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Intramolecular vibrational energy relaxation seen as expansion in phase space. I. Some experimental results for H2O+(X̃ 2B1), C2H4 +(X̃ 2B3), and HCN+(B̃2Σ +)
http://hdl.handle.net/2268/186472
Title: Intramolecular vibrational energy relaxation seen as expansion in phase space. I. Some experimental results for H2O+(X̃ 2B1), C2H4 +(X̃ 2B3), and HCN+(B̃2Σ +)
<br/>
<br/>Author, coauthor: Lorquet, JeanClaude; PavlovVerevkin, V. B.
<br/>
<br/>Abstract: It has been shown by Heller that a nonstationary wave packet resulting from a FranckCondon transition evolves on the potential energy surface of the final electronic state and propagates through phase space at a rate which can be determined from the autocorrelation function \C(t)\2 =  〈∅(0) ∅(t) ) 2. Since C(t) can be obtained by Fourier transformation of an optical spectrum S(E), i.e., from an observable quantity, it is possible to derive from an experimental measurement information concerning the density operator of a socalled dynamical statistical ensemble (DSE). This density operator, denoted ρav, represents a statistical mixture of the eigenstates of the system with weights determined by the dynamics of the system. It becomes diagonal after a socalled break time Script T sign;B. Its measure, according to a definition due to Stechel, can be interpreted as an effective number of states (denoted script N) that significantly contribute to the dynamics. The break time Script T sign;B represents the finite period of time allowed to expand in the phase space and after which no further progress can be made. Therefore, the number script N∞ of phase space cells which are accessed after a very long interval of time (or in practice after the break time) remains limited. Information on the validity of statistical theories of unimolecular reactions is contained in the fraction ℱ of the available phase space which is eventually explored. In order to assess the representativity of the sampling, it is necessary to account for the selection rule which requires all the states counted in script N ∞ to belong to the totally symmetric representation. It is also appropriate to estimate the role played by Fermi resonances and similar vibrational interactions which bring about energy flow into zeroorder antisymmetric modes. A method to carry out the necessary partitionings is suggested. The functions script N T and ℛ T, and the quantities Script T signB, script N ∞, t script N, and ℱ have been determined from experimental data in three cases. In each case, the rate ℛT = d script N r/dT starts from an initial value of zero, increases up to a maximum which is reached after a time of the order of 1014 s, and then exhibits an overall decrease upon which oscillations are superimposed. For state X̃ 2B1 of H2O+, Script T signB ≃a 2.4×1014 s and Script T sign ≃ 0.3. The wave packet never accesses that part of the phase space that corresponds to the excitation of antisymmetric vibrations. For state X̃ 2B3u of C2 H4 +, Script T signB ≃1.6 × 1013 s and Script T sign ≃ * 5×104. This fraction raises to 6 × 10 3 if measured with respect to the effectively available phase space. When the spectrum consists of a discrete part followed by a dissociation continuum, the method can be extended to study the behavior of the bound part of the wave packet only. This has been applied to state B̃ 2Σ+ of HCN+ which is characterized by a very irregular spectrum. This case offers an example of complete occupation of phase space after a break time which is of the order of 2 ×10 13 s. © 1990 American Institute of Physics.

Graphene with Adatoms: Tuning the magnetic moment with an applied voltage
http://hdl.handle.net/2268/186471
Title: Graphene with Adatoms: Tuning the magnetic moment with an applied voltage
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<br/>Author, coauthor: Pike, Nicholas

Model for the spindependent Seebeck coefficient of InSb in a magnetic field
http://hdl.handle.net/2268/186470
Title: Model for the spindependent Seebeck coefficient of InSb in a magnetic field
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<br/>Author, coauthor: Pike, Nicholas; Stroud, David

Plasmonic Waves on a chain of metallic nanoparticles: effects of a liquidcrystalline host
http://hdl.handle.net/2268/186468
Title: Plasmonic Waves on a chain of metallic nanoparticles: effects of a liquidcrystalline host
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<br/>Author, coauthor: Pike, Nicholas; Stroud, David

