomena have been classically explained in the context of homogeneous media, but it has been a subject of increasing interest in the context of periodic structures in recent years as well. This thesis is devoted to the study of different effects found in sonic and phononic crystals associated with transmission, reflection and absorption of waves, as well as the development of a technique for the characterization of its dispersive properties, described by the band structure. We start discussing the control of wave propagation in transmission in conservative systems. Specifically, our interest is to show how sonic crystals can modify the spatial dispersion of propagating waves leading to control the diffractive broadening of sound beams. Making use of the spatial dispersion curves extracted from the analysis of the band structure, we first predict zero and negative diffraction of waves at frequencies close to the band-edge, resulting in collimation and focusing of sound beams in and behind a 3D sonic crystal, and later demonstrate it through experimental measurements. The focusing efficiency of a 3D sonic crystal is limited due to the strong scattering inside the crystal, characteristic of the diffraction regime. To overcome this limitation we consider axisymmetric structures working in the long wavelength regime, as a gradient index lens. In this regime, the, [ES] Los cristales fonónicos son materiales artificiales formados por una disposición periódica de inclusiones en un medio, pudiendo ambos ser de carácter sólido o fluido. Controlando la geometría y el contraste de impedancias entre los materiales constituyentes se pueden controlar las propiedades dispersivas de las ondas. Cuando una onda propagante se encuentra un medio con diferentes propiedades físicas puede ser transmitida y reflejada, en medios sin pérdidas, pero también absorbida, si la disipación es tenida en cuenta. La presente tesis está dedicada al estudio de diferentes efectos presentes en cristales sónicos y fonónicos relacionados con la transmisión, reflexión y absorción de ondas, así como el desarrollo de una técnica para la caracterización de sus propiedades dispersivas, descritas por la estructura de bandas. En primer lugar, se estudia el control de la propagación de ondas en transmisión en sistemas conservativos. Específicamente, nuestro interés se centra en mostrar cómo los cristales sónicos son capaces de modificar la dispersión espacial de las ondas propagantes, dando lugar al control del ensanchamiento de haces de sonido. Haciendo uso de las curvas de dispersión espacial extraídas del análisis de la estructura de bandas, se predice primero la difracción nula y negativa de ondas a frecuencias cercanas al borde de la banda, resultando en la colimación y focalización de haces acústicos en el interior y detrás de un cristal sónico 3D, y posteriormente se demuestra mediante medidas experimentales. La eficiencia de focalización de un cristal sónico 3D está limitada debido a las múltiples reflexiones existentes en el interior del cristal. Para superar esta limitación se consideran estructuras axisimétricas trabajando en el régimen de longitud de onda larga, como lentes de gradiente de índice. En este régimen, las reflexiones internas se reducen fuertemente y, en configuración axisimétrica, la adaptación de simetría con fuentes acústicas radiando haces, [CA] Els cristalls fonònics són materials artificials formats per una disposició d'inclusions en un medi, ambdós poden ser sòlids o fluids. Controlant la geometría i el contrast d'impedàncies dels seus materials constituents, és poden controlar les propietats dispersives de les ondes, permetent una gran varietatde fenòmens fonamentals interessants en el context de la propagació d'ones. Quan una ona propagant troba un medi amb pèrdues amb propietats físiques diferents es pot transmetre i reflectir, però també absorbida si la dissipació es té en compte. Aquests fenòmens fonamentals s'han explicat clàssicament en el context de medis homogenis, però també ha sigut un tema de creixent interés en el context d'estructures periòdiques en els últims anys. Aquesta tesi doctoral tracta de l'estudi de diferents efectes en cristalls fonònics i sònics lligats a la transmissió, reflexió i absorció d'ones, així com del desenvolupament d'una tècnica de caracterització de les propietats dispersives, descrites mitjançant la estructura de bandes. En primer lloc, s'estudia el control de la propagació ondulatori en transmissió en sistemes conservatius. Més específicament, el nostre interés és mostrar com els cristalls sonors poden modificar la dispersió espacial d'ones propagants donant lloc al control de l'amplària per difracció dels feixos sonors. Mitjançant les corbes dispersió espacial obtingudes de l'anàlisi de l'estructura de bandes, es prediu, en primer lloc, la difracció d'ones zero i negativa a freqüències próximes al final de banda. El resultat és la collimació i focalització de feixos sonors dins i darrere de cristalls de so. Després es mostra amb mesures experimentals. L'eficiència de focalització d'un cristall de so 3D està limitada per la gran dispersió d'ones dins del cristall, que és característic del règim difractiu. Per a superar aquesta limitació, estructures axisimètriques que treballen en el règim de llargues longituds d'ona, i es comporten com a lents de gradient d'

