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This article reviews the most recent results concerning second harmonic generation (SHG) experiments of non-phase matchable and phase matchable powder samples at high pressures and explains the pressure dependence of the intensity of the SHG signal by correlating it to the ratio between the average coherence length and the average particle size. The examples discussed here include pressure-induced structural changes in quartz, ZnO, ice VII and KIO3. It is shown that the second harmonic generation technique is a unique tool for the detection of pressure-induced structural phase transitions. It is laboratory based and allows fast measurements. It is complementary to X-ray diffraction and provides additional information about the presence of an inversion center for unknown or controversially discussed structures at high pressure.
As the density of matter increases, atomic nuclei disintegrate into nucleons and, eventually, the nucleons themselves disintegrate into quarks. The phase transitions (PT's) between these phases can vary from steep first order to smooth crossovers, depending on certain conditions. First-order PT's with more than one globally conserved charge, so-called non-congruent PT's, have characteristic differences compared to congruent PT's. In this conference proceeding we discuss the non-congruence of the quark deconfinement PT at high densities and/or temperatures relevant for heavy-ion collisions, neutron stars, proto-neutron stars, supernova explosions, and compact-star mergers.
Nanocarbon structures, such as fullerenes and nanotubes, have generated considerable interest and research, due to their unique properties and potential applications. In this thesis, we present a study of the phase transition properties of nanocarbon clusters,in particular, we pay special consideration to fullerenes. The work presented in this thesis is largely theoretical and computational in nature, employing as a tool, molecular dynamics simulations to probe the dynamic stability of fullerenes and associated nanocarbon structures such as graphenes and nanotubes.
The deconfinement transition region between hadronic matter and quark-gluon plasma is studied for finite volumes. Assuming simple model equations of state and a first order phase transition, we find that fluctuations in finite volumes hinder a sharp separation between the two phases around the critical temperature, leading to a rounding of the phase transition. For reaction volumes expected in heavy ion experiments, the softening of the equation of state is reduced considerably. This is especially true when the requirement of exact color-singletness is included in the QGP equation of state.
The core of neutron stars consists of extremely dense matter at relatively low temperatures. In such an environment the appearance of exotic strongly interacting particles beyond nucleons appears quite natural. In this context we consider hybrid stars that, in addition to nucleons and hyperons, also contain quarks as further degrees of freedom. We investigate the impact of quarks on the properties of these compact stars. In addition, we discuss new constraints on such objects arising from the recently measured gravitational wave signal of two merging neutron stars.
Human societies are characterized by three constituent features, besides others. (A) Options, as for jobs and societal positions, differ with respect to their associated monetary and non-monetary payoffs. (B) Competition leads to reduced payoffs when individuals compete for the same option as others. (C) People care about how they are doing relatively to others. The latter trait –the propensity to compare one’s own success with that of others– expresses itself as envy. It is shown that the combination of (A)–(C) leads to spontaneous class stratification. Societies of agents split endogenously into two social classes, an upper and a lower class, when envy becomes relevant. A comprehensive analysis of the Nash equilibria characterizing a basic reference game is presented. Class separation is due to the condensation of the strategies of lower-class agents, which play an identical mixed strategy. Upper-class agents do not condense, following individualist pure strategies. The model and results are size-consistent, holding for arbitrary large numbers of agents and options. Analytic results are confirmed by extensive numerical simulations. An analogy to interacting confined classical particles is discussed.