TightBinding Model for Adatoms on Graphene: Analytical Density of States, spectral function and induced magnetic moment
http://hdl.handle.net/2268/186467
Title: TightBinding Model for Adatoms on Graphene: Analytical Density of States, spectral function and induced magnetic moment
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<br/>Author, coauthor: Pike, Nicholas; Stroud, David

Nanosession: Multiferroic Thin Films and Heterostructures
http://hdl.handle.net/2268/186396
Title: Nanosession: Multiferroic Thin Films and Heterostructures
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<br/>Author, coauthor: Burton, J. D.; Yin, J; Li, X. G.; Kim, Y.M.; Borisevich, A. Y.; Li, Q.; Tsymbal, E. Y.; Pantel, D.; Goetze, S.; Alexe, M.; Hesse, D.; Geprägs, S; Opel, M; Goennenwein, S T B; Gross, R; Zanolli, Zeila; Wojdel, J C; Iniguez, J; Ghosez, Philippe; Glavic, A; Voigt, J; Schierle, E; Weschke, E; Brückel, T; Fontcuberta, J; Fina, I; Fàbrega, L; Martí, X; Sánchez, F; Lorenz, M; Ziese, M; Wagner, G; Esquinazi, P; Grundmann, M
<br/>
<br/>Abstract: This chapter presents the theoretical and experimental evidence of a novel magnetoelectric mechanism producing a giant resistive switching effect at the interface between a ferroelectric perovskite oxide, BaTiO3 (BTO), and a complex oxide manganite electrode, La1xSrxMnO3. It presents a detailed study of the magnetic properties of multiferroic hybrid systems consisting of BTO as the ferroelectric and Ni or Fe3O4 as the ferromagnetic layers. The chapter discusses the possibility of achieving electric control of the magnetization, possibly at room temperature, through a specific (trilinear) coupling of the polarization with two other nonpolar lattice instabilities which occurs in the socalled hybrid improper ferroelectrics. Firstprinciples modelling techniques are used to investigate a promising system: BiFeO3/LaFeO3 superlattice. It presents the investigation of the multiferroic properties in TbMnO3 thin films with soft Xray resonant magnetic scattering (XRMS) performed at the UE46PGM1 beamline of BESSY II.

Multifractality of quantum wave functions in the presence of perturbations
http://hdl.handle.net/2268/186352
Title: Multifractality of quantum wave functions in the presence of perturbations
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<br/>Author, coauthor: Dubertrand, Rémy; GarciaMata, Ignacio; Georgeot, Bertrand; Giraud, Olivier; Lemarié, Gabriel; Martin, John
<br/>
<br/>Abstract: We present a comprehensive study of the destruction of quantum multifractality in the presence of perturbations. We study diverse representative models displaying multifractality, including a pseudointegrable system, the Anderson model, and a random matrix model. We apply several types of natural perturbations which can be relevant for experimental implementations. We construct an analytical theory for certain cases and perform extensive largescale numerical simulations in other cases. The data are analyzed through refined methods including double scaling analysis. Our results confirm the recent conjecture that multifractality breaks down following two scenarios. In the first one, multifractality is preserved unchanged below a certain characteristic length which decreases with perturbation strength. In the second one, multifractality is affected at all scales and disappears uniformly for a strongenough perturbation. Our refined analysis shows that subtle variants of these scenarios can be present in certain cases. This study could guide experimental implementations in order to observe quantum multifractality in real systems.

Maximal fidelity between symmetric multiqubit states and entanglement classes
http://hdl.handle.net/2268/186303
Title: Maximal fidelity between symmetric multiqubit states and entanglement classes
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<br/>Author, coauthor: Neven, Antoine; Mathonet, Pierre; Gühne, Otfried; Bastin, Thierry
<br/>
<br/>Abstract: We present the results of our research concerning a conjecture about the maximal fidelity between a symmetric (permutation invariant) multiqubit
state and the states belonging to a given entanglement class.

