Phase diagrams of a laser with absorber

Thermodynamic phase diagrams permit a comprehensive and compact account of steady states and limit cycle behavior of a laser with absorber.     

Phase diagrams and elementary excitations

On the phase boundary separating two crystalline phases, it is shown that d(Tⁿ)/dp/_T=0=constant. The index n depends on the dominant elementary excitations, being 4,$\text{5}\text{2}$ and 2 for phonons, magnons and electronic single-particle excitations respectively.     

Phase diagrams of Ising films with competing interactions

The axial next-nearest-neighbour Ising (ANNNI) model of finite thickness is studied. Using mean-field theory, Monte Carlo simulations, and low-temperature analyses, phase diagrams are determined, with a distinct phase diagram for each film thickness. The robustness of the phase diagrams against varying the couplings in the surface layers is analysed. Received 19 March 2002 and Received in final form 2 April 2002 Published online 6 June 2002     

Phase diagrams of lattice systems with residual entropy

We introduce an equivalence relation on the family of ground states and generalize the Peierls and Pirogov-Sinai theory of phase transitions to systems with residual entropy. The idea consists in the replacement of the periodic ground states by equivalence classes together with an entropy factor. We apply these results to discuss the phase diagrams of diluted spin-1/2 systems.On leave of absence from the Central Research Institute for Physics, Budapest, Hungary.     

Phase diagrams of decomposing nanoalloys

The thermodynamics of nucleation and decomposition in small isolated particles are considered. There exist three possibilities: phase separation, prohibition of decomposition and a metastable state. We investigate the peculiarities of phase diagrams related to depletion of the nanosize parent phase even at the nucleation stage. For small particles the equilibrium diagram becomes split (and shifted and size dependent). Concentration, size and temperature hystereses take place. Size-dependent ‘critical supersaturation’, increasing with decreasing size, has been analysed.     

Phase diagrams of magnetic nanotubes

Analytical expressions for the total magnetic energy of two characteristic internal configurations of nanometric tubes are calculated. A magnetic phase diagram with respect to the aspect ratio of the tubes is obtained which allows a discussion about the possibility of getting ensembles of nanotubes with low coercive fields. A comparison with recently reported coercive fields of three different cobalt nanotube arrays agrees well with the phase diagram derived here.     

Phase diagrams of intercalation materials with polaron-type carrier localization

A study is reported on the effect of the position of the polaron band relative to the Fermi level on the phase diagram. The validity of the phase stability criterion obtained is tested in the specific example of silver-intercalated TiSe₂ and TiTe₂.     

Phase diagrams of multilayer adsorbed methane

We propose multilayer phase diagrams based on recent observations of methane adsorbed on graphite and gold (111). Methane wets graphite at all temperatures observed, but it fully wets gold only above the bulk triple point. Possible reasons for this difference in behavior are discussed. The methane-graphite phase diagram also includes layer by layer condensation with critical points leading to a predicted bulk roughening temperature, and an extension of the bulk melting curve into the multilayer film region where it closes at a triple point with a compressed incommensurate first layer solid phase. Experimental evidence for these features is presented and discussed.     

Phase diagrams of lyotropic cholesteric fluids

Experimental investigations of lyotropic cholesterics fluids are presented which show that changes in the shape anisotropy and chirality of the micellar population determine the topology of the temperature-concentration phase diagrams. For given amounts of the substances which induce the chirality and modify the shape anisotropy of the micelles, two distinct biaxial cholesteric phases are disclosed in the phase diagrams. This is interpreted in the framework of the catastrophe theory of phase transitions.     

Phase diagrams of quasispecies theory with recombination and horizontal gene transfer

We consider how transfer of genetic information between individuals influences the phase diagram and mean fitness of both the Eigen and the parallel, or Crow-Kimura, models of evolution. In the absence of genetic transfer, these physical models of evolution consider the replication and point mutation of the genomes of independent individuals in a large population. A phase transition occurs, such that below a critical mutation rate an identifiable quasispecies forms. We show how transfer of genetic information changes the phase diagram and mean fitness and introduces metastability in quasispecies theory, via an analytic field theoretic mapping.     

Phase diagrams of laser-processed nanoparticles of brass

Nanoparticles of brass are prepared by ablation of a brass target in ethanol using radiation of a copper-vapor laser at various laser fluences. The nanoparticles are characterized by TEM and optical spectroscopy. The multipulse laser irradiation leads to formation both the nanoparticles in liquid and well-ordered micro-structures on a surface of a target. It is revealed that both the morphology and absorption spectra of brass nanoparticles depend on presence of the micro-structures. Nanoparticles with the various phase diagrams are formed from a flat brass surface and from the same surface with micro-structures. The results are compared with a model of phase diagrams, in which size and composition effects are taken into account.     

Polar smectic subphases: Phase diagrams, structures and X-ray scattering

We analyze a discrete phenomenological model accounting for phase transitions and structures of polar Smectic-C* liquid-crystalline phases. The model predicts a sequence of phases observed in experiment: antiferroelectric SmC _A ^* –ferrielectric SmC _FI1 ^* –antiferroelectric SmC _FI2 ^* (three-and four-layer periodic, respectively)–incommensurate SmC _α ^* –SmA. We find that, in the three-layer SmC _FI1 ^* structure, both the phase and the module of the order parameter (tilt angle) differ in smectic layers. This modulation of the tilt angle (and therefore of the layer spacing d) must lead to X-ray diffraction at the wave vectors Q _s =2πs/d(s=n±1/3) even for the nonresonant scattering.     

Phase diagrams of a transverse Ising nanowire

Phase diagrams of a cylindrical nanowire described by the transverse Ising model are investigated by the use of two theoretical frameworks, namely the mean field theory and the effective field theory with correlations. The phase diagram of the system is strongly affected by the surface situations. Some characteristic phenomena are found in the phase diagram, depending on the ratio of the physical parameters in the surface shell and the core.     

Phase diagrams for the triangular Ising lattice with re-entrant ferromagnetism

We present the phase diagrams in a 2D spin 1/2 Ising model for the triangular lattice. Using the finitecluster approximation and renormalization technique we studied a nearest-neighbour random interactions. Ferromagnetic exchange interactionsJ are considered with concentrationp and exchange interactions J (||1) with concentration (1-p). The phase diagrams were obtained for this model. They show re-entrant behaviour in certain ranges of the concentrationp and different .     

Phase diagrams of Heusler alloys with inversion of the exchange interaction

The phase diagrams of magnetically ordered Heusler alloys with the inversion of the exchange interaction have been studied using the phenomenological Landau theory of phase transitions. It has been shown that the shape of the phase diagrams in these alloys depends on the magnitudes and signs of the phenomenological parameters in the Landau functional. At certain magnitudes and signs of the parameters of the Landau functional, the phase diagrams have thermodynamic paths that allow one to explain the experimentally observed sequences of the phase transitions in the Heusler alloys.