Tesis por compendio, [EN] Phononic crystals are artificial materials formed by a periodic arrangement of inclusions embedded into a host medium, where each of them can be solid or fluid. By controlling the geometry and the impedance contrast of its constituent materials, one can control the dispersive properties of waves, giving rise to a huge variety of interesting and fundamental phenomena in the context of wave propagation. When a propagating wave encounters a medium with different physical properties it can be transmitted and reflected in lossless media, but also absorbed if dissipation is taken into account. These fundamental phenomena have been classically explained in the context of homogeneous media, but it has been a subject of increasing interest in the context of periodic structures in recent years as well. This thesis is devoted to the study of different effects found in sonic and phononic crystals associated with transmission, reflection and absorption of waves, as well as the development of a technique for the characterization of its dispersive properties, described by the band structure. We start discussing the control of wave propagation in transmission in conservative systems. Specifically, our interest is to show how sonic crystals can modify the spatial dispersion of propagating waves leading to control the diffractive broadening of sound beams. Making use of the spatial dispersion curves extracted from the analysis of the band structure, we first predict zero and negative diffraction of waves at frequencies close to the band-edge, resulting in collimation and focusing of sound beams in and behind a 3D sonic crystal, and later demonstrate it through experimental measurements. The focusing efficiency of a 3D sonic crystal is limited due to the strong scattering inside the crystal, characteristic of the diffraction regime. To overcome this limitation we consider axisymmetric structures working in the long wavelength regime, as a gradient index lens. In this regime, the, [ES] Los cristales fonónicos son materiales artificiales formados por una disposición periódica de inclusiones en un medio, pudiendo ambos ser de carácter sólido o fluido. Controlando la geometría y el contraste de impedancias entre los materiales constituyentes se pueden controlar las propiedades dispersivas de las ondas. Cuando una onda propagante se encuentra un medio con diferentes propiedades físicas puede ser transmitida y reflejada, en medios sin pérdidas, pero también absorbida, si la disipación es tenida en cuenta. La presente tesis está dedicada al estudio de diferentes efectos presentes en cristales sónicos y fonónicos relacionados con la transmisión, reflexión y absorción de ondas, así como el desarrollo de una técnica para la caracterización de sus propiedades dispersivas, descritas por la estructura de bandas. En primer lugar, se estudia el control de la propagación de ondas en transmisión en sistemas conservativos. Específicamente, nuestro interés se centra en mostrar cómo los cristales sónicos son capaces de modificar la dispersión espacial de las ondas propagantes, dando lugar al control del ensanchamiento de haces de sonido. Haciendo uso de las curvas de dispersión espacial extraídas del análisis de la estructura de bandas, se predice primero la difracción nula y negativa de ondas a frecuencias cercanas al borde de la banda, resultando en la colimación y focalización de haces acústicos en el interior y detrás de un cristal sónico 3D, y posteriormente se demuestra mediante medidas experimentales. La eficiencia de focalización de un cristal sónico 3D está limitada debido a las múltiples reflexiones existentes en el interior del cristal. Para superar esta limitación se consideran estructuras axisimétricas trabajando en el régimen de longitud de onda larga, como lentes de gradiente de índice. En este régimen, las reflexiones internas se reducen fuertemente y, en configuración axisimétrica, la adaptación de simetría con fuentes acústicas radiando haces, [CA] Els cristalls fonònics són materials artificials formats per una disposició d'inclusions en un medi, ambdós poden ser sòlids o fluids. Controlant la geometría i el contrast d'impedàncies dels seus materials constituents, és poden controlar les propietats dispersives de les ondes, permetent una gran varietatde fenòmens fonamentals interessants en el context de la propagació d'ones. Quan una ona propagant troba un medi amb pèrdues amb propietats físiques diferents es pot transmetre i reflectir, però també absorbida si la dissipació es té en compte. Aquests fenòmens fonamentals s'han explicat clàssicament en el context de medis homogenis, però també ha sigut un tema de creixent interés en el context d'estructures periòdiques en els últims anys. Aquesta tesi doctoral tracta de l'estudi de diferents efectes en cristalls fonònics i sònics lligats a la transmissió, reflexió i absorció d'ones, així com del desenvolupament d'una tècnica de caracterització de les propietats dispersives, descrites mitjançant la estructura de bandes. En primer lloc, s'estudia el control de la propagació ondulatori en transmissió en sistemes conservatius. Més específicament, el nostre interés és mostrar com els cristalls sonors poden modificar la dispersió espacial d'ones propagants donant lloc al control de l'amplària per difracció dels feixos sonors. Mitjançant les corbes dispersió espacial obtingudes de l'anàlisi de l'estructura de bandes, es prediu, en primer lloc, la difracció d'ones zero i negativa a freqüències próximes al final de banda. El resultat és la collimació i focalització de feixos sonors dins i darrere de cristalls de so. Després es mostra amb mesures experimentals. L'eficiència de focalització d'un cristall de so 3D està limitada per la gran dispersió d'ones dins del cristall, que és característic del règim difractiu. Per a superar aquesta limitació, estructures axisimètriques que treballen en el règim de llargues longituds d'ona, i es comporten com a lents de gradient d'