The onset, evolution and magnetic braking of vortex lattice instabilities in nanostructured superconducting films
http://hdl.handle.net/2268/186132
Title: The onset, evolution and magnetic braking of vortex lattice instabilities in nanostructured superconducting films
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<br/>Author, coauthor: Adami, ObaïdAllah; Jelic, Zeljko; Xue, Cun; AbdelHafiez, Mahmoud; Hackens, Benoit; Moshchalkov, Victor V.; Milosevic, Milorad V.; Van de Vondel, Joris; Silhanek, Alejandro
<br/>
<br/>Abstract: In 1976 Larkin and Ovchinnikov [Sov. Phys. JETP 41, 960 (1976)] predicted that vortex matter
in superconductors driven by an electrical current can undergo an abrupt dynamic transition from a fluxflow regime to a more dissipative state at suficiently high vortex velocities. Typically this transition manifests itself as a large voltage jump at a particular current density, socalled instability current density J, which is smaller than the depairing current. By tuning the effective pinning strength in Al fi lms, using an artifi cial periodic pinning array of triangular holes, we show that a unique and well defi ned instability current density exists if the pinning is strong, whereas a series of multiple voltage transitions appear in the relatively weaker pinning regime. This behavior is consistent with timedependent GinzburgLandau simulations, where the multiplestep transition can be unambiguously attributed to the progressive development of vortex chains and subsequently phaseslip lines. In addition, we explore experimentally the magnetic braking e ffects, caused by a thick Cu layer deposited on top of the superconductor, on the instabilities and the vortex ratchet effect.

Abinitio calcualtion of spindependent transport quantities in disordered materials
http://hdl.handle.net/2268/186075
Title: Abinitio calcualtion of spindependent transport quantities in disordered materials
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<br/>Author, coauthor: Di Gennaro, Marco

The lightfront gaugeinvariant energymomentum tensor
http://hdl.handle.net/2268/186006
Title: The lightfront gaugeinvariant energymomentum tensor
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<br/>Author, coauthor: Lorce, Cédric

Spinorbit correlations in the nucleon
http://hdl.handle.net/2268/186005
Title: Spinorbit correlations in the nucleon
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<br/>Author, coauthor: Lorce, Cédric

Gauge symmetry and background independence: Should the proton spin decomposition be path independent?
http://hdl.handle.net/2268/186004
Title: Gauge symmetry and background independence: Should the proton spin decomposition be path independent?
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<br/>Author, coauthor: Lorce, Cédric

Coherence and manybody effects in the transport of Bose–Einstein condensates
http://hdl.handle.net/2268/185909
Title: Coherence and manybody effects in the transport of Bose–Einstein condensates
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<br/>Author, coauthor: Dujardin, Julien
<br/>
<br/>Abstract: This thesis presents investigations on the interplay of coherence and manybody effects in the quasi onedimensional transport of BoseEinstein condensates (BEC) through scattering potentials. Such configurations can be realized with guided atom lasers that provide a coherent atomic beam. An exact theoretical description of the dynamics is out of reach due to the presence atomatom interactions. Different levels of approximations are nevertheless possible with their strengths and weaknesses. The meanfield approximation, where the dynamics of the BEC is governed by the GrossPitaevskii equation, is most commonly used in the field of ultracold atoms.
In this thesis the truncated Wigner method is used to go beyond the standard GrossPitaevskii description. This method is adapted in order to study the scattering of BoseEinstein condensates in onedimensional waveguides where atomatom interactions and external potentials are nonvanishing only in a finite region of space. In this case, the truncated Wigner method is combined with the smooth exterior complex scaling method and incorporates quantum noise that originate from the vacuum fluctuations in the waveguide. Inelastic scattering is shown to play a major role in the resonant transport of BEC through a symmetric double potential barrier effectively forming an atomic quantum dot. Indeed, fully resonant transmission is prohibited and incoherent atoms as well as collective oscillations are detected in the transmitted beam. It is also shown that inelastic scattering destroys Anderson localization in the case of transport through disordered potentials. The classical (incoherent) ohmic transmission is recovered for finite atomatom interactions.
The validity of the truncated Wigner method is then assessed using the semiclassical van VleckGutzwiller propagator in the Fock space of the manybody system. It is shown that the truncated Wigner method corresponds to the socalled diagonal approximation, and it is possible to identify the leading correction to the truncated Wigner results, which is provided by the socalled coherent backscattering (CBS) contribution. Coherent basckattering in Fock space is a genuine quantum manybody effect that lies beyond the reach of any meanfield approach. For the case of closed BoseHubbard models, the relevance of CBS is confirmed by numerically comparing the (classical) truncated Wigner evolution probabilities to the exact quantum probabilities in BoseHubbard models: While a CBSinduced enhancement of the return probability to the initial state is clearly seen in the exact quantum simulations of the bosonic manybody system, this enhancement is absent in the classical calculations. The magnitude and dependence of the CBS contribution on gauge fields, which break timereversal invariance, is numerically confirmed. For the case of disordered open systems, it can be shown that this contribution as well as nextto leading order contributions vanish thereby confirming the validity of the truncated Wigner method.; Cette thèse présente les investigations réalisées sur la relation entre les effets à plusieurs corps et la coherence lors de phénomènes de transport quasiunidimensionels de condensats de BoseEinstein (CBE) à travers divers potentiels de diffusion. De telles configurations peuvent être réalisées avec des lasers à atomes qui créent des faisceaux coherents de matière. Une description exacte de la dynamique à plusieurs corps est hors de portée à cause des interactions entre atomes. Malgré tout, différents niveaux d'approximation sont possibles, chacun possédant leurs forces et faiblesses. L'approximation en champ moyen, où la dynamique du CBE est régie par l'équation de GrossPitaevskii, est la plus utilisée dans le domaine des atomes ultrafroids.
Dans cette thèse, la méthode de Wigner tronquée, qui est une amélioration de la description fournie par l'équation de GrossPitaevskii, est utilisée. Cette méthode est adaptée pour l'étude de la diffusion de condensats de BoseEinstein dans des guides d'ondes unidimensionels où les interactions entre atomes et les potentiels extérieurs ont un support fini. Dans ce cas, la méthode de Wigner tronquée est combinée avec la méthode de dilatation complexe extérieure lissée (smooth exterior complex scaling) et avec du bruit quantique, provenant des fluctuations quantiques dans le guide d'onde. Les effets, non négligeables, des collisions inélastiques sont mis en évidence lors du transport résonnant d'un CBE à travers une double barrière de potentiel symétrique formant un point quantique. En effet, une transmission résonnante parfaite est prohibée et des atomes incoherents ainsi que des oscillations collectives sont détectées dans le faisceau atomique transmis. Il est aussi démontré que la diffusion inélastique est responsable de la destruction de la localisation d'Anderson dans le cas du transport à travers des potentiels désordonnés. Une transmission ohmique (incohérente) est retrouvée pour des interactions finies entre atomes.
La validité de la méthode de Wigner tronquée est évaluée en utilisant le propagateur semiclassique de van VleckGutzwiller dans l'espace de Fock du sytème à plusieurs corps. Il est démontré que la méthode de Wigner tronquée correspond à l'approximation diagonale et qu'il est possible d'identifier la correction dominante appellée rétrodiffusion cohérente. La rétrodiffusion cohérente dans l'espace de Fock est un effet à plusieurs corps purement quantique et ne peut être reproduite par aucune théorie en champ moyen.
L'analyse numérique des probabilités de transitions quantiques pour des systèmes de BoseHubbard confirme la présence de rétrodiffusion cohérente alors qu'elle est absente pour des simulations utilisant la méthode (classique) de Wigner tronquée. L'amplitude ainsi que la dépendance visàvis d'un champ de jauge de la contribution de rétrodiffusion cohérente est confirmée numériquement. Dans le cas de systèmes ouverts désordonnés, il a été montré que la rétrodiffusion cohérente ainsi que les corrections d'ordre supérieur sont inexistantes, confirmant la validité de la méthode de Wigner tronquée.

Direct Numerical Simulation of Mixed Convection in Turbulent Channel Flow: On the Reynolds number dependency of momentum and heat transfer under unstable stratification
http://hdl.handle.net/2268/185877
Title: Direct Numerical Simulation of Mixed Convection in Turbulent Channel Flow: On the Reynolds number dependency of momentum and heat transfer under unstable stratification
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<br/>Author, coauthor: Sid, Samir; Dubief, Yves; Terrapon, Vincent
<br/>
<br/>Abstract: Direct numerical simulations of unstably stratified turbulent channel flow have been performed in order to investigate the Reynolds number effect on mixed convection. Six different cases are considered with friction Reynolds number Re_\tau =180 and 395 and friction Richardson number Ri_\tau = 0, 100 and 1000. It is shown that both friction coefficient and Nusselt number increase under unstable stratification for a sufficiently large Richardson number. At low Richardson number, the friction coefficient can either increase or decrease depending on the Reynolds number. The drag reduction is associated with an increase of mean velocity due to an enhanced dissipation of Reynolds shear stress by pressure strain in the buffer region. The breakdown of the Reynolds analogy is demonstrated as the turbulent Prandtl number exhibits a nonconstant behavior due to buoyancy.

A zigzag antiferromagnetic quantum ground state in monoclinic honeycomb lattice antimonates A3Ni2SbO6 (A=Li, Na)
http://hdl.handle.net/2268/185845
Title: A zigzag antiferromagnetic quantum ground state in monoclinic honeycomb lattice antimonates A3Ni2SbO6 (A=Li, Na)
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<br/>Author, coauthor: Zvereva, E.A.; Stratan, M.I.; Ovchenkov, Y.A.; Nalbandyan, V.B.; Lin, J.Y.; Vavilova, E.L.; Iakovleva, M.F.; AbdelHafiez, M.; Silhanek, Alejandro; Chen, X.J.; Stroppa, A.; Picozzi, S.; Jeschke, H.O.; Valentí, R.; Vasiliev, A.N.
<br/>
<br/>Abstract: We present a comprehensive experimental and theoretical study of the electronic and magnetic properties of two quasitwodimensional (2D) honeycomblattice monoclinic compounds A3Ni2SbO6 (A=Li, Na). Magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic (AFM) long range order at low temperatures with Néel temperatures ~ 14 and 16 K for Li3Ni2SbO6 and Na3Ni2SbO6, respectively. The effective magnetic moments of 4.3 Bohr magnetons/f.u. (Li3Ni2SbO6) and 4.4 Bohr magnetons/f.u. (Na3Ni2SbO6) indicate that Ni2+ is in a highspin configuration (S=1). The temperature dependence of the inverse magnetic susceptibility follows the CurieWeiss law in the hightemperature region and shows positive values of the Weiss temperature ~ 8 K (Li3Ni2SbO6) and ~12 K (Na3Ni2SbO6) pointing to the presence of nonnegligible ferromagnetic interactions, although the system orders AFM at low temperatures. In addition, the magnetization curves reveal a fieldinduced (spinflop type) transition below TN that can be related to the magnetocrystalline anisotropy in these systems. These observations are in agreement with density functional theory calculations, which show that both antiferromagnetic and ferromagnetic intralayer spin exchange couplings between Ni2+ ions are present in the honeycomb planes supporting a zigzag antiferromagnetic ground state. Based on our experimental measurements and theoretical calculations we propose magnetic phase diagrams for the two compounds.

Soutien télématique à la résolution de problèmes en physique en première année de bachelier
http://hdl.handle.net/2268/185804
Title: Soutien télématique à la résolution de problèmes en physique en première année de bachelier
<br/>
<br/>Author, coauthor: Marique, PierreXavier
<br/>
<br/>Abstract: Présentation d'un projet de soutien à l'enseignement proposé aux étudiants éprouvant des difficultés en résolution de problèmes de physique.; Presentation of a learning support project for students experiencing difficulties in solving physics problems

Intramolecular vibrational relaxation seen as expansion in phase space. III. The longtime limit
http://hdl.handle.net/2268/185797
Title: Intramolecular vibrational relaxation seen as expansion in phase space. III. The longtime limit
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<br/>Author, coauthor: PavlovVerevkin, V. B.; Lorquet, JeanClaude
<br/>
<br/>Abstract: Asymptotic formulas that describe the behavior of the function N(T) measuring the phase space volume sampled by a nonstationary wave packet during its time evolution are derived. It is shown that, in the longtime limit, N(T)∼T1 when the dynamics is regular, whereas N(T)∼T2 In T for the chaotic case. © 1997 American Institute of Physics.

Abinitio study of thermoelectricity of layered tellurium compounds
http://hdl.handle.net/2268/185792
Title: Abinitio study of thermoelectricity of layered tellurium compounds
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<br/>Author, coauthor: Ibarra Hernández, Wilfredo
<br/>
<br/>Abstract: In this thesis, we explore the electronic, dynamic and thermoelectric properties
of different telluriumbased compounds. We perform abinitio calculations
within the Vienna Abinitio Simulation Package (VASP) that works in
the framework of Density Functional Theory (DFT). For the thermoelectric
properties, we use the Boltztrap code that solves the Boltzmann Transport
Equations (BTE) for electrons within the Constant Relaxation Time Approximation
(CRTA). This computational package allows us to obtain accurate
values of the Seebeck coefficient as a function of temperature and carrier concentration
(this last with the help of the rigid band approximation). While
for the calculation of the lattice contribution to the thermal conductivity, we
use the ShengBTE code that solves the BTE for phonons iteratively. The first telluriumbased compound that we study is the best room temperature
thermoelectric material, Bi2Te3. We obtain results comparable with
experimental data for the Seebeck coefficient at room temperature and pressure.
Afterwards, we proceed to explore the evolution of the electronic properties
and the thermoelectric performance under pressures up to 5 GPa. We
reproduce the overall trend of the Seebeck coefficient as a function of pressure
for two different values of doping, however, our results do not reproduce the
small improvement found in experiments close to 1 GPa. Nevertheless, we
support the experimental evidence of an Electronic Topological Transition
(ETT) around 2 GPa and we explain this particular behavior. We also perform calculations on the telluriumbased phasechange materials
(GeTe)x(Sb2Te3)1 (with x = 1, 2, 3). We show results for different
stacking configurations since for some compositions, the stacking arrangement
of the atoms in the primitive cell is still unsettled. We find that the
change of the atomic arrangement leads to the systems to go from semiconductors
to metals. We find that the semiconductor arrangements systematically
overestimate the experimental values for the Seebeck coefficient,
whereas the metallic stacking sequences are in very good agreement with the experimental data for the Seebeck coefficient and for the lattice contribution
to the thermal conductivity. We show that (GeTe)x(Sb2Te3)1 materials could
reach values of ZT=0.5 around 600 K with a proper optimization of S with
respect to the carrier concentration. We also report that in the case of x=3,
the most accepted stacking configuration is dynamically unstable, therefore
we proposed another sequence. Finally, we discuss the discrepancies between
our work and recent theoretical reports that claim the existence of a Diraccone
like band structure for (GeTe)2(Sb2Te3)1. We explain the conditions
necessary to obtain such electronic topology.

Intramolecular vibrational relaxation seen as expansion in phase space. 4. Generic relaxation laws for a spectroscopic clump profile
http://hdl.handle.net/2268/185763
Title: Intramolecular vibrational relaxation seen as expansion in phase space. 4. Generic relaxation laws for a spectroscopic clump profile
<br/>
<br/>Author, coauthor: PavlovVerevkin, V. B.; Lorquet, JeanClaude
<br/>
<br/>Abstract: We examine the volume of phase space sampled by a nonstationary wave packet when the spectral function consists of a single clump or of a series of them. The relaxation laws are expressed in terms of reduced time variables tau, whose definition involves either the average density of states (for a single clump) or appropriately weighted average densities of states (when the spectrum consists of many clumps). Introducing reasonable approximations, very simple generic relaxation laws are derived for the ratio N(tau)/Ninfinity which measures the fraction of available phase space that has been sampled by time tau. Under certain assumptions, these laws are found to depend neither on the number nor on the individual features (shapes and widths) of the clumps. However, they strongly depend on the nature (regular or chaotic) of the underlying dynamics. When the dynamics is regular, the relaxation law is expressed in terms of tau(1), whereas the corresponding equation in the chaotic limit is slightly more complicated and involves terms in tau(2) and tau(2) ln tau. Phase space is thus explored according to essentially different relaxation laws in the regular and chaotic limits, the difference being appreciable during the entire relaxation. These laws reflect in the time domain the difference in the distribution of nearestneighbor level spacings observed in the energy domain (Poisson or Wigner statistics).